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Edge Rolling in High Vanadium Knives
#1
Edge Rolling in High Vanadium Knives Sharpened with
Aluminium Oxide versus CBN/Diamond

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PLAN

The plan is to use the SET method (Structural Edge Testing) to test edge resistance to rolling in high vanadium knives with vanadium content ranging from 1% to 10%, sharpened with Aluminium Oxide versus Cubic Boron Nitride (CBN) & diamond abrasives.
 
The goal is to obtain experimental data for the ongoing discussion among knife enthusiasts whether sharpening high vanadium knives with abrasives other than CBN and diamond enhances their edge propensity to rolling.
There is no smoke without fire, and the more people own high-end knives, the more we hear about this. The most plausible explanation is that the common abrasives weaken steel matrix around the vanadium carbides – being too soft for the vanadium carbides they only abrade the steel around the vanadium carbides rather than polish them.
 
A priori expectation is that we will see no significant difference in edge rolling before some threshold content of vanadium. Obvious practical application would be to allow the common abrasives for sharpening steels with lower than that vanadium content, and use exclusively CBN and diamond for higher.
 
Vanadium carbides are not the only high wear resistant carbides - niobium, cobalt, molybdenum and wolfram (tungsten) carbides also are, and should respond similarly to abrasives.

SET METHOD

Structural Edge Tester (SET) is a method and device developed by Edge On Up for testing edge stability. In a nutshell, the edge is subjected to controlled rolling, the extent of which is quantified.
Edge sharpness tester used in the study: PT50A Industrial.

[Image: SET_tester.JPG]

Impact cycle  explained
The impact roller is a linear bearing slant at 10° to the horizontal base or in other words at 80° to the plane of the blade clamped vertically.
Standard impact assembly weight is 150 grams.

[Image: SET_testing10.JPG]
[Image: SET_Cycle.png]
The impact roller is lowered at "A", then moved (rolled) over to "B" and then back to "A".
A-B-A is one cycle. 

See our video on YouTube https://youtu.be/EdGOSWjrM0E

Our standard SET testing procedure is to measure edge sharpness after every cycle for the first 5 cycles (Phase I), then after every 5 cycles to 50 cycles (Phase II), and then (i.e. from the 50th to 100th cycles) after every 10 cycles (Phase III).
Where by the 100th cycle the edge hasn’t blunted to 500 BESS, we continue rolling, measuring sharpness every 20 cycles till reach 500 BESS.

Sharpness of the majority of knives (apart from CPM “supersteels”) nears or exceeds 500 BESS, i.e is rendered blunt, by the 100th impact cycle, allowing us to watch the full life cycle of the edge within one 11-minute test.

The testing procedure yields additional information about events happening in the edge through the three distinctive phases:

·        Phase I “Elastic deformation” from the 1st to the 5th impact cycle, when sharpness is measured after every cycle – considering that interval between subsequent impact cycles is about 30 sec, this break in impact allows the edge to partially recover from rolling. This phase takes about 2.5 min.

·        Phase II “Elasto-Plastic transition” from the 6th to 50th impact cycle, where the edge gets 5 impact cycles between sharpness measurements – edge is challenged for resistance to plastic deformation. The elastic deformation transits to plastic here. Weaker steels simply crash in this phase. This phase takes 5 min.

·        Phase III “Plastic deformation” from the 51st to 100th impact cycle, where the edge is continuously rolled 10 times before each next sharpness measurement, testing the edge stability to permanent rolling. This phase takes about 3.5 min.

Key indicators:
§ Overall average sharpness over 100 impact cycles;
§ Average sharpness in the Phase I (elastic deformation) - calculated as an average of sharpness scores in the first 5 impact cycles;
§ Sharpness by the end of the Phase II (elasto-plastic transition) – calculated as an average of 3 sharpness scores: after 40, 45 and 50 impact cycles;
§ Number of impact cycles to turn the edge blunt at 500 BESS (resistance to permanent rolling).

Overall, each SET test takes 11 minutes to estimate life cycle of the edge.

SELECTION OF KNIVES
 
For the purpose of a comparable selection, we selected steels with minimum content of other than Vanadium alloys. The table below illustrates how we picked steels from the knives in our disposal – those in bold were selected for this research.

[Image: selection2.png]

As a CONTROL TEST, to see if the sharpening abrasive as such imparts any difference, we sharpened in the same way a vanadium-free but high-carbon knife in SR-101 steel (Busse Swamp Rat knife), its chemical composition follows.
[Image: SR101.JPG]
[Image: control_comp.png]

SHARPENING METHOD
We know from our previous SET tests that the results depend on the edge angle and initial sharpness.

All knives were sharpened and honed the same way on Tormek T-7 and T-8 machines at the same edge angle of 12 degrees per side (24° included) and to the same sharpness within 80-100 BESS.
Sharpness of 100 BESS is midway between safety razors and utility blades; for those new to BESS - the lower the score, the sharper is the edge, e.g. a safety DE razor scores 50 BESS, and utility blades 150-200 BESS.

Edge angle was ground with the help of our computer software for Tormek and verified with a CATRA laser protractor.

