repeat heat treat

[trennick]

Hello,

Is there a degrading effect (maybe beneficial?) from repeated cycles of heat treating? For example, I have a friend that is trying to achieve a specified hardness in 4130 steel and the first attempt didn't quite get to the level he wanted. Is there any problem with trying again?

Also, what is the empirical formula to relate Rockwell C to tensile strength?

Thanks,
Tim

University of Chicago

 

[NickE]

You might see grain growth on the re-austenitize. and some de-carburization, other than that AFAIK you can re-heattreat steels an innumerable number of times.



Nick
I love materials science!

 

[rd400guy]

There shouldn't be a problem with re-heat treating 4130, but I would advise your friend to examine his heat treating practice to try to determine why he didn't get the hardness he wanted in the first place. There is a myriad of reasons why heat treatment doesn't work the first time. Depending on the criticality of the part, a little more time and effort may be required to successfully obtain the desired hardness.

As for the hardness/tensile relation, a Google search on "hardness to tensile" brought me to this:

http://www.unified-eng.com/scitech/hardness/hardness.html

 

[trennick]

Thank you both for the good information. I suspected that it wouldn't be a problem to repeat heat treatment, primarily because the methods seem to be so established and there never is a discussion on starting material.

Also, thanks for the good link on hardness to tensile.

Have a great day,
Tim

 

[unclesyd]

If the part has any intricacies and you have the ways and means I would Normalize (1625°F, air cool) the part prior to reheat treating to minimize the possibility of any cracking problems. Not really a problem but a possibility. If the part is very intricate I would Anneal (1550°F, furnace cool 20° F/h to 1250° F then air cool) prior the reheat treatment. The maximum hardness to expect on a 1/2" section with a water quench from 1575° F is Rc 50 with a considerable drop off as the section increases.