Optimum grits for specific steels

B

beckerhead

Joined
Feb 11, 2005
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While perusing a gem polishing site I saw various polishes and powders from 12,000 to 200,000 grit. After reading here about the various sizes and percentages of carbides in differing steels, what would be the finest possible grit for some of the common steels such as 1095, VG-10, D2, AUS8, etc. to still see a measurable benefit? Bear in mind I am NO knifescience guy by any means, just a curious george? Heck, I use a little 3M 2000 wetdry and then some green compound on a strop and do just fine for my Neanderthal purposes . How far can a bona fide knifeknut go before he needs the white huggy jacket with shiny buckles?
 
I find that 1/2 micron (50,000 grit) diamond compound gave me a distinct improvement over 1 micron (14,000) compound when I stropped on sheet plastic or photographic paper (moderately stiff substrate). This was with somewhat recalcitrant stainless steel like 440A. I didn't notice nearly as much improvement when I went from 50,000 grit to 100,000 grit.

For stainless steel and D2 I would use diamond abrasive. This will allow you to cleanly cut even the hardest or most ductile carbides in your steel. You can probably use softer abrasives on the 1095 just as well.

A recent idea of mine is that for the extremely fine grit you probably need a rather hard strop surface or the grit will just get pushed into the strop. Since you want the grit to not just slide on your strop surface you might want to make it from copper or soft steel. I have a kit for using diamond grit to polish plane blades and the final stage uses glass as a substrate for diamond grit paste. The earlier stages use a wood-based material.
 
Would a super fine diamond paste somewhat remedy the issue of carbide breakout from sharpening steels like D2 to a very low angle? I have read that uneven removal of the carbides vs. the surrounding media promotes a very unstable edge. Kinda like a big rock in a very thin layer of cement is easy to knock loose.
 
In my experience really fine edge finish only slices well if the blade is honed to a low angle (say 10 degrees per side). On most blades I am happy with the performance if I finish using a fine ceramic hone. Stropping with .5 micron diamond grit does very nice things to shaving performance on an acutely honed blade.
 
Regarding steel with large carbides (like D2) I think that the superfine diamond grit will leave an edge that looks more like concrete that has been cut with a diamond saw rather than concrete that has been chiseled to shape. The carbide lumps will be shaped in situ in the softer iron matrix. I expect some modest improvement in edge stability, but the edge will still be subject to breakdown. The big difference I expect is in initial edge performance. Using the diamonds you can get a pretty nice shaving edge on D2. When it wears you will lose that shaving smoothness, but gain an aggressive slicing performance due to the development of edge microserration.
 
So the lowest practical angle for the intended use, coupled with the finest edge polish, will provide better performance to some extent for all steels.
With regard to seeing more benefit, would a very low (10 deg. and under), super fine polish (50K and up) be more useful on something like AEB-L, 8Cr13MOv, or s30v, D2, for stability and overall function in say, a small to medium fixed bushcraft blade?
 
No a high polish is not always better or provide a better preformance for all steels. A coarse finished edge will slice much better and depending on how you do use your knife the highest polish may not work well at all for a person. I have personally found the carbide issue to be a non factor for me, even with D2 at around 12 degrees per side and a medium finish like a norton 4000 grit. If you did want an under 10 degrees per side edge on your knife and found that thin you had problems you could always put on a micro bevel at a larger angle for a little stronger edge and I'd bet you wouldn't notice any preformance difference in your normal use of a fixed bushcraft knife.
 
db said:
No a high polish is not always better or provide a better preformance for all steels. A coarse finished edge will slice much better and depending on how you do use your knife the highest polish may not work well at all for a person. I have personally found the carbide issue to be a non factor for me, even with D2 at around 12 degrees per side and a medium finish like a norton 4000 grit. If you did want an under 10 degrees per side edge on your knife and found that thin you had problems you could always put on a micro bevel at a larger angle for a little stronger edge and I'd bet you wouldn't notice any preformance difference in your normal use of a fixed bushcraft knife.
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So then 2 matched blades at maybe 64Rc in D2 at 4000 grit, 12 deg. & say, 1095 at 10 deg. 50K grit high polish, would give the D2 a distinct advantage for average bushcraft use, (cleaning game, lots of woodworking, batoning, etc.?) The reason I ask is that while of course a very toothy edge is a great slicer, that a polished edge is very good for push cutting which is more akin to woodwork. planes, chisels, etc. utilize a very tight edge with much higher performance than coarser edges in regard to retention. Again, if I am stumbling here, I am NO expert, just trying to get my sea legs, so to speak.

In regard to D2, to really see it shine performance wise shouldn't it be at the upper end of it's hardness? Wouldn't that compromise it's toughness, just as running it softer would compromise it's great edge holding abilities, and ability to take a crisp edge?
I think it is a right steel for the right knife/usage, but not an end all. I have always wanted a nice D2 skinner from Dozier or the like, but even after reading many rave reviews about guys here having "super tough" D2 knives that they use as heavy duty beaters, I don't see D2 as an optimum impact use steel. No different than not thinking an L6 blade would be optimum for use in a saltwater setting, great steel, but not for that scene.

Sorry if I rambled away from the topic a bit, just seeking some opinions and insight. And thanks for the helpful feedback guys.
 
db said:
Either do I, but I also don't see a knife as an optimum impact use tool.
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I'm thinking more along the lines of chopping, splitting, batoning, not chiseling concrete or attacking battleships, but I get your drift. While a razor blade is in fact a wedge, it's not exactly in the same class as a GB splitting maul.
 
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