Heat treating questions

[ChuckTilbury]

I have heat treated 4 blades now and I have a couple (actually a bunch) of questions. I am using lump charcoal with a blower for my heat source and I am trying to keep the metal as high in the fire as I can (trying not to decarbonize it) and still get it hot. In general, I am heating it just to the critical point (dull red) on the blade only and leaving the tang below critical and quenching it as quick as I can out of the fire. I have tried W1 and O1 steels, and I have separate questions about them.

1. All of them appear to have raised spots when I grind the scale off after hardening. Is that normal? Sign of something wrong?

2. I heated the first knife (made of O1) to where the magnet did not stick, but it was not dull red. It did not really get that hard, but the blade will take an edge. I have not tested it to see if it holds the edge or if it is flexible. To test it, I am thinking if driving it through a 2x4 with a mallet like they do for the ABS test. If the edge curls, at least that will not destroy the blade. To see if it is flexible, is there a non-destructive test? Or do I need to really bend it?

3. I wonder if I reheat the blade to a lower temp (O1 at just barely, or a very dull red), but still to critical (magnet does not stick), and do it several times, will that help it to get hard? It did not really get that hard when I tried heating it one time before, but the blade positively did not warp. When I heated it hotter, it seemed to harden well, but the blade warped really bad. The edge (which I guess was way to thin) warped to a wavy shape and I had to make the blade much shorter to fix it.

4. I made an unsuccessful blade from a worn out file (W1 steel, I guess) that I had laying around. When I annealed it, I put it in the charcoal fire and let it set overnight. That worked OK, but I suspect that the steel was over heated. It had areas that looked as though it had melted and there was thick scale all over. Some of it was more like slag and quite hard to grind off. I went ahead and made a blade, hardened it in fresh water and it warped pretty bad. I tempered it at 400F for an hour. I dropped it on a concrete floor and the blade snapped like glass. It looked all rough and crystalline in the break and did not really fit back together. The question is: Does that seem like the metal was over heated when I annealed it? Or did I harden/temper it badly?

5. I think I have handles down as far as brass and wood goes. I made one from solid aluminum that turned out well, too. I need better information of recipes for hardening and tempering, though. Anyone have a favorite site or book?


Thanks everyone!
Chuck Tilbury

 

[LRB]

The magnet does not tell you when to quench. Non-magnetic is only 1414°. Knife steels require a minimum of 1450° and range up to 1525° for carbon, and as much as 1950° for stainless. That's one major reason your blade did not harden. 01 is a steel for those with ovens, salts, or other temp controlled methods of heating. 01 requires a soak at quench temp of 15/20 minutes, 1475° to near 1500°, or it will not come out well. It sounds like the file was over heated. That can be corrected with heat cycling, but for now, stick with steel like 1075/80/84. Any of those are much easier to work with in heat treat with the equipment you have. Read the "STICKIES" on this forum, and you will learn a good deal about HTing various steels. BUT, definately forget the magnet, except as a guide to tell you to increase the heat a bit more. The term, "critical heat" has seemingly evolved from being synonymous with non-magnetic, to being the particular target heat for a good austenite solution in a given steel type, and it's subsequent quenching. Many common blacksmiths still use the term for non-magnetic, but most bladesmiths and knifemakers use it otherwise. This change in definition has confused many, and continues to do so.