Hardening
What is Hardening?
Stainless steel hardening refers to a group of heat treatment techniques used to increase the hardness and strength of stainless steels. This process is vital in enhancing the wear resistance and durability of components used in high-performance or structurally demanding applications, without significantly compromising corrosion resistance.
Stainless Steel Hardening Process
1. Austenitising
The stainless steel is first heated to a sufficiently high temperature to transform its structure into austenite.
2. Quenching
Immediately after heating, the stainless steel is rapidly cooled, often in water, oil, or salt brine, to suppress the formation of softer phases and produce martensite, a supersaturated structure.
3. Tempering
Freshly hardened martensitic stainless steel is often brittle and loaded with residual stress, therefore, the next step is tempering, which involves heating it to a moderate temperature and cooling it slowly. This process reduces brittleness and stress by coarsening some precipitates, while often retaining high strength.
4. Surface Hardening
For parts requiring a hard surface and tough core, only the surface is transformed using methods like carburising or nitriding for wear resistance.
17-4 PH Stainless Steel
17-4 PH is a chromium-nickel-copper alloy capable of high strength through precipitation hardening. Its behaviour is affected by both traditional and additive manufacturing methods.
- Laser Powder Bed Fusion (LPBF) produces a finer microstructure but requires post-processing heat treatments to match conventionally hardened properties.
- The precipitation of copper-rich phases during ageing (typically at 480–620°C) is responsible for the alloy’s high strength.