increasing tensile strength of 4140 shaft 7ft?

jawadayub · Feb 20, 2021

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?

Limy Sami · Feb 20, 2021

Sub it out to China

Nerdlinger · Feb 20, 2021

200ksi is about 43HRC. We have 4’, 5’, and 10’ long tubes that need to get hardened. We used to send them to Bodycote because, as the story goes, they were the only ones close to us that had a furnace large enough to do those long bars...built for heat treating some old Polaris missile component. Well whatever....they never used it so there was a big charge to fire it up just for us so we started sending them to an induction outfit that works just fine. Good luck!

jawadayub · Feb 20, 2021

Nerdlinger said:
200ksi is about 43HRC. We have 4’, 5’, and 10’ long tubes that need to get hardened. We used to send them to Bodycote because, as the story goes, they were the only ones close to us that had a furnace large enough to do those long bars...built for heat treating some old Polaris missile component. Well whatever....they never used it so there was a big charge to fire it up just for us so we started sending them to an induction outfit that works just fine. Good luck!

We don't have furnace large enough to accompany 7ft bars, the cost for building such big furnace is way too high for through hardening. So the only solution i have is do surface hardening. My question is that does it increase the tensile strength despite increasing surface harden

Illinoyance · Feb 20, 2021

A company I know got out of the Olympic bar business. Competition from China was one reason. The other was that to get the diameter and physical properties they needed requires a mill run of steel and a $40K to 60K up front investment.
The diameter/strength combo is not a stocked item. I suspect you can buy a bar for about the same price as getting your bar heat treated.

4GSR · Feb 20, 2021

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

Nerdlinger · Feb 20, 2021

jawadayub said:
We don't have furnace large enough to accompany 7ft bars, the cost for building such big furnace is way too high for through hardening. So the only solution i have is do surface hardening. My question is that does it increase the tensile strength despite increasing surface harden

In your OP you asked if induction hardening would work. I am saying it will work. Yes - increasing the hardness of the steel will increase its yield and tensile strength.

hanermo · Feb 20, 2021

To the OP in Pakistan.
Surface hardening will somewhat increase the strength overall.
It is likely, imo, to be sufficient for barbells, but I suspect it will not be perfectly steady and reliable to be industrially rated above 205 ksi.
IMO:
Yes it works, No we cannot certify it -- says the insurance (lab).

Someone has a bigger quenching setup.
Industrial (auto, truck, machinery) and artisanal quenching goes on all the time in pakistan.
And quenching goes on in every big economy that makes modern pieces.

Imho:
Ask the tooling companies like kyocera, iscar, sumitomo and mitsubishi for who does quenching.
The tooling reps always know who does what.

And this is one of the few questions they can answer.
Most of the time the tooling reps cannot answer anything to anyone, to keep their trust.
(Like rigging reps).

The MD of any of the tooling reps is actually likely to be happy to talk to You.
(I was in that position several times.)
He is likelt to help You.

Rickyb · Feb 20, 2021

jawadayub said:
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?

Yes, induction hardening will give you the same surface microstructure and strength as as a water quench and temper. Actually this can be a better solution than through hardening.
The main issue with through hardening is that it can have tensile residual stresses on and below the surface which actually makes the weaker wherever they are present.

Induction hardening will always result in compressive residual stresses on and below
the surface reducing the applied stresses by that same amount. Essentially it is stronger in that the bar will realize lower applied maximum stress and have a higher fatigue life.

The depth of the induction hardening depends on the traversing speed and the frequency of the coil. You will have to find someone with a low frequency coil to get a hardening depth of about 50% of the radius of the bar. High frequency coils are more common in induction shops and penetration depths are shallow. Dwell is not a good option to compensate for too high of a coil frequency.

If you feel you need higher core properties 4340 is a good option.

jawadayub · Feb 21, 2021

4GSR said:
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 problem with getting already heat treated at required tensile strength is not machinable at such high hardness. The knurling tool won't be able to work on it, i have to get the bars annealed, knurl the bar and then send to heat treater to increase the UTS. The furnance here ain't big enough to do 7ft bars thats the problem. The only solution i have is do induction hardness.

jawadayub · Feb 21, 2021

hanermo said:
To the OP in Pakistan.
Surface hardening will somewhat increase the strength overall.
It is likely, imo, to be sufficient for barbells, but I suspect it will not be perfectly steady and reliable to be industrially rated above 205 ksi.
IMO:
Yes it works, No we cannot certify it -- says the insurance (lab).

Someone has a bigger quenching setup.
Industrial (auto, truck, machinery) and artisanal quenching goes on all the time in pakistan.
And quenching goes on in every big economy that makes modern pieces.

Imho:
Ask the tooling companies like kyocera, iscar, sumitomo and mitsubishi for who does quenching.
The tooling reps always know who does what.

And this is one of the few questions they can answer.
Most of the time the tooling reps cannot answer anything to anyone, to keep their trust.
(Like rigging reps).

The MD of any of the tooling reps is actually likely to be happy to talk to You.
(I was in that position several times.)
He is likelt to help You.

The autoindustry send there parts mostly smaller ones to these heat treatment facilities the maximum is till 6ft, if they have somewhat bigger part they do flame hardening. In terms of cost induction hardness is a way to go compare to through hardening. I'm just concern if that will increase barbell strength and UTS.

gbent · Feb 21, 2021

Are you strong enough to bend your existing bar, or is this a commercial product development? Look into cut knurling and I believe you can knurl heat treated bars.

jawadayub · Feb 21, 2021

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

alphonso · Feb 21, 2021

4GSR said:
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

jawadayub said:
The problem with getting already heat treated at required tensile strength is not machinable at such high hardness. The knurling tool won't be able to work on it, i have to get the bars annealed, knurl the bar and then send to heat treater to increase the UTS.

ETD 150 cuts like butter. Not sure if it can effectively be heat treated to increase tensile strength. I do know it is not considered weldable.

HuFlungDung · Feb 21, 2021

Consider knurling a sleeve and then shrink fitting or loctite to secure it in position. Don't have to literally knurl a thin sleeve, you can knurl a chunk of bar stock or heavy wall tubing if you want, and then bore it out to make a sleeve.

4GSR · Feb 21, 2021

alphonso said:
ETD 150 cuts like butter. Not sure if it can effectively be heat treated to increase tensile strength. I do know it is not considered weldable.

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.

alphonso · Feb 21, 2021

4GSR said:
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.

We turn Stressproof, EDT150, 4140ann,Ht, really HT, 4145 QT, 4340 as rolled, and HT to Rc40-45 every day. So, yeah, it cuts like butter.

BTW, how did the Alcoa auction go?

Nerdlinger · Feb 21, 2021

I thought induction hardening would harden all the way through, but I am totally wrong. Why doesn’t it? Does the core just never reach austenitizing temp for some reason?

jawadayub · Feb 22, 2021

alphonso said:
We turn Stressproof, EDT150, 4140ann,Ht, really HT, 4145 QT, 4340 as rolled, and HT to Rc40-45 every day. So, yeah, it cuts like butter.

BTW, how did the Alcoa auction go?

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

jawadayub · Feb 22, 2021

My question is that if i do induction hardness since it is surface hardness will the bar deform anyway?

increasing tensile strength of 4140 shaft 7ft?

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