AISI 431 / EN 1.4057 / SUS 431 Open-Die Forgings
Forged round, square, flat and hex bars, hollow bars, sleeves and bushings, seamless rolled rings, discs, blocks and plates, shafts, piston rods, spindles, pump and valve components. Manufactured by Jiangyin Jiangnan Metal Co., Ltd., Jiangyin, Jiangsu, China.
AISI 431 (UNS S43100, EN 1.4057, X17CrNi16-2, JIS SUS 431) is a martensitic chromium-nickel stainless steel with 15 to 17 percent chromium and 1.25 to 2.50 percent nickel. It is magnetic and heat treatable, has the best corrosion resistance of the common martensitic grades, and reaches roughly 800 to 1350 MPa tensile strength depending on the tempering temperature. It is specified for pump and propeller shafts, valve stems, bolts and high torque shafting. Jiangyin Jiangnan Metal Co., Ltd. produces AISI 431 in open-die forged form, including bars, hollow bars, seamless rolled rings, discs and shafts. Contact sales@steelforgepieces.com or +86-189-2135-9659.
1. Grade Designations and International Equivalents
AISI 431 is cross-referenced under many national standards. Any of the designations below is accepted on an enquiry as the same material.
2. AISI 431 Chemical Composition
| Standard | C | Si | Mn | P max | S max | Cr | Ni | Mo | Fe |
|---|---|---|---|---|---|---|---|---|---|
| AISI 431 / UNS S43100 ASTM A276 | 0.20 max | 1.00 max | 1.00 max | 0.040 | 0.030 | 15.00-17.00 | 1.25-2.50 | - | Bal. |
| EN 1.4057 / X17CrNi16-2 DIN EN 10088-3 | 0.12-0.22 | 1.00 max | 1.50 max | 0.040 | 0.030 | 15.0-17.0 | 1.50-2.50 | - | Bal. |
The two specifications overlap but are not identical. EN 1.4057 sets a carbon minimum of 0.12 percent and a nickel minimum of 1.50 percent, while ASTM 431 has no carbon minimum. If the drawing calls for dual certification to ASTM A276 or A473 and to EN 10088-3 or EN 10250-4, state this on the enquiry so the heat is chosen to meet the narrower window.
3. Mechanical Properties
3.1 ASTM bar properties against tempering temperature
| Condition or tempering temperature | Tensile strength Rm (MPa) | 0.2% proof Rp0.2 (MPa) | Elongation (% in 50 mm) | Hardness (HB) | Charpy V (J) |
|---|---|---|---|---|---|
| Annealed, Condition A | 862 | 655 | 20 | 285 max | - |
| 204 °C | 1345 | 1055 | 20 | 388 | 50 |
| 316 °C | 1295 | 1035 | 19 | 375 | 53 |
| 427 °C (avoid) | 1350 | 1080 | 19 | 388 | low |
| 538 °C (avoid) | 1140 | 965 | 19 | 321 | low |
| 593 °C | 1015 | 770 | 20 | 293 | 64 |
| 650 °C | 960 | 695 | 20 | 277 | 84 |
Grade 431 is most often supplied in Condition T, with a specified tensile strength of 850 to 1000 MPa. Annealed Condition A is rarely stocked, because the grade hardens even on slow cooling.
3.2 EN 10088-3 quenched and tempered conditions
| Condition | Section t (mm) | Rp0.2 min (MPa) | Rm (MPa) | A min, longitudinal (%) | Hardness |
|---|---|---|---|---|---|
| Annealed (+A) | - | - | 950 max | - | 295 HB max |
| +QT800 | t up to 60 | 600 | 800-950 | 14 | - |
| 60 to 160 | 600 | 800-950 | 12 | ||
| +QT900 | t up to 60 | 700 | 900-1050 | 12 | - |
| 60 to 160 | 700 | 900-1050 | 10 |
3.3 Proof stress at elevated temperature
| Condition | 100 °C | 150 °C | 200 °C | 250 °C | 300 °C | 350 °C | 400 °C |
|---|---|---|---|---|---|---|---|
| +QT800 | 515 | 495 | 475 | 460 | 440 | 405 | 355 |
| +QT900 | 565 | 525 | 505 | 490 | 470 | 430 | 375 |
The service range for 1.4057 is about minus 40 °C to plus 400 °C. Above the tempering temperature the alloy over-tempers and loses strength, and at sub-zero temperatures ductility falls.
