Replies to This Discussion

Permalink Reply by Halicon on November 19, 2011 at 10:12

Carbon, every single time. It's two completely different creatures and once you get into the top department of hard HRC tools the difference becomes more and more extreme to the point where it's simply impossible to not notice it.

 

There are many factors and this is only a  generalization, but carbon steel can be forged to be incredibly hard as well, the only difference is that the entire steel was thought of for different uses. With carbon you want a trusty and dependable action that removes small chips (guess I could say normal dulling) whereas the stainless has other uses in mind.

 

I'd also like to throw in that we have become far too "stainless" as of late. We trade down to largely inferior alloys because we have simply become used to a steel not staining much if any at all. There are good alloys and smiths that know how to treat them but in comparison to the number of carbon steel smiths out there the number is dwarfed, a bit off-topic but I don't like this trend at all.

 

So anyhow, stainless for 20-40 years ago was actually steel that was meant to tackle rougher tasks, tasks that a carbon steel simply chipped too much at. That kind of steel gives a much larger reward for your sharpening work compared to a "polluted" steel that has compounds which affects it's molecular quality negatively in order to render it almost impregnable to staining.

 

That kind of steel, properly forged and with a normal to harsh heat treatment is as close to a nightmare as I can come when working on the stones. The time spent is doubled or tripled. The tool sticks to the stone making flatness extremely hard to perform especially on large bevel tools like chisels. Even more-so on laminated tools since the tool stick across the bevel yet the wrought iron is many times softer than the steel resulting in a bevel that is convex and inaccurate unless you don't have the training and expertise to work around it (easier said than done).

 

Then again, there's not much that can beat the feeling you get after taking a translucent shaving of a very dense tropical hardwood burl which makes it all worth it.

Permalink Reply by Steve Hanner on May 12, 2013 at 9:05

So much has changed today with new steels, blends and heat treating quality that many of the old techniques have gone out the door!

KnifeMakerPermalink Reply by Vance Wade Hinds on July 10, 2013 at 18:52

I would respectfully disagree with Halicon and agree with Steve.  I will offer my nonscientific and totally lay opinion to this debate.  What makes a steel stainless is its chromium content.  Anything about 14% or over is considered stainless.  The stainless steels back in the day were definitely inferior to plain high carbon steels.  But modern techniques and processes have done away with this old adage.  To call one steel as high carbon and stainless steel as not high carbon is a misnomer.  What makes a knife steel capable of getting hard enough to be used as a knife blade is its carbon content.  All good knife steels are high carbon whether stainless or not.   I am not a metallurgist so I am sure I am about to butcher this discussion.  High carbon steel is any steel that has about .60% carbon and above.  For example 1095 carbon steel has .95% carbon but no chromium (1084 has .84% carbon) plus low additional alloys.  Whereas 440C Stainless is about .90% carbon and about 16% chromium plus alloys.  Both are high carbon, but 440C is stainless because of its chromium content.  Alloy steels adds additional alloys at varying percentages.  Newer processes like powder metallurgy contribute to the equation as well.  Just for percentage comparisons: D2 is 1.5-2.0% carbon and 10.5-12% chromium plus additional alloys.  ZDP-189 is 3.0% Carbon and 20% chromium plus additional alloys.   The steel industry keeps tweaking the alloy percentages and the processes.  A high end stainless steel today is a whole different matter than one forged in the 1950s and 1960s.  As with all things technology and time changes the game. 

Permalink Reply by Alexander Noot on July 11, 2013 at 2:41

I kind of agree with Vance, except that I think his comment about Chromium content is incomplete.

What is REALLY making steels hard to sharpen is carbide content. Whether that carbide be vanadium, chromium, niobium or something else. THAT is what's making it hard to sharpen.

The reason for this is that those carbides are many times harder than the steel that they're imbedded in. Where the steel can be hardened to maybe rockwell 61. A vanadium carbide is about 80-85 (!!!!) on the rockwell C scale.

The problem with this is then that those carbides are fairly big (comparatively speaking) and that if enough material around them is removed they stick out and make sure that you can't make as refined an edge as most of the carbon steels. And once all the material around them is removed they tend to break out of the edge leaving a carbide shaped hole in the steel and creating a form of micro serration.

In short, most of the stainless steels won't sharpen to as fine an edge as most carbon steels. Good examples of this are D2 (semi stainless) and S30V which has a lot of Vanadium (the V stands for Vanadium). Both of these steels are sometimes said to "take a crappy edge but keep it forever" and there are multiple examples of this.

So if you want something to be the absolute summum of sharpness....you'll need a finegrained steel with very little carbides....and in general that'll be a carbon steel.

If you want a steel that'll retain it's edge for a long time however...most stainless steels are better suited.

(And we've not even talked about toughness yet....which is a whole extra story)

Permalink Reply by Alexander Noot on July 11, 2013 at 2:43

I never actually answered the question did I.

With two knives where the Rockwell C value is the same, the one being stainless and the other not. In general the stainless knife will be harder to sharpen. (There might be exceptions to the rule)

KnifeMakerPermalink Reply by Vance Wade Hinds on July 11, 2013 at 8:19

I didn't know that a vanadium carbide is 80-85 on the Rockwell scale.  Thanks for the clarification.  Vance

 

Permalink Reply by Alexander Noot on July 11, 2013 at 8:24

By comparison Chromium carbides are around 70 on the Rockwell C scale.

KnifeMakerPermalink Reply by Vance Wade Hinds on July 11, 2013 at 8:31

I was told  that the powder metallurgy makes a more uniform and fine grain steel.  Is this not true for the carbides? I may have misunderstood all the way around.   I am very interested in knife steels.  Thanks.  Vance

Permalink Reply by Alexander Noot on July 12, 2013 at 2:15

It's still true, what it'll mean however is that the carbides in powdersteel vs non powder steel will be better distributed. They don't actually change in size.

But do to the more uniform distribution of the carbides throughout the steel there will be less regularities and this less chance of chipping/breaking.

Carbides are a LOT bigger than the particles that make up the rest of the steel. That doesn't chance because of the production method.