Talk to me about hardened steel, or tempering...

Factual Questions
1

Alright, I’ve struck upon an idea for a small hand tool and manufactured a prototype out of mild steel, which predictably deformed and eventually failed after extensive testing. No worries, I was really looking for proof of concept, which I got, but now I’m doing patent searches and nearly ready to fill out the forms, and I’d really like to be able to write something other than ‘hardened steel of as yet undetermined quality’ on the application.

The nominal specs, approximately- (nearly triangular in cross section)
5/8" base tapering to 1/8" point over 1/2" height

The beating- 50-60 consecutive blows with a 22 oz framing hammer, some minutes of rest, repeat. Used intermittently in this manner for 30 years.

The question-I’d like a grade of steel (or tempering/hardening process) with could sustain the above in all ambient temperatures without exhibiting anything more than cosmetic damage, while still being able to be machined with simple shop tools (angle grinder, drill press, band saw, etc.) and the cost of 1"X 1/2"x 12" bar stock (plus heat treatment, as necessary) coming in under $15, preferably under $10.

Is such a thing possible, or is this a pipe dream on my part?

2

What’s wrong with ordinary tool steel for your purpose? You have a toolbox full of it already; is that the kind of thing you need? Would your chisels do the job if they had the right shape, for instance?

ASTM 4340 is the most common tool steel alloy, and pretty cheap too. You don’t need to specify material in your patent specification, btw.

3

What he said, and I’ll add you probably don’t want to mention the grade of steel used if you think your idea’s going to be the next Vise Grip or Leatherman. As soon as your patent’s published, those crafty Chinese will be looking to make cheap knockoffs, and if you don’t mention the grade of steel in the construction, they’ll either come to market with a vastly inferior product, or it’ll take them a bit longer to go into production.

4

Sorry if my question is rudimentary, but I’m really a metal working novice. I’ve been thinking of tool steel, but didn’t know how workable it would be, not to mention the specific grade best suited to my purpose, ie, the correct balance of hardness and toughness. For instance, Wiki shows 11 grades of tool steel, of which I’d pick the’ S’ grade for its shock resistance, but I hate to think how many different permutations of that grade there may be, not to mention cost…

Concerning the chisel-I’m not for certain. Probably it would serve for some period of time, but I am looking for something to last basically a lifetime without deforming. I don’t even know if it’s possible, especially in the dimensions given and in the price range I’m shooting for; my ignorance in this arena knows no bounds.

To clarify the OP, the tool would NOT be driven along the long axis, like a nail or chisel. It would be struck from the side, like hitting a piece of 1/2"X 1"X 12" piece of bar stock on the 1" side, approximately 2" from the end. There would be some ‘give’, but at the most stressful, probably advance only 1/8" to 1/4" inch per blow.

Basically I am looking for 3-12 candidates for extensive testing, but I’d really not like to waste any more money than possible by just ordering stock blind.

Regarding the Patent App.-I didn’t think it was necessary, but I’m just sort of anal retentive about knowing specifics before shooting my mouth off. And it certainly won’t be the Next Big Thing, just a little expedient/contrivance that fulfills a little niche, which I might be able to manufacture and market myself, regionally at least.

5

How about the steel from a hammer?

Increasing hardness is going to lead to less workability, by definition.

6

Regarding the steel from a hammer-again, I’m not sure. A hammer is designed so that the mass and shape reinforces the steel; my design would be much more vulnerable. Some local amateurs (albeit much more knowledgeable than myself) seem to think mild steel properly hardened/tempered could work, but again, I’m looking for unimpeachable durability. I’d hate to sell something with say, a 30 year guarantee, then find out every single piece breaks after 12…

I guess instead of all out hardness, I am looking for the proper combination of hardness/impact resistance/fatigue resistance.

BTW, thanks for all the replies so far.

7

Tool steel is readily workable before you heat-treat it. Then it gets hard and brittle on the outside, with less hardness and more toughness as you go deeper in.

Hitting a bar on the side might put enough bending stress into it that the brittle outside layer might fail - but it’s easy and cheap enough to get some and try it. There are a host of other alloys that might do the trick, but definitely start with the common and obvious one.
The key in patent applications is to be as broad as possible in your list of claims while still being able to call them novel and useful (and those terms are pretty broad, too)… Not picking a particular alloy or heat treatment means your shape is covered no matter what it’s made out of.

8

You might want to pose the question here. I don’t have any of my materials books handy (they’re all at work), but some of the old timers there have got that kind of thing memorized, and could no doubt give you some good pointers. (Heat treating some materials can be a real bitch.)

9

Why does it have to last 30 years? Nobody expects a centre punch or cold chisel or anything else that gets beat on as its primary raison d’etre to last forever without any deformation. Ideally I would think it should be softer than a hammer, so that it does deform (slowly) over time. After all, if you strike hammer faces together you can get one splintering off a fragment that flies off at extreme speeds. I know that using one hammer to drive the claw of another in between two items to be pried apart is not uncommon, but it can be rather dangerous for that reason.

Anyways, if people have to buy replacements after a while, that’s more potential sales! :wink:

10

Let us know when you patent it, seems like a pretty neat tool, whatever it is.

11

Carbon tool steel should work for you. You only need high speed steel if will get hot enough to lose the temper. If it needs sharpening, that can happen pretty easy on a grinder…but for a prototype, you just need to take care not to overheat it.

If I was making it, I’d use O1 tool steel. Readily available as drill rod. You can buy 3’ lengths of 1/2" diameter for $10 or thereabouts. (been a while, so it might be more these days). McMaster-Carr or MSC will have it. If you have a Metal Supermarkets franchise in your area, you can probably buy it by the inch.

