Originally Posted by Peregrino

OK - I'm sacrificing myself for the greater good. I don't normally throw myself on live grenades but this one I've got to see. What's confusing me is the definition of hardness. Rockwell #s aside, I thought hardness (as a factor in edge holding ability) was a function of % of carbon in the steel, the heat treat, and the resulting grain size and density of the carbides. Softer steel = fewer carbide crystals in the iron matrix. (Assuming a quality heat treat with controlled grain size/growth that doesn't leave the steel brittle and prone to cracking.) Since the exposed carbides (ideally troosite after martensite is converted during tempering) along the edge (earlier lecture on S30V) do the cutting, and resist wear better than the iron matrix, how is a softer steel going to hold a better edge? I've been able to get softer steels sharpened with less work and (without an electron microscope to make the comparison) they seemed as sharp as the harder steels, but heavy use - dressing game, cutting meat, hides, leather, etc. - required frequent touchups to maintain the edge. Every time I've used a cutting tool (machete, axe, sickle, sythe, etc.) it's been a softer steel and it always lost its edge with use. I didn't pay much attention to the particular steels used because they were cheap work implements often locally manufactured from scrounged materials with more art than science. On the other hand my Yarborough knife still has the factory edge and it will still shave anything that'll hold still long enough. Am I reading too much into this? Inquiring minds want to know - :munchin Peregrino

Originally Posted by Bill Harsey

Most files are designed to cut steel and have a very high carbon content for maximum hardness. This makes them hard to work (make into a knife) and they tend to be brittle in hard use.

A better answer is yes they will make a good knife for some applications but the difficulty of working the file into a usable knife blade would put it down on my list of materials to use.

Originally Posted by Peregrino

OK - I tried the "search" button and did a little deductive reasoning. Are we thinking in terms of exotic carbides e.g. the vanadium carbides in the S30V and the CPM154? As in the supporting iron matrix having a lower hardness number to give it greater toughness/shock resistance and the sharpness/edge holding characteristics being derived primarilly from the exotic carbides? As best I can grasp it - the only way to accomplish this is with the Crucible steels or some similar sintered metal process. :confused: Peregrino

Originally Posted by Bill Harsey

The fastest simple time honored hardness test is to grab a steel cutting file and file on the work piece.

Most steel cutting files are in the Rockwell "C" Scale 62 range.
This means if the file cuts the test piece easy it is softer than R "C" 62.
If the file can't cut anything and just skids off the surface of the test piece, it is harder.
If one tests many pieces of tool steel this way it can become possible to "feel" the subtle differences.

Before I take my CPM S-30V blades to the Rockwell tester, I file them (carefully over the unsharpened edge) to see if I can guess the hardness.

The last time I did this almost caused panic because I thought I was going to have to do the heat treat over again for not being hard enough but the blades tested right at R "C" 58.5, right in the hard use hardness range we like.
There's a lesson in this story too.

Originally Posted by HOLLiS

I have use the file test before, it is easy and often available to most people.

Originally Posted by Bill Harsey

Guys and Gals,

This will greatly increase the chances of the weld not cracking on castings, shafts, springs, etc. Use 7018 Low Hydrogen rod on DC Reverse polarity of possible. If your welding on cases or around things that have bearings in them, place the ground clamp within 6 inches of the weld, either coming or going as the magnet will deflect the arc.

This stuff is so good I should charge money for it. :D

Originally Posted by Ambush Master

What do you think about "Square Wave" Machines?!?!:D

Originally Posted by LibraryLady

Mr. Harsey,

You mentioned in another conversation, knife makers like the waterjet vs the laser as there's no heat residual when working with the high end "tough stuff". So if you cut the knife blank, (and I'm assuming you do this first) then go through the Martensitic Transformation process, won't that negate any of the heat issues from the laser? Or does repeated applications of heat affect the carbon atom structure development?


LL