What Does Steeling Do? Part 1

Even the name is confusing.  Knife steel.  Butcher’s steel.  Honing rod.  Sharpening steel.  Do they remove metal or just “re-align” the edge? What does “re-align” mean?   Are “honing” and “sharpening” different things?  Scanning through opinions found on the internet will leave you more confused than enlightened.  This series examines what actually happens at microscopic scale.

It is a common misconception that steeling does not remove metal, but simply “re-aligns the edge.”  I have shown that re-alignment is one of the four results of stropping in What Does Stropping Do?  However, in my experience this type of re-alignment rarely occurs.  In the vast majority of cases, the steel near the apex is too damaged to be straightened, and instead simply breaks away rather than realign.  Secondly, with typical use in slicing applications, blades usually become “dull” through abrasion (including micro-chipping) or blunting and thickening of the apex, rather than by rolling (or “major deflection”) of the edge.  Rolling-like deflection can occur in a limited number of cases; for example by cutting into the non-abrasive lip of a glass.  More commonly, cutting non-abrasive materials produces a blunted, mushroom-shaped apex, as shown in the image below.

Delica_cardboard_02
Cross-section SEM image of a typical dull knife blade. The apex is blunted and “mushroomed” through both abrasion and movement of softened steel.

One of the first articles I wrote on this blog was to define the terms “sharp” and “keen” as they relate to sharpening/honing/stropping blades.  In this series of articles, I will demonstrate the effect of steeling with the various types of honing rods, and show that steeling improves keenness by removing metal.   In simple terms, steeling primarily produces a micro-bevel.  To be consistent with these definitions, steeling does not sharpen the blade – if we accept that sharpening requires thinning the blade by grinding the bevel.  For example, we may choose to sharpen a knife at 30 degrees (15 degrees per side) creating a millimeter wide bevel and then maintain the cutting ability of the knife by steeling at 20 degrees per side (40 degrees inclusive) to form a micro-bevel.

For this study I primarily use Olfa carbon steel cutting blades and dull them with a few cutting passes into the edge of sharpening stone.  This produces a blunt apex with minimal damage to the underlying steel.

When “steeling” the edge, I use the traditional edge-leading, heel to tip slicing motion with light force applied at an angle slightly higher than that of the existing bevel.  A range of honing rods are compared; a traditional ribbed steel (Wustof), a smooth ceramic rod, a smooth/polished “butcher’s” steel (Victorinox), a tungsten carbide sharpener (Chestnut tools Universal Sharpener), the Spyderco Sharpmaker (204MF) and a diamond-embedded rod.   In part 1 of this study, I will demonstrate that steeling improves keenness through metal removal rather than “re-alignment of the edge.”

Ribbed Steel

The set of images below demonstrate that the traditional ribbed knife steel does not “re-align” a “rolled” or deflected apex.  The rod simply produces a micro-bevel.  In the first image, the profile of the “factory” edge of the blade is shown and in the second image, the same blade after “rolling the edge.”

Olfa_new_05
Cross-section view of the factory edge on the Olfa blade.  The blade has been sharpened/ground at angle just below 30 degrees and buffed or stropped to produce a micro-convex with excellent keenness.
rolled_glass_03
Cross-section view of a “rolled” edge, produced by attempting to cut into the lip of a glass beaker at an off-normal angle to push the blade to one side.

The blade was then steeled in the traditional fashion, edge leading at an angle of approximately 30 degrees.  The blade was imaged, confirming that keenness had been restored to the apex and revealing that this was achieved by removal of steel; creating a new micro-bevel.  There is some evidence of softened metal being redistributed; however, a micro-bevel is unquestionably formed through metal removal.

rolled_glass_steel_EL_06
Edge-view of the rolled edge after steeling on a conventional ribbed steel rod (edge leading) demonstrates keenness has been restored.
rolled_glass_steel_EL_02
Cross-section view of the steeled blade with the white overlaid lines showing the factory geometry.  Comparison with the cross-section image of the factory edge proves that keenness has been restored by metal removal with the formation of a micro-bevel, not by re-alignment of the rolled edge.  Some subtle redistribution/burnishing has also occurred, particularly visible on the lower left of the bevel where metal is observed outside the white triangle.

