Forged vs Stock Removal Knives

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Kippington said:
Nah grain size is fine - I deal with it after normalization. It's one of the easiest things to check when quenching in water... (ting!)
wJ7UtlW.jpg

The carbide banding is in the hardened section too, its just that the martensite doesn't react to the etchent in the same way as pearlite, so you don't see the banding there.
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Next time snap it across the unhardened bit, too. You will see the the grain is bigger.
 
Dan P. said:
Next time snap it across the unhardened bit, too. You will see the the grain is bigger.
Click to expand...
To what end? The unhardened spine is not likely to have any kind brittle failure anytime soon, nor will it need to hold a working edge - Not forgetting they both came from the same parent phase, the grain size won't be wildly different between the two areas.
70E1B5V.jpg

The grain will look bigger in unheardened steel, yes - but I'm not about to compare an unhardened grain size to a hardened control. I think it would be as useful as checking grain size on a pre-hardened knife, then ignoring the hardened end result.

It occurs to me that maybe you're trying to point out that pearlite grains look larger than martensite grains? I think most bladesmiths (that do testing) know of it.
My understanding is that it's just the nature of how they break at the boundaries - even if the grain size is the same they will look different. Your wording is confusing though, you seem to genuinely think the grains are of different size due to the quench, even though their parent phase had the same grain size?
 
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Kippington said:
My understanding is that it's just the nature of how they break at the boundaries - even if the grain size is the same they will look different. Your wording is confusing though, you seem to genuinely think the grains are of different size due to the quench, even though their parent phase had the same grain size?
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I'm not questioning the integrity of your HT!
Rather, it’s a mystery to me why the grains are (or appear to be!) bigger in the unhardened part. I had indeed genuinely believed the grains were a different size, though the grain size in the "parent phase" would seem immaterial as, having undergone different heat treatment regimens, the two parts would now be composed of two or more phases anyway and therefore perhaps unsurprisingly have different grain sizes.
It hadn't occured to me that some mechanical property would cause the unhardened section to fracture or tear in a way that gave an appearance of enlarged grain.
I just thought it was interesting, that's all!
 
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As I understand it, when an austenite grain gets transformed into martensite it divides up into plates/lathes as it hardens, so you could say it has become finer. However, we still reference the size of the parent grain because the martensite is still heavily based off the original grain shape and can have some 'memory' of what it used to be. It can almost revert back to its parent grain if the conditions are right because it went through a diffusionless transformation.

Shape memory alloys work off this principle.

Meanwhile austinite-to-pearlite conversions create whole new grains with no chance of going back to the old configuration, but they stay at similar sizes to the parent grain.

I'm happy to be totally wrong here. Where did Larrin go? o_O
 
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Kippington said:
As I understand it, when an austenite grain gets transformed into martensite it divides up into plates/lathes as it hardens, so you could say it has become finer. However, we still reference the size of the parent grain because the martensite is still heavily based off the original grain shape and can have some 'memory' of what it used to be. It can almost revert back to its parent grain if the conditions are right because it went through a diffusionless transformation.

Shape memory alloys work off this principle.

Meanwhile austinite-to-pearlite conversions create whole new grains with no chance of going back to the old configuration, but they stay at similar sizes to the parent grain.

I'm happy to be totally wrong here. Where did Larrin go? o_O
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My question is unrelated, but is equally important...do you ever sleep?
 
I have a blade (125sc) that apparently by accident was not fully immersed in oil during a quench and that was probably part of the reason why it cracked (it was also ground a bit too thin on the edge). The cross section looks like this:

The whole blade after HT:

AE541614-FD09-4840-98BA-94515613AE34.jpeg



The arrows show the transition in apparent grain size (I am saying ‘apparent’ because this is not a direct grain test):

F6CD169B-996D-46D0-96BA-96F6A9CC2E31.jpeg
 
Matus said:
I have a blade (125sc) that apparently by accident was not fully immersed in oil during a quench and that was probably part of the reason why it cracked (it was also ground a bit too thin on the edge). The cross section looks like this:

The whole blade after HT:

View attachment 57455


The arrows show the transition in apparent grain size (I am saying ‘apparent’ because this is not a direct grain test):

View attachment 57456
Click to expand...

That's the very thing I'm talking about!
I noticed this years ago, but my understanding of heat treatment is more along the lines of practice rather than theory, so I always put it down as a mystery.
Seems hard to believe that the difference in appearance is down to something other than grain size?
 
Matus said:
I have a blade (125sc) that apparently by accident was not fully immersed in oil during a quench and that was probably part of the reason why it cracked (it was also ground a bit too thin on the edge). The cross section looks like this:

The whole blade after HT:

View attachment 57455


The arrows show the transition in apparent grain size (I am saying ‘apparent’ because this is not a direct grain test):

View attachment 57456
Click to expand...
How did you break the unhardened part so cleanly? I can't do the same without lots of plastic deformation. Was there a sub zero treatment involved?
 
The blade was quenched (not by me) in a Durixol V35 oil (should be faster than Parks 50). The breaking was done with a single hammer blow while the blade was clamped in a vise
 
Dan P. said:
Personally I cannot see how grain enlargement in forging is a problem unless the smith lacks a basic level of competence in managing his heat and material.
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It's not necessarily a problem. But typically the opposite claim is made, that forging has refined the grain.
 
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