How much tempering is enough?

[Andybrock]

I’m using Sandvik 14c28n for my folders, I run my HT program, leave the blade in the freezer overnight and it comes out at a consistent 61hrc ( measured) I then run my temper cycle for 2 hours which brings it down to 59.5 / 60 hrc which is where I want it.
Is that 1-1.5 hrc reduction enough temper for this steel for a folder?

 

[Stacy E. Apelt - Bladesmith]

Tempering is a change in the structure from a more brittle arrangement of the atoms to one that has more toughness. The temperature of the temper cycle is what controls this change the most. Time has an effect, but it takes a lot of time to change the hardness even one point while a 10° change in temperature may affect it the same amount as an extra 10 hours. If a blade is too chippy after tempering, raise the temperature 10° and give it another cycle. BTW, two temper cycles are the best procedure. as the second cycle corrects some changes from the first cycle. Two one hour cycles are sufficient for most steels.

To answer your question, I would expect a drop to Rc59.5/60 to be sufficient. The real way to tell is to do some testing on the blades. The brass rod test is probably the best one to determine if the blade is still too hard vs toughness.

 

[Andybrock]

Tempering is a change in the structure from a more brittle arrangement of the atoms to one that has more toughness. The temperature of the temper cycle is what controls this change the most. Time has an effect, but it takes a lot of time to change the hardness even one point while a 10° change in temperature may affect it the same amount as an extra 10 hours. If a blade is too chippy after tempering, raise the temperature 10° and give it another cycle. BTW, two temper cycles are the best procedure. as the second cycle corrects some changes from the first cycle. Two one hour cycles are sufficient for most steels.

To answer your question, I would expect a drop to Rc59.5/60 to be sufficient. The real way to tell is to do some testing on the blades. The brass rod test is probably the best one to determine if the blade is still too hard vs toughness.

Thanks Stacy, much appreciated.