Mr. Zowada,

I have been messing around with old tiller blades, files and various "scrap" stuff.  I am going to order some 0-1 to seriously forge some blades.  My question is this- In my situation of not having a heat treat oven what would you do to harden and temper blades in 0-1?  

I was considering a simple edge quench, and temper in my conventional oven. What would method would you use in my situation. What's the best oven temp for 0-1, how many temper cycles, how long per cycle?

Also, when I'm forging the blades how do I know when to stop forging?

Again, Thanks.

Mat Lamey

Matt,

Thanks for your questions. The nice thing about O1 is that it is adaptable to many different techniques, to suit your equipment and desires for the finished blade. Since you forge before heat-treating I'll cover that first.

The blade should be forged in a temperature range from 1550F to 1950F. So on the hot side of the forging range it should look bright orange in a dimly lit room. Avoid yellow and white colors as this is definitely overheating the steel. O1 is one of those steels that if you get it too hot it will crumble when you hit it. Below the point where the steel crumbles you can still do some damage so it is safer to forge on the cool side.

On the cool side of the forging range it is a good idea to stop forging at 1550F or so. Forging below the critical temperature can cause fractures in the steel lattice. These won't be visible cracks in the blade but they do weaken it considerably. A dependable indication is to look for "shadows" starting to form as the blade cools. When you see these shadows, quit forging.

Remember to allow for decarberization during forging. Forge everything at least 0.020" oversize. Normalize and anneal the blade after forging.

For heat treating, I recommend that you harden the whole blade. Then soften the back if you desire.

In heating the blade for hardening, it is very easy to overheat the edge, if you are trying to heat just the edge using a torch. Overheating by as little as 100F can turn an otherwise good blade into junk. It is better to heat the entire blade in the controlled environment of a forge or kiln. Heat the blade slowly and evenly watching for those telltale transformation shadows to disappear. When the shadows disappear the blade will also become non-magnetic. When this happens, it is time to immediately quench the blade.

I prefer to quench the entire blade. It results in a knife with higher tensile strength than a blade that is only edge quenched. The edge-quenched blade would have higher impact strength, but that relates mostly to swords. If your desire is to do a sword or have a temper line, then I suggest that you consider using the Japanese clay technique. It gives much better and more beautiful results than edge quenching.

Quench the blade tip down into warm oil. The type of oil doesn't matter much with O1 as you have seven seconds to get the blade below 1000F. Warm (150F) oil usually works better than cold. As the blade enters the oil begin moving it from edge to back. This further speeds the cooling. After several seconds, remove the blade from the oil. The blade should be smoking but not flash. You are trying to interrupt the quench at about 400F. After the blade has cooled to room temperature it is time to temper.

Tempering is easiest to control in an oven. Just be sure that your oven control is accurate. Buying a quality candy thermometer is a good investment. Tempering is usually done two or three times for 45 minutes to one hour. With Carpenter O1, 425F should result in a hardness of 60HRC. If you prefer a softer back on your blade, heat the back of the blade to a blue color with a torch after oven tempering. Be careful to not allow the edge of the blade to get hot.

I hope this helps.