SUS630 Material Equivalent: UNS S17400, EN 1.4542 and the H-Condition Properties

What SUS630 Is and Where It Sits in the Standards

SUS630 is the Japanese designation for a chromium-nickel-copper precipitation-hardening stainless steel, standardised for bar in JIS G4303 and for plate, sheet and strip in JIS G4304 and JIS G4305. The same alloy is listed as UNS S17400 in the United States, where bar and forging product is ordered to ASTM A564 and plate, sheet and strip to ASTM A693. In the European system the grade is 1.4542, written X5CrNiCuNb16-4 in EN 10088, and the Chinese equivalent is 0Cr17Ni4Cu4Nb. All of these designations describe the same 17 % chromium, 4 % nickel, 4 % copper chemistry with a niobium addition.

The alloy is valued for a combination that austenitic grades cannot offer: strength comparable to a low-alloy quenched and tempered steel, achieved by a low-temperature aging treatment rather than by quenching to martensite, with corrosion resistance closer to that of type 304.

Chemical Composition Across Standards

Element, %	ASTM A564 / A693 (S17400)	EN 1.4542
Carbon (C)	0.07 max	0.07 max
Silicon (Si)	1.00 max	1.00 max
Manganese (Mn)	1.00 max	1.00 max
Phosphorus (P)	0.040 max	0.040 max
Sulfur (S)	0.030 max	0.030 max
Chromium (Cr)	15.00 - 17.50	15.00 - 17.00
Nickel (Ni)	3.00 - 5.00	3.00 - 5.00
Copper (Cu)	3.00 - 5.00	3.00 - 5.00
Niobium + Tantalum	0.15 - 0.45	0.15 - 0.45

Copper is the element that forms the strengthening precipitates during aging; niobium combines with carbon and contributes to the hardening response. Because copper and niobium are the controlling additions, the aging temperature determines the property level more than any variation in the base chemistry.

Heat Treatment and Resulting Properties

The alloy is solution annealed at about 1040 °C and cooled rapidly in air or oil, which produces a soft, machinable, essentially martensitic structure. Strength is then developed by aging in the 480 to 620 °C range for one to four hours, followed by air cooling. Aging temperatures are tied to the H-condition designations used on drawings and purchase orders.

Condition	Aging temperature	Tensile min, MPa	Yield 0.2 % min, MPa	Elongation min, %	Hardness min
H900	about 480 °C	1310	1170	10	40 HRC
H1025	about 550 °C	1070	1000	12	35 HRC
H1075	about 580 °C	1000	860	13	31 HRC
H1150	about 620 °C	930	725	16	28 HRC

Minimum values follow ASTM A564 for the 630 grade. The pattern is deliberate: the highest strength and hardness come from the lowest aging temperature, while toughness, ductility and resistance to stress corrosion cracking improve as the aging temperature rises. Selection is therefore a trade between the strength needed to carry load and the toughness needed to survive impact, fatigue and a corrosive environment.

Corrosion Resistance and Limitations

In the H1150 and over-aged conditions the alloy performs broadly like type 304 in atmospheric, fresh water and mildly acidic service, and it resists stress corrosion cracking better than the higher-strength conditions. It is not a substitute for a molybdenum-bearing grade in chloride-rich or strongly acidic environments, and hydrogen embrittlement must be considered for cathodically protected or high-strength components. Where maximum strength is combined with a wet chloride environment, fatigue and cracking behaviour have to be assessed rather than assumed.

Product Forms and Applications

The precipitation-hardening response allows large sections to be strengthened without the distortion and cracking risk of a conventional quench. Typical uses include valve stems, pump shafts and impellers, hydraulic and aircraft fittings, nuclear reactor components and control-rod drive parts, plastic injection moulds and die components, gears, fasteners, and surgical and dental instruments. Plate is supplied from roughly 0.5 mm to 100 mm, bar in round, square and hexagonal sections, together with tube and wire forms; delivery condition is normally stated in the contract, since the aging condition fixes the mechanical properties.

Machining is carried out in the solution-annealed condition where possible, then the part is aged to final properties. Welding, when required, is performed before aging, and the aging treatment then restores properties across the weld zone.

Frequently Asked Questions

Q: What is the material equivalent of SUS630?
A: UNS S17400 in the ASTM system, ordered to A564 for bar and forgings or A693 for plate and strip; 1.4542 (X5CrNiCuNb16-4) in EN 10088; and 0Cr17Ni4Cu4Nb in the Chinese system.

Q: Which condition gives the highest strength at SUS630?
A: H900, aged at about 480 °C. Minimum tensile strength is 1310 MPa with 1170 MPa yield strength, but elongation falls to 10 % minimum and impact toughness is the lowest of the usual conditions.

Q: Why is H1150 sometimes chosen instead of H900?
A: Over-aging improves ductility and toughness and raises resistance to stress corrosion cracking and hydrogen embrittlement. Minimum tensile strength drops to 930 MPa with yield at 725 MPa, which is still well above most austenitic grades.

Q: How is SUS630 heat treated?
A: Solution anneal at about 1040 °C followed by rapid cooling, then aging between roughly 480 and 620 °C for one to four hours and air cooling. The aging temperature is set by the required H-condition.

Q: Is SUS630 as corrosion resistant as type 304?
A: In the over-aged conditions it is broadly comparable in atmospheric and fresh water service. It has less molybdenum than type 316 and is not selected for chloride-rich or strongly acidic duties, and high-strength conditions are more sensitive to cracking.

Q: What are the common applications of SUS630 stainless steel?
A: Valve and pump components, shafts, gears, fasteners, hydraulic and aerospace fittings, nuclear power parts, plastic moulds and dies, and medical or dental instruments, where high strength and moderate corrosion resistance are both required.