17-7PH vs 17-4PH
These two grades are listed as equivalents of each other: their chemistry windows overlap and they serve the same applications. They are not always identical — check the differences below before substituting, especially in certified designs.
17-7PH
Stainless Steel
17-7PH (type 631) is a semi-austenitic precipitation-hardening stainless supplied soft and formable, then transformed and aged to very high strength in sheet form. It is the classic stainless spring and aerospace diaphragm material.
Standards: DIN 1.4568 · AISI 631 (17-7PH) · JIS SUS631 · GB 07Cr17Ni7Al
17-4PH
Stainless Steel
17-4PH (type 630) is the most widely used precipitation-hardening stainless steel, combining near-316 corrosion resistance with strength levels up to about 1300 MPa after a simple low-temperature age. It hardens with minimal distortion, so parts are machined soft and aged to final strength.
Standards: DIN 1.4542 · AISI 630 (17-4PH) · JIS SUS630 · GB 05Cr17Ni4Cu4Nb
Chemical composition compared (%)
| Element | 17-7PH | 17-4PH |
|---|---|---|
| C | ≤0.09 | ≤0.07 |
| Si | ≤1.00 | ≤1.00 |
| Mn | ≤1.00 | ≤1.00 |
| P | ≤0.040 | ≤0.040 |
| S | ≤0.030 | ≤0.030 |
| Cr | 16.00–18.00 | 15.00–17.50 |
| Ni | 6.50–7.75 | 3.00–5.00 |
| Al | 0.75–1.50 | — |
| Cu | — | 3.00–5.00 |
| Nb | — | 0.15–0.45 |
Properties compared
| Property | 17-7PH | 17-4PH |
|---|---|---|
| Delivery condition | Annealed (Condition A) for forming, then aged | Solution treated (Condition A) or aged |
| Hardness (Condition CH900) | ~49 HRC | — |
| Tensile strength (CH900) | ~1650 MPa (sheet) | — |
| Density | 7.80 g/cm³ | 7.80 g/cm³ |
| Magnetic | Yes (after conditioning) | Yes |
| Hardness (H900 aged) | — | ~40 HRC |
| Tensile strength (H900) | — | ~1310 MPa |
| Yield strength (H900) | — | ~1170 MPa |
Sourcing either grade?
Nasteel stocks both families from Shenzhen with EN 10204 3.1 mill certificates by heat number.
Ask for a quotationSee full data sheets: 17-7PH · 17-4PH. Substitution decisions for certified parts stay with the design authority.