Heat Treating 4130 Pipe Under Torsion

Bendak · Sep 19, 2020

Hi all,
I have a 0.375" OD by 0.259" ID 4130 pipe 16" long that needs to be heat treated to increase its yield strength to at least 1300MPa without becoming too brittle. From what I can find online, I need to raise it to 1575°F for 30 minutes followed by an oil (instead of water due to fragile dimensions; need to reduce cracking and distortion) quench and then temper it for two cycles at 400°F for 60 minutes each. This should bring the yield strength to about 1331MPa with a hardness of 47-49HRC. Based on my calculations and simulations in SolidWorks, the pipe will be able to withstand up to 70-71ft*lbs of torque under these conditions. Unfortunately I cannot find 4140 or 4340 pipe with these OD and ID dimensions, so I need to stick with 4130.
I realize that at this hardness, the yield strength will be close to its ultimate tensile strength (1600MPa) and therefore have much less flexibility under torsion. The pipe will have a hollow screw made machined out of 4340 TIG welded on one end for cutting into live wood, and so will be hand operated at about 60 RPM.
Do you all think this is reasonable? I do not want to risk breaking the shaft under a load that may reach up to 65+ ft*lbs of torque, so there needs to be at least some flexibility.

Regards,
Jack

4GSR · Sep 20, 2020

Go for it!!!

I believe 4130 at that hardness is a tad too hard. Really need a material like 6150 but I know that material may be hard to find. Next would be going to a tool steel like a S1, S2 grade material. Why not 4340 like the ends are made of. Your other issue is welding high heat treated materials. Going to loose hardness from welding. Ken

Bendak · Sep 20, 2020

It sure would be nice to make the whole thing out of 4340, but unfortunately I do not have access to a gun drill able to drill a 0.259" through 16" of material. The actual cutting threads will be made out of 4340 to that it can be hardened to a higher hardness than the shaft. I know of something very similar made out of A2 tool steel at 48HRC. That's another question as to whether or not it should be welded after or before quenching and/or tempering. I will be getting it professionally welded. Based on further calculations, the pipe will undergo around 45 degrees of angular deflection at max torque (72 ft-lbs).

aarongough · Sep 20, 2020

Just to clarify:
Heat-treating the steel will not change how flexible it is (modulus). It will change how much flex it can undergo before becoming plastically deformed however.

May not be relevant to your use case, but you mentioned flexibility after heat-treatment so I just wanted to clarify.

All welding should be done before heat-treatment with a rod/wire that will harden similarly to the base material. Welding after heat-treatment will locally alter the hardness of the steel and potentially make it brittle and prone to cracking.

Gut instinct says 45º of twisting deflection is a lot. I'll be curious to see how it holds up!

-Aaron

4GSR · Sep 20, 2020

I don't see where you are gaining anything using a hollow tube. Make it solid and turn the OD down a bit to get the flexure you want. But in 16" in length, you're not going to get hardly any flex without over stress and yielding. Make it all one piece so you don't have any welding involved. You have to remember, regardless the welding process, it will require preheat to get any weld process to stick to the metal. That means, you will loose heat treat in the heat affective zone in the parts being welded. And do you really trust SW's over hand cranked calculations for determining stresses involved. I don't, I back up all with calculations in my workplace. Ken

wesg · Sep 20, 2020

I thought maybe he's tapping maples for sap. Checked his profile if he's in Vermont... 'dendrochronology'. He's taking core samples, so it has to be hollow.

Dan from Oakland · Sep 20, 2020

You really don't need a gundrill to drill thru 16". That's only 8" from each end. A good quality aircraft drill will easily drill that deep. Just saying.

Illinoyance · Sep 20, 2020

Why not just buy an increment borer? Just google that term and you will find many sources.

I can't see how you could save money by attempting to make one.

DDoug · Sep 20, 2020

Bendak said:
Hi all,
I have a 0.375" OD by 0.259" ID 4130 pipe 16" long that needs to be heat treated to increase its yield strength to at least 1300MPa without becoming too brittle. From what I can find online, I need to raise it to 1575°F for 30 minutes followed by an oil (instead of water due to fragile dimensions; need to reduce cracking and distortion) quench and then temper it for two cycles at 400°F for 60 minutes each. This should bring the yield strength to about 1331MPa with a hardness of 47-49HRC. Based on my calculations and simulations in SolidWorks, the pipe will be able to withstand up to 70-71ft*lbs of torque under these conditions. Unfortunately I cannot find 4140 or 4340 pipe with these OD and ID dimensions, so I need to stick with 4130.
I realize that at this hardness, the yield strength will be close to its ultimate tensile strength (1600MPa) and therefore have much less flexibility under torsion. The pipe will have a hollow screw made machined out of 4340 TIG welded on one end for cutting into live wood, and so will be hand operated at about 60 RPM.
Do you all think this is reasonable? I do not want to risk breaking the shaft under a load that may reach up to 65+ ft*lbs of torque, so there needs to be at least some flexibility.

Regards,
Jack

You expect us to doo your homework assignment ?

At the required heat treated level, what is the elongation numbers ?

you only quote Rc numbers.

