Steel testing underway...
- Thread starter aarongough
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The blade of that knife is bent into a pretzel unfortunately. I doubt there's any possibility I'd be able to get a section of it flat.
I'll have a go at it with the hardness testing files though and see if I can get a ballpark figure.
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Great! Thanks Mitch, I'll do one A2 blade at 62HRC, and one at about 60.5HRC
I was impressed the the gains gotten by the heat-treat you guys recommended, nearly 4 points HRC! I'm excited to see how it all works out once the temper is sorted!
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Mitch: what temperature do you temper your blades at after heat-treating them as we discussed elsewhere?
I've tempered one of the blades to 450ºF in an effort to get it down to 60HRC, but it's still at 63HRC. I am hesitant to go above 450ºF because I'm worried about tempered martensite embrittlement, but I know you've followed a similar regime to mine and tempered to 60HRC somehow...
-Aaron
I've tempered one of the blades to 450ºF in an effort to get it down to 60HRC, but it's still at 63HRC. I am hesitant to go above 450ºF because I'm worried about tempered martensite embrittlement, but I know you've followed a similar regime to mine and tempered to 60HRC somehow...
-Aaron
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Ok, so I may well have answered my own question. From reading a few different papers about Tempered Martensite Embrittlement is seems this is not an issue with high purity steels, and tools steels are generally of very high purity.
On that basis I'm doing a temper now on the 2nd A2 blade at 500ºF in order to get it down to 60HRC.
On that basis I'm doing a temper now on the 2nd A2 blade at 500ºF in order to get it down to 60HRC.
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So today felt like a bit of an unproductive day. Unfortunately I basically spent the last 14+ hours sitting around waiting for blades to temper... It's 3am now and I'm on my way home, ended up sleeping at the shop for a bit.
The A2 blades turned out to need a much higher than anticipated temperature for tempering, seemingly due to the really high initial hardness that we achieved. Getting the second blade down to 60HRC was a frustrating process of tempers at ever increasing temperatures.
Here is quick synopsis of the heat-treat that was used in the end for the A2 blades:
Stress Relieve:
Coat in anti-scale compound
Ramp to 1200ºF, hold 2 hours
Furnace cool to 900ºF
Cool in still air to ambient
Austenitize:
Ramp to 1740ºF @ 400ºF/hr, hold 20 minutes
Oil quench until no longer glowing, then cool in still air to room temperature
Sub-zero treatment in dry ice and isopropanol for 45 minutes
Temper:
360ºF - 64.6HRc
400ºF - 63.3HRC
425ºF - 62.5HRC
500ºF - 62.0HRC
550ºF - 61.5HRC
600ºF - 60.5HRC
I ended up with 2 blades, 1 at 62.5HRC, 1 at 60.5HRC.
I'm very, very, excited to see what these blades are going to be able to do. Testing will resume in ernest tomorrow afternoon.
The A2 blades turned out to need a much higher than anticipated temperature for tempering, seemingly due to the really high initial hardness that we achieved. Getting the second blade down to 60HRC was a frustrating process of tempers at ever increasing temperatures.
Here is quick synopsis of the heat-treat that was used in the end for the A2 blades:
Stress Relieve:
Coat in anti-scale compound
Ramp to 1200ºF, hold 2 hours
Furnace cool to 900ºF
Cool in still air to ambient
Austenitize:
Ramp to 1740ºF @ 400ºF/hr, hold 20 minutes
Oil quench until no longer glowing, then cool in still air to room temperature
Sub-zero treatment in dry ice and isopropanol for 45 minutes
Temper:
360ºF - 64.6HRc
400ºF - 63.3HRC
425ºF - 62.5HRC
500ºF - 62.0HRC
550ºF - 61.5HRC
600ºF - 60.5HRC
I ended up with 2 blades, 1 at 62.5HRC, 1 at 60.5HRC.
I'm very, very, excited to see what these blades are going to be able to do. Testing will resume in ernest tomorrow afternoon.
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That would be enough. Just to see if it is "close to 60hrc" or rather "close to 55hrc". That are "values" I give after testing with files.
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Ok, so last night I will admit I was a bit confused and worried about the hardness testing numbers I was seeing. The same sentiment was echoed by another forum member so I was spurred on to do a bit of digging around and see whether these numbers are really fishy or not.
Below is a simple visualization I put together of the heat-treatment details for the A2 as well as the tempering results:
You cane see that the austenitizing temperature that was used was the one that gave the highest as-quenched hardness, add very fast quench and the sub-zero treatment to that and that blade would have been VERY hard before the temper.
