Well my friend was having so much fun playing with the throwing knife I just built that I figured I would make another one. The first throwing knife I built (shown on a previous post) was about 12 inches long and 3/16 inch thick and weighed about 14 ounces. This time I up-sized and made the knife about 14 inches long and 3/8 inches thick. This guy weighs just one ounce shy of 2 pounds. It definitely took longer to shape this one out than the first, but it seemed to come out alright and is about as heavy a knife as I have seen available specifically made for throwing.
I made a regular set of leather handles for it, but I liked the colors so much I decided to make some curly maple handles, probably will exchange them for the leather when I throw it.
I have had a number of inquiries since I made this about the heat treatment that I am using. I have been doing bone and charcoal color case hardening for several years and have studied it quite extensively. The basic principle is that for steel to respond to heat treatment there must be a sufficient quantity of carbon present. Mild steel has about .18 of 1 percent of carbon and will not respond to heat treatment to any appreciable degree. A typical carbon steel such as 1095 has .95 of one percent carbon present and is fairly close to what Cold Steel uses for many of its knives. The problem with high carbon steel is that there is a bit of give and take. Once you have hardened it the steel is so brittle that it can literally shatter like glass. Though this condition has great wear resistance and edge holding ability, it would not be practical to use for most applications at this level of hardness. To make it more suitable for different applications it goes through a second process called tempering to convert some of the hard martensite structure back to a softer structure known as pearlite. If you bring it into the middle of these two extremes you have essentially made a spring. So the dillema is whether you want a tough, durable knife, or one that has extreme edge holding ability, but is also fragile.
I like to think, that for this application, you can have your cake and eat it to. With case hardening, such as was used in this knife, I took a piece of low carbon steel and added some carbon to the exterior. The depth of the process used creates a high carbon zone about .032" deep. It is possible, and I have done it, to completely penetrate the cross section of the steel with carbon essentially converting it to crude form of tool steel, but this is not desirable for this application. By limiting the depth of carbon penetration you can have a very high carbon layer surrounding a soft, low carbon core. Essentially this means that after the material has been hardened it can be left in a maximum hardened state without much fear of breakage since the softer material underneath supports the hardened shell. The end result is a surface that is extremely resistant to wear, but is not brittle. About the only area that I bother to temper is the very tip of the knife where the thinner cross section (which is where four surfaces converge) could potentially have been completely penetrated by the carbon rendering it brittle. In short, all of these qualities seem to be about ideal for a throwing knife which shouldn't be sharpened on the cutting edge and only occasionally needs to have the point touched up. Also, if the case ever wears through after many, many, years, the process can be repeated giving it a new lease on life.
The colors that are produced by this process are interesting in their own right due to a very complex surface structure, most industrial case hardening or carburizing processes do not produce them however. Though attractive, they will wear away with time, but even when the color is long gone the positive effects of the heat treatment will remain. Hopefully that explains my reasoning for making a knife out of mild steel.
I made a regular set of leather handles for it, but I liked the colors so much I decided to make some curly maple handles, probably will exchange them for the leather when I throw it.
I have had a number of inquiries since I made this about the heat treatment that I am using. I have been doing bone and charcoal color case hardening for several years and have studied it quite extensively. The basic principle is that for steel to respond to heat treatment there must be a sufficient quantity of carbon present. Mild steel has about .18 of 1 percent of carbon and will not respond to heat treatment to any appreciable degree. A typical carbon steel such as 1095 has .95 of one percent carbon present and is fairly close to what Cold Steel uses for many of its knives. The problem with high carbon steel is that there is a bit of give and take. Once you have hardened it the steel is so brittle that it can literally shatter like glass. Though this condition has great wear resistance and edge holding ability, it would not be practical to use for most applications at this level of hardness. To make it more suitable for different applications it goes through a second process called tempering to convert some of the hard martensite structure back to a softer structure known as pearlite. If you bring it into the middle of these two extremes you have essentially made a spring. So the dillema is whether you want a tough, durable knife, or one that has extreme edge holding ability, but is also fragile.
I like to think, that for this application, you can have your cake and eat it to. With case hardening, such as was used in this knife, I took a piece of low carbon steel and added some carbon to the exterior. The depth of the process used creates a high carbon zone about .032" deep. It is possible, and I have done it, to completely penetrate the cross section of the steel with carbon essentially converting it to crude form of tool steel, but this is not desirable for this application. By limiting the depth of carbon penetration you can have a very high carbon layer surrounding a soft, low carbon core. Essentially this means that after the material has been hardened it can be left in a maximum hardened state without much fear of breakage since the softer material underneath supports the hardened shell. The end result is a surface that is extremely resistant to wear, but is not brittle. About the only area that I bother to temper is the very tip of the knife where the thinner cross section (which is where four surfaces converge) could potentially have been completely penetrated by the carbon rendering it brittle. In short, all of these qualities seem to be about ideal for a throwing knife which shouldn't be sharpened on the cutting edge and only occasionally needs to have the point touched up. Also, if the case ever wears through after many, many, years, the process can be repeated giving it a new lease on life.
The colors that are produced by this process are interesting in their own right due to a very complex surface structure, most industrial case hardening or carburizing processes do not produce them however. Though attractive, they will wear away with time, but even when the color is long gone the positive effects of the heat treatment will remain. Hopefully that explains my reasoning for making a knife out of mild steel.
