12Cr1MoVR is a pearlitic heat-resistant steel widely used in power generation equipment, including steam boiler drums, headers, and piping systems operating at service temperatures up to 565°C. Its alloying elements—chromium for oxidation resistance, molybdenum for high-temperature strength, and vanadium for precipitation strengthening—provide excellent creep resistance. However, these same elements create significant welding challenges that demand rigorous procedural control.
The primary concern is the steel's hardening tendency and cold cracking susceptibility. With a carbon equivalent (Ceq) of approximately 0.50% (falling in the 0.4–0.6% range), 12Cr1MoVR is prone to martensitic transformation in the heat-affected zone (HAZ) during welding. This hardened microstructure, combined with diffusible hydrogen and residual stress, substantially increases the risk of cold cracking.
Effective precautionary measures begin with preheating. Preheating temperatures typically range from 150°C to 300°C depending on section thickness and welding method, with the preheated zone extending at least 100mm from the weld centerline. Interpass temperature must be carefully controlled, generally between 150°C and 300°C, to prevent both excessive hardening and overtempering.
Welding procedure requires low heat input with multi-pass, narrow-bead techniques, avoiding wide weaving motions. For tube-to-tube butt joints, gas tungsten arc welding (GTAW) is preferred for the root pass, with shielded metal arc welding (SMAW) for filling and capping. Single-V groove preparations with precisely controlled root gaps ensure complete penetration. All welding consumables must be properly dried before use.
Finally, post-weld heat treatment (PWHT) is essential to temper hardened microstructures, relieve residual stresses, and restore ductility. Without strict adherence to these precautions—preheating, controlled heat input, and PWHT—the risk of cracking and premature failure in high-temperature service becomes unacceptably high.
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