Opinions wanted- 440C heat treat with RC readings and pics

Cardinal Knife

Cardinal Knife

Joined
Nov 25, 2007
Messages
340
Good Afternoon,
I treated these two this morning and am a bit confused :confused: as to why the clip point hunter has such a wide range of readings. the rear of the tang is a lot softer than the blade. Both blades were heated at the same time in double seamed foil, spine down, tang towards door.

Austenizing- The recipe ramped for about 2.5 hours to 1880 and first blade soaked for 15 minutes. I added ten minutes for second blade to get back up to temp so second blade (clip point) soaked for 25. My kiln is 110v so I cannot have it ramp any faster.

Tempering- 2 hours at 225. Kiln was still too hot from first heat cycle and went all the way to 297 before it slowly dropped back down to 225. Was still at 237 60 minutes into the temper.

Quench- two 1/4" aluminum plates (all I have right now, I know I need thicker) on top of 10lb steel weight to help ventilate heat. Another 10 lb weight on top of upper alum plate. Small fan on hi blowing on whole operation. Blades remained in foil for plate quench

Other variables- I used a soft freezer pack to cool the plates back down between quenches which left water on the plates would this have any affect? The clip point sizzled and spat.



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Thanks in advance
 
Surface grind the tang and rc test again, perhaps scale/decarb/can residual affecting rc#.
 
I have noticed the same thing happening on a couple of blades I did not too long ago, the cause for me was I did not de-burr the holes I drilled in the tang and the burr kept the plates from sitting flat during the quench.
Usa knife maker sells some 1" quench plates at a reasonable price, go the biggest you can afford. I stand my plates on their side in my milling vise I then drop the blade in and clamp down with moderate pressure.
 
Just a comment, but I doubt that you are getting accurate readings along the edge area. The tang and ricasso should read right if they are flat and smooth. Grind off the surface de-carb before any test.

The readings from 60.5 to 62 on the one blade are within the normal range of test error and variability in hardening.
If the readings are accurate, there is a significant drop in hardness on the tang area of the other blade. It is far more than any variation due to test error, temper, or cooling rate. I suspect that the tang never was heated fully in austenitization.

I would suggest that you soak for a longer time ... 30 minutes is normal....and don't start counting the time until the oven is at austenitization temp. I bet that would take care of your variations.
 
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