Sort a few things out here:
Hardening is hardening. You are taking up a piece of hardenable steel to its Austenite condition, which is the condition where all of the carbides go into "solution" and become atomically liquid = not part of the Iron/carbon matrix. This condition is also the point a little above that temp. where the steel becomes non-magnetic known as "critical" temp. For most simple steels, this temp. can be anywhere from 1413 - 1525 degrees, providing the steel is non-stainless.
By quenching in a medium to reduce this temp and condition to below 1000 in 1-4 seconds, depending on the steel type/amount of carbon/amount to alloys, you change the steels condition to Martensite, which is a hard piece of steel.
The quench medium must remove the temp at a particular speed and rate to match the steels alloy content. Different steels with different alloys and amounts, require different "speeds" of oil/medium to reduce the austenitic temp to below 1000 or so in the specified amount of time.
Along with this hardness, come brittleness and "retained austenite" - austentite that did not "make" the transition to martensite.
A "soak" at a much lower temp of 350 - 400 degrees, completes the "retained austenite" transformation to martensite, and relaxes the brittleness. This lower temp/soak time is kown as "TEMPERING"!!!
Now, with the new martensite being formed from the "retained austenite", the steel needs to be tempered AGAIN to relieve hardening stresses of the new martensite.
Thus, the term you may have heard of double or even triple tempering.
Know your steel, know what industry standards are for THAT steel, what quench medium to use, what tempering temps. to use for what hardness is desired, etc.
This entire process is called "HEAT TREATING", which includes the entire processes of forging, normalizing, annealing, hardening and tempering.
Each of which are distinct and seperate steps of a long and drawn out process with specific times and temperatures for each step. Individually Handcrafted Knives for the Outdoor Enthusiast