The Edge of Darkness.

Mark Barone

Mark Barone

Well-Known Member
I notice when I pull my blade out of the kiln, a mm or so of the edge loses its red color quickly before it hits the quench. . Is that a problem? Is my edge too thin? There is about dime width.
 
Good morning, Mark. How does the edge preform after your HT?
That might not be a problem because the whole purpose of quenching is cooling the steel fast enough to avoid the re-transformation of the steel molecules from FCC (face centered cubic or austentie) to BCC (body centered cubic or ferrite). Depending on the steel, and how long it takes to get into your quench, what you might be actually be doing in the quench is cooling the rest of the steel quickly so that it doesn't re-heat the edge.
I think this question might be related to the recent discussions on plate quenching thinner blades that are made from steels that are supposed to be oil quench steels.
 
billyO said:
Good morning, Mark. How does the edge preform after your HT?
That might not be a problem because the whole purpose of quenching is cooling the steel fast enough to avoid the re-transformation of the steel molecules from FCC (face centered cubic or austentie) to BCC (body centered cubic or ferrite). Depending on the steel, and how long it takes to get into your quench, what you might be actually be doing in the quench is cooling the rest of the steel quickly so that it doesn't re-heat the edge.
I think this question might be related to the recent discussions on plate quenching thinner blades that are made from steels that are supposed to be oil quench steels.
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They perform well short term so far. I haven’t been experienced in testing hardness. I think I am getting more concerned because I sold a few.
 
How are you observing that? I mean are you walking to your quench tank? Or pausing to study the blade?

When I quench, there is no messing around and no time to observe things like that. It's out of the kiln and plunged into the quench in one fluid motion.

You don't need to be crazy or recklessly fast when quenching, but generally when it comes out of the kiln, it should be heading for the quench asap.
 
I would have to agree with John , after reading this I had to see what my the time elapse time is , from my oven to by tank is less then 2 seconds.
 
Freds Edge said:
I would have to agree with John , after reading this I had to see what my the time elapse time is , from my oven to by tank is less then 2 seconds.
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Freds Edge said:
I would have to agree with John , after reading this I had to see what my the time elapse time is , from my oven to by tank is less then 2 seconds.
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J. Doyle said:
How are you observing that? I mean are you walking to your quench tank? Or pausing to study the blade?

When I quench, there is no messing around and no time to observe things like that. It's out of the kiln and plunged into the quench in one fluid motion.

You don't need to be crazy or recklessly fast when quenching, but generally when it comes out of the kiln, it should be heading for the quench asap.
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no My quench tank is inches from my kiln. probably too close. I really just noticed it the last time o went to quench as I was pulling it out. im Also trusting my gauge on the Paragon
kiln I have.
 
Another thought , is your edge up or down , this can make a difference as your floor can act as a heat sink.
 
opaul said:
Explain this one to me.
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There's a lot to that one liner.... There is a lot of interaction between heat, mass, and how a particular items "holds" or allows heat to migrate and/or escape. The metallurgy answer is that heat dissipates equally in all directions from hot to cold. I choose to view, and use it in another way..... as it applies to what we do in Bladesmithing, and/or the heat treating of blades..... heat always travel up, if all things are equal.

For my purposes, when dealing with heating and cooling blades, things are not equal. There is always a thinner edge section, and a thicker/heavier spine and/or ricasso section. That thicker/heavier spine and/or ricasso section will "suck" heat away from a thinner edge section (its a "heatsink"), until things are equalized. (that's along the lines of what Fred is talking about....right Fred?)

Let's say I am using a torch for a differential heat treat....which I routinely do. How I hold the blade while heating plays a significant role in the ease or difficulty of my task. I hold the blade with the edge up, and heat the spine area just until I can start to see color in a dim environment. Then I concentrate the torch flame just below the blade's edge (edge is facing up), and work until I achieve the desired temp. As I am arriving at the desired temp, I flip the blade edge down, then a few more swipes with the flame, and edge down onto the "limiter plate" in my quench tank. I understand that not everyone differentially heat treats.... but that is a way to help explain things.

Here's the part that is likely of interest to most who are having issues....regardless of what your heat source is.... the portion you wish to harden, whether that be the edge or the entire blade, must be at the hardening temp WHEN IT HITS THE QUENCH. I deal with this problem almost everyday via phone or email.... people have issues hardening, and long story short..... they heat a blade to temp, then walk several steps/feet to their quench tank.... and quench. The issue is...by the time they get from their heat source, to the tank, and quench, the blade has cooled significantly below the required temp, and they don't get full hardening. It's amazing just how difficult it is to get this concept through to some folks. :)

