Tempering Strange thing

This is a little hidden tang knife that I started this morning. It is 5.25" long point to tip of tang of 5/32" 01 steel. I cut it out, shaped the profile and ground it with 60grit, 120 grit, used 120 grit and then I heat treated it and quenched in Canola oil. Then I hand sanded it with 100 grit and 150 grit and 220 grit. This evening I tempered it in my toaster oven 1 hour at 450* and cool, another hour at 450* and cool and this is what I got. I've never seen this before and it's kinda cool - may change the handle and leave it like this. Can anybody tell me what happened? Yeah, that is a big burn blister on my finger. Thanks guys,

Wallace

My guess is your toaster oven isn't accurate. Sometimes the thermostat in them just gives up or works incorrectly. If you put an oven thermometer in there I bet your at least 50 degrees hotter than your dial. Maybe 100. It may still be usable, but may be too soft now..... If it were mine I would start over with an oven thermometer to make sure your at the right temp. 450 is a little high for a knife that size using O-1 tool steel in my opinion. .A Rockwell tester would verify your exact hardness if you can get it tested. On a knife like that I would go 400 instead of 450

Ok, 450° might have been a little hot for the steel which could account for the purple patina or it could have been due to the coils in the toaster oven getting too hot as mentioned above. You could buffer the effect of the coils in the toaster oven cycling by putting the blade in a tray of dry sand to create a thermal mass.

If I understand your post you quenched then sanded the blade and then tempered it. You should not let a blade set untempered that long or you risk breaking your blade due to the stress built up in it when it was quenched. Let your blade cool all the way down to where it comfortable to touch and then scrub in hot soapy water to remove any residual oil and then get it right into your tempering oven for at least one cycle and you might as well go ahead and do a second cycle if you have time. At least do that first cycle as soon as the blade cools.

What you can do is put and edge on it and try to cut through a brass rod by striking on the spine with a mallet (note that I said mallet and not hammer). If the edge rolls, which I'm thinking that it will you will have to reharden the blade and retemper it. As above I would recommend that you try 400°. If the edge doesn't roll or chip (doubtful) then your blade is fine but that dark purple makes me think that it's over tempered.

Doug

When you mentioned "toaster oven", the red lights went off in my head. Toaster ovens are famous for wild temp swings......after wrecking several blades using one, I've not used a toaster oven for tempering since. Even after cladding the exterior with kawool, the temps will still swing 50+ degrees. If the colors in the pics are accurate, the "sky" blue is way over done.

One the other side of the coin, the oxides that form during tempering are cumulative....meaning that they basically "pile up" and a second tempering cycle will show the next color band, or a mix thereof, within the tempering colors, and so on. As an example, my 1084 blades, tempered at 415F will come out of the first cycle a medium straw color, after the second it will be medium straw mixed with vermillion, and the third cycle will have those two colors mixed with tinges of purple.

What those pics tell me is that you experienced both....temp too high, and an oven that fluctuates too broadly.

Another possibility is that you may have had some oil on the blades from the hand sanding. Any residue changes the colors that result.

I still think Ed's correct though.

I agree with Ed, especially about toaster ovens:3:. I know you didn't ask for tips on the tempering rage, but I agree with the other folks about that as well. O-1 has a sweet spot where toughness and strength come together at an optimum, and of you get much below 60.5HRC you are missing a lot of this steels potential. If you knife is a larger chopper you can draw it back more but finding another steel better suited to toughness would be the better route. However in this case yours is a very nice little knife that is just right for all the things that O-1 has to offer, so I would leave it up there in the hardness range where O-1 can give it to you.

wmhammond said:

This is a little hidden tang knife that I started this morning. It is 5.25" long point to tip of tang of 5/32" 01 steel. I cut it out, shaped the profile and ground it with 60grit, 120 grit, used 120 grit and then I heat treated it and quenched in Canola oil. Then I hand sanded it with 100 grit and 150 grit and 220 grit. This evening I tempered it in my toaster oven 1 hour at 450* and cool, another hour at 450* and cool and this is what I got. I've never seen this before and it's kinda cool - may change the handle and leave it like this. Can anybody tell me what happened? Yeah, that is a big burn blister on my finger. Thanks guys,

Wallace

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probably need to try a different tempering furnace. when i do O1, it is straight into 300 degree oven after i wipe off quench oil. temper for an hour, then start the clean and sand. then temper for use, a knife like that i would do at 350 or 375 which should give you Rc62-63 which i have found with O1 takes and holds an edge without chipping