Ceramic Rod

Unlike the traditional metal butcher’s steel, it is undeniable that a ceramic honing rod removes metal, since the black steel swarf is visible on the white surface after use.  In the following example, the blade was dulled by cutting into an abrasive stone, leaving a cleanly blunted apex.  Honing with the ceramic rod is also observed to produce a micro-bevel with a keen apex.

Olfa_dulled_02
Cross-section view SEM image of an Olfa blade dulled by cutting into an abrasive stone.
Olfa_dulled_ceramic_hone_x5_02
Cross-section view SEM image of the dulled Olfa blade following honing on a the ceramic rod. A keen micro-bevel has been formed.

In the SWARF! article, it was shown that traditional hones remove metal by cutting furrows into the metal of the blade producing curled metal chips – microscopic versions of the chips found in any metal fabrication shop.  This type of metal removal is generally termed abrasive wear and occurs when a hard, sharp abrasive cuts into a softer metal surface.

SG2k_swarf_04
Micrograph of metal swarf produced by a conventional (Shapton Glass 2k) hone. The sharp abrasive ejects curls of metal waste.

Traditional honing rods do not have sharp protrusions, and the metal swarf found on the surface is observed as flattened or smeared patches of metal.  This type of metal removal (or transfer) is generally termed adhesive wear.  Adhesive wear occurs at points of very high pressure that occur when the contact area is very small.

Ceramic “steels” have become common and are often preferred to traditional ribbed knife steel.  Although these ceramics are composed of micro-sized sintered grains, the surfaces are relatively smooth and do not display a “grit-like” texture.  These rods appear to remove metal predominantly via adhesive wear rather than abrasive wear (grinding).

ceramic_hone_scalpel_swarf_02
Conventional Electron image of the ceramic honing rod shows the surface roughness of the ceramic and steel debris transferred from the knife blade.
ceramic_hone_scalpel_swarf_01
Back-Scattered electron image of the ceramic honing rod.  In this image, the ceramic is dark and the metal removed from the blade is bright.  Comparison with the previous image allows identification of the metal particles on the hone surface.
ceramic_hone_scalpel_swarf_03
Higher magnification image of the metal swarf on the surface of the ceramic rod.  The morphology of the metal “chips” is typical of adhesive wear rather than abrasive wear.

It is commonly suggested that honing rods are “only effective for simple and soft steel” blades. In the following example, steeling a high hardness vanadium steel blade (Buck, S30V) is shown to produce a microbevel in same manner as observed in the carbon steel Olfa blade.  In this case, the knife was freehand sharpened at about 30 degrees (inclusive) and used as an every day carry for routine tasks until it was in need of sharpening.  The first two images, below, show that the blade deteriorated by both blunting and chipping and also some slight deflection occurred in one area.  It is noteworthy that the deflection occurs at a much larger length scale and independent of the blunting.

S30V_dull_07
Cross-section view of the dull S30V steel knife displays mushrooming of the apex.
S30V_dull_02
Edge view image of the dull S30V knife apex displays areas that are chipped (top), slightly deflected (middle) and blunted (bottom).

The knife was “steeled” with edge leading strokes in a slicing motion at about 25 degrees  on the ceramic rod.  The image below shows that, once again, steel has been remove to form a microbevel with a relatively keen apex.  Note that this image is taken with the same magnification (scale) as the mushroomed apex image.

S30V_ceramic_steeled_03
Cross-section view of the S30V steel knife apex after steeling with the ceramic rod. A micro-bevel with an included angle of about 45 degrees was created with a relatively keen apex.

Polished (Smooth) Steel Rod

Abrasive wear typically requires ‘sharp’ grit-like features to scratch or cut into the steel, while adhesive wear does not.  Instead, adhesive wear occurs when the local pressure at a relatively smooth “bump” is very high.  Pressure is defined by the applied force divided by the contact area.  As a result, when the contact area is microscopically small, the local pressure will be extremely large.  When steeling a dull knife, at an angle higher than that of the existing bevel, the contact area is microscopically small since contact occurs only along the width of the newly formed micro-bevel.  While this bevel is less than a few microns wide, the local pressure (even with light applied force) will be sufficiently high to enable adhesive wear to occur.

