How to weld alloys?

[Anonymous Poster]

Does anyone (Harv) know how to weld chromoly metal. I don't even know if I'm spelling it right. There is a pretty big outfit that races little minisprint cars in this neck of the woods, and they tell me that the frames are chromoly. One of them was asking me the other day if I could repair his frame. I guess they figure that since the cars run motorcycle engines, that I will know the first bleeding thing about their sport. Anyway, it got me wondering if you need special wire to weld it. I'm not too keen on fixing his frame, because of the inherent liability associated with frame repair. I am keen on most things motorsport related though, and have to wonder about welding this type of alloy.

 

[RJohnson]

Yamaben

The first thing you have to determine is the actual grade of material. There are four general types of low-alloy molybdenum steels: AISI 4000 series carbon-molybdenum, 4100 series chromium-molybdenum, 4600 and 4800 series nickel-molybdenum, and 4300 and 4700 series nickel-chromium-molybdenum. Each series may require a different welding electrode depending upon whether you are trying to match all of the chemical and physical characteristics of the material.
If you have a chrome-moly steel then any low-carbon, low-hydrogen electode should suffice for strength and ductility. Of course these are crack sensitivity materials and will require a preheat and postheat treatment to eliminate cracking.
After saying all that I not sure that you first thought about liability is not correct and you should send the man to a welding shop that specializes in chrome-moly welding. Good luck.

Randy

 

[Anonymous Poster]

I think I knew the answer before I asked it. It takes more effort than I can muster. Also, if I would consider doing it I would want to use the mig (my stick welder is cheap and too hot on the lowest setting). Thanks for the input though.

 

[RJohnson]

Yamaben

You will need a ER80S-B2L classification for chrome-moly steel which is also going to require you to 98% Argon and 2% Oxygen to minimize undercutting and improve your toughness.

Randy

 

[Anonymous Poster]

Do you think preheat and postheat are still needed with the wire welder?

 

[wroughtn_harv]

I've never messed with chromoly. In California one of my neighbors built midgets and sprints. He used tig and chromoly for everything. Hearing him talk about bad welds and fatal accidents cured me from even considering working with the stuff on racecars.

It's used when you want minimum weight and maximum strength. You could weld it up just fine. It could look pretty as a picture. But on impact you'll probably have this failure deluxe. Your weld will hold fine. It will be the material a quarter inch or less away from the weld that will separate just like tempered glass.

If I was you I'd take their work. Sub it out to a professional who specializes in quality tig and has considerable experience with chrome moly.

That way they get the quality they have to have for their own safety and you minimize the risk of them getting hurt and you getting sued. And if you think about it if you didn't do it right then you'd deserve to be sued.

They went to chrome moly for it's strength and lightweight. When they did they stepped into an area where the costs are not only high, they're very very high.

 

[RoyJackson]

Welding chromalloy is a lot like welding stainless steel.

When you weld tubing, you really want a gas backup to the weld. Rig a tube (automotive vaccum tubing works well) from your regulator (you may need a "Y" connection) to a open end of the tube structure. Closer to the weld location is optimal, by the way. Use something to seal off any other openings so the gas doesn't just flow through. We used a combination of plastic, duct tape (what would we do without duct tape!!!???). We used a plastic jar lid with a hole drilled through for gas tubing...then duct taped the lid to the tube.

A weld can be contaminated from the side opposite the weld joint. That's why the gas back up is important.

This is especially important with the more exotic materials such as chromalloy. These are normally used in high strength situations (racing vehicles) due to their good strength to weight ratios. Hence, more caution is needed when joining these types of materials.

Now, titanium welding really needs to be done in an inert atmosphere (glove box). Production welding of titanium is done in a vaccum using electron beam welding.

What I described is what we did on military aircraft components. This was mostly TIG with a few MIG welds as well.

 

[Anonymous Poster]

I figured that it would be out of my league. I'm a mechanic that welds a little, and he needs a welder that wrenches a little. You're right about being sued. When you own a business, somedays it feels like there are wolves at your door. I pay a sore butt's worth of insurance every year to protect myself, and I shouldn't invite a possible lawsuit. Thanks all for the input.

 

[Anonymous Poster]

<font color=blue>Welding chromalloy is a lot like welding stainless steel.</font color=blue>

What does it take to weld stainless? I needed to weld a stainless steel exhaust system, and wondered if my mig would do it. I tried it and it worked just like regular sheet steel. Wasn't structural though, just patching a hole.

 

[RoyJackson]

"What does it take to weld stainless? "

When I wrote that, I meant you'll get a small puddle, use a sharp tip (for TIG) electrode.
Stainless isn't as subject to contamination as the more exotic metals are. If I recall correctly, you can use a stainless filler material when welding some of these metals.
Of course, the gas backup, as described in my earlier post, is always advisable.