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Old 04-26-2003, 07:01 PM   #1 (permalink)
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Question DOM vs CHROMOLY???

Ok I'm looking for some advice from those that know. I'm looking to build a full tube buggy for insane rock crawling. I don't have the $$$ to replace the chassis every time I take a major hard roll roll. I'm willing to sacrafice a LITTLE weight for strength. I'm looking at either 1.50 x 0.120 DOM tubing for its flexability or 1.50 x 0.120 chromoly tubing for its shear strength. Will the chromoly crack with a hard hit on the rocks? Will the DOM bend and deform with a hard hit? WHICH IS BETTER???
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Old 04-26-2003, 07:12 PM   #2 (permalink)
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This was covered recently. Do a search - should be able to find lots of info. DOM is not specific enough. You have to specify the type of material. DOM is the process in with the tubing is made. There is DOM cromoly tubing. Anyway, I would suggest using 1020 DOM .120 wall. 1020 is a mild steel, fairly cheap, and weld easily with a mig type welder. This should be plenty strong. Some people are using HREW tubing with good success. It is not quite as strong as DOM.
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Old 04-26-2003, 07:20 PM   #3 (permalink)
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Yes 1020 mild steel DOM tubing vs seemless cromoly tubing of the same thickness 1.50 x 0.120.
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Old 04-26-2003, 07:30 PM   #4 (permalink)
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That's 4130 seamless chromoly vs 1020 DOM mild steel. You really think the mild steel would hold up better to some really hard blows on the rocks than chromoly?
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Old 04-26-2003, 07:43 PM   #5 (permalink)
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Are you going to heat treat the chassis, probably not, so you are wasting you money with 4130. Commonly available DOM tubing is usually 1020 or 1026 so you dont need to be specific on the type of DOM. In the normalized condition 4130 tubing comes in, it is not much sronger than DOM, you would probably never tell the difference if you built two identical chassis, one 4130, and one DOM and did some sort of testing. DOM will work just fine, I wouldn't waste my time with HREW, it has many uses like jigs, shelves, trailers, etc, but I wouldn't spend all that time making a chassis out of it. The drawback to using DOM is that you won't be able to tell people that "my buggy is built out of chrome moly", its kind of like saying "ooh my axles are made out of 300M" when a properly designed 4340 or 4140 axle would work just fine and the is other drawback is that chrome moly is lighter and stiffer than DOM












I'm just kidding, that last part is wrong.
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Old 04-26-2003, 08:03 PM   #6 (permalink)
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Red face

Yes I agree. I'm not realy impressed with 1010 HREW. I've crushed and bent it too many times to build an entire buggy out of it.

When you say heat treat the chassis I assume you mean to prevent the loss of temper in the steel due to welding? What kind of temps are we talking about. I'm not sure where I'd find an oven that BIG.
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Old 04-26-2003, 08:21 PM   #7 (permalink)
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Are you welding it yourself or having it fabbed?
How tallented is the fabricator?
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Old 04-26-2003, 08:27 PM   #8 (permalink)
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Fabbed by Avalanche.
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Old 04-26-2003, 08:28 PM   #9 (permalink)
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Quote:
Originally posted by TearUmUpTim
When you say heat treat the chassis I assume you mean to prevent the loss of temper in the steel due to welding? What kind of temps are we talking about. I'm not sure where I'd find an oven that BIG.
No, that is not what he means.
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Old 04-26-2003, 08:37 PM   #10 (permalink)
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Question

Than WHAT??? I'm not real sure what's involved in the heat treating prosses. Please explain...
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Old 04-26-2003, 08:43 PM   #11 (permalink)
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Than WHAT??? I'm not real sure what's involved in the heat treating prosses. Please explain...
Do a seach on the benefits of heat treating high carbon steels.

Here is was 30 seconds of research provided from this wonderfull place we call PBB.

http://www.pirate4x4.com/forum/showt...=heat+treating
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Old 04-26-2003, 08:47 PM   #12 (permalink)
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Originally posted by TearUmUpTim
Fabbed by Avalanche.
Then if you trust them enough to fab it for you, why not go by their recommendations?
What did avalanche recommend for your needs?
I know that the race car owners who come to Welder Boys shop to have their Chromo cages welded are very very particular about how well the welds look, and everything has to be Tig welded. If a guy has been working with metals long enough to be a high quality Tig welder, then he should be very qualified to give you his recomendations,...and if he is gonna be your fabricator you should probably be willing to trust his recomendations.
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Old 04-26-2003, 09:08 PM   #13 (permalink)
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Thanks Pig that was some great reading!
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Old 04-26-2003, 09:13 PM   #14 (permalink)
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they mostly use thinner wall .083 chromoly tubing to save weight and thicker .120 wall 1020 DOM for strength. About 30% stronger I'm told. But they tell me the .083 x1.50 chromoly holds up fine so far. I just wanted to get some other opinions.
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Old 04-27-2003, 03:07 AM   #15 (permalink)
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What Goat1 said....except that last part...that's wrong

Some reading for your research:

http://www.pirate4x4.com/tech/billav...nce/index.html
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Old 04-27-2003, 09:12 AM   #16 (permalink)
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Quote:
Originally posted by TearUmUpTim
Yes I agree. I'm not realy impressed with 1010 HREW. I've crushed and bent it too many times to build an entire buggy out of it.

