Title of Invention	A PROCESS FOR MANUFACTURING HEAT TREATED ALLOYED GRAY CAST IRON TOP PINCH ROLL SHELL FOR HOT STRIP ROLLING,THE METHOD OF PREPARING SUCH ALLOY AND THE ALLOY THEREOF
Abstract	The process for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip rolling comprising the steps of top pinch roll shell moulding, proof machining and Grinding of the moulded shell, testing of the surface of the shell material using process of ultrasonic testing, final machining and grinding wherein the said process is characterized by heat treatment cycle of the gray cast alloy after the step of proof machining and proof grinding followed by a final testing of surface of the shell after the final grinding process.

Title of Invention

A PROCESS FOR MANUFACTURING HEAT TREATED ALLOYED GRAY CAST IRON TOP PINCH ROLL SHELL FOR HOT STRIP ROLLING,THE METHOD OF PREPARING SUCH ALLOY AND THE ALLOY THEREOF

Abstract

The process for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip rolling comprising the steps of top pinch roll shell moulding, proof machining and Grinding of the moulded shell, testing of the surface of the shell material using process of ultrasonic testing, final machining and grinding wherein the said process is characterized by heat treatment cycle of the gray cast alloy after the step of proof machining and proof grinding followed by a final testing of surface of the shell after the final grinding process.

