the truth about mild vs. chromemoly steel
11-07-2007, 10:53 AM
#1
the truth about mild vs. chromemoly steel several people over the years have inquired about the weight differences between these two metals. when somebody states the fact that a particular component is lighter weight due to it being constructed of chromemoly(vs. mild steel) they are for the most part *wrong*. the two materials are the same mass for equal amounts of whatever part.
this misconception is largely due to the NHRA rules of rollcage specs. people say that its lighter because its moly, well true, compared to the same NHRA legal spec between the two materials. heres why. on the spec'd tubes in a roll cage NHRA minimum wall thickness is .083 for chromemoly, .118 for mild steel. this is per the sonic wall test equipment that the certification members use. the difference in weight between the two is the wall thickness, not the mass of the material. it takes that much more mild steel to be comparable in strength to 4130N chromemoly tube. I do not claim to be a metalurgist, but i've been in this business long enough and built enough cars that i can tell you this.
depending on manufacturers, some choose to use different grades of mild steel. the two most common used in roll cages are 1020 DOM, and ERW commonly called electraweld. DOM tubing keeps a much better manufacturing tolerance than ERW, therefore a thinner wall will certify. ERW cages most often use .134 wall tubing to be able to certify. prices of the material are as expected with this. moly is the most costly, followed by DOM, then ERW.
the bigest difference between the mild steel and the chromemoly material is strength. the 4130 chromemoly(normalized material) compared to 1010 or 1020 mild is much stronger, due to a hardening process, and the alloy composition of the steel. two identical pieces of material, the moly will be stronger than the mild steel and WEIGH THE SAME!
In the end... don't be fooled by a person trying to sell a component that is lighter because its made from chromemoly. call the manufacturer and get the facts!
this misconception is largely due to the NHRA rules of rollcage specs. people say that its lighter because its moly, well true, compared to the same NHRA legal spec between the two materials. heres why. on the spec'd tubes in a roll cage NHRA minimum wall thickness is .083 for chromemoly, .118 for mild steel. this is per the sonic wall test equipment that the certification members use. the difference in weight between the two is the wall thickness, not the mass of the material. it takes that much more mild steel to be comparable in strength to 4130N chromemoly tube. I do not claim to be a metalurgist, but i've been in this business long enough and built enough cars that i can tell you this.
depending on manufacturers, some choose to use different grades of mild steel. the two most common used in roll cages are 1020 DOM, and ERW commonly called electraweld. DOM tubing keeps a much better manufacturing tolerance than ERW, therefore a thinner wall will certify. ERW cages most often use .134 wall tubing to be able to certify. prices of the material are as expected with this. moly is the most costly, followed by DOM, then ERW.
the bigest difference between the mild steel and the chromemoly material is strength. the 4130 chromemoly(normalized material) compared to 1010 or 1020 mild is much stronger, due to a hardening process, and the alloy composition of the steel. two identical pieces of material, the moly will be stronger than the mild steel and WEIGH THE SAME!
In the end... don't be fooled by a person trying to sell a component that is lighter because its made from chromemoly. call the manufacturer and get the facts!
11-07-2007, 08:23 PM
#12
When inquiring about suspension components, be sure to ask about the wall thickness. Moly parts are often made thinner for weight reasons, but long term durability can be compromised.
Stronger alloys, (such as moly) can often fracture, whereas mild steel will usually bend first. Something to keep in mind on a street car. I would rather bend a front lower control arm on a pothole, instead of breaking one in half. This is not to say lightweight moly is dangerous on the street, but it should be used with caution & inspected often in the area of the welds.
For reference, my car has all moly suspension, so I am not speaking against it. I would use mild steel on a daily driver though.
I have broken moly torque arms... (a now discontinued FlowTech model) not a fun experience on the street when it rips the rear brake hose off & the DS loop gouges your driveshaft. At least the loop kept it from hitting the ground... that could have been real bad.
Moral of the story, if you cannot afford good chassis components, do not buy cheap stuff. On the street, get the extreme duty parts for your protection.
Stronger alloys, (such as moly) can often fracture, whereas mild steel will usually bend first. Something to keep in mind on a street car. I would rather bend a front lower control arm on a pothole, instead of breaking one in half. This is not to say lightweight moly is dangerous on the street, but it should be used with caution & inspected often in the area of the welds.
For reference, my car has all moly suspension, so I am not speaking against it. I would use mild steel on a daily driver though.
I have broken moly torque arms... (a now discontinued FlowTech model) not a fun experience on the street when it rips the rear brake hose off & the DS loop gouges your driveshaft. At least the loop kept it from hitting the ground... that could have been real bad.
Moral of the story, if you cannot afford good chassis components, do not buy cheap stuff. On the street, get the extreme duty parts for your protection.
11-08-2007, 10:01 AM
#14
well put Lonnie...
and as far as that goes, if someone want to look at or buy any particular chromemoly component, make sure it is TIG welded. chromemoly amd MIG welding are not happy together, and for that matter, is against NHRA rules.
SSOTRUE... I'm a racer doing things for racers, so expect nothing less. taking care of my customers is #1.
and as far as that goes, if someone want to look at or buy any particular chromemoly component, make sure it is TIG welded. chromemoly amd MIG welding are not happy together, and for that matter, is against NHRA rules.
SSOTRUE... I'm a racer doing things for racers, so expect nothing less. taking care of my customers is #1.
11-12-2007, 01:19 PM
#16
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I'm guessing this is exactly why chromoly cages are verboten by SCCA rules?? Maybe they are worried about the multiple impacts that often happen in road racing vs. the (usually) single impacts that occur in NHRA drag racing?
11-11-2014, 08:28 PM
#18
TECH Enthusiast
4130 chrome-moly steel:
The ‘41’ indicates a low alloy steel containing chromium and molybdenum and the ‘30’ indicates a carbon content of 0.30 percent. Below is a table showing the chemical composition of 4130 Chrome-Moly shown in percentages.
Carbon 0.28 – 0.33
Chromium 0.8 – 1.1
Manganese 0.7 – 0.9
Molybdenum 0.15 – 0.25
Phosphorus 0.035 max
Silicon 0.15 – 0.35
Sulphur 0.04 max
It doesn't take much chrome or moly to alter the property of the steel. In the boilers I used to operate P22 chrome-moly tube was used in the hottest parts of the boiler where superheated steam was running through the tubes (2-1/4% chrome - 1% moly). There's many variations of Cr-Mo to suit your specific needs for chemical resistance, corrosion, higher temperature resistance, strength, etc.
The ‘41’ indicates a low alloy steel containing chromium and molybdenum and the ‘30’ indicates a carbon content of 0.30 percent. Below is a table showing the chemical composition of 4130 Chrome-Moly shown in percentages.
Carbon 0.28 – 0.33
Chromium 0.8 – 1.1
Manganese 0.7 – 0.9
Molybdenum 0.15 – 0.25
Phosphorus 0.035 max
Silicon 0.15 – 0.35
Sulphur 0.04 max
It doesn't take much chrome or moly to alter the property of the steel. In the boilers I used to operate P22 chrome-moly tube was used in the hottest parts of the boiler where superheated steam was running through the tubes (2-1/4% chrome - 1% moly). There's many variations of Cr-Mo to suit your specific needs for chemical resistance, corrosion, higher temperature resistance, strength, etc.
Last edited by Firebrian; 11-11-2014 at 08:34 PM.
