[jimmontg]

You're using 440c right? That steel is pretty much straightforward. Best is a double temper @ 300 with LN in-between. How long are you tempering and you do an oil quench which is permissible with 440c? Dtech the issue may, may be the thin parks-50 oil you use. What is your quench temperature? It should be around 1800 and Parks may form a vapor barrier like water at that temperature. I oil quenched 440c at work, but we used an 80 viscosity oil. The quenchant is the only thing that could make a difference if the material is marked correctly.

What you are looking for is a fine grey velvet looking grain on a break test. I do not see the point if the part passes the brass rod test though. I do not do a brass rod test on stainless. I use files of a known hardness. You need to find a machine shop with a Rockwell tester and have them test small files that you temper at differing temps, plus what you run through your oven, use 1095 as the hardness and tempers are a known quantity.

Those Rc files they sell at some knife suppliers are in 5 point graduations and not much use to you. They are more expensive than paying a shop to RC test for you, $125 btw. 55 to 60 is a big jump. 58 is my bottom line and with 440c 62-63 is your as quenched. Perfect is 59-60 with it. Call Alex at Texas Knifemakers Supply and ask him. He can RC those files as well and can give you a quote for them.