PWHT - Alloy vs CS 2

[JesperDK]

Gentlemen and experts,

I have just recently moved into the welding inspection game.
One of the things that facinates me is PWHT(call me a geek)

So my question to you is:

Why do we only PWHT CS at about 650 degrees?
Is it because we only want to stress releave it?
What happens if we go above 721 degrees AND cool slow?
Why does Cr alloy get PWHT at about 750 degrees?
Is it because we want to change micro structure and by doing so lower the hardness?

I hope I made myself clear, english is not my spoken language.

Rgs.

 

[metengr]

JesperDK;
My first bit of advice to you is to search this forum, and

forum794,and forum725,
and,forum292.

Key words for searching would be PWHT of carbon steel. You should find numerous threads that should answer your questions.

Second bit of advice is to use Google and search for PWHT of carbon steel. You will find plenty of information to review.

 

[JesperDK]

metengr,

Thank you, I was "afraid" that I would get an answer like that, I have searched and searched without finding exact answers.
I will try to be more creative in my search words....

Rgs

 

[stanweld]

JesperDK,
The PWHT differences are based on recrystallization temperatures differnces, the responsiveness to effective hardness reduction at temperature and desireable secondary carbide precipitation.

 

[JesperDK]

Thank you Stanweld.

 

[strider6]

you heat at 650 °C 'cause you've to stay below the A1 temperature of the material. the material with Cr are heated at higher temp 'cause the Cr increase the A1 temp of that materials.

if you go to this site you'll find a lot of information modules and wonderful animation on steel metallurgy.. probably the best site for education on steel metallurgy..

http://www.steeluniversity.org/content/html/eng/default.asp?catid=213&pageid=2081272221

http://www.steeluniversity.org/content/html/eng/default.asp?catid=195&pageid=2081272018

hope this help u

S.

Corrosion Protection & Corrosion Control