Improper HT?

[rhrocker]

This is some O1, the blade is a rather large Bowie that I'm making. While finishing at about 400 grit, I started noticing the "blotchy" pattern. If I slowly run my fingernaeil across these areas, I can feel that it's rougher, maybe "micro-pitted" if you will. I used Brownells PBC at about 550 F and got a nice dark coverage, then ran the temp up to 1550, with the blade in the furnace (Lindberg), soaked 30 min, edge quenched in Brownells super, I did not heat the oil, but rather followed the instructions on the can. The blotchy pattern was in the oil. Then tempered at 400 for one hour, twice. I'be backed down to 220 grit, but it hasn't taken the problem out, will try aggressive 120 today. The other side of the blade is beautiful. Any ideas, any solutions?

[JGardner]

Have you had success with the 30 minute soak at 1550F before?

Justin

[rhrocker]

Justin, this is my first time with O1 in the Lindberg, so no, I have no past info to go to. Do you feel the 30 min is to long?

[JGardner]

It seems long to me. I remember something like 1/2 hour per inch of thickness, but I don't recall where I read it, and I couldn't find it again this morning. I made a few knives year or so ago and if memory serves it was heat to 1500F to 1550F hold until uniformly heated then quench. I would like to hear what others have to say on the subject for my knowledge as well as yours.


Justin

[JGardner]

Something else occurred to me. When I first purchased my Evenheat oven I continued to test my blades with a magnet until I gained some confidence that X temperature on the controller would be nonmagnetic when I quenched. You might check your blades with a magnet at 1400F, 1450F, 1500F, etc to see when they become nonmagnetic. It might by that the calibration on you oven has slipped a bit resulting in a higher temperature that expected.

Justin

[rhrocker]

That's possible, however the strange pattern on the blade might be due to how I applied the PBC, or maybe the blade was oily or dirty there?? At 550, the oil or dirt may well not have burned off. Anyway, all's fine. I took my air sander with 220, and really worked the entire blade this AM, and followed with hand woring 120-1200, and things look fine. I'm going to chalk this one up to improper use, or inadequate temp of the blade when applying the PBC. I have a digital thermocouple, and will also be checking and verifying the temps. My Lindberg is an old fossil, and so the calibration, setpoint, etc may be way off. Thanks for your help!

[Jerry Oksman]

Robert,

I am no expert on any of this, but I seem to recall other knifemakers commenting on having difficulty with some 0-1. It seems that they where getting pitting on their blades and it was deemed a source problem. They got a bad batch of steel. I am not saying that this is the case here and I hope someone with a better memory (or had it happen to them) will chime in and confirm it one way or the other.