now i know what happens when a blade fails heat treat.

Mark Van Loon

Mark Van Loon

Joined
Jun 2, 2002
Messages
41
well it had to happen sooner or later i guess, just got done heat treating 2 knives and they both went snap, two real big cracks in both blades, both about the same place on each, these were blades # 3-4 that i have heat treated. funny thing is i did my first 2 a while back, and they both are a-ok, the not so funny part is i didnt really like the first 2 blades they were my test projects you could say, i really liked the profile and shape these last 2 had. all the blades were 1084 clay coated and quenched in water, im thinking i may have had a slightly thinner edge on these last 2, also may have gotten them a little hotter, (i use the magnet method in quenching, im too poor for a digital furnace at this time.) the water temp was the same as the first 2 i quenched so ive taken that varible out, any ideas from the expierenced heat treaters out there? as these were the first 4 knives total i have made i gues im not doing too horrible 50% aint all bad i guess, i was really looking forward to seeing the hamon on those darn blades though, oh well ive got the first knife i ever attempted almost done polishing now and will be posting pics soon, you all dont be too hard on me ok? well i just had to vent the frustration a little ,...back to polishing the 2 that turned out.
 
I believe you should be quenching 1084 in warm oil instead of water. I have yet to have cracks in the blade with oil. 1095 would be better with water quench.
 
water shocks badly if the clay is not right.
you may need more clay on the spine..
what temp did you temper the edge at?
the safer way for you to start out with
would be the oil quench. test test test...
 
1084 is normally an oil quenched steel. If the steel has not been anealed and normalized it will have stress. This stress will be agravated by the water quench and can cause the cracking you spoke of. I would try the quench in warm oil.
 
When you are quenching it, do you leave it in the water till its cool? if so, thats a big no no. If you are using water, you have to interupt the quench. in the water for a sec or 2, out for a sec, in for second or 2, out for 1, etc. This way, it lets the steel get used to the stresses.

Also, where did the blade crack? Plunge cut? Where the clay stopped on the back?

I respectfully say "Bah" to those who say not to quench 1084, 1095, O-1, L6 in water:p Oil is recommended, but water also works for some steels, depending on the usage and procedures used with the water quench. I have quenched in warm water, ice water, and havent really noticed a difference. ice water cuz it was winter and my quench bucket was partially frozen :rolleyes:. O-1 quenches well in oil, as does 1084, but they also work well in water, too. And water is less messy. And with the low cost of 1084, you can practice more. 6' of 1/8" thick by 1.5" wide 1084 from sheffields is around $9 or $10, compared to 9 ro 10 per foot of some other steels. And you get a nice temper line as well.

I have done all of these steels in water. Yeah, some cracked, and some came out incredible. I did a 1084 blade, 1/8" thick, full flat grind with a water edge quench. I then tempered at 400 in the oven. passed brass rod test, took a wicked edge. Then came the bending tests. Clamped it up in the metal vise jaws, no piece of wood here to soften the jars up. Flexed to 90, then back to vert, then to the other 90. 10 times. The edge popped in a few places, but only 1/4" or so, the blade was approx 1" wide. After the 10 flexes, i went down to almost 180, or as far as my vise would let me go to there, then back to vert, and then the other 180, 2 times before the blade broke. The grain in that blade was incredibly fine.

I did an O-1 blade with a water quench to get the curve in the blade. HT it 3 times. First time was to get the curve, second came out, but i tempered too much with the torch, 3rd time i took it out, used the torch on it for a tiny bit, and then ran into the house and stuck it in a 400 degree oven. Between each time I HT'd it, i would bring it up to critical and let air cool. that blade took one of the finest edges i have done to date.

Point being, water quenched work on steel that is usually o-1 quenched. 440C can be oil hardened, but many people use an air quench with it. Water quench takes some time and patience, but works out nicely. I know many people use 1084 for knives with hamon lines. If you are using clay, make sure the clay doesn't have any sharp lines in the clay line that might cause stress. I usually heat the blade up, dunk in for a sec or 2, remove for a second, then back in for a sec or 2. if you leave it in, they will often pop, and if you dont temper them quickly, they will pop. I usually use the torch on them until i just start to see straw color at the back, and then they go into the kitchen oven for tempering. If you HT and leave them around for a few min, they have a very good chance of breaking. Also, remember to normalize the steel before HT'ing it to further reduce stresses. Make sure the edge is smooth and thicker than what the finished edge will be, and that there are no deep belt scratches, 90 degree angles, etc. Good luck and email me if you want more info!

Please dont take offense to the Bah. I have had several convo's with other makers about the water vs oil debate and do both, depending on my mood that day :) Both will work, but the water quench takes different methods and has less room for error.
 
thanks for the info taz and all the others, first let me say i did anneal and normalize these blades, and i interrupt the water quench also, they cracked about where the hardened edge is, right along where the clay went from thin to thick, both about 4 inches from the tip and again an inch further back from the initial crack. both blades were hira zukuri style tantos. everything was done the same as my previous 2 blades, (time in water, temp of water, etc.) and both earlier blades came out very nice. i did measure the edge thickness on the 2 and they were both a little thinner than the others, ( about 1/16"on the cracked ones, to about 1/10" on the earlier edges). so im thinking that might have played a part. the reason i use water is these blades are tantos with a hamon, and ive heard that oil give a somewhat "sleepy" hamon when compared with water. i do have some daggers that im planning that i will use clay but oil quench, because the "temper line" will not need to be as distinct. i really want to thank all the people on this forum, every time i post a question i get great responses you are all so friendly and helpfull to us newbies out here. this is a great forum and i hope to participate in it for a long time.
 
I use either the "Goop" quench or oil quench for my blades but, hey listen to what Taz has to say. One great thing about this Forum is the exchange of ideas. I know it made me feel good when I put some "questionable" HT ideas on this Forum, then a few other tried and liked them. YOU NEVER KNOW!

J.
http://www.mountainhollow.net
 
So the blade cracked lengthwise? Am i reading that correct? Also, is the hira style the basically full convex/flat grind, or does it have the grind liner going lengthwise? My cracks were usually perp to the edge. How are you judging the heat before the quench? magnet, colors, etc? If it is too hot, it might cause grain growth and crack? If you are judging by eye, it gets really tricky and the clay really hold heat well, so it may be the differing thicknesses of the clay. i have done blade where I only clay the spine and back of the blade, and don't use any clay on the part I want to get hard.

some other things to consider is if the curve becomes more pronounced at that point, stresses in grinding, etc. This is the prob with water quenching. It is such a stress to the steel that it is much more tempermental than other methods. The benefits are usually very specific, ie hamon line and quench curve. Also, how curvy is your clay pattern? Water quench has soo many variables, but it is very fun to play with and not as messy as oil.

the edge thickness might have something to do with it as well.
 
well the blades cracked perp to the edge and then horizontal to the edge, right along the temper line, the clay pattern on these latest 2 was quite a bit more "dramatic" than my first 2, (slow gradual waves).
i use a magnet for temp when heat treating, i dont have the funds for a digital furnace at this time, as soon as the blade is no longer magnetic i run through the forge for 30-45 sec longer then quench immediatly, interrupting the quench as i go, i never leave it in the quench untill fully cool. i must admit i might have brought these latest blades up to temp a little faster than the others also, could this have helped/caused additional stresses to the blades? all in all i treat his as a learning expierence, without failure we couldn't learn, and correct the mistakes we make. i am just starting along this wonderfull path and look forward to many more "learning expierences" lol.
 
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