Chrome Moly or Mild Steel

[dtchdiger]

What is the difference between chrome moly and mild steel frames?

[Graff Spee]

One is lighter and tends to crack more than the other. LOL

[talclipse]

Chrome moly (typically 4130) has approximately 1 percent chromium and 0.2 percent molybdenum. These two elements make chrome moly what it is. These elements provide additional strength and "memory" to the tubing.

MS has at most trace amounts of these two elements in it. Making it lighter; but, weaker.

In order to have the same strength between CM and MS you would need to make the MS tubing thicker and it would still have the tendency to crack with cyclical loading. (CM can have the same tendency if not welded/ stress relieved properly.)

Most chassis builders do not increase the tubing thickness of their MS stuff so the CM cars are typically heavier but are much more durable. Due to their rigidity they have a narrower "sweet spot" than an MS car has but the CM cars generally last longer and age better.

Minor weld repairs are the same for both CM and MS chassis (you need to be conscience of how much heat you put into the piece as well as how quickly it cools).

[MasterSbilt_Racer]

I was under the impression that builders did reduce wall thickness when using chrome moly?

If you have two pieces of tubing of the same diameter and wall thickness (one mild steel and one moly), they will weigh basically the same. (The differences are very small). Both tubes will have essentially the same stiffness. The difference is how much force it takes to permanently deform the two tubes. The chrome moly will take more force to permanently deform it.

[MasterSbilt_Racer]

For the engineering minds, here are links to some properties.

4130 quenched
http://www.matweb.com/search/DataSheet.aspx?MatGUID=bcb1f2dd2fc347d38abfd357bb2 f33d9&ckck=1

1026 cold drawn
http://www.matweb.com/search/DataSheet.aspx?MatGUID=f3c08781eced413ebd167d9a9d1 211f2

Compare density (to get weight), elastic modulus(to get stiffness), and yield strength(to see when it is permanently deformed)

[talclipse]

Thanks for the correction.

I guess I shouldn't have based my statement on such a narrow scope.

[billetbirdcage]

For the engineering minds, here are links to some properties.

4130 quenched
http://www.matweb.com/search/DataSheet.aspx?MatGUID=bcb1f2dd2fc347d38abfd357bb2 f33d9&ckck=1

1026 cold drawn
http://www.matweb.com/search/DataSheet.aspx?MatGUID=f3c08781eced413ebd167d9a9d1 211f2

Compare density (to get weight), elastic modulus(to get stiffness), and yield strength(to see when it is permanently deformed)

Didn't read 100%, but moly used in racecar construction is not quenched it is used in annealed condition. 1020 is much more commonly used then 1026 on the mild steel.

Typical listing on strengths are; 80 KSI tensile for 1020 DOM and 90 KSI for 4130 CDS/NORM

Should also add MS and moly weight the same, if same size and thickness they will be the same weight. You get the weight savings from using thinner tubing on the moly as it's stronger and can be thinner to get the same strength. It depends on the manufacturer, but usually a moly car may have thinner tubing usually one wall thickness size (like .083 verses .095).

[MasterSbilt_Racer]

Didn't read 100%, but moly used in racecar construction is not quenched it is used in annealed condition. 1020 is much more commonly used then 1026 on the mild steel.

Typical listing on strengths are; 80 KSI tensile for 1020 DOM and 90 KSI for 4130 CDS/NORM

Thanks Billet. I just pulled some versions of the materials and went with it. They were not for tubing. It was just to give an idea.

[billetbirdcage]

Even looking up different brands, you will see some variance in the rating on tubing. I've seen anywhere from 70 to 80 on 1020 and 85 to 90 on 4130N

A side note: the welded seam tubing (1010 CREW or HREW) is only 55 KSI. This is a huge difference over 1020 DOM and why it shouldn't be used in a racecar unless in a non critical point. Yes, it's cheap but getting close to half the strength of DOM or Moly.

[andy16]

chrome moly will always be better for any chassis. the difference in practical terms are as follows

1- it is stronger in every way so it can be lighter because its strong.

2- it has "memory" meaning it can flex and return to original shape more. mild steel bends and does not flex back. when you bend chrome moly in a bender it flexes back way more...so CHASSIS builders have to work harder.

3- Chrome moly when welded ALWAYS should be tig welded. mild steel can be mig welded... so CHASSIS builders have to work harder. then after welding, the area around the weld must be stress relieved by a TORCH lol not the powder coating oven ??? so Chassis builder works harder.

4-Tubing selection is important. the way it is quenched is most impotant. some tubes are dipped into water some tubes are sprayed w water. the ones sprayed w water are very inconsistant and prone to cracking because it was not cooled corectly.(used in construction not motorsports or aviation) the ones dipped in water are the ones made for constant stressing and flexing specifically for boeing(aviation and motorsports)... but they cost more than the other china steel so... CHASSIS builder works harder

5- so the biggest difference in the two are how hard the chassis builder has to work and for what... cars that last 4-5-6 yrs like brand new having to stress relieve every weld more time on the bender more expensive tubing its just not cost effective for them.


