MattBower

Last March of the Ents. (Yes, I'm on a bit of a Tolkein kick at the moment.)

Yeah, basically, although commercial casting sands use specific mixes of different proportions of different grain sizes to give the sand the desired properties (porosity, green strength, moldability, surface finish, etc.). And of course it needs a binder -- bentonite clay for "green" (clay-bonded) sand, with just a little water.

It took me a second to figure out what you mean, but yes, that sounds like a pretty good idea for hollow grinding.

Not mine, by the way! Just to be clear on that. I wish I had that kind of skill. Or half of it.

No offense, but you can't have looked very hard. Viking Age forges were simple side blast designs and used charcoal for fuel. There is much to recommend a side blast design from the perspective of simplicity of construction. You'll see very fancy side blast forges with water cooled cast iron tuyeres, but it doesn't have to be that complicated. You could make a side blast with a firebrick "shield" fairly easily, I'd think. Lots of other simple forge designs at that second link. (And click the link at the bottom to see part 1, which features even simpler forges.)

I've heard the same: he can be a little slow to respond when he has a lot of orders.

Please don't take my point about cryo vs. cold treatment as critical; it was intended to be informative, partly because I realize English isn't your native language, and partly because you're new to blades. The knife looks pretty good to me. You said you're doing everything by hand; did you use files and stones to put in the bevels? I notice what looks like a little bit of rounding where the plunge starts. I can't seem to get that perfectly square -- yet -- even with a guide for the file to ride against.

Theoretical adiabatic (without heat transfer) flame temp is what you see quoted in the flame temperature tables, and it's very different from what you can achieve in a forge or furnace in the real world. You would be really pushing the envelope to hit 3000 degress in a propane forge, I think, and many forges can't even hit the ballpark 2300 or 2400 you want for forge welding mild steel. In actual practice, 2300 degree fiber blankets hold up pretty well at forge temperatures (even forge welding), especially if they're protected with a thin layer of castable refractory as a hotface. What's more, overheated fiber blankets begin to shrink and lose some of their insulating value, but they remain usable well beyond the classification temperature. (At least the traditional ceramic fibers do. I've heard different concerning SuperWool.) I know of at least one guy who makes wootz -- which requires making molten high carbon steel) -- in a "furnace" composed of nothing more than a tube of several wraps of ceramic fiber blanket. I'm sure the stuff doesn't last long at those temps, but it illustrates the point.

First, congratulations. I look forward to seeing pics! (Hint, hint.) Second, I had no idea residential freezers get that cold. I've never actually measured the temperature in mine. (I believe you. I did a little googling, and -27 C/-16 F is well within reason. It was just a surprise to me.) Third, although Steve is being perhaps a little more curmudgeonly than is absolutely necessary here , he's right that within the bladesmithing world there's commonly a distinction made between "cold" treatment" and "cryo" treatment. The exact dividing line isn't clear -- hey, we love our poorly-defined jargon as much as anyone else, and we also love to argue over the definitions -- but many bladesmiths would say that a home freezer treatment isn't "cryo." Liquid nitrogen clearly is. A dry ice and acetone bath? Hmm. That one could probably start an argument. Ultimately, though, that's a question of semantics. If your manufacturer says holding at -15 C for time "X" will eliminate retained austenite (and that is what the data sheet suggests), then that's a pretty good place to start. -15 C is not cold enough to have any significant effect on retained austenite in most steels that tend to retain austenite, but perhaps yours is right on the edge of full hardness at room temperature. (If that's true, then the cold treatment will make very little difference in final hardness. But that's OK. You're running the freezer anyway.) Again, we'll be waiting for pictures.

Water expands its volume by something like 1600 times when it flashes to steam. If it happens to be covered with molten metal, nasty things happen. Since nearly all molten metals have a melting point *way* above the boiling point of water, they will flash water to steam instantly if the two come in contact. If you put a skimmer that hasn't been preheated into a crucible full of molten metal, or pour a molten metal into a metal mold that hasn't been preheated, or add metal to the molten charge without preheating it . . . you get this: http://www.liveleak.com/view?i=93a_1251647793 This is the kind of thing I was talking about when I said you need to read up on the safety aspects of casting before you try it. Green sand casting involves moist casting sand. The difference there is that the sand is porous, which lets the steam escape without building up any pressure.

Fangorn Forest. :)

It may turn out OK. And if it doesn't, it'll be a learning experience.

Yes, they're very conductive. I would think that serious electrical grounding would be essential if you were heating a salt pot with something like an electric kiln. As to corroding the heating elements, I think that's only if you let the salts out of the pot -- which you're not supposed to do. (That "wink" there is because keeping the salts in the pot apparently isn't always as easy as it sounds.)

