Increasing strength of steel through rolling

Try induction-hardening for the edge?

Flash

Robin:

You can buy A-2, D-2, 0-1, etc., sheet stock in .030 thickness. Saw out your parts, machine the edges, have it heat treated. A-2 doesn't move much on heat treatment. What you suggest might very well work, but beyond the learning experience, why go to the expense and trouble?

Robin:

If you're worried about the parts turning into potato chips after heat treating... make them thicker, heat treat 'em, have them double disk ground, then grind your cutting edge on them.

I should have mentioned that production quantities could be in the bazillions so cold processing the parts to a good surface finish/ flatness without secondary operations is a necessity.

Thanks for the suggestion though. You'd be bang on if I was only making a handful.

Regards,

Robin

The ASM Metals Handbook indicates that .60% to 1.00% carbon steel can be cold worked up to around 150 ksi tensile by drawing to a 80% to

100% reduction in area. Whether this is practical by rolling is another matter. I'm sure there are rules of thumb for the forces and power for rolling, but I'm not sure where to go to find them. If you want to run the numbers yourself a good place to start would be googling "hertzian contact stress."

I have done some work on hot rolling mill design, working at temps where the materials' yield was down around perhaps 20 ksi. One mill was rolling bars about 5/8" diameter. Each stand required around 100HP and must have weighed 2 tons. And since you're deforming the material and introducing lots of internal stresses, it's not easy to maintain flatness while rolling. Levelling or straightening is generally a separate operation.

Bob, Nice to see a post from you. Robin is Canadian, he likes to struggle. :)

Robin, I concur with Bob. If flatness is an issue you can get it heat treated between plates.

Best to you both, Steve

Robin, maybe you can find out what the razor blade people are using for raw stock?

Best, Steve

A 100% reduction in area? Like, "gone"?

Gak. I'll continue to look, but after looking at the first six links or so, the math exceeds me.

Any idea what the precent reduction was per pass? This will give me a rough idea I think...

While I've never done rolling myself, it seems the the load/ deformation is symetrical. I could see wear/sloppy manufacture being an issue, but assuming the mill is built with the intent of creating a high-quality finish/flatness specification, it seems that one would achieve good results. Obviously I can throw this idea out the window if the blank material was not correctly manufactured for this purpose... And, of course I could just be dreaming anyhow.

I was thinking of hardened/ground rollers several inches in diameter, a couple or more HP with significant gear reduction, and a frame that would (vastly) exceed requirements (no welded tubes!) so that nothing moves. Flex in the rollers would destroy any hope of flatness.

Anyway, thanks for the helpful info Ned. Certainly the type of help I was hoping for.

Regards,

Robin

I thought about that originally. Wasn't sure if that would do anything for the flatness (potato chip once the plates open). Have you seen this work? Neat idea for sure.

Regards,

Robin

I have had things annealed between plates, but not heat treated. I would think it would be feasible. Quenching might be the stumbling block.

How about something like 17-4 that hardens at a relatively low temp?

Best, Steve

That's an excellent idea as well. Very similar application.

Just looked on Google. I'll have to do a more in-depth crawl tomorrow. A fair amount of junk. I get the feeling these are guarded processes...

Regards,

Robin

I thought about that originally. Wasn't sure if that would do anything for the flatness (potato chip once the plates open). Have you seen this work? Neat idea for sure.

Regards,

Robin

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I'm sure you realize that if you work-harden the piece overall, and then heat-treat the edge, you're going to have three zones: the hard heat-treated zone, a fairly hard cold-worked zone, and a very soft heat-affected zone in between the two. The size and nature of that zone will depend on how you heat-treat the edge.

In any case, you're going to have some hellacious stresses there, just from the different densities of martensite and ferrite, no matter how narrow you can make that zone to be. It ought to warp like hell.

If you're going to heat-treat it, you're better off heat treating the whole thing, IMO. If you're going to work-harden it, just work-harden it.

I say this assuming I didn't miss something along the way, in which case I might be misleading you. But if I didn't miss anything, then I'm not.

-- Ed Huntress

That's an excellent idea as well. Very similar application.

Just looked on Google. I'll have to do a more in-depth crawl tomorrow. A fair amount of junk. I get the feeling these are guarded processes...

Regards,

Robin

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If Gillette is still doing what they did when they were my customer, their steel stock is a custom alloy and they'll cut the dick off of anybody who makes it public. It says so right in their contracts. d8-)

-- Ed Huntress

Ed, I had a customer that needed to sharpen some blade stock for arthroscopy balloons and tried to find out how the razor folks did their sharpening. It's as you said, a closely guarded secret. I didn't realize that the steel was a trade secret also.

Best, Steve

Back about 1960, a major razor blade manufacturer bought all the rails from the Irondale, Bancroft and Ottawa Railway (the IB&O was so slow it never got past Bird's Creek, just outside of Bancroft) This was a light rail rolled in IIRC Birmingham. A few months latter Gillette brought out their "Super Blue Blade". Gerry :-)} London, Canada

Well, almost gone. If you take a 1/2" diameter rod and draw it down to .050 wire that's a 99% reduction in area.

Just looking at the formulas should give you an idea of what you're up against. To keep the forces low you want small diameter rolls; go too small and the rolls are too flexible. Small working rolls with larger support rolls backing them up is the usual solution to that problem.

A Sendzimir mill ("Z-mill") is the extreme case, and is the norm for rolling high tensile materials to tight tolerances and high finish.

You do have the advantage that your pieces are small, so you wouldn't need long rolls.

Around 15%.

I'm no expert, and there may be ways of controlling curl, but in the couple mills I've been around that were rolling discrete pieces rather than continuous sheet, distortion was an issue.

Thus the Z-mill.

No problem.

That sounds like 2" sections of wide bandsaw blade. What material will it be cutting? You do realize that hardening or cold-working the steel won't make it any more resistant to deflection, right? Harder steel can bend further without taking a set, that's all.

I made some paint scraper blades out of a 10-for-a-buck blue hacksaw blade yesterday. It bent almost to a right angle before breaking, and the steel is so hard that it snapped like glass with no deformation at all. The blades stay sharp MUCH longer than the one that came with the scraper.

Today's project is making a 41" brake to bend aluminum to cover the window trim.

Jim Wilkins

There was an episode on the History channel on cutting tools and razor blades was one segment. maybe the History channel on line has the episode. look for cutting or sharp things. I forget the exact name of the show.

Thank You, Randy

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Robin-What about buying a fine tooth bi-metal bandsaw blade and grinding your teeth into that? I know that in production quantities thin edges are heat treated using induction. The blade passes through the induction heater coils on a conveyor of sorts. Then depending on the material either air or fluid is used as a quench. Followed by another induction tempering coil if needed. I have seen film of this process. The HAZ is skinny and does not tend to warp the parts. Cheers, Eric