Overview

17-7 PH is a precipitation-hardening stainless steel which combines high strength and hardness.

The alloy has excellent fatigue properties, good corrosion resistance and is easily formed. Due to the alloys good mechanical and physical properties, 17-7PH is particularly popular in the aerospace sector. The alloy can be used in the manufacture of flat springs up to 315°C (600°F).

17-7PH Precipitation Hardening Alloy is a semi-austenitic stainless steel which is austenitic in the annealed condition, but martensitic in the hardened condition. 17-7PH provides high strength and hardness, excellent fatigue properties, good corrosion resistance and minimum distortion upon heat treatment. It is easily formed in the annealed condition, then hardened to high strength levels by simple heat treatments to Conditions RH 950 and TH 1050. The exceptionally high strength of Condition CH 900 offers many advantages where limited ductility and workability are permissible. In its heat treated condition, this alloy provides exceptional mechanical properties at temperatures up to 900 °F (482 °C).

Limiting Chemical Composition, %

Iron.......................................................................................................................................................................................70.59-76.75

Nickel..........................................................................................................................................................................................6.5-7.75

Chromium............................................................................................................................................................................16.00-18.00

Manganese...............................................................................................................................................................................1.00 max.

Carbon.......................................................................................................................................................................................0.09 max.

Silicon........................................................................................................................................................................................1.00 max.

Sulphur.......................................................................................................................................................................................0.03 max.

Phosphorus...............................................................................................................................................................................0.04 max.

Aluminium.................................................................................................................................................................................0.75-1.50

Physical properties 

Mechanical Properties

Corrosion resistance

17-7PH stainless steel is a precipitation-hardened stainless steel alloy with excellent corrosion resistance for a variety of applications requiring high performance materials.

Its corrosion resistance under all heat treatment conditions is the same as that of other stainless steel types, and surface rust can occur in some environments. For example, in the Marine environment, stainless steel will show signs of rust after a relatively short exposure time. However, after a year or two of exposure, the amount of rust is hardly more than the amount of rust after six months. Like all martensitic stainless steels, 17-7PH stainless steels may crack under stress environments containing hydrogen sulfide and are therefore not recommended for use in such applications.

In addition, because 17-7PH stainless steel contains aluminum, it also has a good stress cracking resistance, suitable for a variety of high temperature and high stress environments. At the same time, it also has good plasticity and hardening ability, can control hardness through heat treatment, and can carry out a variety of cold working and hot working processes. In terms of welding, 17-7PH stainless steel has good weldability in conventional welding, high-frequency induction welding and arc welding.

Heat treatment

For heat treating stainless steel grade 17-7 PH, three important steps need to be carried out – austenite conditioning, cooling to transform the austenite to martensite, and precipitation hardening to condition TH 1050 or RH 950.