12CrMoV

12% chrome CrMoV steels are specifically designed to operate under critical temperature conditions, offering notable creep resistance up to at least 550°C. The high chromium content ensures excellent performance regarding resistance to steam and combustion corrosion, surpassing those of lower composition CrMo steels ranging from 2% to 9%. These steels are mainly used in the production of cast and wrought components for high-pressure pipelines, steam headers, heat exchangers, and turbine parts, finding their primary application in the power generation sector and occasionally in petrochemical fields.

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 hardness of the weld metal at room temperature exceeds 500 HV across a wide range of cooling conditions. The EN 3580 standard requires preheating to 400°C, with a maximum interpass temperature of 500°C. These temperatures exceed the austenite-martensite transformation range (Ms-Mf of about 350-150°C). Recent welding procedures have utilized preheating between 200°C and 350°C to reduce granularity and encourage some tempering of the weld metal during the partially transformed multipass cycle. Following welding, it is essential to cool the joint slowly to 120°C (with a range of 100-150°C) and hold it at this temperature for 1-2 hours to allow the transformation before post-weld heat treatment. If immediate heat treatment is not possible, cooling should be followed by post-heating at about 350°C for 1-4 hours to facilitate hydrogen release, before allowing cooling below 60°C. Under these conditions, the hardened weld area can be vulnerable to stress corrosion cracking (SCC) and should remain dry, minimizing the waiting time before PWHT. Post-weld heat treatment (PWHT) usually occurs at temperatures between 730°C and 770°C, requiring a minimum duration of three hours for processing, varying according to thickness; for further details, it is important to refer to the relevant application code.