Chromoly vs DOM

[Boostwerks.com]

I'm honestly a little surprised no one has really addressed the Benefit to cost ratio. In this case of 4130 VS standard mild DOM, the benefit is very small. The main benefit IMO is not the ultimate yeild strength, but 4130s resistance to bending once heat treated. Whether or not it's worth it, is up to you and how much $ your willing to spend.

 

[XJ_ranger]

I'm honestly a little surprised no one has really addressed the Benefit to cost ratio. In this case of 4130 VS standard mild DOM, the benefit is very small. The main benefit IMO is not the ultimate yeild strength, but 4130s resistance to bending once heat treated. Whether or not it's worth it, is up to you and how much $ your willing to spend.

yeild strength, and ultimate strenght are not the same, ultimate-yeild strength confuses me... Which do you mean?

Maybe I missed a few classes, but I thought the yeild strength of the material was related to bending... Material section, and material strength are the 2 design factors... no?



benifit to cost ratio ?

my only question is: How much do I have to spend, so it doesnt break...

done...

if you look at it from a yeild strength / dollar standpoint, you're missing the big picture... what if civil engineers just looked at a material on a strength / dollar and picked what was 'in the budget'? We'd have bridges falling down all the time!

now - I can understand the cost benifit of looking at material weight / dollar for the same strength...

 

[Phil]

What if it bends...elastically?:looney:

I think material section is way overlooked...something that would be interesting to me would be 2x.25 4130 round versus 2x2x.25 A500 CREW structural steel. :greensmok

And then take it up to the checkout counter.:confused1

yield strength, and ultimate strength are not the same, ultimate-yield strength confuses me... Which do you mean?

Maybe I missed a few classes, but I thought the yield strength of the material was related to bending... Material section, and material strength are the 2 design factors... no?



benefit to cost ratio ?

my only question is: How much do I have to spend, so it doesn't break...

done...

if you look at it from a yield strength / dollar standpoint, you're missing the big picture... what if civil engineers just looked at a material on a strength / dollar and picked what was 'in the budget'? We'd have bridges falling down all the time!

now - I can understand the cost benefit of looking at material weight / dollar for the same strength...

 

[Boostwerks.com]

yeild strength, and ultimate strenght are not the same, ultimate-yeild strength confuses me... Which do you mean?

Maybe I missed a few classes, but I thought the yeild strength of the material was related to bending... Material section, and material strength are the 2 design factors... no?



benifit to cost ratio ?

my only question is: How much do I have to spend, so it doesnt break...

done...

if you look at it from a yeild strength / dollar standpoint, you're missing the big picture... what if civil engineers just looked at a material on a strength / dollar and picked what was 'in the budget'? We'd have bridges falling down all the time!

now - I can understand the cost benifit of looking at material weight / dollar for the same strength...

Whoops. It's been a while since my MET classes! lol.

What I mean't was ultimate strength. I could honestly care less about ultimate strength as both materials are strong enough considering the size of tube most guys utilize, and more often than not the link will fail at the welded tube end (from what I've seen). I also didn't really mean "resistance to bending" but 4130s better ability to yeild under bending forces yet return to it's original heat treated shape (hence why it's used in most racing and aftermarket sway bars). This to me is really the ONLY benefit for this particular application. For the $, most are better off using the largest mild DOM they can fit especially due to the fact that thick wall 4130 is hard to find and VERY expensive.

We're not building bridges here, we're building a simple suspension link for a realitively light rig.

Simple cost comparison:

2" OD 1/8" wall 4130 ~ $15.50 a foot

2" OD 1/8" wall mild DOM ~ $8.80 a foot

2" OD 5/16" wall mild DOM ~ $15.50 a foot

Which would you rather have?

 

[Weasel]

4130, 4140, 4340 and 4340V (300M) respond well to heat treatments and can be modified to have very high yield and toughness properties. Other steels don't exhibit the same behavior and thats why the Chromoly series is used.

A500 is a structural steel that has a yield of 50ksi, 4130 has a yield of 66.7ksi typical. From the chemical comp it looks like a modified 1020 steel as the carbon content is only ~0.23-6% while 4130 is ~0.30%

For 2" 0.25 tubing I=0.78381in^4
For 2" 0.25 square I=0.91146in^4

But while the I is greater the strength is less and the square weighs more. This is where you loose in the weight vs strength area.

Control arms can fail at the welds but the arms can also buckle, I have seen both.

Twisted Customs rigs are ~3000 pounds and most of our rigs weigh more then that. The arms they have that are 2" DOM 0.5" wall have a noticeable bend in them.

The Spidertrax arms are ~160ksi and stay straight even under Tracy Jordans comp rig.

And no we are not building bridges but the same math applies so really it's the same thing.

I don't understand why this subject keeps coming up and goes on for 2-3 pages, it all been covered before and nothing has changed.

 

[Sherman_thetank]

Whoops. It's been a while since my MET classes! lol.

What I mean't was ultimate strength. I could honestly care less about ultimate strength as both materials are strong enough considering the size of tube most guys utilize, and more often than not the link will fail at the welded tube end (from what I've seen). I also didn't really mean "resistance to bending" but 4130s better ability to yeild under bending forces yet return to it's original heat treated shape (hence why it's used in most racing and aftermarket sway bars). This to me is really the ONLY benefit for this particular application. For the $, most are better off using the largest mild DOM they can fit especially due to the fact that thick wall 4130 is hard to find and VERY expensive.

We're not building bridges here, we're building a simple suspension link for a realitively light rig.

