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Lerch
07-22-2011, 10:13 PM
Hi all

I searched a bit for this answer but could not find it, so if this is a repeat of a previous question i apologize.

I am currently working with 440C and will also do some CPM154. The blades i have done so far were all 440c and this has been my process.

Steel foil wrap the blade with a small piece of wood for oxygen take up. initial heat treat is 1900deg for 15min. I plate quench until i can pick the blade up bare handed. I place a fan in front of the open oven door to speed cooling and once the oven is at 375deg i place the blades back in for a 2hr tempering at 375deg. After the 2hr tempering the oven shuts itself off and begins slowly cooling down. What i have been doing is leaving the blades in the oven while it cools down until i reaches around 100deg, this takes around 2hrs or a little more.

after this i take the blades and place them in between two blocks of dry ice in a yeti cooler for around 12-24hrs. i use the yeti cooler because it locks up so tight the ice will last for about 2days as opposed to about 10hrs if i put them in my refrigerator freezer.

after this i let the blades warm to room temp and place them back in the evenheat oven for two more 2hr temper cycles and the same cooling in the oven process as before.

is this good or what would be better?? once the 2hr cycle is over should i remove the blades to let them cool more quickly in open air? should i lay them on my aluminum blocks to cool a little more quickly?

thanks
steve

Knifemaker.ca
07-22-2011, 10:41 PM
Your current process for 440C is fine - with a couple of comments though. Fan cooling the oven, or even leaving the door open when its real hot, will reduce the life of the elements. Many recommend a flash temper before cryo for complex parts. The trade off is that maximum benefit comes from cryo if it is part of the quench - pretty much off the plates at room temperature and into cryo. In any event, if using a flash temper it could be much shorter and cooler to avoid stabilizing the RA before the cryo can convert it. Oven cooling from temper is no problem at all, unless maybe you're in a hurry. Cooling them quicker on the plates might speed it up for a bit and won't make any difference. For hardness, I'd predict about RHC56/57 with your 375F and if you were to lower to about 345, more like RHC59.

For CPM154, we use 1950F - 45 minute soak - plate quench to room temperature - into cryo overnight - temper 2 x 2hrs at 450 - 500 for RHC61.5 or 60 respectively.

I presume you are already leaving the blades in the foil till they come off the plates at room temperature.

Lerch
07-22-2011, 11:48 PM
Thanks for the info

So if im right are you saying to cease with the snap temper and instead go from the heat treat to the plate quench, wait until i can hold bare handed, and then go to the cryo treatment? if so then do i temper twice after as i have been doing or do i still need to do a 3 temper cycle as i was doing when i was trying the snap temper??

thanks for the info on the fan and open oven door, i wont be doing that anymore :)

also as a newbie i am not sure what RA means in this sentance, "In any event, if using a flash temper it could be much shorter and cooler to avoid stabilizing the RA before the cryo can convert it"

sorry for the ignorance, but hell ya gotta learn :)

thanks
steve

Knifemaker.ca
07-23-2011, 06:42 AM
So if im right are you saying to cease with the snap temper and instead go from the heat treat to the plate quench, wait until i can hold bare handed, and then go to the cryo treatment? if so then do i temper twice after as i have been doing or do i still need to do a 3 temper cycle as i was doing when i was trying the snap temper??

thanks for the info on the fan and open oven door, i wont be doing that anymore :)

also as a newbie i am not sure what RA means in this sentance, "In any event, if using a flash temper it could be much shorter and cooler to avoid stabilizing the RA before the cryo can convert it"

sorry for the ignorance, but hell ya gotta learn :)

thanks
steve

Morning Steve

I'm not telling you to skip the flash temper, but I'm saying we generally do. (remember we're talking air quench steels here). There is also a school of thought that favors the snap quench. I try for close to room temp before cryo rather than just cool enough to hold. Two tempers are in my opinion enough - except for a few alloys where the manufacturer specifies three - like CPM3V.

By RA, I was referring to retained Austenite. Our goal is to convert the steel's hot structure -Austenite - to the structure we want when cool - Martensite. In cryo and even tempering, we aim to convert some of that austenite that didn't make the conversion during quench. A temper before cryo will stabilize some of that remaining austenite, limiting the cryo's effect somewhat.

Lerch
07-23-2011, 08:01 PM
thanks for the info, i will try that on my next blades.

thanks for the lingo clear up :)

would there be any benefit to continue with a 3 temper process, like all three back to back? or is two good enough