In the example below, the Olfa blade was dulled by cutting into an abrasive stone, and then steeled with a smooth, polished steel rod (Victorinox Honing Steel – round smooth polish).  Once again, a obvious micro-bevel has been formed through metal removal.

olfa_dull_04
Cross-section view SEM image of an Olfa blade dulled by cutting into an abrasive stone.
olfa_dull_smooth_steel_08
Cross-section view SEM image of the dulled Olfa blade following honing on a the polished steel rod. A keen micro-bevel has been formed.
olfa_dull_smooth_steel_07
Cross-section view SEM image of the dulled Olfa blade following honing on a the polished steel rod. A keen micro-bevel has been formed.

….to continued in part 2….

  33 comments for “What Does Steeling Do? Part 1

  1. August 22, 2018 at 5:18 pm

    Cool! I’d never have guessed that steeling removes material. I always thought it just caused plastic deformation on the edge.

    Like

  2. eKretz
    August 22, 2018 at 5:54 pm

    Another interesting entry. One suggestion – use a bit more quantitative description of the pressures you’re using. I never would have expected that a steel actually removed
    much material.

    Like

    • August 22, 2018 at 6:12 pm

      The pressure is enormous, but only because the contact area is small. The applied force, however, is just enough to make contact. I work with these blades loose, holding the end between my thumb and forefinger, so there is really no way to apply much lateral force.

      Liked by 1 person

  3. Dr. Matt
    August 22, 2018 at 6:10 pm

    Very interesting. I was definitely one of the ones who thought the steels just realigned. As I look at these pics, I don’t know if I can really tell a difference between the ribbed steel, ceramic rod and the polished steel. Is there one that makes for a better edge as far as use goes?

    Like

    • August 22, 2018 at 6:21 pm

      That’s an important question, and I plan to discuss that in detail in part 3. The key point is that the nano-scale keenness and structure of the apex primarily determines the cutting efficacy.

      Like

      • Liam
        March 27, 2020 at 8:59 am

        For daily kitchen knife maintenance I’ve personally tried a ribbed steel, a ceramic rod and a leather strop. I found the ribbed steel to be the most agressive and damaging to the knife, producing a very irregular and agressive edge. The leather strop loaded with CrOx had limited effect and was nor really able to restore cutting efficiency (as confirmed by the Dulling on Glass article). In the end the ceramic rod seemed to be a good compromise. I don’t have a smooth polished steel or a diamond-embedded steel to try so I’d be very interested to have some feedback on those for daily knife maintenance before going out and spending 80€ on one. After this article I think I’m more tempted by the smooth polished steel which seems to restore cutting performance and I hope without too much damage to the knife.

        Looking forward to part 3.

        Like

  4. Andr3w
    August 22, 2018 at 7:17 pm

    Awesome stuff as usual. I’ve been waiting for this for months. I knew the imaging would show more than just aligning an edge. I see you focussed on edge leading strokes, any input on the extract same thing but with edge trailing? I’ve always assumed steeling and stropping should be done in the same method, but everyone always says edge leading only for ribbed steels, but in practice I have found 5 or 6 very firm & slow edge trailing strokes, per side, works best in practice for kitchen knives for draw cutting.

    Like

    • August 23, 2018 at 3:50 pm

      I haven’t looked at edge trailing in detail, other than to confirm that it doesn’t straighten a rolled edge, or observably change the micro-bevel. The cleanliness of the apex does seem to be affected, and I’m not surprised that you observe a more aggressive draw cutting performance with edge-trailing strokes.

      Like

      • Liam
        March 27, 2020 at 9:02 am

        Like Andr3w I have also assumed that edge trailing strokes should be used on a steel/honing rod rather than edge leading, especially with a smooth polished steel – mainly under the assumption that it would be more effective at realigning the edge or burnishing the microbevel. In the light of this article which shows that even with a smooth polished steel there is metal removal I would assume that edge trailing strokes would still be preferred as they would produce a keener microbevel in a similar fashion to edge trailing strokes as the final step on a polishing stone.

