On Tue, 06 Oct 2015 19:53:17 +0700, John B.
wrote:

On Mon, 5 Oct 2015 21:40:06 -0700 (PDT),
wrote:

What would be the heat treating process if i bend the 4130 25.4mm OD 3mm Thickness pipe at an angle of 45Deg, just for relieving stresses?

I believe that the standard stress relief for 4130, after welding, is
to hold the material at 650 degrees(C) for 1 hour per inch of
thickness.

Right, but that's for re-converting the martensite produced in
welding. When you bend it, there is little production of martensite
and it's much more evenly distributed, which is less troublesome.

4130 is an oddball in terms of heat treatment. Most 4130 tube is sold
in the normalized condition; it can take quite a bit of bending,
relative to its strength (and compared with a plain-carbon steel of
comparable strength); and it's likely that all that would happen from
bending it that much is a local increase in strength.

But I'm not going to make any recommendations because I don't know the
initial condition, the application, the OP's resources for heating it,
or anything else. The key things to remember about 4130 are that it's
marginally air-hardening, so you can wind up hardening it when you
think you're annealing it; and that overheating it can lead to cracks
in the direction of the grain.

If you haven't welded it, and unless the required properties are
critical and very specific, I'd leave it alone after bending.

--
Ed Huntress