- Joined
- Jan 5, 2015
- Messages
- 15
I have made several batches of simple kitchen paring knives using 440C from Admiral (1/16" starting thickness). The first couple batches I ran up to 1850F in my Paragon furnace and held it there for 25 minutes. I then immediately air/plate quenched to room temp. I then immediately placed blades in dry ice/RV antifreeze which freezes at -50F for 24 hours. Then tempered twice at 300F for two hours each time. All went well and knifes sharpened well using Razor Sharp 80 grit grinding wheel and honing wheel. Super sharp.
The next couple batches I inserted a step after air/plate quench where I cooled the blade in deep freeze from room temp to approx 0F for a couple hours (or overnight on one batch) prior to cryo. The thought was to avoid possible warping when I had gone from room temp to -50F (even though I did not previously get warping - I know, if it ain't broke, don't fix it!). I also got a bit distracted on one batch and did not get the final temper completed (still as 300F twice for two hours) until a day later. The result was most of these knives being impossible to sharpen with the Razor Sharp grinding wheel. I was able to put an acceptable edge on these using my 2 x 72 belt grinder using 220 grit, then 300, then 600, then 1200. However, it was not crazy sharp like the first couple batches.
I then tried the same heat treat, air/plate quench, cool to 0F in deep freeze for a few hours, then -50F shallow cryo for 24 hours, then changed the temper to 400F twice for two hours each time to try to lower the RC hardness. No luck. I still could not sharpen with the grinding wheel (3000 rpm with 80 grit that I re-gritted several times thinking the grit had worn off too much).
I have been making knives for about 18 months and still need to get a RC hardness tester. I know, get the right tools so you can do the job right. However, at this point I cannot tell you what the resulting RC hardness was in any of the above described procedures. I am getting a tester this week to help diagnose the problem.
If it is not an issue of the RC being too high, the other idea I had is that the delay between air/plate quench and cryo (by putting the blades in my deep freezer), as well as the 24-48 hour delay between cryo and tempering could have caused carbides to form which are too hard to sharpen with the Razor Sharp grinding wheel.
Thoughts? Thanks in advance for your input.
The next couple batches I inserted a step after air/plate quench where I cooled the blade in deep freeze from room temp to approx 0F for a couple hours (or overnight on one batch) prior to cryo. The thought was to avoid possible warping when I had gone from room temp to -50F (even though I did not previously get warping - I know, if it ain't broke, don't fix it!). I also got a bit distracted on one batch and did not get the final temper completed (still as 300F twice for two hours) until a day later. The result was most of these knives being impossible to sharpen with the Razor Sharp grinding wheel. I was able to put an acceptable edge on these using my 2 x 72 belt grinder using 220 grit, then 300, then 600, then 1200. However, it was not crazy sharp like the first couple batches.
I then tried the same heat treat, air/plate quench, cool to 0F in deep freeze for a few hours, then -50F shallow cryo for 24 hours, then changed the temper to 400F twice for two hours each time to try to lower the RC hardness. No luck. I still could not sharpen with the grinding wheel (3000 rpm with 80 grit that I re-gritted several times thinking the grit had worn off too much).
I have been making knives for about 18 months and still need to get a RC hardness tester. I know, get the right tools so you can do the job right. However, at this point I cannot tell you what the resulting RC hardness was in any of the above described procedures. I am getting a tester this week to help diagnose the problem.
If it is not an issue of the RC being too high, the other idea I had is that the delay between air/plate quench and cryo (by putting the blades in my deep freezer), as well as the 24-48 hour delay between cryo and tempering could have caused carbides to form which are too hard to sharpen with the Razor Sharp grinding wheel.
Thoughts? Thanks in advance for your input.
