Unusual Rc tests with W2

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Warren Krywko

Well-Known Member
After the Southern Alberta Hammer In, I did some tests on my W2 stock (Aldo's new batch) and found the sweet spot in my shop at 1460f austentize after normalization and grain refinement. As I was experimenting in 10f intervals, at 1470, there was a lot of inconsistency in the readings with a low of Rc66, and a high of Rc70.5. At 1480f, the overall Rc dropped to Rc64.

Averages were:

1440f, Rc63
1450f, Rc66
1460f, Rc68 (Consistent 67-69)
1470f, Rc68 (a lot of variance 66-70.5)
1480f, Rc64

Is there an explanation for the 1470f high reading other than equipment error? I am using a handheld tester, which is pretty accurate, but at the edge of its range it can be a bit less accurate. I have never had a reading that high before.
 
The outer limits of any test equipment are generally to be avoided, either high or low. Handheld testers are very persnickety in their use and are not accurate on thin sections. Some of Aldo's steels require extensive normalizing to get things to behave. Though it's generally considered to be a very small effect, happening to test on a large carbide cluster that was not dealt with through normalization could possibly cause such high readings. The cluster would have to nearly be visible with the naked eye, and you'd need a perfect storm of issues with normalization to make one, but anything is possible in the world of knives.
 
I know I have variance of Rc1.0 when I get down to about Rc50/51. It's pretty accurate in the low to mid 60s, so tester variance is a definite possibility getting up around 70. I was wondering about carbides, but there was a post on this that suggested it was not likely.
 
You are getting the same results as the rest of us (I don't have a tester...I cannot verify my results accurately...but I am using the same numbers as you and the others). Willie71 on another forum had the same results as well. 66-70.5 on Aldo's W2. 1460F hardening temp, soak for a few minutes. Crazy hard!!!!! Awesome steel. Warren, don't count those carbides out. My suggestion to Willie, and he was going to contact Kevin Cashen about this, was that the 70.5 readings are on top of carbides. Then Willie came up with the idea that maybe some excess carbon got trapped in the grain boundaries, causing the erratic readings. I wouldn't think that would be the case with an aust temp of 1460F, but I'm not complaining!!!!! Love the stuff. Triple tempers give the best Rc readings. That third temper seems to make the variance go from 1.5 Rc difference with one temper, to 1 Rc difference with 2 tempers, to .5 Rc difference with 3. Assuming everything went right, of course.

Oh, for crying out loud, R2D2, is that you? It IS you, it IS you! I thought, gee, another person with the EXACT SAME results as Willie!?!? Don't blame me. I'm an interpreter. I'm not supposed to know a power socket from a computer terminal.
 
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Samuraistewart, I am Willie71. This forum changed my user name to my actual name, and I don't know how to change it back lol!
 
I thought it was you! I saw you are in Sturgeon County, and went to bladeforums and saw Willie71 was from Sturgeon County. :) I was thinking, man someone else had the exact same results as Willie71 did!!!
 
Measuring hardness on top of a carbide won't generally get a reading from the carbide. It will just be pushed into the matrix, which is much softer, and the carbides are MUCH smaller than the diamond penetrator used for Rc testing. In a steel like W2, I don't know how you'd make a carbide or cluster big enough to cause interference like that. When hardness readings are taken for carbides, they are done with microhardness testing and the results converted to an approximate HRc reading, since that is what everyone is familiar with now. Can the 70 range numbers be repeated, or are they a one shot deal?
 
It was just one test in the series of 5 on the test coupon. As noted, there was much more variance in this heat treat than the lower temps. It might have just been equipment error. I could try another coupon at that heat treat and see what happens
 
Warren Krywko said:
Samuraistewart, I am Willie71. This forum changed my user name to my actual name, and I don't know how to change it back lol!
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It's that much cooler to know someone for who they really are, in my opinion. Keep your name!!!!

I'm interested in your findings with this steel... What type of thermal cycling are you doing previous to testing, if any?
 
