What is so tricky about heat treating a steel optimally?

Hi everybody, after researching anything there is to know about kitchen knives and surfing this and other forums I think I got the main parameters that determine a good knife straight. However, there is something that really bugs me because I just cannot make any sense of it. I know that much more important than the kind of steel used is the specific heat treatment of that steel. So, apparently VG10 is an ok steel If heat treated bs Tanaka, it however sucks and is chippy if done by Shun. Soooooo....but why?!!
Is the knowledge of properly heat treating a widely used steel so exklusive and secret that a large manufacturing company with quite a commercial punch does just not figure out the extremely mysterious secret? Or do they just like to do it this way for some sensible reason that just eludes me? So....why's good heat treatment such a difficult thing to achieve? Thanks for any info in advance as this question that actually has been bugging me for a while is posted under influence.

First, check your assumptions. VG10 heat treatment by Shun does not produce knives that are "chippy". That's an internet meme that is totally false, yet is given new life almost continually. Shuns, as well as other knives, may chip when misused by people accustomed to softer German knives.

Second, proper heat treatment of steel is not "exclusive", nor "secret". It is done routinely by major manufacturers every day as well as smaller concerns and individual bladesmiths. It is the quality and quantity of attention to the process that makes the difference between mass-produced knives and those made in small batches or one at a time.

Have I refuted your non sequiturs sufficiently?

Rick

For every Tanaka knife that sells, Shun sells 1000. You are going to hear way more about Shun problems.

One thing to add about heat treatment/chippy edges. Some knives that have excellent heat treatment will have chipping issues until after the first sharpening due to weakened steel along the edge. Once past that with a full sharpening, many knives no longer exhibit the same 'problems'.

Pensacola Tiger said:

First, check your assumptions. VG10 heat treatment by Shun does not produce knives that are "chippy". That's an internet meme that is totally false, yet is given new life almost continually. Shuns, as well as other knives, may chip when misused by people accustomed to softer German knives.

Second, proper heat treatment of steel is not "exclusive", nor "secret". It is done routinely by major manufacturers every day as well as smaller concerns and individual bladesmiths. It is the quality and quantity of attention to the process that makes the difference between mass-produced knives and those made in small batches or one at a time.

Have I refuted your non sequiturs sufficiently?

Rick

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Actually I can see where he's coming from, although Shun might be a bad example. For example in discussions about 'white or blue' I recall people bringing up the exact point that it's all about the heat treatment. Thereby implying that apparently this is the crux of creating a quality knife. I vaguely recall Murray Carter saying something along the same lines in his explanation of choosing white steel.
Not that I have a good answer, but the question at least seems valid...

One thing to think about though is that 'optimal' heat treatment can mean different things; usually more hardness means less toughness and I guess it's difficult to increase one without reducing the other within the same steel. You treat it to a certain hardness based what you think the end-user will do with your product.... and problems mainly occur when there's a mismatch. Same goes for edge angles.

Jovidah said:

Actually I can see where he's coming from, although Shun might be a bad example. For example in discussions about 'white or blue' I recall people bringing up the exact point that it's all about the heat treatment. Thereby implying that apparently this is the crux of creating a quality knife. I vaguely recall Murray Carter saying something along the same lines in his explanation of choosing white steel.
Not that I have a good answer, but the question at least seems valid...

One thing to think about though is that 'optimal' heat treatment can mean different things; usually more hardness means less toughness and I guess it's difficult to increase one without reducing the other within the same steel. You treat it to a certain hardness based what you think the end-user will do with your product.... and problems mainly occur when there's a mismatch. Same goes for edge angles.

Click to expand...

Yes, perhaps it is a valid question posed poorly.

As to why there is a difference in the performance of knives made from the same steel by different makers, this may be a matter of experience coupled with how far the smith wants to push the envelope. One of the things a bladesmith trying to wring the last bit of performance from a steel has to deal with is failure rate. If you are concerned with production yield, you don't push the envelope much.

I'll agree that a good part of the Shun's chippiness is probably due to misuse by those who do not understand the differences between typical German vs. J-knives.

And Jovidah makes a good point about "optimal" heat treatment--there's got to be a range, depending on how people sharpen and use their knives.

