What to do about warped edge after HT?

[pso]

What can be done with a blade if the edge warps and wavy after heat treat? The blade was hand filed out of 1074 (an old bandsaw blade). The edge ended up very thin after the hand sanding and is hard enough that a file does not bite. In fact it will cut the skin of an avocado.

Can the edge be straightened? If so, how?

If I annealed it and re-hardened it, would it likely warp again?

Can I grind off the warped part and end up with a useable knife? I may have to quench it a gain since only the lower third was quenched and I may end up grinding away most of the hardened part.

I also noticed that after normalizing three times, the whole blade curved. I straightened it before hardening. What causes the curve? Did it's past life as a bandsaw blade contribute to the curving?

Thanks for your help.

Phil

 

[peter nap]

Phil, it's not uncommmon for a thin blade to do that. First, have you tempered. It appears that it is too hard if a file won't cut it after tempering. I always leave a fair amount to grind after HT. This is one of the many things Ed Fowler has shown me on this forum that I feel important. It is a little more difficult with a bandsaw or hacksaw blade but leave as much as possible. If the distortion is not too much, a final grinding should take care of it. If it is way out of line you may want to back up and go throung the Heat treating process again. Sometimes with just a little misalignment, you can straighten it with a knife steel. I recommend a smoothe steel.

There is a certain amount of "memory" in a bandsaw blade but I find most of the curving is due to too fast and uneven heating. Try to bring the heat up slowely and turn the piece often to keep the heat even.

 

[Andrew McLurkin]

Ah, so many questions! Without looking at the knife and/or watching you make it, my best quess would be that you got the edge too thin. Additional factors may have been uneven filing along the length and uneven heat prior to quench. I would recommend annealing the blade and filing it out. Check your symmetry by holding the blade both edge up and spine up. Heat it evenly starting with the thicker sections and quench straight down in warm oil. Lots of posts on this last part if you do a search on quenching or hardening.

Let us know how it turns out.

 

[pso]

Peter and Andrew

I have not tempered it yet. I don't think that I will be able to grind the waves out without reducing the width of the blade significantly. The edge was so thin that if it did not warp, I could have soaked in vinegar to remove the scale, sharpened it on the Spyderco crock sticks and ended up with a useable blade. I am using files and sandpaper and did not realize how fast the sandpaper would cut.

I presume that the blade heated evenly during the three normalizing cycles and before the quench since I put it into the heat treat oven they have at work. I got the oven up to temperature, with a piece of scrap to test for non-magnetic, then put the blade in for about 5 minutes each time to heat it up. The blade was a dull orange when I pulled it out. Does sticking the blade into a hot oven heat it up too fast?

I did not heat up the oil. The quench tank is pretty big. I will have to figure out a way to do it next time.

Thanks again for your help.