Thread: My Heat-Treating Process

Great post. I appreciate you taking the time to spell this out for us.

Thank you for posting this Josh. A very interesting plethora of information.

Josh,

Thanks for for the walk-thru on the hardening and tempering processes. Now all I have to do is get grandpa's cast iron forge with hand cranked fan going and it's martensite city.

Long ago when I fancied myself as boy blacksmith I did use that forge when it was still on the farm to make a new burner grate for grandma's stove. No heat treating, grinding, or honing necessary, thank heavens.

Very good post! Thanks for putting this together.

The only observation I have is the "soaking" time. Most of the recommended soak times are for a piece of steel that is one inch thick. Our blades are much thinner so I do not think that we need to soak them that long at critical temp. I am trying to catch mine maybe 30 seconds after the magnetism is gone. I am using 1095 and old files.

I agree on using 400 as a temp for tempering. 350 is not enough.
I temper for one hr, let cool to room temp, then repeat. I have finished one blade using that routine and it is hard but it can be honed.

Randy,

You're right about the recommended soak times being for steel 1" thick. But from what I understand it's still good to soak any piece of steel for at least a couple of minutes, just to be sure you have full solution. The spine on my blades is usually 1/4" thick, and I like to make sure it's evenly heated all the way through.

1086 and similar steels come into full solution pretty quickly. Steels like O1 need five to 10 minutes in blade cross sections. I think the soak time for O1 is 30 minutes per 1" of thickness, so you can extrapolate downward from that.

The soaking thing is assuming that you're able to control the temperature to the point where you aren't going to overheat the blade. If you have some control, soaking won't hurt anything except maybe cause a little extra decarb, which you'll grind off anyway.

If you can't control the temperatures fairly well, soaking is risky. Overheating is just about the worst thing you can do to a blade...

Josh

Also, on the tempering cycle... A lot of guys recommend doing two or three one-hour cycles, but from what I understand there's no difference between doing two one hour tempers and one two hour temper. The reason guys like Kevin Cashen let the blade air cool every hour is to do hardness testing. Kevin likes to zero in on an exact RC by tempering in stages.

Maybe Mike will jump in and clarify a few things...

Josh

Josh,

Great post, I just read, reread then read it again. I really appreciate you taking the time to document and post this.

Charlie

Not much to clarify Josh. This is a good summary of the whole process, and a very good piece to defuse the need to have all sorts of high test equipment. If a simple system does the job, so much the better. I notice that you substitute the human computer for the digital controller in this arrangement. That saved you about 400 bucks right there, but then you don't have to feed or entertain a digital controller....LOL.

I'm lucky. I have the good equipment, but I still baby sit my salt pots. Even for the thin section blades I make, I soak them for at least 3-4 minutes. I can see the limitations of doing that in a more aggressive atmosphere like an open forge because you have to make the blades thicker to account for the scaling. But you can design a simple, controllable forge like Josh's that will "hold" at a temperature and that's the secret to beating the grain growth problem.

It's all good stuff. Being aware of the variables is the key. Controlling them with the tools you have and being able to explain how you approach them is really helpful, especially when educating customers.

Originally Posted by JoshEarl

Also, on the tempering cycle... A lot of guys recommend doing two or three one-hour cycles, but from what I understand there's no difference between doing two one hour tempers and one two hour temper.

Josh

There is a small difference between using one temper cycle versus two or three: any Retained Au,stenite is converted to Martensite during the cooling after the blade is heated to tempering temperatures, so the blade has some fresh Martensite along with the (more desirable) tempered Martensite after the first cycle. A second tempering cycle would temper the new Martensite and not alter the old stuff if you use the same temperature, but would make for a slightly better/more uniform microstructure. But the extent of this is based on the type of steel and effectiveness of the heat treating process.

There are even a few guys that recommend 2 or 3 two hour tempering cycles to be absolutely positive that the R.A. is converted and that the Martensite is tempered properly, but they mostly work with swords etc. So, for a razor, 2 or 3 one hour cycles wouldn't hurt and would be a slightly better procedure.

Otherwise, Great job!

Thank you Josh, Mike and Russel. This area of knowledge is vast and it takes a whole lot of people sharing their technical knowledge, methods and experience to make it all work. The one thing I am sure of is that the handmade razors we are making have a better heat treatment than the mass produced razors.