Initial toughness Vs higher temper

My error - I should not have been typing "martensite" in the post. My main point was that this is not an issue with knives.
 
My feelings are:
Embrittlement ( of both types) isn't an issue because it really does not affect knife performance. You can detect it in a lab, and find it on charts, but in real world use - it isn't a significant issue.
 
Stacy E. Apelt - Bladesmith said:
My feelings are:
Embrittlement ( of both types) isn't an issue because it really does not affect knife performance. You can detect it in a lab, and find it on charts, but in real world use - it isn't a significant issue.
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Blades aren't breaking left and right, so it isn't an issue from that standpoint.

What gets me scratching my head is why anyone would take a high carbon steel blade and temper it down to 58 Hrc when it decreases both edge holding and toughness to do so.
 
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RX-79G said:
Blades aren't breaking left and right, so it isn't an issue from that standpoint.

What gets me scratching my head is why anyone would take a high carbon steel blade and temper it down to 58 Hrc when it decreases both edge holding and toughness to do so.
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Softer steel is cheaper to grind and sharpen.
 
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The posted 1095 graph shows a big drop in torsion after 325F => 1. torsion is more important for rotational tools (e.g. drill bits) than edge tools (e.g knives). 2. insufficient(I didn't read/find paper/article) microstructure data - as reason for this big loss in torsional toughness, thus whether it's applicable to knife ht or not.

RX, I agree HC edge tools with 58- rc is puzzling - maybe less is more :p nah
 
bluntcut said:
The posted 1095 graph shows a big drop in torsion after 325F => 1. torsion is more important for rotational tools (e.g. drill bits) than edge tools (e.g knives). 2. insufficient(I didn't read/find paper/article) microstructure data - as reason for this big loss in torsional toughness, thus whether it's applicable to knife ht or not.

RX, I agree HC edge tools with 58- rc is puzzling - maybe less is more :p nah
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I think this is arguable a torsional failure:

ba2qo.jpg
 
Saying that torsional failure doesn't mean nothing regarding knives it is something like saying that rockwell testing is not valid since your knife won't be penetrated by a diamond cone in normal use ;)

It is just the way we setup one test in order to measure the material behaviour in numbers.
You could make the same chart using the charpy impact scale and draw the same conclusions, showing the same dip in toughness for that tempering temperatures range, because no matter how you numbers it, it is still what happens to the steel microstructure.

While probably we shouldn't expect the knife exploding in normal use, at the edge micro level any loss in toughness means less edge stability.
Also i can't see why we should accept less than the optimal treatment for each steel. What's wrong in buying different optimal steels for different applications?
 
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Are there more than one such graph exists? Even if this graph is factual, what microstructure does it based on?

Somehow the whole edge tools & steel industries are ignorant of such torsional disaster in certain temper temperature range for all kind of hardened steels (deduction: if 1095, probably applicable to most steels with 0.9+%C) ... thus be skeptical of one graph/study/claim.
 
bluntcut said:
Are there more than one such graph exists? Even if this graph is factual, what microstructure does it based on?

Somehow the whole edge tools & steel industries are ignorant of such torsional disaster in certain temper temperature range for all kind of hardened steels (deduction: if 1095, probably applicable to most steels with 0.9+%C) ... thus be skeptical of one graph/study/claim.
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Sure. There are plenty of them. It is based on TME. Here's one for O1:

o1_torsional.jpg


4140:
113.jpg


I wouldn't call the industry ignorant. It seems to be well known and avoided by industry. Knife makers are a different story. But it is in Verhoven, on Wikipedia, etc. In industry, no one would select O1 steel for a job that would require tempering down to 58 Hrc, because O1 is brittle at 58 Hrc. If the toughness of what you'd hope O1 would be at 58 Hrc (but isn't) is desired, you'd pick 5160 or something like that.

TME is when the tempering temperature and time is especially hospitable to the formation of a certain type of cemetite (Widmanstatten needles or plates), and that cemetite in that amount makes the crystal structure more brittle.