I did 10 min at 1650, cooled to magnetic, 10min at 1550, cooled to magnetic, 10min at 1450, cooled to magnetic, 1200 for 1/2 hour and cooled to room temp. I unfortunately cannot recheck the coupon, or my 52100 for that matter, as the cat had a lot of fun playing with the steel coupons which were on a piece of paper with the specs listed for each piece. :49: I have no idea which piece is which anymore. I will try another piece at 1470f and see if it has a lot of variance too.
 
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Warren, do you find the 1200 degree soak necessary? How do you feel it's benefiting? Seems like the grain refining/thermal cycling would be more than enough to eliminate any stressors...
 
The 1200 isn't necessary. I probably should amend the cycle in the kiln. I was using it for 52100, but I don't think it's needed there either. I was following the cycles used by a well known maker who finishes the cycling with a 1200 soak.
 
The 1200F soak forms spheroidial carbides, which are easier to move around. Without the 1200 soak, you have lammelar pearlite, I think it is....which is fine for machining. The spheroid structure is just a joy to work with, tho....but entirely not necessary.
 
I repeated my 1470f austentize. I used the same normalizing program in the evenheat as the previous run, and without tempering, the numbers I got were:

64, 65, 66, 67, 62 low, 63, 66, 67, 68, 66, 66, 69 high, 66, 67, 66, 66, 68, 67.

I was unable to duplicate the 70.5 high on the previous test, so I will chalk it up to tester error. So, in my shop, with my equipment, 1460f is the sweet spot, and overall hardness and consistency goes down in as little as 10f up or down from there.
 
Very cool information! Really appreciate it! I wonder what a quench after each thermal cycle would do to consistency, if it would tighten it up at all or not?
 
I think that at 1470f, an excess of carbon is starting to get into solution, and the low areas are retained austentite, or carbon going into the grain boundaries. Someone correct me if I'm wrong please (Kevin Cashen??) At 1460f, the Rc#'s were within 1/2 point of each other over 5 readings. At 1480, there was variance, with overall lower numbers by a few points. I think this is caused by retained austentite.

On the other hand, a blade made out of W2 with the 1470 or 1480f heat treat "could" make a serviceable blade, tempered down to Rc60-62. It just won't be optimum. I can't get salt bath heat treat consistency with my kiln either, so I'm still not optimum. I did a kitchen knife at 1460f tonight with hamon. After 410f temper, I was Rc64, just a hair lower than I expected.

BTW, I'm doing the same testing for Hitachi white (very little info out there- 1450 gave me Rc67 average), 15N20, and 52100, the steels I work with the most. I am going to do O1 as well, as I do a few kitchen knives out of it. I need to optimize it before I do any more.
 
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Warren, Murray Carter is one of the most well known bladesmiths who had mucho experience with White and Blue steel. I found out his heat treat numbers some how some where, and wrote them down. For Blue Steel, which he is no longer working with, austenitizing temp is 1490F with a 392F temper. His White Steel is hardened at 1450F with a 356F temper.
 
I too found lower tempering temps are needed for Hitachi white steel. I find it's interesting since it tempers lower than W2 or 1095, considering how similar the composition is to 1095.
 
I always get very suspicious of the presence of BS when I see austenitizing or tempering temperatures listed in plus or minus of round numbers, as if one or two degrees either way could make a measurable difference. Can you believe that a 392°, or a 356° temper can measured and shown to be better or different than a 390° or 355° temper? Sorry, I don't buy it, and it makes me believe such numbers are just part of a hype presentation, whether it really is or not.
 
LRB said:
I always get very suspicious of the presence of BS when I see austenitizing or tempering temperatures listed in plus or minus of round numbers, as if one or two degrees either way could make a measurable difference. Can you believe that a 392°, or a 356° temper can measured and shown to be better or different than a 390° or 355° temper? Sorry, I don't buy it, and it makes me believe such numbers are just part of a hype presentation, whether it really is or not.
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Weather it makes a difference or not, I can't speak to. My personal feeling if I ventured a guess is it does not make a difference. The question for me is what device are they using to get that type of control and consistency? Household and toaster ovens won't hold that close, neither will heat treating ovens of any brand that I'm aware of. Heck, even my salts which will consistently keep my temps within a single digit range of my target temp won't hold right on. (I know you don't use high temp salts for tempering. :D)

How are they getting that kind of control?
 
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