Post heating for 1.25Cr-0.5Mo Steel
Post heating for 1.25Cr-0.5Mo Steel
(OP)
PWHT always require for this low alloy steel. I have no doubt for PWHT for stress relief. How about post heating? Do we also need to hold approx 300 -400 C for 15 minutes after welding? I understand that it can decrease the lamellar tearing. Are there any standards about post heating.
I checked previous WPS...However, there were no post heating as above. Please comment.
I checked previous WPS...However, there were no post heating as above. Please comment.
RE: Post heating for 1.25Cr-0.5Mo Steel
Any standard will simply follow the normal post-quench tempering guidelines for the grade in question, available in reference books like the ASM Metals Handbook. Page 28.16 in the desk edition.
A by-product of tempering is stress relief.
RE: Post heating for 1.25Cr-0.5Mo Steel
RE: Post heating for 1.25Cr-0.5Mo Steel
Regards
John www.gowelding.com
RE: Post heating for 1.25Cr-0.5Mo Steel
John Dyson makes a good precautionary point about the possibility of hydrogen embrittlement. If the weld is stressed ( residual or applied )and if hydrogen has been picked up, the un-tempered martensite is quite susceptible to delayed cracking. See the same Metals handbook, desk edition page 30.28.
However, the PWHT, which to answer your question should be right after welding, will temper the martensite. In 10 minutes at 400C the hardness of untempered martensite will drop from HRC 66 to 50. To reduce the hardness another 5 points will require another 5-10 hours.
Stress relieving is slower. About 50% of the stresses are relieved in one hour at 400C. Going to 6 hours gives another 10%. In both processes increasing temperature is more effective. If you successfully temper and stress relieve you will also address the need for hydrogen out-gassing.