STS630 STS631 Precipitation Hardening Stainless Steel

Can STS630 reach HRC 50 or above through heat treatment?
It is difficult to achieve directly, and it needs to be combined with surface quenching or nitriding treatment.
Why does STS631 need cold treatment?
Cold treatment (-73℃) promotes the transformation of austenite to martensite, providing more strengthening sites for subsequent aging.
What is the corrosion resistance of the two materials?
STS631 has higher Cr and Ni content and better corrosion resistance than STS630, especially in acidic environments.

 

17-4PH vs 17-7PH stainless steel

Grade	Standard	Type	Strengthening Mechanism	Key Features
STS630	JIS G4303	Martensitic PH Steel	Cu Precipitation	High strength, corrosion resistance, and weldability; used in aerospace and energy sectors.
STS631	JIS G4303	Austenitic-Martensitic PH Steel	Al Precipitation	Balanced strength and toughness; ideal for high-stress applications like springs and fasteners.

 

Chemical Composition (wt%)

Element	STS630 (17-4PH)	STS631 (17-7PH)
C	≤0.07	≤0.09
Cr	15.5–17.5	16.0–18.0
Ni	3.0–5.0	6.5–7.7
Cu	3.0–5.0	-
Al	-	0.75–1.50
Nb	0.15–0.45	-

 

High-strength PH steel  Heat Treatment Processes

Solution Treatment

Purpose: Dissolve carbides and form a uniform matrix.

Temperature:

STS630: 1020–1060°C (1870–1940°F) for 1 hour.

STS631: 1000–1030°C (1830–1885°F) for 1 hour.

Cooling: Air or water quenching to suppress carbide formation.

Ageing Treatment

Purpose: Precipitate strengthening phases (e.g., Cu-rich particles for STS630, Ni-Al for STS631).

Parameters:STS630:

H900: 480°C (896°F) × 4 hours → Hardness HRC 40–45.

H1150: 620°C (1148°F) × 4 hours → Balanced strength and toughness.

STS631:

TH1050: 760°C (1400°F) × 1.5 hours + 15°C (59°F) × 0.5 hours → Age at 565°C (1050°F) × 1.5 hours.

RH950: Cold treatment (-73°C/-99°F) + ageing at 510°C (950°F) × 1 hour → HRC 43–48.

STS630 mechanical properties

Property	STS630 (H900)	STS631 (TH1050)
Yield Strength	≥1100 MPa	≥1035 MPa
Tensile Strength	≥1380 MPa	≥1240 MPa
Elongation	≥10%	≥12%
Hardness	HRC 40–45	HRC 40–45
Corrosion Resistance	Moderate (similar to 304)	Excellent (acidic environments)