Full Text	BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a process for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip rolling with improved life and better strip quality which is suitable for use in hot strip mill of all the steel plants, the method of making such gray cast iron alloy and the alloy thereof. The pinch roll application requires a material that possesses a balance between the critical properties of wear resistance, resistance to pick up, good thermal stability and conductivity and thorough hardening capability. Considering the above fact, a technology for manufacturing heat-treated alloyed gray cast iron material has been produced and one top pinch roll shell has been made which shows improved wear resistance, resistance to pick up, good thermal stability and conductivity and through hardening capability. The most demanding pinch roller application is that of a hot strip steel mill coiler. Due to the constant desire to increase hot strip steel mill productivity, strip quality, and coil presentation, the coiler pinch rolls are now accepted as highly critical components in the hot strip steel mill. Also, the pinch rolls have been the area of great concern for Steel Plants because of severe surface deterioration of both the pinch rolls and the hot strip. On investigation it has been established that the metal pick up as well as scratches are occurring due to excessive metal pick up, high adhesive and uneven abrasive wear of top pinch roll. Consequently, it is for this pinch roll application that most of the technology advances in materials and design are taking place. DESCRIPTION OF THE RELATED ART Pinch rolls comprise an entire family of non-reducing rolls that are used to redirect the travel of a strip mill product and to provide strip tension for a downstream process. Pinch rolls are used in nearly all the metallic strip producing industries including steel, aluminum, brass and bronze. These rolls are found in hot and cold strip mill applications and in specialty processing lines like continuous picklers. Regardless of the specific application, the pinch roll has to perform their function without negatively effecting mill productivity or product quality. One of the most demanding pinch roll applications is that of the hot strip steel mill coiler. Roil material and heat treatment are where the biggest difference lies with the various technologies. Stainless weld overlay is a common technology used for top pinch rolls. Mild steet is used as a base and the cladding is done on top up to a depth of around 15mm. The wear resistance property of these rolls is quite good. However the overlay or cladded roll has a strong tendency to pick up. Many of the high production, high quality hot strip mills, while recognizing the wear properties of the stainless rolls, have stopped to use them due to the tendency toward pick up. In the hot strip steel mill coiler application the pinch rolls are a set of top and bottom rolls at the entrance to the coiler. Their purpose is to receive the head end of the hot band and direct it into the coiler area. In addition, the pinch rolls also provide back tension for the strip during coiling. The top pinch roll is engaged with only the head-end and tail end of the hot band during coiling. An increase in hot strip mill productivity typically means that the rolls are subjected to longer hot strip lengths (larger coils), longer campaigns, and increased tonnage over the life of the rolls. These productivity requirements imply that the pinch rolls possess resistance to wear, pick up resistance, thermal stability, high thermal conductivity, and thorough-hardness. As in all hot strip mill applications, the materials that contact the hot product must possess good thermal properties. The pinch roll application is no exception to this rule. With longer coils being coiled, and longer campaign lengths, the amount of heat generated at the surface of the pinch rolls can lead to severe surface deterioration of both the pinch rolls and the hot strip. A material with a high thermal conductivity will dissipate the heat more rapidly and thus reduce the surface deterioration and risks of friction welding. A material with a low modulus of elasticity will be less susceptible to cracking due to thermal stresses. Thermal stability refers to the ability of the material to maintain its heat-treated properties under the elevated temperatures experienced during service. A material with good thermal stability will maintain its strength and hardness at elevated temperatures and be less susceptible to softening while in service. Both abrasive and adhesive (frictional) wear mechanisms occur in the pinch roll application. The percentage of each of the wear mechanisms depends on the pinch roll material being used. Abrasive wear results when a harder material removes particles from a softer surface. In the pinch roll application, the hardness of the hot strip being coiled is soft relative to the hardness of the pinch roll, and therefore, the hot strip itself does not abrasively wear the pinch rolls. However, extraneous materials (scale, mill debris, and hard particles carried by the coolant and transferred through the water sprays) invoke abrasive wear. Adhesive, or frictional wear, results from the scuffing action between two surfaces that come into contact. Adhesive wear occurs when appreciable heat is generated by friction between the surfaces. Often, projecting surface asperities present on the roll and product being coiled are locally heated when the surfaces come into contact. The localized heat can cause the surfaces to gall as a result of frictional welding. Upon further relative motion, the particles tear out and produce new asperities on the roll surface. The resistance to wear, either abrasive or adhesive, or both, is a direct function of the pinch roll material, its hardness, and its microstructure. The ability of a pinch roll to be through hardened is a positive attribute when considering overall performance. A thorough-hardened material has a consistent hardness throughout the cross-section and thus can be used to scrap size without re-hardening, re-sleeving or welding. Also, application stresses can be more evenly distributed over the entire hardened cross-section. In addition to the above productivity requirements, the pinch rolls also possess resistance to "pick-up" to ensure adequate hot strip surface quality. Pick-up, as it is referred to in this text, is a condition whereby foreign material becomes adhered to the surface of the pinch roll during service. The foreign material is usually adhered metal from the actual product being rolled. Pick-up on a pinch roll occurs when the product being coiled becomes fused to the roll surface due to extreme localized temperatures and pressures. When small imperfections or raised areas on the hot strip pass through the roll bite, they are subject to localized temperatures and pressures, which cause them to become friction welded to the pinch roll surface. Once welded to the surface of the roll, the areas are pulled from the product as it continues through the roll bite. The picked-up material on the pinch roll surface will harden as it passes by the water sprays. As the pinch roll continues to coil, the pick-up can transfer marks on any subsequent hot strip being coiled, thus drastically degrading the surface quality of the hot strip. NIPPON STEEL CORP; KUBOTA LTD, Japanese published patent document JP000001278906AA, discloses a somewhat similar arrangement to prolong service life of rolls by forming a using layer out of a graphite crystallization Cr cast iron mainly composed of carbide, graphite, and bainite and containing specific percentage, by wt., components of C, Si, Mn, P, S, Ni, Cr, Mo, and Fe. The top layer of a hot run table roller and a pinch roll for coiler is composed of, by wt., 2.8W3.5% C, 1.5W2.5% Si, 0.5W1.0% Mn,=0.1% P, =0.08% S, 3.5W4.5% Ni, 3.5W5.0% Cr, 0.3W1.0% Mo, and balance Fe. As for a structure graphite crystallization Cr cast iron mainly composed of carbide, graphite, bainite was used. Toughness, wear resistance, seizing resistance of rolls were improved because the component composition contains proper Ni, Cr and carbon 5 component forms carbide and graphite is crystallized. Therefore, service life of the rolls is prolonged. NIPPON STEEL CORP, Japanese published patent document JP00000915782AA discloses method to prevent the sticking of foreign matter at the time of carrying a steel strip at a high speed and a high tension by forming sprayed coating by or ceramics on the surface of a process roll for carrying a cold steel strip and sealing the projected parts therein by resin. To solve the purpose the inventor suggested that the surface of the process roll for carrying a cold steel strip such as a deflector roll, a pinch roll or the like, sprayed coating 2 having 0.5 to 10 surface roughness Ra by ceramics composed of metal or alloy such as Ni, Ni-Cr or the like or by ceramics such as WC, TiC, NbC or the like by 5 to 20\|_im coating thickness. The recessed parts 3 in this sprayed coating 2 by ceramics are sealed by chemically stable resin 4 of Teflon series, epoxy series, silicone series or the like. The sticking of foreign matter such as iron powder or the like is prevented at the time of carrying a steel sheet to improve the durability of the roll, and, moreover, the occurrence of flaws caused by foreign matter on the steel strip to be carried is reduced to improve the quality and yield of the steel strip. BJOERKLIND TOBIAS (SE); BJOERKMAN CARL (SE); PENTTINEN MARTTI (SE), PCT Publication No. WO03095692 discloses substantially perlitic, grey cast iron alloy comprising, by weight, 3.2 - 3.49% carbon, 1.8 - 2.2% silicon, From the above discussion it becomes obvious that the pinch roll application requires a new and improved material that possesses a balance between the critical properties of wear resistance, resistance to pick-up, good thermal stability and conductivity, and through-hardening capability, 6 SUMMARY OF THE INVENTION Considering the above fact, it is an object of the present invention to provide an improved process for manufacturing heat-treated alloyed gray cast iron material for making top pinch roll shell having improved wear resistance, resistance to pick up, good thermal stability and conductivity and through hardening capability which contains a relatively low level of expensive alloying ingredients. Also a process for manufacturing a heat-treated alloyed gray cast iron shell for top pinch roller for hot strip rolling. The heat-treated alloyed gray cast iron top pinch roll shell of the present invention possesses a balance between the critical properties of wear resistance, resistance to pick up, good thermal stability and conductivity and through hardening capability. Therefore, according to the present invention, there is provided a process for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip rolling comprising the steps such as top pinch roll shell moulding, proof machining and Grinding of the moulded shell, testing of the surface of the shell material, final machining and grinding wherein the said process is characterized by Heat treatment cycle of the gray cast alloy after the step of proof machining and proof grinding followed by testing of the surface of the shell after the final grinding process. Also, there is provided a method for the preparation of a gray cast iron alloy having high wear resistance, resistance to pick up, good thermal stability and conductivity and through hardening capability, the alloy consisting essentially of, in weight percent, about 2.9 to3.2% carbon, from 130% to about 1.50% silicon, from 0.70% to about 0.90% manganese, about 0.012% maximum phosphorus, about 0.15% maximum sulphur, from 0.40% to about 1.00% chromium, from 0.40% to about 1.00% nickel, from about 0.42% to about 0.60% molybdenum, 7 from about 0.15% to about 0.20% niobium and balance essentially iron, moreover, an alloy having the aforesaid composition. The elements carbon, silicon, sulphur, phosphorous, manganese, chromium, nickel, molybdenum and niobium and the balance there between, are critical in every sense. In the improved embodiment having superior wear resistance, resistance to pick up, good thermal stability and conductivity and through hardening capability, the niobium range is critical. Omission of one of the elements, or departure of any of these critical elements from the ranges set forth above results in loss in one or more of the desired properties. During the development of the technology for manufacturing heat treated alloyed gray cast iron top pinch roll shell material in the laboratory of RDCIS, the main criterion was to improve the wear resistance of the alloyed gray cast iron without jeopardizing the resistance to pick-up or other critical properties. The ultimate choice of alloying the alloyed gray cast iron material with Niobium and other metals met this criterion. Other methods could have been successfully used to increase the wear resistance of the alloyed gray cast iron material. The cell material is expected to possess the following unique properties, which are ideal for pinch roll: - • Niobium carbide enhances the wear resistance property. • The graphite flake present to provide thermal stability and natural lubricating characteristic, which in turn provides resistance to pick-up. • The tampered martensitic matrix contributes to overall strength and toughness, as well as providing an increased hardness for resisting wear. • This material maintains the through hardening capability, excellent thermal conductivity and thermal stability. 8 Accordingly, it is a principal object of the invention to manufacture a top pinch roll shell material for hot strip rolling, for use in steel industry. Another object of the present invention is to manufacture a top pinch roll shell using the heat-treated alloyed gray cast iron roll material. To accomplish the principle objective of the invention the constituents of the shell material are so designed so that following characteristics can be achieved which are ideal for a top pinch roll shell. a) wear resistant. b) Thermal stability and natural lubrication. c) Resistant to pickup and fire cracking. d) High tensile strength and tough. e) Thermal conductivity and Thermal stability. The different objectives for an ideal top pinch roller are achieved with experiments carried out at RDCIS laboratory. The amount of graphite, the length of the flakes in the matrix directly influences the thermal stability and pick up resistance. The tampered martensitic matrix in which the graphite is distributed provides the basic strength of the alloyed gray cast iron material. The wear resistance is aided by natural lubricity of the graphite, but is more of functional tampered matrix and carbides contained and distribution Niobium has been added to increase the resistance. Niobium has the ability to form hard primary carbide that do not form the boundaries of the eutectic cell, thus there is no detrimental effect on toughness. In addition to this, Niobium when used as alloying element in gray iron has been found to decrease the size of eutectic cell, thereby increasing strength. It is yet another objective of the present invention to set out a process of hardening and tempering of the shell to achieve the desired results. 