Heat treat information we need on blade steel

[Twindog]

We talk a lot about steel alloys, which is important, but we almost never have any information about the heat treat. If lucky, we know the Rc hardness of the blade. But that's not enough.

To my thinking, the real information we need is the steel alloy, hardness and microstructure of the steel (grain size). Something about inclusions (imperfections in the steel that result in weakness) would be good, too. Without that information, we really don't know much about the steel's performance.

Bluntcut regularly posts incredible information about his heat treat, taking ordinary steels up to high hardness, with small grain size, that give excellent performance for toughness (resistance to breaking and chipping), as well as strength (resistance to bending or rolling).

Hardness, measured by Rc, is highly correlated to strength, but we know little about toughness. We might know something about inclusions if the steel is high-tech powder steel, but we don't know much about inclusions if it's a simple carbon steel.

Juha Perttula has an interesting post in the knife testing subforum about how toughness can vary a lot, even with steel blades at the same Rc. He has a graph showing various heat treats of 80CrV2 -- a carbon steel -- where impact toughness varies from about 75 J/cm2 to 15 J/cm2 on 80CrV2 steel blades all at 60 Rc hardness.

The difference is in the microstructure of the steel, where grain size ranges from less than 0.01 mm (very tough) to 0.05 mm (not nearly as tough). A good heat treat doesn't just give us the target hardness, but it also affects the grain size. Two knives of the same alloy run at the same hardness can vary wildly on performance because of differences in the microstructure of the steel.

My thinking is that we should ask makers of high-quality knives and the more successful custom makers to include blade alloy, Rc hardness and grain size in their description of their blades. Without that information, we can't get a good measure of the steel's performance.

 

[Mo2]

Mass produced knives won't bother giving you more info. Your lucky if you even get an HRC rating and even then it can be out of spec at random.

 

[ATJ999]

Exactly!!! SO many people here think that HRC is everything! They don't realize that the same steel with the exact same HRC, with different heat treat protocols, can perform vastly different. I guess some get tunnel vision when it comes to knives and their specs.
People also get hung up on PM steels ruling over all, but don't realize that steels like AEB L, when HT'd properly can have very fine grain microstructure, and perform better than some PM steels.
It is always good to learn more about stuff you enjoy. Keep on researching. It will help, especially when you can ask the maker enough questions to get a much better idea of the knifes performance.
Good thread!

 

[Dangerously]

I not only want to know the grain size, I want to know how many grains, what their names are, and if any grains have ever had any high risk behaviours.

Seriously though, just adding grain size as another proxy for performance (like HRC) won't really tell us the whole story either. It will eventually be gamed just like HRC. These numbers are proxies for some element of real world performance, and they do not capture all of it. I wouldn't turn down the knowledge, but I worry it wouldn't be as informative as we'd like. And it would incentivize makers to optimize it for marketing rather than performance.

I'd be happier if more makers would measure the thickness at the shoulder if there is one, or thickness 1mm back from the edge on a zero grind. But again, that's not the full story either.

 

[Twindog]

I don't know if knife makers could optimize grain size and hardness in a way that doesn't also correlate highly to performance. They can do that with just Rc information alone. I think that Sal Glesser at Spyderco doesn't like to release Rc because, by itself, it can become a misleading indicator of blade performance and quality.

For knives retailing for more than $200 or so, it shouldn't be a major problem to provide this information. Otherwise, we're left waiting for someone willing to baton their expensive knife through a concrete block.

And you're right, Dangerously, the width of an edge bevel at the shoulders is key information for how well that knife will slice.

As long as we knife enthusiasts don't demand that information, we're not likely to get it.

 

[mete]

We who are really in the know , metallurgists like myself, Roman Landes ,and other highly knowledgeable types always have the problem of hype and distortion .Customers wanting the highest hardness , toughness in the latest fad steels distort things even unintentionally Makers don't want to explain every little details to each customer . I would like to see Informative , well written websites . Is it possible to avoid the hype ?

 

[SpySmasher]

Is it possible to avoid the hype ?

Probably not in any environment where people are eagerly selling something to other people who are eagerly buying.

 

[Twindog]

We who are really in the know , metallurgists like myself, Roman Landes ,and other highly knowledgeable types always have the problem of hype and distortion .Customers wanting the highest hardness , toughness in the latest fad steels distort things even unintentionally Makers don't want to explain every little details to each customer . I would like to see Informative , well written websites . Is it possible to avoid the hype ?

Good points. My sense is that the hype is possible when information is misleading, incomplete or wrong and consumers are not well educated enough to know it.

