What is this black line and what caused it ???

A

archangelblader

Joined
May 31, 2017
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I recently heat treated my first knife ever. Made of 1095, heated it till I saw the shadow move through it, and it became non magnetic. Let it sit another few minutes then went to quench in the random mix of motor oil that I had around(can afford nice oil currently). It warped, disappointing but I knew there was a chance going in. I then tempered it twice at 500 for two hours in my oven letting it cool to room temperature between tempering. After all this I attempted to fix the warp by over correcting the warp with a washer, some clamps, and a block of wood, while heating it to 325 for 45 minutes. It didn't fully take out the bend so I set it up again to go in again to finish straightening. It broke in three pieces sadly. So I took this as an opportunity to examine the grain and try to learn about the grains. When I looked at the pieces I noticed this straight black/dark blue line along the edge on the inside that runs part way down the second broken piece. I have no idea what it is or what caused this odd discoloration in the metal. It runs a perfect 8th of an inch from the edge up, but only from the inside. Hoping someone can answer this and help me complete this quest for knowledge.
 
I don't see an image and sure others that may be of better help if you could post one. Also canola oil is very cheap. Get rid of your motor oil, spend $10 and get some canola oil.
 
I'm guessing here, but it may have cracked in your motor oil and the color is a result of the oil.
 
Is there a way to test to see, I am just curious now at this point. Also I have every intent of changing up my quenching oils before I try again, also switching to 5160 or 1084 as iam told those are easier steels to heat treat.
 
Those are the place where the cracks started. The dark part was the crack that oxidized while hot. The shiny part is the break line from the crack that happened when the blade was cold, so it did not darken.

There are may problems here that could contribute to this:
1) Forge 1095 onl at 1700-2100F DO NOT forge down to dull red or it may form cracks that will show up in the quench
2) Motor oil and suckh os a bad quenchant to start with, and totally insufficient for 1095. A gallon or two of Canola oil from the grocery store will work.
3) You have to heat the blade to 375F or more, BEFORE you apply the stress to the blade, or you may crack it while trying to straighten it. Put it in the calmp and only slightly snug it down. Place in the oven and after 15 minutes take it out and tighten to overfex by the amount of the bend. Place back in and heat for an hour. If the blade is still curved, re-do it with more flex ... but only apply the full flex once the blade is hot.
 
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