grain size as it pertains to knives

greetings y'all
recently i took an old simonds file and turned one end (no teeth at this point) into a knife, or started to. to make a long story short after forging
and rough grinding and heat treating i decided i wasn't real satisifed with the results. so i went and broke it. call it destructive testing. i got 2 breaks, 1 started at the edge the other at the spine. upon close examination (looking at it through the wrong end of 10x50 binoculars (i think i owe alvin for that tip)) each starting point for the cracks seemed to have oxidation colors. the grain under that magnification looked similar to sugar under the naked eye perhaps 1/2 or 2/3 that size. what i'm wondering is is this a reasonable grain size or is it too large? if it is large what can i do different? i'm judging temps by color and quenched in water. for quenching i dunked the blade at bright red / maybe starting to glow orange. for tempering i used a torche to draw the spine to blue which resulted in straw/bronze at the edge. i've got another blade forged but not heat treated (did anneal it) that i like much better. before i heat treat it and recommendations? would it be better to use oil and if so will peanut oil work (have a couple of gallons on hand).
thanks in advance.
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rpayne wrote:

I've tried a few files. I found out that file steel can be hot short. The forging temp range is narrow and you can overheat it while forging. This overheat can (and did) produce stress fractures during quench. Oil would slow the quench rate and reduce the thermal shock stress. I use Vet grade mineral oil, so peanut oil should be okay, just lock up the elephant first so the smell doesn't drive him rogue.
Charly
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