Type 410 martensitic stainless steel is typically used in highly corrosive environments within petrochemical installations due to its resistance to halide stress corrosion cracking, hardenability, and low cost compared to austenitic stainless steel. However, the industry has experienced difficulties in meeting the ASME toughness, and NACE hardness requirements for wet sour services of Type 410 steel welds. Recent studies have shown that these problems are related to the wide compositional ranges of Type 410 base metals and welding consumables, leading to exceeding the A1 temperature during postweld heat treatment (PWHT) and formation of fresh martensite, and to retention of significant amount of delta ferrite in the final weld metal and heat affected zone microstructures. These studies have identified two Type 410 optimized weld metal compositions that met the specified hardness and toughness requirements.
The objective of this work was to quantify the tempering response in one of the optimized welding consumables and in two Type 410 base metals. Samples of these materials were subjected to a series of PWHTs at temperatures corresponding to the lower and upper limits of the ASME code recommended temperature range (760 C and 800 °C) and at 10 °C below the A1 temperature of each material. The PWHT durations were 5 and 30 minutes, and 1, 2, and 4 hours. The hardness values related to all PWHTs performed below the corresponding A1 temperatures were used to generate Holloman–Jaffe type equations for all tested materials. As expected, the PWHTs performed above the A1 temperatures resulted in the formation of fresh martensite.