What is 1.4568 stainless steel ?
1.4568 is the EN standard grade for 17-7PH stainless steel (equivalent to AISI 631 / UNS S17700 / X7CrNiAl17-7), a precipitation-hardening stainless steel that maintains excellent spring properties at temperatures up to 316°C. It is commonly used in demanding applications such as aerospace, petroleum, chemical, and specialized machinery industries.
What is 1.4568 steel grade equivalent to?
1.4568 steel (X7CrNiAl17-7) is a German DIN/EN standard designation for 17-7PH stainless steel. It is a precipitation-hardening, semi-austenitic alloy characterized by high strength, excellent elasticity, and good corrosion resistance. It is primarily equivalent to AISI 631, UNS S17700, and JIS SUS631.
17-7PH, 631, X7CRNIAL17-7, UNS S17700, 1.4568 Stainless Steel - Chemical Composition (Weight Percentage)
| Grade | Chemical composition WT % | |||||||
|---|---|---|---|---|---|---|---|---|
| C (Max) | Mn (Max) | Si (Max) | P (Max) | S (Max) | Cr | Ni | Al | |
| 17-7PH | 0.09 | 1.0 | 0.5 | 0.025 | 0.025 | 16.00 – 17.25 | 6.50 – 7.75 | 0.75 – 1.25 |
| S17700: AMS 5529/5528, AMS 5644, AMS 5678 | 0.09 | 1.0 | 1.0 | 0.040 | 0.030 | 16.0 – 18.0 | 6.5 – 7.7 | 0.75 – 1.50 |
| X7CrNiAl17-7, 1.4568 | 0.09 | 1.0 | 0.7 | 0.040 | 0.015 | 16.0 – 18.0 | 6.5 – 8.3 | 0.7 – 1.5 |
| SUS 631 | 0.09 | 1.0 | 1.0 | 0.040 | 0.030 | 16.00 – 18.00 | 6.50 – 7.75 | 0.75 – 1.50 |
Physical Properties
| Property | Value |
|---|---|
| Density | 7.8 g/cm³ (0.282 lb/in³) |
| Modulus of Elasticity at 20°C | 200 GPa (29 × 10⁶ psi) |
| Modulus of Rigidity | 75 GPa (11 × 10⁶ psi) |
| Electrical Resistivity at 20°C | 0.8 Ω·mm²/m (80 microhm-cm) |
| Thermal Conductivity at 20°C | 16 W/m·K (9.5 Btu·ft/hr·ft²·°F) |
| Coefficient of Thermal Expansion (20-100°C) | 15.5 × 10⁻⁶ /K (8.5 × 10⁻⁶ /°F) |
| Specific Heat Capacity at 20°C | 500 J/kg·K (0.12 Btu/lb·°F) |
| Magnetic Permeability (Annealed Condition) | 1.4-3.6 (Weakly Ferromagnetic) |
Mechanical properties of 17-7PH, 631, X7CRNIAL17-7, UNS S17700, and 1.4568 stainless steel
| Condition | Ultimate Tensile Strength, MPa (ksi) | 0.2% Yield Strength, MPa (ksi) | Elongation in 50mm (2″), % | Hardness |
|---|---|---|---|---|
| Annealed (Condition A) | 900-1100 (130) | 280 min (40) | 35 | B85 |
| TH1050 | 1345 (195) | 1205 (175) | 8 | C42 |
| RH950 | 1550 (225) | 1380 (200) | 7 | C47 |
| Cold Worked (Condition C) | 1620 (235) | 1517 (220) | 6 | C48 |
| CH900 | 1827 (265) | 1793 (260) | 2 | C49 |
1.4568 Stainless Steel Heat Treatment
1.4568 (17-7PH) stainless steel requires a three-step heat treatment process to achieve high strength: austenitizing, cooling to induce martensitic transformation, and precipitation hardening (aging). Common heat treatment processes include TH 1050, RH 950, and CH 900, with aging typically performed in the temperature range of 480°C to 500°C to achieve optimal performance. This material is used in the manufacture of high-strength springs and aerospace components.
1.4568 Stainless Steel Corrosion Resistance
1.4568 (17-7 PH) stainless steel exhibits good to excellent corrosion resistance, generally comparable to AISI 304 stainless steel and superior to 400 series martensitic stainless steels. It demonstrates good corrosion resistance in freshwater, industrial atmospheres, and mild oxidizing environments. Because it maintains its corrosion resistance even at temperatures up to 482°C (900°F), it is often used in the manufacture of springs and high-strength parts.
1.4568 Stainless Steel Machinability
1.4568 (17-7 PH) stainless steel has moderate to difficult machinability, rated at approximately 60–75% of B1112 free-cutting steel. It is best machined in the solution-annealed condition, where it behaves like 300-series austenitic stainless steel, requiring rigid setups and slow speeds to manage strong, gummy chips and significant work-hardening.
1.4568 Stainless Steel Delivery Condition
1.4568 (17-7PH) stainless steel is primarily delivered in the annealed (soft) condition for good formability, or in cold-rolled/hardened conditions (Condition C, CH900, TH1050) for high-strength spring applications. It is typically supplied in forms like strip, wire, sheet, and bar with bright or polished surface finishes.
