Hey Y'all,

I would like to describe how I've been heat treating my knives and see if what I am doing is moderately correct or way off base, and to see what sort of comments I can get on improvements to my technique.

First off let me say that I do this for a hobby only. I have made 22 knives at this point so I am really just getting started, but it is very fun. I get 1/8" x 1 1/2" inch 1095 barstock and do stock removal. I grind the knife to almost finished but I leave the blade edge about the thickness of a hair. I've been doing a convex edge grind on most of these knives. Then I finish it to a clean 220 grit surface.

I heat treat right now with a hobby torch that uses little cylinders of MAPP gas and oxygen. It seems to work good for knives up to about 5" long, so that is as large as I make my knives right now. I do one stress relieving heat to red color and then aircool until cold.

When I heat treat I get that torch going with a little pencil blue flame and I lay it to the blade mostly at the spine and thick parts of the blade first to get it good and hot. I only heat the blade back to the ricasso area. I keep checking it on a big magnet that really sucks it down hard if it ain't got to the right temperature yet. Once it gets nonmagnetic I move it about a foot and quench it in about 1/2" of goddard goop (bacon grease, parrafin wax, and transmission fluid) that I heat until it turns liquid. I quench the blade by rocking it back and forth until the whole blade loses its red color and turns black.

Then I take it out of the quench oil and walk about 10 feet out the door of my shed and run it under a fast running outdoor faucet until it is cold, 3-4 seconds I would say. I take the blade back in the shed and check it with a file for that glassy feeling on the edge, then I wirebrush the scale off and pop it into my toaster oven. I have a oven thermometer in the toaster oven to check the temp.

I put it on 450 F and heat it for two hours. When I take it out it is a light purple color that looks yellow when you move it around. I don't take it out until it is cool to the touch. When it is cool I put a temp edge on it and try it on a brass rod and it cuts into the rod. That quench oil makes the steel very hard, but It is flexible to a good degree. I can flex it against my thumb and it flexes well and returns to true, but if I bend it past a certain point (maybe 25-30 degrees) it does take a set and stays that way. Have never had a problem with the edge cracking yet, and when I destroy one I have to bend it 8 or more times 90 degrees each way before it breaks.

Now my questions. Should I be running the blade under the faucet to finish off the quench? I tried putting it in the oil by laying it on its side but it kept warping. Should I be using quench oil in a can so I can submerge the blade instead? When I etch the blades I always get a good strong temper line where I edge quenched, but from the water I usually get a swirly pattern on the spine, and sometimes it looks like there is a hardened grey area along the spine with the soft dark part in the middle of the blade. What should I do to get a true spring temper to the back of the blade while keeping the edge hard. I have tried these knives on deer and farm chores and they work well and hold a good edge. Do they take a set because I am using eigth of an inch barstock or because I am getting the back too soft or running the temper temp too high? When I do the temper should I let the knives aircool from 450 F or should I take them and quench in some water when they are done? Thanks for any info, help or comments any of you provide.

Chuck

I almost hate to say this after all that typing, but this would best be answered by Ed Caffrey. Why not copy this over to his forum?

Rob and I tend to be high alloy guys...

Chuck, I agree -- Ed's the man for this one.

Moving to Ed's Workshop...

Here's how I do it--and remember, there are many fine smiths out there who all have their tried and true techniques that work for them. Round up a lot of advice, try it all, and stick with what works for you.

I heat my blade to non-magnetic and then edge quench in vegetable oil which has been heated to about 120 degrees F. I submerge the point and then drop the edge of the knife into the oil very quickly, rocking it back and forth quickly, and moving it from side to side in my oil pan so that it doesn't stay in the same place for very long, thus heating the oil around the blade to much. I hold it in the oil until all color is gone then I submerge the entire blade and keep it moving until it is no longer radiating heat. Then I move it to a room temp oil can and quench it in that until comfortable to hold. I then clean the blade in soapy water, and file test the edge. I then clean the blade to shiny metal and bake in an oven at 375 degrees F. for about 3 to 3 1/2 hours--checking the blade every 30 minutes for color changes. When finished I end up with a blade which is between a brassy to light bronze color which most people call straw color.

