17-4PH Stainless Steel (UNS S17400)
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Overview of 17-4PH Steel (ASTM A564, ASTM A693, AMS 5604):
17-4PH is a high-strength, corrosion-resistant, precipitation-hardening (PH) stainless steel that is commonly used in industries requiring superior mechanical properties, such as aerospace, chemical, and defense sectors. The “17-4” refers to the steel’s nominal composition, containing 17% chromium and 4% nickel. The “PH” designation indicates that the material undergoes a precipitation-hardening process to achieve its high strength. This process involves heat treatment to increase its hardness and tensile strength.
Features:
- Excellent Strength and Hardness: 17-4PH is capable of reaching very high tensile strength and hardness after heat treatment, making it ideal for demanding applications.
- Good Corrosion Resistance: It offers excellent resistance to corrosion in both atmospheric and marine environments, as well as to many acids and chemicals.
- Precipitation Hardening: The steel can be heat-treated to provide increased strength, allowing for a wide range of applications that require a combination of toughness and hardness.
- Good Fatigue and Stress-Corrosion Cracking Resistance: 17-4PH shows good resistance to fatigue, stress-corrosion cracking, and pitting in harsh environments.
- Weldability: Although 17-4PH can be welded, its mechanical properties may be slightly reduced in the weld area. It is often recommended to heat treat welded sections to restore strength.
- High-Temperature Performance: It maintains good mechanical properties at elevated temperatures (up to about 600°F or 316°C).
Specifications:
- ASTM A564: Standard Specification for Hot-Rolled and Cold-Finished Age-Hardening Stainless Steel Bars and Shapes
- ASTM A693: Standard Specification for Precipitation-Hardening Stainless Steel Plate, Sheet, and Strip.
- UNS S17400: Unified Numbering System designation for 17-4PH stainless steel.
- AMS 5604: Aerospace Material Specification for precipitation-hardening stainless steel in bar form.
Composition of 17-4PH Stainless Steel:
| Element | Percentage |
|---|---|
| Chromium (Cr) | 15.0 – 17.5% |
| Nickel (Ni) | 3.0 – 5.0% |
| Copper (Cu) | 3.0 – 5.0% |
| Iron (Fe) | Balance |
| Manganese (Mn) | 1.0% Max |
| Silicon (Si) | 1.0% Max |
| Carbon (C) | 0.07% Max |
| Phosphorus (P) | 0.04% Max |
| Sulfur (S) | 0.03% Max |
Physical Properties:
| Property | Value |
|---|---|
| Density | 7.75 g/cm³ |
| Melting Point | 1400–1450°C (2550–2640°F) |
| Hardness (Rockwell B) | 95-100 HRC (age-hardened) |
| Tensile Strength | 1000-1300 MPa (145,000-188,500 psi) |
| Yield Strength | 850-1100 MPa (123,000-160,000 psi) |
| Elongation | 10-15% |
| Modulus of Elasticity | 200 GPa |
| Thermal Conductivity | 24 W/m·K |
| Coefficient of Thermal Expansion | 17.4 × 10⁻⁶ /°C |