Are these chassis made of mild steel?

[kipps]

Is there any hardening, tempering, etc in these squarebody chassis? Can you heat, weld, and reshape the chassis all you want without concern for changing the metallurgical properties?

Specifically, I'm looking at hot-dip galvanizing a chassis. There's some slight chance of warpage, but I'm willing to risk that. Will the heating and cooling process weaken the frame at all?

[HAULIN' IT]

In an effort to try to answer your questions, I'll start with "Question 1". I don't think there is anyone or any vehicle that would answer YES to that question. Metal changes with heat & bending...the more you do, the more trouble you are heading for.
"Question 2" Im not sure what the heat involved in the "hot-dip" process, however I would not guess it is all that hot (400-500 degrees ?) Zinc melts at something under 1000 so a molten tub of zinc could be quite a bit lower than that & still be liquid, however there may be "ideal" temps for dipping that are closer to molting point or something.

Im going to say I think there is a BIG difference between question 1 & 2. I know a fellow that hot-zinc dipped a Jeep frame then drove it for MANY years without an issue. The only real negative was dealing with the threaded holes, bores for bushings, ect. Just my thoughts, Lorne

[kipps]

Thanks for the reply! I see folks frequently shortening frames, notching frames for lowering, plating frames, etc. So it appears that heat-inducing modifications aren't out of the question.

The bolt holes are nearly a non-issue. The only threaded holes in these chassis that I know of, are the holes for brake-line and fuel-line clamps. And those are all using self-tapping screws, so no problem there. Any other bolt holes that are reduced in size should be easily reamed out with a drill bit.

I was quoted $450 to hot-dip a sandblasted frame. This is not much more than buying the ultimate chassis paint from Eastwood, and it's likely going to be better quality. The downside is I won't have a nice matte black chassis, but practicality trumps cosmetics on this project.

[LS short box]

I used to work for a manufacturing company that built equipment that required heavy wash down cleaning. The machine frames were 1018 mild steel. We used hot galvanizing because it was the best metal protection at the time (early 1980's) until power coat came on the scene and then stainless steel became more available at a more affordable price point.. Never had a frame problems with the hot galvanizing. It's not real pretty. Kind of scalely and rough.

[superdav]

Steel mill worker here, low carbon alloy steel is used today but I have no idea what square frame chemistry is. Many alloy steels today didn't exist 10 years ago and thinner steels are needed for weight which also means formability is highly important. Low carbon alloy has good weldability, remember new vehicles frames are welded on during their build and easy is also a requirement from manufacturers which was the same in the 80's but with lower quality steel. If it were mine I would have zero concerns welding although I wouldnt take a torch and go heating up red hot any large stressful areas. I doubt hot dip would cause any problems either.
If someone could send me a piece of frame I could take it to work and find the exact chemistry.

[kipps]

Originally Posted by superdav

If someone could send me a piece of frame I could take it to work and find the exact chemistry.

How large of a piece would you need? I've got the rear half of a mid-70's c20 chassis that's going to scrap sometime soon.

[superdav]

Originally Posted by kipps

How large of a piece would you need? I've got the rear half of a mid-70's c20 chassis that's going to scrap sometime soon.

at least a 2 inch square


ETA IM sent

[LT7A]

This is very interesting in all of its aspects. And I really like the fact that there's a guy on here that could get metal from a frame analyzed and is willing to offer that. Thanks superdav, very cool. As far as the galvanizing, I think it's a great idea. Zinc is a soft enough metal that you can scrape or sand any irregular areas to get it as smooth as you want. You could even polish it and it turns to a very bright, reflective appearance. It will reoxidize and get dull, like aluminum does, so polishing is not practical for a chassis, but still... I think the uniform matte gray will be a nice backdrop for any other chassis related components. $450 sounds very reasonable and I will consider it if I ever do an off-frame restoration.

[Desert1957]

WOW, This thread is fascinating. If "Superdav" can do this go for it.

[special-K]

I don't see anything risky about your plan. Whatever the mild steel chemistry is, these frames have been getting cut, welded, heated to bend/straighten and I have never seen, heard of, or personally experienced any adverse effect. My buddy had his frame break behind the rear spring hanger on one side from all the trailer hauling he had done. He didn't baby the truck. The truck was an '85 K10 that had 1t running gear and he'd haul everything and anything out of anywhere. He welded up the break and plated it. Keep on working the truck same as ever. I've had trucks that commercial body/equipment upfitters had done frame welding on. I have a guy local to me who reconfigures used commercial trucks. On anything w/o a tempered frame he alters wheelbase all day long and has been for decades. He'll make a garbage compactor truck out of a box delivery truck. They get state inspected and legally registered, also subject to DOT scrutiny. I'm sure you'll be fine with hot-dipping

[Warrens69GMC]

In for the results

[Keith Seymore]

I checked the generic info packet at the GM Heritage Center archive and both the 1973 and the 1987 packets refer to the frames as "Carbon Steel - 39,000 psi".

https://www.gmheritagecenter.com/doc...olet-Truck.pdf

K

[kipps]

Originally Posted by Keith Seymore

both the 1973 and the 1987 packets refer to the frames as "Carbon Steel - 39,000 psi"

What does that mean, though? I'm clueless about metallurgical properties.

[68post]

Remember - no welding or torch cutting galvanized metal, it creates poisonous gasses !

[4X4GMC1972]

39,000 psi is the yield strength (mechanical property, not metallurgical). It would make it low carbon steel. Anywhere from .15-.20% carbon (metallurgical property). It is weldable without going through any pre or post heat treatment process. To be safe, warm the weld area to about 200 degrees prior to welding. Slow cool by wrapping the welded area with a welding blanket. If the carbon content is any higher than .30% welding becomes tricky. The carbon content in steel usually determines the weld procedure.