9 It is yet another objective of the present invention to set out ideal processes of testing the shell surface of cracks or any other disorder. It is yet another object of the invention to provide the alloyed gray cast iron top pinch rolls, which leads to an appreciable economy in cost of production due to extended working life of the roll and quality of the strip. It is yet a further object of the invention to provide alloyed gray cast iron top pinch rolls suitable for use in Hot Strip Mill of all the steel plants. These and other objects of the present invention will become readily apparent upon further review of the following specification BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS FIG. 1 is a general arrangement of pinch rolls in a hot strip steel mill; FIG. 2 is a flowchart for the manufacture of the pinch roll. FIG. 3 is a chart showing the weight of different constituents of the alloy in percentage. DETAILED DESCRIPTION OF THE INVENTION The top pinch roll shell material is a hypoeutectic gray cast iron, alloyed with sulphur, phosphorus, manganese, nickel, chromium, niobium and molybdenum. The selected alloys are present within the gray iron at levels that provide a balance between carbide formation and graphitization. 10 The chemistry contains enough alloys to allow for thorough hardening of the standard wall thickness of the sleeves used in top pinch roll designs. The composition and microstructure dictate the properties of the heat-treated alloyed gray cast iron top pinch roll shell material. The microstructure of shell material consists of flake graphite, discontinuous primary ferritic carbides, and a tempered martensitic matrix. Although each of the constituents of the microstructure affects all of the properties, each affects certain properties more than others do. The amount of graphite, the length of the flakes, and how they are distributed in the matrix directly influence the thermal stability and pick-up resistance. The tempered martensitic matrix in which the graphite is distributed provides the basic strength and hardness of the alloyed gray cast iron material. The wear resistance is aided by the natural lubricity of graphite, but is more a function of the tempered matrix and carbide content and distribution. The preferred process technology for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip roiling with improved life and better strip quality which is suitable for use in hot strip mill of all the steel plants composition exhibiting superior wear resistance, resistance to pick up, good thermal stability and conductivity and through hardening capability, consists essentially of, in weight percent, about 2.9 to3.2% carbon, from 1.30% to about 1.50% silicon, from 0.70% to about 0.90% manganese, about 0.012% maximum phosphorus, about 0.15% maximum sulphur, from 0.40% to about 1.00% chromium, from 0.40% to about 1.00% nickel, from about 0.42% to about 0.60% molybdenum, from about 0.15% to about 0.20% niobium and balance essentially iron. In turn, this microstructure establishes the properties that enable the heat-treated alloyed gray cast iron top pinch roll shell material to perform well in the top pinch roll application. 11 The wear resistance of the alloy material could have been improved by increasing the amount of primary ferritic carbides in the matrix. Increasing the cooling rate(cool inside furnace) after casting can increase the amount of primary ferritic carbides. However, the ferritic carbides are often present at the eutectic cell boundaries. A high concentration of the ferritic carbides at the boundaries would also decrease the overall toughness of the material by promoting brittle fracture along the boundaries under impact loading. Further more, Niobium has been added as the alloying element to increase the wear resistance. Niobium has the ability to form hard, primary carbides that do not form at the eutectic cell boundaries and, therefore, do not have a negative effect on toughness. Also, Niobium when used as an alloying element in gray iron has been found to reduce the size of the eutectic cell, thereby increasing strength. Niobium metal also has advantages over other strong carbide formers because it does not significantly affect the inoculation process. During inoculation, non-Niobium metastable carbides are formed, which upon decomposition provide free carbon to nucleate graphite. Some carbide formers dissolved in the melt during inoculation may decrease the power of the metastable carbides to nucleate graphite. In the case of Niobium, however, this problem is not critical since at usual inoculation temperatures most of the Niobium is already combined as primary Niobium carbides. Any Niobium remaining after solidification will remain as a solute or precipitate out in the solid state as Niobium carbide. Consequently, the formation of graphite (necessary for pick-up resistance) is unaffected. The gray iron based materials are melted in electric furnace, and then typically static cast into a shell moulding. Shell moulding is a variation of sand moulding in which the mould is formed of a thin layer or shell of a special type of sand. The shell is formed by coating a hot metal pattern with resin impregnated sand. The heat melts the resin, which then holds the grains of sand together forming a shell. The shell is formed by coating a hot metal pattern with resin impregnated sand. 12 The heat melts the resin, which then holds the grains of sand together forming a shell. Shell molding is also similar to sand molding except that a mixture of sand and 3-6%resin holds the grains together, Set-up and production of shell mold patterns takes weeks, after which an output of 5-50 pieces/hr-mold is attainable. Aluminium and magnesium products average about 13.5 kg as a normal limit, but it is possible to cast items in the 45-90 kg range. Shell mold walling varies from 3-10 mm thick, depending on the forming time of the resin. The different stages in shell mold processing includes: 1. initially preparing a metal-matched plate 2. mixing resin and sand 3. heating pattern, usually to between 505-550 K 4. investing the pattern (the sand is at one end of a box and the pattern at the other, and the box is inverted for a time determined by the desired thickness of the mill) 5. curing shell and baking it 6. removing investment 7. inserting cores 8. repeating for other half 9. assembling mold 10. pouring mold 11. removing casting 12. cleaning and trimming/ frettling The mould is then taken out and proof machining is carried out. The machining operation is carried out for a depth of 1 or 2mm preferably internally and externally as per the requirement and the dimensions of the shaft. Rough grinding is carried out over the surfaces and testing is being carried out using 13 ultrasonic testors for burrs, cracks, marks and flows. The top pinch roll shell size is made preferably to 2000x 0900mm. The most important operation used in the process of making shells for top pinch rollers is heat treatment cycle. The treatment cycfe consists of 3 steps which ia hardening, quenching and tampering. The hardening is carried over the said cast alloy shell by placing the shell in a furnace. The loading temperature of the shell and furnace is room temperature. The furnace is heated at the rate of 30 degree Celsius/ hrs (max) to a temperature of 400 to 420 degrees Celsius. The soaking time for the shell at soaking temperature is around 4 to 5 hrs inside the furnace. The temperature has a marked effect on microstructure and on mechanical properties such as hardness and tensile strength. Air quenching is used for cooling the hardened alloy shells. The shell is so mounted that the forced air through the blowers can reach all sections of the piece. Parts cooled with circulated air are placed for uniform cooling. Compressed air is used to concentrate the cooling on specific areas of a part. The airlines must be free of moisture to prevent cracking of the metal. The shell is then allowed to cool (quenching) in forced air with blowers up to room temperature so that the required strength and other physical properties can be developed by a mild quench. Tempering is done immediately after quench hardening. When the steel cools to about 40 °C (104 °F) after quenching, it is ready to be tempered. After quenching, castings are usually tempered at temperatures well below the transformation range for about 1h per inch of thickest section. As the quenched iron is tempered, its hardness decreases, whereas it usually gains in strength and toughness. Herein the hardened shell is tempered by reheating the shell from room temperature to a temperature of 400 to 420 degree Celsius at a rate of 30 degree Celsius/ hrs (max). Here also the soaking time for the hardened shell at soaking temperature is around 4 hrs. The cooling of the shell is done inside the furnace to room temperature. 14 Gray irons are hardened and tempered to improve their mechanical properties, particularly strength and wear resistance. After being hardened and tempered, the shell hardness is made to an average of 36.2 HRC. The hardened irons usually exhibit wear resistance approximately five times greater than that of perlitic gray irons. The sample is then subjected to a machining and grinding process, which removes the effects hardening and tampering, and ensures a flat surface. The purpose of grinding is to lessen the depth of deformed metal to a point. Belt, disk, and surface grinders, cylindrical grinders can be used which further uses abrasives bonded to a surface. After machining and grinding the shell is subjected to ultrasonic testing for a second time. Ultrasonic testing (UT) is one of the most widely used techniques for discontinuity detection and material characterization in various engineering fields. The advantages of UT as compared to other nondestructive techniques for metal tests are higher penetration, higher sensitivity and greater accuracy. The top pinch roll is typically a four-piece fabricated shell design. The components consist of the, two hubs or centers, and a through shaft. The shaft, requiring a reasonable level of bending and torsional strength, is generally made from heat-treated low alloy forged steel. The components are machined to tight tolerances and the components are mechanically fit precisely together, as the top pinch roll must be balanced for proper operation in the mill. The standard balancing specification used is ISO 1940/1-1986, G6.3 at 360 RPM. Top pinch roll shell size is 2000XF 900 mm, strip temperature ranging from 600-700°C and having roll speed of 19m/sec. The shell is assembled over the shaft by shrink fitting, and held in place through mechanical stops, shaft keys and face keys. Weld is sometimes used to affix the shell, but certain shell materials are not easily weldable. A slight variation in this typical design features stub shafts welded into each hub, instead of the through-shaft, but this design is becoming less common as the length of the shaft is becoming longer. Newer features on 15 the top pinch roll coiler assemblies, such as counter-balancing components on the idler end shafts and hydraulic-controlled side guides, require the shafting on both the drive and idler ends to be longer. The gray iron based materials exhibit good thermal properties, Including thermal conductivity and thermal stability. The wear resistance is good due to due to the presence of the graphite microconstituent The graphite provides a natural lubricating element and promotes the formation of hard oxide at the surface of the rolls. The tow as-cast hardness of the gray iron can limit the wear resistance of the material. Chemical composition is an important parameter influencing the heat treatment of gray cast irons. Silicon, for example, decreases carbon solubility, increases the diffusion rate of carbon in austenite, and usually accelerates the various reactions during heat-treating. Silicon also raises the austenitizing temperature significantly and reduces the combined carbon content (cementite volume). Manganese, in contrast, lowers the austenitizing temperature and increases hardenability.. Manganese, niekel, and molybdenum are the recognized elements for increasing the hardenability of gray iron. Although chromium, by itself, does not influence the hardenability of gray iron, its contribution to carbide stabilization is important. The above-described embodiments of the invention are intended to be examples of the present invention. Numerous modifications changes and improvements within the scope of the invention will occur to the reader. Those of skill in the art may effect alterations and modifications thereto,, without departing from the scope of the invention which is defined solely by the claims appended hereto. 16 We claim: 1. The process for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip rolling comprising the steps of: - top pinch roll shell moulding; Proof machining and Grinding of the moulded shell; testing of the surface of the shell material using process of ultrasonic testing; -final machining and grinding wherein the said process is characterized by heat treatment cycle of the gray cast alloy after the step of proof machining and proof grinding followed by a final testing of surface of the shell after the final grinding process. 2. The process as claimed in claim 1, wherein the said heat treatment cycle is characterized by processes of hardening, quenching and tampering of the moulded shell and further the said heat treatment cycle produces a hardness of 36.2 HRC. 3. The process as claimed in claim 2, wherein the hardening process includes heating the grinded top pinch roll shell in a furnace with loading temperature as room temperature and the furnace is heated at the rate of 30 degree Celsius (max) /hour and further the soaking temperature of the top pinch roll shell in the furnace is 400 to 420 degree Celsius and the soaking time is 4 to 5 hours. 4. The process as claimed in claim 2, wherein quenching process is characterized by cooling the sample to room temperature with forced air with blowers. 5. The process as claimed in claim 2, wherein the tampering process includes heating the grinded top pinch roll shell in a furnace with loading temperature as room temperature and the furnace is heated at the rate of 30 degree Celsius (max) /hour and further the soaking temperature of the top pinch roll shell in the furnace is 400 to 420 degree Celsius and the soaking time is 4 hours. 6. The process as claimed in claim 5, wherein the heated top pinch roll shell is cooled inside the furnace. 7. The process as claimed in claim 1, wherein the shell is machined to tight tolerances and assembled with the core shaft and end plates by using taper end ring, the assembled roll is then dynamically balanced. 8. The process as claimed in claim 1, wherein the top pinch roll shell size is machined to 2000XF 900 mm, strip temperature ranging from 600-700°C and having roll speed of 19m/sec. 9. The method of preparation of gray cast iron alloy for the process for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip as claimed in claim 1, wherein the said alloy consist essentially of, in weight percent, about 2.9 to3.2% carbon, from 1.30% to about 1.50% silicon, from 0.70% to about 0.90% manganese, about 0.012% maximum phosphorus, about 0.15% maximum sulphur, from 0.40% to about 1.00% chromium, from 0.40% to about 1.00% nickel, from about 0.42% to about 0.60% molybdenum, from about 0.15% to about 0.20% niobium and balance essentially iron. 10. The gray cast iron alloy consist essentially of, in weight percent, about 2.9 to3.2% carbon, from 1.30% to about 1.50% silicon, from 0.70% to about 0.90% manganese, about 0.012% maximum phosphorus, about 0.15% maximum sulphur, from 0.40% to about 1.00% chromium, from 0.40% to about 1.00% nickel, from about 0.42% to about 0.60% molybdenum, from about 0.15% to about 0.20% niobium and balance essentially iron. Dated this day of January, 2005. To, The Controller of Patents, The Patent Office, Kolkata The process for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip rolling comprising the steps of top pinch roll shell moulding, proof machining and Grinding of the moulded shell, testing of the surface of the shell material using process of ultrasonic testing, final machining and grinding wherein the said process is characterized by heat treatment cycle of the gray cast alloy after the step of proof machining and proof grinding followed by a final testing of surface of the shell after the final grinding process.

