From: "Larry list account" <list@marketvalue.net> wrote...
> Here are my questions.
>
> Is normalization required after any method of welding? MIG, TIG, or OA?
It's a good idea.
> Is normalization required just around the weld?
You need to bring the entire heat-affected area up to a very dull red color
and allow it to slowly air cool without any breezes, etc.
> Can you weld chrome moly tubing with MIG and normalize the welded area
with
> OA?
Sure. Small things could be put into an oven, but a good neutral to
slightly carburizing flame on an OA torch will do great. You want a big,
soft flame, and don't dig in - play it over the whole area to be normalized
till everything is evenly heated. FOr something huge, 2 torches (and maybe
2 people) might be easier, but usually you can do this alone. If youj OA
weld, one good way to accomplish this is to normalize as you finish
welding - everything is pretty hot already - you just need to even out the
heat and then cool it slowly. But for complex structures it's probably
better to do a final normalization after all welding is finished. Otherwise
you may complete one area, normalize it, and then re-introducing external
stresses from welding in an adjacent area.
> If the previous statement is true, how much heat is required to normalize,
> and how much of the area needs to be heated?
Dull red, and beyond the HAZ created by the initial welding.
> These questions are a result of my plans to build a roll cage for a
vintage
> race car. I've been told the weight savings of using chrome moly would
not
> out-weigh the issues around having to normalize the cage after welding.
>
> I have a source for some chrome moly tubing that would allow me to
purchase
> it for nearly the price of new mild steel tubing. This makes the chrome
> moly tubing an attractive alternative to mild steel.
Chrome moly is NOT exotic. The strength of chrome moly is better than 1020,
etc., but it's not titanium or anything.You'll probably be using 4130
seamless tubing. You should weld it with mild steel rod, not chrome moly
rod. the welds are sufficiently larger that the strength is just fine. Any
decent weld is going to be stronger than the surrounding tubing anyway. If
the welds are good, you'll never break them - the tube around the weld will
break first.
However, 4130 does have a little greater potential ffor heat treatment than
1020, etc. (mild steel). For most tube-structure applications, you DO NOT
want heat treatment, thus you want to normalize after welding to remove any
inadvertent, uncontrolled heat treatment that may have occurred in
fabrication and welding.
One of 4130's biggest advantages is more corrosion resistance - tube
structures can rust internally, and chrome moly is a little less prone to
rust that mild steel. But only a little... For aircraft use, it's highly
recommended to oil the inside of the structure with linseed oil or something
similar after all welding is completed. Some guys even drill holes while
fitting things up to ensure that oil can get everywhere, but most people
just oil longerons and larger members, individually. And seal it well once
it's been oiled, to keep any moisture out.
Any aircraft supply can supply you with all the sizes you could ever wish,
and the price differential over mild steel is just no big deal compared to
all the other costs of a typical project.
Good luck - I bet you'll really enjoy chrome moly. The name is impressive,
but it's really simple to work with.
Happy New Year !!
Karl
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