Guidance on what TIG welding rod to use on Ferritic stainless steels
Ferritic Type 409 & 430 Stainless Steels
The 400 series of plain chromium stainless steel materials includes ferritic-martensitic and some precipitation hardening stainless alloys. They are iron alloys that contain more than 10% of chromium. The chromium forms a self-healing transparent continuous protective Nano-film.
Usually if the carbon content is kept below 0.10% the alloys are single- phase ferritic alloys, whereas beyond this level of carbon, the materials are martensitic. A popular ferritic and lower cost grade is the 10% Chromium very low carbon content type 409, which is widely used for corrosion resistant car exhaust systems 409Ti is further stabilised with up to 0.5% Ti addition. 409 & 409Ti grade stainless welding wires possess excellent weldability and are generally welded with matching chemistry TIG welding rod.
The other popular ferritic stainless steel is type 430 with 16-18% Cr content. The higher Cr level provides extra corrosion and scaling resistance. It is also welded with matching 430 grade TIG welding rod. A lower welding heat input safeguards against excess grain growth. A range of other applicable TIG filler rod include; 308, 309, 316, 312.
There are a number of fine variants of 409 and 430 alloys and the above welding data applies.
Welding of Martensitic Grade Stainless Steels
- 410 & 410NiMo
- 420, 430, 440 & variants
- Jethete
- 416 free-matching grade
- 431 variant
The 400 series of harden able Martensitic stainless engineering high-alloy-iron materials typically contain 11.5 to 18% 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, & original Staybright alloy.
- 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 & 410NiMo and welded using high purity AMS 5823 and specialised procedures.
410 is a harden able martensitic stainless alloy used for highly stressed parts needing good corrosion resistance and strength. Can be heat-treated to obtain high-strength properties with good ductility. It is the most widely used Martensitic grade. Welding is achieved with 410, 309L, 312, FM82 and 409Ti welding wires is also adopted.
420 to 440 grades are high carbon, martensitic, straight chromium high-hardenability stainless steels. Characterized 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 welding wires, in order to minimise HAZ defect-formation.
431 martensitic alloy is a 0.2C 18Cr variant and is often welded using austenitic superalloy TIG filler rods such as 80/20 , 625 and 82 grade filler rods, unless absolutely matching properties are essential.
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