On Sat, 15 Nov 2014 18:18:01 +0000, Sandarpan Mukherjee
wrote:

replying to Steve W. , Sandarpan Mukherjee wrote:
csr684 wrote:

Actually his numbers are at the minimum that are allowed in an Olympic
bar.
The lower end bars are 170K tensile. The good ones are up around 210K!
The idea is that the bar has to flex when you lift, that helps you by
storing energy that helps you flip during the lift. The bars also have
bearing inside the weight sleeves so that as you lift the plates don't
apply any torque to the bar and spoil the lift.
I have friends who lift HEAVY and most seem to use Eleiko, York or
Werksan bars. They are not cheap but they do seem to last.
When they do clean/jerk lifts that bar looks like a wet noodle.
--
Steve W.



What you are saying is absolutely true. This link ebay. co
m.au/itm/F-OLB-Force-USA-Olympic-Lifting-Bar-20-Kg-Cross-Fit-Warranted-for-Crossfit-Use-/321487232831
(delete the spaces) advertises a bar of 216000 psi TS and it's mentioned
that the bar is made from SCM 440 (same as AISI 4140) heat treated steel.
What's bothering me is the hardness. Firstly I want to machine the bar and
I also don't want it to be too brittle. Even if the yield strength is
exceeded, I want the bar to bend not break.

Thanks

It's not easy to find specific elongation properties of 4140 when it's
heat-treated to 216 kpsi tensile. At the extreme end, 285,000 psi,
elongation is 11% and machineability is 65%. Hardness is 578 Brinell
or Rc 55.

That's more machineable than I expected, although it's carbide-only at
285 kpsi, and I didn't even know that it could develop 285 kpsi
tensile strength. That kind of tensile strength, in diameters larger
than wire, usually is associated with fairly brittle specialty steels
and very low elongation.

So, at 216,000, elongation can be expected to be over 11%. That's not
terrible. It shouldn't be inclined to break as soon as the yield
strength is exceeded.

The thing is, heat-treating sounds tricky -- normalize, reheat for
time, oil-qnench and extended temper -- and it probably requires real
expertise to achieve those extreme properties without brittleness. You
can buy it normalized but the time/temperature sounds like a job for
carefully controlled furnaces.

http://www.matweb.com/search/datashe...a46a1f1 eb1c3

Good luck!

--
Ed Huntress