welding a chromoly frame?

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welding a chromoly frame?
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Posted: Jan 9, 2008 at 20:16 Quote
vinceliberatore wrote:
ajaxpowder wrote:
[PI=1589141 size=m align=c]ala mig weld Big Grin
hope your face will be restored keith xD

Was it heat treated? I think (i'm not an expert) heat treating would've prevented this. Maybe Hummeriod will help me out on this one...

WELL, 4130 (cro-moly) should be pre/post heated. If this had been done correctly chances are it wouldnt have cracked, but yes, Vince is right. To have done it completely right, the frame would have to have been heat treated (by me?) afterward if the tubing the company used was hardened/ half hard before the welder even hit it with the mig. 4130 is fairly forgiving though, so I wouldnt worry about it too much.

BUT theres no way that that snapped frame is from someone welding it. Snapping in the middle of a tube would not be caused by this.

Posted: Jan 10, 2008 at 6:03 Quote
From all the people I have talked to 4130 THIN WALLED TUBING, does not require pre or post heating. There are a lot of bike frames that claim to be heat treated but the heat treating process was done on the tube before the frame was made. So no you don't need those processes. Some companies like SnM are doing post production treatments. Brazing IS bad, there is too much heat put into the tube in a much larger area than welding. TIG puts more heat into the peice than any other method BUT the welds are done in 1-2" beads letting the frame cool before continuing, so the heat affected zone is a few mm as opposed to brazing which produces a large zone. This is where most cracks start then travel into the weld. So your frame CAN be welded, but there are 3 filler wires you can use which are expensive and if you are welding close to an area already welded you are taking away from the strength. If you got a peice of 4130 and made a bit of a gusset it would probably do alright.

Posted: Jan 10, 2008 at 13:12 Quote
ricar wrote:
From all the people I have talked to 4130 THIN WALLED TUBING, does not require pre or post heating. There are a lot of bike frames that claim to be heat treated but the heat treating process was done on the tube before the frame was made. So no you don't need those processes. Some companies like SnM are doing post production treatments. Brazing IS bad, there is too much heat put into the tube in a much larger area than welding. TIG puts more heat into the peice than any other method BUT the welds are done in 1-2" beads letting the frame cool before continuing, so the heat affected zone is a few mm as opposed to brazing which produces a large zone. This is where most cracks start then travel into the weld. So your frame CAN be welded, but there are 3 filler wires you can use which are expensive and if you are welding close to an area already welded you are taking away from the strength. If you got a peice of 4130 and made a bit of a gusset it would probably do alright.

I am a professional heat treater and fabricator. To quote the ASM heat treaters guide on the section for 4130- "4130 is weldable, but because of its fairly high hardenability, preheating and postheating must be used."

I am not trying to start a war, BUT the CORRECT way to be doing this is as I, and ASM say. :-) By no means am I saying that nobody has EVER welded 4130 and not had it crack without pre/post heating :-)

Posted: Jan 10, 2008 at 19:26 Quote
Again if you look at the Lincoln Electric site or any other site, you will find that thin walled tubing does not. You may be in the buisness but I have asked guy's that do work for aerospace companies and they all say the same. Thin walled tubing will loose it's heat to quickly and you can end up with weird things happening to the structure causing weak spots. Any substantial peice then yes, you need to pre-post heat.

Posted: Apr 10, 2012 at 19:37 Quote
This thread is ridiculously entertaining to me.

I am going to print it off and pass it around the lunch room. Smile

Jaliyl

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