17-7 PH is a precipitation hardening semi-austenitic stainless steel. It is able to develop a very high strength due to the strengthening of aluminium particles. It is usually found in strip or wire form for spring applications.
Approximate Composition – 17% Cr, 7%Ni, 0.05% C, 1.0% Al (Exact composition ranges vary between EN and ASTM standards).
This grade combines the following characteristics:
- Good corrosion resistance better than 17-4 PH close to that of 304
- Very high strength up to 1700 MPa minimum UTS in EN 10151 or 1655 MPa minimum in ASTM A693
- Excellent fatigue strength
- Low distortion in heat treatment
- Weldable with matching consumables
17-7 PH provides a combination of very high strength and moderate corrosion resistance. Its metallurgy is complex involving several stages of processing to develop the necessary microstructure. The highest level of strength is achieved by cold working to produce martensite followed by an ageing treatment at about 480°C. This restricts the use of the grade to thin sheet and wire products. Other heat treatment conditions are also available to produce softer and more ductile material.
Applications which illustrate these features include:
Springs, Belleville washers, aerospace, orthodontic wire, strain gauge, load cell, pressure transducer.