Grade dossier
431 Stainless Steel
431 stainless steel is a nickel-bearing, high-chromium martensitic grade identified as UNS S43100. Its 15–17% chromium and 1.25–2.50% nickel range supports a useful combination of heat-treated strength, toughness and corrosion resistance for aerospace fasteners, fittings, shafts and other highly loaded components where a conventional martensitic stainless grade is required.
Identity before substitution
Define 431 by standard, section size and heat-treatment condition
The grade name alone does not define a purchasable condition. For 431, the product standard, diameter or section, annealed or quenched-and-tempered condition, target strength, surface condition and corrosion environment all affect acceptance. ASTM/UNS S43100 and EN 1.4057 are widely cross-referenced, but their chemistry limits are not identical, so substitution should be approved against the actual order specification.
431 stainless composition
UNS S43100 composition reference
Cross-reference chemistry must be checked
Carpenter lists UNS S43100 at C ≤0.20%, Cr 15.00–17.00% and Ni 1.25–2.50%. EN 1.4057 / X17CrNi16-2 commonly uses C 0.12–0.22% and Ni 1.50–2.50%. Treat 1.4057 as a recognized cross-reference, not an automatic chemistry-identical substitution.
| C | 0.20 max |
|---|---|
| Mn | 1.00 max |
| Si | 1.00 max |
| P | 0.040 max |
| S | 0.030 max |
| Cr | 15.00–17.00 |
| Ni | 1.25–2.50 |
| Fe | Balance |
431 stainless properties
Use condition-specific mechanical properties, not one generic strength value
EN 1.4057 reference · QT800 condition
| 0.2% yield strength | ≥ 600 MPa |
|---|---|
| Tensile strength | 800–950 MPa |
| Elongation A5 | ≥ 14% |
| Impact energy · 25°C ISO-V | ≥ 25 J |
EN 1.4057 reference · QT900 condition
| 0.2% yield strength | ≥ 700 MPa |
|---|---|
| Tensile strength | 900–1050 MPa |
| Elongation A5 | ≥ 12% |
| Impact energy · 25°C ISO-V | ≥ 25 J |
Swiss Steel / Deutsche Edelstahlwerke publishes these values for EN 1.4057 heat-treated conditions and notes that properties for dimensions at or above 160 mm must be agreed separately. Do not apply these figures automatically to every ASTM/AMS 431 form or heat; the governing specification and MTC control acceptance.
Selection boundary
Use 431 when high martensitic strength needs more corrosion resistance and toughness
431 is often selected above simpler 12–13% chromium martensitic grades when strength, toughness and corrosion performance must be balanced. It is still a martensitic stainless steel, so chloride exposure, heat treatment, weld procedure and surface condition remain design variables rather than assumptions.
Good reasons to evaluate 431
Aerospace fasteners and fittings requiring high yield strength and toughness
Pump, propeller or drive shafting where strength and moderate corrosion resistance are both required
Marine-atmosphere structural members after detailed chloride and surface-condition review
Valve, petrochemical and mechanical-engineering parts supplied in a defined quenched-and-tempered condition
Stop and review before release
Severe chloride, crevice or immersion service being treated as equivalent to 304/316 corrosion performance
Service or fabrication with prolonged exposure around 420–520°C, where 1.4057 guidance warns about 475°C embrittlement
Welded assemblies released without preheat, filler and post-weld heat-treatment review
Substitution between S43100 and 1.4057 without checking the actual chemistry and product specification
Fabrication route
Build 431 performance through controlled hardening, tempering and surface finish
For EN 1.4057, hardening guidance is about 950–1060°C followed by air or oil cooling. Section size, distortion risk and the ordered specification must define the actual cycle.
Temper to the required strength/toughness condition. Published 1.4057 guidance flags 420–520°C as an embrittlement range to limit during fabrication and service.
Matching-filler welding commonly uses about 100–300°C preheat and prompt tempering; the most uniform properties require re-heat treatment of the complete part.
Machinability follows the hardness level. Final grinding or polishing and removal of heat tint matter because smoother, clean surfaces give better corrosion performance.
431 stainless supplier checklist
Order 431 by form, size, condition and mill-source evidence
Carpenter lists 431 in bar, rounds, billet, strip, wire and rod, while Universal Stainless lists round bar, RCS billet, flat bar and ingot. Supply form is therefore source-dependent. A purchase order should identify the governing standard, dimensions, tolerance, heat-treatment condition, finish, quantity and test certification rather than assuming every form is interchangeable.
Bar / rounds · ASTM A276 or A479 as applicable
Billet / forging stock · source and project specification required
Strip, wire and rod · verify exact ASTM/AMS coverage before order
Flat bar / ingot · mill-source availability varies
Stock and certificate checkpoint
As a concrete market reference, thyssenkrupp Schulte lists 1.4057 drawn or ground-and-polished round bar in 6–80 mm diameter, roughly 2950–3200 mm production lengths, tempered and supplied to EN 10088-3 with EN 10278 tolerance. Treat this as source-specific evidence, not a universal stock promise. Release production only against the supplier’s current availability plus the heat-specific MTC.
Interactive selection check
Test 431 against the controlling procurement question
Procurement FAQ
Questions to close before ordering 431 stainless steel
What is 431 stainless steel?
431 is a nickel-bearing martensitic stainless steel identified as UNS S43100. Carpenter lists 15–17% chromium and 1.25–2.50% nickel, giving the grade a useful combination of heat-treated strength, toughness and corrosion resistance.
What is the EN equivalent of 431 stainless steel?
EN 1.4057 / X17CrNi16-2 is the standard European cross-reference and is explicitly listed against AISI 431 by Swiss Steel. The chemistry is not perfectly identical to every S43100 specification, so the actual standard and heat analysis must still be checked before substitution.
Can 431 stainless steel be hardened?
Yes. 431 is martensitic and quench-hardenable. Swiss Steel’s 1.4057 guidance uses approximately 950–1060°C hardening followed by air or oil cooling, with tempering selected for the required strength and toughness.
What are two important application constraints for 431?
First, aggressive chloride or crevice service requires a separate corrosion review even though 431 has strong corrosion resistance for a martensitic grade. Second, 1.4057 guidance warns about 475°C embrittlement and limiting exposure around 420–520°C during fabrication and service.
What should a 431 RFQ include?
State UNS S43100 or EN 1.4057, the governing standard and edition, product form, dimensions and tolerances, surface finish, annealed or QT condition, required tensile/yield/impact properties, service environment, MTC requirement and any NDT or supplementary testing.
Sources, scope and RFQ
Trace 431 chemistry, heat treatment and mill-source evidence before release
UNS S43100 identity, chemistry, heat-treatable martensitic positioning, aerospace-fastener/fitting use cases, applicable ASTM/AMS specifications and listed forms including bar, rounds, billet, strip, wire and rod.
EN 1.4057 / X17CrNi16-2 cross-reference, chemistry, QT800 and QT900 mechanical properties, hardening/tempering guidance, welding preheat, embrittlement range, surface-condition note and section-size qualification.
Universal Stainless lists 431 round bar, RCS billet, flat bar and ingot with ASTM A276 / AMS 5628-related supply capability. thyssenkrupp Schulte lists a concrete 1.4057 round-bar stock range, providing source-specific form and dimension evidence without claiming universal availability.
Use the current ASTM, AMS, EN or project specification for the actual form and condition. The heat-specific MTC, agreed dimensions, heat treatment, surface condition and acceptance tests—not a generic web table—control final release.