SUS 631 vs 17-7PH Stainless Steel: What’s the Difference?

SUS 631 vs 17-7PH Stainless Steel: What's the Difference?

SUS 631 and 17-7PH stainless steel are often used interchangeably in technical and industrial contexts, leading to confusion among engineers and buyers. But are they truly different materials? The short answer: SUS 631 and 17-7PH are equivalent in composition and performance, though their naming conventions differ based on regional standards.

In this article, we explore the key differences (and similarities) between SUS 631 vs 17-7PH stainless steel, focusing on chemical composition, mechanical properties, standards, and applications.

 

What Is SUS 631 Stainless Steel?

SUS 631 is the Japanese designation (JIS G4313) for a precipitation hardening (PH) stainless steel, chemically equivalent to 17-7PH (AISI 631 / UNS S17700). It is a chromium-nickel-aluminum alloy designed for high strength, good corrosion resistance, and heat treatability.

Standard: JIS G4313

Grade Name: SUS 631

Equivalent to: AISI 631 / 17-7PH / UNS S17700

 

What Is 17-7PH Stainless Steel?

17-7PH is a U.S. standard precipitation hardening stainless steel, commonly used in aerospace, spring manufacturing, and precision instrumentation. It's heat-treatable to extremely high strengths and maintains good formability in the annealed condition.

Standard: ASTM A693, AMS 5528 / 5529

Grade Name: 17-7PH / Type 631

UNS Number: S17700

 

17-7PH Stainless Steel Equivalent Material

STANDARD	WERKSTOFF NR.	UNS	JIS	AFNOR	BS	GOST	EN
SS 17-7 PH	1.4568	S17700	SUS 631	Z8CNA17.07	301S81	–	X7CrNiAl 17 7

 

SUS 631 vs 17-7PH Stainless Steel:Chemical Composition

Element	SUS 631 / 17-7PH Stainless Steel
Chromium (Cr)	16.0 – 18.0%
Nickel (Ni)	6.5 – 7.8%
Aluminum (Al)	0.75 – 1.5%
Manganese (Mn)	≤ 1.0%
Silicon (Si)	≤ 1.0%
Carbon (C)	≤ 0.09%
Phosphorus (P)	≤ 0.04%
Sulfur (S)	≤ 0.03%

 

SUS 631 vs 17-7PH Stainless Steel: Mechanical properties

Property	SUS 631 / 17-7PH (RH950 Condition)
Tensile Strength	≥ 1500 MPa
Yield Strength	≥ 1310 MPa
Hardness	~45 HRC
Elongation	≥ 5%
Modulus of Elasticity	~200 GPa

 

17-7PH Stainless Steel Heat Treatment

For heat treating stainless steel grade 17-7 PH, three important steps need to be carried out - austenite conditioning, cooling to transform the austenite to martensite, and precipitation hardening to condition TH 1050 or RH 950.

 

17-7PH Stainless Steel Welding

Common arc and resistance methods can be used with stainless steel grade 17-7 PH. It is recommended that during fusion welding inert gas shielding should be performed to reduce the oxidation of aluminum during the process.

 

17-7PH Stainless Steel Annealing

Annealing of stainless steel grade 17-7 PH is performed at 1066°C (1950°F) for 3 min for every 0.1 inch (2.5 mm) of thickness, and then air cooled.

 

Is 17-7PH Stainless Steel magnetic?

17-7PH stainless steel is magnetic, though its magnetism varies based on its condition. It is considered weakly ferromagnetic in the annealed state but becomes strongly magnetic after heat treatment (precipitation hardening), which converts it to a martensitic structure. It is generally less magnetic than other precipitation-hardening (PH) grades.

 

17-7PH Stainless Steel Applications

17-7PH stainless steel is a precipitation-hardening alloy widely used for high-strength, corrosion-resistant components in aerospace (fasteners, springs, bulkheads), chemical processing, and medical devices. It is ideal for flat springs, Belleville washers, and diaphragms due to its high fatigue strength, minimal distortion, and temperature resistance up to 800°F (427°C).

 

If you have any project needs for 631 17-7PH stainless steel, please feel free to place an order. GNEE has a large inventory of popular products for you to choose from. It can be processed into various practical product forms, including plates, coils, pipes, bars, and wires. For detailed chemical composition and free samples, please contact our factory immediately. We offer competitive prices and excellent service.