Heat treating is so fascinating and opinionated to bladesmiths because the properties of any given steel get pushed to extreme limits once it gets to be as thin as the edge of a knife. Those extremes get pushed even further when they reach the end user who ultimately decides the jobs the blade will be used for - which may be inconsistent with the ideas of the bladesmith.

Also, factors come into play that standard heat treating methods may not take into account (e.g. grain size and structure) that have a huge impact on a cutting edge.

Tobes said:

So....why's good heat treatment such a difficult thing to achieve?

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Good is easy to achieve. But for people like us, good isn't good enough!

Hi all and thanx for answering!

I did not mean to start a philosophical debate about right or wrong assumptions and valid or invalid conclusions based on these or others.

And by no means I wanted to dive into the putative "Shun-chippiness" issue.

I am seriously just curious about what it actually means if some maker "nails" a heat treatment
and another one just doesn't seem to get it quite as right and what the reasons for these differences might be.

The Shun-VG10-thing just quickly came to mind as an example because this argument shows up quite often.

So, if we disregard the Shun-topic, which might or might not be a suitable example for my question, there is still this (or similar) sentence/s that if truth be told shows up very often in knife recommendations.

"This is a great knife, because maker XX is spot on with the heat treatment. And this knife using steel YY is thus better than another knife made from the same steel by a different maker".

Guess, I am just curious about the ins and outs of heat treatment, be it technical, economical or else, and why some manufacturers/makers opt for an apparently less than optimal solution.

So, that's why I was wondering whether they just cannot do it technically or whether they don't want to for reasosns I would be curious about. :detective:

Check out the recommended heat treatment of various steel datasheets. One I've read for 1095 says anneal by heating to 1475F and cool at a rate no faster than 50F per hour, and Temper twice at 2 hours each allowing the steel to cool back to room temperature between cycles. Doing a bit of math shows that you have to spend more than 32 hours on heat treating a knife if you want to do it right. You think that's possible if you have a factory trying to crank out hundreds/thousands of knives out everyday? Of course not, unless the factory is willing to spend an ungodly sum of money in being able of consistently and massively parallelizing the heat treatment process. People will always try to reduce the amount of time to heat treat a knife by taking shortcuts. Heat treatment according to recommended specs is time consuming and expensive as I would imagine. How much do you want to pay for the knife to get the last couple of percent out of the steel?

In addition to the answers above, the starting material plays a roll in how many steps a blacksmith has to do to get the optimal grain structure and material properties. The blacksmith can order bar, plate or cross rolled plate as his starting stock from any given chemistry and then has to develop a forging cycle where he has to control temperature and reduction of material in each step of the shaping of his blank. Quenching plays a big roll where thin edges have a different quench rate along with die chill (hammer and anvil quench). There are many steps in forging a blade blank and you can do it in one or many steps that all take a lot of time - optimizing these variables to give the best strength to toughness results give rise to blacksmiths that rise to the top of the trade.

Thats more than 32 hours if you include the annealing step. Some forms of knife manufacturing may not include that step but would still take more than 5 hours for a proper heat treat. There's also possibly cryo treatment you can include.

I see, things start making sense, really interesting, thanx for your input. So it basically takes time and effort and cutting corners saves money. I suspected as much and now I have a better understanding how that comes about exactly.

Tobes said:

I see, things start making sense, really interesting, thanx for your input. So it basically takes time and effort and cutting corners saves money. I suspected as much and now I have a better understanding how that comes about exactly.

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Part of the craft is gained knowledge - some blacksmiths use the steel color (as it comes out of the forge) as a measure of temperature this is a skill honed over many years and they use this as a gage to go to the next step in the process. Not all blacksmiths have this ability and have to use secondary methods to know the optimum temperature for hammering or quenching. It is not a simple process to get the best of the best (strength vs toughness) properties out of a given steel.

Chicagohawkie said:

For every Tanaka knife that sells, Shun sells 1000. You are going to hear way more about Shun problems.