4. Physical Properties
| Grade | Density (kg/m³) | Elastic modulus (GPa) | Mean CTE (µm/m·°C) | Thermal conductivity (W/m·K) | Specific heat 0-100 °C (J/kg·K) | Electrical resistivity (nΩ·m) | |
|---|---|---|---|---|---|---|---|
| 0-100 °C | 0-315 °C | at 100 °C | |||||
| 431 / 1.4057 | 7750-7800 | 200 | 10.2 | 12.1 | 20.2 | 460 | 720 |
The alloy is ferromagnetic in every condition, annealed as well as hardened. A magnet is a quick shop floor check against austenitic 304 and 316 material.
5. Heat Treatment and Forging Practice
5.1 Hardening and tempering
AISI 431 is austenitised at 980 to 1065 °C, held about half an hour, then quenched in oil or air. Complex parts and parts that have already been hardened are pre-heated at 760 to 790 °C before the full austenitising soak. A full anneal is not possible on this grade because it hardens during slow cooling. The practical softening treatment is a process anneal at 620 to 660 °C followed by air cooling, and EN practice gives 680 to 800 °C with furnace or air cooling.
5.2 Forging window used at our works
AISI 431 is rated as medium forgeability and needs close control of temperature. Our open-die practice is to heat slowly to about 850 °C so the section equalises, then raise quickly to about 1180 °C, forge between 1150 °C and 950 °C, and cool slowly under control. Hot forming in general takes place between 800 °C and 1100 °C with slow cooling. The grade air hardens, so uncontrolled cooling after forging is a frequent cause of quench cracking. Every heat we ship is slow cooled and then process annealed before machining.
5.3 Welding and machining
Welding 431 is difficult and carries a cracking risk. Where welding cannot be avoided, pre-heat to 200 to 300 °C, keep the interpass temperature above 200 °C, and apply a post weld heat treatment at about 650 °C. Matching 410 filler can be used, and more ductile joints are obtained with austenitic fillers such as 308L, 309 or 310, or the EN equivalents 1.4430 and 1.4370. Shielding gases containing hydrogen or nitrogen are not suitable. For machining, 431 cuts reasonably in the annealed state but becomes very difficult above 30 HRC, so machine before final hardening wherever the tolerances allow.
6. Corrosion and Heat Resistance
Grade 431 has the best corrosion resistance of the standard martensitic stainless steels, from its 15 to 17 percent chromium content plus the nickel addition. It resists salt water well, which is why it has long been used for marine shafting. Overall its corrosion resistance is similar to grade 304 or slightly below it, and lower than grade 316 in warm tropical waters. Resistance is highest with a smooth bright metallic surface finish and with the material supplied hardened and tempered. The grade can suffer intergranular attack, so service where weld decay is a risk should be reviewed before selection.
For scaling resistance, 431 can be used to about 925 °C in intermittent service and 870 °C in continuous service. It should not carry load above its tempering temperature, since mechanical properties fall away.
7. AISI 431 Forged Products We Manufacture
| Product form | Description | Typical use |
|---|---|---|
| Forged bars | Round, square, rectangular, flat and hexagonal forged bars and billets | Shaft blanks, fastener stock, machining stock |
| Hollow bars and sleeves | Forged sleeves, bushes, bushings, pipes, tubes, barrels, casings, shells, cylinders, hubs, housings | Pump casings, bearing housings, cylinder liners |
| Seamless rolled rings | Ring rolled forgings, plain or profiled, across a wide diameter range | Flanges, bearing races, retaining rings, valve seats |
| Discs, blocks and plates | Forged discs, disks, blocks, slabs and plate forgings | Die blanks, closure plates, tube sheets |
| Shafting and rods | Forged shafts, stepped shafts, piston rods, spindles | Pump and propeller shafts, outboard motor driveshafts |
| Pump and valve parts | Near net shape forged pump and valve components | Valve stems, bodies, bonnets, impeller hubs |
Delivery standards for this grade include ASTM A473, the specification for stainless steel forgings covering austenitic, austenitic-ferritic, ferritic and martensitic forgings for general use and for low or high temperature service, and EN 10250-4, which covers open die steel forgings in stainless steel for general engineering purposes as well as forged bars and products pre-forged and finished in ring rolling mills. Bar is ordered to ASTM A276 and semi-finished product to EN 10088-3. EN 10204 3.1 material certificates are supplied.