        You say you’re not surprised at the observation that more aggressive draw cutting performance is achieved with edge-trailing strokes, but why? Do edge trailing strokes produce a foil burr due to burnishing? Does this burr chip off to give an irregular agressive draw cutting edge? Which of edge-trailing or edge-leading produces the cleanest edge / best edge for a kitchen knife ?

        Is there more metal removed with edge-leading and more burnishing with edge-trailing? That’s what I imagine anyway, especially after reading the article on card scrapers.

        Like

  5. Matt
    August 22, 2018 at 9:21 pm

    How many strokes did you take on each side of the steel before re photographing the edge?

    Like

    • August 23, 2018 at 3:46 pm

      Generally 10. I will expand on this in a later part of the series.

      Like

  6. lars tougaard
    August 23, 2018 at 9:08 am

    congratulation scienceofsharp. Again weldocumnentated news!

    Den tor. 23. aug. 2018 kl. 00.03 skrev scienceofsharp :

    > scienceofsharp posted: “Even the name is confusing. Knife steel. > Butcher’s steel. Honing rod. Sharpening steel. Do they remove metal or > just “re-align” the edge? What does “re-align” mean? Are “honing” and > “sharpening” different things? Scanning through opinions found on” >

    Like

  7. mtknivesnet
    August 23, 2018 at 1:22 pm

    Love reading your articles, great images and explanations. Never stop learning 😉

    Like

  8. Rob
    August 23, 2018 at 2:18 pm

    GREAT REPORT AS ALWAYS, I WILL LITE’N UP ON MY STEEL. OFF SUBJECT, I AM GOING TO USE YOUR METHOD FOR S RAZOR SHARPENING , TWO QUESTIONS: 1. ON LINEN PASTE STROP, DO YOU STROP WET OR DRY? HOW OFTEN DO YOU ADD PASTE( FRITZ). 2. ON LEATHER WITH DIAMOND SPRAY, DO YOU STROP WET OR DRY( DRY I THINK, SPRAY, LET DRY, RE SPRAY). BOTH ARE HANGING STROPS. ANY SUGGESTIONS ON HOW TO SET UP BLUE JEAN STROP IN ORDER FOR IT TO HANG? I REMAIN AN AVID SUPPORTER OF YOUR OUTSTANDING WORK. THANK YOU; ROB H

    Like

    • August 23, 2018 at 3:42 pm

      I always let the paste dry on the denim and then work it in with the shank of a screwdriver, but I prefer pastes that have a waxy base like Mother’s Mag polish, not so much the dry ones like Wenol. I probably get one or two thousand stropping laps out of a strip of denim – i’ll replace it when its black. The diamond spray on leather should also dry – these last a very long time, probably tens of thousands of laps.

      The denim can be duct-taped to the bench, or make a loop by gluing with white glue and clamping it until it’s dry. I hang mine from the bottom of the pegboard.

      Like

  9. Dragos
    October 10, 2018 at 2:27 am

    As usual some PhD level stuff in here. I am curious about the hardness of blade materials versus yield strength as a predictor of edge holding ability. While only Hardness is marketed, yield strength seems to me much more important in holding a fine edge as the failure modes are both tension and compression related. The low yield strength of ceramics might be behind the chipping experienced while sharpening and use. Also high carbide blades seem inferior to simple HT alloy steel in their edge holding and their thickness is huge to compensate for their low yield strength. I do not doubt the huge advantage of high hardness ceramics in machining, but there is no sharp edge used there and most tools are designed for compression stress. Do you perhaps have any thoughts on this Hardness vs. Yield?

    Like

    • December 6, 2018 at 1:29 pm

      That’s a complex question. In general, hardness and yield strength are MACRO-scopic properties while “edge holding” is determined by MICRO-scopic properties. Although the macroscopic properties are determined by the microstructure, I’m not convinced that there is a simple correlation. On top of this, it is not obvious that the sharpened edge or near-apex metal has the same microscopic properties as the bulk of the steel. And further, there are several different mechanisms by which the edge is “lost.”

      Like

  10. Andrew Le
    March 4, 2019 at 9:11 pm

    Is part two coming out soon?

