Any oil will work. I have used peanut oil - left over from turkey fry - it has a high flash point. And I've used mineral oil, which is nice because it doesn't go rancid. Motor oil is just fine for a one off. It's pretty smelly though.
I may be telling you something you already know, so excuse me in advance if I am, but 1045 will only quench in oil if it's in fairly thin sections. 1045 is a water-hardening, plain-carbon steel. If the part you want to harden is thin, oil is no problem. In fact, it probably will help resist warping a bit. But it won't quench 1045 fast enough in thicker sections.
What's "thick" and "thin"? I don't have any hard data, but I'd guess that
1/4" is the limit for oil-quenching 1045.
It's not a straight-line relationship, BTW. You have to reach a critical threshhold of quenching rate, or you get no hardening at all -- none, nada, zilch. But there is a narrow range in which you get more or less hardening. That quench-rate zone is quite narrow.
The tool is a bench block I made, cylindrical in shape, similar to the Starrett blocks. The main difference is there are 6 , M6 threaded holes around the circumference to allow clamping to the block. Diameter 3.000" Height 2.500" Wall Thickness .300" Top thickness .500"
My knowledge of heat treating is mostly theory, but not much practical work. I was thinking about case hardening, as I have 10 pounds of Kasenite, but I figured if I could harden it, then temper, that would be better, as I also have a portable Rockwell tester, and I wanted the practice.
I was reading the Machinery Handbook, and gathered that quenching in water would not produce the desired effect, as the oxygen would cause , more or less, uneven hardening.
Here's my best guess for a short answer: given the shape of your part, no. I'd go with oil. But that doesn't mean that oil will do the job you want. It means that I think there's too much risk of cracking or at least building in too much stress if you use water. You're going to do some pounding on this thing, after all. If oil does it, you're home free. If it doesn't, at least your bench block will be safer.
And here's the longer answer. Your bench block is an excellent example of why slow-quenching tool steels were developed. Fairly massive, it will not through-harden in any plain carbon steel, anyway. And the faster quench rates required by plain carbon steel will stress that part, potentially causing trouble at the holes. If you've studied some heat treating you probably know why that is. Cracks could develop at the edges of the hole(s).
The best material for that block is an air-hardening tool steel. With some skill in heat treating, it's probably also a safe candidate for an oil-hardening steel, which, by my guess, is what Starrett probably uses. If you're going to make it out of carbon steel, which is what I'd do at home, I'd make it out of 1020 and case harden it -- especially if I had as much Kasenit around as you do.
The trouble with 1045 for this job is that it's a little high in carbon, given the great difference in section thicknesses between the places with holes versus those without, for water quenching -- including water quenching for the purpose of case hardening.
On the other hand, it's a medium-carbon steel that isn't going to be subject to the fairly extreme expansion stress (the result of conversion to martensite) that you'd experience with a higher-carbon steel like 1095. So you may get away with it.
If you had used 1020 or another low-carbon steel made for case hardening, you'd probably be on safer ground because, although a rapid quench will cause some stresses due to thermal contraction, at least you won't compound the problem with differential expansion as a result of martensite conversion, which would add to the thermal stress.
1045 can be hardened up to Rc 58 with a water quench. I don't have the maximum value for oil quenching handy, but 1045 often is oil-quenched in industry. You're probably going to have to agitate the part to get enough heat conduction away from it to get any hardening at all, using oil, given its mass. Oil can harden it but it may fail entirely if the heat conducted from inside the block prevents the surface (which is all you really care about, of course) from attaining an adequate quench rate. That's the threshhold business I was talking about. The gentle quench can do some hardening AS LONG AS your actual quench rate isn't impeded by heat conduction from the mass inside. That's the classic problem with judging which medium to use for quenching, in middle-of-the-road cases like this.
Here are some links that will clear up some of these points, given that you know something about heat treating. The first two are from a 1920s edition of Machinery's Handbook. The last two are from Timken. In the very first one, scroll down until you get to the section on 1045. If you *really* want to get into it, search on Heat Treating 1045 Steel, without quotes, on Google. There's a regular cornucopia there.