Full Text

BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a process for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip rolling with improved life and better strip quality which is suitable for use in hot strip mill of all the steel plants, the method of making such gray cast iron alloy and the alloy thereof. The pinch roll application requires a material that possesses a balance between the critical properties of wear resistance, resistance to pick up, good thermal stability and conductivity and thorough hardening capability. Considering the above fact, a technology for manufacturing heat-treated alloyed gray cast iron material has been produced and one top pinch roll shell has been made which shows improved wear resistance, resistance to pick up, good thermal stability and conductivity and through hardening capability.
The most demanding pinch roller application is that of a hot strip steel mill coiler. Due to the constant desire to increase hot strip steel mill productivity, strip quality, and coil presentation, the coiler pinch rolls are now accepted as highly critical components in the hot strip steel mill. Also, the pinch rolls have been the area of great concern for Steel Plants because of severe surface deterioration of both the pinch rolls and the hot strip. On investigation it has been established that the metal pick up as well as scratches are occurring due to excessive metal pick up, high adhesive and uneven abrasive wear of top pinch roll. Consequently, it is for this pinch roll application that most of the technology advances in materials and design are taking place.
DESCRIPTION OF THE RELATED ART
Pinch rolls comprise an entire family of non-reducing rolls that are used to redirect the travel of a strip mill product and to provide strip tension for a