    Like

    • March 5, 2019 at 3:31 pm

      There hasn’t been enough interest to motivate me to continue with this.

      Like

      • Andr3w
        March 5, 2019 at 5:07 pm

        Noooo! I get excited every time I get any notification about any comment or post on this blog.

        Like

      • Liam
        March 12, 2019 at 11:03 am

        I too check back regularly looking for comments and I look forward to reading new articles. I am more interested in kitchen and utility knives than razors so I am particularly looking forward to more articles on steeling, knife sharpening and maintenance. I also hope you will do a comparison between different pull through knife sharpeners (parallel to the edge rather than edge leading or edge trailing).

        Liked by 1 person

      • Eddie
        April 14, 2019 at 7:50 am

        I’m sorry to hear that. I just discovered your site and am reading through it with keen interest (ha!). I would love to read more of what you have learned about steel usage, and I hope someday you find the motivation it takes.

        Best regards,

        Like

  11. alex cahoj
    March 21, 2019 at 9:15 am

    Very good article. I would be interesting to see images after “honing” on glass!

    Like

  12. caponsky
    June 27, 2019 at 2:38 am

    Finally a valid source on the topic, thank you!

    Like

  13. arthur brogard
    January 26, 2020 at 3:11 am

    This is beautiful, thanks very much. I just had a discussion on the topic which ended very badly when I wouldn’t accept that steeling just ‘straightens’ the blade. Got me googling. Brought me here. Vindicated me. Lovely.

    But I don’t quite understand the photos. What’s the big black ‘V’ in most of them? It looks like you’ve cut down into the blade. Or is it a photoshopped thing you’ve put on the pics to clearly show the profile?

    Like

    • January 26, 2020 at 8:17 am

      The blades have been cut perpendicular to the edge (cross-sectioned) with a focused ion beam. This is really the only way to visualize the profile.

      It amazes me that people can be so certain of ideas for which they have no evidence and how intransigent they can be when faced with irrefutable evidence that they are wrong.

      Like

      • arthur brogard
        January 26, 2020 at 12:18 pm

        ah, thank you. It looked like a cut but I couldn’t see what might make such a cut… I’m not familiar with this sophisticated apparatus you’re using here. Very wonderful stuff :).

        Yes, people literally seem to love their ideas sometimes as though they were real things. In this particular case of mine I think I see a desire to claim status through ‘higher knowledge’ and thus bolster a very shaky and uncertain self esteem.

        Not an unknown mechanism. Why they wouldn’t choose the iron walls of logic and reason and experimental proof as a bolster I don’t know… wouldn’t it be good if we could subject such phenomena to electronic microscopy etc…

        Like

  14. Mike Shults
    March 24, 2020 at 12:51 am

    What would a smooth tungsten carbide blank do to a knife edge?

    Like

  15. Liam
    March 27, 2020 at 8:56 am

    On the subject of edge damage you show pictures of three types of edge damage. Deformation (folding or mushrooming), I presume would be representative of cutting food on a ceramic plate or glass board.
    Abrasion might be representative of repeatedly cutting cardboard, or maybe cutting on a wooden board.
    Chipping might happen hitting a bone in meat.
    The chipped edge of your Buck S30V pocket knife is finally the most interesting because it shows that in daily use a knife suffers all sorts of damage and not just one.
    An interesting development would be to compare the type of edge damage of cutting on different surfaces (edge grain wood / bamboo / plastic / rubber / glass).

    Like

  16. Liam
    March 27, 2020 at 9:04 am

    In this article you demonstrate the effects of a ribbed steel, smooth polished steel, and a ceramic rod, but what about the effects of the tungsten carbide sharpener, the Spyderco Sharpmaker and a diamond-embedded rod that you eluded to in the beginning of the article ?

    Like

  17. Liam
    March 27, 2020 at 9:06 am

    You show three ways the Buck S30V knife has deteriorated through use, and you note that the chipping happens on a very different length scale to the edge deflection and mushrooming (very evident in one of the images). After “steeling” on the ceramic rod we can see that a new microbevel is formed at the scale of the mushroomed edge, but what happens at the chipped portion of the blade? Was the chipped section improved significantly?

    Like

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