So, how hard is "not fully hardened"?

B

bkshafer

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Jul 31, 2004
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With all the talk of improper quench oils we hear a lot that some steel (like the 10XX) will not fully harden when quenched in say canola instead of parks 50. But how hard is not fully hard? How would the hardness of say 1095 quenched in canola oil compare to 5160 or O-1, also quenched in canola? And how much harder would 5160 or O-1 be when quenched in proper oil instead of canola?

Brian
 
There is no simple answer to that.

If you run at half the speed of someone else, you can say you went half as far.
If you put $10 worth of gas into your tank instead of $20 worth, you can say you filled it half as full.
.....But, if you quench a blade in oil that is half as fast as Parks#50. it doesn't get half as hard.
It gets a mixture of pearlite, retained austenite, some martensite....but the hardness is not a linear product of these things. What you get is a softer blade with less edge retention, and most likely some other less than desirable attributes. While we often refer to the hardness in Rockwell C terms ( Rc57-59) that is only a reading used to describe hardness, but it isn't a linear scale of the hardness of a blade.

If you have sex , you are not a virgin anymore. It doesn't matter how long you have it or how good it was....virginity is one of those "You are ,or,You aren't" things.
Blade hardness isn't a black or white issue,like virginity,...... there is room for some level of degree, but not much room.

Mostly what you get with less than adequate quenches is a trade-off in the quality of the blade. I think the word QUALITY is a better term than hardness to describe the reason to use the proper quenchant. One might be tempted to make a blade that was less hard, but few would want to make a blade that was lower quality.

Stacy
 
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One might be tempted to make a blade that was less hard, but few would want to make a blade that was lower quality.

Stacy[/QUOTE]

Well said Stacy.
Ken
 
If one blade is underhardened, to ...say Rc 58, through underheating, or
improper quench, and a second blade is properly heated and quenched to Rc 64, then drawn back to Rc 58....you have two blades @ Rc 58....but they're far from
equal. The first is a mix of structures, as Stacy discribed. The second will be around 90-95% martinsite which is what you want for edge retention, and resistance to
edge deformation.

.02.....
 
Stacy I read your post and i agree 100% correct. Why drive a toyota tundra when you could drive a real truck like a dodge . kellyw
 
HEY! I happen to love driving my Tundra!:D

When It's all said and done testing, preferably against a known blade is very helpfull. I've got a ATS-34 kitchen knife that was heat treated by Paul Bos that I use to compare when doing cutting test.
 
For 1095 blades in canola it can average as high as 62-64, never have heard of one getting to 65-66 though. A friend of mine has had some tested.

I'm not going to make any value judgments on it. That's up to you. However, there are a lot of variables involved, variance in carbon content, temps., soak times, geometry etc. Although, as I recall, he did seem to have the best results quenching from the high end of the specified spectrum with a substantial soak.

You can always try water.
 
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Brian,
I neglected to answer the second and third part of your question.

1095 is a shallow hardening steel, and needs to be cooled down much faster than 5160 or O-1. 5160 is a deep hardening steel, and can be fully quenched in most any oil. O-1 is very deep hardening, and can be quenched in oil, grease, lard....anything resembling an oil quenchant.
1095 has .9 seconds to get down below 1000F from the moment it hits the oil. It takes a fast oil to do this. As far as I know, no simple oil quenchant does this ( canola, peanut, ATF, etc.) Parks #50 and similar fast oils will just squeak by. Water and brine are the only things faster....and may cause some severe problems with warp and cracking if not used exactly right.

As said 1095 needs to be below the pearlite nose in .9 seconds. 5160 gives you 5 seconds to do the same. O-1 takes even longer and misses the nose at 7 seconds, and for comparison, A-2 has 7 minutes to get below 1000F.
So, if 1095, 5160 and O-1 were quenched identically in canola oil:
The 1095 might have some hardness on the edge, but would have a mix of structures in the rest of the blade, and even on the edge in places. No way to know what it will be, but it will be poor ,most likely.
5160 would fully harden and be a great blade if soaked at austenitization temp for about 5 minutes prior to quench.
O-1 would fully harden and make a great blade,too, but should be held at austenitization temp for about 7-10 minutes.

Hope that answers the rest of your questions.

Stacy
 
Russ Andrews said:
If one blade is underhardened, to ...say Rc 58, through underheating, or
improper quench, and a second blade is properly heated and quenched to Rc 64, then drawn back to Rc 58....you have two blades @ Rc 58....but they're far from
equal. The first is a mix of structures, as Stacy discribed. The second will be around 90-95% martinsite which is what you want for edge retention, and resistance to
edge deformation.

.02.....
Click to expand...

That's a great explanation for a total greenhorn like myself. :thumbup:
 
Stacy, your facts are spot on, but I question some of your assumptions and conclusions. I think that geometry also plays a key role in cooling rates etc., and that with thin blades from 1095, (1/8th inch or less), canola will harden them to a very high degree, edge to back. This is why I only use (or recommend) 1/8 inch (or less) 1095 with a canola quench. I would venture to say that it'll get around the pearlite nose in under .75 seconds. However, the tests my friend did from my previous post were thicker along the back, (3/16ths as I recall) and Rockwell tested in several places, not just along the edge. Once he worked it out, he consistently got 63-64 throughout the entire blade. I'd be surprised if Parks #50 does significantly better,... maybe only one (maybe two) Rockwell point, maybe... I think it's a lot of fuss and "hoopla" over such a small thing.

For even thicker blades from 1095, there's always water. :)

Another thing to consider with "alternative" (to water) quenching mediums like Parks #50 and canola oil is that, a slower quench is obviously less stress to the steel... too much stress, NOT good!
 
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Tai Goo said:
Stacy, your facts are spot on, but I question some of your assumptions and conclusions. I think that geometry also plays a key role in cooling rates etc. maybe... I think it's a lot of fuss and "hoopla" over such a small thing.
Click to expand...

I think small things create significant weakness in larger things. I agree that geometry plays a key role as well, however pockets of retained austenite are what we wish to avoid - not necessarily a target rockwell hardness. There is a great deal of evidence that shows the thicknesses and geometries we're discussing benefit from fast oils, including things such as vapor jacketing and stress reductions that other oils do not perform as well at.
 
I'll personally give you one Rockwell point,... if it makes you that happy. :)
 
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