Grain size Ok so or should I go finer?

R

rolynd

Active Member
Title says it All, I want your opinion on the grain size of a test piece.

Steel is 80crv2 - this is a new steel for me so some testing is in order.
I hardened a test piece and broke a section off after each step.

Top one is after 1x normalize
Middle one after 2x Normalizing
Botom one after hardening.

It was definitely hader to break a section off after hardening compared to the first step.



forgot to add : the photo is shot under 8x magnification.
Best regards
rolynd
 
Rolynd - I won't comment on the grain in the photos, hard for me to tell anything. I had the same question, it was suggested to compare the grain in piece in question to the grain in a file that's been broken. A file normally would have good small grain. The files I've broken the grain looks - to the naked eye - almost like a pure gray, almost no visible grain.

Perhaps someone with knowledge will comment on the photos.

Ken H>
 
So the first two pieces are from just normalization and no hardening afterwards?

I was always under the impression that you would want to normalize, then harden, and check the grain. Then take a separate piece of the same steel and then normalize twice and then harden and then check the grain. That will show you the differences between the two cycles.

Most people do two - three cycles. I end up doing 4 or 5.
 
Yeah, I'm trying to undertand the question being asked as well. You don't want to check grain just after normalizing a piece of steel. You want to normalize, usually a minimum of three times, with decending temperatures, bring it up to austenitizing temp, quench it, and then check the grain.
 
I would say that the first two show and increase in refinement of the crystal structure between one and two cycles. The hardened blade doesn't look too bad but you might be able to get it just a bit finer with a third cycle. I've definitely seen a lot worse.

Doug
 
To evaluate fractured grain size you want to do it from a quench hardened condition. If the steel is not primarily martensitic the fracture mechanisms will involve much more shear and slip, resulting in a much rougher surface than a more accurate representation of the grain size would be. This is a contributing factor to one part the edge packing mythology; edge quenchers would break their blades and see the really fine grained look at the edge and the rough looking texture on the pearlitic spine and then go bananas over how affective their edge packing was:rolleyes:

Fine pearlite or even upper bainite will result in a rougher surface, and thus a more difficult reading of grain size, than fully hardened steel. This is one of the differences between fractured grain size analysis (Shepard) and ASTM standard grain size analysis, which is done with a microscope on cut and polished surfaces where martensite (hardened steel) can make things tougher to see. It all has to do with how you open the steel up to see the inside.
 
I made a test blade from very thin stock 80crv2 ended up with 1,4mm = 0,055 inch (if my conversion is right) its the bottom one in the pic. I did some testing, nothing overly scientific - just what came to mind and finally broke it to see what it can take. The blade was hardned the normal & tempered way and then differentially tempered on the back.








the crincling noise you hear is the epoxy giving up.

[video=youtube;ISSlz8SaTcE]http://www.youtube.com/watch?v=ISSlz8SaTcE[/video]

After breaking:



The full test can be seen here with more pics and breaking of the other knife as well.

I am satisfied with the results and I think thats tough enough for me since its such a thin knife.

Best regards
rolynd
 
Thin blades work great - just think of most machetes. They are thin, limber, take a beating, and keep working.

I read your other thread - very good tests, and you did good on the knifes.

Ken H>
 
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