full hard?

hardheart

hardheart

Joined
Sep 19, 2001
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I was wondering if there's any way to get a full hard blade that won't snap like a twig. From what I've gathered, higher hardness does not in and of itself mean a propensity to shatter, and in fact makes for a stronger blade that will not fail as easily as lower hardness would allow a blade to bend until useless. But, the steel must be tempered after the quench to take care of the stresses in the martensite from the transformation. Does marquenching allow the steel to be left at a higher hardness without the internal stresses?
 
Hardness only tells you part of the story.It's a convenient measure but doesn't tell us many things.Each steel is different and they have their own optimum hardness ranges .You have to balance type of use , type of steel, and hardness range. Marquenching minimizes warping and cracking ,it's not there to provide higher hardness.
 
Thus the "differential" HT. Fairly ez to do with "simple carbon" steels (10xx, O1 W1, W2), and not so easy with air-hardening variety.

The idea is to have the spine softer than the cutting edge . Having the spine "full-hard" serves no purpose, it is the cutting edge that does, well ;) ,
the cutting.

The exam that one has to pass to become accepted to knifemakers
guild, is to have a knife pass BOTH the cutting test and 90 degree blade bend.
 
Temper it GOOD. Just yesterday I had a fully hardened blade straight out of the quench and tried to nudge a bend out. BAD IDEA BEFORE TEMPER - SNAP

Anyway, I had to get up EARLY to get that 9" bladed camp knife reground and ready for heat treat this morning. Good feeling to have that work done again by 8 in the morning :)

Just temper it well and dont shortcut that part. You shouldnt be crobaring a knife anyways in the real world use.
 
rashid11 said:
Thus the "differential" HT. Fairly ez to do with "simple carbon" steels (10xx, O1 W1, W2), and not so easy with air-hardening variety.

The idea is to have the spine softer than the cutting edge . Having the spine "full-hard" serves no purpose, it is the cutting edge that does, well ;) ,
the cutting.

The exam that one has to pass to become accepted to knifemakers
guild, is to have a knife pass BOTH the cutting test and 90 degree blade bend.
Click to expand...

I've seen pictures of very old knives where they were used so much that the cutting edge moved back further and further until it was very close to the spine.

I bring this up because I think it makes two very good points. One, fully hardening did not cause these knives to fail prematurely. I.e., it never snapped in two.

Second, if it had been differentially hardened, it would have become useless as a cutting tool as soon as the edge moved back to where the hard part ended.
 
mete said:
Hardness only tells you part of the story.It's a convenient measure but doesn't tell us many things.Each steel is different and they have their own optimum hardness ranges .You have to balance type of use , type of steel, and hardness range. Marquenching minimizes warping and cracking ,it's not there to provide higher hardness.
Click to expand...
Is it something universal for the martensite? Different steels naturally should have different properties, otherwise industry wouldn't have created them, but AFAIK, none of them are used full hard. With the varying actual measure of full hardness, carbide sizes, alloying contents and such, I'm just wanting to understand the temper need a bit more, I guess. I know that it's done for good reason, as blgoode mentioned, but if those stresses theoretically weren't there after the quench (magical stress free martensite without a temper), then would the highest practical hardness be full hard? It's a weird question, I'm not sure if I'm presenting it right. ZDP-189 tempered to 67 Rc is being used in William Henrys, a lot of other steels don't hit that number full hard, some just barely do-but is the martensite alone of different steels all about the same when tempered appropriately and comparably?
 
Can the average person sharpen a knife that test at 67rc? Is the knife edge just extreamly hard or is it also tough? Is it ductile?
Developing a good usable blade is a matter of tradeoffs. Hardness being only one of the considerations.

jm02cts worth, Fred
 
Part of the stresses are what makes martensite hard !! We want some stresses but not too many .When it comes to blades always temper immediately after quench.Marquenching does in fact temper some of the martensite as it is formed !
 
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