What temperature and how long should I temper a 52100 filet knife
Standard tempering time is 2 hours, at temperature. The exact temperature is very difficult to say since it is quite dependent on your specific heat treatment for that steel. I would say 375°F to 400°F with preference for the lower end. But, if it were me, I would do hardness testing, start at 350°F and "walk in" my Rockwell by 25°F increments until I had 61 or 62 HRC