Precipitation Hardening Steels

Precipitation Hardening stainless steels are chromium and nickel containing steels that provide an optimum combination of the properties of Martensitic and Austenitic grades. Like Martensitic grades, they are known for their ability to gain high strength through heat treatment and they also have corrosion resistance of austenitic stainless steel.

The high tensile strengths of precipitation hardening stainless steels come after a heat treatment process that leads to precipitation hardening of Martensitic or Austenitic matrix. Hardening is achieved through the addition of one or more of the elements Copper, Aluminium, Titanium, Niobium and Molybdenum.

The most well known precipitation hardening steel is 17-4 PH, the name comes from the additional 17% Chromium and 4% Nickel. It also contains 4% Copper and 0.3% Niobium, 17-4 PH is also known as stainless steel grade 630.

The advantage of precipitation hardening steels is that they can be supplied in a “solution-treated” condition, which is readily machinable, After machining or another fabrication method, a single, low-temperature heat treatment can be applied to increase the strength of the steel. This is known as aging or age-hardening. As it is carried out at low temperature, the component undergoes no distortion.

Composition limits for 17-4 PH and 15-5 PH, with their EN and UNS names, are in the precipitation hardening grade family. What each heat-treatment condition buys is set out in the precipitation hardening article.