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Martensitic Stainless Steel

Martensitic stainless steels combine 12–18 % chromium with 0.1–1.2 % carbon, so they transform to martensite on quenching like an alloy steel: 410 reaches about 40 HRC, 420 about 50 HRC and 440C 58–60 HRC. They are magnetic, the strongest of the plain stainless groups and the least corrosion-resistant — chromium tied up in carbides is not protecting the surface — so they live where hardness and strength come first and the exposure is fresh water, steam or mild chemicals.

Popular martensitic stainless grades

Compare in the explorer
GradeYield, MPaTensile, MPaDensity, g/cm³MachinabilityWeldabilityBest for
4103105177.7GoodFairShafts, valve parts, fasteners to about 40 HRC
4203606907.75FairPoorCutlery, instruments and molds at 48–52 HRC
440C4507607.68FairNot recommendedBearings, valve seats and blades at 58–60 HRC
4317609507.75FairPoorTough high-strength shafts; best corrosion of group
440A4157257.68FairPoorBlades and wear parts with better toughness
410S2654607.7FairVery goodWeldable non-hardening 12 % Cr for heat shields
S30V6209007.43PoorNot recommendedPremium knife blades; edge retention

All 109 martensitic stainless grades

Choose martensitic stainless for

Shafts, valve stems and seats, pump and compressor parts, fasteners, knife and scissor blades, surgical and dental instruments, bearings, nozzles, gauges and molds for plastics — parts that must be hard or strong and only moderately corrosion-resistant.

Look elsewhere when

The part is welded and cannot be post-weld heat-treated (304L or 410S), sees chlorides or marine service (316L or 2205, or 17-4 PH for strength with corrosion), needs high strength without a quench-and-temper cycle and its distortion (17-4 PH ages at 480 °C), or needs toughness below 0 °C. For wear above 60 HRC a tool steel such as D2 is the better answer.

Yield strength against max service temp, Martensitic (400 series, higher C) among every stainless steel grade

No materials in view have both of these properties.

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Martensitic stainless by application

Shafts and valve trim
410 quenched and tempered for pump shafts, stems and seats; 431 where the shaft needs 850–1,000 MPa tensile with better toughness and corrosion resistance; 422 for steam-turbine parts to 650 °C.
Blades and cutting edges
420 and 420J2 for kitchen and surgical blades; 440C, 1.4116, 440A, S30V and 420V for premium edges — the more carbon and vanadium, the longer the edge holds and the harder the steel is to grind.
Bearings and wear parts
440C at 58–60 HRC for balls, races, valve balls and nozzles in fresh water or mild chemicals; grind and lap after hardening.
Corrosion-resistant molds
420 (1.2083) and CX for PVC, optical and medical molds where P20 would pit; 48–52 HRC and mirror-polishable.

Working with martensitic stainless

Machining
Machine annealed (410 at roughly 55 % of the speed of free-cutting steel, 440C lower), then harden and finish-grind — 440C and 420 at full hardness are ground or hard-turned with CBN, not milled. 416 is the free-machining twin of 410 when volume matters.
Heat treatment
Austenitize 980–1,050 °C, oil or air quench, then temper at 150–370 °C for full hardness and best corrosion resistance. Avoid tempering at 425–540 °C, where toughness and corrosion resistance both drop. 440C benefits from a sub-zero treatment to convert retained austenite before final tempering.
Welding
Weldable with matching (410, 410NiMo) or 309 filler after preheating to 200–300 °C, followed by tempering; 420 and 440C are rarely welded — they crack. Use 410S or a PH grade when the design needs many welds.
Finishing
Corrosion resistance depends on a hardened, tempered and clean surface: polish and passivate (citric or inhibited nitric, ASTM A967 — plain nitric can etch 410 and 420). Black oxide, nitriding, PVD or hard chrome extend wear life; the standard blade finish is a fine grind or satin.

Other stainless steel series

Martensitic Stainless Steel — frequently asked

What is martensitic stainless?

Martensitic stainless steels combine 12–18 % chromium with 0.1–1.2 % carbon, so they transform to martensite on quenching like an alloy steel: 410 reaches about 40 HRC, 420 about 50 HRC and 440C 58–60 HRC. They are magnetic, the strongest of the plain stainless groups and the least corrosion-resistant — chromium tied up in carbides is not protecting the surface — so they live where hardness and strength come first and the exposure is fresh water, steam or mild chemicals.

Which grade of martensitic stainless should I use?

410 for shafts, valve trim, pump parts and fasteners that need 700–1,000 MPa yield and moderate hardness. 420 (and 420J2) for cutlery, surgical instruments, molds and gauges at 48–52 HRC; 1.4116 is the European kitchen-knife grade. 440C when the job needs 58–60 HRC — ball bearings, valve seats, nozzles, high-end blades — with 440A and 440B trading a few points of hardness for toughness and corrosion resistance. 431 (16 % Cr, 2 % Ni) is the tough, high-strength shaft grade with the best corrosion resistance of the group; 410S is the low-carbon non-hardening version for welded parts; S30V is the powder-metallurgy knife steel with 4 % vanadium for edge retention.

Which grade of martensitic stainless is the strongest?

VG-10 has the highest yield strength in the series at 1,850 MPa; 7Cr17MoV follows at 1,700 MPa. Values are for each grade's default condition.

Which grade of martensitic stainless is easiest to machine?

1.4035 (machinability very good, 70/100), then 1.4029 (65/100).

Is martensitic stainless heat-treatable?

Yes. These grades gain their strength from heat treatment; the conditions and their properties are listed on each grade page.

420 or 440C for a blade?

420 hardens to about 50 HRC, is tough, easy to grind and sharpen and resists corrosion better — the right steel for kitchen knives, surgical blades and anything that gets abused. 440C reaches 58–60 HRC with large chromium carbides, so it holds an edge far longer and takes a keener grind, but it chips more readily, rusts sooner and takes longer to finish. Choose 440C, 1.4116 or S30V when edge retention is the selling point; 420 when durability is.

Why did my hardened 410 part rust?

Martensitic stainless is at the bottom of the corrosion ladder and needs everything in its favour: a full hardening cycle (chromium stays in solution instead of in carbides), a temper outside 425–540 °C, a smooth passivated surface and no chlorides. A part left annealed, tempered in the wrong range, or shipped with grinding dust embedded in it shows rust spots within days in humid air. For anything wet, 431 or 17-4 PH holds up much better.