When welding mild steel to stainless steel, which filler metal is commonly used for the root pass?

When welding mild steel to stainless steel, which filler metal is commonly used for the root pass?

• A. 309
• B. 308
• C. 316
• D. 347

Answer: (A)

When joining dissimilar metals like mild steel and stainless steel, you want a filler that can bond well to both base materials and tolerate the dilution that occurs from the carbon steel. A nickel-chromium austenitic stainless filler with higher nickel content is ideal for the root pass because it remains ductile as it mixes with mild steel and provides good corrosion resistance. This balance helps prevent cracking in the root and creates a solid foundation for subsequent weld passes. Fillers intended for stainless-to-stainless joints, such as 308, 316, or 347, don’t handle the carbon steel dilution as well and can be more prone to cracking or suboptimal corrosion performance in a dissimilar joint.

When joining dissimilar metals like mild steel and stainless steel, you want a filler that can bond well to both base materials and tolerate the dilution that occurs from the carbon steel. A nickel-chromium austenitic stainless filler with higher nickel content is ideal for the root pass because it remains ductile as it mixes with mild steel and provides good corrosion resistance. This balance helps prevent cracking in the root and creates a solid foundation for subsequent weld passes. Fillers intended for stainless-to-stainless joints, such as 308, 316, or 347, don’t handle the carbon steel dilution as well and can be more prone to cracking or suboptimal corrosion performance in a dissimilar joint.