Issue of post-weld heat treatment time for chromium-molybdenum heat-resistant steel
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Is heat treatment required immediately after welding chromium-molybdenum heat-resistant steel pipes and lines? What is the allowable delay time? Is it okay to wait for 72 hours?
These issues are specified in the regulations; what should be done if heat treatment cannot be carried out immediately.
It should be done immediately. Heat-resistant steels have Cr and Mo as their main alloying elements, with a matrix structure of pearlite (or pearlite + ferrite); common types include 15CrMo and 12CrMoV. The heat-affected zone resulting from the welding of heat-resistant steel develops a hard and brittle martensitic structure, which makes it prone to the formation of cold cracks. High-temperature tempering should be carried out immediately after welding to prevent the formation of delayed cracks, relieve stress, and improve the microstructure. The post-weld heat treatment of pearlitic heat-resistant steel should be avoided in the temperature range of 350–500°C to prevent embrittlement.
I wonder what would happen with other steel grades?
Post-weld heat treatment for different steel grades should be included in the manual.