[ Welding ] preheating but must be heated after the weld has been completed to preserve its structural integrity . Precipitation hardening stainless steels can be readily welded through standard fusion and resistance methods ; however , special care should be taken during heat treatment process to ensure the optimum mechanical properties for weldability are achieved . Achieving the same mechanical properties in the weld as in parent material is difficult for precipitation hardening steels . Careful preparation is required to utilise the matching filler and heat treatment after welding can be used to help the weld achieve close similarities to the parent metal .
Weldability to mild / low carbon steel Carbon in mild steel typically ranges from 0.05 % to 0.25 % by weight . Welding of stainless to mild steel is not difficult as the two metals have almost the same properties . MIG welding or GMAW is an excellent process to weld stainless to mild steel . Selecting the proper wire is important ; the best filler metal is 309 4 which has a low carbon content and a small amount of ferrite to prevent cracking . Grade 309 has enough chromium and nickel to counter the mild steel dilution problem . As a result , the deposited weld metal will have excellent corrosion resistance .
Medium & high carbon steel Medium-carbon steel consists of 0.30 % to 0.60 % carbon , whereas high-carbon steel contains more than 0.60 %. As the carbon content increases , the steel becomes stronger , harder , and less ductile . a . Medium carbon steels containing 0.30-0.60 % carbon and 0.60-1.65 % manganese are stronger than low carbon steel but are more difficult to weld as they are more prone to cracking . Weld using a low-hydrogen welding process or controlled hydrogen fillers . b . High-carbon steels containing 0.60-1.0 % carbon and 0.30- 0.90 % manganese are extremely hard and strong , but have poor weldability and are difficult to weld without cracking . Medium and high carbon steels are typically considered ‘ hard to weld ’ because of the hardening effect of heat at the welded joint . As the steel cools , they may readily form the hard and brittle martensite phase . Because of the high carbon content and the heat treatment usually given to these steels , their basic properties are impaired by arc welding . Therefore these steels will most likely require very thorough preheating and post-heating processes . Austenitics such as grade 304 or grade 316 can be welded to plain carbon steel using MIG and TIG welding . When welding stainless to plain carbon steel by MIG welding process , the use of filler material is preferred 5 .
Weldability to galvanised steel When welding stainless steel to galvanised steel , the zinc coating around the area to be joined should be removed beforehand . If molten zinc is present in the weld fusion zone it can result in embrittlement or reduced corrosion resistance of the finished weld . 6
Weldability to aluminium Welding aluminium and steel is utilised in the aerospace , automotive and shipbuilding industries to reduce weight and enhance efficiency . There is a huge difference in melting points of aluminium and steel , a great disadvantage for the process . Two techniques were developed to isolate the metals from each other during the arc welding process to avoid the formation of very brittle intermetallic compounds .
• The first uses bimetallic transitions , where aluminium and stainless steel are joined by methods that do not create the compounds . This allows the joining of the two metals by only welding aluminium to aluminium and stainless steel to stainless steel .
• The second is to coat the stainless steel with aluminium or silver solder and arc weld the aluminium to that instead . 7
Weldability to copper Electron beam welding is the preferred welding process for this , mainly because it is a great process for welding copper , which is the more challenging of the two metals to weld . Welding copper and stainless together is extremely difficult and offers very little structural strength . 8
Conclusion Welding stainless steel is not significantly different to welding standard carbon steel . However , one
must exercise more care and control concerning heating and cooling stainless steel , and it is important to properly match the filler metals with the material being welded .
References : 1 https :// www . atwf-inc . com / blog / 3- common-methods-for-weldingstainless-steel
2 https :// adslaser . co . uk / what-are-the- 5-types-of-stainless-steel /
3 https :// www . onlinemetals . com / weldability-of-stainless-steel
4 https :// www . materialwelding . com / how-to-weld-stainless-steelto-mild-steel /#:~: text = Simple % 20 Answer % 2D % 20YES ., not % 20 suitable % 20for % 20heat % 20 treatment .
5 https :// www . marlinwire . com / blog / welding-carbon-and-stainlesssteel #:~: text = Austenitic % 20 stainless % 20steels % 20such % 20 as , use % 20filler % 20material % 20 are % 20preferred .
6 https :// bssa . org . uk / bssa _ articles / welding-stainless-steels-toother-steels /#:~: text = When % 20 welding % 20stainless % 20steels % 20 to , resistance % 20of % 20the % 20 finished % 20weld
7 https :// weldingmastermind . com / how-to-tig-weld-aluminum-tostainless-steel-the-full-guide /
8 https :// learntomoonshine . com / howto-solder-braze-and-weld-stainlesssteel-to-copper /#:~: text = So % 20 can % 20copper % 20and % 20 stainless , offers % 20very % 20 little % 20structural % 20strength
About the author
Dr Ashok K Vaish is President of the Aryabhata Newton International Research and Educational Foundation ( ANIREF ) and , until recently , was the Ministry of Steel Chair Professor at the MS University of Baroda , India .
www . stainless-steel-world . net Stainless Steel World November 2022 25