4130/MIG/TIG contraversy

cleartoy

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I have been told by a few people that when working with 4130 moly, you need to TIG weld and heat\stress relieve it.

Over a discussion, someone told me that you dont have to do that, and to just MIG it.

Whats the real deal? Ive been using mild steel\MIG , so it hasnt been an issue for me yet.

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CRAIG_HALL

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FROM MILLERS WEB SITE

<A target="_blank" HREF=http://www.millermotorsports.com/mboard/showthread.php?s=400948cc9167c0b577a2793d0d7256eb&threadid=213>4130 ?</A>

<A target="_blank" HREF=http://www.millermotorsports.com/mboard/search.php?s=400948cc9167c0b577a2793d0d7256eb&action=showresults&searchid=727&sortby=&sortorder=>THIS WAS A SEARCH ON THEIR SITE</A>


<A target="_blank" HREF=http://www.lincolnelectric.com/knowledge/articles/content/chrome-moly.asp>THIS IS FROM THE LINCOLN SITE</A>

CRAIG
 

NorCal_Prerunner

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Oh Man, here we go again. I don't know what to think anymore regarding welding 4130 with a MIG.

From the link above: Miller's site.

It is very common. If it is a non-critical tube for a support brace, most teams will mig it. If it is an actual roll bar or a critical component like a control arm, steering shaft or frame member, it should be TIG. I know alot of people have done it and gotten away with it. But I would hate to be the one who didn't. You can stress relieve the weld joint with a torch and a 900 deg temp marker. Mark about 1" away from the weld joint and heat with a neutral flame avoiding hot spotting until the marker changes. This will help the joint regain some of it's elongation or flex incase it is subjected to a hard crash. Otherwise the weld will tear or crack.
Stay away from heat treating the entire chassis in an oven. This does change the parent metal and you would lose base metal strength.



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FABRICATOR

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Re: "If it is a non-critical tube for a support brace, most teams will mig it."

This is misleading and not accurate for off-road racing, especially if the rest of the chassis is TIG welded.

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ntsqd

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From reading CRAIGHALL's links I don't think there would be a problem in using a MIG on 4130.
However, unless you change your spool to one of the recommended filler alloys what you will have when you are done is a bunch of mild steel beads holding 4130 tubes together. That seems like a waste of money to me.

Both Lincoln & Miller say that you don't have to Normalize the welds afterwards if the tube wall thickness is less than .120" and is not a critical structure like a control arm. Notice they said DON'T HAVE TO, I still think it prudent to do so unless the total life expectancy of the chassis is one season and then it gets destroyed, not sold off. The metal in the weld puddle and immediately adjacent metal will have changed condition to a very brittle structure. Normalizing the welds restores the metal to a more ductile condition. Normalizing the welds means you won't be chasing as many cracks during the service life of the frame.

TS

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