13 Myths about Heat Treating Knives

Another informative article, especially for a layman like my self who has steel, and a brand new forge to ruin said steel!
 
Nice article.

I understand that heat treatments are generally considered a trade secret, but I think the lack of transparency regarding expected hardness and toughness (after heat treatment) is a bit concerning. If knife makers and production companies actually sincerely believed that their heat treatments provided a competitive advantage, you would expect them to actually disclose this information.
 
Danke42 said:
I think folks love love love the idea that somehow they've got a knife with a bit of black magic mixed into the blade that gives miraculous performance.

Nothing wrong with custom blades or most of the folks that make them but once you start to believe the hype it's not good.
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Just out of curiosity, how much black magic are we mixing in while making knives? Is it the "ha, I gave that guy the runs and a wart" level or more like turning the townfolk into newts and uh-oh here comes the Spanish Inquisition?
 
Danke42 said:
No I'm saying people love to believe in magical thinking like a spiel from some custom builder who can only heat treat knives during a planetary alignment because the extra gravity waves help organize the carbides by height and in alphabetical order.

There's no doubt that super steels are super.

The hype comes into this when someone pretends that what they do is the long lost secret of the Damascus steel or whatever. Instead of selling on their attention to detail of balancing the right steel with the correct heat treat protocol and effective blade shape and edge. In other words; boring.

Jay Fisher is obviously the Guinness World Record holder for making outsize claims but he's not the only one.
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Oh, I see. Thank you.
 
Karl H said:
Nice article.

I understand that heat treatments are generally considered a trade secret, but I think the lack of transparency regarding expected hardness and toughness (after heat treatment) is a bit concerning. If knife makers and production companies actually sincerely believed that their heat treatments provided a competitive advantage, you would expect them to actually disclose this information.
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There are a few reasons that this kind of transparency might backfire.

Let's say you test each blade and issue a certificate. What does it accomplish? Maybe it reassures some customers who are worried they're not getting the "best" heat-treat, but what if they're not satisfied with the number? What if they want it a few points harder it softer?

As far as competitive advantage for publishing numbers, it's only an advantage if you can convince the world that your hardness/toughness is "better" than the competition. That's a big risk to take.

There's also the risk that your manufacturing process isn't as precise as your customers would like. If you're keeping costs down by running big batches and allowing for 5% of blades to come out at +/- 2 RC in your quality control tests, how are you going to explain that to the guy who prefers blades at the top end at 64 and got his at 59? Is the $150 RC 59 blade really substantively "bad" enough to recall? If it is, how many do you test to catch the 5% of "sub-standard" hardness? W

if your grinding process changes your final edge hardness, and you can't even test it reliably but you're happy with performance in other tests?

It's a bigger liability than an advantage, IMO.
 
JacksonKnives said:
If you're keeping costs down by running big batches and allowing for 5% of blades to come out at +/- 2 RC in your quality control tests,
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Then you should rethink your heat treating process because +/- 2 RC is really a HUGE interval!
M390 steel at 62RC is excellent and at 58RC it's subpar. As a customer when I buy a knife I expect a good quality knife and not a lottery ticket. And one way to reassure me about the quality of your product is to publish numbers. I want transparency about expected and measured hardness and toughness.
 
Larrin Larrin Ok, dumb question time. This topic is connected thru several articles so I probably missed the answer (ahh just like in college).
https://knifesteelnerds.com/2018/12/03/cryogenic-part1/
In the first chart of the above article, the horizontal axis is time.

1. How do you determine what time to keep the blade at 1840 degree? 1840 is a rough estimate based on the graph of course.
2. How do you determine the time to temper 1 and temper 2?

Is the time based on the data sheet for the specific metal used?
 
gazz98 said:
Larrin Larrin Ok, dumb question time. This topic is connected thru several articles so I probably missed the answer (ahh just like in college).
https://knifesteelnerds.com/2018/12/03/cryogenic-part1/
In the first chart of the above article, the horizontal axis is time.

1. How do you determine what time to keep the blade at 1840 degree? 1840 is a rough estimate based on the graph of course.
2. How do you determine the time to temper 1 and temper 2?

Is the time based on the data sheet for the specific metal used?
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1. Time at austenitizing time is based on the steel composition (certain elements move slower than others) the temperature required to get the right hardness level (higher temperature means elements move around more quickly, grain growth may be more rapid), and the thickness of the part. Recommended times are typically found in datasheets.
2. Tempering times are generally a bit more generic, like 1-2 hours per inch of thickness. Some steels and tempering temperatures definitely need 2 hours while others may be fine with 1 hour. This is generally controlled by austenite destabilization which I don't think I can explain in a short space. The effect of tempering in terms of hardness "levels off" after some amount of time, so there isn't much difference really between tempering for 1 hour and tempering for 4 hours.
 
Larrin said:
1. Time at austenitizing time is based on the steel composition (certain elements move slower than others) the temperature required to get the right hardness level (higher temperature means elements move around more quickly, grain growth may be more rapid), and the thickness of the part. Recommended times are typically found in datasheets.
2. Tempering times are generally a bit more generic, like 1-2 hours per inch of thickness. Some steels and tempering temperatures definitely need 2 hours while others may be fine with 1 hour. This is generally controlled by austenite destabilization which I don't think I can explain in a short space. The effect of tempering in terms of hardness "levels off" after some amount of time, so there isn't much difference really between tempering for 1 hour and tempering for 4 hours.
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Ahh thanks for the response.
 
