Effect of weld intercooling temperature on the structure and impact strength of ferritic–martensitic steels

The effect of inadequate weld intercooling (cooling prior to post-weld heat treatment) on the structure and impact properties of 9Cr–1MoVNb (ASME Grade 91) and 12Cr–1Mo–WV (Type 422 stainless) steels was studied. A range of weld intercooling conditions were simulated by air-cooling the two steels from the standard 1050 °C normalization temperature to temperatures ranging from 250 to 450 °C for Grade 91 and 100 to 300 °C for Type 422, and then immediately tempering at 760 °C for 2 h. For Grade 91 steel, austenite retained at the intercooling temperature transformed to ferrite during tempering; final microstructures were mixtures of ferrite and tempered martensite. For Type 422 steel, austenite retained at the intercooling temperature was stable in the tempering condition and formed martensite upon cooling to room temperature; final microstructures were mixtures of tempered and untempered martensite. Hardness and impact properties of the two steels reflected the changes in microstructure with intercooling temperature.