Ran into a problem I've never encountered before. HTed a 6" blade of 01, 1/8"x 1 1/8" wide, along with another larger blade. Evenheat oven, presoaked at 1200° for 20 minutes. These blades were stock removal and well coated with PBC. They soaked at 1475° for 20 minutes, then were quenched point down in Parks AAA warmed to 130°. Big blade went in first, came out fine. Hard, and no problems. I left the smaller soaking another 5 or so minutes while I checked the larger, Then quenched the smaller. The smaller was soft enough for a dull file to cut it at the last 3/8" of the point, on the edge. The rest being good and hard. Ran it through the entire process again, and got the same result. Last 3/8" soft. Cut the point back 1/2" and reground and reshaped where necessary, ran it again through the entire process, and got the same result. Last 3/8" soft. Made a 1/16" thick small trial blade, with bevels, and even a thinner point than the problem blade. Ran it through the same HT, came out perfect. To me, it seems like a longitudinal band of bad steel in that last inch or so nearing the point of the problem blade. This was Starret brand 01. Any ideas???
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Soft Point
- Thread starter LRB
- Start date
- Joined
- Dec 20, 2008
- Messages
- 1,937
that is the first I've ever heard about a starrett brand anything failing. It does sound like maybe that bit didnt get any carbon... so here's my stupid uneducated guess...if you put it back in spine down and slightly tipped foreward and brought back to and held at austenizing temp for 15-20 minutes would any carbon migrate to the tip via gravity I wonder?...
You may be 'spot on' with your steel problem suggestion. There are a couple things to try that may help. The first is to harden at the top end of the range rather than the middle. Your kiln's thermocouple is at the top and may routinely be 25 degrees hotter than your blades.
The next may be to grind down a bit to see if there is a narrow decarb layer near the tip - the area which heats up first and most.
I haven't used the PBC powder, but IIRC doesn't it require heating to apply it? I wonder if the tip is hotter affecting application?
I don't think it has anything to do with your problem, but I don't think the 1200 degree equalize is necessary with something as thin as a knife blade.
Lastly, (for now), I wonder if proximitry to the heating coils - either too close, or relatively sheltered - might make a difference.
OK, there is more. Was the steel cool before testing? It should be. Also, you may want to temper before passing judgement. Tempering can reduce RA.
You may be right, but it's hard to imagine a quality steel having a band of faulty alloy. I'd be looking somewhere else. I'm not sure I have the expoerience to suggest where.
Rob!
The next may be to grind down a bit to see if there is a narrow decarb layer near the tip - the area which heats up first and most.
I haven't used the PBC powder, but IIRC doesn't it require heating to apply it? I wonder if the tip is hotter affecting application?
I don't think it has anything to do with your problem, but I don't think the 1200 degree equalize is necessary with something as thin as a knife blade.
Lastly, (for now), I wonder if proximitry to the heating coils - either too close, or relatively sheltered - might make a difference.
OK, there is more. Was the steel cool before testing? It should be. Also, you may want to temper before passing judgement. Tempering can reduce RA.
You may be right, but it's hard to imagine a quality steel having a band of faulty alloy. I'd be looking somewhere else. I'm not sure I have the expoerience to suggest where.
Rob!
All that you mentioned is pretty well covered. That's why I find it extremely weird. There was no decarb, and after grinding back the point 1/2", the soft steel was still there. It would not have decarbed that deep. I did temper after the first quench at 450° for two hours just to see how it would react. I have found that the sub-critical thermocycle reduces warp and stress relieves. This is the 22.5 deep oven. I set my blades directly under the thermocouple on slotted fire bricks. They are only a couple of inches away. I did let the steel cool before testing, in fact allowing a half an hour to pass, then retesting. PBC is applied at 600° before the thermocycle. Remember, I also ran a test blade even thinner with perfect results, so the soft spot blade is just the one of three with a different result, from the same process, and the failure is limited to just one area. I quench vertically point down and in first. In the past, I have HTed small folder blades of 3/64" 01, with the bevels already ground in, and had no problems. I am very relieved so far, that others find it as weird as I do, but I would still like to hear more on this. Thanks for your input.
