Chrome Moly vs. Mild Steel

ChromdOutDubs · Feb 6, 2008

I plan on making my own Lower Control Arms and i was just wondering how much of a difference there is in plain Mild Steel Tubing and Chrome Moly tubing. I see you can get both kinds on k-members but most of the control arms i see say they are made of Chrome Moly.

I want to use mild steel because i got tons of it at my fabrication shop and wouldn't be anything for me to make some up. If i went with Chrome Moly it would take some time for it to come in and also that stuff inst cheap at all!

Thanks

-AJ

347HO · Feb 6, 2008

Well... since you fabricate, then you know mild steel takes well to mig and chromolly does really well with tig.
I can tell you there is a considerable weight difference between the two when you weigh the finished products!
Don't forget to use the "seamless" stuff.
Just my thoughts... and they aint worth much.

88mouse · Feb 6, 2008

The chromooly will hold up to more abuse that the mild steel. But it will have to be tig welded.

ChromdOutDubs · Feb 6, 2008

Thanks for the info.... But iv been looking at the prices of rod ends and it might be almost as cheap to buy some built, lol. Those QA1 rod ends are ridiculous.

-AJ

Sicarius428 · Feb 7, 2008

Another thing to consider is if something were to happen, chromoly will just break and mild steel will have more give and bend. Definately get seamless.
Kevin

SVT32VDOHC · Feb 7, 2008

I have a customer who has a beautiful 66 GTO that he has spent his life building. Every year he has updated and upgraded parts. He has a motor that made about 700FTLBS of TQ. Anyways....all he talks about is chrome-moly this and chrome moly that. He swears buy it, but he also has over 100,000 in his car. I guess it depends what you are looking to do.

ChromdOutDubs · Feb 7, 2008

SVT32VDOHC said:
but he also has over 100,000 in his car.

Yeah me too, lol.

Ya i guess it is preference, im gonna go ahead and make them out of mild steel and if they break then i will go CM...

-AJ

SVT32VDOHC · Feb 7, 2008

ChromdOutDubs said:
Yeah me too, lol.

Ya i guess it is preference, im gonna go ahead and make them out of mild steel and if they break then i will go CM...

-AJ

Really? DAMN!!! In that case get the moly!!

Mike85000 · Feb 7, 2008

The way i see it is Chromoly has a much higher UTS and USS. THerefore you can use less material when constructed from chromoly. Or if both piece are the same dimensions, the Chromoly will be much stronger than the MS.

Id say a properly designed set constructed of mild steel would be fine. But remember to factor in the strength of the material when selecting a tubing size.

ChromdOutDubs · Feb 7, 2008

I was going to use 1-5/8" Tubing with .120" Wall Thickness. I could make it out of solid Mild Steel Shaft, that would actually be the easiest and strongest but the weight would be the only issue. But for an extra 5-10 lbs it probably wont even matter.

-AJ

Mike85000 · Feb 7, 2008

I wouldn't go soild stock. Tubing has a larger bending moment for a given amount of material than a solid piece. Solid would be quite heavy. Just take a look at what the aftermarket company's are using. If the suspension is setup properly most of the loading should be tension and compression, not bending. For 1 5/8 tubing i'd venture a guess that.250 wall would be more than enough. What kind of torque numbers are you running? THis is a street/strip car right?

347HO · Feb 8, 2008

1 5/8" appears a bit large????

millhouse · Feb 8, 2008

I think some are confusing strong for more rigid. While chromoly is by far more rigid...it's that rigidity that makes it more brital. That birtalness is what will make it far more prone to failing during street use. You'll find that quite a few places will recommend chromoly suspension components for track use only...as they won't see many of the daily impacts that you would on the road.

samickguy15 · Feb 8, 2008

347HO said:
1 5/8" appears a bit large????

X2

I would go to a local speed shop or a buddies house with some tubular arms and reverse engineer them. Either that or do the stress/strain and bending moment calculations.

347HO · Feb 8, 2008

millhouse said:
I think some are confusing strong for more rigid. While chromoly is by far more rigid...it's that rigidity that makes it more brital. That birtalness is what will make it far more prone to failing during street use. You'll find that quite a few places will recommend chromoly suspension components for track use only...as they won't see many of the daily impacts that you would on the road.

Seamless Chromolly is far, far superior to mild steel anywhere as to wall thickness being equal. You will not find very much mild steel in high performance, professional race cars pertaining to suspension and chassis components.

vristang · Feb 8, 2008

millhouse said:
I think some are confusing strong for more rigid. While chromoly is by far more rigid...it's that rigidity that makes it more brital. That birtalness is what will make it far more prone to failing during street use. You'll find that quite a few places will recommend chromoly suspension components for track use only...as they won't see many of the daily impacts that you would on the road.

Nothing personal against you, but I do have a different perspective.

Along with the rigidity comes higher fatigue resistance...
Having a crack propagate through a part slowly isn't any better than having a crack propagate quickly through a part.

Either way the part has failed.
BUT, the chromoly will withstand higher cyclic loads before a crack develops.....
(or it will last for a longer cycle count at the same loads )

My opinion... chomoly is less often used on the street because of the cost associated with its use.

Whenever possible, use the best materials you can

jason

millhouse · Feb 8, 2008

vristang said:
Nothing personal against you, but I do have a different perspective.

Along with the rigidity comes higher fatigue resistance...
Having a crack propagate through a part slowly isn't any better than having a crack propagate quickly through a part.

Either way the part has failed.
BUT, the chromoly will withstand higher cyclic loads before a crack develops.....
(or it will last for a longer cycle count at the same loads )

My opinion... chomoly is less often used on the street because of the cost associated with its use.

Whenever possible, use the best materials you can

jason

None taken.

My whole point however is what may cause a thin walled chromoly part crack can cause the thicker walled mild steel to flex....or in the worse case, bend. It's chromoly's rigidity which is it's weakness in high impact situations.

Really, I never saw a huge price difference in manufacturers offering offering both mild and chromoly.

ACSPONY · Feb 9, 2008

samickguy15 said:
X2

I would go to a local speed shop or a buddies house with some tubular arms and reverse engineer them. Either that or do the stress/strain and bending moment calculations.

Are you an engineer by chance? I was about to check out the elastic modulus on Chrome-Moly vs Steel

347HO · Feb 9, 2008

ACSPONY said:
Are you an engineer by chance? I was about to check out the elastic modulus on Chrome-Moly vs Steel

Get with vristang. He does all that crazy stuff with metal alloys and whatnot.
I believe he's a metals engineer for some large aircraft manufacturer.

vristang · Feb 9, 2008

347HO said:
Get with vristang. He does all that crazy stuff with metal alloys and whatnot.
I believe he's a metals engineer for some large aircraft manufacturer.

lol
I thought about posting some numbers, but it's tough to do a fair comparison when you don't know exactly what how the finishing is done.
heat treatments, manufacturers, etc.

I'll try to find some representative numbers on the net (that we can link to) later today (unless someone can beat me to it )
Usually google comes up with a decent variety...

jason

EDIT:
I don't engineer stuff, I just test stuff.
Cyclic loading and static loading to failure.

Chrome Moly vs. Mild Steel

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