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 3094 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.
- 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.
- 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 preferred5.