The results that I was seeing after the different tempers have been graphed against the curves that Uddeholm provide. You can see that the results I got reflect the curve quite nicely, they're just 1 point or so higher.
After seeing this my worries are pretty much calmed. We had to temper higher because of our higher initial hardness, the graph shows the same phenomena for different austenitization temperatures quite clearly.
I'll be double checking the calibration of my hardness tester, and the hardness of the blade once I get to the shop, but I don't think the numbers are an error at this point. Quite a relief!
Below is a simple visualization I put together of the heat-treatment details for the A2 as well as the tempering results:
You cane see that the austenitizing temperature that was used was the one that gave the highest as-quenched hardness, add very fast quench and the sub-zero treatment to that and that blade would have been VERY hard before the temper.
The results that I was seeing after the different tempers have been graphed against the curves that Uddeholm provide. You can see that the results I got reflect the curve quite nicely, they're just 1 point or so higher.
After seeing this my worries are pretty much calmed. We had to temper higher because of our higher initial hardness, the graph shows the same phenomena for different austenitization temperatures quite clearly.
I'll be double checking the calibration of my hardness tester, and the hardness of the blade once I get to the shop, but I don't think the numbers are an error at this point. Quite a relief!
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Ok! I have just re-checked my hardness tester.
Measuring the 63.7HRC test block = 63.6HRC
Measuring the 46.5HRC test block = 46.8HRC
The A2 blade #2 tested at 60.3HRC. I think that's confirmation that the numbers are not incorrect!
Measuring the 63.7HRC test block = 63.6HRC
Measuring the 46.5HRC test block = 46.8HRC
The A2 blade #2 tested at 60.3HRC. I think that's confirmation that the numbers are not incorrect!
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Just had a go at it. The O1 forge blade seems like it's around 55HRC at the section that bent strangely. The section that stayed straight feels a bit below 60HRC.
Hope that's helpful!
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Ok guys! Well unfortunately I didn't get near as far today as I'd hoped (that's getting to be a bit of a theme!)...
I ran a series of the edge retention tests cutting sisal rope, but unfortunately the numbers were coming out very different between runs, very noisy. I still haven't worked out why this is (or why it worked fine the first time round). It may simply be that it's too subjective and maybe I'm more or less sensitive now that I was as was suggested previously.
I experimented with a couple of things to try to find another test that was more repeatable and hopefully less subjective.
Basically what I'm doing now is cutting corrugated cardboard into strips (with the corrugations), stopping every 20 cuts and testing the edge on notebook paper. When a blade was failing the sisal rope test it was still fully capable of shaving hair, by the time the blade is failing this test it is visibly rolled and clearly not shaving hair anymore. The notebook paper test is done by starting a slicing cut at a sharp section of the blade (near the ricasso), then moving toward the tip during the cut. The blade fails the test once it has a section that does not cut, and instead either tears the paper or skates across the paper.
The cutting of the cardboard is focused into a 1" wide area halfway up the blade, I hold the knife by amping up on the blade with my thumb alongside it, and make sure that the cardboard is touching the tip of my thumb for the majority of the cut.
The cardboard I'm cutting is prepared into 5.5" wide 'planks'. Therefore we can calculate the amount of cardboard cut simply by multiplying the width by the number of cuts.
I've done a couple of runs so far and the numbers coming out are far more consistent between runs than what I was seeing with the sisal rope and phonebook paper test. Right now the best blade is cutting about 770" (64 feet!) of cardboard before failing the test, the worst is consistently only cutting around 165" (13 feet).
I'm going to do as many runs as I can stand to do of the cardboard test the next time I'm back in the shop. Larger sample size is always good to help iron out any subjectivity.
After that's sorted I'll be moving on to the destructive tests:
• Tip strength test
• Edge impact strength
• Break test
I ran a series of the edge retention tests cutting sisal rope, but unfortunately the numbers were coming out very different between runs, very noisy. I still haven't worked out why this is (or why it worked fine the first time round). It may simply be that it's too subjective and maybe I'm more or less sensitive now that I was as was suggested previously.
I experimented with a couple of things to try to find another test that was more repeatable and hopefully less subjective.
Basically what I'm doing now is cutting corrugated cardboard into strips (with the corrugations), stopping every 20 cuts and testing the edge on notebook paper. When a blade was failing the sisal rope test it was still fully capable of shaving hair, by the time the blade is failing this test it is visibly rolled and clearly not shaving hair anymore. The notebook paper test is done by starting a slicing cut at a sharp section of the blade (near the ricasso), then moving toward the tip during the cut. The blade fails the test once it has a section that does not cut, and instead either tears the paper or skates across the paper.
