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Re: [MW:13198] Hot cracking mechanism in stainless steel

By Materials & Welding
Hot cracking is a cracking mechanism that occurs at high temperature during the last solidification phase.
 
Hot cracking can occur because of
 
1. Low melting eutectic like Sulphur,Arsenic,lead which forms low melting compounds with iron
2. Wide gap between the liquidus and solidus curve.
 
The above associated with the welding stress.
 
What happens in the weld is that, the weld metal tends to solidify from the corners of the base metal to which it is joined. As the solidification proceeds the low melting eutectics are concentrated in the centre and remains liquid which is torn apart by the stress associated with the welding resulting in centreline crack.
 
The presence of delta ferrite about 5-10% solves this hot carcking problems. Since delatferrite is the first phase that forms from the liquid phase and which has a higher solubility limits for the low melting eutectics(impourity Atoms), there will not be any low melting eutectics during the last phase of solidification and hence no hot carcking.
 
The gap between liquidus and solidus curve can be controlled by limiting the interpass temperature below 150degC which promotes fast cooling and hence no hot cracks.
 
Thanks & Reagrds
 
J.Gerald Jayakumar
00968-93281596
From: Ary Agung Prasetyo <ary_mt05@yahoo.com>
To: "materials-welding@googlegroups.com" <materials-welding@googlegroups.com>
Sent: Sunday, December 11, 2011 8:49 PM
Subject: [MW:13192] Hot cracking mechanism in stainless steel

Dear experts,

can expert explain to me how hot cracking mechanism in stainless steel?
many reference shows delta ferrite is a cause of hot cracking in SS, but i'm still confuse about the mechanism.
Thanks
 
Salam,

Ary
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