Title of Invention

METHOD OF QUENCHING

Abstract

A method of quenching a heated metal part comprising the steps of (vi) dissolving 2 to 5% of starch powder in water at between 85 to 95 degrees Celsius; (vii) holding the slurry so formed for 5 to 15 minutes until the starch is completely gelatinised; (viii) allowing the starch solution to cool down to room temperature; (ix) pouring the starch solution so prepared into a quenching bath; and (x) immersing the heated metal part in the quenching bath.

Full Text

FORM-2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE Specification (Section 10; rule 13) METHOD OF QUENCHING TATA CONSULTANCY SERVICES of Bombay House, Sir Homi Mody Street, Mumbai 400 023, Maharashtra, India, an Indian Company THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THIS INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED:- 5 APR 2004 This invention relates to heat treating methods and particularly to a method of quenching heated metal parts i.e., parts fabricated from steel, alloy steel, aluminum and aluminum alloys. Hardening of steel components is one of the most commonly practiced heat treatments operation in the steel industry. The hardening process comprises of heating the steel components to austenitizing temperature (~800-900°C), soaking at that temperature for thermal homogenization followed by quenching in an appropriate medium to room temperature. Quenching is a process whereby a steel component heated to a given elevated temperature is rapidly cooled by immersion in a quench bath containing compositions having a high heat-extracting potential such as air, water, brines, oils or polymer solutions. The rate of cooling is an important parameter during the quenching process. Cooling rates are dependent on factors such as the size, shape and composition of the component being quenched as well as the composition, concentration, degree of circulation and temperature of the quench bath. Depending on the cooling rate during quenching, the austenite phase can be transformed into a variety of other phases such as ferrite, pearlite, bainite and martensite. Of the various phases, ferrite is the softest phase, whereas martensite is the hardest phase. Slow cooling rate result into formation of ferrite phase, whereas fast cooling rate provides martensite 2 phase. Formation of martensite phase is generally the main aim of hardening treatment. It must be noted that, cooling rates are not uniform throughout a component; surface regions are better able to dissipate heat and thus cool faster than interior regions. The difference in cooling rates and temperature gradient within the component produce thermal stresses. If the cooling rate is very high, the thermal stresses can result into warping, distortion and even cracking of the component. Therefore, during the quenching process, the cooling rate of a component should be fast enough to prevent formation of soft ferrite phase, but not too fast to prevent distortion and cracking. The quantification of too fast or too slow cooling rate mainly depends on the steel grade and accordingly appropriate quenching media is selected for a particular grade of steel. For example, medium alloyed air hardening grade steels (AISI A2, A3, A4, A10, etc.) can be hardened by air cooling, oil hardening grades (AISI 01, 02, 06, etc.) can be hardened through quenching in oil, whereas water hardening grades (AISI Wl, W2, W3, etc.) require high cooling rates which can be obtained only through water and brine quenching. Of the various quenching media, oil is one of the most common quenching media in the industry. Generally, oil provides moderate cooling rate and therefore results in minimal distortion in the component. Therefore, many of the precision components such as gears, and bearing rings are hardened by oil quenching. 3 Although oil exhibits this highly advantageous cooling response, currently, the use of oil as a common quenching medium for hardening of steel is associated with several environmental liabilities such as oil fumes, smoke emissions, fire hazard, oil spills, leaking underground storage tanks, ground water contamination and waste oil disposal liabilities. With increasmg environmental awareness as well as strict regulations, the use of oil as quenching media is being discouraged in many of the environmentally conscious countries. For example, in USA, used quenching oil is considered a hazardous waste and its disposal is regulated by EPA's strict used oil management standards. In the comprehensive technology roadmap "Vision 2020" prepared by ASM Heat Treating Society, in close collaboration with leaders in heat treatment industries, replacement of oil as a quenching media has been given very high importance to achieve zero emissions from heat treatment industry. Significant efforts have been put in towards the development of synthetic organic polymer quenching media as an alternative to Oil. However, most of these synthetic quenchants are proprietary and expensive which makes their usage very limited. U.S.PatNo. 