Quote Originally Posted by Mike Blue View Post
Magnification should not be needed. If it's a fine gray smooth surface you're on the right track. Grain growth that's bad is like sand, you can't miss it.

Try tempering one of your leftover pieces for a couple hours at 400 F then attempt to break that piece and see if you notice a difference.
I tempered the scrap of O-1, at 400 for 1 hour, and tried to break it again today...
Pre temper it was very hard, but brittle...
After the temper, I put it in my vice, and tried everything I could to break it... I failed.
It threw sparks when hit with a hammer, and dented the hammer, but didn't break.
It had a small jagged edge pre temper from where I cut it off to make my blades, and that slightly mushroomed and has some very fine cracks, but only visible under magnification... it also has some shiney spots that look like polished silver, but I think that's from the hammer, not the O-1
The mushrooming of the jagged area is almost too small to see with the naked eye.
This chunk of steel is tough...