17-7 PH is a semi-austenitic precipitation-hardening stainless steel (chromium-nickel-aluminum alloy) designed for high strength, excellent fatigue performance, and good corrosion resistance (comparable to 304 stainless steel), with a maximum operating temperature of 600°F (316°C). Due to its minimal distortion during heat treatment and high strength, it is commonly used in aerospace, springs, washers, and bellows applications.
17-7 PH stainless steel (UNS S17700 or Grade 631) is a semi-austenitic precipitation-hardening alloy with high strength, excellent fatigue properties, and corrosion resistance. Key standards include ASTM A693/A564 (plate/bar), AMS 5528/5529 (aerospace plate/strip), and SAE J217 (spring wire).
ASTM A564 UNS S17400, also known as 17-4 PH, is the most versatile, high-strength stainless steel alloy available for processes and applications where corrosion and mechanical performance are of prime importance.
| Element | Content (%) |
|---|---|
| Chromium, Cr | 16-18 |
| Nickel, Ni | 6.50 - 7.75 |
| Manganese, Mn | 1 max |
| Silicon, Si | 1 max |
| Aluminum, Al | 0.75 - 1.50 |
| Carbon, C | 0.09 max |
| Phosphorous, P | 0.040 max |
| Sulfur, S | 0.030 max |
| Iron, Fe | Balance |
The physical properties of stainless steel grade 17-7 PH are tabulated below.
| Properties | Metric | Imperial |
|---|---|---|
| Density | 7.80 g/cm3 | 0.282 lb/in3 |
The following table shows mechanical properties of stainless steel grade 17-7 PH (TH1050, bar and forgings).
| Properties | Metric | Imperial |
|---|---|---|
| Tensile strength | 1170 MPa | 170000 psi |
| Yield strength | 965 MPa | 140000 psi |
| Modulus of elasticity | 204 GPa | 29600 ksi |
| Poisson's ratio | 0.27-0.30 | 0.27-0.30 |
| Elongation at break | 6% | 6% |
| Hardness, Rockwell C | 38 | 38 |
The thermal properties of stainless steel grade 17-7 PH are given in the following table.
| Properties | Metric | Imperial |
|---|---|---|
| Thermal conductivity | 16.4 W/mK | 114 BTU in/hr.ft2.°F |
| Thermal expansion co-efficient (@0.000-100°C/32-212°F) | 11 µm/m°C | 6.11 µm/m°C |
Stainless steel grade 17-7 PH is primarily used for applications requiring corrosion resistance, good strength, and mechanical properties up to 427°C (800°F) in operation. It is also commonly used for intricate parts due to its low distortion in heat treatment.
17-7 PH and 17-4 PH are both high-strength precipitation-hardening stainless steels offering excellent corrosion resistance, but they differ primarily in structure and application. 17-4 PH is a martensitic alloy known for superior, high-strength structural parts, whereas 17-7 PH is a semi-austenitic alloy offering superior elasticity, fatigue resistance, and higher temperature stability up to 800°F (427°C).
17-7 PH and 15-5 PH are both high-strength, corrosion-resistant, precipitation-hardening (PH) stainless steels, but differ in composition and application. 17-7 PH (Cr-Ni-Al) offers maximum strength, high fatigue resistance, and good formability, making it ideal for springs and aerospace components. 15-5 PH (Cr-Ni-Cu) is a martensitic alloy designed for superior transverse toughness,, ductility, and easier heat treatment, commonly used for heavy-duty forged parts and shafts.
GNEE is a trusted supplier of precipitation-hardening stainless steel and specialty alloys in China. We supply 17-4 PH, 15-5 PH, and 17-7 PH alloys in various forms including bars, plates, profiles, and forgings. All products are sourced from certified steel mills and undergo rigorous chemical composition and mechanical property testing to ensure reliable quality.
Whether you are in the aerospace, oil and gas, marine engineering, or defense industry, we ensure that every batch of our products meets international standards and your specific application requirements.
Click here to view our complete range of precipitation-hardening alloys: PH Alloys.
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