3,022,205 (No Indian equivalent application available) discloses an aqueous quenchant medium containing between 0.2 g and 4.5 g, per gallon of water, of an ethylene oxide polymer having a molecular weight of between 100,000 and several million. U.S.Pat, No. 3,220,893 (No Indian equivalent application available) discloses a metal quenchant medium containing an aqueous solution of an oxyalkylene polymer containing both oxyethylene units and higher molecular weight oxyalkylene units such as units derived from propylene 4 oxide. The polymers are further described as having an oxyethylene to oxyalkylene ratio by weight of from about 70:30 to about 90:10, and an average molecular weight of from 600 to 40,000. The specific polymer exemplified is a polyglycol containing 75 percent by weight of oxyethylene units and 25 percent by weight of oxypropylene units, having a viscosity of about 90,000 Saybolt seconds at 100 degree.?, and an average molecular weight of from about 12,000 to about 14,000. U.S.Pat. No. 3,475,232 (No Indian equivalent application available) discloses an aqueous quenchant containing a normally liquid water soluble oxyalkylene polymer having oxyethylene and higher molecular weight oxyalkylene units, and a water soluble alcohol selected from the group consisting of glycerol, glycols containing from 2 to 7 carbon atoms, and mono-lower alkyl ethers of said glycols in which the alkyl group contains from 1 to 4 carbon atoms. A polymer comprising about 75 percent by weight of oxyethylene units and about 25 percent by weight of oxypropylene units, having a viscosity of about 150,000 Saybolt seconds at lOO.degree.F. is particularly preferred. U.S.Pat. No. 4,381,205. (No Indian equivalent application available) discloses a metal quenching process using an aqueous quenchant bath containing from about 0.5 to about 50% by weight of the bath, of a liquid, water-soluble or water dispersible capped poiyether polyol. The object of this invention is to provide a suitable eco-friendly natural quenchant, which can replace quenching oil from the heat treatment industry. The commercial aspects such as being a low-cost and 5 availability have also been considered. It is a further object of this invention that the quenchant should have following characteristics: (i) The quenching intensity should be at least equivalent to that of oil, and at the same time it should not be very high to introduce distortion and cracking in the as quenched component. (ii) It should be reusable and possess long shelf life. It should not age appreciably with time and repeated use. (iii) It should not generate fumes during quenching operation. (iv) The spurting should be minimal during the quenching operation. This is especially important for salt bath hardening, where vigorous spurting occurs during water quenching. (v) It should be biodegradable and the disposal of used quenchant should not pose any environmental problem. (vi)In addition to the above characteristics, commercial issues such as: low cost and availability must be addressed. In accordance with this invention it has been found that the best approximation of the cooling curve characteristic of oil can be achieved using an aqueous solution of starch with or without the addition of gums and resins. Starch is a low cost, abundantly available natural organic product. In this invention, potential of starch solution for application as quenching media has been envisaged. Commercially, starch is available in the form of powder. Starch solution is obtained by breaking up of hydrogen bonds 6 between the molecules by hydration, which results in swelling of starch granules and solubilization of starch molecules. These events, referred collectively as gelatinization, are commonly effected by heating a slurry of starch granules in water. Accordingly this invention provides a method of quenching a heated metal part comprising the steps of (i) dissolving 2 to 5% of starch powder in water at between 85 to 95 degrees Celsius; (ii) holding the slurry so formed for 5 to 15 minutes until the starch is completely gelatinised; (iii) allowing the starch solution to cool down to room temperature; (iv) pouring the starch solution so prepared into a quenching bath; and (v) immersing the heated metal part in the quenching bath. Typically, 1% by weight formaldehyde is added to the starch solution to preserve the solution from degradation.. Typically the starch powder is corn starch powder. Alternatively, the starch powder is selected from potato, rice or tapioca. The starch used may be at concentrations between about 2% and 5% product by volume, which closely approximates the desired cooling curve characteristic of oil. Corn starch can be readily cooked at low temperature and is also stable during use. Further the corn starch is not unstable during aging or when subjected to heat. Alternatively, laundry starch between 2- 7 3% can also be used. It may be noted that depending on the steel grade, the type of starch and its concentration can be tailored to match the desired cooling rate. The corn starch quenchant in accordance with this invention is prepared in following manner: Required quantities of corn starch powder and water were taken, depending upon the concentration of starch solution to be prepared, and the corn starch was dissolved in water at 90°C. The slurry was held at this temperature for about 10 minutes before cooling it down to room temperature. After holding at 90°C for a period of 10 minutes almost complete gelatinization (> 90%) takes place. During the heating and cooling cycle, stirring of the solution is required to prevent granulation and lump formation. After the starch solution was prepared, 1% (by wt) formaldehyde was added to in order to increase its shelf life. Starch solution without formaldehyde degraded within a day, whereas no degradation of the starch solution containing formaldehyde was observed even after three to four weeks. In the accompanying