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.
Speaking of Precision Blog 
[…] Cold drawing of steel is a process that applies a sufficient load to the metal to make the atoms in the steel take new positions with respect to each other, resulting in lowered ductility, increased tensile and yield strength and new dimensions or shape. These properties are often helpful in improving the machinability of the steel, allowing you to more economically produce the parts and components that are essential for today’s technologies. […]