Stainless steel 17-4PH - 1.4548 - UNS S17400 - AMS 5643 - AMS 5622 - S17400

Everything You Need to Know About 17-4PH Stainless Steel

Like all stainless steels, the chromium present in 17-4PH allows the formation of a passivation layer on the metal's surface, granting it resistance to oxidation and rust. This martensitic PH ("Precipitation Hardening") steel alloy undergoes heat treatment through solution treatment followed by aging and offers good corrosion resistance and high-temperature performance up to 316°C. It hardens during aging, unlike QT-type (Quenched and Tempered) martensitic steel, which reaches its peak hardness after quenching and is softened by tempering.

Heat Treatments

The mechanical properties of 17-4 PH are achieved through a two-step heat treatment. Solution treatment (Condition A) involves heating the alloy to approximately 1040°C, then quenching it to obtain a relatively soft martensitic structure. Aging, performed at lower temperatures (between 480°C and 620°C) for varying durations, causes the precipitation of fine particles that harden the material.

Different aging conditions (H900, H1025, H1075, H1150, etc.) each offer different trade-offs between strength, ductility, and corrosion resistance. For example, the H900 condition provides maximum strength and hardness, while the H1150 condition prioritizes corrosion resistance and ductility.

Mechanical and Chemical Properties

After precipitation hardening, 17-4PH steel can achieve a tensile strength of up to 1552 MPa, a yield strength exceeding 1236 MPa, and a hardness of 444 (HB).

While it has good corrosion resistance in many environments for a martensitic stainless steel, 17-4PH has certain limitations. It is generally less resistant than austenitic stainless steels such as 304 or 316, but close to them in chloride-containing environments (such as seawater). The choice of heat treatment condition significantly influences corrosion resistance, with lower hardness conditions generally offering better resistance but at the expense of mechanical properties.

Machinability and Weldability

The 17-4PH grade has good machinability, influenced by its heat treatment condition. In Condition A, it is comparable to that of some austenitic stainless steels, exhibiting some adhesion to cutting tools.

After aging, its increased hardness requires more robust tools, reduced cutting speeds, and effective cooling.

Finally, this grade can be welded using most processes. Welding is preferably performed before aging to avoid weakening the heat-affected zone.
It can also be forged through hammering, pressing, rolling, extrusion, or upsetting to produce a wrought structure. For maximum hardness, a re-solution treatment should be considered.

Industrial Applications

Thanks to its mechanical properties and corrosion resistance, 17-4PH steel is commonly used in:

• The aerospace industry
• The medical and surgical industry
• The chemical, oil, and gas industry. Tooling and prototyping (pump wheels, pipes, and valves), gas turbine components.
• The automotive industry
• Defense and firearms, etc.