Professional Soldiers ® - View Single Post - Knife Steels-Material Science

**Bill Harsey** · 05-07-2006, 09:26

Before this rodeo gets out of control with too much detail and I lose all interested readers, I'll try to explain why we are going into this detail.

A knife cuts well because of how the cross section of the blade is shaped or what knifemakers call blade and edge geometry.

The thinner the blade and acutely sharper the angle of the edge, the better it will cut.

The limiting factor on blade geometry is the strength of the steel and even the size of the carbides.

When we have a given blade steel with optimum heat treat and we need it to stand up to increasingly tougher jobs, the only way to make it stand up to the demands is to increase the thickness of the blade and the edge. Think of how swords are different than paring knives.

About carbide size
I've worked with the tool steel called D-2 for many years. It's a common planer blade steel used in my regions sawmills. People keep bringing me handfuls of used planers blades made of this stuff. I keep thinking it might be useful for something someday. The pile keeps growing.

Much of the D-2 I've actually made into knives and master drill/machining patterns was purchased new. Here is the thing with D-2, it has the largest carbide size of any tool steel i know about. This is a problem because you CANNOT place an extremely fine or acute edge on a blade made from this without having carbide chip-out on that edge.
Edges on D-2 have to be less acute of an angle.
The macro grain on this steel can be seen thru the grinding and buffing stages of finishing the blade.

There can be very large and discernible differences in how tool steels perform when made into knives.

Edited to add: D-2 is a legitimate knife blade steel. Some good knifemakers use it very successfully.
Here is the difference, you cannot grind D-2 into a super thin edge (like .015 to .007 thousandths of an inch thick before first sharpening) and expect it to hold up. It has to be left a bit thicker and I'd be comfortable with an edge thickness more like .035 thousandths of an inch thick for a folding knife or fixed blade hunter.
D-2, because of it's big carbide/grain structure does not have the transverse bend fracture strength of other tool steels so the edge will not stand up as well to prying or side load.

05-07-2006, 09:26	#38
Bill Harsey Bladesmith to the Quiet Professionals Join Date: Feb 2004 Location: Oregon, Land of the Silver Grey Sunsets Posts: 3,879	Before this rodeo gets out of control with too much detail and I lose all interested readers, I'll try to explain why we are going into this detail. A knife cuts well because of how the cross section of the blade is shaped or what knifemakers call blade and edge geometry. The thinner the blade and acutely sharper the angle of the edge, the better it will cut. The limiting factor on blade geometry is the strength of the steel and even the size of the carbides. When we have a given blade steel with optimum heat treat and we need it to stand up to increasingly tougher jobs, the only way to make it stand up to the demands is to increase the thickness of the blade and the edge. Think of how swords are different than paring knives. About carbide size I've worked with the tool steel called D-2 for many years. It's a common planer blade steel used in my regions sawmills. People keep bringing me handfuls of used planers blades made of this stuff. I keep thinking it might be useful for something someday. The pile keeps growing. Much of the D-2 I've actually made into knives and master drill/machining patterns was purchased new. Here is the thing with D-2, it has the largest carbide size of any tool steel i know about. This is a problem because you CANNOT place an extremely fine or acute edge on a blade made from this without having carbide chip-out on that edge. Edges on D-2 have to be less acute of an angle. The macro grain on this steel can be seen thru the grinding and buffing stages of finishing the blade. There can be very large and discernible differences in how tool steels perform when made into knives. Edited to add: D-2 is a legitimate knife blade steel. Some good knifemakers use it very successfully. Here is the difference, you cannot grind D-2 into a super thin edge (like .015 to .007 thousandths of an inch thick before first sharpening) and expect it to hold up. It has to be left a bit thicker and I'd be comfortable with an edge thickness more like .035 thousandths of an inch thick for a folding knife or fixed blade hunter. D-2, because of it's big carbide/grain structure does not have the transverse bend fracture strength of other tool steels so the edge will not stand up as well to prying or side load. Last edited by Bill Harsey; 05-07-2006 at 09:44.
Bill Harsey is offline