Title of Invention

PROCESS FOR SHIELDED METAL ARC WELDING OF STEEL BODIES MADE FROM DISSMILAR STEEL COMPOSITIONS

Abstract

A process for shielded metal arc welding of steel body made from dissimilar steel composition, particularly dissimilar medium carbon steel compositions. The process comprises heat treating the steel bodies in order to bring down the hardness of the steel bodies to a range of 250 to 400 BHM (Brinell Hardness Number) comprising one or several stages of heating and/or subsequent cooling of the steel bodies, preparing the weld joint comprising providing a suitable groove between the joining faces of the steel bodies, shielded metal arc welding providing root run and first layer cladding and at least one stage of build up by electrode. The process of invention is particularly useful for joining two broken steel parts of a critical machine component made from dissimilar steel compositions and eliminates the requirement of manufacturing a new component to replace the broken steel part

Full Text

PROCESS FOR SHIELDED METAL ARC WELDING STEEL BODIES MADE FROM DISSIMILAR STEEL COMPOSITIONS Field of invention The present invention relates to a process for shielded metal arc welding of steel bodies made from dissimilar steel compositions In particular, the invention relates to a process for shielded metal arc welding of steel bodies made from dissimilar medium carbon low alloy steel grades The process of the invention is particularly useful for joining two broken steel parts of a critical machine component made from dissimilar steel compositions and eliminates the requirement of manufacturing a new component to replace the broken steel part Background of the invention Conventionally different welding processes are used for joining two metal parts, hard surfacing of engineering components for wear and corrosion protection, fabrication of utility items, repair and reclamation of worn our parts and similar applications The known welding methods of joining metals parts are Manual Metal Arc Welding, Submerged Arc welding, Open Arc welding etc. These joining methods differ from each other in terms of low or high heat input, the form of welding consumables, the method of shielding arc, the design of equipments used in different methods and such other features All the known welding methods, like the ones discussed above, are applicable only to joining of metal parts made from the same composition They are not applicable for welding two metal/steel parts made from dissimilar composition and usually result in weak and unreliable joints Moreover, each of the joining methods has its own merits and dements with respect to its use in a particular situation Thus, the known processes are highly dependant on the specific composition of the metal parts to be welded and has to be customized and modified based on the specific requirement A 2 single process providing suitable weld for joining all types of steel composition is not known in the art The problem is specifically acute in siluations where it is required to join two broken parts of a critical machine component Often a suitable welding process for joining two broken pieces of steel shafts which are part of a critical machine component and made from different steel compositions is required As such a process is not known, the entire machine part or shaft has to be replaced by a new one and is thus uneconomical Most of such machine shafts require high strength and tolerance to high levels of stress and shocks None of the known methods provide a weld that will be able to meet such requirements and the only possible solution is to replace the entire shaft/machine part This leads to larger durations of break down period of a main production line leading to production loss Object of the invention Thus the object of the present invention is to provide a process for welding steel bodies made from dissimilar steel compositions Another object of the present invention is to provide a process that will be applicable for joining steel bodies made from a wide range of steel compositions Yet another object of the present invention is to provide a process that will ensure a strong and long lasting welded joint A further object of the present invention is to provide a process for welding steel bodies such that the joint meets the strengh requirements of a critical machine part In order to meet the above-mentioned objects, the applicants have undertaken extensive research based on the joining schedules required for several specific jobs comprising study of the metallurgical characteristics of wide variety of steel grades 3 and analysis of the services required. The research was based on the selection of the welding consumables, designing and preparing the weld joint, formulation of pre weld treatment schedule and welding parameters, formulation of post weld treatment schedule and finishing The applicants have now found a process for welding dissimilar steel bodies made from a variety of steel compositions Summary of the invention Thus according to the present invention there is provided a process for shielded metal arc welding of steel bodies made from dissimilar steel compositions comprising the steps of (i) heat treating the said steel bodies in order to bring down the hardness of said bodies to a range of 250 to 400 BHN (Brmell Hardness Number) comprising one or several stages of heating and/or subsequent cooling of said steel bodies, (n) preparing