O1 steel questions

Dacks

Well-Known Member
I'm a hobby maker with about 20, or so, knives made so far all using O1 steel(some of my work....http://knifedogs.com/showthread.php?t=3466) .
While I believe my heat treat/temper process has been adequately producing usable knife blades, I don't know that to be the case.

Because my wife is an instructor at the Canadian Coast Guard College here in Sydney, I have been able to use some of the resources and equipment housed in their Mechanical Engineering building. There they have a rather large heat treating oven suitable for anything up to 36" in length(big oven!).

My process has been to:
- preheat the oven to 1350F
- bake the knife blades(I've done four at one time) until critical is reached(non-magnetic)..... approx 20 minutes at temp.
- quench in heated used motor oil(being careful to move the blades back and forth for 10-15 seconds)
-immediately run to the College's kitchen where I place the knives in a preheated 350F oven for one hour.

There... that's my process.

The resulting blades will then be hard enough to not scratch when worked w/ a file, and the grinding sparks will be "whiter" then those from the annealed steel.

I have not done a 90 degree blade bend test, or had the hardness accurately checked.

From this description, am I on the right track?
I have read of the process of "thermal cycling(??)" by heating the blades to critical temp then cooling to room temp. Do I need to be doing this w/ O1 steel?

What more, or different should I be doing to produce a superior blade?
 
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The HT charts I have read for O-1 recommend tempering twice for 2 hours each time. And 350 sounds a little low.
 
If you can get a termometer and place it in the oven for a practice run and watch how much fluxuation you get. Then if you can get a toaster oven (used one) check the same thing. You might have to work with the temp but most of the time you should get less fluxuation. If there is less you can get a better blade. These are just my thoughts. Some of the more experienced makers will know more.
 
You said the heat treating oven is heated to 1350? And you're able to reach non-magentic there? Or are you raising the temp until non-magnetic is reached and then holding?

Curie point for iron (when it goes non-magnetic) is 1414F. Indicated hardening temperature for O-1 is anywhere from 1450-1550. I personally go for around 1475 and hold 20 minutes once temperatures equalize. As long as you have good temperature control, the extended time at temperature won't hurt except for decarb.

As for your quench, you may find more consistent results with canola or mineral oil for O-1. Heat it to around 130F and agitate as you stated. However, instead of just quenching for 10-15 seconds, I would just leave the blades in the quench until they are cooled to the quenchant's temperature. Then, take them out and let them cool ALL THE WAY to room temperature before putting them in the tempering oven to ensure a more complete transition from austenite (formed at critical temperature, i.e. 1450-1550F) into martensite (the stuff we want in a hardened blade). It sounds as if you may be putting still-warm/hot blades into the tempering oven. Keep in mind that the martensite conversion doesn't start until somewhere in the mid-400's F. The quench is to ensure that the steel doesn't have time to transition into pearlite, which would happen to an extent if you let this particular steel cool slowly from critical temperature.

As Denton points out, O-1 really needs 2 tempers at 2 hours each. The first tempering cycle will convert retained austenite into martensite in addition to stress relieving the existing martensite. The second cycle is to temper the freshly created martensite. And 350 is a little low. 400-450 will make a tougher blade with continued excellent edge retention.

Hope this helps.

--nathan
 
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Sounds Like Nathan has you on the right track but her is some of my experince with it.
I have made a few blades using O-1. Some people recomend doing a thermal cycle after you are done grinding just before the heat treat. I never have. I have read that 0-1 can benifit from a little soak time so it sounds like you are on the right track there. I have always brought the blade up to critical (1475 for me) let it soak for 10 or 15 minutes or so then quenched in vegtable oil. I have always tempered mine at 425 deg F for 2 hours twice. I have gotten some preety good results. My father is a butcher so we butcher our own beef. Last weekend I skinned and gutted 2 large beef with one of my knives made from 0-1. The knife was shaving sharp when I started I did not have to sharpen it through the process, but after the second beef was complete the edge was no longer shaving sharp but still had a very good edge on it that would still cut and skin very well. Another test I also do is an edge flex test. I learned this from Ed Fowler. Stick a metal rod in your vise like a honing rod put the edge of your knife on the rod at an angle as to bend the edge. Then put just about all the wait you can on it and draw the edge of the knife across the honing rod. If it is to hard the edge will chip and fracture. On most of my knives I can get at least 5 flexes on each side. Then you can also do some cutting tests on hemp or sisal rope. If the edge is to soft then you won't get very many cuts. I can usually get up around 300 cuts on 1/2 inch rope and sometimes more sometimes less. Most manufactured knives I have tested and read test results on usually don't get over 100 cuts most don't make it to 75 cuts. So I would think if you get at least 150 your doing pretty good. So I hope some of this rambling helps.
 
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Denton, James, Nathan and Shane -

Thanks for the advice. That's what was hoping for.

It seems there is some agreement that my process is a bit lacking.

As for my oven temp.... I was following the info on a chart in the Mech. Eng. building at the College. After about 15-20 min at that temp(assuming the digital thermometer was reading correctly) the steel was non-magnetic. However, for the next batch I do I'll follow the advice of reputable knife makers and turn it up to 1475, and alter my tempering process accordingly as well.

