Cru Forge V Toughness Testing

Moderately short soak times were used for all samples.

Did not use any step down for the cryo, just lowered slowly into LN2.

Right now we are looking for discernible patterns of behavior. Based on what we see so far, there will be another round of tests.

Hoss
 
I have fast and medium quench oil, I want to get some AAA or equal, some where in the middle.

Hoss
 
Interesting that the slight increase of pre quench heating drops the hardness by that much. How does quench oil temperature play into this?
 
Here are the tempering results. The datasheet recommends 400-500°F, so I was wondering if tempering lower would end up with incredibly low toughness, similar to the overly high 1550°F austenitizing treatment. However, in this case there is a simple decrease in toughness with increasing hardness. Therefore, one can optimize the properties for a given knife by testing for the required hardness and toughness.

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Looks like a 350 temper would make a wicked cutter. Thanks for doing and sharing all of this.
 
Larrin, 400-425F is the tempering range that a number us use for CFV. The "get it hot, get it wet" theory holds that you should get 59-61 with those temps with the 1500F austenizing temp. I have been wondering for a while what would happen if you used the slightly lower austenizing temps like people have done with 52100? Are those toughness numbers based on the reduced size samples because they seem kind of low compared to what I can find with C notch numbers for O-1, 52100 and such.
 
jdm61 said:
Larrin, 400-425F is the tempering range that a number us use for CFV. The "get it hot, get it wet" theory holds that you should get 59-61 with those temps with the 1500F austenizing temp. I have been wondering for a while what would happen if you used the slightly lower austenizing temps like people have done with 52100? Are those toughness numbers based on the reduced size samples because they seem kind of low compared to what I can find with C notch numbers for O-1, 52100 and such.
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It does seem like the rule of thumb holds that the minimum austenitizing temperature required to achieve the target hardness should be used, outside of things like stainless steels. More testing is required to determine the optimum combination.

The toughness was tested on quarter-thickness unnotched charpy samples (2.5 x 10 x 55 mm rather than 10 x 10 x 55 mm). They should not be compared to full size c-notch numbers.
 
Larrin, I'm curious if you employed a soak while austentizing, like 10 minutes, or simply equalize/quench.
 
I measured the retained austenite of three broken charpy specimens from the three austenitizing temperatures. The two major types of measuring retained austenite are x-ray diffraction (XRD) and magnetic saturation, and perhaps in third place would be metallographic methods such as EBSD. XRD is the most commonly reported, so it has the benefit of being standard, on the downside there is some interpretation of the data required, and sample preparation, x-ray source, etc all impact the number so different labs can get different results. Magnetic saturation is very fast and is very consistent between different labs; however, the number is affected by anything nonmagnetic in the steel, not just retained austenite (RA is nonmagnetic). Magnetic saturation simply works by measuring how magnetic the sample is and comparing that to what is expected from a steel of the same size without retained austenite. Retained austenite measured with magnetic saturation is usually significantly higher for MS than XRD.

Anyway, here are the numbers:
1450°F - 12.3%
1500°F - 10.9%
1550°F - 12.4%

Generally, more retained austenite is expected with higher austenitizing temperatures, because that leads to more carbon and other alloy in solution which increases the austenite stability and lowers the Martensite start temperature (reducing it to below room temperature). Therefore, I'm not sure that the lower value at 1500°F is "real," and is more easily explained through experimental variation. The more important finding is that the retained austenite is not significantly higher at the 1550°F, so retained austenite is not making a large contribution to toughness differences between 1500 and 1550°F austenitizing temperatures. Also, if we assume that grain growth is slow at 1550°F, then that leaves plate martensite as the most likely cause of low toughness for the high austenitizing temperature condition.
 
Did you find heavy decarb on as-rolled samples..?
Were the RA test samples tested as quenched..?
 
Russ Andrews said:
Did you find heavy decarb on as-rolled samples..?
Were the RA test samples tested as quenched..?
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Charpy specimens were all ground to final dimensions, removing all decarb. RA samples were from broken charpy specimens, as stated in my description, which were fully heat treated, including tempering.
 
Are those RA level a bit high for a "simple" carbon steel with cryo?
 
jdm61 said:
Are those RA level a bit high for a "simple" carbon steel with cryo?
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I couldn't say since this is the first high carbon tool/alloy steel I've ever measured with magnetic saturation. With XRD it would probably be 5-7%.

Edit: Cementite has much lower magnetic saturation than iron and is likely contributing to higher values.
 
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Okay. 5-7% sounds more like that noble goal we seek.:D
 
jdm61 said:
Larrin, 400-425F is the tempering range that a number us use for CFV. The "get it hot, get it wet" theory holds that you should get 59-61 with those temps with the 1500F austenizing temp. I have been wondering for a while what would happen if you used the slightly lower austenizing temps like people have done with 52100? Are those toughness numbers based on the reduced size samples because they seem kind of low compared to what I can find with C notch numbers for O-1, 52100 and such.
Click to expand...


I haven't used any CFV yet, but I was going to test it at 1475 +/- 10f until I hit optimum hardness. I figured it would be optimum below 1480, like 1095, W2, 52100, and O1. I think Larrin and DevinT will let us know where the optimum ends up. I always thought get it hot and dunk was just not good enough,
 
There was a recent thread about toughness differences between transverse and longitudinal directions. A couple people offered the opinion that they thought the differences were insignificant between the two. As expected, the difference is quite large, and can be even greater with alloys with high impurity content or banding. The trends are essentially the same but the transverse values average about 60% of the longitudinal toughness. I have seen several knifemakers try to maximize material by cutting knives in different directions from sheet; I would recommend against this type of practice, especially if you would like to avoid broken tips.

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