Effects of Stress Relief of 2.25%Cr 1%Mo material 1

[GGEFAB]

What effect does increasing the cooldown period have on the hardness of the HAZ after welding and then stress relieving at 1200F for 1.5 hours.

 

[Metalguy]

Probably very little if any. You don't have austenite at that temp. so nothing will transform during cooling.

If there is any effect it would be mechanical (strain).

 

[davefitz]

it may depend on the thickness of the component. Less than 1/2" thk it probably doesn't matter. Thicker than 4" then it probably does matter.

Recent work by ORNL and EPRI on reheat aging of HAZ and its relationship to type IV creep cracking may provide some data on HAZ hardness and ductility/toughness as a function of cool down rate and wall thickness.

 

[stanweld]

It will have some effect in increasing hardness only because of decreased time in the tempering region. On P91alloy materials we have seen considerable difference in hardness of welds slow cooled at 200F/hr from 1400 F to 600 F versus 600F/hr.

 

[Metalguy]

1400 deg. steel should be austenitic, especially coming down from welding temps. Completely different than cooling down from a max. of 1200 deg. of a stress relief!

 

[davefitz]

Metalguy:
Per Mannesman/Vallourec, for SA335 P91 ( ferritic) the normal PWHT is from 1380 F, cooled at a rate of -280F/hr.

 

[stanweld]

1400 F is also below the lower critical temp for 2 1/4 Cr - 1 Mo steel - approximately 1480 F.

Lower critical for P91 is approximately 1490F. Depending on the Ni+Mn+N content of the filler metals used to weld P91, the lower critical can be below 1360 F.