Steel testing underway...

Wow just read through this entire thread. Very informative, thanks for all the work you put in Aaron!
 
Really good info even for a user only like myself. Thank you Sir.

surprised by the cpm 154. And a bit by the o1. The rest not so much. Looking forward to hardness results from test 1....and the results of test 2.
 
Firstly: Thanks for all your testing, really interesting and a great read.

aarongough said:
Ok guys! The next batch of test blades have just gone into the kiln for stress relieving. I'm doing a full spread of steels again in order to compare optimized heat-treats across all the steels. Steels being tested: A2 (2 blades), O1, CPM154, CPM3V, 440C.

Highlights of the new heat-treats:

Sub-zero treatments before tempering: last time most of the sub-zero treatments I did were in between the tempers, this means that some blades may have had retained austenite that was stabilized by the first temper. This time all blades will undergo sub-zero treatments before the first temper in order to help fully eliminate retained austenite.

.........
Sub-zero treatment in dry ice and isopropanol for 45 minutes
Click to expand...

I would be interested to know why did you decide on the dry ice and isopropanol rather and a sub zero treatment rather than deep cryogenic treatment with Liquid Nitrogen?

From a bit of research and looking around to people that know more than me here is a few comments:

""Sub-zero" has been around for a long time and is the -100 F dry ice temperature.

"Cryo" [cryogenic treatment] is a newer process and is the - 300 F liquid nitrogen temperature.

Sub-zero just reduces the amount of RA.

Cryo reduces the amount of RA and permits the formation of eta carbides"

A bit more research:

Comparison of Effects of Cryogenic Treatment Different Types of Steels : A Review by P. I. Patil and R. G. Tated

"Any changes in property are attributed to the micro-structural
changes. Thus in tool steels, the following are the possible
processes changes that need to be considered for the property
change [41]
The effectiveness of the cryotreatment at liquid nitrogen
depends on;
- Elimination of retained austenite.
- Transformation of retained austenite to more stable as
tempered martensite matrix.
- Formation of Eta – carbides
- Precipitation, nucleation and growth of ultra fine small
secondary carbides (SSCs) with high population
density.
- Homogeneous and well distributed Microstructure.

As reported (Deep Cryogenic Treatment) DCT has many benefits. It not only gives
dimensional stability to the material, but also improves abrasive
[7,32-34] and fatigue, wear reistance [35] and increase strength
and hardness of the material [33,14,36]." Page 3.

Another article:

metals-cryogenic-quenching-steel-revisited

I know of a few makers that use RWL-34 (equivalent to CPM-154) that use liquid nitrogen treatment and I believe (under correction) Phil Wilson uses a liquid nitrogen quench for his CPM-154 blades as well.
 
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marthinus said:
Firstly: Thanks for all your testing, really interesting and a great read.



I would be interested to know why did you decide on the dry ice and isopropanol rather and a sub zero treatment rather than deep cryogenic treatment with Liquid Nitrogen?

From a bit of research and looking around to people that know more than me here is a few comments:

""Sub-zero" has been around for a long time and is the -100 F dry ice temperature.

"Cryo" [cryogenic treatment] is a newer process and is the - 300 F liquid nitrogen temperature.

Sub-zero just reduces the amount of RA.

Cryo reduces the amount of RA and permits the formation of eta carbides"

A bit more research:

Comparison of Effects of Cryogenic Treatment Different Types of Steels : A Review by P. I. Patil and R. G. Tated

"Any changes in property are attributed to the micro-structural
changes. Thus in tool steels, the following are the possible
processes changes that need to be considered for the property
change [41]
The effectiveness of the cryotreatment at liquid nitrogen
depends on;
- Elimination of retained austenite.
- Transformation of retained austenite to more stable as
tempered martensite matrix.
- Formation of Eta – carbides
- Precipitation, nucleation and growth of ultra fine small
secondary carbides (SSCs) with high population
density.
- Homogeneous and well distributed Microstructure.

As reported (Deep Cryogenic Treatment) DCT has many benefits. It not only gives
dimensional stability to the material, but also improves abrasive
[7,32-34] and fatigue, wear reistance [35] and increase strength
and hardness of the material [33,14,36]." Page 3.

