Stainless Steel Heat Treatment: Annealing, Quenching & Tempering Guide
Heat treatment is critical to achieving the desired properties in stainless steel — from corrosion resistance to hardness to machinability. Unlike carbon steel, stainless steel heat treatment varies dramatically by family (austenitic, ferritic, martensitic, duplex). This guide explains the key heat treatment processes for each stainless steel type.
1. Austenitic Stainless Steel (304, 316, 321)
Solution Annealing is the primary heat treatment for austenitic grades:
- Temperature: 1010–1120°C (1850–2050°F) depending on grade
- Process: Heat to target temperature → Hold 30–60 min per 25mm thickness → Rapid quench in water
- Purpose: Dissolve chromium carbides that may have precipitated during welding or forming, restoring full corrosion resistance
- Result: Soft, ductile condition (typical hardness: 150–200 HB), maximum corrosion resistance
Important: Austenitic stainless steels cannot be hardened by conventional quenching and tempering. They are non-heat-treatable for hardening purposes. Hardness can only be increased through cold working.
2. Ferritic Stainless Steel (430, 409, 441)
Ferritic grades undergo annealing to relieve stresses from cold working:
- Temperature: 780–850°C (1435–1560°F)
- Cooling: Air cool or water quench
- Purpose: Recrystallize grain structure, restore ductility after cold rolling or forming
- Result: Softer, more formable condition
Caution: Avoid holding in the 400–540°C range for extended periods — this causes “475°C embrittlement” in high-chromium ferritic grades.
3. Martensitic Stainless Steel (410, 420, 440C)
Martensitic grades CAN be hardened by heat treatment — similar to carbon steel:
Hardening:
- Austenitizing: 980–1050°C (grade dependent)
- Quenching: Oil quench (410, 420) or air cool (some grades)
- Result: Martensitic structure with hardness of 50–58 HRC
Tempering:
- Temperature: 150–700°C depending on desired hardness/toughness balance
- Rule: Higher tempering temperature = lower hardness, higher toughness
- Caution: Avoid tempering in 300–400°C range — causes temper embrittlement
| Grade | Austenitizing °C | Quench | Temper °C | Final Hardness HRC |
|---|---|---|---|---|
| 410 | 980–1020 | Oil | 200–600 | 30–50 |
| 420 | 1000–1050 | Oil | 200–600 | 40–55 |
| 440C | 1010–1065 | Air | 150–370 | 54–60 |
4. Duplex Stainless Steel (2205, 2507)
Duplex grades require careful solution annealing to maintain the balanced 50/50 austenite-ferrite structure:
- Temperature: 1020–1100°C (2205) or 1050–1120°C (2507)
- Cooling: Rapid water quench — air cooling is NOT acceptable
- Purpose: Dissolve intermetallic phases (sigma, chi) and restore phase balance
- Result: Optimal combination of strength and corrosion resistance
Critical: Slow cooling through 600–1000°C causes sigma phase precipitation, which drastically reduces toughness and corrosion resistance.
5. Stress Relieving
For all stainless steel types, stress relieving may be needed after welding or severe cold working:
- Austenitic: 290–425°C (low-temperature stress relief) — avoid sensitization range
- Ferritic: 540–650°C
- Martensitic: Same as tempering temperature (already tempered)
Conclusion
Proper heat treatment is essential for stainless steel performance. The correct process depends on the steel family and the desired properties. CoreMetal Steel supplies stainless steel in all major families with various heat treatment conditions. Contact us to specify the right material condition for your application.