weldinguide.com

all about welding





QW-407.1 lower and upper transformation temperatures

QW-407.1 lower and upper transformation temperatures

Postby kuvilync » Sat Nov 30, 2013 9:16 am

Dear all,

Could you please explain which are the lower and the upper transformation temperatures that are mentioned in ASME IX, QW-407.1(a)(2) and QW-407.1(a)(3) respectively?

regards
kuvilync
kuvilync
 
Posts: 13
Joined: Tue Jun 18, 2013 3:10 pm

Re: QW-407.1 lower and upper transformation temperatures

Postby mohd » Sat Nov 30, 2013 3:28 pm

Dear one,

I will explain the lower and the upper transformation temperatures in context of plain carbon steel.
Lower transformation temperature: 723 deg C and Upper transformation temperature: 910 deg C.

QW-407.1(a)(2): separate WPS requires for PWHT below the lower transformation temperature.
QW-407.1(a)(3): separate WPS requires for PWHT above the upper transformation temperature.

PWHT below the lower transformation temperature is considered to be stress relieving since no phase transformation takes place below this temperature and the heating only causes the residual stresses to relieve and the hydrogen to diffuse out.

So, up to the lower transformation temperature no WPS re-qualification is needed (design code restrictions may apply).

Instead, PWHT above the lower transformation temperature changes the phase from ferrite to austenite and thus the original properties of base metal, weld metal and HAZ will change. For example mechanical properties of base metal like toughness, tensile, hardness will not be as specified in the original MTC (material's test certificate).

Please refer to Fe-C diagram for details.

I hope some experts may explain Fe-C metallurgy in deep.

regards,
mohd
mohd
 
Posts: 74
Joined: Mon Jul 08, 2013 2:17 pm

Re: QW-407.1 lower and upper transformation temperatures

Postby techupon » Tue Dec 03, 2013 10:39 am

I fully agree with Mohd and I think he has effectively explained the query.

Regarding Fe-C phase diagram, please have a look here below where:
α = ferrite, γ = austenite, AC1 = lower transformation temperature, AC3 = upper transformation temperature.
It is clear that above AC1 ferrite starts to transform to austenite and above AC3 the whole of the steel transforms to austenite. So, that's the reason the QW-407.1 separates cases with respect to PWHT temperature since the mechanical properties of steel change upon phase changing.

thanks
techupon
Attachments
Fe-C phase diagram.png
Fe-C phase diagram.png (68.65 KiB) Viewed 4097 times
techupon
 
Posts: 18
Joined: Thu Nov 28, 2013 9:50 am


Return to Pressure vessel, boiler & valve welding

Who is online

Users browsing this forum: No registered users and 1 guest