Rickyb · Sep 20, 2020

Bendak said:
It sure would be nice to make the whole thing out of 4340, but unfortunately I do not have access to a gun drill able to drill a 0.259" through 16" of material. The actual cutting threads will be made out of 4340 to that it can be hardened to a higher hardness than the shaft. I know of something very similar made out of A2 tool steel at 48HRC. That's another question as to whether or not it should be welded after or before quenching and/or tempering. I will be getting it professionally welded. Based on further calculations, the pipe will undergo around 45 degrees of angular deflection at max torque (72 ft-lbs).

Just so you understand. 4130 doesn’t have enough carbon to respond to the heat treat. You won’t get properties that you are expecting. You will end up with low carbon martensite and not be near as strong as a fully martensitic structure. Even if it could respond it would fail at the weld. Doesn’t matter if you weld before or after. Worse after but still bad. Welding by it’s very nature is melting the parent materials. Melted grain boundaries cannot be corrected by heat treat because you have almost pure iron around those enlarged grains with the strength of pure iron. There is nothing that can be done to correct this. These grain boundaries will be your failure sites. Welded structures are therefore relegated to working in a much lower stress environment than you are planning.
You might consider one material like 8620 and carburize it.

Bendak · Sep 20, 2020

I like the challenge of making my own borer and they can get quite expensive in longer lengths, say 24". I would make it all out of one part but want to be able to make a few different lengths anywhere from 16" to 32" long. Furthermore the hole tapers at the very end down to 0.2" for taking the core sample. Last time I made one the weld failed in a tree, but it was laser welded, so I am thinking TIG would hold better. Calculating by hand, the borer will be able to withstand ~64ft*lbs (41° twist) instead of the 71ft*lbs given by SolidWorks.

mjr6550 · Sep 20, 2020

As an engineer, this smells bad. You are going to try do-it-yourself heat treating to hopefully get a tiny increase in yield strength. Then your calculations show that you need 65 foot pounds torque rating and calculations show you should have 71. Not much of a factor of safety.

If this is something you are doing for yourself I would try it without heat treating and maybe see if you can do something to reduce the torque requirement. If this is something that you want to sell, pick a different material or increase the size.

Bendak · Sep 20, 2020

It's actually quite a significant increase in yield strength. The 4130 pipe is sold normalized with a yield strength of 435MPa vs 1331MPa after QT. I will probably make as many as 10 of these tools and test them at various hardness's. However, I may very well be limited to softwood trees for coring diameters greater than 32" given my resources. This is certainly not something I will be able to sell, at least not in lengths of 16"+.

DDoug · Sep 21, 2020

www..eng-tips.com is the place for YÜÜ.....

EmGo · Sep 21, 2020

Look up Vascomax. Comes in 250,000 , 300,000 and 350,000 psi levels. Easy heat treat, ductility is off the charts. I had a girlfriend could stand up and put one leg behind her ear, vascomax is at that level. Very easy heat treat, too.

You won't like the price, though.

Bendak · Sep 21, 2020

I just contacted them, but they unfortunately do not sell Vascomax in the form of tubing. Definitely something to keep in mind though. I wonder if I could drill 8" sections and weld them together to form longer sections of tubing while still retaining a high yield strength and flexibility?

1953chevB · Sep 21, 2020

Bendak said:
Hi all,
I have a 0.375" OD by 0.259" ID 4130 pipe 16" long that needs to be heat treated to increase its yield strength to at least 1300MPa without becoming too brittle. From what I can find online, I need to raise it to 1575°F for 30 minutes followed by an oil (instead of water due to fragile dimensions; need to reduce cracking and distortion) quench and then temper it for two cycles at 400°F for 60 minutes each. This should bring the yield strength to about 1331MPa with a hardness of 47-49HRC. Based on my calculations and simulations in SolidWorks, the pipe will be able to withstand up to 70-71ft*lbs of torque under these conditions. Unfortunately I cannot find 4140 or 4340 pipe with these OD and ID dimensions, so I need to stick with 4130.
I realize that at this hardness, the yield strength will be close to its ultimate tensile strength (1600MPa) and therefore have much less flexibility under torsion. The pipe will have a hollow screw made machined out of 4340 TIG welded on one end for cutting into live wood, and so will be hand operated at about 60 RPM.
Do you all think this is reasonable? I do not want to risk breaking the shaft under a load that may reach up to 65+ ft*lbs of torque, so there needs to be at least some flexibility.

Regards,
Jack

Please advise what is to be welded at the end of the tubing? what is material of end piece?
does it need to be hollow to get core samples?
you can actually machine a cutting teeth at the end of tubing.
as long as the tube is not yielded and does not go into plastic state it will work, how ever there will be more than torsional stress.
it will want to buckle with compressive stress, keep working at it. there is a solution. they make drill bits out HSS for a reason.

1953chevB · Sep 21, 2020

you may want to look at three drills instead of one
use three drills, 2 shorter drills and a long drill

Bendak · Sep 21, 2020

Yeah, the pipe does not undergo such torque values as high as 65 ft*lbs until it is over 3/4ths of the way into the tree. I wonder how the maximum permissible torque of the shaft might change based on whether it is outside or inside of the tree where there is a wall of compressed wood surrounding the tool.

Bendak · Sep 21, 2020

The threads are to be made out of 4340, probably heat treated as well which needs to be hollow in order to retrieve core samples.

Heat Treating 4130 Pipe Under Torsion

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