What is 1.4568 Stainless Steel?

1.4568 stainless steel, commonly known as 631 or 17-7PH (UNS S17700), is a semi-austenitic precipitation-hardening stainless steel. It is known for its unique ability to be formed in a soft, ductile condition and then heat-treated to achieve very high strength and hardness, along with good corrosion resistance. This makes it ideal for aerospace springs, high-stress fasteners, and medical instruments.

 

This versatile precipitation-hardening grade is standardized under key international systems.

Standard	Equivalent Grade
EN (Europe)	1.4568
ASTM/AISI (USA)	631, 17-7PH, UNS S17700
JIS (Japan)	SUS631

Its composition includes aluminum for age-hardening.

Element	C	Si	Mn	Cr	Ni	Al
Content (%)	≤ 0.09	≤ 1.0	≤ 1.0	16.0 - 18.0	6.5 - 7.75	0.75 - 1.50

Mechanical properties vary dramatically with heat treatment condition.

Condition	Yield Strength (Rp0.2)	Tensile Strength (Rm)	Elongation (A)	Hardness (HRC)
Condition A (Annealed)	~ 380 MPa	~ 1030 MPa	~ 20%	~ 28 HRC
Condition C (TH1050)	~ 1030 MPa	~ 1240 MPa	~ 7%	~ 40 HRC

 

Key Characteristics and Applications of 1.4568 / 17-7PH

High Strength with Good Ductility: Can achieve tensile strengths over 1200 MPa after precipitation hardening while retaining useful ductility.

Excellent Fatigue and Spring Properties: Widely used for springs, diaphragms, and other components requiring high fatigue resistance and elastic properties.

Good Corrosion Resistance: Comparable to Type 304 stainless steel, making it suitable for applications requiring both strength and moderate corrosion resistance.

 

Primary Applications:

Aerospace: Bellows, springs, fasteners, and structural components.

Medical: Surgical instruments, orthopedic implants, and dental tools.

Chemical Processing: Valve parts and pump components requiring strength and corrosion resistance.

Precision Instruments: Critical components requiring dimensional stability and high strength.

 

What is the typical heat treatment sequence for 17-7PH (1.4568)?
The most common treatment is the TH1050 condition. First, the material is solution treated at 1040°C and cooled rapidly (Condition A). It is then conditioned by heating to 760°C, holding, and cooling to room temperature within 1 hour. Finally, it is age hardened at 565°C for 90 minutes. This sequence transforms the austenitic structure to martensitic and then precipitates hardening phases, achieving high strength. Different conditioning and aging temperatures produce various strength levels.

 

How does 17-7PH compare to 17-4PH in terms of properties and applications?
Both are precipitation-hardening grades, but 17-7PH is semi-austenitic while 17-4PH is martensitic. 17-7PH generally offers better formability in the annealed condition and can achieve higher strength levels (especially in spring applications) with excellent fatigue resistance. 17-4PH typically has better machinability and is often chosen for complex machined parts. 17-7PH is preferred for thin sections and formed components like springs and bellows.

 

Looking for a Reliable Supplier of 1.4568 / 17-7PH Stainless Steel?
GNEE Steel supplies high-performance 17-7PH (1.4568) stainless steel in strip, wire, bar, and sheet forms, available in various heat-treated conditions to meet specific mechanical requirements. We provide full material certification and processing support. If you have any requirements, please feel free to contact us.