17-7PH
Data verified17-7PH (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.
Chemical composition
| Element | Content (%) |
|---|---|
| C | ≤0.09 |
| Si | ≤1.00 |
| Mn | ≤1.00 |
| P | ≤0.040 |
| S | ≤0.030 |
| Cr | 16.00–18.00 |
| Ni | 6.50–7.75 |
| Al | 0.75–1.50 |
Weight percent, per the governing standard ranges. Actual values per heat are on the mill certificate.
Properties
| Delivery condition | Annealed (Condition A) for forming, then aged |
| Hardness (Condition CH900) | ~49 HRC |
| Tensile strength (CH900) | ~1650 MPa (sheet) |
| Density | 7.80 g/cm³ |
| Magnetic | Yes (after conditioning) |
Heat treatment
Anneal 1065 °C (Condition A, formable); condition by cooling to -73 °C (Condition R) or austenite conditioning at 760 °C (Condition T), then age at 482–566 °C to precipitate NiAl.
Equivalent grades
| Standard | Designation |
|---|---|
| din | 1.4568 |
| aisi | 631 (17-7PH) |
| jis | SUS631 |
| gb | 07Cr17Ni7Al |
Compare side by side: 17-7PH vs 17-4PH
Equivalents overlap in chemistry and use but are not always identical — see our equivalents guide before substituting in certified designs.
Applications & Processing
Applications: Springs, diaphragms, retaining rings, aerospace sheet parts, bellows, washers.
Processing: Complex multi-step heat treatment compared with 17-4PH; excellent formability before conditioning; welding is limited and usually followed by full re-treatment.
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Ask for a quotationVisit NasteelSource: ASTM A564 / EN 10088 published ranges · Last updated 2026-11-03. Data is indicative — verify critical values against the governing standard and mill certificate before use.