Welding Tips and Tricks

Hello I am new to this forum . I had a query regarding welding of Cast Iron? Where to post the questions. Please guide me through.

Welcome, Sushant,

If you'll scroll down the index page, you'll see we subdivide welding topics by their process, such as stick, MIG and TIG.

Questions that aren't specified by process can always be put under "General Shop Talk", which is where I'll copy your post to.

Steve S

My limited experience...

Welding cast iron can be a bit fraught...
The high carbon content makes the material very hard.
Or more precisely, it gets tempered by the sudden change in temperature.

You will observe Jody doing a small quick test on a small piece of material, and it goes as hard as glass.
Try it for yourself - it's quite a surprise to see the difference.

This hardening means that welding can lead to cracks and stresses.

I used a 316 rod, to repair a cast iron pulley with tig.
Not a perfect rod for the job, but it went very well.
I preheated the part, welded the cracked bit back on, and it looked great.
I was about to re-heat it to cherry red to relieve the stresses, when I dropped the pulley, and the repaired bit shattered like glass - the stresses must have been immense...

I'll now have to grind back, and build up with braze to carry out the repair (again with tig).. Ho hum...

You can get specific rods for cast iron - both arc and tig - not played with them.

Brazing is a good alternative, and is what I will be doing to repair a crack in a classic car manifold - the braze flexes more, and is less prone to cracking.

Muggyweld makes 2 rods for cast iron that can be used as a stick rod or as tig filler rod. I have used other Muggyweld products but not the cast iron stuff. I have nothing bad to say about the stuff l have used.

When I go for welding nodular Austenitic Ductile iron ,the problem I face is of graphitization.When I did the microstructure analysis I find graphite flakes rather than graphite nodules.The chemistry of the job is maintained as per standard. Please guide me through. So instead of repairing we have to replace the component.

When nodulare cast-iron is welded it loses the specific properies as the carbon nodules start to break up and won't re-form so you lose the properties of the material (as you experienced) in and around the weld. Various sources are pretty clear on that.

Eg from http://www.welding-advisers.com/Welding ... -iron.html

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When Welding-ductile-iron one should remember that the fusion zone will not resolidify as ductile iron because the graphite will precipitate as vermicular or quasi-nodular.

That is why ductility and impact resistance will be drastically reduced, and some carbides are likely to form, particularly in the pearlitic grade.

Furthermore the Heat Affected Zone will produce martensite, hard and brittle, especially in the pearlitic grade, that must be heat treated as explained down this page to restore some ductility.
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Or: http://www.esabna.com/euweb/oxy_handbook/589oxy15_4.htm

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Like malleable iron, nodular iron cannot be fusion welded and retain all of its original properties. This is especially true of nodular iron castings which have been heat-treated after casting. A fusion weld made in nodular iron may not cause loss of tensile strength, but will almost always reduce the shock resistance of the part.
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Brazing can be an alternative as this has much less impact on the base material but of course the filler material will be softer and may not be a suitable soluton depending on the intended use.

Bye, Arno.