8. Typical Applications of AISI 431
High torque strength, good toughness at high hardness and marine grade corrosion resistance make 431 a common choice for rotating and threaded parts. Recorded applications include pump shafts and propeller shafts, outboard motor driveshafts, valve stems, bolts, nuts and aircraft fasteners, bomb racks, beater bars, marine systems and laboratory equipment. By sector, the grade is used in mechanical engineering and turbine construction, the automotive and aviation industries, the chemical, petrochemical and oil industries, and power plant construction.
Choosing an alternative grade
If 431 is not the right fit, the usual substitutions are 410 where a lower hardened strength is enough, 416 where free machining matters more than strength and corrosion resistance, and 440C where higher hardness is needed. Where precipitation hardening suits the part better than quench and temper, see our 15-5PH, 17-7PH and PH13-8Mo forgings.
9. Frequently Asked Questions
What is AISI 431 stainless steel?
AISI 431 is a martensitic chromium-nickel stainless steel with 15 to 17 percent chromium, 1.25 to 2.50 percent nickel and up to 0.20 percent carbon under ASTM. It is magnetic and heat treatable, with high tensile and torque strength and good toughness, which is why it is used for pump shafts, propeller shafts and valve stems.
What is the equivalent of AISI 431?
UNS S43100, EN 1.4057, X17CrNi16-2, JIS SUS 431, BS 431S29 or En57, SS 2321, AFNOR Z15CN16-02, AMS 5682, PN 2H17N2 and UNE F.3427 all designate the same material.
Is 1.5919 the same as AISI 431?
No. 1.5919 is 15CrNi6, a case hardening steel to DIN 17210 and EN 10084 used for carburised gears. The European material number for AISI 431 is 1.4057, X17CrNi16-2.
What hardness can AISI 431 reach?
About 388 HB, roughly 41 to 42 HRC, when tempered at 204 °C, falling to about 277 HB when tempered at 650 °C. Annealed material is specified at 285 HB maximum under ASTM and 295 HB maximum under EN.
At what temperature should AISI 431 be tempered?
Harden from 980 to 1065 °C with an oil or air quench, then temper below about 400 °C for maximum strength, or above about 590 °C where toughness governs. Avoid the 425 to 600 °C range.
Why is tempering between 425 °C and 600 °C avoided?
Because 431 loses impact toughness in that band. Charpy V values of 50 to 53 J at 204 to 316 °C and 64 to 84 J at 593 to 650 °C sit either side of a trough, so tempering is specified outside the range.
Can AISI 431 be forged?
Yes. It is rated as medium forgeability. Heat slowly to about 850 °C, then rapidly to about 1180 °C, forge between 1150 °C and 950 °C, and cool slowly to avoid cracking.
Is AISI 431 magnetic?
Yes. It is ferromagnetic both annealed and hardened and tempered, unlike austenitic 304 and 316.
Is AISI 431 more corrosion resistant than 304?
It has the best corrosion resistance of the common martensitic grades and resists salt water well, but overall it is similar to or slightly below grade 304, and below grade 316 in warm tropical waters.
Can Jiangyin Jiangnan Metal supply AISI 431 to ASTM A473 or EN 10250-4?
Yes. We are an open-die forging factory in Jiangyin, Jiangsu, China, supplying AISI 431 forged bars, hollow bars, seamless rolled rings, discs, blocks, shafts and pump and valve parts against ASTM A473, ASTM A276, EN 10250-4 and EN 10088-3, with EN 10204 3.1 material certificates. Contact sales@steelforgepieces.com or +86-189-2135-9659.
10. About the Manufacturer
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The company makes open-die forgings, forged bars, seamless rolled rings, forged hollow bars, discs, blocks and shafting in carbon steel, alloy steel, tool steel, stainless steel and nickel alloys, including AISI 431, 1.4057 and SUS 431. Enquiries: +86-189-2135-9659, sales@steelforgepieces.com, or the contact page.
Standards referenced on this page
- ASTM A276, Standard Specification for Stainless Steel Bars and Shapes.
- ASTM A473, Standard Specification for Stainless Steel Forgings.
- EN 10088-3, Stainless steels, technical delivery conditions for semi-finished products, bars, rods, wire, sections and bright products.
- EN 10250-4, Open die steel forgings for general engineering purposes, Part 4, Stainless steels.
- DIN 17210 and EN 10084, case hardening steels, for the 15CrNi6 comparison in section 1.
- EN 10204, inspection documents for metallic products.
Technical data reviewed September 2026. Values on this page are typical reference data for grade 431 bar and forging product and are not a property guarantee for a specific order. The governing figures are those of the applicable standard and of the mill certificate issued with each heat. A plain text version of this page is available at AISI-431.md.