Importance of Ramping & Equalizing in HT

turbodog10

turbodog10

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Aug 9, 2013
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I made 4 little CPM-154 blades that I sent to Texas Knifemakers Supply for HT and cryo. I got them back and all 4 consistently tested between 55-56 rhc. Obviously unacceptable.

I tend to be too long winded so after realizing this was getting a little long, I figure I'll just cut to the quick right here.

What is the purpose of ramping up and equalizing at different temps with CPM154 (or any steel for that matter)? Most HT recipes I read on here say to ramp up to multiple temps before reaching your the highest austinization temp. What potential harm is done if you put the knives in and just set the oven to 1980 and then hold them there for 30 mins?

I would love to know. Read on if you like reading.

So I called TKS and talked to Alex and got the knives back in the mail to him. He was really nice and willing to work with me and refund the shipping for me to get them back to him and he will redo the HT as soon as he gets them and get them back out to me so I don't loose too much time. I spoke with someone I trust regarding CPM154 last night to get some details on how to achieve the ideal rhc of 61 and got off feeling informed and optimistic. He told me he used TKS Ht service for 3 years and was always happy with their work.

With my handy information from a trusted source, I called Alex back a few minutes ago and asked what process they use to HT CPM-154. He told me the process they use is basically the same they use for 154CM (should that be the case?!) and that is as follows.

15 min at 1900
pull out and clamp in a vice (no aluminum- I confirmed) until room temp.
Put in Cryo overnight
2 hrs at 475
cool to room temp
2 hrs at 475

I know the CPM154 horse has been beaten nearly to death on here and I hate that I'm beating this poor horse even more- but that recipe doesn't seem to match anything anyone says. With that short of an austenization at that low of a temp and then tempering at such a high temp- I'm not really surprised i was getting 55-56 Rhc.

Alex went on to explain to me that they cant ramp up and equalize so before I call him back and tell him to just do 1980 for 30 mins and then temper twice at 400 for 2 hrs, I want to make sure that is an acceptable procedure. Again, the rhC I really want is 61.
 
".....With my handy information from a trusted source, I called Alex back a few minutes ago and asked what process they use to HT CPM-154. He told me the process they use is basically the same they use for 154CM (should that be the case?!) ...."

Yes, it should be the case.
CPM-154, ATS-34, and 154CM are all the same steel. The HT is identical.
CPM-154 is particle metallurgy version from Crucible, ATS-34 is Hitachi mono-steel, and 154CM is the mono-steel version from everyone else.

The reason for ramping and soaking in several steps is to allow certain changes to happen as needed, and to allow them to finish happening before moving to the next step. In general for stainless steels, the steps are 1) equalize, 2) bring up above critical temperature to start austenitization, 3) bring to the temperature needed to put the carbides into full solution and finish austenitization.
The quench only needs to allow the steel to cool at least as fast as air. Any clamping device ( steel vise, aluminum quench plates, etc.) will help maintain straightness while the steel begins to convert to martensite. The cryo ends the conversion, and the tempers stabilize and remove the brittleness in the martensite.

A little study in the stickys and in any metallurgy book will help you understand these things. They are also regularly discussed here in Shop Talk.
 
Thanks for the thorough answer, Stacy. So what is the consequence, if any, of a blade being broought straight up to Austenization temp and soaked there without doing any ramping/equalizing around critical temp?
 
turbodog10 said:
So what is the consequence, if any, of a blade being broought straight up to Austenization temp and soaked there without doing any ramping/equalizing around critical temp?
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Poor conversion/transformation due to not getting alloying elements into solution, probably low hardness, and I would guess lower toughness in the finished blade.

Skipping steps and doing a half-vast HT on complex steels is a waste of time and money.
 
I agree with James. We do our own HT. But the #'s you are getting with that recipe seem way off to me. We use a lot of CPM154, and do a stop along the way...etc. But we go up to 1920 for 1/2 hour, then oil quench, cryo (liquid nitrogen) overnight, and then two tempers for 2 hours around 500. This is giving us the 61 you are aiming for. Seems like with that low of a temper you should be getting a higher RHc. Probably result of skipping steps. This is what was recommended by the manufacturer, and I figure their folks know more about their steel than I do :-)
Don't know if this helps, but I hope so!
 
If TKS can't perform the proper ht then why do they offer the service? I was considering sending them a couple of AEB-L blades because I can't afford $25 per blade, but it sounds like they admit to not being able to do the job correctly. Are there really only 2 companies that knife makers recommend for ht services?
 
MMuhlhauser said:
I agree with James. We do our own HT. But the #'s you are getting with that recipe seem way off to me. We use a lot of CPM154, and do a stop along the way...etc. But we go up to 1920 for 1/2 hour, then oil quench, cryo (liquid nitrogen) overnight, and then two tempers for 2 hours around 500. This is giving us the 61 you are aiming for. Seems like with that low of a temper you should be getting a higher RHc. Probably result of skipping steps. This is what was recommended by the manufacturer, and I figure their folks know more about their steel than I do :-)
Don't know if this helps, but I hope so!
Click to expand...

Do you really quench your CPM-154 in oil? If so, I think you're the first I've heard of doing that. As I understand, CPM-154 is an air hardening stee (see Stacy's post above).

Here's a little follow up. I finally got my blades back on Saturday. :mad: We tested them and they are consistently 61 rhc.

They did not get my knives into heat treat until they started the next batch the following week so now I'm probably going to be late on an order I had in that set. When I found that out, I finally just bit the bullet and bought a roll of Stainless foil ( on Amazon!) so I'll be trying to achieve 61 rhc without cryo from now on.

Any suggested recipes on how to get 60-61 without cryo?
 
Turbo, you don't need cryo. Cryo involves liquid nitrogen and somewhat specialized equipment.
The dry ice treatment (AKA "Subzero") does what you need done and is very simple to do in a rudimentary workshop- all you need is dry ice and the solvent of your choice.
Again, lots of info in the stickies.
 
5-10# of dry ice and a gallon of denatured alcohol will make a tank of -95F final quenchant ( use a metal tank). Do the main quench ( air and/or oil), bring to room temp, place in the sub-zero bath for 15-30 minutes, remove, let warm up to rom temp, temper twice.

The bath will last a couple hours or more. Do three or four blades at a time.

Look at the charts from Crucible and get the temperatures for your HT. 154-CM and CPM-154 both are easy to HT. IIRC, I austenitized at 1950F, and temper at 350F for Rc61-62's.
 
Good deal. Thanks guys! I will definitely do this. I have 4 more cpm154 blades in the works right now.
 
Let the dry ice all evaporate, let the alcohol sit for a while, and pour back in the can for using again. l leave the cap loose for a day to let any dissolved CO2 escape, and then tighten it. I label the can "QUENCH ALCOHOL".
 
turbodog10 said:
Good deal. Thanks guys! I will definitely do this. I have 4 more cpm154 blades in the works right now.
Click to expand...

When you get your HT all dialed in I think you'll be very happy with it. CPM-154 is really good stuff :)
 
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