OK, all that being said, on to Mark's question. The easy answer is that I believe the edge(s) are likely too thin. Remember.... a thin cross section will heat more rapidly, but will also look heat more rapidly, then thicker sections/areas. IF you are setting a heat treat oven at the specific hardening temp for a given steel, then chances are, that the steel has cooled too much, even if the quench tank is just inches away....you still have to pull the blade out of the oven, and it's going to start cooling as soon as you open the oven door. Make sense? So how do we overcome this??? It's a guessing game in the beginning..... heat the blade above your desired temp, by setting your oven temp higher then the hardening temp for the given steel type. How much? That depends on many factors..... from room temp, to how far away the quench tank is, to the time of year is your shop isn't heated to a constant temp. Time, and experimentation will teach you. Circumstances differ in every shop, so there is no "one size fits all answer". You have to deal with your own variables and work past them to get where you need to be. I would also recommend leaving blade a bit thicker at the edge(s). It's not uncommon for me to leave edges as thick as a nickel.... or possibly even more. Remember... I operate off the principle.... I can always remove material if needed....but once it's gone, I can never put it back. ;)

Personally, I don't use a heat treat oven for hardening heat.... because I have a salt tank, that offers me far more control then I can achieve with an oven, along with other benefits.
 
The limiter plate is a plate or other object that only allows your blade to enter into the oil so far. For example, with a differential HT when you put the blade into the oil, edge first, it does not allow you to dip the knife all the way to the spine.
 
Pretty much what Chris said..... Mine is aluminum plate, punched full of holes, with 1/4-20 carriage bolts on each corner, heads down, allowing to raise the plate up/down for various depths.

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Chris Railey said:
Not to jack the thread but how accurate are the testing files in general? I have considered getting some.
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Chris...I actually do not know. I have a rockwell hardness tester. I personally would not want to do heat treating without some means of testing...especially on blades that are being sold. Perhaps experienced guys that have proven their process do not need to test. Since a Rockwell tester is something I had left over from contract machining days, and was over 1K$, I recommended files.
 
The files have a bit of a learning curve, but are not difficult. I would consider them an "in the ballpark" kind of thing rather then a "dead nuts on" thing. :) I fall into what Ted was talking about..... I used to pay the local community college to test my blades.....but but it became so predictable, I was just wasting money paying for the testing. NOW...that being said, I do have a set of the hardness files, and I do use them when I am working up the heat treat on a new steel type. But these days, it's not all that often. Last time I used them was when I was working up 80CRV2, and they were very helpful.

I think for me, I used to get so frustrated at knife shows, when someone would be looking at a knife, and ask the exact Rc hardness.... and I would always say XX to XX, indicating a 2 point variance, and no matter what numbers I said, the response was .... well, if it's not Rc XX (usually something stupid like 65 or higher) I don't buy it. While hardness testers have their place, I believe far too many depend solely on a number in assessing their heat treating quality...... I don't mind saying..... I developed sort a a chip on my shoulder for hardness testers. ;)
 
EdCaffreyMS said:
The files have a bit of a learning curve, but are not difficult. I would consider them an "in the ballpark" kind of thing rather then a "dead nuts on" thing. :) I fall into what Ted was talking about..... I used to pay the local community college to test my blades.....but but it became so predictable, I was just wasting money paying for the testing. NOW...that being said, I do have a set of the hardness files, and I do use them when I am working up the heat treat on a new steel type. But these days, it's not all that often. Last time I used them was when I was working up 80CRV2, and they were very helpful.

I think for me, I used to get so frustrated at knife shows, when someone would be looking at a knife, and ask the exact Rc hardness.... and I would always say XX to XX, indicating a 2 point variance, and no matter what numbers I said, the response was .... well, if it's not Rc XX (usually something stupid like 65 or higher) I don't buy it. While hardness testers have their place, I believe far too many depend solely on a number in assessing their heat treating quality...... I don't mind saying..... I developed sort a a chip on my shoulder for hardness testers. ;)
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Haha...on getting asked about blade hardness at shows.....I remember Bing and I talking between customers about how many times someone would pick a knife up and after a bit say, "What's the hardness?" (certainly expecting a number from the Rc scale). We started responding with random numbers off the brinell scale just to confuse them. We got some very odd looks. :D
 
EdCaffreyMS said:
The files have a bit of a learning curve, but are not difficult. I would consider them an "in the ballpark" kind of thing rather then a "dead nuts on" thing. :) I fall into what Ted was talking about..... I used to pay the local community college to test my blades.....but but it became so predictable, I was just wasting money paying for the testing. NOW...that being said, I do have a set of the hardness files, and I do use them when I am working up the heat treat on a new steel type. But these days, it's not all that often. Last time I used them was when I was working up 80CRV2, and they were very helpful.

I think for me, I used to get so frustrated at knife shows, when someone would be looking at a knife, and ask the exact Rc hardness.... and I would always say XX to XX, indicating a 2 point variance, and no matter what numbers I said, the response was .... well, if it's not Rc XX (usually something stupid like 65 or higher) I don't buy it. While hardness testers have their place, I believe far too many depend solely on a number in assessing their heat treating quality...... I don't mind saying..... I developed sort a a chip on my shoulder for hardness testers. ;)
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I am OK with a ballpark figure. I really want to use it to dial in or perhaps refine my current HT routines. I have no intention of getting obsessive with hardness testing. I am currently starting to use some 80crv2 and man you were right ED. It takes a good thin edge and in my preliminary tests holds it well. I just want to have a little more information about my results so I was thinking on files.
 
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