I've welded 4130 for years, always TIG, you can stress relieve it with a
torch, but not doing it is ok, we weld race car suspension a lot and never
have had a problem with welded only parts.

--
David Algie
Algie Composite Aircraft
http://members.iquest.net/~aca/

http://groups.yahoo.com/group/algiecompositeaircraft/
"Josh Fowler" wrote in message
...
4130 is no lighter than mild steel, their density's differ by only
.02 g/cc. Young's Modulus is also the same for each, meaning that with
the same force applied to an equivalent sample of each, they will both
deform the same amount. Where the two metals differ is their yield and
ultimate strength. 4130 will take a larger force to both permanently
deform it and to break it than 1018 for example.

I don't know much on the finer details of the welding processes, I just
wanted to give the facts on the materials.

Josh

The Hurdy Gurdy Man wrote:

(Please note: I've crossposted this to both rec.crafts.metalworking and
sci.engr.joining.welding since it's valid both places, and possibly of
equal interest to readers of both, so set your follow-ups accordingly if
you're concerned about it!)

So as my welding classes are coming to a close, I happened across some
factoids in my welding text that have me wondering about the wonders of
chromoly steel. The main one, though, is this whole thing about
post-weld
stress relieving using a torch. Just about every book I've read on
fabrication suggests the same post-weld process, except for one; that
book
is "Performance Welding" by Richard Finch. Now previous discussions on
the subject of Mr. Finch have led me to believe that he's not always
playing with a full deck of cards, but my welding textbook for class
said
something that actually matches his opinion on the subject.

Finch writes that post-weld stress relieving of a weld in chromoly steel
using a torch is completely worthless because proper stress relieving
requires a six hour long process that simply can't be achieved with a
torch. My textbook makes a vaguely similar assertion in that it says
that
proper stress relief of a welded joint can take anywhere from one hour
to
six hours for the heating segment of the process, with the point of
diminishing returns on the increase in strength starting at around the
six
hour mark. However, its implication is that SOME amount of stress
relieving will still have a benefit, but that the percentage of
effectiveness is based on the total amount of time the part to be stress
relieved is soaked in the heat.

Here, then, is my first question. Who is right on this subject? Is it
worthless to even attempt post-weld stress relieving of a chromoly part,
or can an appreciable amount of strength be regained through using a
torch
and allowing the part to cool in still air, or better yet, buried in
sand? Does anyone know of a chart that might exist someplace that shows
the relationship between gained strength and duration of applied heat?

That first question then leads me to my second question. According to
Ron
Fournier in his book "Metal Fabricator's Handbook" the best rule to
follow
with chromoly is to simply not use it unless you know EXACTLY why it is
needed. And from my reading, I'm beginning to think that he's
absolutely
right on the money with that. So, when then would you actually need to
use chromoly? I can only think of two times, that being when weight is
a
critical issue and when its strength makes it the only metal appropriate
for the part while its deficiencies do not make for an undesirable
failure
mode (see my example in the next paragraph). Does that sound accurate?

As I tinker with cars a lot, I especially think of this in terms of car
parts, and one part in particular where chromoly shows up a lot in the
aftermarket is with suspension and chassis components. Mr. Fournier
says
to stay away from chromoly roll cages because they tend to break instead
of bend, and that a broken up cage is infintely more likely to kill a
driver than a bent up cage since bends absorb impact and breaks create
sharp spears that turn a driver into hamburger. This sounds absolutely
reasonable to me, after reading about chromoly's deficiencies. But now
I
also wonder, in anything but a track driven race vehicle, couldn't the
decreased weight of a chromoly part have its value offset by the fact
that
it would break instead of bend? After all, if you were to, say, break a
chromoly control arm on the track, there'd be a vehicle to tow you back
to
the pits. However, if you were offroading in the desert or being an
idiot
on the street, a broken control arm could leave you completely stranded
whereas a bent up one might still allow you to limp home. It seems like
chromoly's only place for street and offroad vehicles exists for parts
like sway bars and other things where breakage is either statistically
impossible or not particularly hazardous/lethal.

So those are the questions and my moment of pondering... I look forward
to
hear comments from the smart folks out there with more knowledge and
experience on the subject than I. Thanks!