downstream process. Pinch rolls are used in nearly all the metallic strip producing industries including steel, aluminum, brass and bronze. These rolls are found in hot and cold strip mill applications and in specialty processing lines like continuous picklers. Regardless of the specific application, the pinch roll has to perform their function without negatively effecting mill productivity or product quality. One of the most demanding pinch roll applications is that of the hot strip steel mill coiler.
Roil material and heat treatment are where the biggest difference lies with the various technologies. Stainless weld overlay is a common technology used for top pinch rolls. Mild steet is used as a base and the cladding is done on top up to a depth of around 15mm. The wear resistance property of these rolls is quite good. However the overlay or cladded roll has a strong tendency to pick up. Many of the high production, high quality hot strip mills, while recognizing the wear properties of the stainless rolls, have stopped to use them due to the tendency toward pick up.
In the hot strip steel mill coiler application the pinch rolls are a set of top and bottom rolls at the entrance to the coiler. Their purpose is to receive the head end of the hot band and direct it into the coiler area. In addition, the pinch rolls also provide back tension for the strip during coiling. The top pinch roll is engaged with only the head-end and tail end of the hot band during coiling.
An increase in hot strip mill productivity typically means that the rolls are subjected to longer hot strip lengths (larger coils), longer campaigns, and increased tonnage over the life of the rolls. These productivity requirements imply that the pinch rolls possess resistance to wear, pick up resistance, thermal stability, high thermal conductivity, and thorough-hardness. As in all hot strip mill applications, the materials that contact the hot product must possess good thermal properties. The pinch roll application is no exception to this rule. With longer coils being coiled, and longer campaign lengths, the amount of heat

generated at the surface of the pinch rolls can lead to severe surface deterioration of both the pinch rolls and the hot strip. A material with a high thermal conductivity will dissipate the heat more rapidly and thus reduce the surface deterioration and risks of friction welding. A material with a low modulus of elasticity will be less susceptible to cracking due to thermal stresses. Thermal stability refers to the ability of the material to maintain its heat-treated properties under the elevated temperatures experienced during service. A material with good thermal stability will maintain its strength and hardness at elevated temperatures and be less susceptible to softening while in service.
Both abrasive and adhesive (frictional) wear mechanisms occur in the pinch roll application. The percentage of each of the wear mechanisms depends on the pinch roll material being used. Abrasive wear results when a harder material removes particles from a softer surface. In the pinch roll application, the hardness of the hot strip being coiled is soft relative to the hardness of the pinch roll, and therefore, the hot strip itself does not abrasively wear the pinch rolls. However, extraneous materials (scale, mill debris, and hard particles carried by the coolant and transferred through the water sprays) invoke abrasive wear.
Adhesive, or frictional wear, results from the scuffing action between two surfaces that come into contact. Adhesive wear occurs when appreciable heat is generated by friction between the surfaces. Often, projecting surface asperities present on the roll and product being coiled are locally heated when the surfaces come into contact. The localized heat can cause the surfaces to gall as a result of frictional welding. Upon further relative motion, the particles tear out and produce new asperities on the roll surface.
The resistance to wear, either abrasive or adhesive, or both, is a direct function of the pinch roll material, its hardness, and its microstructure. The ability of a pinch roll to be through hardened is a positive attribute when considering overall performance. A thorough-hardened material has a consistent hardness

