9Cr : why maintaining preheat?
9Cr : why maintaining preheat?
(OP)
Dear all,
It's already known to everybody that welding of 9Cr material need to maintain preheat temperature during welding. In other word: it's not allowed to drop the temperature of weldment to go below preheat temperature until weld is finished. Simple question : what is the reason behind it ?
It's already known to everybody that welding of 9Cr material need to maintain preheat temperature during welding. In other word: it's not allowed to drop the temperature of weldment to go below preheat temperature until weld is finished. Simple question : what is the reason behind it ?





RE: 9Cr : why maintaining preheat?
Interuption of preheat may be performed with adequate intermediate (dehydrogenation) heat treatment.
RE: 9Cr : why maintaining preheat?
RE: 9Cr : why maintaining preheat?
metengr,
What is the temperature that 9Cr welds should be cooled to?
I am assuming conventional 9Cr.
RE: 9Cr : why maintaining preheat?
Best regards,
aburafdi
RE: 9Cr : why maintaining preheat?
There is an excellent AWS paper titled "Welding of Martensitic Creep-Resistant Steels" by L.BERES, A. BALOGH, and W. IRMER . This paper describes the proper selection of preheat and interpass temperature maintenance for 9% Cr and higher steels to avoid post weld cracking concerns related to an improper ratio of austenite to martensite.
Cooling rate was held constant for all specimens evaluated based on preheat near or below the calculated MS value for the steel. The evaluation focused on crack sensitivity after welding.
RE: 9Cr : why maintaining preheat?
Do you mean MS as Martensite Start? For preheat, it's near or below MF, not MS, isn't it ?
RE: 9Cr : why maintaining preheat?
Yes, I was referring to the martensite transformation temperature and not the lower critical. Thanks