DAIKOFCW 9CrMo

9%Cr-1%Mo martensitic alloy for elevated temperature service.

In the PWHT condition the microstructure consists of tempered bainite.

EN W.Nr.: X12CrMo 9 1 (1.7386), X7CrMo 9 1 (1.7388), GS-12CrMo 10 1 (1.7389).
ASTM: A387 gr. 9, A335 gr. 9, A234 gr. WP9 (fittings), A199 gr. T9, A213 gr. T9, A182 gr. F9, A336 gr. F9, A217 gr. C12.

Due to the inherent hardness observed in the as-deposited state, reaching values of up to 450HV, and the relatively diminished fracture resistance characteristic of the martensitic 9CrMo microstructure, it is imperative to implement a preheat and maintain a minimum interpass temperature of 200°C to prevent hydrogen-induced cracking. Ensuring electrodes are meticulously controlled and handled is crucial to achieve weld metal with hydrogen levels below 5ml/100g. In the context of TIG root runs or all-TIG welds, consideration may be given to a lower preheat of 150°C. During welding, complete transformation within the working range of 200-350°C may not be achieved. Therefore, partial cooling to around 150°C is recommended before direct transfer to Post-Weld Heat Treatment (PWHT), followed by Non-Destructive Examination (NDE). If PWHT is intended after complete cool-out and NDE, maintaining the preheat temperature for a specified duration, according to thickness, is advisable to promote effective hydrogen dispersal. Notably, this precaution holds less significance for TIG and solid wire MAG processes. PWHT to temper the weldment typically falls within the range of 705-780°C, as outlined in ASME B31.3 (e.g., 705-760°C). The minimum recommended holding time for this process is two hours. For castings, the suggested minimum PWHT temperature is lower, with specified temperatures as low as 670°C.