More 1084 weirdness

JTknives

JTknives

Blade Heat Treating www.jarodtodd.com
Joined
Jun 11, 2006
Messages
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So I got another batch of 1084 blades that acted up during heat treat. The weird thing is I could tell right away during the first quench that something was up. After you have done as many blades as I have you have a feel for how a quench feels. By this I mean the tongs have a vibration to them as the oil quenches the steel. Hard to explain but with every steel that has failed to harden in parks 50 it has felt different. You can’t feel the turbulence as strongly and the blades come out with a black skin that does not wipe off. I attribute this to the steel not converting to martensite and the scale not popping off which disrupts the vapor jacket. But that’s just a theory.

Anyways here is the blades in question. I these blades these are full of soft spots. I have come across this before in the past and you could see them after surface grinding. We did a long clean up grind so we could have room for testing a few times during tempering. Well after we tested the first one at around 37rc we tested on both ends of the grind area. Some had a large swing in hardness and Others did not not. On blade measured 63 on one end and 53.5 on the other end, probably about 1/4” apart. I have included a few close ups of the test marks and you can see the drastically different depths of dimples. I have asked the customer to look for his order number so I can verify where it’s said to have come from. So just to be clear I’m not pointing fingers at anyone. I’m just posting these pictures to maybe start a conversation about this issue and how we can solve it. Yes these where normalized and quenched at the industry’s recommended standard temps.



Photo%20Nov%2004%2C%204%2001%2010%20PM.jpg


Photo%20Nov%2004%2C%204%2002%2004%20PM.jpg
 
You should start with some basic Rockwell hardness testing requirements. The surfaces have to be flat. You have to be sure you have ground fully through decarb. The surface finish can’t be too coarse. You have to test at least 2.5 diameters of the indentation apart.
 
Larrin said:
You should start with some basic Rockwell hardness testing requirements. The surfaces have to be flat. You have to be sure you have ground fully through decarb. The surface finish can’t be too coarse. You have to test at least 2.5 diameters of the indentation apart.
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All blades are checked for flatness and any bow goes up so it seats on the anvil under the diamond. If I had to guess I would say the test area is probably .01-.02 deep below surface. I had not seen the 2.5x diameter spacing before. I know I have tested really close together before and have not seen it affecting the reading but I will keep that in mind. Would that be more critical on softer material as more material is displaced upwards? I think it’s a 220grit belt I use to make the test area on a 7/8” wheel.

99.9% of the time everything goes smoothly and all RC readings are what we expect and consistent. But that .1% seams to be this carbon steel we get from time to time and it just won’t behave. I’m going to try a 1900° soak on a blade and see if that solves it. It did nothing to the last blades we got but those where from eBay.

P.S. is there a SOP on hardness testing that I can get ahold of?
 
JTknives said:
All blades are checked for flatness and any bow goes up so it seats on the anvil under the diamond. If I had to guess I would say the test area is probably .01-.02 deep below surface. I had not seen the 2.5x diameter spacing before. I know I have tested really close together before and have not seen it affecting the reading but I will keep that in mind. Would that be more critical on softer material as more material is displaced upwards? I think it’s a 220grit belt I use to make the test area on a 7/8” wheel.

99.9% of the time everything goes smoothly and all RC readings are what we expect and consistent. But that .1% seams to be this carbon steel we get from time to time and it just won’t behave. I’m going to try a 1900° soak on a blade and see if that solves it. It did nothing to the last blades we got but those where from eBay.

P.S. is there a SOP on hardness testing that I can get ahold of?
Click to expand...
Using a hollowed out section is not flat. The effect of testing too close to other indents is easy to see. Try it out and see what you get. The most likely explanation for your low readings is that you did not grind all the way through the scale/decarb. You should surface grind both sides and test again.

You can read ASTM E18 for more information on hardness testing. Speaking of which, it says 2.5 diameters from the edge of the specimen, and 3 diameters from other indents.
 
I was thinking for Rc testing you had to grind BOTH sides flat and smooth. Flat, not a "hollow grind" like you have. Try that blade again, but first do a full smooth flat grind on both sides with 220 grit.

I suspect with the scale still on opposite side and only a small hollow ground on the top side the dimple could be a tad different depending on how the scale on bottom side pressed into anvil. I do not know. I've just always ground both sides smooth and flat for testing. It will be VERY interesting to see the results if you would grind both sides smooth and flat for testing.
 
Last edited:
Guys , he get good/expected result on other steel, don t forget that . . . .
 
Larrin said:
OK I won't forget.
Click to expand...
Did you look in his picture ? BW , I learn to use Rockwell hardness tester 35 years ago . I agree that most accurate result will give flat and polished surface , i agree that there is maybe more decarb. BUT here difference is 30 Rockwell and that in his case can not be addressed to 220 grit finish and hollow grind , maybe two-three point .On some blank he get 60-63 Rockwell , how you will explain that ?
 
