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Originally Posted by chicane
Any real reason to why you want ChroMo other than to say its made of ChroMo ??
What kind of events are you considering and which sanctioning body are your rules from ??
I only ask because there is no benifit to using ChroMo unless you heat treat the finished product... and in the fashion of a tubular cage... that would mean that you would have to heat treat the entire chassis, which... isnt going to be done. Not to mention that unless you properly preheat the material before weldment and normalize the material after... there is absolutely no benifit to using ChroMo. The extra expense in material cost yields you zero...
A bit of advise ?? I would pick up a copy of Carroll Smith's "Engineer to Win" and then make your determination on what material you should purchase. In fact... if you are going to be doing any kind of motorsport... I would highly recommend that you purchase his whole line of books... trust me, after you read them... you will look at things in a whole 'nother light. >> Click here <<
I believe... that you would be much better off with using 1018 or 1020 DOM. Especially considering inch and five eighths... o-nine five. That is considered to be the absolute bare minimum size/dia in chassis weights under 3000 to 3200 lbs. Not to forget to mention... in the science of safety... the majority of sanc bodies are making the move towards DOM over that of ChroMo in a unitized chassis. Just the mere fact of 4130/N weld embrittlement would make me run the other way.
Im not saying that ChroMo doesnt have its place, because it sure does and I like to use it myself... but definately not in a unitized chassis. If you built the entire chassis out of ChroMo and had the entire chassis heat treated... I would be all over that !! But... the truth of the matter is, that it is not going to happen.
Educate yourself now... before you make a possible mistake. 
Aircraft Spruce, Industrial Metal Supply, Metals Depot, All Metals Inc, Online Metals... all of which can ship or source the materials you need and in some instances, even locally to you. |
You don't need to heat treat 4130/N. The problem is people TIG it and don't pre-heat and post heat to normalize the weld. The heat is so concentrated in MIG and TIG, the welded area is heat treated and needs to be normalized to prevent failure right next to the weld. I have been welding 4130/N for years on vintage airplanes and only gas weld it to prevent embrittlement. It becomes much harder to gas weld large tubing and keep the heat in it so TIG works much better. However extra steps in pre and post heat have to be taken to prevent the embrittlement.
The only real gain to using 4130 is weight savings. Due to its higher strength than DOM, you can run lighter wall tubing. If you are just running a 4 point, I don't think it is worth it, but if you are building an entire cage, I would go the extra to use 4130.