431 Stainless Steel (1.4057 / SUS 431 / S43100)
A premium high-chromium, low-nickel martensitic alloy engineered for demanding structural and mechanical applications. The addition of nickel distinguishes Grade 431 from other martensitic steels, delivering significantly enhanced toughness and impact resistance alongside high tensile strength and superior corrosion resistance.
Overview & Equivalent Grades
431 stainless steel (UNS S43100, EN 1.4057, DIN X17CrNi16-2) is a premium high-chromium, low-nickel martensitic alloy renowned for its exceptional combination of high tensile strength, excellent hardenability, and superior corrosion resistance. Unlike many other martensitic grades, the deliberate addition of nickel significantly enhances toughness and impact properties, making it a highly reliable choice for demanding structural and mechanical applications.
It is generally supplied in the hardened and tempered condition (Condition T), achieving a tensile strength range of 850–1000 MPa and a Brinell hardness of 248–302 HB. At Fushun Metal, we leverage decades of metallurgical expertise to manufacture and supply 431 stainless steel meeting the most stringent global standards, with optimized production processes ensuring uniform microstructure and defect-free internal quality.
| US / ASTM | UNS | European / EN | DIN | Swedish (SS) | Japanese (JIS) | British (BS) |
|---|---|---|---|---|---|---|
| Type 431 | S43100 | 1.4057 | X17CrNi16-2 | 2321 | SUS 431 | 431S29 |
Applications
Due to its high yield strength and excellent resistance to salt water and industrial chemicals, 431 stainless steel is widely utilized across aerospace, marine, and heavy engineering sectors. Typical downstream products and industries are outlined below.
High-strength bolts, nuts, studs, and heavy-duty screws requiring reliable tensile performance under cyclic loading.
Valve stems, seats, pump shafts, and impellers operating in corrosive chemical or marine environments.
Landing gear components, structural fittings, and tie-rods demanding high strength-to-weight performance and AS9100 traceability.
Propeller shafting, marine fittings, and subsea equipment components exposed to continuous salt water immersion.
Beater bars for pulp and paper production, centrifuge bowls, and extruder parts requiring hardness and abrasion resistance.
Mixers, agitators, and high-pressure vessel components requiring resistance to industrial chemical attack and sustained mechanical stress.
Specifications & Standards
Fushun Metal supplies 431 / 1.4057 stainless steel in strict accordance with the following international standards. All product certifications are traceable to the governing standard and accompanied by an EN 10204 3.1 Material Test Certificate.
- ASTM A276 / A276M — Standard Specification for Stainless Steel Bars and Shapes
- ASTM A314 — Standard Specification for Stainless Steel Billets and Bars for Forging
- ASTM A479 / A479M — Standard Specification for Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels
- EN 10088-3 — Stainless Steels: Technical Delivery Conditions for Semi-Finished Products, Bars, Rods, Wire, Sections, and Bright Products
- JIS G4303 — Stainless Steel Bars
- AMS 5628 — Steel, Corrosion-Resistant, Bars, Wire, Forgings, and Tubing (16Cr – 2.5Ni)
- GB/T 1220 — Stainless Steel Bars (Chinese National Standard)
Available Sizes & Delivery Conditions
Fushun Metal operates a state-of-the-art 6000-ton forging press and a GFM radial forging machine, enabling an extensive and highly customizable product size range for any project requirement.
Supply Range
- Forged Round Bars: Φ50 mm – Φ800 mm
- Rolled Round Bars: Φ8 mm – Φ130 mm
- Forged Flat / Square Bars: Thickness 20–400 mm × Width 50–1000 mm
- Seamless Tubes / Pipes: OD 6–500 mm; WT 0.5–60 mm; Length up to 12 m
- Cold Drawn / Rolled Products: OD 6–200 mm; WT 0.1–20 mm
Delivery & MOQ
- Ready Stock (Common Sizes): Immediate dispatch, no MOQ (1 piece minimum), approx. 7-day delivery
- Custom Forgings / Rolled: Standard MOQ 3 tons; lead time approx. 30 days
- Small Batch Special Melts: From 3–5 tons via flexible induction furnaces
- Large Volume Orders: Processed through 30–60 ton Electric Arc Furnaces (EAF) for fast delivery and cost efficiency
Chemical Composition
The chemical composition of 431 stainless steel varies slightly depending on the governing standard. The table below compares the ASTM, EN, and JIS specifications. Values that differ between standards are highlighted.