[Image: applet1.png]
[Image: laser_12dps.JPG]

The first sharpening was made with Tormek stock 250 mm aluminium oxide wheels, and honing on the Tormek leather wheel with the Tormek honing paste, known to be chiefly of aluminium oxide particles averaging 3 microns in size.
Edge bevel was ground on a freshly trued SG-250 wheel (#220), and edge set on a dedicated SG-250 wheel graded to #1000 with a diamond plate.

[Image: T7.JPG]
[Image: Grading1000.JPG]
[Image: Grading.JPG]
grading to grit #1000

Honing angle was controlled with our FVB for Tormek-7 and computer software.
First round of SET testing was run on these knives.

[Image: applet2.png]
[Image: FVB.JPG]

The same knives were then re-sharpened on Tormek-compatible 254 mm CBN wheels, and honed on a dedicated Tormek leather wheel impregnated with 3-micron diamonds.
Edge bevel was ground on a CBN wheel #400, and edge set on a CBN wheel #1000.
For honing on Tormek with diamonds we normally use a rock-hard felt wheel, but this time used the leather wheel to hone the same way as in the first sharpening.
Second round of SET testing was then run.

[Image: T8.JPG]


To match sharpening done with aluminium oxide and CBN/diamond, in each sharpening we set the edge with 2 passes on the #1000 aluminium oxide or CBN wheel, and were giving the edge the same amount of honing of 2-3 slow passes across the leather wheel, alternating sides.

With this setup, in sense of achievable sharpness I didn’t find aluminium oxide much inferior to CBN or diamonds in sharpening high vanadium steels, though definitely slower in bevelling – having ground the edge angle on a coarse SG wheel, we set the edge with two passes alternating sides on the SG wheel graded to the grit #1000, and honed/deburred with 2-3 slow passes on the leather wheel with the Tormek honing paste – in all cases the sharpness we got was within 80-100 BESS.
It was faster to bevel the edge angle on a coarse CBN wheel, but by setting the edge with the same two passes on the grit #1000 CBN wheel and honing with 2-3 passes on the leather wheel with 3- micron diamonds we were getting the same sharpness.

DATA

All knives are sharpened at an edge angle of 12 dps, to initial sharpness near 100 BESS.

Link to raw data >>

[Image: Key_Indicators1.png]

3% VANADIUM PHENOMEN

“Curiouser and curiouser!” as said Alice in Wonderland.

Numbers tell us that edge rolling does depend on whether we sharpen with aluminium oxide or CBN/diamond, and CBN/diamond gives better lasting sharpness than aluminium oxide, but correlation with the vanadium content is not linear – instead, there is a dramatic rolling in edges with vanadium content of 3% sharpened with aluminium oxide.

DATA INTERPRETATION AND CONCLUSION

Control 0% vanadium (SR-101) – the control test shows some improvement in edge resistance to rolling when CBN/diamond abrasives are used, which is interesting in itself, however the main thing it gives us for the purpose of this research is the baseline difference between the CBN/diamond and aluminium oxide abrasives, so that any numbers less-than-or-equal-to are not related to alloys composition.

Vanadium 1% (D2) - CBN/diamond abrasives moderately improve sharpness over aluminium oxide, with no difference in the initial period.

Vanadium 2% (PGK) - CBN/diamond abrasives have little to no advantage over aluminium oxide, seen only in somewhat prolonged edge life; initially the edge sharpened on aluminium oxide shows even better elasticity and sharpness (Phase I).

Vanadium 3% (Elmax) - CBN/diamond abrasives show high advantage over aluminium oxide, the edge stays sharp by 4 times longer. In saying so we are talking of relative difference, and positive effect of the CBN/diamond as such is not that much different from its neighbours of 2% and 4% vanadium (as seen by the absolute sharpness scores) – it is the aluminium oxide worsened edge retention that makes the numbers so high.

Vanadium 4% (CPM20CV or M390) - CBN/diamond abrasives have moderate advantage over aluminium oxide, clearly noticeable both in the initial period and prolonged life of the edge.

Vanadium 9.8% (Vanadis 10) - CBN/diamond abrasives have moderate to high advantage over aluminium oxide, the working edge lasts 1.5 times longer.

3% vanadium is the threshold content, where sharpening with CBN/diamond becomes preferred over common abrasives.
http://knifeGrinders.com.au
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Messages In This Thread
Edge Rolling in High Vanadium Knives - by KnifeGrinders - 05-17-2018, 06:14 AM
RE: Edge Rolling in High Vanadium Knives - by EOU - 05-17-2018, 04:05 PM
RE: Edge Rolling in High Vanadium Knives - by Jan - 05-18-2018, 02:37 PM
RE: Edge Rolling in High Vanadium Knives - by EOU - 03-15-2019, 10:00 AM
RE: Edge Rolling in High Vanadium Knives - by EOU - 03-18-2019, 12:13 PM
RE: Edge Rolling in High Vanadium Knives - by Jan - 03-18-2019, 02:44 PM
RE: Edge Rolling in High Vanadium Knives - by EOU - 03-19-2019, 09:21 AM
RE: Edge Rolling in High Vanadium Knives - by Jan - 03-19-2019, 02:26 PM
RE: Edge Rolling in High Vanadium Knives - by Jan - 03-22-2019, 01:46 AM

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