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Exactly and the person who buys the Tanaka probably will take much better care of it. I have repaired some shuns with massive chips, broken tips. All from abuse. One damaged shun I fixed kept & used for over a year. No chipping at all. Of coarse as ridiculous as it sounds don't use it to pry apart frozen chicken. Chopping frozen meat so will thaw faster, Hammering through bones, lobster & king crab legs, the list goes on.

Even punched out mass produced knives with fair to high quality steel get a good heat treatment- heat -cryo- heat again lower temp. Perhaps some hand forged blades may get slightly better HT. Not an expert but my guess is difference not large as some claims. Also the reputations of some blades with crap heat treatments is unfounded.

Here are my thoughts on just basic carbon steel, and in this example, W2. Some of the factors you can consider are:

• Steel Quality/Condition
• Pre-Quench Treatments
• Time
• Temperature
• Thicknesses
• Atmosphere
• Quench Medium
• Post-Quench Treatments

You have 1% carbon, which is about 0.2% in excess of full saturation (0.8% C is about the max you can get into solution). The rest ends up as extra carbides, which can result in a lot of different forms, some of which undesirable. There's the issue of retained austenite too. You can easily have 10 different heat treatments that result in 62 HRC after tempering, and all of them behave differently. That tiny bit of extra carbon changes the game kind of significantly.

Lets say one maker austenitizes the steel at 1470*° F for 10 minutes then quenches. Another maker tries the same exact thing, but gets totally different results. Well, the thermodynamics of each maker's forge/kiln/salt pot can drastically change what the steel is doing while soaking at temp. "1470° F" might be 10 degrees hotter or cooler, depending on the measurement devices; it might also vary within the chamber too, and also fluctuate with time. All of these factors affect what the carbon is doing pre-quench, during-quench, and post-quench. Add in the factor of different thicknesses of steel, then the rate of thermal transfer changes again, and same thing with tapers and bevels.

I think even the atmosphere affects temperature and oxygen too, but I don't know about that for sure. From experience I've had forges go super hot and oxidizing on rainy days. I've read elsewhere that some makers do their forge welds during humid days for exactly those reasons too. More food for thought.

The quench matters a lot also. There are a bunch of ways to get from austenite to martensite. A straight quench all the way down to ambient temperature, or an interrupted quench, or a martemper, or any variation of any of those. The quench medium, volume of quench, temperature of quench, and agitation of quench can all affect the outcome.

And then there's the stuff after quenching. Cryo or not? It's debatable for something like W2, but supposedly adds about +1 HRC and transforms retained austenite. Tempering once for 2 hours, or twice for 1 hour each? Grinding isn't exactly part of heat treating, but I bet that some cases of apparently 'poor HT' are actually blown tempers during the grinding stage.

I think this stuff applies to all steels. Once you start adding alloying elements, the recipes change, but the principles stay. Granted, you could just follow the cookbooks for the given steels and probably end up with really good results, but I know most of us like to obsess over the minute details I hope I didn't go way off track.

So to recap, if you think about it, HT is a bit like cooking. it depends on the recipe, the raw ingredients, how you prepare it, time, temperature. Two different cook may follow the same basic recipe and use the same ingredients but the results could be as different as east to west and one with a sensitive tongue could tell you blind who did which dish.

Wow, interesting stuff! Thanx a lot for the detailed explanation. I'm much clearer on this issue now. Really cool to get all this information through KKF!

WingKKF said:

So to recap, if you think about it, HT is a bit like cooking. it depends on the recipe, the raw ingredients, how you prepare it, time, temperature. Two different cook may follow the same basic recipe and use the same ingredients but the results could be as different as east to west and one with a sensitive tongue could tell you blind who did which dish.

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For maximum nerdness, next time you fry a steak call it 'heat treating proteins'. Admittedly you are spot on here.

I think Don summed things up pretty well. As for commercial heat treatment, it comes down to time and money. The cheapest knives I've seen are usually hardened to ~50 hrc, in which they are basically put on a conveyor that runs through an oven, and then into a quenching medium. As you would think, keeping steady temperatures in an open oven can be tricky, and usually the steel used isn't great to start with. In the end, you get what you pay for, and there is a difference between mass produced, and an individual heat treating a piece one at a time. Personal preference for the qualities associated with a particular "recipe" also come in to play, where there will never be a perfect solution, but trade offs in what is deemed more important (i.e. - hardness vs toughness).

