Welding Tips and Tricks

Hello,
I am hoping some can answer a question regarding weld cracking. I am not an expert welder and will basically make brackets, shelving for my work vans. I have a 1/2" thick 4' by 3' carbon steel plate welding table, which I simply wanted to expand by adding (welding on) a 2' by 4' piece of 1/2" plate. Ia s mentioned am no expert but have welded up aluminum, stainless steel and regular (carbon) steel brackets etc...... with regards to the welding of my welding table some really strange things are happing, primarily cracking of the joint! I have beveled and ground both the existing table and the new steel plate, including cleaning of all mill scale. I have placed a 3/32" gap between the two plates and attempted to first tack the steel together in 8 spots. The strange thing is when applying heat, the 2'x4' section begins to almost start bubbling.. I haven't mentioned that I am doing this using a Lincoln squarewave 200 machine using DC TIG with 140 amps and have tried various methods such as just melting the two metals together without any filler (just to tack) and then 308 filler, er70S but for some unexplained reason,
I can tack these together and 15 minutes later I hear a bang and find all tacks have cracked! I am hoping someone here may know what is happening or may have had this happen to them.
As mentioned I have thourghly cleaned the steel and ground to bare metal, have increased / decreased amps, even changed bottle of argon.... I am using E-3 tungsten ground to a point but I have tried various different tungsten's I also went as far as to put the scanner on and attempted with 7018 where I ran six approximately 3 inch long tacks and 20 minutes later again a loud bang and every wild was cracked again any help would be much appreciated !

First, welcome aboard!

This 2' X 4' X 1/2" plate you're trying to add... What alloy is it? Do you know? It sounds like this piece is cast steel, or even cast iron, with the "bubbling" you describe. 1/2" plates of cast steel or iron, planchard-ground to a finish that would make you think it's regular cold- or hot-rolled steel, are common for extension beds on machine tools, like a vertical mill, or even the table of a saw. I'm wagering you're dealing with something cast, not wrought, and it will be a fight to combine the two.

It can be done, but in this case (if I'm right), I'm not sure it should be done.

Other opinions will follow shortly, I'm sure, after which I may give some input on combining the two.

Steve S

If one is cast and one is regular steel you might consider simply building a frame that allows you to bolt them up side-by-side without actually joining them.

If it is cast, it may not be appropriate for welding table duty anyway given the hammering that can go on in service. Why not get a piece of known material plate that you know you can weld and will hold up to rough duty. At the very least you have a great bbq plate to treat the lads and lasses on a Friday afternoon toolbox session, so not wasted.

Thank you for the warm welcome and all of the responses, so quickly.... I apologize for all of the typos, I have an iPhone and Often use voice dictation and I'm sure anyone familiar with that realizes that it gets just enough words correct to get the point across. The bizarre part is I have many bits and pieces hanging around in my shop and actually welded two pieces of this metal together without any cracking to make the 4 foot long section. I just tried to add 2 very small tacks again just now with 160amp and 308 filler. I started a timer and it was just over 8 minutes and bang! I heard it 20 feet away and sure enough both tacks are cracked! I will rip it out and replace it tomorrow but it is beyond me how I can weld two pieces of this metal together but I am not able to weld it to another piece of plate? I am 100% certain that you guys are correct with the composition of this metal! I am a steamfitter plumber and gasfitter by trade And unfortunately did have an opportunity over my career to become quite intimate with cast-iron drain stacks so I know for certain it is not cast-iron as a first ingredient but as was mentioned by you fellows more than likely has some cast-iron in it. I am new to this forum and was attempting to add a photo of this stuff.....
Thank you
David Burnell

If it's some sort of chromium then you need to keep it up to temp until you have 2 or three passes welded all the way. High chrome pipe will also crack like that unless you get a few passes finished out.

It doesn't have to be cast iron to be "cast". Even stainless steel is cast for certain items. I've had hell with welding cast stainless to carbon steel.

Steve S

Does anyone think that applying or preheating with the oxy-acetylene torch and then trying a tack?
Appreciate any input!

You may need to keep it up around or above 500 degrees. Not just to tack it but also until you get it welded half way out.

Personally, I think Josh's first idea is the best option for this dissimilar metal work. Simply frame them together and forget joining them.

The other best idea is to lose the idea and get a known-alloy plate in it's place. The point was made that if it's cast it won't take hammering very well, and we beat the s#!t out of our tables.

Steve S

Why not use a Nickel 99 or 55 rod with your Stick welder to join them? But if TIG welding it, cast iron needs a preheat as mentioned.

Sounds an awful lot like cast with the bubbling and everything.

I never preheat cast when I weld it and I never had it crack either.

Gotta be the alloy, can't think of any other reason its acting up so much, shouldn't be THAT difficult to weld together.

Ductile or nodular iron? Cast steel IS weldable, welds are just cast metal without a mold. Filler metals are much higher quality than most casting alloys. I know CF8 castings and CF8M (304 and 316 stainless resp) are repaired with similar filler as the primary differences are in silicon which adds fluidity.

Cast iron relies on excess carbon for fluidity and this comes out of solution before solidification which is why the tacks break. Also, the cooling rate is high from self quench so it takes only a trifle base metal dilution to make carbon in the weld to jump over 1%. Remember, without other carbon equivalents, all it takes is 0.30% carbon to make welding sporty. Cast iron can have over 4% carbon.

How does this mystery metal drill/grind or spark? Without XRF PMI, ferrous metal ID by grinding sparks is subjective yet informative. If sparks end in a poof like a big firework, welding is going to be difficult.

Drill press with a known good bit..cast iron makes tiny chips or powder. No ductility.Still drills good, especially gray iron as the excess carbon is graphite. Swarf from gray iron stains fingers graphite gray.