You haven't heard of this?
 
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TME is not the same as the 1095 torsional loss graph above. TME affects toughness in general. 1095 TME is not between 325 and 400F, it's about 500-575F.

I am skeptical on torsional loss claim on HC (low or no Cr) when temper temperature range when steel precip is in transitional phase - i.e. sub 50nm dia cementites. Non-localize carbon diffusion taken place above 450F, hence cause cementites to coarsen. Lest not confuse reader by bring in steels with large RA% into discussion.
 
bluntcut said:
TME is not the same as the 1095 torsional loss graph above. TME affects toughness in general. 1095 TME is not between 325 and 400F, it's about 500-575F.

I am skeptical on torsional loss claim on HC (low or no Cr) when temper temperature range when steel precip is in transitional phase - i.e. sub 50nm dia cementites. Non-localize carbon diffusion taken place above 450F, hence cause cementites to coarsen. Lest not confuse reader by bring in steels with large RA% into discussion.
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You're reading a Celsius chart in Fahrenheit. Go to the top for F temps.

The narrow range for TME is 500-550°F, but in industry they give it a larger avoidance range - more like 400 to 600°. The graph demonstrates a loss in toughness that is coincidental with TME, but the graph shows the entire range of toughness vs. temp.

The rest of your post gets into some technicalities that I am not proficient enough to argue with. But TME takes an hour to form in the target temp range - just passing through it isn't an issue. That is why it is known as a tempering issue.


Here's a chart that shows the dips for both TME and later TE:

ih1006-htdr-fig1_lg.jpg



This is all old news to engineers.
 
Please keep discussion in context by show HC (low/no alloy) steels. 4140 is low carbon alloy steel, while O1 is HC high alloy steel. I would appreciate to see chart show similar loss of torsional toughness between 325F-400F (~155-200C). And please let's not broaden the discussion by bring in steels with applicable secondary tempering range (which mostly very high alloy%).
 
bluntcut said:
Please keep discussion in context by show HC (low/no alloy) steels. 4140 is low carbon alloy steel, while O1 is HC high alloy steel. I would appreciate to see chart show similar loss of torsional toughness between 325F-400F (~155-200C). And please let's not broaden the discussion by bring in steels with applicable secondary tempering range (which mostly very high alloy%).
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Why would there ever be a loss of toughness from between 325-400F?

The 1095 chart I posted above is the only 10xx series temper chart I've been able to find. Keep in mind that 1095 is also an alloy, since it contains manganese. Manganese plays a role in TME.
 
I have encountered; understood and solved temper temperature in 275F-375F (depend on matrix) range can caused false-conclusion on loss of toughness more than just torsional. Maybe a vague clue - my 1095 aust temp(with short soak) would be lower than 99.99% hters out there but capable of producing Mf near LN2 temp (actually I don't know how low, would be nice if I can try liquid He). D2 starts after 315F. I think, the author of that graph mis-interpreted the data. Steel matrix may not be a complicated as dna but end results more/less combinatoric depends on sequences it went through.

TE & TME graphs/charts alway tied to 1 or more (avg) set of particular sequences. These sequences maybe common/well-practiced thereby applicable in that context. Using a different sequencing route, embrittlement could: shift in temp range; amplitude change; or non-existence. Science can offer guidelines but actual physics rule!

RX-79G said:
Why would there ever be a loss of toughness from between 325-400F?

The 1095 chart I posted above is the only 10xx series temper chart I've been able to find. Keep in mind that 1095 is also an alloy, since it contains manganese. Manganese plays a role in TME.
Click to expand...

edit to clarify: Mf is when RA < 1%.
 
It isn't one author and one graph. I have seen this same dip in toughness in nearly every temper graph and chart for steels tempered in this range. And all are centered around 500°f. I understand what you're saying about changing the initial conditions, but this really appears to be a crystal structure that grows at a certain temperature. The prior aust. conditions are more likely to change the degree of TME, rather than the range it occurs in.
 
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