Edges and Steels

R

Roman Landes

Joined
Aug 31, 1999
Messages
54
Dear Colleagues,

liked

http://www.schmiedecafe.com/forum/attachment.php?attachmentid=83

you find a PDF download in english as one of my latest works, in steel & knife research ongoing in Germany.
To introduce myself I am knife maker and damascus smith since 1987 in Germany. My profession is graduated engineer in Automotive engineering and Material Science. Meber of the German Knifmakers Guild sinc 1993.

I am also author for the German Book, Messerklingen & Stahl (M&S) Technologische Betrachtung von Messerschneiden (Knife blades and Steel, A technological survey on knife edges © 2002 Wieland Verlag, Bruckmühl, Germany) witch has successfully established a high quality discussion base on scientific research towards knifes and steel. The base of the Book was developed in the early 90’s when I was in my studies.

With this download, you get a little goodie, extracted from the upcoming new book Messerklingen und Stahl, Praxishandbuch der Stähle (Knife blades and Steel; The Practical Handbook of Steels © 2005 Wieland Verlag, Bruckmühl Germany)

What is the download about?
The download shows the so-called “model of the cutting edge” taken from (M&S©2002).
The actual book will show around 50 commonly known tool steels/ -alloys used for knife applications (e.G. ATS 34, 52100, RWL 34, L6, Vascowar, M4,…) an the way to treat them according to this application.

Furthermore, one will see the abilities of the steel used supporting qualities essential for knife application (e.g. edge holding, wear resistance, sharpen ability, cutting ability, cutting edge stability, corrosion resistance,…), SWOT- Analysis…

The model of the edge provided here, shows 5 selected reference alloys commonly known in the worldwide knife society.
· 1.4125 (440C) Reference for traditional stainless steels
· CPM S90V Reference for modern stainless PM-steels
· Talonite Reference for Chrome Cobalt Alloys
· 1.2510 (O1) Reference for hypereutectic tool steels
· 1.2379 (D2) Reference for 12%-Chrome Cutting Steels

What Do you see?
What you see is the 1000x magnification (means all at the same scale) of the inner structure (microstructure) of this alloys, shown as micrographic pictures, in heat treated condition (Austenizing, Quench, Cryo, Temper in multiple cycles; except Talonite) Etching: Beraha 1.

The white spots, are the so-calles Carbides responsible for the wear resistance in a alloy of this kind (The Teeth), surrounded by the Matrix (Meat) (Martensit, except Talonite)

The sheet is designed to get folded on the edges marked. What you get when you do so, is the model of the edge 1000x magnification in 3D. By using the scale of the angel (Adjust in back light with single print) you can adjust every edge geometry between 15° and 90° edge angle.

This means, having the model in 3D in front of you and assuming there is a local limited load applied from a side force towards the edge (occurs constantly in the normal use of a knife), this force will deflect the edge and in dependence of the load, and the steel can take, the edge will draw back in line or chip locally (wear and loose edge).

The carbides will play a major role in the behavior of the steel in the edge
Since they are very hard and brittle, in a fine cutting edge, carbides are the first point to start with chipping, especially when the are to many in relation to the surrounding (meat) or the carbides are so large, e.g. when they will fit nicely into the full range of sharp and dull limits1)

Note, the large carbides of the alloys shown, will by no means get any significant change in size, during the complete heat treatment cycle (except 01, if hardened at to high temperatures, the carbides will dissolve completely and a mess of retained austenite and coarse brittle Martensit-grain will be there).

What you can do with it now?

Taking into account, that a sharp edge1) is around 1µm on the tip and a dull one1) is around 10µm in width, if a critical load to the edge is applied (wear of the edge), the different alloys behave different at different angles adjusted.

Print the download (use A4 for the print-format), fold at the 3 lines marked and start adjusting the angle.

I am sure this will help, to explain something…

...and hopefully start discussion …

Best regards Roman
 
So, basically it shows the optimum angle that an edge can be had for each steel based on the characteristics and carbides and the way they are distributed in each different steel when hardened??.

