410NiMo

Martensitic stainless steel 410NiMo is known for its high strength (>760 MPa) and excellent corrosion resistance. It is distinguished by its resistance to hydro-cavitation, sulfide stress corrosion cracking, and remarkable toughness at low temperatures compared to unalloyed steels with 12% Cr, such as type 410/CA15. The filler metal of this type not only matches but exceeds the strength of the equivalent base material, offering extraordinary protection against failure during PWHT. These characteristics make 410NiMo ideal for welding precipitation-hardening martensitic alloys, provided that the corrosion resistance requirements are compatible with the use of filler metals with lower alloys, and allow for a single PWHT at 450-620 °C for tempering. 410NiMo consumables are also commonly used for cladding mild steels and C-Mn steels. The 13% Cr and 4% Ni alloys are used in cast or forged components, such as hydraulic turbines, valve bodies, pump casings, compressor cones, impellers, and high-pressure pipes used in power generation, as well as in offshore oil, chemical, and petrochemical industries.

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

To optimize performance during welding, a preheat-interpass temperature range between 100 °C and 200 °C is recommended, promoting martensite transformation. It is advisable to cool to room temperature before PWHT. In sour oil conditions, for maximum resistance to sulfide stress corrosion SCC, NACE MR0175 specifies a hardness below 23 HRC. However, achieving this hardness is often challenging since the weld metal and HAZ are highly resistant to softening with PWHT. A double tempering for 5-10 hours is required. Common practices suggest treatment at 675 °C for 10 hours followed by 605 °C for another 10 hours, allowing intermediate air cooling to room temperature. Recent studies indicate that heat treatment at 650 °C followed by 620 °C is optimal and that intermediate air cooling to room temperature or lower is essential. Another entity recommends increasing the first PWHT cycle, including complete austenitization annealing at 770 °C for 2 hours before final tempering. In this situation, controlling distortion becomes more critical. In the case of Supercore 410NiMo Flux cored wire, reducing hardness to 23 HRC was impossible, regardless of the PWHT employed. When 410NiMo consumables are used for welding unalloyed martensitic stainless steels such as type 410 or CA15, the PWHT should not exceed 650 °C, except for a second tempering at 590-620 °C.