Machining Steels

[Youngguns]

I'm not entirely sure where I'm going with this thread, so please excuse my ignorance and bare with me. Since I'm not entirely sure what I'm shooting for, it's going to be short.

What steels would be good for a knife blade, but also machinable in their annealed state with high speed steel/low-end carbide tooling?

I didn't give much to go off of, but if you wanna knock it out of the park and talk about various steels, cutters, speed, what makes something easy/hard to machine, etc. go right ahead. I'm here to listen and learn.

 

[dr_clyde]

I've made knives with 154CM. It comes unhardened, then you send it out for heat treat or do it yourself after you've shaped the knife. Leave a little for final grind and polish.

 

[2mJps]

If you are thinking cheap. A guy that sells high end knifes told me that what he uses is the same steel used in 73/ 87 GM pickup rear leaf springs. He said he made several from springs before he started buying sheets of it and burning out blanks.

 

[longlivepunk]

For a knife you'd typically want a bit of a higher carbon steel I believe, something that you can harden without making overly brittle (or a nice stainless), but if you want something easily machinable you're usually looking at a carbon content under about 30% or the addition of some soft alloying elements (lead, sulfur, or phosphorus)

Basically I don't think that there's something that will machine NICELY but also make a good knife-blade (though I could definitely be wrong about that) But if what you're looking at is making knives and the machining will be the sharpening/cutting/drilling holes I'd definitely go with something more suited to knives, it may not cut nicely, but it will cut, and it'll grind just fine.

 

[383 240z]

I've made a few knives out of old worn out mill files. They worked great. Dull files are EASY to find at flea markets, sharp ones however...

 

[Youngguns]

Well, a high-carbon steel blade is hard from hardening the metal through quenching and tempering, correct? How hard is an annealed (hasn't been heat-treated) high-carbon steel to machine? Is annealed high-carbon steel still too much for HSS cutters?

 

[longlivepunk]

Carbon is what makes it possible to harden steel, but high carbon steels (.6-1.5%) aren't necessarily hardened, it takes heat and quenching to harden steel. Tempering softens the steel slightly after hardening and is used to make the hardened steel less brittle and "tougher". Annealing is the act of normalizing the steel, taking all the hardness out of it.

What machining are you needing to do? I cut mid-carbon steels (.3-.6%) like 4140 (.4%)all the time and they cut great, but the higher you go the more you'd want to use abrasives rather than cutters. Keep in mind your cutter has to be harder than your material, and HSS is a high-carbon steel, so it'd have a hard time with other high-carbons, even before hardening them.

Edit: a possible solution for you might be to use a mid-carbon steel and then caseharden to get a tough surface on it? Maybe someone else on here could clarify whether or not a mid-carbon steel would actually be able to absorb much of the additional carbon from casehardening?

 

[zkling]

What type of knife are you making and what machining operation are you wanting to do? Drilling a few holes or profile milling out a shape? 154CM ATS34, S30V/35, 440 series and then the tool steel series such as D2 are all good choices. The problem you might run into is the heat treat setup. To get the most out of those steels you need to have a pretty exacting heat treat method.

May I ask what your exact project is aiming for?

Although I've done a few stock removal knives, I primarily focused on forging and thus the carbon steels.

 

[Youngguns]

May I ask what your exact project is aiming for?

I guess I have been a little evasive. The idea is to basically make a pocket knife for a school project. So, the dimensions/cuts need to be fairly accurate, I can't just go pound this out with a hammer. Well, I guess I could, and then sand/grind/file it to shape. But, I'm trying to utilize the school's machine shop and machinist to make for a much easier time. I keep getting turned down on material choice because he "can't work with it," but I think the more accurate description is that he has never worked with it and doesn't know if he can (belief derived from the multiple "maybe" responses on some HC and tool steels).
I'm not a machinist, and I don't cut up different steels every day, so I'm not saying I'm correct, I've just been assuming that a heat-treated steel is harder to cut than a non-heat-treated steel. I wish I knew more about the machining process and various materials. Like I said, I'm here to learn. Please help me understand and select a material that will work for my requirements.

P.S. I'm not trying to sound like I know more about metals or machining than the machinist. He is an older gentlemen that I believe has worked for the school for most/all of his career. So, I believe there is a possibility that he has never had to machine HC, tool, or exotic steels.

 

[longlivepunk]

If you want to learn more about the trade, videos online are a great resource. Check out Tom's Techniques, That Lazy Machinist, and Tubalcain. As for recommendations on the actual material, zkling will know better than me, but I'd think a nice tool steel for the blade. Just grind rather than cut it. Only pain in the *** would be the pivot hole, time for a mill with a carbide drill or endmill. Then the body can be just mild steel or what-have-you. Post pictures of your project!

 

[MoonRise]

In the annealed state, pretty much all steels can be machined in some way.

O1, W1, D2, 1095, old Chevy leaf springs, an 'old' file, etc are all various steel alloys that have been used to successfully make knife blades. All are 'machineable' in the annealed state to varying degrees.

What makes steels hard to machine? Generally, their hardness makes them hard.

Machine them in the 'soft' annealed state (and don't 'mess up' when machining them by getting too hot!) and you can pretty much machine any of them.

Once the steel is hardened, grinding is pretty much the only way to 'machine' the hardened steel (leaving out laser, or plasma, or waterjet, or EDM, etc, etc).

State with a piece of annealed steel of your choice, rough machine it, have it hardened (via quenching) and then tempered, and then you do final fitting with various abrasives (stones, grinding, etc). All doable, done all the time.

Your choice of the exact steel alloy you use depends a bit on what final properties you want to end up with and if you are trying to do the heat treatment yourself or will have a competent heat treater do that part of the process for you.

Don't want/need stainless properties? Then don't use a stainless alloy.

Trying to do the heat treatment yourself? Then you will want to use an alloy with an 'easy' heat treatment profile. Probably something like 1095 or O1, where you heat it up and then quench it and then temper it. No need there for 'complicated' time-vs-temperature profiles, no sub-zero temperature treatment, etc.