Individually, we don't have much power. But it was consumers and consumer groups who rose up together to demand credible information about the validity of claims that food sold as organic really is. Hence the USDA organic seal. It's not perfect, but it's better than "buyer beware." Most of us know enough to be suspicious of claims that that organic food from China truly is organic. When Congress forbid the FDA from testing supplement health claims, private groups sprung up like Consumer Labs that tested these supplements and, for a fee, released the results to members.

Maybe if some relatively large manufacturers of high-quality knives -- Spyderco, Kai, Benchmade, etc. -- supported an independent testing lab with a small percentage of sales of their high-end knives, we could get data on the microstructure of steel. Makers willing to submit sample blades picked randomly from the consumer market, might benefit from being able to boast of an independent certificate of steel quality that meets critical performance levels. That wouldn't be hype

 

[BluntCut MetalWorks]

Knives are subjective consumables unlike industrial and engineering required specs. Where scope of knives usage is mostly open ended. Nevertheless, buyers can vote with their money whether asking for ht info (to educate and or inform) as part of the product or not. I am not one of those that think 'maker/producer knows what is best for me' in knives or car or many other things in life. Well informed buyers should able to extract the 'goods' and filter out 'garbages/hypes', given availability of info/evidences/etc...

At minimum: peak and working hardness +- 1.5rc range. Quite a bit a guessing and reverse engineering can be done to find out quality of ht.
Nice have: grain size
Knut: carbide size+volume, martensite type (lath% plate% combination), tempered temperature, ~retained austenite%, etc..

 

[gadgetgeek]

I think it would still be gamed, just as the "organic" symbol is. And thus makers who played would win, and those who didn't wouldn't have the .... (if fake natural products are green-washed, could we call it hard-washing?) I think its better left up to the makers reputation. Yes it means that some guys are going to baton some cinder-blocks, but then we know that Bos 420HC will do X, Rowen 1095 will do Y, Kabar CroVan will do another thing, Nathan C. D3V will do another. Its worked well enough so far, to the point that Busse renames the steel they use based on their heattreat. (unless I misunderstand that)

I don't think its a bad idea, but I don't see how it helps. Its only in the makers interest to tell me the number that makes him look good, and that is totally fair (a car is rarely if ever marketed both on economy and horsepower, they might mention both, but we all know which one is important) For a boutique level maker who can advertise that, or from an OEM perspective of what a heat treating service can provide the home workshop guy, there is advantage there at the pro/ prosumer level, but not at the consumer level.

 

[BluntCut MetalWorks]

Your analytical points are highly correlative to today knife world/market. It would be quite difficult to distill good info from flood of marketing/hype and Ranger Gord experts, so perhaps it is not worthwhile to investigate into a lowly consumable products such as a knife. Seller/maker can 'game' emotional and subjective and impulse of buyers but most businesses know negative impact from imprudent of grossly manipulated (lie) on quantitative specifications the product - i.e. if one want to stay in business for the long term, it's wise to avoid unnecessary self-inflicted liabilities.

I barely have control of one/me, in life journey, prefer to leave behind creations based on best-of-point-in-time-knowledge/skills and minimize mysteries/voodoos. May the internet archive preserves all my knives specs and ht info

I think it would still be gamed, just as the "organic" symbol is. And thus makers who played would win, and those who didn't wouldn't have the .... (if fake natural products are green-washed, could we call it hard-washing?) I think its better left up to the makers reputation. Yes it means that some guys are going to baton some cinder-blocks, but then we know that Bos 420HC will do X, Rowen 1095 will do Y, Kabar CroVan will do another thing, Nathan C. D3V will do another. Its worked well enough so far, to the point that Busse renames the steel they use based on their heattreat. (unless I misunderstand that)

I don't think its a bad idea, but I don't see how it helps. Its only in the makers interest to tell me the number that makes him look good, and that is totally fair (a car is rarely if ever marketed both on economy and horsepower, they might mention both, but we all know which one is important) For a boutique level maker who can advertise that, or from an OEM perspective of what a heat treating service can provide the home workshop guy, there is advantage there at the pro/ prosumer level, but not at the consumer level.

 

[gadgetgeek]

BluntCut, I think we are nearly on the same page with that. I think that for an OEM or heat-treat provider, then having those capabilities stated in a verifiable way would allow the consumer of the service, ie the designer or the smaller makers who contract those services to look at what sort of product they can expect. Maybe a provider says yes, we can push to this level, but our consistency won't be as good, or we can make them all 0.001% different, but then you need to decide which other factor is going to have to be lowered. Or a maker can say where they want the money put, maybe a small-hard blade can be pushed farther without concern for stresses, but a bigger blade would need to be done more slowly so the dollars are spent putting the time in. Its like any other tolerance, you can pay for all of them, but in general there is a sweet-spot where you will get value when you can sacrifice one factor to get some cost savings, and focus on the real priorities. Ultimately that allows the customer to compare the providers in an apples to apples way, since not every provider will fit every situation, each will find their niche in the market, volume, turn-around, consistency, boundary pushing, and the like.

