My first attempt at this bolster didn't quite go as I wanted. The material of the blade is 52100 and the bolster is just mild steel. I'm thinking it might be a little too much pressure? lol. And I was doing so well with it. https://photos.app.goo.gl/p8TNNDacATFEini4A
Hi Tom, Sorry to see that. It looks to me like the heat treatment went sideways on that one. Notice the coarse grain in the steel. There are some hairline cracks extending from the pin holes and those brownish/yellow spots/lines would indicate that those were there at quench time. It may benefit from a few normalizing cycles before quench. Raise to critical temp and let cool slowly in the air. Repeat. This will reduce stresses in the steel and refine the grain. Take a look at the various grains in this video. Chalk this one up as a learning exercise. Dan
Sucks that happened Did you do the heat treatment in a temp-controlled oven? From what I've seen, large grains like that tend to form when you overheat the steel before quenching.
Thanks Dan, thats why I put that pic up. You and a couple others here have been key in the improvement of my work. I do appreciate!
Tom did you actually heat treat that piece of steel after you profiled the knife out of that bearing race ? That is some HUGE grain growth in that steel. I don't know how you squeezed those bolster pins but you must have put a lot of force on them and with the large grain I can see why it broke. I once broke over a dozen filleting knives when I pined the bolster because I marked them with a scribe line in the ATS 34 steel and as soon as I squeezed the bolster the line created a stress riser and they snapped in half. I still have the pieces ,never had the heart to throw them out. Some day i will make little filleting knives out of them.
I should have look at the photos more closely first time! Originally I had assumed you heat-treated the bolsters and the last photo was a broken bolster! But yeah I can see now it’s the blade. I think everyone has hit the nail on the head looking at the grain size. On to the next Tom
Tom, I use a 20 ton pneumatic drive hydraulic press to squash pins. Maybe you have a 100 ton press or something. Tom, your approach was good. The steel is suspect and I'd like to see the bolster pieces as absolutely flat as you can possibly make them to match the surface of the ricasso. You may have had it perfect but the compression distorted things. The mating of the pieces is about precision, the squashing of the pin stock is force. Thanks for sharing the photos. It's a great way for others to learn too. Dan
Hello, and yes I heat treated it. I shaped the knife and took it to about 80% finished thickness. I quenched when it was a dull red color and then I clamp it between 2 boards until cool. In the evening I used the kitchen stove and baked it at 350 degrees for 2 hours. One other thing I got wrong...the pics and description I was going by were for 416 s.s. I put mild steel onto that 52100 and sank the washers into it. oops.
Tom, I am getting confused..... ??? You say you heat treated in a kitchen oven.... ovens don't get to 1500 deg F. The blade should have been taken to 1500 deg, austenitizing temp and immediately quenched in oil (don't understand dull red quench) and then tempered in the kitchen oven at 350. Grain growth like the pictures indicated usually occur from to hot a temp or the steel being held at the temp for to long a time period with to high a temperature being the major contributor.
Sorry, I wrote that in haste before I went to work. The kitchen oven was done at 350 degrees for 2 hours. The quench was done when the steel was a dull red color. As far as I no...I have no way to measure temp that is that high....a dull red is around 1500 degrees. Orange is around 1800. Yellow is around 2100 and white is around 2400 degrees. That has been my understanding of temperature vs. steel color. I don't know if this makes a difference or not but I've heard that your oil should be heated a bit. I don't have a heated quench tank so my oil is same temp as garage. Not freezing but certainly not warm. So, when you said originally to quench at 1500 degrees, to me that meant dull red color.
You may have been after this but next time, you may want to stop the bolster short of the cutting edge. It becomes difficult to sharpen with the bolster extending that far down and eventually (after multiple sharpening's) you'll end up with knife resting on the bolster instead of the edge leaving a gap between the heel and the cutting board. That being said, some knives do have that for safety.
Did you do the heat treatment with the lights out? I'm not very experienced in heat treating with a forge, but when I have done it in the past with a torch, A dull red in daylight or a well-lit shop will actually be closer to orange if the lights were dim. typically those temp to color charts are based on dim lighting from my understanding. Also, did you check with a magnet? I'm not sure what temp 52100 goes non-magnetic, but 1095 is right around 1400F and the austenitizing temp is just beyond that. Based on that what I've done is when the color is starting to look a dull red ill periodically check with a magnet and once it doesn't stick I go just a bit hotter. Another thing to be aware of, it will continue to stay non-magnetic if you get the temp higher, so you want to catch pretty close to right when it's non-magnetic, so you don't overshoot. For the oil, heating the oil actually speeds up the quench, since it reduces viscosity and allows the oil to flow around the blade. 52100 is likely fine with a slower quench from room temp oil. This also depends on the oil. Canola or some other vegetable oil should be heated to around 130F. A proper quenchant like Park's 50 doesn't need heating.
Hi, it was middle of afternoon and I am in my garage...no lights on with the door open. You just educated me again dude. I did not know that I was suppose to quench right around the non magnetic line. I have never used a magnet to test that. I will. Thanks.
Makes sense. I had a boss once that told me " the devil is in the details ".... he was right. Thx man. Every knife is a bit better then the last one thanks to all this input.
I agree. Forget trying to guess the temp by the color. Get a large magnet and heat up till non magnetic and heat up slightly longer (approx 1 minute) then quench in oil that is heated to 120 deg F. Or use Parks 50 oil and that doesn't need heated.
No one likes wasting steel, but it might be worth taking a few pieces to test some heat treating. Try a couple at different points around non magnetic, then break them and check the grain size. I’d even try taking one way too hot to see if you can replicate the massive grains you had on the knife above. After a couple tests you should get a hang of the right spot.