When you say heat treat the chassis I assume you mean to prevent the loss of temper in the steel due to welding? What kind of temps are we talking about. I'm not sure where I'd find an oven that BIG.

To really take advantage of 4130 chrome moly, you would have to heat treat it to RC 28-32, that would involve heating it above the critical temp (1800-2000 deg) quenching in water or oil (forgot the exact process for 4130, I dont have my reference books here at home) and then tempering it to your desired hardness. This is typically done to suspension compenents like trailing arms, a-arm, spindles and other relatively small fabricated and machined parts, heat treating an entire chassis is not very practical or probably even possible. What you can do to a 4130 chassis is to stress relieve it after welding, and I dont mean going over the welds with a rose bud after welding, that is pretty crude and inacurate IMHO, and might do more harm that good. I mean putting the chassis in an oven and stress relieving in the neighborhood of 800-1200 deg, for a good amount of time, something you can't do with the an oxy-actelene rose bud torch. These ovens do exist but, I know there are a few in LA. Also, fabricating parts out of 4130 requires very close attention to detail, close fit-up, cleaning, sometimes preheating, and using the correct rod, I don't thing you would be able to afford the cost of a fab shop doing this correctly and I wouldn't trust Avalanche to do it right either. In the end when you correcly fabricate and stress relieve your chassis out of 4130 tubing, it will only 10-15 % stronger than 1020 DOM. The 1020 DOM will be about 80% stronger than HREW.
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Old 04-27-2003, 11:55 AM   #17 (permalink)
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GOAT1 --

Ive done a bunch of welding on 4130 for our baja car, and the 4130N that we get is fairly soft (< 10 HRC points) and once welded, the joints become 28 - 30 HRC. We've built cars that have been baked afterwards and put them through the same punishment and testing as non-baked cars and haven't seen any difference. (I.E. no weld failures or cracks). (BTW we use MIG). Shock loading becomes a problem when you go over about HRC 48-50, when the material becomes brittle and doesnt deform before failure (it breaks like glass) . (I recently did some heat treating experiments and did some destructive testing on the specimens that show this). Cracking of the welds is not something to be worried about (if you did them right) in a rollover (which is a bunch of shock loading). You can weld up a 4130 cage the right way and not have to go over the welds w/ a rosebud or bake it to stress relieve. It will still be strong and ductile even with the welding residual stress. When cost is a factor, as for most of us, mild steel is a good choice. It will still save your life if done right. 4130 is better due to the amount of weight savings you can have with it. So if you run a comp buggy, 4130 is the way to go. In a trail rig like mine, I will be using mild steel and a mig.
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Old 04-27-2003, 01:17 PM   #18 (permalink)
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fullreversal-

You got some kinda soft 4130N usually it isn't that soft unless the cross section is over an inch, Normalized 4130 thin wall tubing usually comes in 15-20 HRC from the certs I see.

You are right thin wall 4130 you can mig and not stress releive and you probably won't see any problems at all. Goat1's jeep is mostly 4130 tube I think, I know he Tig'd it and didn't stress relieve it. So he knows it's gonna be fine too.

I think Goat1's point was you don't really see any benefit using 4130 over 1026 unless you heat treat it(then a huge benefit)

If you had built your mini baja out of 1026 DOM it still would not have failed and you might have gotten an extra point on the cost analysis portion of the competition.
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Old 04-27-2003, 05:03 PM   #19 (permalink)
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You can weld up a 4130 cage the right way and not have to go over the welds w/ a rosebud or bake it to stress relieve. It will still be strong and ductile even with the welding residual stress.
Oh, sure you can, but the only thing "more" it will be than the equivalent 1020 DOM cage is expensive.
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Old 04-27-2003, 07:53 PM   #20 (permalink)
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I love it! You guys have been SO helpfull. I was leaning toward the 1020 DOM to start with but I just wanted to check out my options. (i.e.-chromoly) Most of you have confirmed my thoughts and pointed me strongly towards the 1020 DOM. Thanks again for all your help. You've saved me alot of $$$!!!
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