On Sat, 23 Feb 2013 13:56:37 -0800 (PST), clark
I'm not sure what you mean by that; 4140 softens with heat just like
every other steel.
As for gun barrels, 4140 has relatively high tensile strength even
when tempered at high temperatures (for example, temper at 800 deg. F,
and yield strength is still 120,000 psi).
The result is a strong steel that has high elongation (13%, in this
case). That means it's strong but not brittle; its ductility is quite
high for such a strong steel. It's relatively safe with high chamber
That makes a good gun barrel. It has good wear resistance, too.
4140 is not really a tool steel. It's a medium-alloy, medium-carbon
steel. Because it contains chromium and molybdenum, it will harden
with only 0.40% carbon to a higher degree than, say, 1040 steel.
Why indeed? Maybe they looked at the real issues and decided it was
the proper steel, rather than using old galvanized water pipe? Maybe
they don't like a barrel splitting when it fails to contain the pressure
from the rounds, when fired?
Don't want HARD, want tough and more important, want a material that
resists erosion from very hot, very high velocity and very high
pressure gas. And what the commercial barrel makers order for steel
isn't 4140 that you get from the local steel merchant. Since they
order tons at a time, they can get an alloy that does the same or
better for physical properties, but is easier to machine and pull
buttons through. If you had a super-hard barrel, it'd probably
grenade, too brittle to take the near-instantaneous pressure load.
Some army officer had the same bright idea, I've got a book that shows
the results of putting case-hardened throats in cannon. Didn't last
more than a few rounds before they shattered. And 4140 is hardly
"tool steel". High chromium and nickel content cuts gas erosion
considerably, back in the early days of smokeless powder, they found
that plain carbon steel barrels that were fine for black powder and
lead bullets just had their rifling go away in a few hundred shots.
Winchester used nickel steel for the first time in their 1894 .30-30
barrels for that reason. A big deal in the late 1890's, using an
There are a few books out there on barrel making, most are short run
printings, but can be had. I've got a couple.
4140 is what i would call a low alloy steel. Chrome and Moly, but no
SAE grade % Cr % Mo % C * % Mn % P
(max) % S (max) % Si
4140 0.80?1.10 0.15?0.25 0.38?0.43 0.75?1.00 0.03
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.