 

[Twindog]

A little over a decade ago, the flashlight industry for enthusiasts was mostly about modders cranking out blinding hot-wire lights converted from Maglites. Then came the revolution in LEDs, which was led by modders. Now, China mostly rules, but there are standards for lumen output (out the front, not at the LED), drop standards, waterproof standards, flicker standards. You can buy a high-end flashlight and be sure of what you're getting.

We don't have that in the knife industry. Even basic information on geometry is scarce, such as edge width at the shoulder and edge angle. Those things we can measure after we buy. But we can't measure heat treat. Rc, if given at all, is usually stated within two points of hardness -- two points that can make a big difference in performance. We know nothing about the heat treat or the microstructure of the steel.

It doesn't seem like it would be that hard to have independent testing of the microstructure of the steel, at least for high-end production knives. Without that, we don't have much of an idea of the steel's performance. I've had mid-tech knives that were so soft I could bend the blades like they were made out of lead. I've had custom knives that I could break easily, and cheap production knives that I couldn't. I've had choppers that chip. Slicers that break. I had a high-end axe that chipped and rolled like crazy from just clearing downed branches over a trail -- even while my machete did the same work with a thin edge and no damage.

It would be nice to have the same testing standards that the flashlight industry has adopted.

 

[DeadboxHero]

A little over a decade ago, the flashlight industry for enthusiasts was mostly about modders cranking out blinding hot-wire lights converted from Maglites. Then came the revolution in LEDs, which was led by modders. Now, China mostly rules, but there are standards for lumen output (out the front, not at the LED), drop standards, waterproof standards, flicker standards. You can buy a high-end flashlight and be sure of what you're getting.

We don't have that in the knife industry. Even basic information on geometry is scarce, such as edge width at the shoulder and edge angle. Those things we can measure after we buy. But we can't measure heat treat. Rc, if given at all, is usually stated within two points of hardness -- two points that can make a big difference in performance. We know nothing about the heat treat or the microstructure of the steel.

It doesn't seem like it would be that hard to have independent testing of the microstructure of the steel, at least for high-end production knives. Without that, we don't have much of an idea of the steel's performance. I've had mid-tech knives that were so soft I could bend the blades like they were made out of lead. I've had custom knives that I could break easily, and cheap production knives that I couldn't. I've had choppers that chip. Slicers that break. I had a high-end axe that chipped and rolled like crazy from just clearing downed branches over a trail -- even while my machete did the same work with a thin edge and no damage.

It would be nice to have the same testing standards that the flashlight industry has adopted.

I think one of the problems is that the testing costs more then in other industries

If you really want to see the microstructure then you need x-ray diffraction, there is a place in Tennessee that does the testing and they also make the x ray diffraction machines. But it's expensive and it takes a qualified tech to use and interpret the data.

I was quoted at $100 bucks for one test.

 

[Twindog]

I think one of the problems is that the testing costs more then in other industries

If you really want to see the microstructure then you need x-ray diffraction, there is a place in Tennessee that does the testing and they also make the x ray diffraction machines. But it's expensive and it takes a qualified tech to use and interpret the data.

I was quoted at $100 bucks for one test.

That's a fair point, Dead. I don't have all the answers, just mild frustration.

But my sense is that decent testing isn't that expensive. I just bought one of Juha's puukkos. He tests and knows exactly what the grain structure is. He knows the exact hardness. For less then $96, I'm getting a handmade puukko with handmade sheath shipped from Finland, which is a high-cost country. The blade hardness is 63 Rc. The spine hardness is 50 Rc.

If your $100 price is correct, let's say Spyderco or Benchmade or ZT puts out a sprint run of 1,000 knives at $250 each. Say they have 10 of those knives chosen at random and tested for grain structure and hardness. That's $1,000. The price of each knife would rise from $250 to $251. That seems doable.

 

[BluntCut MetalWorks]

Knives aren't like lot# chemical assay, so random testing is more suitable for internal QC rather than publish info. Each HT version/recipe associates with repeatable outcome (w/i small variance) microstructure, thus just publish these as reference/baseline specs per ht version. E.g. HRC peak & tempered range (+- 1), grain diameter (+- 3 microns), retained austenite% (+- 3%), toughness##, etc..

HRC: Rockwell hardness tester - cheap & fast in house equipment.

Grain diameter: Light Metallurgical Microscrope - cheap equipment but really cost is in sample preparation (polish & etch). In house or external services.

Grain diameter, boundary, crystal types, carbide info and partial RA info: http://en.wikipedia.org/wiki/Electron_backscatter_diffraction - $20+K instrument, so perhaps using external services.