After cooling, I again clean the color off the blade, and I temper another time with a gas torch. I aim for straw on the edge, reddish purple in the center and bright blue on the back. Much care and practice is needed for that. Some of my first blades ended up all blue very quickly, and had to be re-quenched, etc. etc. Keep a bucket of water close by to quench immediately if the colors begin to move too fast. Some people like to use a heat sink paste on the cutting edge while tempering to prevent the edge from softening too much.

Again, that's what works for me. I use a lot of 1095 and 1084, and find I get a pretty tough blade which has a good cutting edge.

Note: All the above is based on the fact that I normalize after forging 3 times, and once again before quenching if I have done any grinding on the blade. Failure to properly stress relieve a blade by normalizing (heating to non-magnetic and then allowing to cool to room temp in still air) voids all the above, as I found out the first time I short cutted that process and cracked my blade on the quench--after which I didn't have to be concerned with heat treating--only how far I could throw it into the woods. :) Hope this helps. Again, it is not the only way--just what works for me.

I second the multiple normalizing. It will shrink your grain drastically and give you a much better edge and toughness. I'd say you were right in thinking about getting a deeper oil pan to completely submerge the blade afterwards, or even a bucket of water to finish the quench in will work. I'd recommend you temper the blade at least twice and allow it to cool to room temperature, Do Not quench in water after the temper as it will introduce new stresses.

Heat treating with a torch is pretty tricky, but as long as you're getting an even heat over the blade and not overheating any parts, your methods sound good. I consider the magnet essential for heat treating as the numbers in the books don't always correspond to the particular batch of steel you've got. What does your grain look like when you break your test blades?

Unless you draw a spring temper on the back, or quench it when it hits the right temperature to give around a 45-50RC, your blade is going to take a set when flexed past the sticky point (i forget the name). To get more of a spring, you can also increase the width of the hardened portion of the blade, but this will make the blade fail the 90 degree bend test. You have to compromise and determine what the knife will be used for. If you'll be prying with the knife, go with an austemper.

Thanks for the replies so far Dana and Joe. When I break my blades the grain is very small and silky looking, especially in the hardened edge section. What is the benefit of more than one tempering cycle? If I am not forging (strictly stock removal here), do I need to normalize more than once before I heat treat? If so, why, does grinding cause grain growth? When I temper, should I be getting into the purple range? My blades always look purple and yellow at the same time. Thanks for the replies and comments.

Chuck

Well, I had a late day and didn't get to the post in time, but Dana nailed it down! The only things I might add are as follows........
Personally I have found little to no benift from multiple quenching plain carbon steels. Although I do not have scientific facts to back it up, I'm convinced that the small amounts of Cr in some steels is what makes the multiple quench so effective on them.

Normalizing is a vital step in any bladesmithing operation. It not only aids in reduction of grain, but is a stress relieving step that will help minimize warpage latter on. I always normalize after I grind, simply because non of us has the capability to grind the exact amount of material from each side of a blade. This combined with the heat generated during grinding creates stress the will cause a blade to warp when heat treated. By normalizing prior to hardening, you can eliminate about 95% of warpage problems.

The one thing that MUST be understood is that each specific step, from forging at the proper temps, through normalizing and annealing, to hardening and tempering are all inter-related in the completed blade. Each sets up the steel for the next, and if any one is not accomplished, or accomplished incorrectly, it will affect the next, ending in a less than optimum blade.

The purpose of more than one tempering cycle is basically insurance. One cycle may not completly convert the steel. This has been evident to me in blades that have failed the ABS JS test. One blades that have broken, I have often noticed that there was almost a layered effect. When I questioned the individual(s), about tempering, the response was always the same. They had tempered only one time, to one hour. I always temper three times, regardless if the blade was multiple quenched or not. It doesn't cost me anything but a few more hours, and I believe it is the cheapest insurance you can get.

As for the tempering colors you described, I see nothing wrong there. I suspect that with those colors on 1095, you would be able to pass the brass rod test. However, that is one of the joys for me with steel..................Experimenting, not only to achieve optimum results, but to enjoy the learning experience.

Just keep experimenting, and you will come up with the proper cycle of events to achieve the blade performance you seek. Meanwhile, we'll be here to help in any way we can!

Thanks Dana, Joe, and Ed for all of your expert comments. I really feel much better about what I have been doing, and you have all given me ways to improve my technique. Thanks again, you guys are top shelf

Chuck