Thread: increasing tensile strength of 4140 shaft 7ft?

Originally Posted by 4GSR

What do you mean ETD150 cuts like butter. Better make sure your steel supplier sent you the right stuff. If it is really ETD150 it is tough to cut on. It does leave a nice finish. To me, there is no difference in cutting it and 4140HT. Machinibility is 75% of that of 1215 steel, which is considered 100%

http://www.niagaralasalle.com/pdf/etd150casestudies.pdf

Regardless, it's still not high enough in tensile of what he needs.

Something else they could do if allowed, go with a slightly larger OD bar and turn the ends down for the weights to pass on. Just a thought.

I can't go with etd150 the shipping cost would be too high for me, i have to buy from china, they are manufacturing 4140 and 4340 though. Is that a good alternative?

it will deform but not in any relevant way for this application. in induction hardening you vary the deph of the case by the frequency used. 4340 should through harden, but ductility might be impared by a coarse grain structure.

how did you come up with 205 ksi? maybe you should be looking at yield instead.

edit: annealed does not give best hardening results, are you sure its annealed?. you should have hardened and tempered.

Originally Posted by jawadayub

So i can heat treat 4340 to required hardness 40-45 and there is no issue of knurling on it..?

I would knurl it before heat treat.

Originally Posted by dian

it will deform but not in any relevant way for this application. in induction hardening you vary the deph of the case by the frequency used. 4340 should through harden, but ductility might be impared by a coarse grain structure.

how did you come up with 205 ksi? maybe you should be looking at yield instead.

edit: annealed does not give best hardening results, are you sure its annealed?. you should have hardened and tempered.

It’s annealed HRC at 20, I can’t knurl on hardened already tried on a sample didn’t work. Through hardness doesn’t have furnaces for 7ft here, so my only option is induction hardness for now. I probably should go with 4340?

i would stay with what you have. what is the diameter? 1"? 4340T (hardened and tempered) is about 23 hrc. just saying. have it induction hardened and test it with at least double load.

there are of course cheaper and stronger steels that, however, require an "industrial" heat treat.

Originally Posted by dian

i would stay with what you have. what is the diameter? 1"? 4340T (hardened and tempered) is about 23 hrc. just saying. have it induction hardened and test it with at least double load.

there are of course cheaper and stronger steels that, however, require an "industrial" heat treat.

Yes 28mm, 4340 is annealed all the steel bars regardless of grade come here are annealed. I should instruct the heat treatment shop to do at 53 hrc induction hardness. If that helps i hope...

Originally Posted by 4GSR

Get some ETD150 bar. Tensile should be up around 180K. You may find 4340 in a high heat treated condition that may get around 200K tensile. It's that or have it heat treated to get 220K tensile. Ken

The tensile strength is 150ksi (min) that's why it's called ETD150.........

If you get some that 180ksi it's way out of range.

Originally Posted by jawadayub

it deforms when i pull over 250kg, i have to check cut knurling tool availability, usually form knurling tool is in the market.

Any steel with the same cross sectional properties will bend the same amount when you apply the same load. There will be slight variation in E (youngs modulus)) so the deflection could vary a very small amount with different materials.

The difference though is that as the yield strength increases the deflection increases before it yields.

If you really wanted to figure out the yield strength required, you would need the max end weight that's going to used, the position of the knurls (so you can calculate the bending moments) the diameter of the bar (from which you calculate I (second moment of area)), Using those 2 pieces of information you could calculate the bending stress with the max weight at the ends.

So if you calculate a bending stress of 100ksi, and the organisation requires a factor of safety of 1.5, then the yield strength (NOT tensile strength) of the material needs to 150ksi.

Using E (youngs modulus) you can calculate deflection.

For s&g's you could look for pictures of weightlifters lifting large weights, if you knew the diameter of the bar, the distance between the weights, if the picture is clear enough that you can estimate deflection you could figure out the min yield strength req'd

Originally Posted by jawadayub

Hello,

I'm looking to build olympic barbell, i have purchased 4140 grade in annealed form which typical hardness is around 20HRC. I have done knurling on the shaft but i need to increase the tensile strength. the typical tempering and hardness seems to be very expensive to meet the tensile requirements i need it at 205,000PSI. Can i do induction hardness instead? Does induction hardness increase the tensile strength of the bar. We don't have shot peen equipment where i live. How should i meet the UTS with minimum cost?

You need to be thinking in terms of yield strength.

Is the 205'000 tensile strength a customer requirement? Or a requirement you've calculated.

4140 with a tensile strength of 205'000psi, is going to have a yield strength of 195'000psi.

Induction hardening will be fine. Flame hardening will also work. Both will probably cause deformation. Straighten the bar afterward if necessary. Many hardening shops can do this if you can't.

Originally Posted by eKretz

Induction hardening will be fine. Flame hardening will also work. .

Induction and flame are not deep hard.
Sure the skin is hard to Rc test but inside the stock very different than a traditional furnace heat and quench.
I have not done 7 foot long so quite sure talking when not knowing.

Originally Posted by eKretz

Induction hardening will be fine. Flame hardening will also work. Both will probably cause deformation. Straighten the bar afterward if necessary. Many hardening shops can do this if you can't.

it probably depends on whether they can do it in vertical position.

If he really wants 53HRC, I would worry about the knurling acting a stress riser for fatigue cracks. How about a rubber sleeve for grip?

Much safer to use a thicker bar at a lower, tougher and more ductile hardness level. Turn the ends down if necessary to fit the holes in the standard weights.

For teat-treat, surely somebody makes heavy-truck axle shafts, or torsion-bars, in Pakistan? Their material as well as their processs is what I would look at.

Originally Posted by magneticanomaly

If he really wants 53HRC, I would worry about the knurling acting a stress riser for fatigue cracks. How about a rubber sleeve for grip?

Much safer to use a thicker bar at a lower, tougher and more ductile hardness level. Turn the ends down if necessary to fit the holes in the standard weights.

For teat-treat, surely somebody makes heavy-truck axle shafts, or torsion-bars, in Pakistan? Their material as well as their processs is what I would look at.

They do induction hardening i checked and the shafts grades are 4140 and 4340.

Originally Posted by CarbideBob

Induction and flame are not deep hard.
Sure the skin is hard to Rc test but inside the stock very different than a traditional furnace heat and quench.
I have not done 7 foot long so quite sure talking when not knowing.

Problem is the cost is too high compare to surface hardening and no one has such big furnace to cater 7ft bars.

Why re-invent the wheel??? With a weight lifting club in the ‘70’s we had York olympic style bars that were 6150 (good for high $$$ springs). Those bars were chrome plated for corrosion.

The club in Moline had some Swedish made bars that were a stainless steel & those were plated too. I can’t imagine anybody building a free weight bar on the cheap. If you are talking about just a bare bar without the rotating ends then maybe yes & they don't need to be 7 foot long either…

Attached some 6150 data from EMJ. (on edit) the mass effect page doesn't show 205K tensile but tempering at 925F will get to your 205K tensile.

Good luck,
Matt

if we are getting into different alloys, axles are often made out of 1541. apparently it takes bending loads better that 4340.

Originally Posted by dian

if we are getting into different alloys, axles are often made out of 1541. apparently it takes bending loads better that 4340.

Checked in the market, they don't have 1541 and have to go with 4340 i'm going with 53HRC induction hardness. Hope that increases required yield strength.

maybe 43 hrc would make more sense and trying to have a deep case/through harden done?