What is the hardness of SUS321 stainless steel?

The following is the specific hardness range of SUS321 stainless steel (JIS G4303 standard, corresponding to ASTM 321) in different states, combined with common heat treatment and processing technology classification description:

1. SUS321 stainless steel solution treatment (annealing) state (common supply state)
This state is that the stainless steel is rapidly cooled after high-temperature dissolution, eliminating internal stress, with the lowest hardness, the best plasticity and toughness, and is convenient for subsequent processing (such as bending and welding).
Brinell hardness (HB): ≤187 (JIS standard)
Rockwell hardness (HRB): ≤90 (corresponding to HB≤187)
Vickers hardness (HV): ≤200
II. SUS321 stainless steel cold processing state (cold drawing, cold rolling, cold drawing, etc.)
The strength and hardness are improved by cold deformation process (such as cold drawing, cold rolling of thin plates). The hardness increases with the increase of deformation (processing rate). The typical range is as follows:
Brinell hardness (HB):
Mild cold processing (deformation rate ≤10%): 200~250
Medium cold processing (deformation rate 10%~30%): 250~280
Severe cold processing (deformation rate > 30%): 280~300+ (depending on the processing technology)
Rockwell hardness (HRB/HRC):
HRB: 95~110 (corresponding to HB 200~280, suitable for thin plates or pipes)
HRC: 20~30 (When the hardness is higher, use HRC scale, corresponding to HB 220~300)
Vickers hardness (HV): 210~320 (increases with processing volume)
III. SUS321 stainless steel stabilized treatment state
SUS321 contains titanium (Ti), and needs to be stabilized annealed (850~900℃ insulation and air cooling) to prevent intergranular corrosion. The hardness of this state is close to that of solution treatment and slightly higher than that of annealing state:
Brinell hardness (HB): 180~200
Rockwell hardness (HRB): 85~95

IV. Hardness at High Temperatures (Non-Room Temperature)

SUS321 is commonly used in high-temperature environments (e.g., 500–850°C), but its hardness decreases significantly with increasing temperature. The typical hardness variation from room temperature to high temperature is as follows (for reference):

Temperature (℃)	Brinell Hardness (HB)
20	≤187
200	~150–160
400	~120–130
600	~80–90

V. Comparison of Hardness Standards (Reference Values)

Standard	Condition	Max HB	Max HRB	Max HV
JIS G4303	Solution Annealed	187	90	200
ASTM A240	Annealed	201	92	-
GB/T 20878	Solution Annealed	187	90	200