Welding

Me Again (with another stupid question - hopefully you are getting used to them)

Cast iron welding, I have had pieces welded which have been very good but lately the same bloke has welded a few parts and they have snapped apart shortly afterwards. The welding that broke looks very porus like a malteser. Could someome kindly tell me what is going on. I have mig welder could thus be used to weld the parts up? The parts that are breaking are about 30 ml x 14ml.

Have looked at the site but cannot find anything of relevance.

Many thanks for any help you can offer, Alan.

Alan, More info = More replies................

Bear..

Alan,

Please specify what welding process was used and whether the beak was on parent metal, heat affected zone, or weld.

John

The only way to "WELD" cast iron is using oxy /acetylene. Any other systenm is adhesion on a microscopic level.The problem is the free carbon available in the cast iron which has a tendency to embrittle any filler material. The use of nickel helps to reduce this tendancy,because it does not combine with the carbon.

Photo of the part with a rule indicating size etc would help. Also what the part would be used for. I have recently MIG welded with S/steel filler and Argon gas quite successfully on small sections less than 1cm square.
BobH

I agree with Michael Darby. Any method other than ox/ac welding with cast iron rod will give unsatisfactory results.

Mig and Tig are particularly bad because of the very concentrated heat. The mass quench effect of the base metal will create a hard zone that is extremely brittle. Even with ox/ac mass quench can result in hard zones that require post weld anneal to restore machinability.

A chap in Scunthorpe did some very good cast iron welding on exhaust manifolds that lasted the life of the engine, he put manifold in oven and heated to red and then electric welded with special cast iron rods the part was then put back in oven and left to cool over 24 hours or so.

Stan

www.lincolnelectric.com/en-gb/support/welding-how-to/Pages/welding-cast-iron-detail.aspx

Weld was done with an arc welder - having issues trying to upload photos but will try again tomorrow. did create an album but my photos are png and they need to be jpg (way over my head but will get someone else to have a look and see If they can help me

He would have used a nickel based filler which as I stated earlier would not have "Welded" the joint " because the filler could not use up the free carbon it would have "adhered" to the iron molecules in the casting forming a nickel rich iron moleclue. the problem with this is that you have free carbon atatchments to the iron creating brittle edges within the structure of the material hence the post heating cycle to attempt to reduce the brittle edges

As per Stan's reply - pre-heat is key with cast iron then use cast iron specific rods (Arc weld)

+/-

Alan ,

In my experience thorough and sustained both pre and post heating are essential if the repair is to stand any chance of permanence . The last CI item I welded was a bench vice . I thoroughly pre- heated , then used a No 25 nozzle on o-a to complete the weld , before carefully put the vice in a dustbin full of sand for 24 hours . Vice is still in use many years later . If you know anyone with oxy-acet that can do the work for you , but who lack the materials , I can supply you small amount of rod and flux to complete your work for the cother of the postage . Alternatively you may find Cast Iron Welding Services in Coalville on 01530 811308 ( no connection ) helpful .

Thanks everyone for your suggestions. Think I am going to go down the road of cast iron welding rods. Thanks again