I successfully quenched it this afternoon in Parks 50. I can harden in medium speed too, but I use the parks more and more for 1084.
Again, this is 1084 and I changed to this steel for this handle style because of the 5160 air hardening and breaking in the low red to black color while lightly straightening. I think I can adjust my forging procedure a little and continue to use 5160.
This impressed on me that sometimes , on rare occasions, the steel choice may help or hurt your chances, merely in the forging of it. I had never considered that as I do now. The relative narrow and thin cross section of the frame is what lead to the failure.