Heat Treatment of Stainless Steel: Processes and Effects on Properties
Heat treatment is an important process that can significantly alter the mechanical properties and corrosion resistance of stainless steel.
Annealing:
The most common heat treatment for stainless steel. Austenitic grades are annealed at 1010-1120°C followed by rapid cooling to maintain corrosion resistance. This process relieves internal stresses and restores ductility.
Stress Relieving:
Applied at lower temperatures (200-400°C) to reduce residual stresses from forming or welding without significantly affecting mechanical properties.
Precipitation Hardening:
Used for PH grades like 17-4 PH and 17-7 PH. These grades are solution treated, then aged at intermediate temperatures to precipitate strengthening phases.
Hardening:
Martensitic grades (410, 420, 440) can be hardened through heat treatment, achieving high hardness levels suitable for cutting tools and wear applications.
Important Considerations:
- Sensitization: Heating in the 480-820°C range can cause chromium carbide precipitation along grain boundaries, reducing corrosion resistance.
- Distortion: Heat treatment can cause dimensional changes, particularly in complex shapes.
- Surface Condition: Heat treatment in air can cause oxidation and scaling.
Understanding heat treatment requirements is essential when specifying stainless steel for applications involving elevated temperatures or post-fabrication processing.