17-4PH / 17-7PH

UNS S17400 / S17700

17-4PH is a martensitic precipitation-hardening stainless containing copper. In the solution-annealed condition it machines easily; after ageing at 480–620 °C it reaches 1,100–1,300 MPa tensile strength with corrosion resistance broadly similar to 304. It is the standard choice for valve stems, pump shafts and offshore hardware.

17-7PH is the austenitic–martensitic variant, used where the part has to be formed before hardening — springs, diaphragms and aircraft sheet structures. Both are unsuitable for sustained service above about 300 °C.

Properties

• Tensile strength 1,100–1,300 MPa after ageing (17-4PH, H900)
• Corrosion resistance comparable to 304 in atmospheric and mild chemical service
• Simple ageing treatment, low distortion compared with quenching and tempering
• 17-7PH offers good formability before transformation and ageing

Applications

• Valve stems, pump shafts and trim
• Offshore platform and helicopter-deck hardware
• Aircraft structures and springs (17-7PH)
• Food, pulp and paper machinery
• Nuclear waste containers

Forms supplied

• Bar, ring and forgings
• Flanges and fittings
• Sheet and strip (17-7PH)

Standards

ASTM A564 / A693 (bar and forgings), A693 (plate), A313 (spring wire)