I'm contemplating welding a chrome moly brace onto my car's chassis, and I hear that the preferred method of welding for chrome moly is TIG, but I'm told by the workshop that it is better to use MIG welding for automobile chassis as the metal is rather thin. However I've also read that MIG uses very intense heat and the quick cooldown tends to result in more brittle joints. Hopefully some of you guys who know more about welding these materials together can advise me, thanks in advance!
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Welding a chrome moly brace onto a steel car chassis, TIG or MIG?
- Thread starter Gerald81
- Start date
In that case it is usually welded with TIG and a mild steel filler A15 or A18. No preheat, no post weld heat treatment. The weld will be thicker than the tube so it equalises out the difference in strength levels.
This is how they weld rally car roll cages etc, 4130 or T45 tubing
This is how they weld rally car roll cages etc, 4130 or T45 tubing
As you say MIG can result in more brittle joints than TIG which in turn can result in more brittle joints than if oxyfuel were used due to the cooling rates. AFAIK the NHRA are (indirectly) behind many of the stories that TIG is the only/best way to weld 4130 and the like due to their rules mandating TIG for 4130 chassis/cages. The story goes that the main reason for this wasn't metallurgical but because (at the time) TIG kit wasn't really a DIY proposition i.e. more likely restricted to those that new what they were doing
Like TechnicAl said mild steel filler is generally used. Good article on the subject here, obviously based around the use of TIG that also explains why stainless wires should not be used
If cooling rates were addressed with preheat i don't see why MIG shouldn't be used (rules aside if for competition use). Don't really know what to suggest (Al?), thinking at least 60C, maybe 150C? Some sources recommend post weld 'torch normalising' if oxyfuel isn't used for the welding...
Like TechnicAl said mild steel filler is generally used. Good article on the subject here, obviously based around the use of TIG that also explains why stainless wires should not be used
If cooling rates were addressed with preheat i don't see why MIG shouldn't be used (rules aside if for competition use). Don't really know what to suggest (Al?), thinking at least 60C, maybe 150C? Some sources recommend post weld 'torch normalising' if oxyfuel isn't used for the welding...
I agree with the point he makes re 308L, it should not be used. Im not sure what he is saying about the 312. I think hes wrong. 312 should be OK but why go the expense when you dont really get any benefit.
312 filler is designed to be capable of being diluted by upto 40% without forming nasty structures.
I once advised the outfit who were making the roll cages for the Ford WRX team. They were using 312 and were very sceptical when I said they could use MS. Eventually they changed. The 312 never cracked.
312 filler is designed to be capable of being diluted by upto 40% without forming nasty structures.
I once advised the outfit who were making the roll cages for the Ford WRX team. They were using 312 and were very sceptical when I said they could use MS. Eventually they changed. The 312 never cracked.
From the article...
I read that as agreeing with your view Al i.e. it should be fine if weld size is kept sensible but if welds are undersized it'll only add to the problem.
As he said, the suggestion that 312 stainless filler be used is based on at least 40 to 50% filler metal diluted in the high carbon material. If you make almost an autogenous TIG weld (no filler metal) and add just 20% of even 312 stainless you get a Martensitic deposit. You do not obtain the desired microstructure on which folks base their recommendation for a particular stainless alloy rod being acceptable
I read that as agreeing with your view Al i.e. it should be fine if weld size is kept sensible but if welds are undersized it'll only add to the problem.
