Knife steel statistics

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pgugger
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Knife steel statistics

Post by pgugger »

Like many others, I often find myself trying to learn the differences and similarities between knife steels. There are some great resources for all the details (e.g., Zknives), but there are so many steels to sort through and so many elements that can vary, sometimes very slightly. That got me thinking about making one or two graphics to summarize the common knife steels. Here I present a first attempt using statistical method called principal components analysis.

The main plot below shows the various common kitchen knife steels as black labels positioned along an x-axis (PC1) and y-axis (PC2). Steels that are close to each other on the plot are more similar in elemental composition, and those that are far apart are more different. The boxes to the right are my attempt to zoom in on some cluttered spots where the steels are so similar in this analysis that their labels overlap on the plot. The red labels represent the elements and the direction of the arrow points in the direction of increasing amounts of that element. So the long red arrow pointing left to Cr (chromium) means that steels towards the left side of the graph have high Cr content - in other words, they are stainless. In fact, as you move from left to right on the x-axis, you basically go from stainless to semi-stainless to carbon steel. Similarly, V, Mo, Co and W increase as you go down (approximately), as shown by their red arrows.
pca.knife.steels.png
I also made a similar plot for only the popular Hitachi carbon steels, since they are so cluttered above. You can see that the Aogami (blue) steels are especially higher in W (tungsten) but also a little in other elements. Aogami Super, Aogami 1 and Shirogami 1 have slightly higher carbon than the others (follow the red arrow for C).
pca.hitachi.carbon.png
I should mention that the above plots treat the more abundant and variable elements such as Cr as more "important" than the less abundant and less variable elements such as C. For example, Cr varies from 0% to 20% of these steels and C only varies from 0.25% to 3%. You might say that is not fair because C (or any given element) is very important and even little changes can matter a lot. So, another way to analyze the steel composition data is to first standardize the data so that each element contributes equally to the outcome regardless of whether or not it is more abundant overall. Here is that plot:
knife.steel.scaled.png
One drawback of this version of the plot is that the two axes shown do not account for as much of the variation in steel types as the first plot. We would need a three-dimensional (or more) plot to really capture all the differences, which is not easy to look at.

Let me know what you all think. I may try to make these nicer if I have more time in the future. There are also probably ways to make an interactive (3D) plot where you can learn the composition by hovering over the points...



Data source: Zknives (I had to impute some missing values to make this work.)
Software: R 'vegan' package
Last edited by pgugger on Sat Jan 25, 2020 4:37 am, edited 1 time in total.

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pd7077
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Re: Knife steel statistics

Post by pd7077 »

The nerd in me totally appreciates this information, but the carnivore in me would like you to redo this using non-vegan software.

In all seriousness, nice work man!
--- Steve

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lsboogy
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Re: Knife steel statistics

Post by lsboogy »

I guess I kind of have the same inner nerd in me (physicist), but what I have been learning using knives and at work leads more into anneal and quench stuff than just composition. Grain size in metals is dictated by how hot and how long it is kept there, and what I have been learning using a SEM at work is some smiths are able to get smaller grain sizes than others with the same material - too long in heat treat and grain boundaries grow, too quick in quench makes the martensite too abundant etc.

But this is very good information nonetheless, and shows me why I really like AS blades in a kitchen setting, especially in my "wanna be a chef job" - I work for a friend who allows me to learn in a pro kitchen what I will be facing in retirement (gonna run a shelter kitchen). but just to keep things in perspective, I have a Carter Hopkins 52100 blade that takes a great edge and holds it - better edge than most AS steel blades I own, and holds it almost as long or longer than most of them too. The smith is probably a bigger variable than the steel. His knives are very fine grained - well finished and just great performers

pgugger
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Re: Knife steel statistics

Post by pgugger »

Haha, thanks! I thought there might be a few nerds on here.

Good point to emphasize that these plots only capture variation in percent composition of elements, and that a number of important (perhaps more important) factors are not accounted for: PM versus non-PM steel, how the smith treats the steel. I could easily color the PM steels differently on the plots in the next iteration, but unfortunately the different treatments would be be difficult/impossible to account for. At least I hope the plots give a sense of which steels might be similar all else equal (i.e., same treatment by same smith), or help someone see how similar an unfamiliar steel is to one they are already familiar with. I'll be curious to hear if this rings true in the experiences of any smiths or other knife users on here.

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lsboogy
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Re: Knife steel statistics

Post by lsboogy »

What needs to be remembered is that all of these steels are very easy to change - wrongly if you don't know what you are doing. I would guess most of the smiths have secret sauce to make their steels perform well. But the basics of annealing show that higher temps or longer times show increased grain boundary size (bigger grains mean steel will not get as sharp), and Martensite/Austentite/Cementite mixes are what really determines the final hardness of a blade edge. The more I learn about heat treating (we have vacuum, nitrogen and CO atmosphere furnaces at work) the less I seem to know and the more I am amazed at smiths. My 52100 CHII blade has some of the finest grain structure I have seen, as does my HD2 240. A Matsubara B2 and a couple of AS blades are close, and some W1 steel is up there as well.
Hardness, toughness, grain size are all based on heat treat and temper. A base steel can turn out a wonderful blade or a beater - all depends on the smith

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Re: Knife steel statistics

Post by PaulME »

Isbology, how have you evaluated grain size? My past experience with this was sectioning the material potting it, then running it through a series of polishing steps before looking under the microscope. Sectioning a knife would mean destroying it - interesting but not somthing I’m going to do.

As a Mechanical engineer I find it interesting but also a bit of I don’t care as I have yet to acquire a J knife that I felt had a problem with the steel.
Paul

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lsboogy
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Re: Knife steel statistics

Post by lsboogy »

Hi Paul -

I find that grain size in knife steels is mostly in the 2-6um range, but a Buck knife is going to be 20um or bigger. Most German steels are in the 7-15um range(~0.0003" - easy to pick up optically with just a bench microscope) and a good smith can get some white steels into the 500nm or so grain size (my 52100 blade is mostly about 600nm, my Kono HD2 is 800nm). I have seen some tool steels that show 300nm and smaller grain size, but they are very expensive tools used for shaping aero stuff in controlled temp and atmosphere cutting on 6-8 axis machines (Mazaks mostly).
Even with a 20x loupe (just got 3 more from Mark - give them to young engineers at work) you can make out grain size in many J knives. But grain size is just one part - I find that I can sharpen my knives to the point where they cut stuff very well (I like newsprint because I can audibly gauge the sharpness - quiet equals sharp). The knives I use need to get and hold an edge, but also feel right on product. Why many of the real chefs up here go through so many knives searching for what does what well. I'm learning, but I watch folk with knife skills that put mine to pasture, but my skills are far better than they were a couple years ago

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