Differences in Brinell hardness notation: HB, HBS, and HBW

"Hardness HB" refers to a material's ability to resist the penetration of a hard object into its surface. It is one of the important performance indicators for metallic materials. In general, the higher the hardness, the better the wear resistance. The Brinell hardness value (HB) is obtained by applying a certain load (typically 3000 kg) to press a hardened steel ball or a hard alloy ball of a certain size (usually 10 mm in diameter) into the surface of the material, maintaining the load for a certain period of time, then removing it, and calculating the ratio of the applied load to the surface area of the indentation.
The unit is kilogram-force per square millimeter or newton per square millimeter (N/mm²).

HB, HBS, and HBW are all symbols for Brinell hardness, but they have different meanings:

HB refers to the Brinell hardness unit without specifying the material of the indenter.

HBS indicates that the indenter is a hardened steel ball, typically used for measuring materials with a Brinell hardness value below 450, such as mild steel, gray cast iron, and non-ferrous metals.

HBW indicates that the indenter is made of hard alloy (tungsten carbide), generally used for measuring materials with a Brinell hardness value below 650.

According to the standard GB/T 231.1-2009 Metallic materials – Brinell hardness test – Part 1: Test method, section 5.2, only hard alloy indenters are permitted.
The Brinell hardness symbol is HBW, and should not be confused with the older symbol HB or HBS (used when a steel ball indenter was applied).

Therefore, under the current standard, only HBW is valid — HBS is no longer used.