Jovidah said:

Actually I can see where he's coming from, although Shun might be a bad example. For example in discussions about 'white or blue' I recall people bringing up the exact point that it's all about the heat treatment. Thereby implying that apparently this is the crux of creating a quality knife. I vaguely recall Murray Carter saying something along the same lines in his explanation of choosing white steel.
Not that I have a good answer, but the question at least seems valid...

One thing to think about though is that 'optimal' heat treatment can mean different things; usually more hardness means less toughness and I guess it's difficult to increase one without reducing the other within the same steel. You treat it to a certain hardness based what you think the end-user will do with your product.... and problems mainly occur when there's a mismatch. Same goes for edge angles.

Click to expand...

Referring to the statement in bold...Murray (if I recall properly) claimed that white steel is actually superior. The truth of the matter is that white steel is almost impossible to screw up if you have any clue about how to manipulate grain size. There are no alloying elements to form carbides (which is a double edged sword...no carbides also means very little edge retention, as we all know is poor with white steels), and if you thermal cycle properly the grains can be reduced to nothing, thus improving sharpness. This is where Murray's 'methods' come into play. Cold forge blue steel with a power hammer and you will have pieces in short order. Conversely, the pure iron and carbon of white steels will take the abuse of work hardening to a much large degree.

Blue steel however...is a pain in the arse to properly heat treat (to its full potential) unless you're using a PID controlled kiln or high temperature salts. Even then you have to know how to properly thermal cycle it (pre-heat treat processes to set the steel in the best state for hardening). Properly thermal cycled and heat treated blue steels will wipe the floor with white steels in every single category, except that very tiny last little minute amount of sharpness...which trust me, isn't going to be noticeable. A thrown dart at the heat treat (such as Murray's '5 apprentices' analogy) will still net a 'reasonable' knife however, because many of those alloying elements in blue steel help pin down grain size. You will not get the most out of it, but the steel is 'good enough' to mask poor thermal processes and still survive in a professional kitchen. Oddly enough though, people will call the steel 'chippy' (almost as a badge of superiority lol), or cry about a lack of sharpness...when it's the heat treat and/or a lack of dealing with the carbides properly that make it so.

You can do the math as to why someone would claim the polar opposite of what metallurgy tells us are the facts, outside of the very limits of the vague and subjective criteria labeled 'sharpness'. Nothing against Murray of course...we have met and are friendly, but thousands of years of people being taught the world was flat, still didn't make it so. Metallurgy is a very well defined science. There's not a lot of room to argue the specifics of it.

Kippington said:

Heat treating is so fascinating and opinionated to bladesmiths because the properties of any given steel get pushed to extreme limits once it gets to be as thin as the edge of a knife. Those extremes get pushed even further when they reach the end user who ultimately decides the jobs the blade will be used for - which may be inconsistent with the ideas of the bladesmith.

Also, factors come into play that standard heat treating methods may not take into account (e.g. grain size and structure) that have a huge impact on a cutting edge.


Good is easy to achieve. But for people like us, good isn't good enough!

Click to expand...

Add carbides to that list of things most people don't take into account, at least to the level they actually require. Carbide type, size and placement can make a soft HRC blade quite brittle, and can make a very hard blade quite durable. This can be illustrated by doing a brass rod test (like a thumbnail test for edge thinness, on steroids) down a properly heat treated 64-65HRC blade, vs an improperly heat treated 60HRC blade.

The main reason bladesmiths are so very opinionated in regards to heat treating, is because very few have actually taken the time to be able to perform more than will net them a hard edge on a knife. This can be done by eye in a forge with zero true understanding of metallurgy. Myths like 'triple quenching' and 'point your anvil north when forging to align the grain' persist to this day...and using those methods, you can easily pass even the MASTER bladesmith's performance test. Tell any random man he's wrong, and he will come up with 92,000 reasons why he is right. Put that man's edge on a kitchen knife and expect it to perform for a 14hr work day...and he'll say it was abused when it fails.

