According to a 2025 technical guide by TWI, dissimilar metal welding (DMW) between stainless steel and carbon steel is common in piping systems but introduces unique metallurgical challenges. The primary concern is carbon migration from the carbon steel into the stainless steel weld metal, which can lead to carbide precipitation and reduced corrosion resistance in the heat-affected zone.
To mitigate these risks, the standard practice is to use a nickel-based filler metal such as ERNiCr-3 (Inconel 82) or ERNiCrMo-3 (Inconel 625). These fillers accommodate the difference in thermal expansion coefficients and minimize the formation of brittle martensitic layers at the fusion boundary.
Key considerations for DMW include:
• Selection of filler metal based on service temperature and corrosive environment.
• Control of dilution by limiting the weld heat input and using a buttering layer on the carbon steel side.
• Post-weld heat treatment (PWHT) requirements, which often differ for each base material and must be carefully evaluated.
Auditors typically check that the WPS specifies the correct filler metal and that welders are qualified for the specific DMW joint configuration. A common nonconformance is using a standard stainless steel filler for carbon steel to stainless steel joints, which can lead to premature failure.
How do you handle filler metal selection for DMW in your projects?
Source: TWI, 2025