O1 vs S30V : edge retention, ease of sharpening

[Cliff Stamp]

Awhile back I compared a Sebenza in S30V at 58/59 HRC to a 1095 blade at 66 HRC on a few media, cardboard and plastics. The edge on the Sebenza would just buckle at low angles and thus its wear resistance never came into the situation as the edge just cracked off.

Recently I ran it against an O1 blade at 63.5 HRC, three trials cutting 1/8" ridged cardboard, on a slice through 2 cm of blade, edge retention was checked slicing light cord under set tension after a short interval (15 m) and a longer one (35 m).

I used a micro bevel set at 20 degrees to vastly lower the effect of the higher strength of the O1 blade, as I wanted to examine mainly wear resistance. The first round had both edges recut at 3-5 degrees per side, then a light microbevel applied finishing on the fine Spyderco rods. The micro bevel was barely visible, <0.05 mm wide.

After the first short round the Sebenza about half as sharp as the O1 blade. Under mag and the entire microbevel had cracked off in certain sections. While the angle was high enough for strength, the underlying primary edge didn't have the necessary strength.

Next trial I set the secondary bevel about 0.1 mm wide. After the short interval both blades wer cutting similar, however after the long interval the Sebenza was again well behind and again sections of the edge were just broke away, enough to be seen by eye.

This has a massive effect on resharpening, the Sebenza doesn't respond to a steel with the edge broken off, and it takes much more honing as you have to regrind the entire edge, about 10:1 in favor of the O1 blade.

As a final trial, the secondary edge was over 0.15 mm wide. I also got sloppy on the O1 honing and it was only about 75% as sharp as it could be but ran the comparison anyway as I was mainly curious about the Sebenza.

Again the blades held well in the short interval, and after the long interval they were close, the O1 was still ahead, but only by a small amount, <25%, and the Sebenza's edge had only cracked in a few places. Note again though the O1 had a less than optimal initial edge.

As the work continued the blades would move apart as once an edge cracks it piles up stress there and it continues cracking faster. I have some more work planned when I have more cardboard and other stuff to cut to see how they compare if I set heavy micro-bevels, enough so the edge doesn't buckle. I would guess 0.2 mm wide should be enough for cardboard, plastics might need more.

I am not sure in the above how much of it is tensile strength or grain and carbide structure. The primary edge at 3-5 degrees leaves it very thin, if there are large aggregaties they might not be stable there regardless of the hardness.

-Cliff

 

[db]

Why not also toss in the ZDP Caly since it's also about the same RC as the O1?

 

[Cliff Stamp]

The primary edge angle can't be set that low on a flat grind so the strength issue can't be checked. I do have edge retention work planned for it.

-Cliff

 

[Don M]

From this I conclude that S30V is not suitable for a razor.

The relevant question is what angle is the minimum that can be used with S30V for common applications such as wood, rope, and cardboard. 3-5 degrees (per side, I assume) is far thinner than most people use. Even 10 degrees per side is thinner than what 99% of even knife knuts, use.

 

[Cliff Stamp]

From this I conclude that S30V is not suitable for a razor.

I would hope that in general more is seen than that. I didn't do this really to bring up a point about S30V specifically, but more so to explore the influence of strength/hardness and wear resistance in edge retention, continuing the work Alvin and Mike started 10+ years ago on rec.knives.

The relevant question is what angle is the minimum that can be used with S30V for common applications such as wood, rope, and cardboard.

I addressed the minimum durability requirements for microbevels on light materials towards the latter part of the post.

... 3-5 degrees (per side, I assume) is far thinner than most people use.

Yes, mainly due to poor steel for a cutting blade and a huge amount of misinformation on what is necessary for blade angles. It is common to see angles recommended now for hunting knives that a generation ago would have been known to be too abtuse for felling axes.

Even 10 degrees per side is thinner than what 99% of even knife knuts, use.

That is the angle found on puukko's, these are really common now in the bushcraft community and they get used to cut harder materials than cardboard.

-Cliff

 

[sodak]

I've been taking my knives down lower and lower, with sometimes surprising results. The only thing that I wish that I had more of is time. It takes time to grind them thin, using either bench stones or an Edgepro.

These are interesting results. I'm going to make a concerted effort to get some of my knives off to Phil Wilson or someone else who can custom heat treat. The problem that I run in to when trying these types of tests is that I don't know if I'm running into the limit of a steel (given it's geometry), or the limit of the particular heat treat of this knife.

