A Martensite Question & An Austenite Question. 6

[tc7]

Hello,
Martensite Question:
I am looking for data on Martensite Start and Martensite Finish temperatures for carbon steels and its alloys. I have looked in the "Atlas of I-T & C-T Diagrams" available at the nearest (not very near) University but this book only show M-sub-S and M-sub-90 temperatures. An online resource would be ideal or any other recommended reference appreciated. I have not found any.

Austenite Question:
In the Q&T of carbon steels, such as my favorite 4130, I understand that the it is best to quench such that you have arrived at a full martensite structure and then the martensite is tempered to the desired hardness. BUT what is the result if we do not arrive at the full martensite condition? How will the remaining austenite effect acheiveable strength, hardness, ductility and toughness?

Thankyou

 

[NickE]

Your first question is easy. The only reactant that can form Martensite is Austenite.

 

[metengr]

tc7;
I don't mean to sound cocky, but that is why you need to qualify a welding procedure specification.

 

[tc7]

Met-
I have learned so much from you that if you want to be cocky at my expense, then go ahead.

I know very well why we qualify procedures and have done many PQR's to various Codes and Mil specs. I started out with the martensite question by trying to understand why in some weld shops is it felt that we must rush into PWHT right after completion of the weld. I am learning here from you and all these fine folks that the opposite may be the correct thing to do. Maybe it is best to let it cool to an appropriate M-sub-S temperature and allow all martensite to form before we heat treat. I can promise you that little tid bit is not published in any welding handbook for carbon steels. Alternatively, I think, if we prolong the cooling cycle and avoid all martensite formation maybe that is a good thing too. Thus my final question was how do you prolong the cooling cycle and specify it in a meaningful way for production purposes. If you had an answer for that question I would try it in a PQR and if it was successful, then it may become an essential variable.

 

[metengr]

tc7;
Place instructions in the WPS to wrap the weld region with insulating blankets and to cool slowly.