DAIKOFCW 9CrMoV

Modified 9CrMo for high temperature creep resistance.

In the PWHT condition the microstructure consists of tempered martensite with alloy carbides.

EN W.Nr.: 1.4903 (X10CrMoVNb 9 1).
ASTM: A 213 T91 (seamless tubes), A 335 P91 (seamless pipes), A 387 Gr 91 (plates), A 182 / A336 F91 (forgings), A 217 C12A (castings), A 234 WP91, A 369 FP91.
ANFOR: NF A-49213/A-49219 Gr TU Z 10 CDVNb 09-01.

The prescribed minimum preheat temperature is 150°C, coupled with a maximum interpass temperature of 300°C. In practical terms, a preheat-interpass range within 200–300°C is considered standard. To ensure the complete transformation to martensite, it is imperative to cool welds to approximately 100°C before undergoing post-weld heat treatment (PWHT). ASME base material codes and AWS consumable classifications permit PWHT down to 730°C, whereas EN consumable classifications specify 750°C. Optimal material properties are achieved by maintaining a tempering parameter (P) of around 21 or higher, where P = °C + 273 (log t + 20) x 10–3. The maximum PWHT temperature varies; AWS consumable specifications allow 760°C, while EN permits 770°C. EN 10222-1 allows for a maximum of 790°C for base material forgings. In comparison to directly matching weld metal, incorporating some nickel and reducing niobium proves beneficial in enhancing toughness after a conveniently brief PWHT at 750–760°C. It is generally discouraged to conduct PWHT above 765°C for Ni-containing consumables due to the potential re-hardening resulting from the proximity to Ac1. Some regulatory bodies recommend maintaining weld metal Ni + Mn below 1.5% to sustain a sufficiently high Ac1 for potential higher PWHT temperatures, if necessary.