Can someone explain to me about "strength" in a steel, and why it is considered inversely proportional to a steel's "toughness"? I read Joe Talmadge's post: strength- ability to take a load without permanently deforming." But I'm not clear what that means. Thank you.
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question on knife steel faqs
- Thread starter R33
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Strength is the ability to resist deformation and breakage. In terms of knives, it usually applies to how difficult a knife is to bend and how far it can be bent before retaining some permanent bend when released. My definition of toughness (there are many, depending on who you ask) is the ability to withstand impacts without cracking or breaking, such as in chopping and such. In general softer steels have less strength, but wont crack if you're chopping weeds and hit a rock by accident. They may bend, dent or ripple however. Most steels reach maximum toughness at a strenth level that is too soft for a good knife. Within the strength range for knives, some high toughnesses can be found, but its a balancing act, and they are generally thought of as inversly related.
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Just note that when people say "strength is inversely related to toughness", they precede it with "in general". In fact, many steels have a curve (or even a curve with multiple humps), where strength and toughness rise together, until such time as the curve peaks and toughness starts dropping off if strength continues to rise. But, as me2 points out, when we hit good cutlery hardnesses, we often see the peak and what's beyond.
Thanks. I am surprised I was able to say it so easily, since I basically just saw the graphs with the small peaks at very high hardnesses a couple of months ago. Thanks Cliff and Alvin. A good example of this is I'm making a knife from a file, at full hardness. I just cut a notch in it to profile the blade and tried to break it w/ a hammer and couldnt do it after cutting 1/2 way through. I had to nearly cut it completely through before I could break the piece off. The grain is very fine along the break.