Another article:

metals-cryogenic-quenching-steel-revisited

I know of a few makers that use RWL-34 (equivalent to CPM-154) that use liquid nitrogen treatment and I believe (under correction) Phil Wilson uses a liquid nitrogen quench for his CPM-154 blades as well.
Click to expand...

I expect that liquid nitrogen would improve the properties of all the blades at least marginally, however the cost is quite prohibitive. I got some quotes a while ago and I was looking at around $400 per month to keep a dewar of liquid nitrogen in the shop.

If I was able to source it at a lower cost I definitely would have done so.

EDIT: I should add too that from what I have heard from other makers the difference between cryo and sub-zero is nowhere near as pronounced as the difference between sub-zero and nothing. Using the sub-zero treatment we're at least eliminating all the retained austenite, which can be very detrimental to the performance of the blade.
 
aarongough said:
I expect that liquid nitrogen would improve the properties of all the blades at least marginally, however the cost is quite prohibitive. I got some quotes a while ago and I was looking at around $400 per month to keep a dewar of liquid nitrogen in the shop.

If I was able to source it at a lower cost I definitely would have done so.
Click to expand...

If there is a local horse breeder go talk to them. They usually keep liquid nitrogen for cryopreservation of semen. Maybe they can help you out for cheaper?
 
Hey Aaron,

Interesting thread. I've read through a couple of times and still some of your results are surprising to me. Thank you for sharing all your efforts here.

On the liquid nitrogen; keep looking. I have 4 dewars (25+ liters per) charged and serviced - right on our place - and it still works out to less than $100/month. Might check with a few local veterinarians for the scoop. Maybe look into buying a reconditioned tank. We still have one of them that has held up well under rough use for over 20 yrs. The cost was about two-thirds of new tank of same brand/size way back IIRC.

Best to you.
 
marthinus said:
If there is a local horse breeder go talk to them. They usually keep liquid nitrogen for cryopreservation of semen. Maybe they can help you out for cheaper?
Click to expand...

I'm in the middle of the city, so no horse breeders around here unfortunately! :) Thanks for the good idea though!
 
Andy Lewis said:
Hey Aaron,

Interesting thread. I've read through a couple of times and still some of your results are surprising to me. Thank you for sharing all your efforts here.

On the liquid nitrogen; keep looking. I have 4 dewars (25+ liters per) charged and serviced - right on our place - and it still works out to less than $100/month. Might check with a few local veterinarians for the scoop. Maybe look into buying a reconditioned tank. We still have one of them that has held up well under rough use for over 20 yrs. The cost was about two-thirds of new tank of same brand/size way back IIRC.

Best to you.
Click to expand...

I would love to have liquid nitrogen around the shop, even if simply because it's awesome stuff!

Are the necks on your dewars big enough to get a knife blade through? That was the main thing that drove up the cost for me, in order to get a tank with a big enough neck I had to go up several sizes (I think I was looking at 50 liters or so). Do you decant the LN into another container and use it there?

The advice is appreciated guys!
 
Does anyone have any thoughts on the minor decarb I showed in the photos and how it might impact the blades? I want to make sure this isn't a blocking issue before I continue with the testing tonight...
 
My Dermatologist uses liquid nitrogen to burn pre-cancerous spots from his patients skin. Maybe a local Dermatologist could give you some tips or sources for liquid nitrogen? Just a thought.
 
aarongough said:
I expect that liquid nitrogen would improve the properties of all the blades at least marginally, however the cost is quite prohibitive. I got some quotes a while ago and I was looking at around $400 per month to keep a dewar of liquid nitrogen in the shop.

If I was able to source it at a lower cost I definitely would have done so.

EDIT: I should add too that from what I have heard from other makers the difference between cryo and sub-zero is nowhere near as pronounced as the difference between sub-zero and nothing. Using the sub-zero treatment we're at least eliminating all the retained austenite, which can be very detrimental to the performance of the blade.
Click to expand...


I Send my Stainless blades out for this reason, PHT performs Cryo and I don't have to mess with the liquid nitrogen.
 