drawings the following description is provided Figure 1 is a graph showing the variation in viscosity with change in concentration is plotted as seen in Figure 1 of the accompanying drawings. The graph in figure 1 indicates that the viscosity of mineral oil is close to 4% cornstarch solution. Figure 2 shows the cooling curves for various concentrations of starch solutions, filtered potable water, air and quenching oil; Figure 3 shows the results of Figure 2 tabulated in the Table 1 shown in 8 the Figure 2; Figure 4 shows the measured hardness values using different concentrations of corn starch in accordance with this invention. Quenchant Characterization (i) Viscosity Measurements: Viscosity of the quenchant plays a major role in heat transfer during quenching, therefore govern the quenching intensity. Viscosity of 2%, 3%, 4% and 5% cornstarch solutions were measured by the Brookfield viscometer and compared with the viscosity of mineral oil. The variation in viscosity with change in concentration is plotted as seen in Figure 1 of the accompanying drawings. The graph in figure 1 indicates that the viscosity of mineral oil is close to 4% cornstarch solution. Although viscosity is an important parameter for comparing the quenchant characteristics, other parameters such as thermal conductivity and boiling characteristics of the media also affect the quenching performance. The change in viscosity of a starch solution of a particular concentration on changing the pH of the solution was also measured. The results indicated that the viscosity of the starch solution increases as it is made either acidic or basic. (ii) Cooling Curve Measurements in Quenching Media The primary requirement from a quenching media is to provide the desired cooling rate or quenching intensity. Of all the available methods 9 of measuring quenching intensity, those measuring temperature as a function of time (cooling curve) at a specified point within the test specimen are commonly used. Worldwide the standard method for testing of industrial quenching oils is by using a solid Inconel probe (ISO 9950) covered by an Inconel sheath. Experiments were performed to determine the cooling rate imparted by a variety of starch solutions, water and industrial quenching oil. The cooling rates were obtained by recording the rate, at which a particular quenchant cooled the standard Inconel 600 Probe, fabricated as per international standard ISO/DIS 9950. During the cooling curve experimentation, the standard probes were heated for 10 minutes in a muffle furnace held at 825 °C, and quenched in the quenching media. During the holding and quenching period temperature variation with time was recorded using the HP datalogger system at 0.1 sec intervals. During quenching no stirring was done. The cooling curves for various concentrations of starch solutions, filtered potable water, air and quenching oil are shown in Fig. 2 of the accompanying drawings. The results are tabulated in the Table 1 shown in Figure 3 of the accompanying drawings. The general observations are as per following: 1. The maximum cooling rate imparted by water was 214°C/sec at 605°C. This rate of cooling, although greater than the critical cooling rate for almost all grades of steel, is very high and causes distortion of the component being quenched and hence is undesirable. 2. The cooling rate imparted by quenching oil (A cracked petroleum product from Indian Oil) was 65°C/sec at 570°C and is an optimum 10 cooling rate. However, oil quenching is hazardous as it generates toxic fumes of oil during quenching and the disposal of used quenching oil also poses environmental hazards. 3. The cooling rate imparted by 2% (40 grms/liter of water) laundry starch was 65°C/sec at two different temperatures of 580°C and 390°C, which is equivalent to that imparted by oil. When the concentration was increased to 3% (60 grms/liter of water) laundry starch, the peak cooling rate slightly decreased to 59°C/sec, but more important the peak temperature significantly, reduced to 350 °C. The use of laundry starch as quenchant poses no environmental liabilities and it maintains its stability over a long period of time. 4. The cooling rates imparted by 3% (60 grms/liter of water) and 2% (40 grms/liter of water) corn starch solutions were 90°C/sec between 450-400°C and 80°C/sec between 450-400°C respectively, which is an optimum cooling rate. The use of corn starch is environment friendly, however addition of formaldehyde in very small amounts of 0.5% by weight of the starch solution is necessary to maintain its stability over long period of time. 4% (80 grms/liter of water) corn starch gave a very low cooling rate of 38 °C/sec. For 2% and 3% starch, the peak cooling rate and peak temperature were very close. Only the start of peak temperature was at 680°C for 2% corn starch as opposed to 560 °C for 3% corn starch. 5. The cooling rate imparted by 2% (40 grms/liter of water) wheat starch was 38°C/sec at 534°C, which is lower than the critical cooling rate required and hence is not desirable. 