Heat treating a Beet Knife

[Clayton M.]

A friend of mine found an old beet knife in the rubble of his garage when his family tore it down. It was bent pretty good and so he asked me to straighten it for him. I took out the bend with a torch and a hammer. I was trying to keep the temper but I failed when I let the heat run through the blade. I hardened it today and then I tempered it at 200 F for about 20 minutes. Then I went to sharpen it and that is where I ran into my problems.

 

I barely started putting the edge on when a a sizable piece came off as I ran the stone over the blade( I do all my sharpening by hand). The only thing I can think of is I didn't temper the knife long enough or at a high enough temperature to draw back the hardness in the blade. The knife is slightly less than 1/8 inch, I thought if it soaked in the oven for 20 minutes it would be good to go. In my mind it didn't need long to temper.

 

What do you guys think?

 

 

[Clayton M.]

The new beet knives are made of 1095 steel, I don't know if the knife I've got is made of the same steel. Supposedly the knife is about 90 years old. If more pictures are needed just say so and I'll put them up.

[Nobody Special]

I don't know the original steel, but normally, I would take it to non-magnetic and quench. Mildest quenches first. Air, then oil, then water, then brine. Stop at the one when a file skates over it or makes a sound like going over glass. Then temper in the oven at 450-ish. for a couple of hrs, twice for preference. You could do a differential hardening, but if it's only cutting beets, I wouldn't bother. You'll have a little scale to clean up at the right temps, but shouldn't lose too much steel.

[Clayton M.]

I quenched the knife in oil at the non-magnetic point. The file test worked well as it skidded over the blade without taking much with it, and it sounded pretty good. It was the tempering that got me I think. I'll try tempering at 400 F right now. Hope this works. :(

[Clayton M.]

I felt really stupid last night at about 10, I realized that I never tempered any of my knives at 200 F. I always tempered them between 400 to 425 F. I don't know why I thought 200 F was the correct temperature. 

I tempered it at 400 F and it looks a lot better with a deep straw throughout the knife's surface.