DAIKOWT 12CrMoV

12%Cr creep resisting steel also with nominally 1%Mo-0.5%W-0.3%V. The matching base material is generically called X20.

In the PWHT condition the microstructure consists of tempered martensite.

EN W.Nr.: X20CrMoV 12 1 (1.4935): G-X22CrMoV 12 1 (1.4931) cast..
ASTM: AISI Type 422.

The as-deposited weld metal consistently exhibits a room temperature hardness exceeding 500HV under diverse cooling conditions. EN 3580 mandates a preheat of 400°C with a maximum interpass temperature of 500°C. These temperatures extend beyond the austenite-martensite transformation range (Ms-Mf approximately 350-150°C). Recent procedures have shown advantages in adopting a preheat range of 200-350°C, effectively mitigating grain coarsening and facilitating some tempering of partially transformed multipass weld metal. Following welding, gradual cooling to 120°C (100-150°C) is imperative, accompanied by a holding time of 1-2 hours to facilitate transformation before initiating post-weld heat treatment (PWHT). If immediate PWHT is impractical, the transformation step should be succeeded by a postheat at around 350°C for 1-4 hours to release hydrogen before permitting cooling below 60°C. In this state, the hard weld zone is potentially susceptible to stress corrosion cracking (SCC), requiring a dry environment with minimal delay before PWHT. For production welds, the typical PWHT temperature range is 730-770°C, typically lasting a minimum of three hours, with variations based on thickness detailed in the appropriate application code.