The hardness of 630 stainless steel (namely 17-4PH, a martensitic precipitation-hardening stainless steel) is directly related to its heat treatment state, with significant hardness differences observed under different conditions:
Solution-treated (non-aged): 28–32 HRB (approx. lower end of 25–30 HRC), good plasticity, easy for machining and stamping.
Aged: Hardness decreases as aging temperature increases, typical range 30–45 HRC:
* 480°C aging (4h): 39–45 HRC (high strength)
* 550°C aging (4h): 36–42 HRC (balance of strength and toughness)
* 590°C aging (4h): 33–38 HRC (better toughness)
* 620°C aging (4h): 30–32 HRC (good toughness, suitable for low-temperature applications)