throughout the cross-section and thus can be used to scrap size without re-hardening, re-sleeving or welding. Also, application stresses can be more evenly distributed over the entire hardened cross-section.
In addition to the above productivity requirements, the pinch rolls also possess resistance to "pick-up" to ensure adequate hot strip surface quality. Pick-up, as it is referred to in this text, is a condition whereby foreign material becomes adhered to the surface of the pinch roll during service. The foreign material is usually adhered metal from the actual product being rolled. Pick-up on a pinch roll occurs when the product being coiled becomes fused to the roll surface due to extreme localized temperatures and pressures. When small imperfections or raised areas on the hot strip pass through the roll bite, they are subject to localized temperatures and pressures, which cause them to become friction welded to the pinch roll surface. Once welded to the surface of the roll, the areas are pulled from the product as it continues through the roll bite. The picked-up material on the pinch roll surface will harden as it passes by the water sprays. As the pinch roll continues to coil, the pick-up can transfer marks on any subsequent hot strip being coiled, thus drastically degrading the surface quality of the hot strip.
NIPPON STEEL CORP; KUBOTA LTD, Japanese published patent document JP000001278906AA, discloses a somewhat similar arrangement to prolong service life of rolls by forming a using layer out of a graphite crystallization Cr cast iron mainly composed of carbide, graphite, and bainite and containing specific percentage, by wt., components of C, Si, Mn, P, S, Ni, Cr, Mo, and Fe. The top layer of a hot run table roller and a pinch roll for coiler is composed of, by wt., 2.8W3.5% C, 1.5W2.5% Si, 0.5W1.0% Mn,=0.1% P, =0.08% S, 3.5W4.5% Ni, 3.5W5.0% Cr, 0.3W1.0% Mo, and balance Fe. As for a structure graphite crystallization Cr cast iron mainly composed of carbide, graphite, bainite was used. Toughness, wear resistance, seizing resistance of rolls were improved because the component composition contains proper Ni, Cr and carbon
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component forms carbide and graphite is crystallized. Therefore, service life of the rolls is prolonged.
NIPPON STEEL CORP, Japanese published patent document JP00000915782AA discloses method to prevent the sticking of foreign matter at the time of carrying a steel strip at a high speed and a high tension by forming sprayed coating by or ceramics on the surface of a process roll for carrying a cold steel strip and sealing the projected parts therein by resin. To solve the purpose the inventor suggested that the surface of the process roll for carrying a cold steel strip such as a deflector roll, a pinch roll or the like, sprayed coating 2 having 0.5 to 10 surface roughness Ra by ceramics composed of metal or alloy such as Ni, Ni-Cr or the like or by ceramics such as WC, TiC, NbC or the like by 5 to 20|_im coating thickness. The recessed parts 3 in this sprayed coating 2 by ceramics are sealed by chemically stable resin 4 of Teflon series, epoxy series, silicone series or the like. The sticking of foreign matter such as iron powder or the like is prevented at the time of carrying a steel sheet to improve the durability of the roll, and, moreover, the occurrence of flaws caused by foreign matter on the steel strip to be carried is reduced to improve the quality and yield of the steel strip.
BJOERKLIND TOBIAS (SE); BJOERKMAN CARL (SE); PENTTINEN MARTTI (SE), PCT Publication No. WO03095692 discloses substantially perlitic, grey cast iron alloy comprising, by weight, 3.2 - 3.49% carbon, 1.8 - 2.2% silicon, From the above discussion it becomes obvious that the pinch roll application requires a new and improved material that possesses a balance between the critical properties of wear resistance, resistance to pick-up, good thermal stability and conductivity, and through-hardening capability,
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SUMMARY OF THE INVENTION
Considering the above fact, it is an object of the present invention to provide an improved process for manufacturing heat-treated alloyed gray cast iron material for making top pinch roll shell having improved wear resistance, resistance to pick up, good thermal stability and conductivity and through hardening capability which contains a relatively low level of expensive alloying ingredients. Also a process for manufacturing a heat-treated alloyed gray cast iron shell for top pinch roller for hot strip rolling.
The heat-treated alloyed gray cast iron top pinch roll shell of the present invention possesses a balance between the critical properties of wear resistance, resistance to pick up, good thermal stability and conductivity and through hardening capability.
Therefore, according to the present invention, there is provided a process for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip rolling comprising the steps such as top pinch roll shell moulding, proof machining and Grinding of the moulded shell, testing of the surface of the shell material, final machining and grinding wherein the said process is characterized by Heat treatment cycle of the gray cast alloy after the step of proof machining and proof grinding followed by testing of the surface of the shell after the final grinding process.
Also, there is provided a method for the preparation of a gray cast iron alloy having high wear resistance, resistance to pick up, good thermal stability and conductivity and through hardening capability, the alloy consisting essentially of, in weight percent, about 2.9 to3.2% carbon, from 130% to about 1.50% silicon, from 0.70% to about 0.90% manganese, about 0.012% maximum phosphorus, about 0.15% maximum sulphur, from 0.40% to about 1.00% chromium, from 0.40% to about 1.00% nickel, from about 0.42% to about 0.60% molybdenum,
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from about 0.15% to about 0.20% niobium and balance essentially iron, moreover, an alloy having the aforesaid composition.
The elements carbon, silicon, sulphur, phosphorous, manganese, chromium, nickel, molybdenum and niobium and the balance there between, are critical in every sense. In the improved embodiment having superior wear resistance, resistance to pick up, good thermal stability and conductivity and through hardening capability, the niobium range is critical. Omission of one of the elements, or departure of any of these critical elements from the ranges set forth above results in loss in one or more of the desired properties.
During the development of the technology for manufacturing heat treated alloyed gray cast iron top pinch roll shell material in the laboratory of RDCIS, the main criterion was to improve the wear resistance of the alloyed gray cast iron without jeopardizing the resistance to pick-up or other critical properties. The ultimate choice of alloying the alloyed gray cast iron material with Niobium and other metals met this criterion. Other methods could have been successfully used to increase the wear resistance of the alloyed gray cast iron material.
The cell material is expected to possess the following unique properties, which are ideal for pinch roll: -
• Niobium carbide enhances the wear resistance property.
• The graphite flake present to provide thermal stability and natural
lubricating characteristic, which in turn provides resistance to pick-up.
• The tampered martensitic matrix contributes to overall strength and
toughness, as well as providing an increased hardness for resisting wear.
• This material maintains the through hardening capability, excellent thermal
conductivity and thermal stability.
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Accordingly, it is a principal object of the invention to manufacture a top pinch roll shell material for hot strip rolling, for use in steel industry.
Another object of the present invention is to manufacture a top pinch roll shell using the heat-treated alloyed gray cast iron roll material.
To accomplish the principle objective of the invention the constituents of the shell material are so designed so that following characteristics can be achieved which are ideal for a top pinch roll shell.
a) wear resistant.
b) Thermal stability and natural lubrication.
c) Resistant to pickup and fire cracking.
d) High tensile strength and tough.
e) Thermal conductivity and Thermal stability.
The different objectives for an ideal top pinch roller are achieved with experiments carried out at RDCIS laboratory. The amount of graphite, the length of the flakes in the matrix directly influences the thermal stability and pick up resistance. The tampered martensitic matrix in which the graphite is distributed provides the basic strength of the alloyed gray cast iron material. The wear resistance is aided by natural lubricity of the graphite, but is more of functional tampered matrix and carbides contained and distribution
Niobium has been added to increase the resistance. Niobium has the ability to form hard primary carbide that do not form the boundaries of the eutectic cell, thus there is no detrimental effect on toughness. In addition to this, Niobium when used as alloying element in gray iron has been found to decrease the size of eutectic cell, thereby increasing strength.
It is yet another objective of the present invention to set out a process of hardening and tempering of the shell to achieve the desired results.
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It is yet another objective of the present invention to set out ideal processes of testing the shell surface of cracks or any other disorder.
It is yet another object of the invention to provide the alloyed gray cast iron top pinch rolls, which leads to an appreciable economy in cost of production due to extended working life of the roll and quality of the strip.
It is yet a further object of the invention to provide alloyed gray cast iron top pinch rolls suitable for use in Hot Strip Mill of all the steel plants.
These and other objects of the present invention will become readily apparent upon further review of the following specification
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG. 1 is a general arrangement of pinch rolls in a hot strip steel mill; FIG. 2 is a flowchart for the manufacture of the pinch roll.
FIG. 3 is a chart showing the weight of different constituents of the alloy in percentage.
DETAILED DESCRIPTION OF THE INVENTION
The top pinch roll shell material is a hypoeutectic gray cast iron, alloyed with sulphur, phosphorus, manganese, nickel, chromium, niobium and molybdenum. The selected alloys are present within the gray iron at levels that provide a balance between carbide formation and graphitization.
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The chemistry contains enough alloys to allow for thorough hardening of the standard wall thickness of the sleeves used in top pinch roll designs. The composition and microstructure dictate the properties of the heat-treated alloyed gray cast iron top pinch roll shell material. The microstructure of shell material consists of flake graphite, discontinuous primary ferritic carbides, and a tempered martensitic matrix.
Although each of the constituents of the microstructure affects all of the properties, each affects certain properties more than others do. The amount of graphite, the length of the flakes, and how they are distributed in the matrix directly influence the thermal stability and pick-up resistance. The tempered martensitic matrix in which the graphite is distributed provides the basic strength and hardness of the alloyed gray cast iron material. The wear resistance is aided by the natural lubricity of graphite, but is more a function of the tempered matrix and carbide content and distribution.
The preferred process technology for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip roiling with improved life and better strip quality which is suitable for use in hot strip mill of all the steel plants composition exhibiting superior wear resistance, resistance to pick up, good thermal stability and conductivity and through hardening capability, consists essentially of, in weight percent, about 2.9 to3.2% carbon, from 1.30% to about 1.50% silicon, from 0.70% to about 0.90% manganese, about 0.012% maximum phosphorus, about 0.15% maximum sulphur, from 0.40% to about 1.00% chromium, from 0.40% to about 1.00% nickel, from about 0.42% to about 0.60% molybdenum, from about 0.15% to about 0.20% niobium and balance essentially iron. In turn, this microstructure establishes the properties that enable the heat-treated alloyed gray cast iron top pinch roll shell material to perform well in the top pinch roll application.
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The wear resistance of the alloy material could have been improved by increasing the amount of primary ferritic carbides in the matrix. Increasing the cooling rate(cool inside furnace) after casting can increase the amount of primary ferritic carbides. However, the ferritic carbides are often present at the eutectic cell boundaries. A high concentration of the ferritic carbides at the boundaries would also decrease the overall toughness of the material by promoting brittle fracture along the boundaries under impact loading.
Further more, Niobium has been added as the alloying element to increase the wear resistance. Niobium has the ability to form hard, primary carbides that do not form at the eutectic cell boundaries and, therefore, do not have a negative effect on toughness. Also, Niobium when used as an alloying element in gray iron has been found to reduce the size of the eutectic cell, thereby increasing strength. Niobium metal also has advantages over other strong carbide formers because it does not significantly affect the inoculation process. During inoculation, non-Niobium metastable carbides are formed, which upon decomposition provide free carbon to nucleate graphite. Some carbide formers dissolved in the melt during inoculation may decrease the power of the metastable carbides to nucleate graphite. In the case of Niobium, however, this problem is not critical since at usual inoculation temperatures most of the Niobium is already combined as primary Niobium carbides. Any Niobium remaining after solidification will remain as a solute or precipitate out in the solid state as Niobium carbide. Consequently, the formation of graphite (necessary for pick-up resistance) is unaffected.
The gray iron based materials are melted in electric furnace, and then typically static cast into a shell moulding. Shell moulding is a variation of sand moulding in which the mould is formed of a thin layer or shell of a special type of sand. The shell is formed by coating a hot metal pattern with resin impregnated sand. The heat melts the resin, which then holds the grains of sand together forming a shell. The shell is formed by coating a hot metal pattern with resin impregnated sand.
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The heat melts the resin, which then holds the grains of sand together forming a shell.
Shell molding is also similar to sand molding except that a mixture of sand and 3-6%resin holds the grains together, Set-up and production of shell mold patterns takes weeks, after which an output of 5-50 pieces/hr-mold is attainable. Aluminium and magnesium products average about 13.5 kg as a normal limit, but it is possible to cast items in the 45-90 kg range. Shell mold walling varies from 3-10 mm thick, depending on the forming time of the resin.
The different stages in shell mold processing includes:
1. initially preparing a metal-matched plate
2. mixing resin and sand
3. heating pattern, usually to between 505-550 K
4. investing the pattern (the sand is at one end of a box and the pattern at
the other, and the box is inverted for a time determined by the desired
thickness of the mill)
5. curing shell and baking it
6. removing investment
7. inserting cores
8. repeating for other half
9. assembling mold
10. pouring mold
11. removing casting
12. cleaning and trimming/ frettling
The mould is then taken out and proof machining is carried out. The machining operation is carried out for a depth of 1 or 2mm preferably internally and externally as per the requirement and the dimensions of the shaft. Rough grinding is carried out over the surfaces and testing is being carried out using
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ultrasonic testors for burrs, cracks, marks and flows. The top pinch roll shell size is made preferably to 2000x 0900mm.
The most important operation used in the process of making shells for top pinch rollers is heat treatment cycle. The treatment cycfe consists of 3 steps which ia hardening, quenching and tampering. The hardening is carried over the said cast alloy shell by placing the shell in a furnace. The loading temperature of the shell and furnace is room temperature. The furnace is heated at the rate of 30 degree Celsius/ hrs (max) to a temperature of 400 to 420 degrees Celsius. The soaking time for the shell at soaking temperature is around 4 to 5 hrs inside the furnace. The temperature has a marked effect on microstructure and on mechanical properties such as hardness and tensile strength.
Air quenching is used for cooling the hardened alloy shells. The shell is so mounted that the forced air through the blowers can reach all sections of the piece. Parts cooled with circulated air are placed for uniform cooling. Compressed air is used to concentrate the cooling on specific areas of a part. The airlines must be free of moisture to prevent cracking of the metal. The shell is then allowed to cool (quenching) in forced air with blowers up to room temperature so that the required strength and other physical properties can be developed by a mild quench.
Tempering is done immediately after quench hardening. When the steel cools to about 40 °C (104 °F) after quenching, it is ready to be tempered. After quenching, castings are usually tempered at temperatures well below the transformation range for about 1h per inch of thickest section. As the quenched iron is tempered, its hardness decreases, whereas it usually gains in strength and toughness. Herein the hardened shell is tempered by reheating the shell from room temperature to a temperature of 400 to 420 degree Celsius at a rate of 30 degree Celsius/ hrs (max). Here also the soaking time for the hardened shell at soaking temperature is around 4 hrs. The cooling of the shell is done inside the furnace to room temperature.
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Gray irons are hardened and tempered to improve their mechanical properties, particularly strength and wear resistance. After being hardened and tempered, the shell hardness is made to an average of 36.2 HRC. The hardened irons usually exhibit wear resistance approximately five times greater than that of perlitic gray irons.
The sample is then subjected to a machining and grinding process, which removes the effects hardening and tampering, and ensures a flat surface. The purpose of grinding is to lessen the depth of deformed metal to a point. Belt, disk, and surface grinders, cylindrical grinders can be used which further uses abrasives bonded to a surface.
After machining and grinding the shell is subjected to ultrasonic testing for a second time. Ultrasonic testing (UT) is one of the most widely used techniques for discontinuity detection and material characterization in various engineering fields. The advantages of UT as compared to other nondestructive techniques for metal tests are higher penetration, higher sensitivity and greater accuracy.
The top pinch roll is typically a four-piece fabricated shell design. The components consist of the, two hubs or centers, and a through shaft. The shaft, requiring a reasonable level of bending and torsional strength, is generally made from heat-treated low alloy forged steel. The components are machined to tight tolerances and the components are mechanically fit precisely together, as the top pinch roll must be balanced for proper operation in the mill. The standard balancing specification used is ISO 1940/1-1986, G6.3 at 360 RPM. Top pinch roll shell size is 2000XF 900 mm, strip temperature ranging from 600-700°C and having roll speed of 19m/sec. The shell is assembled over the shaft by shrink fitting, and held in place through mechanical stops, shaft keys and face keys. Weld is sometimes used to affix the shell, but certain shell materials are not easily weldable. A slight variation in this typical design features stub shafts welded into each hub, instead of the through-shaft, but this design is becoming less common as the length of the shaft is becoming longer. Newer features on
15

