Metal Hardness vs Impact Properties

[weeeds]

Is there a relationship between the hardness of steel and its impact strength?
Specifically, if the hardness is reduced by heat treatment does that mean that the impact properties will improve?
We are working with SA516GR70N.
Thank you

 

[metengr]

Yes, there is a relationship. In the graphs I have seen containing mechanical properties and impact energy, as the stregnth decreases, by tempering or by heat treatment (normalizing or annealing), the impact energy increases. There is a direct correlation between ultimate tensile strength and hardness.

 

[redpicker]

Just to add to metengr's comments, the relationship between hardness and impact strength is more of a general relationship and not as direct as the realtionship between tensile strength and hardness.

To answer your question,

if the hardness is reduced by heat treatment does that mean that the impact properties will improve?

the best answer is "not necessarily". Depending on the prior microstructure, the heat treatment cycle employed, the chemical composition, and the amount the hardness is reduced, the result could be an actual decrease in impact properties, no change, or an increase in impact properties.

In general, yes, you could expect an increase in impact strength with decreasing hardness, but I've seen many cases where decreasing hardness has either had no effect or a detrimental effect.

I'm not sure this helps,

rp