Category: Quenching
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Introduction to Knife Steel Heat Treating from a Metallurgist
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Intro
I have many articles about all of the nitty gritty details of heat treating and the metallurgy behind every step. However, there may be some cases where knifemakers are afraid of all of the terminology and science and think heat treating is too complicated for them. When it comes down to it, the steps of heat treating are not particularly difficult. When you follow a recipe for how to make cookies you don’t need to know the science behind every step, but following them will still get you cookies at the end. An expert would know what went wrong if your cookies were too crunchy, too puffy, spread out too much, etc. And how to modify the recipe to change the flavor and texture of the cookies. However for most of us we will just follow the recipe. You can do the same thing with heat treating knife steel! So for this article I will tell you how to follow a datasheet. I will include some links to articles with more information about what happens in each step, but you can get to those when you are ready. Another great place to learn more about heat treating is my book Knife Engineering: Steel, Heat Treating, and Geometry.
Which Quenching Oil is Best for Knives?
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YouTube
The following information is also available as a YouTube video for those that prefer watching to reading. The video might be more fun though there are more details and more discussion in the article.
How to Heat Treat 8670
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Podcasts
I appeared on two podcasts this past week, Knife Perspective and Mark of the Maker. Knife Perspective I had been on before so we mostly focused on MagnaCut and other topics. Mark of the Maker was a full interview asking about my background before discussing my book, website, and CPM MagnaCut. So listen to one or the other or both depending on what you’re in the mood for.
How to Use a Steel Datasheet to Develop a Heat Treatment
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How Fast Do You Have to Quench? Hardenability of Steel
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Hardenability
How fast one must quench steel is controlled by its hardenability. Hardenability is not a measure of how hard a steel can get. Instead it is a measure of how fast you have to quench to achieve max hardness for a given composition. Therefore a steel with 0.2% carbon can have high hardenability without being able to reach a particularly high hardness; the steel can be allowed to cool in air and achieve more or less the same hardness as when it is quenched in water. On the other hand, a steel with very high carbon content that can reach very high hardness can have low hardenability, requiring a water quench to achieve its potential hardness.
What Makes Quenched Steel so Hard?
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To harden steel you heat it up to high temperature to form a phase called austenite, followed by rapid quenching to make a very strong phase called martensite. Hardness is a measure of strength. I covered the process of austenite formation in the following post: Austenitizing Part 1. To summarize that post:
Hi very green in the blade smithing hobby, from reading much of your work I’m realising that canola oil isn’t cutting it as a quenchant and parks 50 is out of reach in terms of affordability, there’s a desperation for cheaper alternatives out there and I’d love to see your thoughts or a research video on feasibility of homemade emulsion quenchants for a home bladesmith, I’ve seen one article with the following doi on the topic but the material dimensions don’t really translate to blades
https://doi.org/10.1007/BF00715851