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Originally Posted by TikTock
Good discussion.
Id be very interested to find our how you achieve the dark blues and borderline purples in your blades at around 400 degrees. I temper at above that and never get close to those colors. Do you use salts? I thought the color was a 1 to one ratio on the heat and from what I can find, dark blues come out as follows:
500 brown yellow
510 spotted brown
520 brown purple
530 light purple
540 full purple
550 dark purple
560 full blue
570 dark blue
640 light blue
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I find some steels will color differently, especialy those with other alloys........ and time at temperature also needs to be taken into consideration....so color is an indicator, but not something that I would rely on completely.
With 52100 carbon alloy steel, the ideal hardness range I am looking for in my shop means that the steel is usualy in or entering a purple range.....
.....my temperature range is between 400 and 450F at 2 hr cycles.....
My deciding factor to stop tempering is based on when my 60 Rc file just begins to cut.