Aaron,

The LN2 here is just for typical storage of semen and occasional embyos, and for snap freezing bio samples. I forge and use only simpler carbon steels myself. With little to no RA post heat treat, I haven't found a convincing reason to even try cryo.

Regarding dewar neck size; yeah you could fit an avg edc-type blade down even the smaller of these. The larger size could manage anything less than 2.5" wide as long as it didn't have too radical a sweep end to end (e.g. stainless kukri). These dewars are built around said companies storage canister style. Big mouth tanks have slots for either 5 or 6 monster canisters that each hold a buttload of canes. This looks to be the trend but nobody seemed to ask the guys that actually use them.

LN2 holds surprisingly well under just 6 to 8" of still vapor, even if in a thick-walled styrofoam cooler. Most of your LN2 loss comes with initial exposure and boil off as your material comes down to temp. Trick is to be patient enough to use the vapor phase for this step.
 
Andy Lewis said:
Aaron,

The LN2 here is just for typical storage of semen and occasional embyos, and for snap freezing bio samples. I forge and use only simpler carbon steels myself. With little to no RA post heat treat, I haven't found a convincing reason to even try cryo.

Regarding dewar neck size; yeah you could fit an avg edc-type blade down even the smaller of these. The larger size could manage anything less than 2.5" wide as long as it didn't have too radical a sweep end to end (e.g. stainless kukri). These dewars are built around said companies storage canister style. Big mouth tanks have slots for either 5 or 6 monster canisters that each hold a buttload of canes. This looks to be the trend but nobody seemed to ask the guys that actually use them.

LN2 holds surprisingly well under just 6 to 8" of still vapor, even if in a thick-walled styrofoam cooler. Most of your LN2 loss comes with initial exposure and boil off as your material comes down to temp. Trick is to be patient enough to use the vapor phase for this step.
Click to expand...

When you say 'use the vapor phase' you mean to suspend the blade above the liquid in the 'fog' for the initial cool down?
 
aarongough said:
When you say 'use the vapor phase' you mean to suspend the blade above the liquid in the 'fog' for the initial cool down?
Click to expand...

Exactly. The vapor will average about -95F where the liquid phase is about -320F. Don't get me wrong; still a lot of heat to extract between those temps so major boil off is inevitable.
 
Andy Lewis said:
Exactly. The vapor will average about -95F where the liquid phase is about -320F. Don't get me wrong; still a lot of heat to extract between those temps so major boil off is inevitable.
Click to expand...

Thanks mate! I'l have to look into that more soon!
 
Ok, well all the blades are heat-treated. They've also been sand-blasted and had their identifying engravings covered so they're now indistinguishable from one another.

They blades were then honed along the edge until they were all equal thicknesses at the very edge before starting the testing.

First test, sharpening times! I got 4 of 6 blades sharpened up tonight, and the overall sharpening times have gone up significantly compared to the last test. So far the blades have all been closer to the 9 minute range than the 6 minute range I saw last time! I'll finish sharpening them up tomorrow...

Out of curiosity I tried my hardness testing files on the test blades before I sand-blasted them. I don't really hold much stock in the accuracy of those things, but it seems there is not a knife in this batch that is below 60HRC. Testing the first batch of blades yields much more bite from the files, but that may well be down to surface decarb. I'm getting all the blades hardness tested this friday, I'll be very interested to see the difference between the two batches!

EDIT: Here they are, test blades #7 thru #12:
MpNbuy2l.jpg


Note that the O1 blade is shorter than the others, and therefore I know which one it is. Not ideal really but that blade was my last piece of O1 unfortunately.
 
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I just had a chat to Advanced Technical Products, the company that makes ATP641, they were very helpful!

They said that the reason I saw some decarb when using ATP641 in this instance was actually because the temperature was too low. ATP641 is designed to the higher austenitizing temperatures seen when using stainless.

They recommended I switch to ATP11 or ATP304 both of which are specifically formulated to work with tools steels rather than stainlesses. Just thought this infor might be useful for others out there using ATP anti-scale compounds!
 
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