12-22-2017, 11:33 AM
I agree that softening during grinding the edge is an interesting and important topic, but how do I know if you're talking about a new 120 grit or an old 220 grit? That makes a huge difference!
Mr Jan, I'm sure you know different types of steel use different temps. I haven't heat treated many types of steels. In fact, I have been very single minded about maximizing 52100, but I think all simple tool steels are fairly similar.
Adding carbon and other alloys means slightly higher temps, with longer soaks before quenching. It's more important (and difficult) to harden perfectly. Tempering is easy.
Tempering is two pronged. You manage time at temp. Most bladesmiths temper for two hours, twice, as do I. 350° barely colors the steel. You almost have to see it next to un-tempered steel to see that 350° is very light straw, and only drops RHC 2-3 points. I use 375°, which drops RHC about 4 points, and the color change is easy to see.
That leaves the edge on the hard side- slightly chippy, but I draw everything except about 5/16" of the edge clear down to dark blue (grey is too soft for me), which makes 52100 very springy, with RHC about 47-49 on the spine. There is a video on my website that shows the color and how that HT performs.
470°F probably would be at least deep straw. I've never gone over 425°F, which I thought was fairly deep straw, but there are enough differences in kilns, not to mention opinions on color description, to make it difficult to be very precise. Guys who don't do differential HT temper at 425-450, which leaves a pretty tough blade around RHC 56-57, but the blade would be breakable. Differential tempering allows near magical qualities.
Higher carbon starts harder, but equal tempering drops the RHC about the same amount.
Mr Jan, I'm sure you know different types of steel use different temps. I haven't heat treated many types of steels. In fact, I have been very single minded about maximizing 52100, but I think all simple tool steels are fairly similar.
Adding carbon and other alloys means slightly higher temps, with longer soaks before quenching. It's more important (and difficult) to harden perfectly. Tempering is easy.
Tempering is two pronged. You manage time at temp. Most bladesmiths temper for two hours, twice, as do I. 350° barely colors the steel. You almost have to see it next to un-tempered steel to see that 350° is very light straw, and only drops RHC 2-3 points. I use 375°, which drops RHC about 4 points, and the color change is easy to see.
That leaves the edge on the hard side- slightly chippy, but I draw everything except about 5/16" of the edge clear down to dark blue (grey is too soft for me), which makes 52100 very springy, with RHC about 47-49 on the spine. There is a video on my website that shows the color and how that HT performs.
470°F probably would be at least deep straw. I've never gone over 425°F, which I thought was fairly deep straw, but there are enough differences in kilns, not to mention opinions on color description, to make it difficult to be very precise. Guys who don't do differential HT temper at 425-450, which leaves a pretty tough blade around RHC 56-57, but the blade would be breakable. Differential tempering allows near magical qualities.
Higher carbon starts harder, but equal tempering drops the RHC about the same amount.