Relation of Hardness to Tensile Strength in Carbon Steel

Some relation, but not very much. For one thing, surface hardness will have minor effect on the tensile strength of the whole cross-section.

It the piece is through hardened the relashionship is quite good. It is not to be used for any surface hardened parts if the surface layer has not been ground.

The basic was the Brinell Hardness versus Rm. In the lower range it is almost linear.

There is a relation of tensile strength to the hardness (not the surface hardness) of carbon steel which goes like- the tensile will increase with the hardness of carbon steel. The only reason i understand behind this is, as the hardness increases, the brittleness of Carbon steel increases and during the tensile load test this brittle material absorbs more energy for breaking (for the ultimate load) as the load applied is gradual. Thus the relation. But i suggest you to go for the TENSILE testing of the material as it is not that costly and to be doubly sure of the quality of the material. Also please carry out the impact testing if required by the code.

Mostly the ratio is dividing the HB Hardness by 3 - to receive Tensile Strength (in KSI)

Ofcourse it doesn't apply to C.Steel thin sheets /coils !!

See also conversion Tables of ASTM-E140