It comes annealed, and machines like mild steel. (actually a little better, it isn’t as “gummy” as 1018) BUT you must keep it cool with cutting oil or other machining coolant. If you let it get hot in a small area, the remaining mass can quench and harden small areas. Goes double for welding.
Heat treatment:

Work outdoors. You could well start a fire. Have a fire extinguisher handy…dry chemical, NOT water! A grease fire is not unlikely. Be careful.

Fill an old can half full of used motor oil or similar. Place this in pie pan or similar full of sand (fire/spill precaution).

Use a torch (propane will work for small items) and heat to a dull cherry red. Test with a magnet, if it is still magnetic it is not hot enough. It needs to be a bit hotter than where the magnetism is lost.

Drop it into the oil bath. Expect the oil to catch on fire. Place a lid over the can to put the fire out.

The item is now full-hard. Test it with a file…the file should slip without biting into the steel. This will shatter in your use, so you need to temper the item.

Tempering:

Polish the item with emory paper, steel wool, scotchbright, etc. You need to get all the scale and burned oil off from the quenching operation.

Working in good light, but in the shade, heat the item untill oxide colors appear. You probably want somewhere between light straw and dark brown. For your item it may be easier to place it in a pan of sand, and heat it on the stove.

Quick and dirty tempering method I have used for non cutting tools (hardened washers, custom bolts, and the like). Don’t bother polishing the item. Place it in a shallow pan (I usually use a jar lid, or the dished bottom of an aluminum beer can). Put about 1/4" of used motor oil in the pan. Play a torch on the oil until it starts burning. Keep the torch flame off the part. Get it to where the oil it will stay lit without the torch. Let it burn untill the oil all burns.

There is a lot of data on heat treating O1 online. The tempering is pretty much the same for Oil, Water, and Air hardening steels. O-1 is the cheapest, and the oil quenching isn’t really that much of an inconvienience.

12

If hardness is what you’re looking for, you might consider silicon carbide instead of a metal. I’m pretty sure that steel is tougher than carbide, though. That is to say, steel will deform more than carbide will, but carbide will break more easily.

13

Well, if you want to get serious (and expensive), M2 steel is well-nigh invulnerable to anything you can throw at it. I’ve machined the stuff, and its brutal to work with. It’ll chew up most any toolong you can throw at with nary a scratch.

14

Tell your local amateurs that mild steel won’t respond to heat treatment. It will respond to other treatments, like case hardening, but the impact resistance won’t be there. It will also work harden to probable detriment.
I’ll second the O-1 as being easily worked and cheap. Playing with draws (tempering) would yield a variety of properties between the extremes of hardness and toughness.
Should you wish to avoid heat treating, a variety of “pre-hard” stock shapes can be had. The Rc ( 40’s) hardness would mean some greater difficulty working with average home edge tools.
You might consider a laminated object too, either steels alone or other materials.

15

Right - I doubt carbide would be at all happy under repeated blows from a hammer.

16

Wouldn’t specifying a grade of steel in the patent also provide the copycats with one more thing that differentiates their product from yours? I am not a patent attorney, but I think that patent cases center around how many criteria are shared between the patent and the alleged copy.

17

Another approach – since you indicate that you’re looking for up to 12 samples to try – is to perform a finite element analysis on your tool. Obviously you can’t just do this on your home PC – there’s a lot to it, and it’s not cheap. You can, however, find companies that do this as their livlihood.

In the most simple sense, you provide the CAD, choose the materials, describe the mechanical interactions (hitting it with x force, etc.), and make your decision based on that. You’ll see quickly which material offers the characteristics that you’re looking for, as well as see which potential failure modes are likely to appear, where, and why. Aside from the material study, it may also offer feedback on how to improve the design.

Now it may seem like overkill if this is something that you’re going to sell out of your garage, or if you’re just going to license/sell the patent to another company (they’ll do all that). But if you’re looking for specific steels that offer the performance and machinability that you want, then it looks like you have an eye toward manufacturing it and marketing it yourself. If that’s the case, spending the money now for the FEA could provide data that would help you in any potential product liability lawsuits.

18

You can’t sue someone in China, and I doubt you could have much luck going after the importers. In either case, you have to pay for the prosecution, patent violations are a civil matter, not a criminal one, and patent application costs from what I understand, can run as high as $10K. Pursuing legal action against a patent violation can run into the tens of million of dollars. The upcoming movie A Flash of Genius deals with one poor bastard’s attempt to get the money he was owed after the auto industry ripped him off.

19

You have to understand that I’m talking about farmers, so case-hardening=heat treating, plus God knows how many other processes involving heating. I’d considered case hardening of a cheaper steel for a starter-but you say this wouldn’t respond well to the beating? (shatter outright and/or become brittle with time?)

As far as the heat treating/tempering/case hardening/annealing/normalizing/what freaking have you-My plan had been to manufacture a few prototypes of the various steels recommended here, then have them heat treated at a small local shop, at least at first. I’ve every confidence that I could do this on small scale myself, but I wouldn’t want to cast doubt on the torture testing wondering whether I’d done the hardening/tempering correctly. If I found a combination that suited, I might try repeat the process myself, depending on the costs of farming it out v. setting up a small forge/quenching outfit.

Looks like I’ll start with 01 and ATSM 4340, maybe some case hardened mild steel for context. I got a pretty severe sticker shock from a tool grade steel (S-7, I believe) that sounded as though it may have been suitable-nearly 3X what I was looking to spend on material plus heat treatment.

BTW, Tuckerfan, thanks for the link, I’ll lurk a little bit and maybe post when I’m a bit further along. And Balthisar, I’d love to be able to follow the course you’ve outlined, do this very scientifically, but, as yet, it isn’t justified. I’d really have to do some marketing research before I could go that far, and I haven’t even submitted a patent application.

Thanks everyone, and I promise not to specify a steel on the application.

20

Good points.