The best chrome moly chassis builder iv ever known of is a guy named brad hadman. he has been buiding chrome moly chassis for 20 years and they are 100 % tig welded,stress relieved and last multiple years seeing 40+ races a year and most guys end up only getting front and rear clips. he had a problem w some tubing cracking like what you see in late models these days and traced it back to the quenching method. all chrome moly comes w a batch date and number printed on it and the class he builds for requires that information be kept for every chassis he builds.He knows more about chrome moly in motorsports than anyone hands down.

so... currently most chrome moly latemodel chassis are being built wrong and these guys know it. they dont want to build them its too much work compared to the mild steel ones and in the end will cause cars to last longer. why would they wanna do that? prob why bloomquist has his rules about his cars, because they are built right.

[MasterSbilt_Racer]

chrome moly will always be better for any chassis. the difference in practical terms are as follows

1- it is stronger in every way so it can be lighter because its strong.

2- it has "memory" meaning it can flex and return to original shape more. mild steel bends and does not flex back. when you bend chrome moly in a bender it flexes back way more...so CHASSIS builders have to work harder.

3- Chrome moly when welded ALWAYS should be tig welded. mild steel can be mig welded... so CHASSIS builders have to work harder. then after welding, the area around the weld must be stress relieved by a TORCH lol not the powder coating oven ??? so Chassis builder works harder.

4-Tubing selection is important. the way it is quenched is most impotant. some tubes are dipped into water some tubes are sprayed w water. the ones sprayed w water are very inconsistant and prone to cracking because it was not cooled corectly.(used in construction not motorsports or aviation) the ones dipped in water are the ones made for constant stressing and flexing specifically for boeing(aviation and motorsports)... but they cost more than the other china steel so... CHASSIS builder works harder

5- so the biggest difference in the two are how hard the chassis builder has to work and for what... cars that last 4-5-6 yrs like brand new having to stress relieve every weld more time on the bender more expensive tubing its just not cost effective for them.


The best chrome moly chassis builder iv ever known of is a guy named brad hadman. he has been buiding chrome moly chassis for 20 years and they are 100 % tig welded,stress relieved and last multiple years seeing 40+ races a year and most guys end up only getting front and rear clips. he had a problem w some tubing cracking like what you see in late models these days and traced it back to the quenching method. all chrome moly comes w a batch date and number printed on it and the class he builds for requires that information be kept for every chassis he builds.He knows more about chrome moly in motorsports than anyone hands down.

so... currently most chrome moly latemodel chassis are being built wrong and these guys know it. they dont want to build them its too much work compared to the mild steel ones and in the end will cause cars to last longer. why would they wanna do that? prob why bloomquist has his rules about his cars, because they are built right.

A chassis should be built with an adequate stiffness in mind. Since the stiffness is the same, moly is unnecessary. We cannot take advantage of thinner moly tubing in that case because stiffness would be reduced. It can be justified in the safety portion of the chassis (cage) because of it's extra ultimate strength that would protect the driver in a violent impact.

Chassis break because they have areas that are not stiff enough. The stress is too high at those points.

It is harder to bend because of the higher yield/ultimate strength.

I agree that builders don't correctly use moly. The chassis should be normalized after welding to keep the heat affected zone from becoming too brittle.

[andy16]

the advantage these cars should have when built properly is the ability to flex the same and have the same stress as mild steel but return to original shape more effectively. prolonging the cars "useful" life . the stress on the tubing hasn changed if the structure of the car hasn changed. and personally i wouldn go to a thinner wall. i dont want a lighter chassis i want a longer life.

what has any late model chassis builder said about chrome moly? except they dont feel its necesary? they dont want to use it its a loss for them.

[andy16]

hadmans cars flex six to eight inches every lap. hasn had one break since 2006. and those were due to tubing flaws. if those cars can flex that much and not break were doing somethin way wrong. im just sayin before we blame the tubing lets look at the whole picture. grt actually tigs theres for the last few years he is learning. if it wasn better boeing, the military, and countless aviation frames wouldn be made of it.

[MasterSbilt_Racer]

My point is that a chassis that flexes is a poor chassis. It is doing what the springs should be doing. The chassis should have a much higher torsional rigidity than the suspension tied to it. If it does, it won't flex and moly wont give you a significant increase in fatigue life.

[andy16]

his car is designed to flex and holds many records but its not a circle track car so i wont mention him anymore. the point is all cars flex and deflect. i agree from a egineering standpoint the most rigid chassis is best. but the track unfortunately disagrees. these cars get less and less tubes and smaller and smaller tubes every year. in my humble opinion the difference in a identically built moly car and a dom car is the dom car will permanantly warp from inevitible chassis flex considerably sooner than a properly built moly car. to aswer the mans question . im tired of typing for today...

[sj valley dave]

Brad Hadman builds Top Fuel cars...They have to arch up as that is built into them...He builds some of the very best TF chassis around...McKinney does also! These cars are 300" wheelbase, don't forget!