Natlek said:
Did you look in his picture ? BW , I learn to use Rockwell hardness tester 35 years ago . I agree that most accurate result will give flat and polished surface , i agree that there is maybe more decarb. BUT here difference is 30 Rockwell and that in his case can not be addressed to 220 grit finish and hollow grind , maybe two-three point .On some blank he get 60-63 Rockwell , how you will explain that ?
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With a 30 Rc reading is only a couple mm from a 60 Rc reading, an issue with decarb or the final heat treatment would be the most likely culprit. It would be difficult to produce steel with such an inconsistent structure that an even heat and quench would lead to a soft spot like that.
 
JTknives said:
So I got another batch of 1084 blades that acted up during heat treat. The weird thing is I could tell right away during the first quench that something was up. After you have done as many blades as I have you have a feel for how a quench feels. By this I mean the tongs have a vibration to them as the oil quenches the steel. Hard to explain but with every steel that has failed to harden in parks 50 it has felt different. You can’t feel the turbulence as strongly and the blades come out with a black skin that does not wipe off. I attribute this to the steel not converting to martensite and the scale not popping off which disrupts the vapor jacket. But that’s just a theory.

Anyways here is the blades in question. I these blades these are full of soft spots. I have come across this before in the past and you could see them after surface grinding. We did a long clean up grind so we could have room for testing a few times during tempering. Well after we tested the first one at around 37rc we tested on both ends of the grind area. Some had a large swing in hardness and Others did not not. On blade measured 63 on one end and 53.5 on the other end, probably about 1/4” apart. I have included a few close ups of the test marks and you can see the drastically different depths of dimples. I have asked the customer to look for his order number so I can verify where it’s said to have come from. So just to be clear I’m not pointing fingers at anyone. I’m just posting these pictures to maybe start a conversation about this issue and how we can solve it. Yes these where normalized and quenched at the industry’s recommended standard temps.



Photo%20Nov%2004%2C%204%2001%2010%20PM.jpg


Photo%20Nov%2004%2C%204%2002%2004%20PM.jpg
Click to expand...

this is why I have not started a heat treating business myself. If I haven’t controlled the process from purchase to final temper, too much can go wrong. I heat treat one other person’s blades, and he uses the same supplier as me, and uses stock removal only. Watching this thread closely.
 
JT is a very knowledgeable HT'er and knifemaker. JT HT's more blades in a month than I do in a couple of yr.

I'm looking forward to JT removing scale on both sides with a good flat grind on both sides and retesting. It might not make any difference, but it would be nice to try.
 
Ken H> said:
JT is a very knowledgeable HT'er and knifemaker. JT HT's more blades in a month than I do in a couple of yr.

I'm looking forward to JT removing scale on both sides with a good flat grind on both sides and retesting. It might not make any difference, but it would be nice to try.
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I can bet that he will get almost same readings under condition that there is no decarb. left . Ken , he test in middle of that hollow grind , diamond indenter is very small , technically he test on flat surface ..... He test in this way every knife he HT and he GET excepted result ...... how come ?
RgDOWWX.png
 
Two comments:
1) i would tend to put a LOT if weight on JTs practical experience and “feel” for the process. If something is amiss with the microstructure of the steel, given the energies involved in the transformations, i would not be at all surprised if different types of vibrations are generated.

2) if it ends up helping to inform the situation, i know a person who runs a lab with an ESCA. I might well be able to get that elemental analysis done on a sample...
 
Natlek said:
I can bet that he will get almost same readings under condition that there is no decarb. left . Ken , he test in middle of that hollow grind , diamond indenter is very small , technically he test on flat surface ..... He test in this way every knife he HT and he GET excepted result ...... how come ?
Click to expand...
Oh, I totally agree with JT's experience and knowledge, and with the dimple in the center of the hollow grind I'm sure it will give a good reading. I'm more concerned about the scale on the other side not providing a solid consistent surface, perhaps causing the blade to rock a tad, or perhaps the bottom scale compressing a bit which might cause the Rc reading to vary a bit. As I've said before I am NOT an expert by any means. 90% of my knowledge has been gleaned from the sharing of great folks on this and other forums.
 
Natlek said:
I can bet that he will get almost same readings under condition that there is no decarb. left . Ken , he test in middle of that hollow grind , diamond indenter is very small , technically he test on flat surface ..... He test in this way every knife he HT and he GET excepted result ...... how come ?
RgDOWWX.png
Click to expand...
JT is one of the dudes I follow and listen to every word he posts. But can you tell me from the picture he's in the perfect down ward indention?
 
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