I'll be ordering a knife very soon in O1, so am glad to see some tests done with it. Do you consider 63.5 optimal for a small O1 cutter/slicer? I'm thinking of a nice Hudson Bay style knife in this.

I'll be very interested to see the results of edge retention on your ZDP Caly!

 

[Cliff Stamp]

It takes time to grind them thin, using either bench stones or an Edgepro.

Get an x-coarse SiC waterstone, cut it up into small chunks, use the chunks like a file on the edges. Press very hard. It should take 1-2 minutes to cut down the edge on a small blade, doesn't matter the steel.

The problem that I run in to when trying these types of tests is that I don't know if I'm running into the limit of a steel (given it's geometry), or the limit of the particular heat treat of this knife.

Yes, it isn't like 58/59 HRC is the limit of S30V, most steels used in the cutlery industry are not ran where they should be for optimal cutting performance and edge retention, which is ironic considering this is how they are usually promoted with the various abuse restrictions.

Do you consider 63.5 optimal for a small O1 cutter/slicer?

This is the max hardness, needs cold treatment to get there. So yes, optimal from a cutting/edge holding perspective. Not what I would run on a heavy chopper/prybar, but I would not use O1 there anyway.

-Cliff

 

[me2]

Are you sure that 63.5 is the maximum? I tested a piece I hardened at home and it went to 64, and I'm pretty sure I only hardened it "properly" in the lose sense of the word. I just used a fire brick and a map gas torch, and cooking oil.

 

[thombrogan]

Probably more proper to say that was as hard as the maker could harden the steel.

 

[Cliff Stamp]

Are you sure that 63.5 is the maximum?

No, but the maker is, and I assume is quoting ASM texts. I'll check. As an aside, most people tend to round hardness so 63.5 isn't significantly different from 64, plus hardness variances could change depending on the exact alloy content, there are allowed variances.

-Cliff

 

[me2]

I seem to remember my O-1 having some extra elements not listed in my standard recipe books. It was Starrett and may have had a little V or something.

 

[Steelhed]

Cliff - Seems to me you're finding out why the best straight razors are made of high carbon steel, not stainless. At such low angles stainless tends to chip more than non stainless steels at the same RC. You can feel the difference on you face when you shave with one versus the other. Now that being said, the best safety razors today are all multiblade models sporting various types of stainless steel. The difference I think is related to the fact that no one tries to resharpen a safety razor blade, but everyone is expected to sharpen their own straight razor (usually on a strop). The stainless steel in safety razors last longers because the edges have been optomized and set to take advantage of the steel's wear and corrosion resistance. When it does wear out you simply throw it away.

 

[Cliff Stamp]

Cliff - Seems to me you're finding out why the best straight razors are made of high carbon steel, not stainless.

This isn't just carbon vs stainless, it has to do with hardness, grain size and carbides. D2 for example is a high carbon steel, not stainless, but won't do well for the above work as the maximum hardness is low, the grain size large, and the carbide aggregates very large.

I am not finding it out, just confirming work done by Alvin about 20 years ago, and later redone by Mike, all discussed on rec.knives. It also isn't just a straight razor issue, these are edges run on utility, skinning and kitchen knives. They are in fact more robust than you need actually as with the right steels you don't need to apply those really heavy secondary bevels.

I am still curious about the very fine grained stainless steels which are fairly hard. I would like to see BG-42 and S90V at 63/64 HC in those edges, as well as maybe ZDP-189, though I would be concerned there about the carbide size as Cr carbide tends to be large.

-Cliff

 

[Steelhed]

Cliff - Yeah, I know what mean. It's just that I was reading an article about turn of the century straight razors made in Germany. The writer took a look at the grain structure under magnification and was amazed at how fine a structure they were getting back then. Of course if your modern bias is toward stainless steels with their larger grain structures (on average) then you might be amazed at how well the old carbon steels looked and worked. According to the article, the razor worked very well indeed for its intended purpose - shaving.

I think most knives today are made with the end user in mind. However, that end user is not your typical knifeknut. Most users can't even resharpen their knives, and they don't want to have to think about knife care and corrosion avoidance, hence the proliferation of stainless steels. I too would like to see how BG-42 fairs. It's my favorite stainless steel given that everything else is done right with it (heat treat, blade geometry, etc.).