Heat Treating a 8" Filet Blade

[Ken Wolfe]

I have a client who wants a 8" carbon Steel Filet that's not too hard so it will sharpen easily.
I usually harden in hot Oil at 160 degrees to about R57 or 58. I hardened this one at 170 degrees and it came out HARD. R-60+ checking with my files. My oil is a mix of 2 parts trans. oil, 1 part motor oil and 1 part diesel and I am using Band Saw Blade steel. Only thing I can think of thats too different than what I usually do is the blade is thinner than I usually work with. I thought that warmer oil would give me a softer blade. I also tempered at 400 for an hour with seemed to do nothing and then again at 450 for an hour. Still hard and nice and springy, but difficult to sharpen so I doubt he'd be happy with it. Someone else will so I'l profile out another and start over. What am I doing wrong. Appreciate any help.

Ken

[Todd Robbins]

Ken,
You can get the blade you have soft enough by upping your tempering temperature. Not knowing the steel, I can't look up the data, but I would raise the temp. 25 degrees for two hours and check it again. Keep doing that 'till you get the hardness you want.

Todd

[Ken Wolfe]

Thanks Todd,
I really don't know what the steel is. L6 maybe.

I'll try tempering again at 475 and 500 and hopefully that will bring it down. Any idea why the hardening process didn't produce my usual hardness? I haven't worked with 1/16" thickness before, so I wasn't sure if that might have had something to do with the difference.

Ken

[Chris Daigle]

I would do what Todd suggested and up the temperature. Just keep trying that until you get the hardness you want.

The thinner steel may be throwing you a curve. Could it be that it comes up to non magnetic alot quicker than what you are used to working with? As opposed to only the edge getting harder, you may be experiencing the entire blade getting hard. Just a thought.

Chris

[Quenchcrack]

Very thin blades will certainly cool VERY quickly but quench speed is not what determines hardness. If the steel is actually L6, it has plenty of hardenability and should harden through a much thicker piece. It is the carbon content that determines the hardness. You may have an L6 that is on the higher side of the carbon range, or it might be another steel alloy. I agree that higher tempering should help. Beware of tempering in the 500F-600F range. Some steels become very brittle if tempered in that range.

[Ken Wolfe]

Chris,

I tried to bring it up to non magnetic carefully, but who knows. I'll try the tempering as Todd suggested when I can watch it for 2 hours. My oven is just an old toaster oven. Temp might not be right on also. Thanks.

Ken

[Ken Wolfe]

Thanks all of you.

I found that my little oven takes longer to get up to temp than I thought. Probably most of the tempering problem. Although the temperature is pretty darn accurate for a garage sale oven. I thought that when the little oven light went out it was up to temp., but it cycles for awhile before it's really there. An oven thermometer showed me that my timing was way off. Thanks again for gettiing me to check more closely.

Ken