AISI 631 X7CrNiAl17-7 1.4568 SUS631 PH Stainless Steel

Product Overview

AISI 631, also widely known by its trade name 17-7 PH and its European equivalent EN X7CrNiAl17-7 (Material No. 1.4568), is a semi-austenitic precipitation-hardening (PH) stainless steel. You could find the equivalent from different steel standard, such as: X7CrNiAl17-7/1.4568 from Europe standard EN 10088-3, 07Cr17Ni7Al/

0Cr17Ni7Al from China standard GB/T 1220, SUS631 from Japan standard JIS G4303, 09X17H7Ю from Russia standard GOST 5632-72. This unique class of steel combines the excellent corrosion resistance of austenitic stainless steels with the ultra-high strength of martensitic steels, achievable through a simple heat treatment process.

The alloy's strength is developed not by carbon, but by the precipitation of aluminum-nickel intermetallic compounds during the aging (hardening) phase. This allows 631 to deliver exceptional tensile and yield strengths while maintaining good ductility and fabricability in its annealed state. Its ability to withstand high stresses in corrosive environments makes it an indispensable material for advanced engineering applications.

We supply AISI 631 stainless steel in various forms, including hot-rolled bars, forged bars, plates, sheets, and blocks, all processed with strict quality control from melting to final finishing.

Cross-Standard Equivalent Grades

AISI 631 has corresponding designations in major international stainless steel standard systems, with slight component tolerances adjusted for regional industrial requirements, but consistent core performance and application scenarios.

Product Features

Chemical Composition

The chemical composition of AISI 631 and its equivalent grades is optimized for precipitation hardening, with chromium (Cr) providing corrosion resistance, nickel (Ni) stabilizing the austenitic structure, and aluminum (Al) as the core precipitation strengthening element.

Physical & Mechanical Properties

1. Basic Physical Properties

AISI 631 has stable physical properties that lay the foundation for its processing and application in extreme environments:

• Density: 7.67 kg/m³

• Melting Point: 1415-1450℃

• Specific Heat Capacity: 460.6 J/(kg·℃)

• Magnetic Property: Non-magnetic in solution-annealed state, magnetic after aging hardening

• Thermal Conductivity: 16.2 W/(m·K) (20℃)

• Coefficient of Thermal Expansion: 11.0×10⁻⁶/℃ (20-100℃)

2. Mechanical Properties

Mechanical properties for 07Cr17Ni7Al/0Cr17Ni7Al from standard GB/T1220 and SUS631 from JIS G4303.

Mechanical properties for X7CrNiAl17-7/1.4568 from standard EN10088-3.

AT=Solution annealed

3. Performance Characteristics

• High Strength: Tensile strength up to 1700MPa after 510℃ aging, far exceeding ordinary austenitic stainless steel such as 304/316.

• Temperature Resistance: Maintains 80% of room temperature strength at ≤316℃, suitable for high-temperature working conditions such as aero-engines.

• Formability: Austenitic structure in solution-annealed state allows cold working (cold rolling, stamping, bending) for complex-shaped parts.

• Corrosion Resistance: Superior to martensitic stainless steel (e.g., 410), and stable in atmospheric, freshwater, and weak acid environments.

Supply Specifications, Tolerance & Stock

We provide a full range of hot-rolled and hot-forged products of AISI 631, with strict tolerance control and sufficient stock to meet the customized needs of different industries.

1. Product Size Range

2. Surface Finish & Tolerance

3. In-Stock Sizes (Monthly Stock >10,000 Tons)

• Hot Rolled Bar (Φmm): 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 120, 130, 140, 150, 160, 170, 180, 190

• Hot Forged Bar (Φmm): 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400

Stock changes daily; contact our sales team for real-time availability.

Production & Quality Inspection

1. Steel Making & Forging Process

We adopt advanced smelting and forging technologies to ensure the purity and structural uniformity of AISI 631:

• Smelting Process: EF+LF+VD / EAF+LF+VD / EF+LF+VD+ESR / EAF+LF+VD+ESR (ESR for ultra-high purity requirements)

• Hot Forging Temperature: 900-1150℃

• Cooling Method: Air cooling (avoids internal stress and structural defects)

2. Non-Destructive Testing

All products undergo strict ultrasonic testing in accordance with international standards to eliminate internal defects:

• Testing Standard: EN10228-3 Class III / Sep 1921-84 D/D

• Testing Scope: 100% of bars, plates and blocks (no blind areas)

Heat Treatment Technology

The core advantage of AISI 631 is its adjustable performance via heat treatment. Solution annealing is the basis for forming, while aging hardening is the key to achieving high strength. Strict temperature and time control is required for all processes to ensure precipitation of strengthening phases.

1. Solution Annealing

• Heat the steel to 1000-1100℃ in a furnace and hold for sufficient time (based on product thickness).

