UCS-79(d)(5) warm forming?

[pperlich]

Why does UCS-79(d)(5) exist? Or rather, why is forming in that temperature range a problem?
Is this called "warm forming" in this temperature range? I've never heard that term until today when I started researching this.

 

[metengr]

The reason this is in the Code is to address forming conditions where warm working requires less force because of a drop in yield strength for the steel but the lower temperature does not alleviate all of the forming strains in the steel because the temperature is too low. Removal of forming strains is dependent on temperature.

Residual tensile forming strains can result in reduced corrosion resistance and possible low temperature creep.

 

[pperlich]

Thank you for the reply, metengr.
So how is warm forming worse than cold forming? I understand that it takes less force to warm form and that the warm temperature isn't hot enough to relieve residual stresses. I just don't see how cold forming is better than warm forming as this rule implies.

 

[metengr]

This rule implies nothing regarding which is better, cold or warm forming. The Code addresses forming and dealing with thermal treatment to relieve strains. Cold and warm forming are similar in that a thermal treatment is necessary to relieve strains above a certain percentage.

 

[pperlich]

I think it does imply that that cold forming is better. Imagine two heads built from the same material to the same final dimensions, one CF and one WF. If the ELE is between 5-40% and none of the other conditions of UCS-79(d) are exceeded then the WF head would need stress relieved while the CF head would not. This implies that CF is better than WF.

Perhaps since the yield stress is lower in the warm forming temperature range that the strain pattern is different in a way that raises concern.

 

[metengr]

The warm forming temperature range for certain steels may result in secondary hardening and coupled with residual strains may not be desirable.

 

[Jared1724]

I think this temperature is in the low tempering range, it could cause material embrittlement.
and it is still cold forming.