the top pinch roll coiler assemblies, such as counter-balancing components on the idler end shafts and hydraulic-controlled side guides, require the shafting on both the drive and idler ends to be longer.
The gray iron based materials exhibit good thermal properties, Including thermal conductivity and thermal stability. The wear resistance is good due to due to the presence of the graphite microconstituent The graphite provides a natural lubricating element and promotes the formation of hard oxide at the surface of the rolls. The tow as-cast hardness of the gray iron can limit the wear resistance of the material.
Chemical composition is an important parameter influencing the heat treatment of gray cast irons. Silicon, for example, decreases carbon solubility, increases the diffusion rate of carbon in austenite, and usually accelerates the various reactions during heat-treating. Silicon also raises the austenitizing temperature significantly and reduces the combined carbon content (cementite volume). Manganese, in contrast, lowers the austenitizing temperature and increases hardenability..
Manganese, niekel, and molybdenum are the recognized elements for increasing the hardenability of gray iron. Although chromium, by itself, does not influence the hardenability of gray iron, its contribution to carbide stabilization is important.
The above-described embodiments of the invention are intended to be examples of the present invention. Numerous modifications changes and improvements within the scope of the invention will occur to the reader. Those of skill in the art may effect alterations and modifications thereto,, without departing from the scope of the invention which is defined solely by the claims appended hereto.
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We claim:
1. The process for manufacturing heat treated alloyed gray cast iron top
pinch roll shell for hot strip rolling comprising the steps of: -
top pinch roll shell moulding;
Proof machining and Grinding of the moulded shell;
testing of the surface of the shell material using process of ultrasonic
testing;
-final machining and grinding wherein the said process is characterized by heat treatment cycle of the gray cast alloy after the step of proof machining and proof grinding followed by a final testing of surface of the shell after the final grinding process.
2. The process as claimed in claim 1, wherein the said heat treatment cycle
is characterized by processes of hardening, quenching and tampering of the
moulded shell and further the said heat treatment cycle produces a hardness of
36.2 HRC.
3. The process as claimed in claim 2, wherein the hardening process includes heating the grinded top pinch roll shell in a furnace with loading temperature as room temperature and the furnace is heated at the rate of 30 degree Celsius (max) /hour and further the soaking temperature of the top pinch roll shell in the furnace is 400 to 420 degree Celsius and the soaking time is 4 to 5 hours.
4. The process as claimed in claim 2, wherein quenching process is characterized by cooling the sample to room temperature with forced air with blowers.

