Mig welding cast iron

Metal Handbook, Ninth Edition
Volume 6
Welding, Brazing, and Soldering
1983 edition

It's put out by The American Society for Metals.

In it, it's got various tables and charts and text on selecting the wires, feed rates, and power settings for mig welding the various irons, including cast. The A5.14 wires being the best of course, as this is the nickel and nickel alloys group.

I can't claim to give any recommendations, as I certainly don't recall what I was using in vo-tech long ago. And I'm far enough removed from welding these days to be nothing more then a handy home welder.

The long and short of it though, is that cast iron can be mig welded, and a decent welding supply shop should be able to sell you the right wires and gasses to do the job.

Yes, indeed, AWS 5.14 specifies nickel- and iron- alloy wires, and this spec does cover wires suitable for MIG welding. And, indeed, the ASM handbook gives procedures for MIG welding cast irons.

Howesomever, the term "cast iron" covers a very wide range of materials, and the term "welding" can be read many ways.

Most of the castings encountered in this arena (heads, blocks, manifolds) will be gray cast iron. This can be successfully welded with high-nickel filler metal. However, it has been found by empirical observation that the MIG process does not produce welds of good quality, good penetration and correct metallurgy without additional processes (eg furnace heat treatment) which are outside the scope of almost all users.

This is the reason that most of the major manufacturers of MIG wire do not make wires in that portion of the 5.14 classification which would make them most suitable for use with cast irons - their 5.14 wires are alloyed for use with other materials, eg the high-nickel alloys such as Monel and Inconel.

Now, these wires could be used on gray cast iron, and they would produce a weld which seals. However, the control of the metallurgy of the heat-affected zone would be severly sub-optimal, leading to welds which lack tensile strength, or which are so hard that they are unmachineable.

This is why all of the major manufacturers offer the 5.14 wires which would be most suitable for cast irons only in the form of stick electrodes, or cut-length wires suitable for TIG welding, and sometimes not even that. Using them in the form of a stick electrode allows for the addition of other alloying and shielding agents (in the coating), to improve the metallurgy, which cannot be produced in the MIG or TIG process. To my knowledge, none of the major manufacturers produce a MIG wire electrode which they will recommend for use with cast iron.

Because a spec for the electode exists, and would be applicable, does not make this a practical process for most users. After all, I can "weld" cast iron together with regular steel MIG wire (with a high-argon gas) and produce what looks like a weld. But it will be hard like glass, totally unmachineable, and a good whack with a hammer will shatter it. It is "welded" in the sense that it has been joined by fusion. However, the base material has been so compromised by both the filler and the process that the only thing that the weld can be relied upon for is to stop light from coming through.

In summary, while the process is possible, and while I'm sure that someone, somewhere, makes a high nickel-iron alloy MIG wire, the results are, or can be, severely sub-optimal and it is not a process recommended or generally used.

Not quibbling with the truth of everything you say, merely adding that for the great majority of users, this is not an option which can be relied upon.

llater,

llamas

As I understand it, one advantage of using a MIG welder is that you can weld continusely since you do not run out of "rod" as you would in stick welding. HOWEVER, that would then violate the admonition that I read in my Forney welding book on cast iron, " weld a little, cool a lot". They recomend short welds, 1/2" to 1", which means that you heat the whole part only a little. Then you are to let it cool, essentially back to room temp, before you weld again AND the next pass should be well away from the first or previous pass.

Enjoyed your technical explanation, I always like to expand my learning.

Regards,
Larry

Heating is often not practical and the part must be welded "cold". Short welds are the rule, and while this does not exclude the use of MIG, welding "cold" will only amplify the shortcomings of the process even more. Metallurgical changes in the heat-affected zone will be much more pronounced, and the MIG process does not have the capbility (by electrode shielding) to alter that metallurgy.

llater,

llamas

Thanks guys

Elvy