Carbon Steel Blades and Grain Size

Your test has limitations. All are cutting a single soft item. If you try to cut soft items and hard items. You will find high hardness of the edge, it will easily collapse. If it is cutting leather, the hardness of a great impact, if cutting relatively hard items (such as ebony, PVC, hard plastic), high hardness and no advantage.
 
Fascinating. Insights from people like you with real technical expertise are invaluable. From real world use, I find that my high carbon blades in 1070 and 52100 take a finer edge than current 'super steels', although CTS-XHP seems very fine-grained. I appreciate them all for their varying qualities though -- corrosion resistance and edge-holding is superior in S30V/S35Vn, and D2 is a kissing cousin to those.
 
Wucai Liumang said:
Your test has limitations. All are cutting a single soft item. If you try to cut soft items and hard items. You will find high hardness of the edge, it will easily collapse. If it is cutting leather, the hardness of a great impact, if cutting relatively hard items (such as ebony, PVC, hard plastic), high hardness and no advantage.
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I had a chance to test one of Juha's blades at 63 Rc. My standard test for edge stability [resistance to chipping (toughness) and rolling/denting (strength)] is to chop a piece of bailing wire on a large block of Doug fir. Few edges can pass this test without serious damage. Even the best show some damage.

Juha's blade suffered almost no damage. The edge was dulled and maybe dented a bit, but that's it. The edge clearly showed a lot of edge stability, even on a test that knives are not designed for -- this on a puukko that cost less than $100.
 
Twindog said:
I had a chance to test one of Juha's blades at 63 Rc. My standard test for edge stability [resistance to chipping (toughness) and rolling/denting (strength)] is to chop a piece of bailing wire on a large block of Doug fir. Few edges can pass this test without serious damage. Even the best show some damage.

Juha's blade suffered almost no damage. The edge was dulled and maybe dented a bit, but that's it. The edge clearly showed a lot of edge stability, even on a test that knives are not designed for -- this on a puukko that cost less than $100.
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In real life, special tools (leather cutting knives, etc.) will cut a single thing. Many people in the use of time, will cut the soft things, hard things, slightly hard to hack things. High hardness of the edge will soon damage (prerequisite: the same kind of steel and the same heat treatment program). Different tools require different hardness, such as 20cm knife and 30cm knife is different needs. When I test the knife myself, it will cut PVC, tissue paper, belt, copper, paper shell, rubber, wood, and other things.
 
Wucai Liumang said:
In real life, special tools (leather cutting knives, etc.) will cut a single thing. Many people in the use of time, will cut the soft things, hard things, slightly hard to hack things. High hardness of the edge will soon damage (prerequisite: the same kind of steel and the same heat treatment program). Different tools require different hardness, such as 20cm knife and 30cm knife is different needs. When I test the knife myself, it will cut PVC, tissue paper, belt, copper, paper shell, rubber, wood, and other things.
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I agree with you that many different cutting tests with different material should be made. People are too much focused on only rope cutting and Catra laboratory tests. My puukko blades has cutting edge 63 HRC and spine 50 HRC. The soft spine won't brake. The hard edge has very good cutting ability and edge chipping does not occur. I occasionally test my blades with hammer. Then I totally destroy a blade and study the fractures. If I can find plastic deformation before fracture, the blade has sufficient toughness. Because my blades have extremely small grain size, the edge has sufficient toughness at hardness level of 63 HRC.



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I completely agree with Juha ! very fine grain size with tempered martensite makes high hrc much tougher ... the trick is to keep the very fine grain size through the hardening process ! thank you Juha for telling us your process and sharing your findings.
 
Juha Perttula said:
I agree with you that many different cutting tests with different material should be made. People are too much focused on only rope cutting and Catra laboratory tests. My puukko blades has cutting edge 63 HRC and spine 50 HRC. The soft spine won't brake. The hard edge has very good cutting ability and edge chipping does not occur. I occasionally test my blades with hammer. Then I totally destroy a blade and study the fractures. If I can find plastic deformation before fracture, the blade has sufficient toughness. Because my blades have extremely small grain size, the edge has sufficient toughness at hardness level of 63 HRC.



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Hello, I am very much agree with your tiny size grain view. I also do this, but I will do more complicated. However, very small size of the grain, has been "occupied" a very high dislocation, so the shape, toughness, in some cases is down, and the strength is increased.
 
fine grain=maximum toughness has been written about since the 1930's, and the way to obtain it is really basic: choose a steel with a small amount of vanadium(0.2% or so) which will help reduce grain growth, harden at lowest temperature possible(never exceed 1500F for high carbon steel) in shortest time possible(for me O1 or O7 into preheated 800C furnace, 3/32" material max time of 8 minutes) continuous quench to 32F or less, temper at 350 to 375F. this is a good starting point, multiple quenches or normalization may improve on this a little.
 
other elements also help reduce grain growth: like Niobium – Nb and Titanium :)
 
Interesting thread, I always enjoy reading what metallurgists have to say on this subject.
 
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