What are Martensitic stainless steels and when are they used in the welding industry?

The 400 series of hardenable Martensitic stainless engineering high-alloy-iron materials typically contain 11.5 to 18wt% chromium with a variety of carbon levels. Unlike the austenitic and ferritic grades, the Martensitic series have a body centred tetragonal crystal lattice which responds to a range of heat-treatment regimes.

These materials are ferro-magnetic.

The most commonly used alloys in this series are 410, 410NiMo, and original Staybright alloy. Also, 420, 430, 440, with micro alloyed variations used for tools and wear applications 416 free-matching 410 variant grade; specialised advice required for welding applications.

Jethete, jet engine alloy, widely used for critical containment components. Jethete is a variant on 410 and 410NiMo and welded using high purity filler wire and specialised procedures.

410 is a hardenable martensitic stainless alloy used for highly stressed parts needing good corrosion resistance and strength. it can be heat-treated to obtain high-strength properties with good ductility. It's the most widely used Martensitic grade. Welding is achieved with 410, 309L, 312, FM82 and 409Ti is also adopted.

420 to 440 grades are high carbon, martensitic, straight chromium high-harden ability stainless steels. Characterised by good corrosion resistance in mild domestic and industrial environments, including fresh water, organic materials, mild acids, various petroleum products, coupled with extreme high strength, hardness and wear resistance when in the hardened and tempered condition. Welding requires specialised procedures and filler metal to minimise HAZ defect-formation.

431 martensitic alloy is a 0.2C 18Cr variant and is often welded using austenitic super alloy filler metals such as 80/20, 625, FM82, unless absolutely matching properties are essential.

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