Hey, you could leave it soft and you'll have a useful bench block; as-delivered 1045 ain't all bad. Or you can take a chance and learn something useful. That's what makes this amateur stuff fun.
Oh, I should have pointed out, as an aside, that there's a good chance Starrett hardens these blocks by induction hardening. This part is a natural for that process. You can get a hard surface, to a controlled depth, without generating significant heat in the mass of the part.
But that's for controlled industrial production, with experiments and tests.
you have to understand what you are trying to do... cool the part at a certain rate and do it evenly.... Each oil has a different rate of heat absorption so the different oils will give you different results. Steels have varying requirements depending on the type. There are oil hardening, air hardening and some are done in brine. Dropping the piece in a bucket will give you poor results since there will be uneven heat loss and the part hardness wont be consistent. the oil should be circulated or the part agitated in the oil.... also the oil should not be cold since it will tend to form cracks in the metal in some tool steels. If you keep the part submerged it will not smoke and will not explode. The quantity of oil must cover the piece completely or it will smoke and catch fire. don't hesitate when you plunge it into the oil and don't pull it out until it is cool.
I wonder if you could answer one question: In the description of case hardening from the Machinery's Handbook above, it is suggested that a cast or wrought iron box be used in the carbonizing process. As is the usual case for old literature such as this, the iron box is mentioned in an offhand way, as though everyone has some laying around. As you know, wrought iron stock is effectively equivalent to unobtainium these days. Is there any reason that wrought or cast iron was preferred back when that book was written? Was it just what was most commonly available back then, or is there some advantage to it over, say, steel?
Of course, acquiring the hooves and horns will be another problem! :-)
Whatever you do, the oil must contain NO water. If it does your whole quench container can explode from steam formed when the hot part hits the water. If in doubt, heat the oil to beyond the boiling point of water first to get rid of any water. Then let it cool to about room temp before using it. When yo use it, avoid the tendancy to let the part drop to the bottom of the quench container, because that's where the water may lurk.
I don't think you will be able to tell any difference between various oils in this application. I use used crankcase oil for this regularly. I agree with other posters that, in future, use 4140 or O1 for something like this.
True, stainless steel tool wrap is another example, I think. Or is that just used to seal out oxygen during heat treating?
As a point of info, that description does say that old shoe leather and belting is _not_ suitable material for case hardening. It must be the "impurities" in that leather from the tanning process (and possibly shoe polish?) that make it unsuitable. Doesn't say anything about chewy toys though! :-)
Well, that's what a heat-treating boat does, too. With a metal boat, or a stainless foil wrap, you have to throw in something to keep the carburizing potential up a little bit, even if you aren't case hardening.
BTW, something to keep in mind, if you haven't done this, is that potter's clay makes an effective wrap for slow carburizing. Just roll some out fairly thin (maybe 3/16" or 1/4" at most) with a rolling pin and wrap the part, with some carburizing material, like a burrito or a dumpling. Then pinch the ends closed, poke a couple of holes with a toothpick or whatever to keep it from exploding, and let it dry for a day or two. Warm it up slowly to drive off any remaining water, and then toss it into the coals, or whatever you use for case hardening. When it's done, just crack it open with a hammer.
I've always wondered about that. Leather can be tanned in several different ways, which have very different chemistries.
Next time I'm food shopping I'll get some burritos and give this a try. No, seriously, I take your meaning and it sounds like an excellent idea. I was wondering about using some sort of ceramic pot instead of a steel or iron box. I never thought of just encasing the part in potter's clay along with the carburizing material. Sounds much easier to do than baking a special air-tight ceramic box.
I forgot to mention that you should wrap the part in paper first, to keep the clay from touching it while it's still wet. And, if you're just heat-treating, rather than carburizing, the paper is enough.
If you're inclined to be obsessive, lay a strip of wood lathe or something similar on each side of the clay when you're rolling it out, for screeds. That way you'll get a uniform thickness of clay.