Simple cost comparison:

2" OD 1/8" wall 4130 ~ $15.50 a foot

2" OD 1/8" wall mild DOM ~ $8.80 a foot

2" OD 5/16" wall mild DOM ~ $15.50 a foot

Which would you rather have?

Well that is the thing if i had to pay normal price for Chromoly then ya, i would defiantly be going with DOM, but since i can get it at a fraction of the cost.....That is why i'm leaning toward the chromoly, for strength but also for cost.

 

[Weasel]

if it's a steal go with it.

 

[Boostwerks.com]

if it's a steal go with it.

Agreed. :viking:

 

[Goatman]

As for welding the metal cannot cool fast enough to get brittle, steel is not thick enough. We've welded 12 race chassis with 4130 and ER70 rod and had zero issues period.

Not true. I've seen a number of chromo links fail right at the edge of the weld, on good looking welds. I'll stick with common welding wisdom and personal experience. Also, a complete chassis that uses plenty of structure for strength isn't the same as a link arm that is totally dependant on the strength of the weld. For us garage guys, DOM is a safer choice for links, and plenty strong enough if the proper material is used.

Now, I do need to qualify my statement, since all four of my lower links are heat treated chomemoly. Six of the eight ends are swedged and threaded, which is very strong, and of the two ends that are welded in threaded inserts one of them has broken from smacking down hard on rocks. The welds are good and were cooled slowly, but it broke right at the edge of the weld and ripped the insert apart since the rossette welds held.

I like chromo links for the lighter weight and strength, but I don't like the risk of welds on threaded inserts breaking on 3 link suspensions.

 

[Weasel]

Now, I do need to qualify my statement, since all four of my lower links are heat treated chomemoly. Six of the eight ends are swedged and threaded, which is very strong, and of the two ends that are welded in threaded inserts one of them has broken from smacking down hard on rocks. The welds are good and were cooled slowly, but it broke right at the edge of the weld and ripped the insert apart since the rossette welds held.

Hmm maybe I'm not understanding correctly but if it's breaking outside the weld isn't that where is should break in the Haz zone? Or is it at the root of the weld.

If the DOM links don't do it then maybe there is a way to blub up the weld, I've never seen it done on the many sets of arms we have built or saw built.

 

[Goatman]

Hmm maybe I'm not understanding correctly but if it's breaking outside the weld isn't that where is should break in the Haz zone? Or is it at the root of the weld.

If the DOM links don't do it then maybe there is a way to blub up the weld, I've never seen it done on the many sets of arms we have built or saw built.

I don't really know, and I'm far from a welding expert. What's blub up the weld?

Like I said, I like chromo links, but for the average welder I'd recommend DOM, based on my personal experience and what I understand about welding chromoly. From what I've read, chromoly while stronger is inherently more brittle, and can eventually fail due to cycling forces and stress cracks before DOM would.......even in a chassis. It's strength comes at a price, and it takes a certain degree of expertice to work with it......which I wish I had.

 

[Weasel]

blub = flub

Chromo can form martensite but it's typically id the weld bead is also 4130, ER70-S2 shouldn't. I suppose the haz zone could become brittle but it would have to have a pretty quick cooling rate.

And no it shouldn't be inheriantly more brittle. That depends on the RC hardness, if under 45 RC it should be tougher then anything else. Over it gets pretty brittle.

And again with the right filler even a chassis should be fine. The only time we have ever had issues with our chassis if it wasn't stiff enough and moving 1-1.5" while racing.

Definatly a few issues to consider and be aware of.

 

[XJ_ranger]

Chromo can form martensite but it's typically id the weld bead is also 4130, ER70-S2 shouldn't. I suppose the haz zone could become brittle but it would have to have a pretty quick cooling rate.

come on Craig - HAZ = Heat Affected Zone...

HAZ Zone makes no sense!

 

[Sherman_thetank]

Ok, so basically chromoly is stronger but has more tendency to fail at the weld vs DON...is there any way to really correct that problem od this that just the price you pay from the strength?

 

[XJ_ranger]

Ok, so basically chromoly is stronger but has more tendency to fail at the weld vs DON...is there any way to really correct that problem od this that just the price you pay from the strength?

yeah - you have to weld it the right way, with the right filler rod...

and have all the pieces be chromo, so you're not trying to pull off a bi-metalic weld...

so get some 4130, 4140, 4340 - whatever material you're getting for 'cheap' and then buy some of the same material solid round stock, make friends with someone with a lathe, and make some bungs...

OR -

just get it the right size to thread without the need for bungs...

 

[Sherman_thetank]

yeah - you have to weld it the right way, with the right filler rod...

and have all the pieces be chromo, so you're not trying to pull off a bi-metalic weld...

so get some 4130, 4140, 4340 - whatever material you're getting for 'cheap' and then buy some of the same material solid round stock, make friends with someone with a lathe, and make some bungs...

OR -

just get it the right size to thread without the need for bungs...

Yes, i was planning on getting these to go with the links
http://www.ruffstuffspecialties.com/catalog/chromo-adapter-p-318.html

 

[JeepFreak21]

come on Craig - HAZ = Heat Affected Zone...

HAZ Zone makes no sense!

Doesn't that depend on the VIN number of the vehicle?

Billy

 

[Goatman]

Doesn't that depend on the VIN number of the vehicle?

Billy

No.








It depends on the wheelbase.

 

[Weasel]

come on Craig - HAZ = Heat Affected Zone...

HAZ Zone makes no sense!

:twak: ouch