• Rapid cooling (air cooling/water quenching) to obtain a uniform austenitic structure, with hardness ≤229HBW for easy cold working.

2. Aging Hardening at 510℃

Suitable for high-load structural parts requiring ultra-high strength:

• After solution treatment, heat to 955℃±10℃, hold for 10 minutes, then air cool to room temperature.

• Within 24 hours, cool to -73℃±6℃, hold for 8 hours (cryogenic treatment to transform austenite to martensite).

• Reheat to 510℃±10℃, hold for 1 hour, then air cool to precipitate Ni-Al strengthening phases.

3. Aging Hardening at 565℃

Suitable for parts requiring both strength and toughness (e.g., precision springs, fasteners):

• After solution treatment, heat to 760℃±15℃, hold for 90 minutes.

• Cool to below 15℃ within 1 hour, hold for 30 minutes (martensitic transformation).

• Reheat to 565℃±10℃, hold for 90 minutes, then air cool to achieve a balance of strength and elongation.

Key Application Fields

AISI 631 is widely used in high-end manufacturing fields due to its high strength, corrosion resistance, and heat treatment customizability, and is the material of choice for parts requiring lightweight and high performance:

• Aerospace: Aircraft cockpit frame, wing connectors, aero-engine valve springs, missile/spacecraft structural parts (utilizes high-temperature strength and dimensional stability).

• Chemical & Petroleum Industry: Corrosion-resistant valves, pump bodies, pipelines, high-stress parts of chemical equipment, salt spray corrosion-resistant parts in marine platforms (avoids corrosion in weak acid/alkali environments).

• Medical & Precision Instruments: Surgical instruments, dental equipment, precision instrument springs, sensor components (biocompatibility and high precision).

• Automotive & High-End Manufacturing: High-performance suspension springs, clutch springs, high-strength bolts/pins, precision mechanical parts (lightweight and high load-bearing).

• Electronics & Energy: Semiconductor manufacturing equipment parts, nuclear power plant corrosion-resistant structural components, nuclear waste storage containers (radiation resistance and corrosion resistance).

• Military & Shipbuilding: Seawater corrosion-resistant parts for warships, high-strength structural parts for weapons (resists salt spray and impact load).

• Food & Paper Industry: Food processing equipment, pulp treatment equipment (hygiene and corrosion resistance to food acids/pulp chemicals).

Comparison with Common Stainless Steel Grades

Customers often compare AISI 631 with 304, 316, and 630 (17-4PH) when selecting materials. The following is a detailed comparison of core performance and application scenarios to help with material selection:

1. AISI 631 vs 304/316 (Austenitic Stainless Steel)

2. AISI 631 (17-7PH) vs AISI 630 (17-4PH) (PH Stainless Steel)

FAQ

Q1: Can AISI 631 be welded? What welding precautions are there?

A1: Yes, AISI 631 can be welded (preferably TIG welding), but strict heat input control is required to avoid austenite grain growth. The solution-annealed state is the best welding state; post-weld aging hardening must be performed to restore the strength of the heat-affected zone (otherwise the weld zone will soften significantly).

Q2: What is the corrosion resistance of AISI 631 in seawater?

A2: AISI 631 has limited resistance to high chloride environments such as seawater and is prone to pitting corrosion if used for a long time. It is suitable for marine platform parts with regular maintenance; for long-term seawater immersion parts, 316 or duplex stainless steel is recommended instead.

Q3: Why is cryogenic treatment required for 510℃ aging of AISI 631?

A3: Cryogenic treatment (-73℃) is to completely transform the retained austenite into martensite, which is the basis for the precipitation of Ni-Al strengthening phases during subsequent 510℃ heating. Without cryogenic treatment, retained austenite will reduce the final strength and hardness of the material.

Q4: What is the difference between Condition RH 950 and TH 1050?

A4: These are two standard precipitation hardening treatments.

• RH 950 (Refrigerated & Hardened at 950°F / 510°C): This involves a refrigeration step to transform the structure before aging. It yields the highest strength (tensile > 1230 MPa).

• TH 1050 (Hardened at 1050°F / 565°C): This is a single-step aging process. It produces slightly lower strength but offers improved ductility and toughness compared to RH 950. The choice depends on whether the application prioritizes maximum strength or a balance of strength and toughness.

Q5: Can AISI 631 be used for cold working such as stamping?

A5: Yes. In the solution-annealed state, AISI 631 has a soft austenitic structure (hardness ≤229HBW) and good cold formability, which can be stamped, bent, and cold rolled into complex-shaped parts. Aging hardening is performed after forming to achieve high strength.

Q6: Can you supply 631 stainless steel with special dimensions or tighter tolerances?

A6: Yes, we have the capability to process materials to meet specific customer requirements. This includes centerless grinding, precision peeling, and machining to achieve tighter diameter tolerances or custom lengths. Please provide your detailed drawing or specifications to our sales team for a quotation.

Need a specific size or have a technical question? Contact us today!