Hello. I'm about to set myself into the guidlines and SFI specifications. A litle local debate about the chrome moly SAE 4130 spec's. What are the diffrence between chrome moly 4130 and Super Duplex 2507? looking at each content, i can see that Super Duplex has less Carbon and more Chrome. So Super Dubplex has less corrosion. .............................. Taildragger&fenderless
The percentage of carbon determines the hardenability, more carbon will achieve a higher hardness when heat treated or welded. Hardness is directly related to tensile strength. 4130 was widely used in the early days of acetylene welding airframes together because the welds were not brittle. Corrosion wasn't an issue at the time. Pat
Thanks Pat I have forwarded the question to SFI. Chrome moly 4130 is hard to come by localy, but could get the Super Duplex. Br Kjell .............................. Taildragger&fenderless
....... and high tensile brazing too. While in the U.S. TIG welding of chrome-moly had become common, British and European race cars were still being brazed together well into the '60s or maybe even the '70s.
SFI specs have opened up in the past few years whereby you can use DOM as an alternative so if Xmoly is hard to get perhaps mild steel is doable.
Super Duplex 2507 is a type of stainless steel, it's great for the transfer of chemicals, but I wouldn't build a chassis out of it. What type of car are you building, and how fast will it be?
Thanks guy. What are DOM? ............................... The chassis is an older FED with chrome moly tubing. I need to do some changes. I have also heard that it's recomended to mount a new pipe inside existing "C" tubeing/hoop!? Any advice on this? Br Kjell ............................... Taildragger&fenderless
Mild steel 1020-1026 is commonly referred to as DOM. (drawn over mandrel) If the existing chassis is 4130, pretty much best to just have the material shipped in. If you need bends made, there are many who can do this and ship. Drawings or sketches work. I used to make sections for some people's race cars who supplied electrical conduit samples (soft stl tube, cheap). J
Mild steel tube is available in several forms, including DOM. DOM(Drawn Over Mandrel) is quality mild steel tube that has been pulled over a mandrel. The process eliminates evidence of the weld and other imperfections, makes the dimensions of the tube more accurate, makes stresses in the tube symmetrical, and toughens the tube. It's pretty much the standard material for most roll bars, NASCAR chassis, and general fabrication of high quality structures.
Good explanation, DOM is a process 1020/1026 and 4130 or 4140 are the grade and chemical composition. If you order DOM you want to consider the thermal state you can get it as drawn or stress relieved annealed if your bending it I would go stress relieved annealed. If you go with Stainless wear a mask when welding the fumes are toxic.
Aircraft Spruce 1-877-477-7823 They have International reps that service Norway and a great source for C/M tubing and other materials. Not that it would matter in this case (or could) .The way tubing is checked by the chassie cert people is with a sonic tester that electronicly measures the wall thickness. All tubing made has different wall thickness by material used and that can be used as an indication---- C/M 1 1/2 x .120 vs. DOM 1 1/2 .125 vs. ERW 1 1/2 x .120(real measurment .114). If SFI specs C/M -- better be C/M welding stainless toxic? since when? maybe I dead already and dont know it
Chrome Moly is also offered in annealed version and that is what you want to use. In the late 1970's early 1980's there were sprint cars built with out the annealed or condition N tubing. Famous picture of I believe Van May at Syracuse, sp, the cage sheared off at the welds. As stated earlier gas weld or tig weld only.
Hopefully I am not moving off topic too far. I have an older car with a cage, is there a way to easily determine the material used in the original construction, ie Chrome Moly or DOM. I am asking in case I decide to add bars or other components to the cage? Jay
Sooooo, dont use brake clean,use only actetone or mek or a cleaner designed for stainless. Find someone with a sonic checker (call your local track and find out who does their chassie certs) or you can drill a hole and use a ball end depth mike(or calipers) to measure the difference between the od and the depth, Say the od is 1.75 and you measure the depth at 1.63 that gets me thinking towards C/M, if the depth is larger then i will lean towards ERW mild steel, and if the depth is less then would sway towards DOM. However with the price of DOM vs C/M being so close that I would doubht that it was used much and that racers went with ERW because it was cheaper.