RA%: XRayDiffraction. $40+K, make sense to use external services

Impact Toughness - Izod:

. perhaps use blade like dimension 3x10x55mm than standard dimension. External service or buy/build an izod tester. Izod is more resemblance of blade pry/sheer than charpy.

Sample polish & etch is the most costly part of testing.

 

[Mecha]

I think one of the problems is that the testing costs more then in other industries

If you really want to see the microstructure then you need x-ray diffraction, there is a place in Tennessee that does the testing and they also make the x ray diffraction machines. But it's expensive and it takes a qualified tech to use and interpret the data.

I was quoted at $100 bucks for one test.

I was drooling over hand-held laser mass spectrometers that cost $35,000 new. One zap tells you in great detail every element's percentage in a sample of material, metal alloy or otherwise. I want one so bad it makes my teeth numb.

 

[jdm61]

I can tell you with a HIGH degree of certainty that after seeing a shop tour video where one very popular tacticool knife company showed their "proprietary" heat treatment process for their 1095, I would NEVER consider buying one of their knives even if I could get over their oft times hideous appearance. They basically 'differentially austenized" the blade in a forge by using the old Mark 4 Mod 1 Calibrated Eyeball as a thermocouple as best as I could tell and then dunked it into what looked like a dirty bucket full of old bilge oil. i am pretty convinced that the choice of whether to use best methods or not even in a small production setting is driven purely by cost. I guess there is a bottomline difference between paying a company like Peters $4-5 per blade to do it right and paying for some propane and the hourly wages of a guy to sit in front of a forge and toast his retinas for 8 hours a day. If you were being honest, you could sent them off the Peter, Bos, MetSol et all and say we are spending extra money to HT your knife using the most experienced cats in the business. But it may be more profitable to do crap work and call it your "super secret proprietary heat treatment process. Some people do it the right way in house even with low cost items. If you look at an R. Murphy Knives shop tour video, they have a full blown old school high temp salt pot setup. So does Estwing.

 

[Gaston444]

We don't have that in the knife industry. Even basic information on geometry is scarce, such as edge width at the shoulder and edge angle. Those things we can measure after we buy. But we can't measure heat treat.

This is why I always thought this was not a serious hobby... Makers don't even put forward edge thickness specs anywhere... This is exactly like cars being sold without horsepower specs... It might even be like a car not telling you how many cylinders the engine has, and people still arguing about the chemical content of the paint job...

People talk about how this or that steel performs, but they are not even curious about the basic parameters that are needed to know if the comparisons are valid, which is edge angle and edge base thickness...

Gaston

 

[BluntCut MetalWorks]

Yeah this could be handy to figure out 'mystery/lost' steel type but for this much$ - I rather have a SEM/EBSD instrument.

I was drooling over hand-held laser mass spectrometers that cost $35,000 new. One zap tells you in great detail every element's percentage in a sample of material, metal alloy or otherwise. I want one so bad it makes my teeth numb.

Isn't product/outcome of ht more important than method (how it was done)? For ht method below, I think hardness and grain will be far below average. Perhaps info can help this maker to reconsider their ht method.

I can tell you with a HIGH degree of certainty that after seeing a shop tour video where one very popular tacticool knife company showed their "proprietary" heat treatment process for their 1095, I would NEVER consider buying one of their knives even if I could get over their oft times hideous appearance. They basically 'differentially austenized" the blade in a forge by using the old Mark 4 Mod 1 Calibrated Eyeball as a thermocouple as best as I could tell and then dunked it into what looked like a dirty bucket full of old bilge oil. i am pretty convinced that the choice of whether to use best methods or not even in a small production setting is driven purely by cost. I guess there is a bottomline difference between paying a company like Peters $4-5 per blade to do it right and paying form some prone and the hourly wages of a guy to sit in front of a forge and toast his retinas for 8 hours a day. If you were being honest, you could sent them off the Peter, Bos, MetSol et all and say we are spending extra money to HT your knife using the most experienced cats in the business. But it may be more profitable to do crap work and call it your "super secret proprietary heat treatment process. Some people do it the right way in house even with low cost items. If you look at an R. Murphy Knives shop tour video, they have a full blown old school high temp salt pot setup. So does Estwing.

I see your point however not much in analogy. For benchmark - I think, it is up to the conductor to prepare subject edge geometry to baseline/parity. Remove steel to thin out geometry is easier and less costly than grind edge back to thicken geometry.

This is why I always thought this was not a serious hobby... Makers don't even put forward edge thickness specs anywhere... This is exactly like cars being sold without horsepower specs... It might even be like a car not telling you how many cylinders the engine has, and people still arguing about the chemical content of the paint job...

People talk about how this or that steel performs, but they are not even curious about the basic parameters that are needed to know if the comparisons are valid, which is edge angle and edge base thickness...

Gaston