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431 stainless steel (UNS S43100) is a martensitic stainless steel widely used in oil and gas, marine engineering, automotive, and general industrial applications. Among all martensitic grades, it offers the best corrosion resistance, with the ability to withstand various organic media, nitric acid, and petroleum products, while combining excellent tensile strength and good toughness—making it an ideal choice for shafts, fasteners, and high-stress components.
Grade 431 stainless steels are martensitic and heat-treatable, offering excellent corrosion resistance, high torque strength and toughness, and good tensile properties. These properties make them ideal for bolt and shaft applications. However, these steels cannot be cold-worked due to their high yield strength; therefore, they are suitable for operations such as spinning, deep drawing, bending and cold heading.
Martensitic steels are generally fabricated using techniques that allow hardening and tempering treatments, but they are difficult to weld. The corrosion resistance of grade 431 steels is lower than that of austenitic grades. The use of grade 431 is limited by its loss of strength at high temperatures due to over-tempering and loss of ductility at low temperatures.
Composition Specification (%)
| Grade | C | Mn | Si | P | S | Cr | Mo | Ni | N | |
| 431 | min. | – 0.20 | – 1.00 | – 1.00 | – 0.040 | – 0.030 | 15.00 17.00 | – | 1.25 2.50 | – |
| max. |
431 stainless steel (UNS S43100) belongs to the high‑chromium, low‑nickel martensitic stainless steel family. Its chemical composition contains 15–17% chromium and 1.25–2.5% nickel, with strictly controlled levels of carbon, sulfur, and phosphorus, ensuring its excellent mechanical properties. The presence of 1.25–2.5% nickel gives 431 stainless steel better corrosion resistance and toughness compared to ordinary martensitic steels such as 410. The high chromium content forms a stable passive layer, making this alloy particularly effective in highly corrosive marine environments such as seawater.
Mechanical Property Specification (All values are typical except as noted)
| Tempering Temperature (°C) | Tensile Strength (MPa) | Yield Strength 0.2% Proof (MPa) | Elongation (% in 50mm) | Hardness Brinell (HB) | Impact Izod (J) |
| Annealed * | 862 | 655 | 20 | 285 max. * | – |
| Condition T ** | 850 – 1000 | 635 min. | 11 min. | 248 – 302 | |
| 300 | 1320 | 1020 | 20 | 380 | 75 |
| 400 | 1310 | 1010 | 22 | 395 | 80 |
| 500 | 1350 | 1030 | 20 | 395 | 55 # |
| 600 | 1030 | 800 | 20 | 310 | 45 # |
| 700 | 920 | 700 | 20 | 290 | 70 |
| * Annealed tensile properties are typical for Condition A of ASTM A276; annealed hardness listed is the specified maximum. Grade 431 is only rarely stocked in annealed Condition A. ** Grade 431 is frequently stocked and supplied in “Condition T” to AS 1444 or BS 970, with specified tensile strength of 850 – 1000MPa. Yield and elongation are typically in conformance with the limits listed above. ASTM A276 only lists a Condition A version of Grade 431. # Due to associated low impact resistance this steel should not be tempered in the range 425- 600°C. | |||||
The density of 431 stainless steel is approximately 7.70–7.80 g/cm³, its elastic modulus is 200–210 GPa, and its thermal conductivity at 100°C is about 20.2 W/m·K. The material is magnetic in all heat treatment conditions, which is a typical characteristic of martensitic stainless steels. 431 stainless steel is generally supplied in the hardened and tempered condition (Condition T), with a tensile strength range of 850–1000 MPa and a Brinell hardness range of 248–302.
Physical Properties (Typical values in the annealed condition)
| Grade | Density (kg/m3) | Elastic Modules (GPa) | Mean Coefficient of Thermal Expansion | Thermal Conductivity | Specific Heat | Electrical Resistivity | |||
| 0-100°C (µm/m/°C) | 0-315°C (µm/m/°C) | 0-538°C (µm/m/°C) | at 100°C (W/m.K) | at 500°C (W/m.K) | 0-100°C (J/kg.K) | (nΩ.m) | |||
| 431 | 7700 | 200 | 10.2 | 12.1 | – | 20.2 | – | 460 | 720 |
Due to its high yield strength, the material is not readily cold worked and is therefore not recommended for forming operations such as cold heading, deep drawing, or spinning. In addition, 431 stainless steel has poor weldability and is susceptible to cracking during welding; preheating to 200–300°C is recommended prior to welding. Heat treatment is typically carried out by tempering. Special attention should be paid to avoid tempering in the temperature range of 425–600°C, as this range can cause a significant reduction in impact toughness.
Heat Treatment
Full anneal — Full annealing cannot be performed on grade 431 steels. This grade gets hardened even during slow cooling.
Process anneal — Grade 431 steels are heated to 620 to 660°C and then air-cooled.
Martensitic 431 steels are generally hardened by heating to temperatures between 980 and 1065°C for almost half an hour, followed by quenching in oil or air. The mechanical properties of complex or hardened parts of grade 431 steels can be improved by preheating to temperatures between 760 and 790°C and then tempering. However, tempering these steels at temperatures between 425 and 600°C should be avoided, as this results in a loss of impact toughness.
Applications
Typical applications of grade 431 stainless steels include the following:
- Laboratory equipment
- Pump and propeller shafts
- Nuts and bolts
- Marine systems
- Beater bars
About C&N
C&N focuses on the production of high‑quality pipe fittings and tubes. Our entire production process strictly follows international standards and industry specifications, with rigorous quality control at every stage—from raw material procurement to final product inspection. If you have any requirements, please feel free to contact us.