| Standard | Grade | C (%) | Mn (%) | Si (%) | P (%) | S (%) | Cr (%) | Ni (%) |
|---|---|---|---|---|---|---|---|---|
| ASTM A276 | Type 431 | ≤ 0.20 | ≤ 1.00 | ≤ 1.00 | ≤ 0.040 | ≤ 0.030 | 15.00 – 17.00 | 1.25 – 2.50 |
| EN 10088-3 | 1.4057 | 0.12 – 0.22 | ≤ 1.50 | ≤ 1.00 | ≤ 0.040 | ≤ 0.030 | 15.00 – 17.00 | 1.50 – 2.50 |
| JIS G4303 | SUS 431 | ≤ 0.20 | ≤ 1.00 | ≤ 1.00 | ≤ 0.040 | ≤ 0.030 | 15.00 – 17.00 | 1.25 – 2.50 |
Melting & Processing Routes
Exceptional steel begins with superior melting practices. For 431 martensitic stainless steel, our standard and highly reliable metallurgical route combines precise carbon and chromium control with thorough ladle refining and vacuum treatment to ensure chemical homogeneity and internal cleanliness.
Standard Production Route
EAF = Electric Arc Furnace | AOD = Argon Oxygen Decarburization | LF = Ladle Furnace | VD = Vacuum Degassing
Advanced Remelting Options
ESR = Electro-Slag Remelting | PESR = Pressurized ESR | VIM = Vacuum Induction Melting | VAR = Vacuum Arc Remelting
For applications demanding elevated purity, enhanced fatigue life, and strict non-metallic inclusion limits, Fushun Metal offers ESR or PESR. For the highest aerospace-grade requirements, VIM + VAR is available. Clients are encouraged to consult our engineering team to select the most cost-effective and technically appropriate melting route for their specific application.
Mechanical Properties
The mechanical properties of 431 stainless steel are highly dependent on the tempering temperature applied after hardening. The data below represents typical values at room temperature under various heat-treated conditions.
| Tempering Temp (°C) | Tensile Strength (MPa) | Yield Strength 0.2% (MPa) | Elongation (% in 50 mm) | Hardness (HB) | Impact Charpy V (J) |
|---|---|---|---|---|---|
| Annealed | 862 | 655 | 20 | ≤ 285 | — |
| 204 | 1345 | 1055 | 20 | 388 | 50 |
| 316 | 1295 | 1035 | 19 | 375 | 53 |
| 427 | 1350 | 1080 | 19 | 388 | — |
| 538 | 1140 | 965 | 19 | 321 | — |
| 593 | 1015 | 770 | 20 | 293 | 64 |
| 650 | 960 | 695 | 20 | 277 | 84 |
| Note: Tempering between 425°C and 525°C is generally avoided due to a significant reduction in impact toughness known as temper embrittlement. Specify tempering temperatures outside this range for structural applications requiring adequate notch toughness. | |||||
Heat Treatment
Proper heat treatment is critical to unlocking the full potential of 431 stainless steel. Fushun Metal provides materials in the annealed, or hardened and tempered conditions, based on customer specifications.
| Process | Temperature Range (°C) | Holding Time | Cooling Method | Purpose |
|---|---|---|---|---|
| Process Annealing | 620 – 660 | 2 – 4 hours | Air cool | Soften for machining; relieve residual stresses |
| Full Annealing | 840 – 900 | 2 – 4 hours | Slow furnace cool to 600°C, then air cool | Maximum softness (Max 285 HB) |
| Hardening (Austenitizing) | 980 – 1060 | 30 – 60 min per inch thickness | Oil quench or forced air cooling | Achieve maximum martensitic hardness |
| Tempering | 570 – 700 | 2 – 4 hours | Air cool | Achieve Condition T (850–1000 MPa tensile strength) |
Temper Embrittlement Warning: Tempering in the range of 425°C – 525°C is strongly discouraged. This temperature window induces a severe and irreversible drop in Charpy impact toughness. Always specify a tempering temperature outside this range.
