420 & 431 Stainless Steel Round Bar
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Martensitic steel – stainless that can be hardened
Martensitic bar is a chromium steel (12–17% Cr) with increased carbon content which – unlike austenitic 304 or 316L – hardens much like tool steel: after heating and rapid cooling it forms a hard martensitic structure. The more carbon, the higher the hardness and wear resistance, but the lower the toughness, weldability and corrosion resistance. These steels are magnetic, and they reach their best corrosion resistance in the hardened condition with a smooth, clean machined surface. Learn more in our article Martensitic stainless steel: properties and applications.
Grades in stock – composition and designations
| EN | Designation | AISI | C | Cr | Other |
|---|---|---|---|---|---|
| 1.4006 | X12Cr13 | 410 | 0.08–0.15 | 11.5–13.5 | Ni ≤ 0.75 |
| 1.4005 | X12CrS13 | 416 | 0.06–0.15 | 12.0–14.0 | S 0.15–0.35 |
| 1.4021 | X20Cr13 | 420 | 0.16–0.25 | 12.0–14.0 | – |
| 1.4028 | X30Cr13 | 420 | 0.26–0.35 | 12.0–14.0 | – |
| 1.4034 | X46Cr13 | 420C | 0.43–0.50 | 12.5–14.5 | – |
| 1.4057 | X17CrNi16-2 | 431 | 0.12–0.22 | 15.0–17.0 | Ni 1.50–2.50 |
| 1.4122 | X39CrMo17-1 | – | 0.33–0.45 | 15.5–17.5 | Mo 0.80–1.30 |
Values in wt.% per EN 10088-1. AISI designations are approximate equivalents; "420C" is a customary designation used in bar names as "1.4034 / 420C". The grade of each heat is confirmed by an EN 10204 3.1 certificate.
Grade-by-grade overview
1.4006 has the lowest carbon in the group, welds best and is the toughest – for water and steam valve shafts, blades and bolts. 1.4005 is a free-machining variant with sulfur, designed for high-volume turning of shafts, bolts and pump parts at the expense of corrosion resistance and weldability. 1.4021 is a general-purpose structural grade for shafts, piston rods and valve stems, often supplied as 1.4021+QT. 1.4028 (X30Cr13) reaches higher hardness – for industrial knives, cutting tools and valve parts exposed to wear.
1.4034 (420C) is the hardest of the 13% chromium steels – for blades, food machinery knives, pins and guide bushings. 1.4057 (AISI 431), with 16% chromium and 2% nickel, offers the best corrosion resistance and impact toughness in this group – for pump and mixer shafts, boat propeller shafts, pins and highly stressed fasteners. 1.4122, alloyed with molybdenum, combines hardness with better corrosion resistance than the 13% grades – for knives, rolls and food machinery parts.
Hardenability and delivery condition
The hardness achievable after hardening increases with carbon content: from 1.4006 and 1.4057, used mainly in the quenched and tempered condition, through 1.4021 and 1.4028, to 1.4034 and 1.4122, which can be hardened to tool-steel hardness. Bars are usually supplied soft annealed (+A), which is convenient for turning, or quenched and tempered (+QT) – 1.4021+QT bar, for example, already has its final mechanical properties and needs no hardening after machining. The delivery condition of each heat is stated on the 3.1 certificate.
Ø 10–260 mm, cut to length
The category contains more than 1,000 martensitic bars with diameters from Ø 10 to Ø 260 mm, sold in lengths such as 10 cm or 1 m, or cut to length. The theoretical weight on the product page makes it easy to convert the price to a per-kilogram figure. Bars are typically produced to EN 10088-3 or ASTM A276. For parts that will be hardened, leave a grinding allowance, and check the permitted diameter deviations on the round bar tolerances page.
Martensitic or austenitic?
Martensitic steel is the choice when a part must be hard, springy or wear-resistant. When corrosion resistance matters more – in chlorides, under chemical washdown or in food contact – the non-hardenable 316L / 1.4404 stainless round bar or 304 / 1.4301 stainless round bar is the better fit. For pump shafts in seawater, 1.4462 duplex round bar is increasingly used instead of 1.4057, as it is strong without heat treatment and more resistant to pitting.
See also: the other grades in the stainless round bar category.