JacksonKnives said:
There are a few reasons that this kind of transparency might backfire.

Let's say you test each blade and issue a certificate. What does it accomplish? Maybe it reassures some customers who are worried they're not getting the "best" heat-treat, but what if they're not satisfied with the number? What if they want it a few points harder it softer?

As far as competitive advantage for publishing numbers, it's only an advantage if you can convince the world that your hardness/toughness is "better" than the competition. That's a big risk to take.

There's also the risk that your manufacturing process isn't as precise as your customers would like. If you're keeping costs down by running big batches and allowing for 5% of blades to come out at +/- 2 RC in your quality control tests, how are you going to explain that to the guy who prefers blades at the top end at 64 and got his at 59? Is the $150 RC 59 blade really substantively "bad" enough to recall? If it is, how many do you test to catch the 5% of "sub-standard" hardness? W

if your grinding process changes your final edge hardness, and you can't even test it reliably but you're happy with performance in other tests?

It's a bigger liability than an advantage, IMO.
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Obviously, if you cannot back up your claims, you shouldn't publish them. And if quality control isn't a competitive advantage, then you shouldn't claim that it is.

It is a general best QC practice to do a hardness test for each heat treatment batch. It quite cheap and easy to do. It can be done on scrap material. If a company isn't willing to do that, it tells me that they really don't care very much about the quality of their product. If they cannot grind the edge without significantly adversely affecting the steel, it tells me that they don't care very much about the quality of their product.

However, if a knife maker spends a lot of time and effort to optimize your heat treatments and/or perform good quality control, they should consider it a competitive advantage or a justification for charging higher prices. In this case, it is in their best interest to actually be transparent about their competitive advantages.
 
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This kind of "transparency" has already been discussed. The problem with it is that it feeds the Instagram warriors who need to take photos of an absolute peak HRC knife and doesn't do anything for anyone else.

If you need some kind of special very hard HT knife there are already custom makers that will make these for you. At a price of course.
 
People post HRC test results on instragram, when knife makers aren't transparent or aren't credible. The easy way to avoid negative press is to be both transparent and credible.

Is Chris Reeve Knives loosing business because they published their hardness specification range? Is Benchmade loosing business because they published their hardness specification range? Is Buck loosing business because they published their hardness specification range?

In my opinion, Benchmade's disclosure of their specified hardness range and offer to replace blades that do not meet the specification is exemplary and they should be commended for it.
 
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Karl H said:
People post HRC test results on instragram, when knife makers aren't transparent or aren't credible. The easy way to avoid negative press is to be both transparent and credible.

Is Chris Reeve Knives loosing business because they published their hardness specification range? Is Benchmade loosing business because they published their hardness specification range? Is Buck loosing business because they published their hardness specification range?

In my opinion, Benchmade's disclosure of their specified hardness range and offer to replace blades that do not meet the specification is exemplary and they should be commended for it.
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The last time around the "people" posting the "numbers" had to walk their claims back down because they were doing a poor job of it.

If that number is critical for you to buy a knife then there are some makers that will have that for you.

In the meantime some light reading.

https://knifesteelnerds.com/2018/11/12/rockwell-hardness/
 
Karl H said:
...
Is Chris Reeve Knives loosing business because they published their hardness specification range? ...
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Actually, yes. They've had a "bad reputation" for under-hardening for a long time. I doubt that the lost performance is a significant factor for their core customer base and might provide some benefits (e.g. easier sharpening/less chipping), but for the spec junkies who care about the hardness and are already used to harder blades it's a turn-off.

Edit: which is to say, I'm not sorry I know about it, but IMO it's not a good business move and I support knife manufacturers who resist the urge to brag about hardness but are more than willing to back up their blades with warranty support if there are real problems. (E.g., Spyderco has a run of ZDP that is prone to cracking, and there's a recall. I don't need to second-guess their target hardness, I just need to know they've got my back if my knife breaks in normal use conditions.)
 
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Danke42 said:
The last time around the "people" posting the "numbers" had to walk their claims back down because they were doing a poor job of it.

If that number is critical for you to buy a knife then there are some makers that will have that for you.

In the meantime some light reading.

https://knifesteelnerds.com/2018/11/12/rockwell-hardness/
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I don't understand what point you are trying to make. The primary defense against people posting inaccurate test data about your products is to provide your own accurate test data.

Larrin's points about the shortcomings of hardness testing is essentially a recommendation to do additional types of testing to better optimize a heat treatment process. I understand that hardness test data is not the only or the best possible measure of steel performance, but it is better than having no measure of performance, and it is significantly cheaper and easier to perform than other types of standardized performance testing.

If knife makers published tensile test data, compression test data, or toughness test data, then I would use it to make better informed purchasing decisions. However, I have yet to see any knife maker publish any measure of steel performance other than hardness. So, in lieu of having any other type of performance test data available, consumers that care about steel performance are understandably going to focus on hardness. If the knife maker doesn't publish any test data, consumers will look to third parties for that information.
 
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