SUS431 Stainless Steel: Martensitic Grade With Nickel Addition For High Strength & Corrosion Resistance

SUS431 is a martensitic stainless steel with nickel addition (Cr=15.0%-17.0%, Ni=1.20%-2.00%, C=0.15%-0.25%), which is a high-performance grade in the martensitic series. The addition of nickel improves the toughness and corrosion resistance of the material, and it has high strength after heat treatment. It is suitable for high-strength, corrosion-resistant mechanical components.

Core Parameters

Chemical Composition (wt%): C=0.15-0.25, Si≤1.00, Mn≤1.00, P≤0.040, S≤0.030, Cr=15.00-17.00, Ni=1.20-2.00, Fe=Balance

Mechanical Properties (Quenched & Tempered): Tensile Strength ≥1080MPa, Yield Strength ≥880MPa, Elongation ≥12%, Hardness 38-43HRC

Service Temperature: -40℃ to 450℃ (continuous service)

Equivalent Grades: EN 1.4057, UNS S43100, GB/T 1Cr17Ni2

Performance Advantages: High strength and toughness, tensile strength up to 1080MPa after heat treatment; better corrosion resistance than SUS410L and SUS420 series, especially in atmospheric and weak corrosive environments; good low-temperature toughness, impact toughness ≥50J at -40℃; good weldability and machinability; magnetic.

Typical Applications: Automotive parts (drive shafts, suspension components, brake discs), high-pressure valve bodies and bonnets, pump shafts for corrosive media, marine machinery components, aircraft engine accessories, precision mechanical components requiring high strength and corrosion resistance.

Practical Q&A

Q1: What is the role of nickel in SUS431? A1: Nickel is a strong austenite stabilizer, which can refine the martensite structure during heat treatment, improve the toughness of the material; at the same time, nickel can enhance the stability of the surface passivation film, improve the corrosion resistance of the material, making it better than nickel-free martensitic stainless steel such as SUS420J1.

Q2: What is the optimal heat treatment process for SUS431? A2: Quench at 950-1050℃, oil cool or air cool + temper at 200-300℃, air cool. This process can achieve hardness of 38-43HRC, and the material has the best balance of strength and toughness. For higher corrosion resistance, temper at 600-650℃, but the strength will decrease slightly.

Q3: How does SUS431 compare with SUS410L in performance? A3: SUS431 has higher strength (tensile strength ≥1080MPa vs. ≥550MPa of SUS410L) and better corrosion resistance due to the addition of nickel; SUS410L has better weldability and lower cost. SUS431 is suitable for high-strength and corrosion-resistant scenarios, while SUS410L is suitable for general low-toughness requirements.

Q4: Can SUS431 be used in marine environments? A4: Yes. Its corrosion resistance in marine atmospheric environment is better than that of SUS420 series and SUS410L. It is suitable for marine mechanical components such as ship hull accessories and pump shafts. For components immersed in seawater for a long time, it is recommended to use 316L austenitic stainless steel.

Q5: What welding materials should be used for SUS431? A5: Use ER431 welding wire or E431-16 electrode, which has the same chromium and nickel content as the base metal, ensuring that the weld has the same strength and corrosion resistance as the base metal. Preheat to 150-200℃ before welding, and temper at 200-300℃ after welding to eliminate residual stress.