Saturday, June 6, 2009

[MW:2335] Re: corrosion

Dear Keyvan
i think for low alloy steel & carbon steel ,the different chemical analysis in haz & weld isn't major to occur chemical cell.

 

From: kayvan alyari <k.alyari@gmail.com>
To: materials-welding@googlegroups.com
Sent: Saturday, June 6, 2009 3:17:06 PM
Subject: [MW:2334] Re: corrosion

Dear Friends,
 
The main cause is formation of electro chemical cell between HAZ & BM especially in interfaces!
 
Yours truely
Keyvan

 
On 6/6/09, Owen Jenkins <owen@osjl.co.uk> wrote:
If you'd like to know a bit more about corrosion associated with welding, you can download the following guide to bimetallic corrosion: http://www.npl.co.uk/upload/pdf/bimetallic_20071105114556.pdf . The NPL website has a number of other useful downloads which may help you, as well as some illustrations of various forms of corrosion associated with welding. In some cases the HAZ is more susceptible to attack, in others it is the weld metal itself. You can also visit the following sites for more information:  Corrosion Clinic http://come.to/corrosion, Corrosion doctors http://www.corrosion-doctors.org/CorrDocs/CDs.htm, NASA's KSC Corrosion Technology Laboratory http://corrosion.ksc.nasa.gov/ .
 
A Google search would have turned up all that lot for you. Worth trying occasionally, as I've remarked before.
 
Regards,
Owen.
----- Original Message -----
Sent: Saturday, June 06, 2009 9:49 AM
Subject: [MW:2331] Re: corrosion

 
Hi,
It's about the grain sizes and intergranular changes because of welding i think
After welding you will see a lot of different sections that are affected by heat differently.
In most applications weld metals have fine grains due to recrystallization and tempering effects of the upper beads
[And so upper sections of the weld metal have bigger grains (because they are less tempered)]
In the fusion line there is a non-complete fusion section (grain structure is like a casting)
After that, in HAZ a highly heated (but no fusion) big grain size section comes near the fusion line
This section is the most risky one. In most cases if corrosion cracking happens it does it here.
This doesn't mean that weld metal behaves more noble than base metal i think. the corrosion is between the weld metal and HAZ
I didn't see anywhere anything certain about the causes of this type of corrosion.
--

Best Regards,

Erhan TURGUT


Ali Asghari yazmış:

hi
why corrosion occure preferentially in haz ,especially fine grain location?
why weld metal noble than base metal?
 
regard advance





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