PWHT ASTM A514 ("T1" QT steels)

Date 12-16-2005 01:41

Hi.

I was reading an article about the danger of cracking in T1 steels HAZ , when PWHT in the range of 500 - 650°C is applied. Since the chemical composition of this steels is similar of those of low alloy steels, series SAE 4XXX i wonder why this phenomena appears in T1 type steels. I know QT low alloy steels are subjected to temper embrittlement in the range of 250 - 500°C, but PWHT over 550°C should be safe against that type of embrittlement.
The article says that the cracking is because "grain boundary carbide precipitation", but that doesnt sound to convincent to me, since never hear of that in Cr-Ni-Mo low alloy steels.
By the way i need to do the stress relief heat treatment because of dimensional stability issues, so i doesnt have any suitable temp if i consider this article to be true. (temper embrittlement range plus "carbide precipitation embrittlement" range).

Anyone have a more definitive opinion to this subject??

Regards

By GRoberts (***)

Date 12-16-2005 14:15

It is only partly the main alloying elements that can cause PWHT problems, but the microalloying elements, such as V, Nb, Ti, and B that exacerbate the PWHT embrittlement/cracking problem, as well as the processing route. TMCP (thermo-mechanically controlled process) steels have their own set of issues. A lot of whether the T-1 (ASTM A514 variety) type steels will crack on PWHT depends on the part geometry (restraint), welding procedure, etc.

Here is some more info on A514 steels made by ISG
http://www.intlsteel.com/PDFs/t1.pdf