Hardness estimation
Hardness estimation
(OP)
Is there a good way to estimate (or calculate)expected hardness given a metals chemical composition based on tempering temperature? For instance, if a weld has a hardness of 225 HV10 after a 1125F PWHT, can the hardness after a 1150F PWHT be calculated? Are there ways other than the Hollomon-Jaffe perameter? I am not sure how the Hollomon-Jaffe parameter is used without already having a data set for a given material. For the H-J equation P1=T(B+ln(t)), how is B determined without already having a data set to find the correlation. Does B vary with the composition of the material? I would think so, but I haven't really used it before. Even if you know B, and find the H-J parameter (P1), it seem like you would have to have data to determine the relationship between the parameter and hardness.





RE: Hardness estimation
Yes, you are correct.The relationship between hardness and tempering time/temperature is based on the classic metallurgical rate equation - e.g., Arrhenius rate equation. The Arrhenius rate equation requires a constant and that is where you need actual hardness data combined with time/temperature tempering information for the specific material.
I do know that there are published H-J curves for different materials. Or you can develop your own hardness versus tempering temperature curve for your specific material - keeping time constant.