The cutting of the cardboard is focused into a 1" wide area halfway up the blade, I hold the knife by amping up on the blade with my thumb alongside it, and make sure that the cardboard is touching the tip of my thumb for the majority of the cut.
The cardboard I'm cutting is prepared into 5.5" wide 'planks'. Therefore we can calculate the amount of cardboard cut simply by multiplying the width by the number of cuts.
I've done a couple of runs so far and the numbers coming out are far more consistent between runs than what I was seeing with the sisal rope and phonebook paper test. Right now the best blade is cutting about 770" (64 feet!) of cardboard before failing the test, the worst is consistently only cutting around 165" (13 feet).
I'm going to do as many runs as I can stand to do of the cardboard test the next time I'm back in the shop. Larger sample size is always good to help iron out any subjectivity.
After that's sorted I'll be moving on to the destructive tests:
• Tip strength test
• Edge impact strength
• Break test
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Thanks.
Are you planning to do additional tempering to A2 steel? After the 600F temper? This temper removed much percentage of retained austenite, and changed it into some kind of carbides. Additional tempering in 360F wont hurt.
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Interesting question Idaho, really made me think!
My understanding is that any Retained Austenite transformed by the temper would have been converted into either martensite and then tempered, or it would have converted to un-tempered martensite during the cool from the temper. In the second case it would need to be tempered by the following temper cycle.
Technically you're correct in that there should have been two temper cycles at 600ºF, that's a good catch. However I think I'm probably saved by the fact that I had previously tempered at 550ºF, and that the step to 600ºF was only a small one. Also hopefully by that point there would have been hardly any retained austenite left after our fast quench, sub-zero treatment and multiple tempers.
We shall have to wait and see!
Last edited:
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Well, I'm kind of at my wit's end with the edge retention testing... The numbers are coming out very inconsistent this time and I'm really not sure why. Here are the numbers I have so far:
As you can see there's a LOT of noise in those numbers. Some blades are jumping up and down between runs by as much as 50%. So far that is no so much data as it is noise...
Does anyone have any suggestions? There's really 2 things I need:
1) A consistent, reasonable, and hopefully aggressive, medium for dulling the blades (I've been using cardboard all from the same type of boxes)
2) A reliable and objective way of testing the sharpness of a section of the blade
Until now I've been cutting notebook paper as the sharpness test, once the blade started skating/tearing it was considered to have failed.
If I can't work out a way of getting consistent numbers for edge retention then I will have to abandon that part of the test and move on. Bad numbers are worse than no numbers in my opinion.
Code:
[FONT=Courier New]
Blade Run 1 Run 2 Run 3
7 140 110 40
8 20 30 180
9 20 30
10 40 130
11 90 30
12 40 30
[/FONT]As you can see there's a LOT of noise in those numbers. Some blades are jumping up and down between runs by as much as 50%. So far that is no so much data as it is noise...
Does anyone have any suggestions? There's really 2 things I need:
1) A consistent, reasonable, and hopefully aggressive, medium for dulling the blades (I've been using cardboard all from the same type of boxes)
2) A reliable and objective way of testing the sharpness of a section of the blade
Until now I've been cutting notebook paper as the sharpness test, once the blade started skating/tearing it was considered to have failed.
If I can't work out a way of getting consistent numbers for edge retention then I will have to abandon that part of the test and move on. Bad numbers are worse than no numbers in my opinion.
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No idea on dulling medium.
But for sharpness testing - how about "cutting weight"?
You build a balance weight with uneven arms. On longer arm you place a specific weight. On the other arm - you mount or place a piece of string/line/other cut material.
When force needed to cut the string is larger then counterweight, cutting action will lift counter weight. Ergo - at this moment blade is dull.
But for sharpness testing - how about "cutting weight"?
You build a balance weight with uneven arms. On longer arm you place a specific weight. On the other arm - you mount or place a piece of string/line/other cut material.
When force needed to cut the string is larger then counterweight, cutting action will lift counter weight. Ergo - at this moment blade is dull.
chiral.grolim
Universal Kydex Sheath Extension
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Please pardon another dumb question: You did clean the edges (strop on your pants or other cloth to remove build-up of debris) before each slice of notebook paper, yes? And you are cutting the paper at approximately the same angle each time? I know that these are simple/obvious points, but numbers like that point to a key oversight...
Again, just following along. Thank you.
Again, just following along. Thank you.