Temper problem O1

Interesting, my testing so far:

160 degC - 62 HRC
170 degC - 62 HRC
180 degC - 62 HRC

I'll keep running tests with increasing temp tomorrow.

The things I've modified in my procedure since the first test (with the sub 60 HRC hardness at 180 degC):

  • Increased soak time
  • Lowered austenize temp to 800 degC
  • Did a autotune on my PID for my temper oven
  • Let the blade air cool after temper cycle (quenched in water before)
 
Just for information, there can be variance of 1 or 2 RC points after first temper, 1 or less after 2 tempers, and 0.5 or less after the third.
 
Uhm, I think this kind of got overlooked. Did you double check the temperature in your high temperature oven? I saw you verified the low temp oven with a PID and thermometer.
 
me2 said:
Uhm, I think this kind of got overlooked. Did you double check the temperature in your high temperature oven? I saw you verified the low temp oven with a PID and thermometer.
Click to expand...

Good catch. You're right, I've focused on the temper oven. I need to get me a spare high temp TC then. My current one I use in my temper oven is rated for a maximum of 400 degC.
 
Given your oven readings are correct, consider that even hypoeutectoids reach 66 hrc, but will loose hardness quickly during tempering.
I bet you didn't reach homogeneous diffusion of your carbon in the matrix, so you need more soak time OR to place carbon well diffused with previous normalizing and cycling, and using the latter technique you may get good with a short austenitizing soak. If you didn't diffuse evnly the carbon you got higher carbon around the partially dissolved carbides, but a lower carbon content in the majority of the matrix. That idea seems to be confirmed by your hardness readings.
I suggest placing the blade directly in the preheated oven at the final austenitizing temperature (the quickest speed to austenitization the better, for various reasons)....quench between tempers to prevent chances of precipitations into the grain boundaries, but this is just a detail, not big deal.
 
You must log in or register to reply here.
Back
Top