The difference between HRB and HRC hardness of 304 stainless steel bar
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Difference Between HRB and HRC Hardness for 304 Stainless Steel Bar
In hardness testing of 304 stainless steel bars, HRB and HRC are two Rockwell hardness scales. The core difference between them lies in the type of indenter and load used during the test:
🔹HRB: Uses a 1/16-inch steel ball as the indenter and a 100 kgf load, making it suitable for softer materials like annealed 304 stainless steel, which typically has a hardness range of 85-95 HRB.
🔹HRC: Uses a diamond cone indenter and a 150 kgf load, making it suitable for harder materials. 304 stainless steel, in its annealed state, typically has a hardness of less than 20 HRC and is generally not applicable for HRC testing unless it has undergone special hardening treatments.
304 Stainless Steel Bar Hardness Conversion Table
| HRB (Rockwell B Scale) | HRC (Rockwell C Scale) | Material Condition |
|---|---|---|
| 85-90 | <15 | Fully annealed (soft state) |
| 90-95 | 15-20 | Mildly work-hardened (cold drawn state) |
| >95 | >20 (rare) | Highly work-hardened or specially treated |
🔹Applicable Scales:
304 stainless steel, being an austenitic stainless steel, has a low hardness in its annealed state (85-95 HRB). It is typically tested using the HRB scale (steel ball indenter with 100 kgf load).
The HRC scale (diamond cone indenter with 150 kgf load) is designed for harder materials (like quenched steels) and is typically not used for 304 stainless steel in its untreated form, as it typically has less than 20 HRC.
🔹Material Conditions:
Fully annealed 304 stainless steel (soft state) will have hardness in the range of 85-90 HRB.
Mildly work-hardened 304 stainless steel (like cold-drawn) will show hardness between 90-95 HRB.
Highly work-hardened or specially treated 304 stainless steel might show hardness above 95 HRB, though HRC values for such materials are typically still low.
🔹Conversion Limitations:
There is no strict linear conversion formula between HRB and HRC scales. The data in the table is based on actual testing and industry experience and is meant for reference purposes only.
When testing, it's important to choose the appropriate scale based on the material's condition to ensure accurate results.
🔹Effect of Processing:
Cold drawing or cold rolling will increase the hardness of 304 stainless steel (raising the HRB value), and it may result in a slight increase in HRC. However, 304 stainless steel cannot be significantly hardened through heat treatments like quenching, and its hardness ceiling is much lower than that of martensitic stainless steels (like 410 or 420).