the weld joint comprising providing suitable groove between the joining faces of said steel bodies, (in) shielded metal arc welding providing root run and first layer cladding, and (iv) at least one stage of build up by electrode Detailed description of the process The process of the present invention is applicable preferably for medium carbon low alloy steel grades comprising 0 3 to 0 5 wt% carbon, 0 5 to 0 85 wt% manganese, 0 15 to 0 3.5 wt% silicon, 0 5 to 2 wt% chromium, 0 25 to 0 4 wt% molybdenum, 0 to 2 5 wt% nickel, sulphur and phosphorus together 0 to 0 1 wt% with carbon equivalent of around 0 65 to 1 0 wt% 4 The first step of the process comprises heat treating the steel bodies Dissimilar grades of steel have different hardness values and the main purpose of the heat treatment is to bring the hardness of both the steel grades to a range of 250 to 400 BHN, preferably 300 to 350 BHN Such heat treatment consists of several cycles of heating the steel bodies and subsequent cooling, preferably air cooling to room temperature or slow cooling using lime depending on the steel grade Preferably, this treatment if carried out by normalizing the bodies followed by tempering The step of normalizing comprises at least two cycles of heating the bodies, holding them at the elevated temperatures for some time and then air cooling to room temperature Preferably in the first cycle, the bodies are heated to a temperature between 500 to 800°C at a rate of 40 to 80°C/hr They are then held at that temperature for at least half an hour Thereafter, they are further heated to a temperature between 600 to 1000°C at a rate of 60 to 120°C/hr The steel bodies are held at that temperature for at least 2 hours and then allowed to air cool to room temperature The step of normalizing is followed by tempering wherein the bodies are heated to a temperature between 200 to 600°C at a rate of 60 to 120°C/hr, held for at least 4 hours and then allowed 1o air cool to room temperature After heat treating the steel bodies, the weld joint is prepared by providing suitable groove-between the faces of the bodies Preferable, both faces of the joint are ground to form an included angle, preferably 45 degree If the steel bodies are hollow shafts, then one of the shafts are also surface ground in order to make the outside diameter of the face ground portion of the shaft equal to the inner diameter of the other shaft This enables to fit the surface ground shaft into the other shaft and also create a substantially V groove between the faces of the shafts The bodies are then welded The welding schedule comprises root run and first layer cladding which is preferably carried out by a non-hygroscopic electrode for high penetration and joining strength The diameter of the non-hygroscopic electrode is preferably 2 5 mm The root run and first layer cladding is preferably carried out at 80 Amp current and between 40 to 60V-voltage 5 The final step of welding is the step of build up The step preferably comprises two build up stages namely initial and final build up which are carried out with Nickel base electrodes The diameter of electrodes used for initial and final build up is preferably 3 15 and 4 mm respectively The initial build is preferably carried out at 130 Amp-current-and-45 to 60V voltage The final build up is preferably carried out at 160Amp current and 45 to 60V voltage. In order to avoid distortion the process is preferably carried out using jigs and fixtures During the welding operations the preheat and interpass temperatures were preferably around 270 and 250°C respectively After welding the joined portions are preferably undergone post weld and stress relieving treatments The joint is then ready for machining and ultrasonic testing The invention will now be demonstrated with reference to a non-limiting example and figure of the drawing in which Figure 1 shows the weld joint preparation Example: Process for joining hollow shafts made from En19 and En24 grades forged steel The chemical compositions (in wt%) of En19 and En24 grades are as follows Grade C Mn Si Cr Mo Ni S&P Carbon Equivalent En19 0 40 0 75 0 25 1 00 0 24 - upto 0 05 0 77 En24 0 40 0 60 0 25 1 20 0 30 1 60 upto 0 05 0 90 The En24 grade shaft was normalized by first heating to 650°C at the rate of 60°C/hr and holding for 1 hour The shaft was then further heated to 825°C at a rate of 6 85°C/hr, held for 4 hours and air cooled to room temperature After normalizing the En24 shaft was tempered by heating to 400°C at a rate of 85°C/hr, held for 6 hours and air cooled to room temperature After heat treating the hardness obtained was around 300 to 320 BHN The En19 shaft was also heat treated by heating to 350°C for 1 hour and slow cooling using lime The hardness obtained was around 350 BHN After heat treatment the weld joint was prepared by machining the joining faces of the two shafts to form included angles of 45 degree. The surface of the shaft having smaller inside diameter is surface machined in the face machined portion in order to lower the outer diameter and make it equal to the inner diameter of the other shaft so that the surface machined shaft fits inside the other shafts near the joint Figure 1 shows the weld joint preparation wherein En24 grade shaft (1) is face machined as well as surface machined and the En19 grade shaft (2) only face machined so that the En24 fits inside En19 creating a V-groove (3) Shielded metal arc welding is carried out