I noticed that your supplier does carry O1 and 5160, both of which are much more common blade steels for beginners or near-beginners. I'm just saying. . . . Good luck with your heat treat.

That's good advice, Rich. in his other thread I mentioned that he isn't exactly starting slow, which was probably a little too subtle. But I gather that he's already got the steel and the kiln, and in his place I probably wouldn't be able to resist trying them out, either. Personally, I'm stickin' with my 1075-1084 for now. :)

Thanks, Grant. You're right. That wasn't as clear as it should've been.

Sorry, you did say that; it slipped my mind somehow. Still and all, the composition of N690 is right in the same range as that of Panzer36 with respect to the most important alloying elements. I would treat them as the same, at least as a starting point for experimentation. As Thomas explained, with stainless and high alloy tool steels, an important reason for soaking is to get the carbides into solution. Alloying elements like chromium, vanadium and molybdenum get in the way of the carbon dissolving out of the carbides and going into solution in the iron, which is why those steels need longer soaks at higher temperatures compared to simple carbon steels. I think you are absolutely correct not to extrapolate to 6 minutes for a 3mm thick blade. I doubt that's long enough to get everything into solution. I'd try 20 min., quench in oil as recommended by the manufacturer, and see what happens. Be prepared to temper immediately after the quench, and also be prepared for the possibility that you'll lose the blade in the quench. It happens. That's just part of bladesmithing. If it happens to you with this steel, consider trying plates for the quench on the next blade. Plate quenching simply involves pressing the blade between two thick plates of aluminum, which will suck the heat out of it quite rapidly compared to air, but not as fast as a liquid quenchant. At least that's the theory. I've never done it, so I can't give you any practical tips. I bet some here can, though. Scroll down on this page for a visual, and a description of hardening 154CM (another stainless knife steel) with plates: http://mickleyknives...ml/page_21.html

According to the manufacturer, Bohler-Uddeholm, you need a 20 minute soak at austenitizing temp. (Presumably that's for blade thicknesses, since N690 is designated as a knife steel). They also call for ramping up the temp in stages, with 15 minute soaks in the ranges of 650-705 deg C, and 815-870 deg C. Also note that although the data sheet says it's an oil quench steel, the heat treat summary says a plate quench with forced air is typical. That's more in line with what little I know of heat treating stainless steels. They tend to be very deep hardening, so it surprised me when you said (and I verified via the data sheet) that N690 is listed as an oil quench steel. The oil quench recommendation may be for much thicker cross-sections than a typical knife. It is common to use more severe quenchants as the size of the cross-section increases, because large pieces hold so much heat that it can present problems in achieving an acceptable cooling rate. But what works well for a very large piece may destroy a thinner cross-section of the same steel All of the above is based on the manufacturer recommendations and my own limited knowledge. (I use much simpler steels than you're dealing with, because I lack the tools to properly heat treat fancy steels.) If you can find a knifemaker who has experience heat treating your steel -- I read this morning that N690 is a common blade steel in South Africa -- you should certainly listen to what he has to say.

You heat the blade for quenching in a bath of molten salts. Rapid, more uniform heat transfer, which minimizes warping, and no oxidation problems because the salt protects the steel. But there is also some real danger involved.

(1) It was dumb to leave a pressure vessel in the vehicle. (2) It was really stupid to leave the valve open, however slightly. That's the kind of thing you have to triple-check. (3) It was incredibly stupid to start the car while it was full of acetylene. (4) @clinton: The older of a high school friend of mine used to do the same thing, except they used pieces of toilet paper as fuzes. Eventually one of the ballons went off in the truck, which set off all the others. The damage was impressive, although nowhere near as impressive as the pics at the link above.

Iron is very far from the simplest metal to cast. If you're new, start with aluminum.And you need to do a lot of reading ahead of time, with a particular emphasis on safety. There's a good bit to learn. Lindsay Books sells a number of good titles. The books by Steve Chastain are very good. And as Thomas P always points out, you can get them from your library via inter-library loan.

I know folks who've done it. What do you plan to melt?

For what you're doing, the real right answer is a high temperature salt pot.

True adobe is clay, sand, water, and an organic fiber like straw or grass. Tim added wood ash for insulation. It adds little if anything, and I'm not even sure it retains any insulating value when mixed in with adobe.

Go ahead and use metric. We have google to do the conversions. Your steel is very close to N690. Very unusual stuff. It should make a very good blade. You're not exactly starting slow. ;)