This is why yield strength doesn’t correlate well to hardness…

These samples sure yielded...

Cold drawing of steel bars changes the mechanical properties of the hot roll bar feedstock. With standard draft:

  • Tensile strength increases by 25-30%;
  • Yield strength increases 60 to 80%;
  • Brinell Hardness  increases about 15%;
  • Ductility DECREASES 25-30% typically with standard draft.

As can be seen by the yield strength increase  compared to hardness increase by cold drawing, the yield strength picks up about  a 4 times multiple compared to hardness. Poor correlation.

Hardness correlates well with tensile strength in most steels.

In fact, my rule of thumb for estimating either  tensile strength or hardness is that

Tensile Strength divided by 500= Brinell Hardness

 for most low and medium carbon steels. Or

Brinell Hardness multiplied by 500= Tensile Strength.

Try it with your data.