Topic: Chromo Vs. DOM

[TacoRunner]

Chromoly 1.5" OD .095 Wall     $6.65/LF

DOM 1.5" OD   .120 Wall   $6.52/LF

Question, to those that know.  Since Chromo is about 1/2 the weight of DOM, which of the above two materials is stronger and would hold up better when used as roll cage material?

If you have experience with these materials please feel free to give your opinion. If you are offering your opinion and you have no experience, please refrain from answering. Im just trying to eliminate the guess work.

[MiniSimp]

Chromoly is not necessarily much lighter, but it IS stronger, so you can use tubes with less wall thickness and save weight but retain the same strength. A caveat: most racing organizations (SCCA, NHRA, NASA, etc. require that chromoly is welded with TIG, not MIG. Also, chromoly becomes very brittle in the weld zone unless it is normalized correctly (mega-mega-$$$). Stick with mild-steel because it's FAR easier to build with and will BEND in the event of an impact instead of BREAKING as un-normalized chromoly would. In a simple 12-point cage, chromoly would probably only deliver a 40-60 lb. weight savings anyway –not really worth the extra cost and headache anyway.

[TacoRunner [OP]]

What do you mean by normalized? (heat treated after welding)

And, does it become brittal when MIG'd only, or does that include TIG?   

[MiniSimp]

Simple explination: 4130 before heat treating, it's almost shatter-proof.

Most 4130 when bought new is in a condition called "Normalized." In this condition the yield strength is 75,000 psi and the ultimate is 95,000 psi. It is sold this way so the user can work it (machine it for example) more freely. To develop its highest strength it is then heat treated. This will take it to a yield to over 100,000psi and the ultimate to over 125,000 psi. If you are possibly going to buy some 4130 make sure you know if it's "Normalized" or "Heat Treated."  All the surplus 4130 I've seen has been was normalized.

[TacoRunner [OP]]

Ok, so buy normalized 4130 not heat treated??

I figure that by dropping my hardtop I saved about 100lbs
If I ditch the tail gate I can drop another 40lbs
And if I can save 50lbs on a cage then great. And at the same cost (nearly) then I'll go for the Chromo.

[Hyena]

DOM steel tubing is manufactured the same way as mild, including the welding. The alloy is typically 1018 up to 1026, the higher the number, the higher the carbon content. DOM means Drawn Over Mandrel, which “trues” the tube and hides the weld, giving it more accurate dimensions. DOM is about twice the cost of mild, and almost as much as 4130.

4130 chromoly steel tubing is a true seamless tube, with chromium and molybdenum added for strength and light weight. 4130 is very expensive and is used most often in big budget builds. It requires heat treating after welding to achieve maximum strength. Some say that if a 4130 chassis is not heat treated, it is no stronger than the other steels. 4130 suspension components should definitely be heat treated.

All that was taken from here - http://www.pirate4x4.com/forum/showthread.php?t=386480

[TacoRunner [OP]]

Some say that if a 4130 chassis is not heat treated, it is no stronger than the other steels. 4130 suspension components should definitely be heat treated.


Does this mean that if I were to use 4130 1.75" OD .095 Wall , that it would be as strong as DOM 1.75" OD .120 wall material?

[TacoRunner [OP]]

 Why is it that I can never get quotes to work right on here.

[kneedownnate]

Do you insert your text inside the quote like this 

Why is it that I can never get quotes to work right on here.  MY OWN TEXT

Or do you make sure your text is outside the quotes... 

Why is it that I can never get quotes to work right on here.

Like this?

[Huhwhye]

Maybe a stupid question but how do you heat treat a race car chassis?

[Duffil]

you treat each weld with a torch; it is not necessary to re-treat the whole chassis, just the welds.  Also, if you are using a TIG, there is filler rod called ChronoTron (and probably many similar) that do not need to be annealed after welding.

[Huhwhye]

Ah, I see.  That makes sense I guess it wouldn't make sense otherwise.