Is there a max time limit between heat treat and temper that I should be aware of? Can I bring the hardened blades home and do the temper in my kitchen oven even several hours after heat treat?
 
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There is a time concern, but I'm not sure what how much time it is. With O-1, you likely won't have to worry about the blade going "ping" if you don't temper right away like you do with some steels like 1095 (internal stresses are just too much for the blade to take without the stress-relieving temper).

The main concern with extended time between your hardening and your tempering is that retained austenite will stabilize over time and then you will not be able to convert it to martensite with a temper. For a steel like O-1, the amount of RA isn't huge, but I try to get my knife into the oven within the hour. There shouldn't be a problem in letting the blade cool to room temperature and then taking it home to temper in your oven. I just wouldn't wait overnight or something.

As for your hardening temperature, if you got to non-magnetic, the oven is likely hotter than it is reading or you're getting a ton of radiant heat from the elements onto the blade. If you are able, let the oven come up to temp and sit there for about 30-40 minutes prior to putting in your blade. This will help the oven get heat soaked and decrease the number of on/off cycles the elements have to go through and maybe decrease large temp fluctuations and radiant heat directly to the blade. If it is reading high, I'd shoot of the low side of the hardening range, say 1450F for your hardening temp. That way if you overshoot by up to 100F, you'll be ok. Another idea would be to use a baffle of some kind. Get a non-galvenized pipe large enough in diameter to put your blade in, and heat it inside the pipe inside the oven. The pipe will take the radiant hit, and your knife should get to a more uniform temperature. I'd still check with the magnet to make sure you're in the ball park prior to removing the knife. I check with the magnet and observe the blade's color, then I close the door and let the blade equalize in temp again before taking it out to quench.

--nathan
 
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Nathan - The College has some VERY thick foil that I was told was for heat treating, but my instructor friend did not know how to use it. Does this foil serve the same function as your pipe-baffle set-up?.

And.... thanks so much for taking the time to answer my questions. I just visited your web site: you do some very fine work.
 
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Yes and no. The foil is actually made of stainless steel rather than aluminum. I use the stuff on my stainless steels as a decarb protection method. Stainless steels and some other complex alloys have to be held at temperatures quite a bit higher than O-1 (1800-2000F), and they have to held often for up to 45 minutes. That high of temperature for that long of time can cause major decarb/scale and pitting. With those steels, you use a foil packet that is crimped air-tight, and when you pull the blade packet ouf of the oven, you can quench between aluminum plates without opening the packet. That works for air hardening steels, but not for oil hardening steels, as you'd have to cut open the packet, remove the blade, and then quench in the oil for a fast enough quench. That takes time, and you'll drop to too low of a temperature often before you quench.

What you could do is make a 1/2 circle "tube" of stainless foil (shaped like an old airplane hangar :) )to act as a radiant shield for your blade. It won't prevent decarb, but it can be used over and over as a crude baffle. If the thermocouple tip extends into the oven chamber from the top, you could even include it inside the baffle to make sure you are at a correct temperature. Just make sure the foil doesn't touch the elements in any way as the elements in heat treating ovens are live and anything that touches them also goes "live" and sometimes "un-alive" depending on where the current courses :eek:.

Hope that makes sense....

And thanks very much for the compliment. I do appreciate it!


--nathan
 
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Thanks, Jerry. I don't know it all, to be sure.

As I've thought about this, my only concern with a baffle like I recommended would be that you would need to take the temp from within the baffle to get the best results. My only concern would be that you don't get hot enough within the baffle with too short a soak. It should all equalize out over time, but you might need a slightly longer soak. Like I said, the best thing would be if you could include the thermocouple tip inside the baffle. Also, don't make the baffle longer than necessary to sheild the knife. You want it to be open to air on either end so that temps can equalize better.

--nathan
 
Nathan, I have a Wahl hand healt with a 24" probe. I take all temps inside the baffel.
Now- something else
A few times, I screwed up, and after quinch, I re heated and quinched again. It seems that I get a much harder blade when I do that. Don't have a rc tester but the way everything works it sure seems harder. What is your take on that? Jerry
 
Thanks for all the help guys.

Is it important that I keep the blades raised off the floor of the oven? I see racks/holders sold by Evenheat for this purpose, but I've also seen photos of blades placed flat on the floor of forges prior to quenching.

edit to add: I imagine its quite important.
 
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Dacks, I always set my knifes on their spine in a little holder I fashioned from a fire brick. This allows a more even heating. Setting a blade on the floor of the oven might insulate the side against the floor slightly. Not too much of a problem usually, but in a game where anything can happen, I like to eliminate as many "possibles" as I can.

Jerry, I couldn't say. It could be an issue of grain refinement where your multiple heating cycles have reduced the grain size. This is normally done by thermal cycling prior to heat treating, but it's most important in a forging situation where you've likely caused a good bit of grain growth during the forging process by over-heating the steel. When you bring the blade to critical and then cool it, you "reset" the grain size. Normally you would do this during your forging process by heating to lower and lower heats for the last several heats of your work, then annealing the work. That's just a shot in the dark, though.

--nathan
 
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