DAIKOFCW 4140 N-L-H

12%Cr-4.5%Ni-0.5%Mo (410NiMo) soft martensitic alloy.

In the PWHT condition the microstructure consists of tempered martensite with some retained austenite.

EN W.Nr.: 1.4313 (X3CrNiMo13-4).
ASTM: F6NM, CA6NM.
ANFOR: Z6 CND 1304-M.
UNS: S41500.

It is recommended to maintain a preheat-interpass temperature range of 100-200°C during welding to facilitate martensite transformation. Cooling the components to room temperature before Post Weld Heat Treatment (PWHT) is advised. Achieving a hardness level of <23HRc, as specified by NACE MR0175 for maximum resistance to sulphide-induced Stress Corrosion Cracking (SCC) in sour oil conditions, can be challenging. This is due to the inherent resistance of weld metal and Heat-Affected Zone (HAZ) to softening during PWHT. To address this, a double temper for 5-10 hours is deemed necessary. Common practice involves a two-step tempering process: 675°C/10h followed by 605ºC/10h with an intermediate air cool to ambient temperature. Recent research suggests that optimizing the tempering process involves temperatures of 620°C ÷ 650ºC, with intermediate air cooling to ambient or lower being an essential step. Another approach proposes elevating the first PWHT cycle for a full austenitization anneal at 770°C/2h before the final temper. It is noteworthy that distortion control may become more critical in this scenario. In the case of the Supercore 410NiMo flux-cored wire, reducing the hardness to 23HRC has proven challenging, regardless of the PWHT applied. When considering 410NiMo consumables for welding plain 12Cr martensitic stainless steels like type 410 or CA15, it is advisable not to exceed a PWHT temperature of about 650°C, unless a second temper at 590-620°C is applied.