So as I understand the heat treat process it is a sequential process of normalization, followed by the quench, then ultimately the temper. Here is my dilemma:
I forged a piece of 5160 with intentions of making a filet knife for a fisherman buddy. I made sure to only strike while the steel was a dull orange color or brighter. After forging I profiled and did my preliminary grind to make the final grind easier. I normalized twice ( I have recently read on this forum the preferred number is 3 and will implement this next time), quenched in preheated oil and tempered at 400 for 2 hours and allowed it to cool inside the oven down to room temp. I got that straw color I have heard is a pretty good signal that you didn't overheat it. Final grind completed and as I was getting ready to sharpen it, I decided to test the flex on the blade to see if I needed to grind it a little thinner or not. I felt crunching (like a twig right before it snaps) and figured it was the glue on the handle separating and made a note to address that. I flexed it the other way and it snapped revealing a pretty large grain structure which leads me to believe that the crunching i felt was the blade getting ready to give way. My question is, what does everyone here do differently to ensure a tight grain structure. I'll be a little flabbergasted if 1 extra normalization cycle was all I needed to tighten up that pile of sugar crystals I saw. Also, when I normalized I heated to nonmagnetic and allowed it to cool back to black. It was still hot enough to likely melt a hole in my palm if I handled it. Should I be allowing it to cool further before starting the next normalization cycle? If so, how cool should it get? Room temp?
