Dear Khatri,
--
-- In addition to the reasons mentioned below u have to take care of Sensitization phenomenon as following:
One of the common problems found when welding the austenitic grades is referred to as carbide precipitation, or sensitization. When heated to the welding temperatures, a portion of the base metal reaches temperatures in the 8OO0-1600"F range, and within this temperature range, the chromium and carbon present in the metal combine to form chromium carbides. The most severe temperature for this formation is about 1250°F, and this temperature is passed through twice on each welding operation cycle, once on heating to weld and again on cooling to room temperature.
These chromium carbides typically are found along the grain boundaries of the structure. The result of their formation is the reduction of the chromium content within the grain itself adjacent to the grain boundary, called chromium depletion, resulting in reducing the chromium content below that required for resisting corrosion. The final result of this chromium depletion of the grain is a reduced corrosion resistance of the grain itself due to its reduced chromium content. In certain corrosion environments, the edges of the grains corrode at a high rate, and is called intergranular corrosion attack, or IGA.
and to prevent sensitization of austenitic SS during welding can being by several methods:
1-Reheating the complete structure by 1950-2000 F. but may distortion will happen.. followed by rapedly quenching in water to avoid reformation of chromium carbides.
2-Addition of stabilizers to the base and filler metals such as titanium or niobium in ammounts equal to 8 or 10 times the carbon content.
3-Reduction of the carbon content in the base and filler metals, such as low carbon austenitic SS.
On Fri, Jul 8, 2011 at 1:04 PM, prem nautiyal <prem_nautiyal26@yahoo.com> wrote:
From: khatri ankit <nids01dme011@gmail.com>
Subject: [MW:11627] preheating of austenitic ss
To: "Materials & Welding" <materials-welding@googlegroups.com>
Date: Friday, July 8, 2011, 1:58 PM
Dear Experts,
i want to know the technical reason that "why preheat is not required
in Austenitic SS"
what will the effects of that?
plz clarify me the reason.
Thanks and regards,
Ankit Khatri
--
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--
Best regards,
Tarek Yehia
QA/QC Inspection Engineer
Tarek Yehia
QA/QC Inspection Engineer
AWS-CWI (Cert.# 11042201)
BEMCO Steel Industries, Jeddah, Saudi Arabia
E-mail: t.yehia2009@gmail.com
BEMCO Steel Industries, Jeddah, Saudi Arabia
E-mail: t.yehia2009@gmail.com
Cell. #+966546154198
+966567726160
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