Thread: Heat Treatment on a thin edge

i accidentally started to final grind a blade when i realized that i hadn't done the heat treatment on it done hahaha right now the thickenss of the edge is down to .5mm thick, it is a wedge so its not .05mm for half the blade so i think i might be in luck... i have never heat treated a blade this thin before and when i was thinking about it i figured that the edge was going to heat up a heck of a lot faster than the spine, so to reduce stress i thought about having the soak time being really short... aside from that i really cannot think of anything else i should do different on this blade.

i have once heard of someone at charlies get together HT a blade that was really thin and kind of remember the person saying they were successful at it..

the blade is san mai, 1095 core, nickel shim(dont think the nickel matters) with mild steel cladding...

thanks in advance gents

With the blade that thin, you take your chances, might work well, or it might not. I would heat treat in gas forge running about 1500 or less, (preferable less) where I could watch the blade edge change and go through decalesence then fast into the quench.

might work, might not, you play the game you take your chances

with that thin an edge, id be concerned with a couple things.

one is getting the body of the blade up to temp at the same time as that thin edge. you might try it with a forge, or a torch, and heating til the edge is close to temp, then pulling back and letting some heat penetrate, then doing it again. the idea is to give the thicker portions some time to build up the heat. then even things out as best you can and then go to the quench.

the second biggie is something that I don't hear talked about much. and that is losing heat at the edge during the trip from the nice toasty warm forge to the quench. if the edge loses too much heat during that trip, then it wont harden. you can see that on a single steel blade as scale hanging on at the edge after the quench.

I would not worry about the spine/back or rest of blade, especially in this case the other layers will not harden anyways. I would put all my efforts into the thin half of the blade.

Originally Posted by spazola

With the blade that thin, you take your chances, might work well, or it might not. I would heat treat in gas forge running about 1500 or less, (preferable less) where I could watch the blade edge change and go through decalesence then fast into the quench.

might work, might not, you play the game you take your chances

thats exactly what i remember from the story, is they did it in the forge and watched for that and right when it hit quenched... i only have a kiln.... if this was just a regular piece i wouldnt be so worried about it lol... ill just have to wait till im around a forge since that may increase my odds, thanks!

Originally Posted by caltoncutlery

with that thin an edge, id be concerned with a couple things.

one is getting the body of the blade up to temp at the same time as that thin edge. you might try it with a forge, or a torch, and heating til the edge is close to temp, then pulling back and letting some heat penetrate, then doing it again. the idea is to give the thicker portions some time to build up the heat. then even things out as best you can and then go to the quench.

the second biggie is something that I don't hear talked about much. and that is losing heat at the edge during the trip from the nice toasty warm forge to the quench. if the edge loses too much heat during that trip, then it wont harden. you can see that on a single steel blade as scale hanging on at the edge after the quench.

i like your thinking, i think it wouldnt be a bad idea to do this HT though a torch... im not too worried about the spine since its mild steel so im with spaz on that unless im missing something... Thanks for the ideas

the idea of a interrupted heating isn't so much to get the spine to harden, but to get some heat into the spine so it doesn't act as a heat sink and rob the heat from your edge.

so you have a blade that has a very thin edge, you begin heating it with whatever you have, be it a forge, kiln, torch. you are trying to get enough of the edge hot enough to harden, but not so hot that it overheats, and you need to not only get it to that temp, but to make sure it gets to that temp and stays at that temp until it hits the oil and cools the way you want it to.

so your cutting edge on this razor is 1095, its shallow hardening so the spine probably wont harden anyways and lets shoot for the magical temp that is in the books of 1475. lets also say its 80 degrees in your shop, and you get your quench tank to as close a distance, and in a straight line from the opening of your kiln so you can open the door, grab the blade, and get into the quench as smooth and quickly as you can.

you get the thin part of the razor to 1475, open the door {losing heat}, stick your tongs in {losing heat while you get ahold of the blade}, grab the razor, and then it goes from a toasty 1475 {or maybe the kiln has dropped to 1400 by the time you get ahold of it}, to a spine chilling 80, and then to the quench.

so the air is robbing heat, and if you don't have enough heat in the rest of the blade to be giving heat to the edge, then it is also robbing heat. and it can be very easy to drop below critical and you don't get all the hardness you could have gotten.

now lots of guys grind real thin on purpose prior to heat treat to save a couple bucks on grinding belts. and then complain about decarb, and edges that don't last very long, and a lot of times I wonder if it is decarb, or if it is that they ground too thin and the very edge didn't harden, and they aren't grinding off decarb, but steel that got too cold and didn't harden.

if you have a torch, and can practice on a scrap piece, I think that would be a good choice to try. with a torch, you can have the blade very close to your quench tank and really shorten the time that thin edge is exposed to the cold air.

On the 1095 ttt diagram it looks like the top of the curve is about at 1375, so if you hit the quench after cooling down to 1400 everything should be fine and you will beat the nose of the curve if you are fast enough.

I have done this with both my kiln and in a forge. Speaking from experience, my biggest problems with thin blades has been warping not beating the nose of the curve.

I'd just give it a go and see what happens. If you already consider the blade lost, it can only improve.
At half a mil, it could still work out pretty well. I've quenched things that thin and usually it goes well.

And if you're really concerned, you can simply take 1/8 off the width so that you have a thicker edge section.

Yep, I've done it too. Mine wasn't a success and I ended up with a potato chip razor. I normalized 2x. I worked the blade in and out of the pipe in my gas forge working on bringing up the spine heat and trying to not overheat the thin steel. I file tested out of curiosity and IIRC, there was a spot on the heal of the razor that didn't take. I assume it cooled too quick before hitting he quenchant. It was trash anyways and literally went there.