Welding Tips and Tricks

I welded cast steel today, violating almost every rule.

Here's the root pass, for a broken ear on a 30 HP hydraulic motor. I welded this with the motor assembled and attached to the hydraulics. Outside. In the wind.
-20 torch, small gas lens, 1/16 thor. tungsten, #7 cup, 35 CFH. Used 1/16" 70-s2 at 80A (machine set to 120A). Had to keep the heat low to prevent coking the oil (on the inside... The oil embedded in the metal was another matter).

I also quenched the weld with water after every second pass. The whole time, I was waiting to hear that "tink" that tells me I've cracked it. Here it is, finished:
What I did wrong? Instead of hi-Ni rod, or even 309, I did 70-s2. I could not/did not pre-heat. Post-cool was a water bath.

I was stunned at the results. I actually got 100% penetration on a cast weld. I suggested a lap-welded strap for insurance when I proposed this solution, and could have avoided it if the boss hadn't spec'd it in his e-mail to the client. Fortunately, that went well, too, but I forgot to get a picture of it.

Steve S

Def the def of down n dirty. Most all have made repairs the wrong way when we have had to.

I like it, any idea what caused the initial failure?

Damark wrote:...I like it, any idea what caused the initial failure?

Yes.

The mount this motor bolts to had the threads stripped out. That's the next repair in this sequence... I'll be drilling out the mounting threads and re-tapping to 9/16-12 thread. I'll be creatively adapting the drill press as a threading tool to keep everything as close to square as I can.

Thanks for asking!

Steve S

Steve,
If you had done everything right it assuredly would have cracked, you know how that goes. I think that since the metal between the two welds is so small that it was able to cool almost as fast as the weld on either side of it. I'm thnking if it had more meat to it, it would have cracked with the quenching. One thing about it is it was already broken and there wasn't a lot to lose. Some days you get the bear.

Len

......and other days you get the horn....

Great repair Steve. Cast can be fun if it all is going right and you have the correct equipment/fillers but as you have proven sometimes we can get around it.

I did a cast repair a few weeks ago that went very badly. It was a huge chunck aso pre het was fun. It cooled off so fast I needed a second person there holding the torch but didn't hve the second body. In the end I poored the heat to it and post heated it, covered it up and went to bed. The welds I put down were machined off and it turned out all right. For that I used 99% Ni tig filler.
-Jonathan

Nice job!

Nice job Steve...I had a similar repair a few weeks back on a smaller scale (gear box), I used 309L. The hardest part is all the nasty as old fluid coming out, and keeping the heat out so you don't coke the internal fluid or damage the seals.

Thanks, everyone!

I was thrilled with how well this went, as I was expecting far more trouble.

Len, this is the pump drive for an AMKO-built LAR trailer (arrived with nearly a full load). The front pump support this bolts to is aluminum. Could there be a more stupid design?

Steve S

That turned out real good - I've heard of people mig welding half inch at a time in a similar fashion - "cold welding" the cast iron.

Have not tried it myself - nice save

I could design something more stupid. I'm a natural at picking the hardest most, useless way.

Steve,
You should know from working on their own designed LHY trailers that if there is a more stupid way to design something they've found it. I don't think that I've seen any AMKO trailers, but the Cryenco hydraulic trailers were POS for sure.

Len

This design was pretty good....

Terminator 2?

Don't get me started...



Steve S

What, you telling me that it's not highly factual?

Cast steel is welded just like plain carbon steel of the same composition. "Casting" of carbon steel is no different than what happens as your weld metal freezes.

Sometimes because of the complex configuration of some cast steels and possible variations in chemistry, cracking can be ann issue butt its not the same as with cast iron. Cast Steel is used in many service applications including pressure containing devices. http://www.flowserve.com/files/Files/Li ... CT0002.pdf

weldin mike 27 wrote:What, you telling me that it's not highly factual?

It would be interesting to see what would happen if Liquid Nitrogen was poured into a molten steel crucible wouldn't it?

A bit of study of the Welding Engineer's Handbook reveals there are a few "cast steels for pressure purposes" that contain less than .25% carbon, and require no preheat or post heat to weld. There are many more that do require preheat, post-heat, and control of interpass temperature, so I suppose there was some luck involved in having a readily weldable casting that would tolerate the repeated quenching.

Whatever made it go so well, I'm grateful.

Steve S

Gerald, thanks for the link.

I weld in cast stainless valves all the time, and know that many cast products are intended to be welded. I did not really expect a hydraulic motor to be one of them, at there is no application that comes to mind where welding directly to/on one would be anticipated. Apparently, though, the high-pressure operation required an alloy that was also easily weldable, so a happy coincidence for me.

Another day where I learned something!

Steve S

Yes. I think the carbon content is the biggest issue as opposed to the method of manufacture. Cast Steel with .020 carbon will weld essentially just like plate, sheet, strip etc... of the same carbon equivalency.

Of course with a casting there may be issues with part geometry that could cause difficulty. You can ALMOST never go wrong with a little preheat.

Besides the spark test, you can identify grey cast iron by rubbing a piece of white paper across an area where it has been ground or filed. The paper will turn grey similar what is caused by a pencil. The reason is, the free graphite in the cast iron. That is also a source of carbon in the weld metal which increases the hardness of the weld, low ductility, and the likelihood of cracking.

When I get the grey on the paper, its time to bring out some preheat or some bronze rods and flux.