WingKKF said:

Check out the recommended heat treatment of various steel datasheets. One I've read for 1095 says anneal by heating to 1475F and cool at a rate no faster than 50F per hour, and Temper twice at 2 hours each allowing the steel to cool back to room temperature between cycles. Doing a bit of math shows that you have to spend more than 32 hours on heat treating a knife if you want to do it right. You think that's possible if you have a factory trying to crank out hundreds/thousands of knives out everyday? Of course not, unless the factory is willing to spend an ungodly sum of money in being able of consistently and massively parallelizing the heat treatment process. People will always try to reduce the amount of time to heat treat a knife by taking shortcuts. Heat treatment according to recommended specs is time consuming and expensive as I would imagine. How much do you want to pay for the knife to get the last couple of percent out of the steel?

Click to expand...

I can tell you for a fact, that none of those annealing stages are in the least necessary to get the absolute best out of 1095. Well, excepting the tempering cycles after hardening of course. Metallurgical rules for industry have only the loosest relationship with metallurgical rules for bladesmiths. I would argue that traditional annealing processes actually produce a much poorer condition in the steel, as compared to various other, more quickly performed processes (by quicker I'm talking 6hrs vs the 32hrs you spoke of).

Don Nguyen said:

Here are my thoughts on just basic carbon steel, and in this example, W2. Some of the factors you can consider are:

• Steel Quality/Condition
• Pre-Quench Treatments
• Time
• Temperature
• Thicknesses
• Atmosphere
• Quench Medium
• Post-Quench Treatments

You have 1% carbon, which is about 0.2% in excess of full saturation (0.8% C is about the max you can get into solution). The rest ends up as extra carbides, which can result in a lot of different forms, some of which undesirable. There's the issue of retained austenite too. You can easily have 10 different heat treatments that result in 62 HRC after tempering, and all of them behave differently. That tiny bit of extra carbon changes the game kind of significantly.

Lets say one maker austenitizes the steel at 1470*° F for 10 minutes then quenches. Another maker tries the same exact thing, but gets totally different results. Well, the thermodynamics of each maker's forge/kiln/salt pot can drastically change what the steel is doing while soaking at temp. "1470° F" might be 10 degrees hotter or cooler, depending on the measurement devices; it might also vary within the chamber too, and also fluctuate with time. All of these factors affect what the carbon is doing pre-quench, during-quench, and post-quench. Add in the factor of different thicknesses of steel, then the rate of thermal transfer changes again, and same thing with tapers and bevels.

I think even the atmosphere affects temperature and oxygen too, but I don't know about that for sure. From experience I've had forges go super hot and oxidizing on rainy days. I've read elsewhere that some makers do their forge welds during humid days for exactly those reasons too. More food for thought.

The quench matters a lot also. There are a bunch of ways to get from austenite to martensite. A straight quench all the way down to ambient temperature, or an interrupted quench, or a martemper, or any variation of any of those. The quench medium, volume of quench, temperature of quench, and agitation of quench can all affect the outcome.

And then there's the stuff after quenching. Cryo or not? It's debatable for something like W2, but supposedly adds about +1 HRC and transforms retained austenite. Tempering once for 2 hours, or twice for 1 hour each? Grinding isn't exactly part of heat treating, but I bet that some cases of apparently 'poor HT' are actually blown tempers during the grinding stage.

I think this stuff applies to all steels. Once you start adding alloying elements, the recipes change, but the principles stay. Granted, you could just follow the cookbooks for the given steels and probably end up with really good results, but I know most of us like to obsess over the minute details I hope I didn't go way off track.

Click to expand...

You nailed it brother .

A very interesting thread.
As Chris eloquently pointed out, the steel a bladesmith or knifemaker chooses will be chosen in part according to that maker's processes and capacity.
Heat treating steel is not really tricky at all, you just need to have the knowledge and the means to achieve the end you desire.
I would mostly emphasize the acquisition of knowledge through study of the science but also particularly through personal experience, because only the maker knows every detail of what they are doing to the steel, e.g. stock removal vs. forging, etc.

The thread survives longer than expected and keeps yielding very interesting information. So thanx again for all the input! I feel much enlightened!