Wedling 4130 CroMO

BradM

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<blockquote><font size=1>In reply to:</font><hr>

I was told that gas welding is not as strong as tig since the grains in the metal will be melted when you gas weld. So once your piece has cooled down, it has lost its strength since there are no more grains inside the metal to hold itself together.

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That must be the problem. No more grains.

It sounds like you heard that from someone who may have known what they were talking about but you didn't remember all of what they said.

The grain structure in and around the weld area can change due to the temperature at which the material is heated relative to the critical temperature. There are, many different grain structures that can be present in a given material and it is the grain structure that defines the material properties like strength, ductility, etc. The grains are not lost but rather different molecular bonds are created which result in a different grain structure and thus different mechanical properties.
 

1992f150

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Dont believe everything that you hear. Had a fab shop tell me you werent allowed to gas weld roll cages.
Keep in mind once a weld gets strong enough, the base metal will fail long before the weld does. Weld some thin stuff together then try to break the weld or destroy the piece, you will be supprised how strong it is.

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Kritter

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A weld is only stronger then the base metal when it is thicker or of a stronger alloy...I can't stand when people say the weld is always the strongest part.

Kris
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1992f150

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actually....weld 2 pieces of metal together, stretch it in a machine, the base metal tears before the welded area does. So yes it is stronger. Obviously if you do a crappy weld it will be the first thing to fail. If your welding 2 pieces of 1/8th inch metal together, a good weld will never be the same thickness as the metal. The only way to do that would be to weld it, then grind down the weld. Either that or use no filler rod at all and tig/gas weld it.
As far as alloy, People dont use strips of mild steel as filler rod, so the weld will never be the same composition as the base metal, unless you use coat hanger wire.
 

Dave_G

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RE: "A weld is only stronger then the base metal when it is thicker or of a stronger alloy"

Uh,uh,uh,uh.....I need to take you to the inertia welding guru in Long Beach and you'll have a different out look on that statement. ;-)

Dave

"I know it all, but I can't remember most of it..."
 

ntsqd

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First off, what ever you think a weld is, forget it unless you think of it as an 'on-site' casting because that's all it is. Boiled down to the bare essence it can't be much of anything else. I'm not talking about spin welding, friction stir, etc; I'm talking about a classic weld bead as made by a MIG, GTAW, Oxy-Fuel, etc. "As cast" it may be stronger or weaker than the base metal, there are too many variables to generically predict which it will be. It is only in the post weld handling and treatment of the structure that the weld metal becomes closer in grain structure and properties to the base metal. The higher the alloy, the more post weld processing is required or at least should be done for optimum strength, ductility, etc.

Usually welds done with no filler and no allowence for extra material in the base metals loose section thickness.

"People dont use strips of mild steel as filler rod, so the weld will never be the same composition as the base metal...."
Experienced aluminum body builders shear a strip off the body material and use it as filler. Even then it isn't exactly the same because of the different heating and cooling cycle(s) it's been thru.

TS

"It only seems kinky the first time"
-- Bumpersticker seen in Lost Wages
 

BIG_FAT_LOSER

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It sure was a beautiful outside today.

How much of this is actually applied to the majority of race vehicles ?

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AZmiik

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So it sounds as though the whole thing is a prefrence issue not a technical issue. I get what your saying about the trailing cup and the impurites but it would be hard to get a cup to follow around a tube to tube joint and be very effective. I like the comment about friction stir welding though one more point is that it only work on aluminum. Trying to stick the HSS tooling into a piece of steel just doesn't seen to work as well.

Mike
 

fishd00d

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Has anyone seen my keys????????

Go Big Or Go Home
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ntsqd

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Yea, they were right next to the lost beer.

TS

"It only seems kinky the first time"
-- Bumpersticker seen in Lost Wages
 

ntsqd

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While you could use the trailing cup on a lot of beads in a race vehicle. I think you're right, it wouldn't be very practical. There is a lot of science to welding metals. There is also a lot of art. Much is known about the topic, but how to go about achieving the desired results with manual process' is still very much an individual thing. Automatic process' are far more exact, but in a lot of cases even they require an expert welder to 'teach' the system.
I've been oxy-fuel welding for 20+ years and GTAW for 10-12 and I consider myself to be somewhere btwn a beginner and an intermediate welder.
For sticking HSS to mild, I'd go the 'cemented' route. Use either braze or silver solder. Order some of the silver solder dust bearing flux from Brownell's and try it.

TS

"It only seems kinky the first time"
-- Bumpersticker seen in Lost Wages
 

Dave_G

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RE: "How much of this is actually applied to the majority of race vehicles ?"

Actually we've been doing quite a bit of Inertia welding lately. We have also bonded non similar materials like 300M and 300 Maraging. Makes wonderful stub axles!

Dave

"I know it all, but I can't remember most of it..."
 

MNotary

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The "best" stub axles come out of old VWs'. Must be Friday.

I HAVE seen a bunch of aftermarket stub failures in the past two years. Not so much this year.
 

partybarge_pilot

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Inertia welding? Isn't that what happens when you run out of oil? I had an ex-girlfriend that was a master at it.........
 

AZmiik

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Thom I would have to agree with you on the whole adhesive bonding but what I was talking about is with friction stir welding a piece of HSS penetrates the aluminum and spins to form the weld joint. In order to use friction stir on a mild or low carbon steel a that is much more heat resistant would have to be used and I am not sure that there is a material suitable for that application.

Mike
 

ntsqd

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As a footnote to my comment about welding aluminum body sections, these should be welded with an oxy-fuel torch. GTAW welds are brittle in the as welded condition, which then cracks in the post weld metal working, and the annealing process will warp the body almost beyond use. Oxy-fuel results in an annealed weld that doesn't crack.
I think this is illustrative of the need to chose the best welding method for the desired results.

TS

"It only seems kinky the first time"
-- Bumpersticker seen in Lost Wages
 
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