comprising root run and first layer cladding by a non-hygroscopic electrode of 2.5 rnm diameter Current was maintained at 80 Amp and Voltage at 50V Thereafter, initial and final build up was carried out by Nickel base electrodes of 3 15 and 4 mm diameter respectively Current during the initial build up was maintained at 130 Amp and voltage at 50V while during the final build current was maintained at 160 Amp and voltage at 50 V In order to avoid distortion the process was carried out using jigs and fixtures The preheat and interpass temperatures were maintained at 270 and 250°C respectively 7 We claim: 1 Process for shielded metal are welding of steel bodies made from dissimilar medium carbon low alloy steel grades comprising the steps of: (i) heat treating the said steel bodies in order to bring down the hardness of said bodies to a range of 250 to 400 BHN comprising one or several stages of heating and/or subsequent cooling of said steel bodies; (ii) preparing the weld joint comprising providing suitable groove between the joining faces of said steel bodies; (iii) shielded metal arc welding providing root run and first layer cladding; and (IV) at least one stage of build up by electrode. 2. Process according to claim 2, wherein said medium carbon low alloy steel grades comprises 0.3 to 0.5 wt% carbon, 0.5 to 0.85 wt% manganese, 0.15 to 0.35 wt% silicon, 0.5 to 2 wt% chromium, 0.25 to 0.4 wt% molybdenum, 0 to 2.5 wt% nickel, sulphur and phosphorus together 0 to 0.1 wt% with carbon equivalent of around 0.65 to 1.0 wt%. 3. Process according to claim 1, wherein step (i) comprises three stages namely first, second and third stages of heating and subsequent cooling of said steel bodies. 8 4. Process according to claim 4, wherein said first stage comprises heating said steel bodies to a temperature between 500 to 800°C at a rate of 40 to 80°C/hr, holding the heated bodies for at least half hour 5. Process according to claim 5, wherein in said first stage the bodies are heated to a temperature of 650°C at a rate of 60°C/hr and holding the heated bodies for 1 hour 6. Process according to claim 4, wherein in said second stage the bodies are heated to a temperature between 600 to 1000°C at a rate of 60 to 120°C/hr, held for at least 2 hours and then allowed to air cool to room temperature 7. Process according to claim 7, wherein in said second stage the bodies are heated to a temperature of 825°C at a rate of 85°C/hr, held for 4 hours and then allowed to air cool to room temperature. 8. Process according to claim 4, wherein in said third stage the said bodies are heated to a temperature between 200 to 600°C at a rate of 60 to 120°C/hr, held for at least 4 hours and then allowed to air cool to room temperature 9. Process according to claim 9, wherein in said third stage the said bodies are heated to a temperature of 400°C at a rate of 85°C/hr, held for 6 hours and then allowed to air cool to room temperature 10. Process according to claim 1, wherein in step (n) said groove is a V-groove with included angle of 45 degrees 11 Process according to claim 1, wherein in step (iii) said root run and first layer cladding is carried out using a non-hygroscopic electrode 9 12. Process according to claim 11 wherein said non-hygroscopic electrode has a diameter of 2 5 mm. 13. Process according to claim 12, wherein said root run and first layer cladding is carried out at 80 Amp current and 40 to 60V voltage 14. Process according to claim 1, wherein step (iv) comprises two stages of build up, the stages being that of initial and final build up 15. Process according to claim 15, wherein said stage of initial build up is carried out with nickel based electrode having diameter of 3 15 mm 16. Process according to claim 15, wherein said stage of initial build up is carried out at 130Amp current and 45 to 60V voltage 17. Process according to claim 15, wherein said stage of final build up is carried out with nickel based electrode having diameter of 4 0 mm 18. Process according to claim 15, where stage of initial build up is carried out at 160Amp current and 45 to 60V voltage 19. Process according to claim 1, wherein the said steel bodies are hollow steel shafts 10 A process for shielded metal arc welding of steel body made from dissimilar steel composition, particularly dissimilar medium carbon steel compositions. The process comprises heat treating the steel bodies in order to bring down the hardness of the steel bodies to a range of 250 to 400 BHM (Brinell Hardness Number) comprising one or several stages of heating and/or subsequent cooling of the steel bodies, preparing the weld joint comprising providing a suitable groove between the joining faces of the steel bodies, shielded metal arc welding providing root run and first layer cladding and at least one stage of build up by electrode. The process of invention is particularly useful for joining two broken steel parts of a critical machine component made from dissimilar steel compositions and eliminates the requirement of manufacturing a new component to replace the broken steel part

Documents:

00255-kol-2003-abstract.pdf

00255-kol-2003-claims.pdf

00255-kol-2003-correspondence-1.1.pdf

00255-kol-2003-correspondence-1.2.pdf

00255-kol-2003-correspondence.pdf

00255-kol-2003-description(complete).pdf

00255-kol-2003-drawings.pdf

00255-kol-2003-form-1.pdf

00255-kol-2003-form-18.pdf

00255-kol-2003-form-2.pdf

00255-kol-2003-form-3.pdf

00255-kol-2003-pa.pdf