Heat Treating OCD question.

[Alex Baliles]

Previously ive always either sent my blades for HT or have used a forge for simple steels. I now have an Oven and going to do my first batch of 80CRV2. I have the data from NJSB but a bit confused about something. It states not to put the blade in a cold oven. To put it in at Austentizing temp or close. At least thats how I see it. The instructions state to get the steel to temp and then soak for 5-10min.
My question is about that window of time between putting the blade into the oven which is at temp and the time it takes to get the steel up to temp. I dont have a way of checking the steel temperature. For reference it is a 12” blade at 3/16. Im guessing the soak time is after the steel has reached temp. How are you guys determining if the steel is where it needs to be before you start the “Soak” clock?
Thanks in advance.

 

[SirSpice]

This article will answer all of your questions starting out.

Introduction to Knife Steel Heat Treating from a Metallurgist - Knife Steel Nerds

Heat treating is easy and I can prove it - I taught my seventh grader son how to do it. You can heat treat knives too!

knifesteelnerds.com

Especially this part:

Soak Time

After the steel has reached the austenitizing temperature it needs to be held at that temperature for some period of time, called a “soak.” The soak time recommended in a datasheet is supposed to start after the steel has reached the temperature. Sometimes I cheat and start the timer after the furnace has “rebounded” to the temperature (it cools down from opening the door and inserting a cold piece of steel). Once the steel has reached the same color as the furnace it has reached the temperature. You are only seeing the surface but steel is highly conductive and knives are thin so once the surface has reached the temperature it is only seconds before the center has as well.

You will notice that the MagnaCut chart above shows different soak times for each austenitizing temperature, as higher temperatures will often mean a shorter required soak time. The thickness of the steel also matters, the datasheet for MagnaCut says “Min soak time” and if the steel is thicker than 1/8″ (3.3 mm) it may need a few more minutes.

Some knifemakers are afraid of soaking because they think that holding it at temperature will grow the grain size. It is true that holding steel longer will grow the grains but temperature matters much more than time. Holding a steel for 30 minutes is not going to hurt it if the temperature is correct. Undersoaking is a more common issue than oversoaking.

I don't know which kiln controller you are using, but in mine (TAP) you program in the soak timer to start when the oven rebounds to the the set temperature. I add an extra step afterwards at the same temperature so that the oven doesn't immediately start dropping the temperature at the end of the soak.