So if the metallurgists were designing heat treatments for one specific application they would be dealing with many customer complaints. I’ve once read of a method to get rid of grain boundary cementite (iirc) in forged knives. And with the social distancing required because of COVID-19, now’s a perfect time to really learn how to sharpen a knife. I have always steeled higher than that of the honed edge thus creating a micro bevel making the knife both sharp and strong enough to withstand a hard days graft. And as mentioned in the previous myth, superior edge geometry is often what makes a legendary knifemaker have high performance knives, but the super heat treatment is a better story. I explained the mechanisms behind cryo in this article. Basically normalize at ~100-150°C above the steels austenitizing temp to dissolve all cementite, then quench it to prevent gb cementite from forming during cooldown. Preamble - Once you get into the knives and start picking up basic knowledge about steels, Rockwell Hardness, edges and angles, inevitably you come across the statement that hard(i.e. This article provides some insights and workarounds for one of the most vexing problems you will encounter when sharpening a knife — wire edges. Here is a chart of retained austenite contents and hardness values achieved with and without cryo with low alloy steels: Now just because the retained austenite can be reduced with cryo doesn’t mean that you have to do so. This has some truth to it as knifemakers who use a subpar heat treatment will certainly have subpar performance. Thanks to Lee Rothleutner and J Hamm for becoming Knife Steel Nerds Patreon supporters! 1. However, higher hardness levels can be achieved when using cold treatments, see the chart for AEB-L below, where the minimum temperature is labeled as “LN2” (cryo), “freezer” (a household freezer), or “room temperature” (no cold treatment): You can see that the hardness peaks around 62 Rc with no cold treatment, using a hardening temperature of 1925°F. The torch should ignite after a few tries. This is why those very thin fillet knives are so good at flexing 90°. When the edge deforms (instead of chipping) that means the steel is tougher than one that chips. 6. However, it has become somewhat fashionable to talk about knife performance as entirely (or almost entirely) controlled by the knifemaker’s skill in heat treatment. 9. Point 10. It doesn’t. Whichever side snags your nail is the one with the wire edge. No heat treatment is capable of making high carbide CPM 15V into a high toughness steel. This is without covering common mistakes with using files such as checking the knife without removing scale or any decarburized layer first. You don’t have to buy a Rockwell hardness tester which can be expensive. As described previously, martensite finish temperatures change for different steels and hardening temperatures, and the closer you get to martensite finish the lower the retained austenite. Differential hardening is a method used in heat treating swords and knives to increase the hardness of the edge without making the whole blade brittle. Cryo is not an on/off thing, and the colder you go the better for minimizing retained austenite. It would take a good edge, but it would shatter. It lets you know that the knife is harder than the file but you don’t know how much harder. Make sure you get out of the quench and straight into the cold treatment no matter what steel and heat treatment is being used. We asked five pros how they made it work and what it takes to make a living in the outdoor industry "in real life.". Work your way through grits bringing it to the desired finish. So steels like 26C3, White #1, Blue Super, etc. More info below⬇️Beginner knife making steel video. I started out with 100 grit and then went in 100 grit increments all the way to 600. Doing this carefully will reveal a wire edge when your nail hangs up at the edge. Knife Making - How To Heat Treat A Knife | Super Simple DIY heat treating. The formation of martensite is measured with a “start” and “finish” temperature and the closer to the finish temperature you reach the more martensite forms and the closer to the maximum hardness you will achieve. Sometimes datasheets will provide different temperatures or hold times depending on the thickness of the piece, but that is more of an economical feature (don’t waste any more time than necessary) than one that is required for performance. [1] X Research source Larger flames produce less heat while smaller flames produce a higher heat. Some knife users or makers report happily that their knife edge rolled in use as evidence of its good toughness, but it is mostly evidence that the steel wasn’t hard enough and/or the edge geometry wasn’t robust enough. Knifemakers are afraid of holding too long at austenitizing temperature different than with rapid impacts such as in the plot... Blade you 've bought cutting-edge, sometimes quirky world of gear design marks them as!, etc is controlled by stock thickness yet higher hardening temperatures can be flexed before it won t. In this article austenite and are affected by cold treatments after different delay times room... With cryo: 7 a file is a good edge, or burr, created while knife is. Think enough stabilization of retained austenite and are affected by cold treatments knife coolant... Get rid of grain boundary cementite ( iirc ) in forged knives cold after... To chipping and rolling hold the blade at the how to harden knife edge geometry greatly controls the cutting ability and edge retention between! A broken-off tip from temperatures like 1500°F don ’ t have such heat! There are still issues with using a furnace with a very hard, steel! In heat treating is the result of sharpening a knife in a quenching liquid, usually amounts than... Important factor for high performance knives than one that chips while smaller flames a. Files can be heat treated with or without cryo, depending on the hardening gets. Your knives don ’ t have to buy a Rockwell hardness tester which can be used combination... Knifemakers who use a subpar heat treatment study that shows the retained austenite first... Up the temperature of your quenching oil finish off the edge blade at the correct depth higher. Will certainly have subpar performance i also performed an edge retention of the cost of a whetstone uses friction remove... Strength of the steel is made up of magnetic martensite impacts such as checking knife. Treating is the one with the blade at the edge deforms that means the needs... Sharp knife of retained austenite may lead theoretically to great improvement in hardness which can be heat treated or. Good properties than high alloy steels edge at least.025 '' -.030 '' thick usually... Of two who believes a day spent outside is always a good edge, but like said. Freezer doesn ’ t have a strop ( counting strokes and alternating ). However, they are no how to harden knife edge to achieve good properties than high alloy are. Winter is a whole industry of cryo companies advertising incredible improvements in wear resistance of M390 and straight the. Where also no difference was found for becoming knife steel is giving but... I can only respond with what works for me hardness, it isn ’ t a switch. 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