Martensitic Stainless Steel: Fields of Use, Hardening and Grade Selection
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What Defines Martensitic Stainless Steel
Martensitic stainless steel is a chromium-bearing alloy whose mechanical properties are set by quenching and tempering rather than by cold work. On cooling from the austenitizing temperature the matrix transforms to martensite, which is why this family is also described as hardenable stainless steel. Carbon content drives the achievable hardness, while chromium in the 11.5-14 % range provides the corrosion resistance baseline.
The classic examples are the Cr13 grades: 2Cr13 (AISI 420, EN 1.4021), 3Cr13 and 4Cr13 (higher-carbon 420 types, EN 1.4034 / X46Cr13), plus higher-carbon grades such as AISI 440C. Composition limits for bars and shapes are given in ASTM A276, for plate in ASTM A240, and for European semi-finished products in EN 10088-3.
Chromium: 11.5-13.5 % in 2Cr13 and 3Cr13, 12.0-14.0 % in AISI 420, up to 18 % in 440C
Carbon: about 0.16-0.25 % in 2Cr13, 0.26-0.35 % in 3Cr13, 0.36-0.45 % in 4Cr13, near 1.0 % in 440C
Nickel: normally below 1 %; the martensitic chromium-nickel and precipitation hardening types deliberately raise it
Molybdenum: added in 1.4112 type cutlery steels to improve tempering resistance and edge stability
Hardness and Strength After Heat Treatment
Tempering temperature decides the final property mix. Tempering at 150-200 °C keeps hardness at roughly 48-54 HRC with low toughness, while tempering between 500 °C and 650 °C trades hardness for ductility and impact strength. The values below are the ranges routinely quoted for Cr13 grades in the hardened and tempered condition and are confirmed against the mill certificate for each heat.
| Condition | Hardness | Tensile strength | Typical duty |
|---|---|---|---|
| Annealed | 235 HBW max | 750 MPa max | Machining and forming |
| Quenched and low tempered | 48-54 HRC | 1600-1900 MPa | Cutting edges and wear parts |
| Quenched and high tempered | 28-35 HRC | 900-1100 MPa | Shafts and structural parts |
Because hardening relies on a through-thickness transformation, heavy sections deserve a hardenability check: hardness is verified at the core and not only at the surface, and a double temper is normal practice to reduce retained austenite.
Fields of Application
Martensitic grades are chosen where hardness and wear resistance matter more than the general corrosion performance of austenitic grades. Representative fields include:
Energy equipment: steam turbine blades, shrouds and valve internals
Cutlery and household ware: knives, scissors, tableware and blades for food processing
Medical and surgical instruments: scalpels, forceps, clamps and dental tools
General engineering: pump shafts, spindles, moulds, fasteners, gauges and measuring tools
Transport equipment: springs, brake components and wear plates
Hardness of 48 HRC and above suits cutting and wear duty, while the 28-35 HRC range is preferred where parts must absorb shock loading without cracking.
Composition-Based and Mechanism-Based Classification
By chemical composition the family splits into martensitic chromium steels, which rely on chromium plus carbon, and martensitic chromium-nickel steels, which add nickel to improve toughness. By structure and strengthening mechanism the practical split is threefold: plain martensitic grades hardened by a martensitic transformation; martensitic and semi-austenitic (semi-martensitic) precipitation hardening grades, supplied soft and strengthened by an aging treatment; and martensitic aging steels such as 17-4 PH, where copper-rich precipitates form during aging at about 480-620 °C.
Selection, Welding and Corrosion Limits
Martensitic stainless steel is magnetic in every condition, which is convenient for magnetic clamping and sorting but disqualifies it where a non-magnetic material is required. Welding calls for preheat in the 150-300 °C range on thicker sections, a controlled interpass temperature and a post-weld tempering treatment; without it the heat-affected zone forms untempered martensite that is hard and crack sensitive. Corrosion performance is adequate in atmospheric, fresh water and mildly acidic service, yet the grade is not a substitute for 304 or 316 in chloride-rich, strongly reducing or highly oxidising environments. Passivation after machining or grinding removes embedded iron and restores the protective oxide film, and machining is best performed in the annealed condition because hardness above 35 HRC shortens tool life sharply.
Frequently Asked Questions
Q: Is martensitic stainless steel magnetic?
Yes. Its body-centred tetragonal martensitic structure is ferromagnetic in the annealed, hardened and tempered states, unlike annealed austenitic grades such as 304.
Q: Can martensitic stainless steel be welded?
It can, with preheat, controlled heat input and post-weld tempering. Components that cannot be tempered after welding are better made from a stabilised ferritic or an austenitic grade.
Q: What is the difference between 2Cr13 and 4Cr13?
Mainly carbon and therefore hardness. 2Cr13 with roughly 0.16-0.25 % carbon is tougher and easier to machine, while 4Cr13 at 0.36-0.45 % carbon reaches higher hardness for cutting edges.
Q: Which grade is used for steam turbine blades?
Low-carbon Cr13 types such as 2Cr13 and the martensitic chromium-nickel variants, because they combine adequate strength at temperature with the toughness needed to resist vibration.
Q: Is it more corrosion resistant than 304?
No. The lower chromium and higher carbon content give it less corrosion resistance than 304 or 316; its advantage is hardness and wear resistance, not chemical resistance.
Q: How is the hardness actually obtained?
By austenitizing, quenching to form martensite and then tempering to the required hardness and toughness balance, typically austenitizing near 1000 °C followed by oil or air quenching.