5. The process as claimed in claim 2, wherein the tampering process includes heating the grinded top pinch roll shell in a furnace with loading temperature as room temperature and the furnace is heated at the rate of 30 degree Celsius (max) /hour and further the soaking temperature of the top pinch roll shell in the furnace is 400 to 420 degree Celsius and the soaking time is 4 hours.
6. The process as claimed in claim 5, wherein the heated top pinch roll shell is cooled inside the furnace.
7. The process as claimed in claim 1, wherein the shell is machined to tight tolerances and assembled with the core shaft and end plates by using taper end ring, the assembled roll is then dynamically balanced.
8. The process as claimed in claim 1, wherein the top pinch roll shell size is machined to 2000XF 900 mm, strip temperature ranging from 600-700°C and having roll speed of 19m/sec.
9. The method of preparation of gray cast iron alloy for the process for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip as claimed in claim 1, wherein the said alloy consist essentially of, in weight percent, about 2.9 to3.2% carbon, from 1.30% to about 1.50% silicon, from 0.70% to about 0.90% manganese, about 0.012% maximum phosphorus, about 0.15% maximum sulphur, from 0.40% to about 1.00% chromium, from 0.40% to about 1.00% nickel, from about 0.42% to about 0.60% molybdenum, from about 0.15% to about 0.20% niobium and balance essentially iron.

10. The gray cast iron alloy consist essentially of, in weight percent, about 2.9 to3.2% carbon, from 1.30% to about 1.50% silicon, from 0.70% to about 0.90% manganese, about 0.012% maximum phosphorus, about 0.15% maximum sulphur, from 0.40% to about 1.00% chromium, from 0.40% to about 1.00% nickel, from about 0.42% to about 0.60% molybdenum, from about 0.15% to about 0.20% niobium and balance essentially iron.
Dated this day of January, 2005.
To,
The Controller of Patents,
The Patent Office,
Kolkata

The process for manufacturing heat treated alloyed gray cast iron top pinch roll shell for hot strip rolling comprising the steps of top pinch roll shell moulding, proof machining and Grinding of the moulded shell, testing of the surface of the shell material using process of ultrasonic testing, final machining and grinding wherein the said process is characterized by heat treatment cycle of the gray cast alloy after the step of proof machining and proof grinding followed by a final testing of surface of the shell after the final grinding process.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=f7m3YgJHLh0ZcOGE+LxQmA==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

269046

Indian Patent Application Number

56/KOL/2005

PG Journal Number

40/2015

Publication Date

02-Oct-2015

Grant Date

29-Sep-2015

Date of Filing

31-Jan-2005

Name of Patentee

STEEL AUTHORITY OF INDIA LIMITED

Applicant Address

RESEARCH & DEVELOPMENT CENTRE FOR LRON&STEEL,DORANDA,RANCHI-834002,

Inventors:

#	Inventor's Name	Inventor's Address
1	SINGH KRISHNA KUMAR	RESEARCH AND DEVELOPMENT CENTRE FOR LRON AND STEEL,STEEL AUTHORITY OF INDIA LTD.DORANDA,RANCHI-834002,
2	ROY ARUP KUMAR	RESEARCH AND DEVELOPMENT CENTRE FOR LRON AND STEEL,STEEL AUTHORITY OF INDIA LTD. DORANDA,RANCHI-834002,
3	KRISHNA BINOD	RESEARCH AND DEVELOPMENT CENTRE FOR LRON AND STEEL,STEEL AUTHORITY OF INDIA LTD.DORANDA,RANCHI-834002,
4	ROY GALINA PETROVNA	RESEARCH AND DEVELOPMENT CENTRE FOR LRON AND STEEL,STEEL AUTHORITY OF INDIA LTD. DORANDA,RANCHI-834002,
5	VERMA RAMA SHANKAR	RESEARCH AND DEVELOPMENT CENTRE FOR LRON AND STEEL,STEEL AUTHORITY OF INDIA LTD. DORANDA,RANCHI-834002,

PCT International Classification Number

C22C37/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA