An Experiment, a Contest, and a Giveaway

M

me2

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Oct 11, 2003
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I recently did some experimenting with a blade of 1095. Nothing fancy, just a dropped edge blade with a convex grind and an almost symetrical spear point. The experimental part was exploring the possibilities of a microstructure I had not used before. The contest and give away parts are the blade will go to the first member of less than 4 years to guess the heat treatment and/or microstructure based only on the information given below. If no body has guessed after 100 posts, I'll keep it.

The micro structure has a higher amount of carbide than the usual quenched and tempered heat treatment. Toughness is measurably less than tempered martensite of the same hardness. I'm going to say here that ductility will be the same or better than martensite, but I'll have to check and be sure.

Edge holding tests were done by cutting cardboard and checking the edge after a certain number of cuts. The first round of cuts was roughly 20 on 2" wide strips, using a marked 2" section of the blade (5.5" overall). After this it would still shave hair off my arm. Steeling of the edge was also used, mostly because I was curious about it, as I don't use it often. The next round of cuts was roughly double the previous one, 20 on the first, then 40, then 80, and so on. The edge was checked after each round and steeled lightly with 3 to 5 passes per side. The edge angle was 18 to 20 degrees, applied with an 80, 120, and worn 180 grit belt, then finished by power stropping on leather on the 1x30 sander. The leather was loaded with white compound. This was the first time the knife was sharpened, which is the reason for the very coarse belt sequence.

After the second round (88 cuts), the edge would no longer shave. However the steeling returned it basically to it's beginning sharpness. This also happened after round 3 (188 cuts), and round 4 (415 cuts). In these rounds the edge recovered to basically original sharpness after light steeling. After round 5 (830 cuts) the edge was steeled and, though still pretty sharp, it was noticably duller than before. This is the end of the cutting, as I'm out of cardboard, and my hands are tired. After rounds 2-4, the edge would still slice paper, but would not shave my arm. So after cutting roughly 1300 inches of cardboard, a quick steeling was all that was required to restore the edge.

So any guesses? The post count goes from 2 to 102.
 
I'll refrain from confirming until all the guesses are in. Also, one thing to keep in mind about all this cutting. The blade did (and does) not have a handle. It's just a full tang end. So, during the cardboard cutting, the discomfort didn't get high enough that I had to stop. It wasn't pleasant, but the discomfort was not high enough that I had to stop.
 
The high ductility and low toughness part makes me think of spheroidite. The carbides are shaped in a way that it should be fairly ductile, but the relatively uneven distribution of the larger carbides could weaken the grain boundaries and decrease the toughness. As for the higher carbide content part, I'm thinking you took measures to prevent the diffusion of carbon? Maybe a carburizing heat treatment or use of foil or plates?

To buck and CK: Austenite is a metastable phase found at higher temperatures. After the knife cools down the austenite crystal structure should shift a little to form the martensite.
 
Pretty good guesses so far. At this rate it'll be a while before we reach 100.
 
You austempered and ended up with bainite. Maybe used a salt bath for quenching at a fairly high temperature to get that bainite to form. Bainite is ductile but still should hold a decent edge. I think that Howard Clark heat treated his Japanese swords to get bainite and they were supposed to be very tough and cut well. But I ain't no metallurgist and I don't like to stay at Holiday Inns either.
 
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There's no use to keep going really. Tsujigiri is the winner. All that cardboard was cut using a blade made from cold rolled and spheroidize annealed 1095, as it was recieved from sheffield knife makers supply. Email me your address and I'll send it out next week, after one more round of cutting tests for comparison with another, hardened, blade Im testing. Just so you know, it has a prototype rough finish, I think 80 or possibly worn 40 grit.
 
I wish I could understand the terms used above and the winners answer. So if someone would be willing to take the time to explain it I would greatly appreaciate it.
 
I'll be happy to explain, just let me know what you want clarification on! As a general overview, though, steel is made up of "grains," separated by "grain boundaries." Metals have a crystalline structure for the atoms in their grains; for the iron in steel it's a body centered cubic. But at high temperatures, the crystal structure changes a little, which allows the crystal structure to absorb more carbon. This form is called austenite. When the steel cools, the carbon diffuses out and forms precipitates inside the grains and at the grain boundaries. The microstructure inside the grains is named based on how the carbon is distributed. If you look at the steel under an electron microscope, you could see alternating dark and light bands, or a dark spiky structure, or various other forms. Spheroidite is when the carbon rich phase forms little spheres. A steel's strength is determined by how well it resists being moved around at the microscopic level; since what we see on a macroscopic level as bending, for instance, is what you'd see on a microscopic level as crystal planes sliding over each other. Spheroidite's round form doesn't stop crystal deformation as much as a longer, spikier form, so the metal is more ductile. Large carbides, however, do decrease the toughness of a metal since they are very brittle. The part about cold rolling that me2 mentioned is a method of strengthening the steel (I've seen it in engineering classes, but this is the first I've heard of its use in a knife). It's basically a way of mashing the steel around to harden it, since the more you shift the crystal structure around, the more entanglement you get and the more the steel resists further movement.
 
This was kind of a trick question, but no, the first spheroidite was the winner. I'm exploring how much value super high wear resistance really has, so this was my bottom blade. If cutting cardboard, which is widely accepted as quite abrasive, rolls the edge instead of wearing it away, what happens at higher hardness and much higher wear resistance (S30V compared to annealed 1095). The nature of the contest did limit it to people who have a good grasp of heat treatment and what happens. I have another give away, but will have to think of a more broad topic for the contest.

The sticky threads at the Bladesmith's Shop Talk forum will give a great deal of good information and detail. Tsujigiri jumped right in. There are several people here that know a LOT about steel.

For the record, this piece of 1095 was cold rolled (like rolling cookie dough) before the annealing treatment, so the final piece I have has no strength left from the cold rolling process. In this case, cold rolling is used to provide a consistent thickness and a good surface finish. Cold rolled steel comes out looking like about a 400-600 grit finish, quite nice. Were it not for the need to grind and shape the knife, a cold rolled finish would be quite good IMO for a knife.
 
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