Surface Finish & Machining
Fushun Metal supplies 431 stainless steel in a variety of surface conditions tailored to your manufacturing workflow.
- Black Surface (Raw Forgings)
- Standard finish for forged products requiring subsequent machining. Suitable for roughing operations before final dimensioning.
- Turned / Peeled (Round Bars)
- Surface roughness Ra 3.2–6.3 μm with IT9–IT11 dimensional tolerances. Suitable for most machining-to-print operations.
- Centerless Ground (High Precision)
- Bright, flawless finish achieving Ra 0.8–1.6 μm with tight h9/h11 tolerances. Ideal for precision components with tight fit requirements.
- Milled Flat Bars & Blocks
- Milled surfaces on flat bars and blocks; custom CNC precision machining also available to final dimensions and drawings.
Machinability Note: Grade 431 is readily machinable in its annealed condition (≤ 285 HB). Machining becomes significantly more difficult above 30 HRC, requiring rigid tooling setup, carbide grades, and reduced cutting speeds to maintain tool life and surface integrity.
Quality Assurance & Inspection
Quality is non-negotiable at Fushun Metal. Our comprehensive quality control system spans the entire production cycle—from raw material selection to final dispatch. We are certified to ISO 9001 and AS9100 aerospace quality management standards.
100% internal flaw detection per SEP 1921 Class C/c, D/d or ASTM A388, guaranteeing complete internal soundness.
Chemical composition via OES, room & elevated temperature tensile testing, hardness (HB/HRC), and Charpy impact testing.
Dimensional measurement, flattening and drift expanding tests, and comprehensive metallographic microstructure examination.
Eddy current testing and magnetic flux leakage testing for surface and near-surface defect detection on all critical products.
All shipments include a 3.1 Material Test Certificate (MTC). EN 10204 3.2 certification available upon request.
Routinely coordinated with SGS, TÜV, and Lloyd's Register. Witness inspection appointments available on request.
Packing & Shipping
We ensure that your 431 stainless steel arrives in pristine condition, regardless of global destination. All materials are coated with a premium anti-rust oil and packed with desiccants, guaranteeing they remain completely corrosion-free throughout long-haul ocean freight.
- Bars tightly bundled and secured with heavy-duty steel wire
- Prevents shifting and container damage during sea transit
- Anti-rust oil applied to all exposed surfaces
- Desiccant packs placed within each bundle
- Protective plastic wrapping applied to each bar individually
- Cardboard tube sleeves for round bars; wooden crates for flat bars
- Multi-layer protection preserves Ra finish and dimensional accuracy
- Desiccant and moisture-barrier film for ocean freight
Frequently Asked Questions
Technical questions from procurement engineers and design teams about 431 / 1.4057 stainless steel.
Can you cut 431 stainless steel to my specific length?
Yes. Fushun Metal is equipped with advanced band saws and CNC cutting machinery. We can cut round bars, flat bars, and tubes to your exact required lengths with tight tolerances, saving you processing time and material waste.
What is the hardness of 431 stainless steel in the annealed condition?
In the fully annealed condition, the hardness of 431 stainless steel is typically a maximum of 285 HB (Brinell). This state provides the best machinability before the final hardening and tempering processes are applied.
Is 431 stainless steel suitable for low-temperature or sub-zero applications?
No, it is not recommended. Like most martensitic stainless steels, 431 experiences a substantial drop in impact toughness at sub-zero temperatures, making it brittle and unsuitable for cryogenic service. For low-temperature or cryogenic applications, austenitic stainless steels such as Grade 304 or Grade 316 are the technically correct choice.
How is the weldability of 1.4057 / 431 stainless steel?
Welding 431 stainless steel is difficult due to its high hardenability, which creates a significant risk of cold cracking in the heat-affected zone (HAZ). If welding is unavoidable, the material must be pre-heated to 200–300°C. Post-weld heat treatment (PWHT) at 650°C is strongly recommended to restore ductility and relieve weld stresses. Grade 410 filler rods are typically specified for this application.
Ready to Source 431 Stainless Steel?
Contact our engineering team today to discuss your specification, request a material certificate, or obtain a competitive quote. Stock available for immediate dispatch.