6. Typically, it was observed that with increase in starch concentration, the cooling rate decreases and the peak temperature shifts towards lower temperature. Depending on the grade of steel, the starch type and 11 concentration can be varied to obtain an optimal cooling rate. Experimentation in accordance with this invention Four components of EN 31 grade steel were taken, and after heating in salt bath furnace they were quenched in oil, 2%, 3% and 4% corn starch solutions. During the oil quenching, large amount of fumes were observed whereas no such fumes were observed while quenching in starch solutions. Little spurting was observed while quenching in starch solution while no spurting took place during oil quenching. However, compared to vigorous spurting observed during water quenching, the spurting observed during quenching in starch solution is much lesser and should not pose a working hazard. Subsequently, hardness measurements were carried out on all the quenched samples. Four measurements were made on each of the quenched components. The measured hardness values are plotted in Fig. 4 of the accompanying drawings. As is evident in the Fig. 4, hardness values of components quenched in starch solutions are slightly higher the oil quenched components. The slight decrease in hardness value with increase in starch concentration observed in the figure 4, may be due to the increased viscosity and decreased quenching power (cooling rate) with increased concentration. More important is that all the four components satisfied the desired hardness value of greater than 60 Re, and therefore shows that the starch 12 solution can be used as an alternate quenchant to oil. Microstnictures of the oil quenched component and the component quenched in 3% starch solutions were observed. The two microstnictures were very similar and showed uniform dispersion of carbides. The observed microstnictures are also similar to the oil quenched microstructure reported in literature. The experimentation shows that starch based solutions have the potential to be used as quenchants for industrial hardening operations. This quenchant will offer following benefits: (a) The starch solutions offer the quenching power similar to the oil media (b) The concentration can be tailored depending on the steel grade and the desired cooling rate (c) It is eco-friendly with no hazardous fumes, and disposal liabilities, which are major concerns during oil quenching. (d)The spurting is minimal and should not pose any working hazard. (e) For improving shelf life, the biodegradation of starch solution can be inhibited by small addition of formaldehyde solution. (f) It is relatively inexpensive and easy to prepare, therefore it can be readily implemented by both large and small scale heat treaters. • This invention therefore envisages the feasibility of replacing quenching oil as a quenchant by starch solutions. The starch solutions are environmentally friendly, having no toxic fumes and no after usage disposal liabilities as compared to oil fumes, • Depending on the grade of steel, critical temperature and desired 13 cooling rate, the composition and concentration of the starch quenchant can be tailored to provide the required cooling characteristics. Other biodegradable materials like sorghum, gum, and resins can be added to the starch or the starch can be used as a combination of one or more starches from different sources such as corn, potato, rice and tapioca [sago] in accordance with an alternative embodiment of this invention. As will be readily appreciated, numerous variations and combinations of the features set forth above can be utilized without departing from the present invention as set forth in the above description of the invention. These quenchants can also be used for quenching other non-ferrous materials. Such variations are not regarded as a departure from the spirit and scope of the invention, and all such modifications are intended to be included within the scope of the above description. 14 We Claim 1. A method of quenching a heated metal part comprising the steps of (vi) dissolving 2 to 5% of starch powder in water at between 85 to 95 degrees Celsius; (vii) holding the slurry so formed for 5 to 15 minutes until the starch is completely gelatinised; (viii) allowing the starch solution to cool down to room temperature; (ix) pouring the starch solution so prepared into a quenching bath; and (x) immersing the heated metal part in the quenching bath. 2. A method of quenching a heated metal part as claimed in claim 1, in which 1% by weight formaldehyde is added to the starch solution. 3. A method of quenching a heated metal part as claimed in claim 1 or claim 2 where the starch powder is corn starch powder. 4. A method of quenching a heated metal part as claimed in claim 1 or claim 2 where the starch powder is laundry starch powder. 15 5. A method of quenching a heated metal part as claimed in any one of the preceding claims, in which the starch powder is selected from potato, rice or tapioca. 6. A method of quenching a heated metal part as described herein with reference to the accompanying examples. Dated this 7 day of June 2001 Mohan Dewan Of R. K. Dewan & Co., Applicants' Patent Attorney 16

Documents:

94-mum-2001-cancelled pages(23-1-2001).pdf

94-mum-2001-claims(granted)-(5-4-2004).doc

94-mum-2001-claims(granted)-(5-4-2004).pdf

94-mum-2001-correspondence(11-9-2006).pdf

94-mum-2001-correspondence(ipo)-(11-8-2003).pdf

94-mum-2001-drawing(5-4-2004).pdf

94-mum-2001-form 1(25-1-2001).pdf

94-mum-2001-form 1(25-5-2007).pdf

94-mum-2001-form 19(21-5-2003).pdf

94-mum-2001-form 2(granted)-(5-4-2004).doc

94-mum-2001-form 2(granted)-(5-4-2004).pdf

94-mum-2001-form 3(12-6-2001).pdf

94-mum-2001-form 3(5-4-2004).pdf

94-mum-2001-form 5(5-4-2004).pdf

94-mum-2001-form 6(1-9-2004).pdf

94-mum-2001-petition under rule 138(5-4-2004).pdf

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