Brake clean and TIG is a big no no. Brake clean when combined with argon makes phosgene gas...you know mustard gas. This is tig welding 101...Don't know about the mask, how about just not making phosgene to begin with.
My book specs .090 wall on C/M and .118 on DOM. I don't know anyone but circle track guys using ERW. You have to orient the seams when using ERW. Safer to use DOM. If weight is an issue, go C/M, but this stuff cracks. I ruined a chassis years ago trailering it to and from the track. Constant vibration and chassis movement. They make airbags now to place under the chassis when trailering...just my .02 worth. Craig
Probably the easiest way is how was it welded? If it's mig'd, probably DOM. If it's TIG'd, most likely C/M. I agree with having it sonic checked. Does it have an NHRA chassis cert sticker?
I hate to be a pain but DOM starts as a electric weld hollow and then is drawn over a mandrel and through a die, if you want DOM that is not from a erw hollow you have to but seamless and chrome moly does not designate the product as DOM it refers to chemistry.
I don't know if the sonic test for wall thickness would work. DOM tube has a +.002/-.004 wall thickness tolerance. (.06-.125 wall dim) Cold drawn alloy, 4130 etc. has a nominal wall tolerance of 10% or 7.5% depending on ID. this info from Jorgensen steel stock list/reference book I can measure some random pcs in the shop later if anybody cares. John
This is an old SCCA race car. It could have been built with either material. I'll check the wall thickness. Thanks for all the replies.
Thickness wont specify grade, I understand you are trying to correlate the two but to be certain you would need to test it. Eiter a small sample for a chemistry met test or a met guy could do a spark test. I did see something intresting recently it was a hand held tester. http://www.youtube.com/watch?v=ezmQz8-ZhGA
There are two ways you can check to find out. The first way is to get a small, sharp drill bit, and drill a hole through a piece of mild steel tubing, then drill a hole in the tube you want to test (Chrome Moly will be naturaly harder to drill than mild steel). The second way (and probably the best way) is to use an automatic center punch tool, the center punch tool will of course make a deeper mark in Mild steel than Chrome Moly. An automatic center punch tool.
Being SCCA I would be about 90% confident it's mild steel DOM, unless it was a high dollar shop that threw away chassis' every year. If its an old car with track miles and was C/M, you would probably see stress cracks by all the welds or signs of repairs. C/M doesn't like to be cycled, and a RR car cycles the crap out of tubing. Craig
To check cm/dom get a guy that knows how to use a sonic tester, cm is so precise that a stick of say 1X.058 will let a stick of 7/8X.058 will let a stick of 3/4X.058 - etc all the way down to 1/4" and sticks vary from 18' to 22' feet long - i think that works out to .009 clearances on the inside diameter. That is for milspec Xmoly and it'll be condition 'n'. Dom is relatively precise but not to those tolerances and a good man with a sonice checker can easily tell. I believe there is an acid they can swab xmoly with and it'll change color too. I find that 4130 drills easier than other metals because it is so clean and uniform, the drilling chips come up in a long spiral and you can keep a constant pressure and watch the drill bit sink right in. Other metals have surface tension and when you break thru that your penetration rate can speed up and you can have inconsistant spots where the metal coming up are more chips and flakes and then it'll toughen again as you break thru the other side. I might know a little more about xmoly but i forgot what it was...
We had some big problems with a thick fabricated Duplex SS parts. Zeron 100, maybe? The blades broke right off. Some geometry issues ( very restrained, which welded tubes cannot be) . Letting the interpass temperature get too high was probably part of the problem.
All my life Ive heard that CM must be gas or TIG welded. However when I googled it there was a long discussion about MIG welding on CM. This article was by a welding engineer and had references to NHRA ect. If I can find it again I will post it. I am by no means a welding expert just curious. Anyone have thoughts on this ?
There were a ton of off-road (BAJA 1000) chassies built by mig welding C/M with out any problems(Now that cycleing a chassie).
Most mass produced Kart chassis are mig welded chrome moly. There is some controversy about the tubing cracking/getting brittle a couple of inches away from the weld after the karts been raced for a few seasons.
On your thickness spec for NHRA cert chassis, DOM steel tubing has to sonic check .118" so the material thickness you have to buy is .125".
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