Built LT1

Anyone know of light weight subframes? made of chromoly or aluminum?

hotpart

Chrome Moly tube is the same weight as typical mild steel. The only advantage you have is if the part is designed and manufactured properly using chrome moly steel you can use thinner wall material to achieve the same strength. I will tell you be very careful when thinking about using chrome moly in any critical suspension components. Many suppliers will tell you it is fine as long as you tig weld it well they are lying to you. Chrome moly after welding needs to be stress relieved and heat treated. If the heat treat and stress relieving process is not done you will have a very expensive part which is only as strong as mild steel with very brittle and potentially hazardous weld area.

Built LT1

Thanks for the info. I guess I won't be using a chromoly subframe. Do you know of the lightest subframe offered however? I'm trying to cut weight in all potential areas.

hotpart

Our round tube subframe connectors weigh in at 14.5 pounds for the pair. This is the link to see them. The link is for the black version. They are also available in red.

http://www.hotpart.com/index.php?p=show&id=32

smoknta

Stress relieving Chrome-moly welds is only recommended on parts thicker than 0.120". You dont have to stress relieve thinner parts. Have you ever tried stress relieving a Chrome-moly roll cage that has been installed in car? Ya cant do it. As long as you use the right filler metal and know how to weld, there is no reason you cant use Chrome-moly on suspension parts. I would not recommend them for subframes, because you would have to weld them to the mild steel chassis. But there is no reason you cant use it for panhard bars and control arms.

NOSCaMaRo

Yes exactly, with the correct welding rod and thickness 4130 can be used with out heat treating or stress releiving. I would not recommend chrome moly SFC's though. Just go with the mild steel version.

hotpart

You are correct you can weld 4130 chrome moly and get away without stress relieving and heat treating but you end up with a part which is only as strong as 1020 or 1018 mild steel. Normalized 4130 yield strength is around 75,000 psi and in an annealed state the yield strength is down around 65,000 psi. Cold drawn 1020 and 1018 yield strength is around 70,000 psi and does not loose strength during the welding process. The only way for 4130 to get the strength back after welding is to stress relieve and then heat treat it. The great thing about 4130 is once the assembly is welded you can heat treat the material to above its base strength of 75,000 psi but I don't know of any aftermarket company willing to spend the money to do that let alone just stress relieve and heat treat it period.

The following is a quote from a great engineer named Carroll Smith out of his book Engineer to Win.

“SAE 4130 Best known of the family of CHROME-MOLY steels, 4130 is often considered, in racing circles, to be the ideal steel for all high-strength/high-stress applications. IT IS NOT! In thin sections (that is, in tube or sheet form) its unique combination of excellent tensile strength, toughness and response to mild heat treatment combined with its good formability in the annealed condition and its outstanding welding characteristics make it virtually unbeatable for fabrications subject to high stress levels. It is critical that all welds be stress relieved. I prefer the use of OXWELD 32 CMS welding rod with 4130 for the simple reason that it both normalizes and heat treats well in conjunction with 4130. Many welders prefer to use a stainless rod, but the high nickel content of stainless welding rods means that the weldment will not respond well to heat treatment. Since I believe that not heat treating 4130 fabrications is DUMB (if you don’t heat treat you end up with an expensive part with the same strength as 1020 – and brittle weld areas), Smith’s law says to use the heat-treatable rod for EVERYTHING. I heat treat 4130 fabrications to Rock-well C Scale 26 to 30 and no higher. This results in an ultimate tensile strength of about 130,000 psi with sufficient ductility that I do not have to worry about brittle parts.

The other side of the 4130 coin, often unknown to (or at least unappreciated by) the racer, is that it possesses poor deep-heat-treating characteristics and has an inborn dislike of varying cross-sections. These characteristics make 4130 a poor choice for machined or forged parts – it doesn’t forge very well anyway. It also doesn’t machine very well, at least in the normalized condition – to gummy. Those people who make hubs, steering knuckles and the like from 4130 are kidding themselves – and their customers. It doesn’t make very good shafts, either, as in drive shaft, or axle, or torsion bar.”

I would recommend picking up this book as it will also go into depth of the crystalline structure of different materials and what effect welding has on them.

smoknta

I guess everyone out there using it for roll-cages are just doing it because they have some extra money to blow. What are you going to do, heat treat the whole car. I do agree it is best the heat treat if you can, but I believe if the right filler metal is used you can get stronger welds and a stronger piece than 1020. 4130 has been used for years in the aerospace and aircraft industries for years without heat treating on thin walled material. There is even info on Lincoln Electrics website about welding chome-moly. They also say that heat-treating material under .120" is not necessary as long as the right weld process is followed.