HT What went wrong?

[alexkuzn]

Is my double tempering wrong?
For tempering I put my O-1 blade into regular oven at 400 deg. for 1 hour. After 1 hour
I turned oven off and let blade cool down with the oven door closed. Then I put the blade in a regular freezer then I repeated oven step again.

After all I tried to file a blade to check for hardness and found that I can file it relatively easy.
Looks like the blade is too soft to me.

I suspect that when I left the blade to cool down in the oven (which is big and insulated very well) it took too long to cool so blade got too soft.

What do you guys think about it?

Thanks,
Alex

[Ray Rogers]

You didn't temper the blade, you annealed it! After hardening, put the blade in the oven at 400 degrees for 1 hour. At the end of the hour, take the blade out aof the oven and let it air cool until you can hold it in your hand comfortably. Then put it back in the oven for another hour if you wish. Skip the regular freezer part as you aren't getting a cryo effect unless you can get the steel to at least -100 F ...

[tonn]

Alex!
First: You knife blade SHOULD be softer than file!!! So, with good quality fine new file, you CAN file it after tempering ! Not for a very long time

Ray may be right about cooling after tempering but not about freezing! Any freeze is better than nothing and with most steels you don't need more than -100C (-148F). Any steel with carbon content higher than 0.6% benefits from freezing. More carbon - deeper freeze - more benefits. With O1 its around -85C (-120F) for maximum martensite transformation ( that is what you want ) But there is not a certain temperature you should reach before something happends.
What is important in freezing - less time between quenching and freezing = better results! You can take it as a continuous cooling. Some people do a QOUICK tempering before freezing, some (including me) not.

About tempering temps. Whether you like a harder or softer blade is a matter of taste, but wear resistance does not depend only on hardness. Softer blades tend to have a smoother cut. I use a steel similar to O1 in my pattern welded blades and temper close to 250C (480F).
Never tested on hardness but manufacturers chart says 60HRC - just about right for a knife. And you can file it
That was a very long post from me Hope you understand

[alexkuzn]

Thanks for your input guys. I just tried to file my kitchen knives and some of them were probably even softer than my blade.

Is there any way to check hardness without Rockwell Hardness Tester?

Thanks,
Alex

[Ray Rogers]

Is there any way to check hardness without Rockwell Hardness Tester?

You just did. Checking to see how easily a new file will cut the steel is an 'official' way of checking a blade's hardness. There are sets of files specifically designed for the purpose if you want to spend the money for them. If the knife performs well without cracking the blade or rolling the edge then the hardness can be considered to be about right...

Another way is to simply use the knife. Cut rope or cardboard, chop wood, whatever you think that knife should do just try to do it and see how well it performs.

[Andrew Garrett]

Alex,

I suspect you are doing your file test in the wrong part of your HT sequence. The only time I test with a file is right after I quench the blade. As mentioned before, the tempering process softens the steel to the point that any usable file will cut it.

Use an old, somewhat dull file to test the edge right after the quench. Use light pressure at an angle. You want the file to "skitter" across. You should try this on steel you know to be soft first so you can tell the difference. It helps to wire brush the blade before you do this because the file will take off the black scale and might make you think its cutting steel when it isn't.

After the temper, do as Ray says--Test the blade in a working environment. If it does what it was designed to do, then re-hone the edge and hand it proudly to its new owner!

Good luck!

[gb6491]

Alex,

The hardness of your blade is more dependent on the temperature of the tempering cycle than how fast it cools from the cycle (though this is not true of all steels; some actually become more brittle if cooled too slowy from tempering heat). Higher temps generally mean a softer blade. Here is an excellent article on tempering.

If you don't already, you might want to preheat your oven before every cycle to let the temp stabilize (measure it with a known good thermometer inside the oven). Many ovens use a bimetal thermostat, they tend to overshoot the dialed in temp and stabilize when the temp drops back down to what is dialed in. In a large, well insulated oven, dependant on the accuracy/tolerance of the thermostat, you could have done much of your tempering at a higher temperature than you planned.

Regards,
Greg

[alexkuzn]

Can I harden my blade a little bit by tempering it again and quenching?
I don't have a forge. Some one partially(no tempering) heat treated it for me then I drove home and tempered it.

Thanks,
Alex

[AwP]

Quenching from tempering temps won't harden it, it needs to get much hotter to harden it. If you have an oxy/ace torch (or mapp or propane torch if the blade is small enough) you can use that to reHT it.

[gb6491]

Alex,

No, as AwP points out, that won't work. Think of it as cutting something to length; once done (tempered where you have it now) you can only leave it there or cut it shorter (tempering at higher temps will reduce hardness). Discounting work hardening, to increase the hardness you will have to repeat the hardening and temper again.

This helped me:

Heat Treatment - A process where steel is subject to treatment by heating/cooling to obtain required properties, e.g. annealing (softening), normalizing (stress relieving), hardening (increasing hardness), tempering (reducing brittleness and removing internal strains caused by hardening). Heating for the purpose of hot-working, as in the case of rolling or forging, is excluded from this definition.

Annealing - Heating steel to, and holding at a suitable temperature (the transformation range) followed by relatively slow cooling. The purpose of annealing may be to remove stresses, to soften the steel, to improve machinability, to improve cold working properties, to obtain a desired structure. The annealing process usually involves allowing the steel to cool slowly in the furnace.

Normalizing - A heat treatment process that has the object of relieving internal stresses (due to machining, forging, bending, and welding), refining the grain size and improving the mechanical properties. The steel is heated to a temperature above the transformation range, held there to allow a full soak and subsequently cooled in still air at room temperature. Normalizing, although involving a slightly different heat treatment, may be classed as a form of annealing.

Hardening - Increasing the hardness of steel by heat treatment. This normally implies heating the steel to, and holding at, a required temperature (transformation range), then immediately quenching (rapid cooling) in a suitable medium, e.g. oil, water, brine, air, molten salts.

Tempering - A heat treatment applied to ferrous products immediately after hardening. It consists of heating the steel to some temperature below the transformation range and holding for a suitable time at the temperature, followed by cooling at a suitable rate. Steel that has been hardened is often harder than necessary, and generally too brittle for most purposes. In addition, it is under severe internal strain. The object of tempering is to decrease hardness (reducing the brittleness) and increase toughness. .

If you decide to have it hardened again, I suggest you have the person doing that give it a snap temper, heating the steel up to tempering temperature briefly, to prevent cracking because of delay in tempering) before you drive home with it.

Regards,
Greg

By the way; it doesn't take much to have your own forge:

http://www.anvilfire.com/21centbs/forges/microfrg.htm

http://www.agocschiropractic.com/kni...ntcanforge.pdf

http://refractory.elliscustomknifeworks.com/