If I read the chart right then a 30degree angle on a D2 would be getting too high or at the least pushing it anyway because of the carbide distribution and content thus making it too brittle or prone to chipping for that angle or from the looks of it 440C maybe more so as well. Yet in S90V or 01 it would be ok for this steep of an angle because the carbide content and distribution would still be surrounded by plenty of 'filler' that limits the carbide chipping problem seenin the other two? Is that what I'm seeing?

If not I'm totally confused but I think I got it unless I've missed something. The instructions are a bit vaque and being that my German is rather weak these days a bit hard to translate.

Someone else want to comment on this?
 
Yes STR,

This is correct, therfore ist is not easy for the D2 e.g. to hold an edge that is very fine e.g. used for high performance pressure cuts with a fine angle between 20-30°
One is forced to apply a steeper angel 40°+ to keep the carbides in place.
and futhermore a blade has to be made much thiker than a blade made out of e.g. 01, because D2, contains a enormus amount of very brittle and large carbides wich result in a higher brittleness and therfore in a lower tensile strength.
Unfortunately a steeper angel and a thiker blade result in essentially lower cuttningability.
The only thing that you can do now is to employ a coarse cuttingedge with the steep angle where a slicecut can be executed...

Concerning the S90V the carbides are homogenious in size and compared to D2 smaller. But not as small as a steel like 01.
One of the problems that come with this type of steel S90V is the enormus amount of carbides compared to the sourrounding Matrix.

There is only a very limited amonunt of Matrix that can take an elastic deflection, so although there is an advantage by PM steel the simple run for high wear resistance has also some tricky sides to deal with.

Therefore this fact will also limit the minimum angle that can be employed. Whole sections of the edge can easily chip off, if you want to go for a steep angle an high cutting ability.

The same for Talonite. The matrix sourrounding is much weaker than the martensitic matrix build up by steel. So a load on a fine cuttingedge 20-30° would easily lead to a remaining deflection and large chips.

RGDS Roman
 
Just seeing the shear size of the carbides in the D2 makeup is astounding proof of the tendency it can have toward brittleness. D2 is one of my favorite cutlery steels but I have been well aware that it cannot take lateral stresses as good as other steels for some time and that the edge geometry and proper thinness/thickness of the steel is very important in whether making a blade made from this steel will work or fail as a cutting tool. Some here and on other forums differ with me on this and even argue with me for stating what I saw as obvious but seeing these 1000x photos not only confirms what I've been saying but shows why.

Thanks.
 
Yes. We had a bit of a problem finding a lamp of sufficient light strength to allow the visual but once that was found we did manage to see what you refer to.

I have made several D2 fixed blades myself. Three of these I had heat treated for me by Bob Dozier. One of those lost a point in a breast plate while field dressing game the following deer season. This was one I made for a relative. When I got it back to sharpen it I fixed the point and it has given him no more trouble. Most all of Bobs work is beyond reproach. His heat treatments are right on and very consistant. He is one of perhaps two people out there that really know how to properly use and heat treat D2 in my opinion. The problem with the point break on this knife I made was more to do with my thinness of the grind for the steel used than anything Bob did or didn't do. Lesson learned.

The D2 ones I had heat treated elsewhere that I made didn't fair as well as Bob's did at all. I won't say where they were heat treated because I don't want to stir that up again. But the bottom line is they fractured during use with some of them and others just didn't hold up well at all to minor lateral stresses. Very brittle stuff that I ended up eating three sales on.
 
Well things happen..

heattreatment ist one essential issue to deal with I havent seen many doing it siutable for a blade. but when the basic choiche of the stell according to the purpose is not siutable the best heattreatement is woth nothing

Did you make Knives out of the other steels in the chart?

what ar your experiances there?
 
Thanks for posting the picture, Cliff. Spectacular shots.

I cannot access the article either. Nor any part of the referenced web site. Is there any possibility you could post the article on your web site? I know I can get there.
Thanks.
 
roman have to got any info on uddeholm hss like the vanadis series? what do you think of them? ive been thinking about getting some vanadis4 for an allround utilityknife since its promoted as the toughest of them (the vanadis series). anyway i like your site, very much good info even though my german is pretty bad, however some of the pdfs are in english :D
 
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