I recommend using 1080 or 1084 because it's easy to heat treat. The reason it's easy to heat treat has to do with the carbon content.
This is a simplified carbon phase diagram.
The vertical line is temperature, and the horizontal line is carbon content. Notice the V-shaped curve forms a point right around 0.80 (it's actually 0.77%). The labels on the different sections tell you the kinds of grains that form at those temperatures and carbon contents under normal circumstances.
To harden a blade, you need to convert as much of it as you can into austenite, then quench it quickly so it forms martensite. Martensite is really hard but also brittle, so you have to temperer the knife to remove some of the hardness and strike the perfect balance between hardness (which helps maintain an edge) and toughness (which prevents the edge from chipping or the blade from snapping).
On the bottom left, steel is a mixture of ferrite (pure iron) and pearlite (a mixture of cementite and ferrite). On the bottom right, the steel is a mixture of pearlite and cementite (basically a hard ceramic made of iron and carbon). But right around 0.80, the steel is completely pearlite with no ferrite or cementite (except what's in the pearlite grain).
When you heat up your steel, you want to convert it all to austenite. To do that, you need to basically dissolve the carbon into the steel so that it's equally distributed. That means you have to break up those grains. If you're on the bottom left, it takes longer because the carbon has to migrate through all that ferrite to become equally distributed. That requires a higher temperature and a longer soak time. If you're on the bottom right, it takes longer and requires more heat because you have to break up the chemical bond of the cementite, and again, the iron has to migrate in such a way to become evenly distributed.
But since Pearlite is a bunch of thin layers of cementite and ferrite, the carbon doesn't have to migrate very far at all. You can get the carbon in solution at a lower temperature with less soak time. You can practically quench it as soon as it comes up to temperature (though I'd soak it at least a minute).
That's one reason 1080 is easy to heat treat. Another reason is because to turn it into Martensite, you have to reduce the temperature really quickly. Since the austenizing temperature is a little lower than it would need to be if there were more or less carbon, you don't have as far to cool your knife off in order to turn it into Martensite. That means you're less likely to fail at turning it into Martensite when you quench it.
A third reason 1080 is easier to heat treat is that by austenizing it at a lower temperature, the grains don't grow as fast. The hotter you get the steel, the faster the grains grow, so it's hard to soak the blade without the grains getting too big. You want fine grains because that makes the steel tougher for a given hardness, and being able to keep it at a lower temperature while austenizing helps control that grain growth.
So for all those reasons (lower temperature = easier to quench and less grain growth, and less soak time), 1080 or 1084 is easier to heat treat than something like 1095.
But it's also inexpensive.
Topic: I want to try to make a few knives.... help (Read 2933 times)
