Thoughts and opinions for 309L on chromoly tube chassis.

By Kix

Date 04-09-2008 13:00

I went to a race shop the other day where they fabricate and build off road baja and pre-runner race trucks. This was a well-known race team in the industry and they had some amazing trucks. The welds where some of the most beautiful welds I've ever seen on tube chassis. Anyway, they where welding 4130 chromoly tubing with 309L stainless wire. It looked really good, but I was wondering why you guys think they might be doing this. NHRA stipulates that all the chassis must be welded with ER70S-2 and maybe some are still using ER80S-D2. I just wanted to pick everyone's brain. Cheers!!

By GRoberts (***)

Date 04-09-2008 19:09

My guess is that with off-road chassis, they are probably looking for some extra ductility to help reduce incidences of cracking.

By James Corbin (**)

Date 04-10-2008 18:59

Just a thought
ER80S-B2 or ER70S-B2L --- Both have a Cr of 1.2 - 1.5 and a Mo of .4 - .65 which would match the 4140 better with Cr of .8 - 1.1 and Mo of .4 - .65
I would think the 309 would have too much Chromium

Again just a thought

By GRoberts (***)

Date 04-10-2008 19:24

The B2 series of filler metals are intended for use with PWHT, and high temperature applications. Since PWHT is not normally done on chassis, then B2 will be hard and brittle.

With HSLA steel containing Cr and Mo, you are not trying to match the chemistry. What chemistry works well for base metal often doesn't work very well for filler metal.

The 309 does have significantly more Cr than the base metal, but it also has significant amounts of Ni, which render it austenitic, and therefore ductile and crack resistant. The 309 seems like it could be overkill, but compared to the price of a chassis, overkill on filler metal will cost you pennies compared to the cost of a failure.