[MW:18066] RE: 18041] metallurgy of weld joint PWHT

You might want to try and obtain a copy of "Welding Metallurgy" Volume
2, by George Linnert, published by the American Welding Society. This
book has an excellent basic discussion of stress relief heat treatment.
(starting on page 159) After reading this you will have a basic
understanding of what can occur during sub-critical PWHT and any
questions that remain will be more sharply focused.

One exception I have to the discussions I've seen is the comment that no
microstructural changes occur. This is not correct. A subcritical heat
treatment will NOT, by definition, result in bulk microstructural
transformations; ie. delta ferrite to austenite. However,
microstructural changes do occur. Atom movements may result in some or
all of the following: creep, tempering, recrystallization, and changes
in carbide morphology. For example, in simple carbon steels, you may
observe a coarsening of the pearlite plates or spheroidization of iron
carbides. For alloy steels you may be able to see changes from
martensitic structures to tempered martensite and carbides.

I don't generally make recommendations, but for any of you who are weak
on the basics of welding metallurgy, I would strongly recommend getting
the two volume set of books by Linnert. Although it may seem somewhat
dated the basics are well detailed without requiring extensive
background knowledge.

John A. Henning
Welding & Materials

-----Original Message-----
From: materials-welding@googlegroups.com
[mailto:materials-welding@googlegroups.com] On Behalf Of sandeep monody
Sent: Friday, June 28, 2013 11:26 AM
To: materials-welding@googlegroups.com
Subject: [MW:18041] metallurgy of weld joint PWHT

Dear experts.,

Recently I came to know that PWHT does not change the micro structure of
weld seam or HAZ.
Please reply me regarding metallurgy of PWHT of weld seam and HAZ in C.S
and low alloy steel.

Please clarify why PWHT required for C.S and low alloy steel.

What is residual stress?

How do we remove residual stress during PWHT?

Sandeep.M.V
QA/QC Engineer

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