Stuart Davenport Knives
Knifemaker / Craftsman / Service Provider
- Joined
- Feb 7, 2022
- Messages
- 431
So I very very rarely have a problem heat treating a blade, but I just now had an issue. I thought I would pick your brain and see what I can learn. The steel is 1095 from Alpha Knife Supply, only 0.060" thick. Chuck's steel is usually in a ready to harden state when you receive it, and while I think Occam's Razor dictates that I should have just quenched the blade, my protocol doesn't seem like it should have caused the issue. But I'm always learning. The blade in question is only about 8" long, 1" tall, and again only 1/16" thick. I was going to grind slight bevels and shoot for a hamon, but decided with such a thin stock to forgo the hamon and only profile the blade. No bevels ground.
2 thermal cycles. One at 1475°F for 10 minutes, the 2nd cycle 1450°F, 10 minutes. DET anneal 1460°F for 20 minutes down to ~1200°F at ~666°F per hour. Austenitize 1475°F 10 minutes, immediately into 80° P50 quench for about a count of 7, with agitation, and into chilled plates to keep straight. Blade was straight, tempered 2x at 325°F for 64-65HRC. When I say immediately into the quench oil, I mean immediate. Takes me about one and a half seconds to go from oven to oil with my rig. There was no color loss at all from oven to oil. I don't have a ton of experience with shallow hardening steels, but I never have had any heat treat problems with deeper hardening steels from AKS like 52100, 80CrV2, CFV, O1, and of course the air hardening tool and stainless steels. I normally do a few cycles and the DET anneal with those low alloy steels as well. I just want to reiterate I don't "think" this is a steel issue from Chuck. I have never had a problem with his steels.
The problems was that when I started to grind in the flats, I noticed an auto hamon that was just sort of splotchy on the blade. It is definitely NOT decarb, as it is perfectly identical on both sides, and I use a liberal coat of ATP641 on each and every heat, other than tempers of course. I know very well how decarb is almost always the culprit when maker's post questions about "why is my blade soft", but I assure you, this is most definitely auto hamon. Those of you who might have used W2 from another supplier back in the day will know exactly what I am talking about. Soft spots.
The P50 is basically brand new and as per the manufacturer was at the sweet spot of basically room temp, slightly warmer. Being as thin as the stock was, I would think it would just about harden in plates alone!
Whenever I pose a question, I like to give my own possible answers.
1. The steel is fine. Nothing wrong with it. The extra thermal cycles and possibly the anneal made it so shallow hardening that the P50 wasn't fast enough. Maybe.
2. The steel is coarse spheroidized and needs to be normalized. Unlikely, but definitely a possibility.
Meanwhile, to salvage this heat treatment and for peace of mind, I'm going to normalize it at 1650°F and cycling it twice around 1475°F, DET anneal, and try again into an interrupted quench (water for a few seconds then P50).
So like I said, the smart move would have probably been to just austenitize the steel and not try to mess with it much, but my protocol doesn't seem like it should have caused the auto hamon. Just a weird deal.
This should be fun.
2 thermal cycles. One at 1475°F for 10 minutes, the 2nd cycle 1450°F, 10 minutes. DET anneal 1460°F for 20 minutes down to ~1200°F at ~666°F per hour. Austenitize 1475°F 10 minutes, immediately into 80° P50 quench for about a count of 7, with agitation, and into chilled plates to keep straight. Blade was straight, tempered 2x at 325°F for 64-65HRC. When I say immediately into the quench oil, I mean immediate. Takes me about one and a half seconds to go from oven to oil with my rig. There was no color loss at all from oven to oil. I don't have a ton of experience with shallow hardening steels, but I never have had any heat treat problems with deeper hardening steels from AKS like 52100, 80CrV2, CFV, O1, and of course the air hardening tool and stainless steels. I normally do a few cycles and the DET anneal with those low alloy steels as well. I just want to reiterate I don't "think" this is a steel issue from Chuck. I have never had a problem with his steels.
The problems was that when I started to grind in the flats, I noticed an auto hamon that was just sort of splotchy on the blade. It is definitely NOT decarb, as it is perfectly identical on both sides, and I use a liberal coat of ATP641 on each and every heat, other than tempers of course. I know very well how decarb is almost always the culprit when maker's post questions about "why is my blade soft", but I assure you, this is most definitely auto hamon. Those of you who might have used W2 from another supplier back in the day will know exactly what I am talking about. Soft spots.
The P50 is basically brand new and as per the manufacturer was at the sweet spot of basically room temp, slightly warmer. Being as thin as the stock was, I would think it would just about harden in plates alone!
Whenever I pose a question, I like to give my own possible answers.
1. The steel is fine. Nothing wrong with it. The extra thermal cycles and possibly the anneal made it so shallow hardening that the P50 wasn't fast enough. Maybe.
2. The steel is coarse spheroidized and needs to be normalized. Unlikely, but definitely a possibility.
Meanwhile, to salvage this heat treatment and for peace of mind, I'm going to normalize it at 1650°F and cycling it twice around 1475°F, DET anneal, and try again into an interrupted quench (water for a few seconds then P50).
So like I said, the smart move would have probably been to just austenitize the steel and not try to mess with it much, but my protocol doesn't seem like it should have caused the auto hamon. Just a weird deal.
This should be fun.
