SUS431 Stainless Steel: Martensitic Grade With Nickel Addition for High Strength and Corrosion Resistance

What Is SUS431 Stainless Steel?

SUS431 is a nickel-bearing martensitic stainless steel standardized in JIS G4303 (bars) and JIS G4304 (plates and strips). It is equivalent to UNS S43100, EN 1.4057 (X17CrNi16-2) in EN 10088, and 1Cr17Ni2 in the Chinese standard GB/T 1220. The nickel addition distinguishes SUS431 from plain chromium martensitic grades: it improves hardenability, raises strength after quenching and tempering, and gives better corrosion resistance in mildly corrosive and atmospheric environments. SUS431 is therefore used where the strength of a martensitic steel and better corrosion behavior than 410 or 420 are required in the same component.

Chemical Composition

The composition limits below follow JIS G4303 and match the EN 10088 designation X17CrNi16-2.

Element	Composition (wt%)
Carbon (C)	0.15-0.25
Silicon (Si)	1.00 max
Manganese (Mn)	1.00 max
Phosphorus (P)	0.040 max
Sulfur (S)	0.030 max
Nickel (Ni)	1.20-2.00
Chromium (Cr)	15.00-17.00
Iron (Fe)	Balance

Carbon provides the hardenability for the martensitic transformation, chromium supplies corrosion resistance and hardenability, and nickel improves toughness in the hardened condition and stabilizes the corrosion behavior of the passive film.

Mechanical Properties and Heat Treatment

SUS431 is usually supplied in the annealed condition for machining and is hardened by oil quenching from the austenitizing range followed by tempering. In the quenched and tempered condition, typical minimum mechanical values are as follows.

Property (Quenched and Tempered)	Value
Tensile Strength min (MPa)	1080
Yield Strength min (MPa)	880
Elongation min (%)	12
Hardness (HRC)	38-43

In practice, hardening is carried out from approximately 980-1060°C with oil quenching, followed by tempering in the range of 600-700°C depending on the required hardness-toughness balance. For the soft condition, SUS431 is annealed at about 650-700°C with slow furnace cooling. The steel should not be tempered in the range of 400-550°C, where temper embrittlement can reduce toughness.

Corrosion Resistance

Because of its higher chromium content and the nickel addition, SUS431 has better corrosion resistance than 410 and other plain martensitic grades in atmospheric conditions, fresh water, mild chemicals and food-contact service. It is not suitable for strong chloride or acidic media, where austenitic grades such as 304 or 316 are required. Like all martensitic steels, the corrosion resistance of SUS431 depends on the final hardness and tempering condition; the hardened and low-temperature-tempered condition offers the least resistance, so tempering should be chosen with the service environment in mind.

Typical Applications

High-strength shafts, spindles and piston rods

Bolts, studs and fasteners for corrosive atmospheres

Valve stems, valve seats and pump parts

Plastic injection mold components and cutting tools

Aircraft and automotive components requiring strength with moderate corrosion resistance

FAQ

What does SUS431 mean?

SUS is the JIS prefix for stainless steel; the number 431 identifies this specific martensitic grade with 15-17% chromium and 1.2-2.0% nickel. The same material is called 1.4057 (X17CrNi16-2) in EN 10088, UNS S43100 in ASTM, and 1Cr17Ni2 in GB/T 1220.

Why is nickel added to SUS431?

Nickel improves hardenability so that thicker sections can be hardened by oil quenching, and it improves the toughness of the hardened steel. It also raises the corrosion resistance of the passive film compared with plain chromium martensitic grades such as 410.

What is the difference between SUS431 and SUS410?

SUS431 contains more chromium (15-17% versus 11.5-13.5%) and adds 1.2-2.0% nickel. As a result it reaches higher strength after hardening (tensile strength over 1080 MPa versus about 540 MPa minimum for hardened 410) and offers better corrosion resistance, at a higher cost.

Can SUS431 be welded?

Yes, but martensitic steels are considered difficult to weld. Preheat and post-weld heat treatment are normally required to avoid hard, crack-sensitive martensite in the heat-affected zone. Austenitic filler metals are often used, and the weldment should be tempered or annealed after welding.

Is SUS431 magnetic?

Yes. SUS431 is a martensitic stainless steel and is strongly magnetic in all conditions, unlike austenitic grades such as 304 which are essentially non-magnetic in the annealed state.

What hardness can SUS431 reach?

In the quenched and tempered condition, SUS431 is typically supplied at 38-43 HRC, giving a minimum tensile strength of 1080 MPa. Lower tempering temperatures give higher hardness but reduced toughness, so the tempering temperature is selected according to the application.