Material change with relation to rate of cooling? 2

[coreman73]

I have two identical sockets. They were made from the same material and were both hot forged at 1600 degrees F. The only difference is that after forging, one socket was air cooled to room temperature and the other was initially air cooled to 1200 degrees F followed by convection/fan cooling to room temperature.

Simply based on this information, what might I expect as far as material changes (decarb, grain size, etc.) and could these negatively affect further forming/machining?

I have just begun sectioning of these parts and will then make mounts for microscopic evaluation. I just wanted to get an idea of what to look for beforehand. I would greatly appreciate any input.

 

[unclesyd]

You have posted a question that can't be covered with as short statement as presented here. I would highly recommend getting a book on the heat treatment of metals to learn about things Martempering, Austempering, TTT diagrams, etc. The structure you end up with is determined by the alloy used for the part.

Here two lessons dealing with the heat treatment of metals that may help you. There is link to The ASM educational materials site has information on various courses of all types you can take on, or self-study..

http://info.lu.farmingdale.edu/depts/met/met205/tttdiagram.html

http://info.lu.farmingdale.edu/depts/met/met205/tempering.html

http://www.asminternational.org/portal/site/

http://www/AsmStore/ProductDetails/?vgnextoid=28ec58c37bf86210VgnVCM100000621e010aRCRD

 

[Wrenchbender]

Without knowing the alloy composition, complete thermal history, and a few things about the forging stock, agree with Syd. It can be over the map. However maybe you could find a published CCT diagram for your alloy and then make some assumptions on cooling rate.

Or if you have the spare time, find the convective heat transfer coefficients for your two cases. (A mech'l engr problem, not too difficult.) Model the socket as a protruding element of a heat exchanger to find cooling rates (non-linear). Refer to the CCT diagram for a better estimation of what the resulting phase morphology might be.

 

[coreman73]

Thanks a ton guys. Unclesyd, those links are great and I will definitely use them for my education. The steel grade is 6160. I'm going to try searching for a CCT diagram. Like Bestwrench sad, at least that way, I can make some assumptions.

 

[TVP]

coreman,

Here is a link to a free CCT/TTT diagram calculator:

http://calculations.ewi.org/vjp/secure/TTTCCTPlots.asp

It is a good resource, but it is not as detailed as some of definitive references like ASM's Atlas of Time-Temperature Diagrams for Irons and Steels.