Heat treatment and grind: how to tell great from good, and good from bad?

[CiderBear]

Hi all, I'm a newcomer to all things knives. I've been reading old posts on the forums and I see people compare different craftsmen on their heat treatment of the same kind of steel, commenting on the consistent (or inconsistent) grinds of knives, etc.

My question is: how do you tell if a knife has good heat treatment? What about grinds - how can you tell if a knife has a good, consistent grind or not? Any tips and tricks on what to look for?

Thanks so much for your opinions!

 

[Tristam Douglas]

To check out grinds I get either a large carrot or parsnip and cut discs slowly using the full length of the bevel. Because the produce is hard you can literally feel the high and low spots.

Then with minimal pressure you can pull the edge across the discs to assess it’s tooth.

 

[lemeneid]

To know good heat treatment, the knife will be easy to sharpen even at high HRC, takes a wicked edge, and has good edge stability so it doesn’t microchip.

 

[CiderBear]

To check out grinds I get either a large carrot or parsnip and cut discs slowly using the full length of the bevel. Because the produce is hard you can literally feel the high and low spots.

Then with minimal pressure you can pull the edge across the discs to assess it’s tooth.

Thank you. What are high and low spots in a grind? And what is tooth?

My apologies if I sound too nooby, all of this is very new and exciting for me

 

[Ivang]

High and low spots are parts of the grind that are, as their name implies, either low or high, like holes or bumps on the surface of the knife. A toothy edge is one that bites instead of sliding across the surface of the product that is to be cut.

 

[Tristam Douglas]

I think of grind as how the sides of blade are shaped after stamping or forging, (by grinding.) High and low spots are imperfections in the surface planes.

Blades can be either symmetrical or asymmetrical.

Ideally you want a knife to cut straight but asymmetrical blades have a tendency to “steer” to the left or right on a gentle arc. But Asymmetry is cool when done correctly.

This is something you should check out.

https://www.kitchenknifeforums.com/threads/a-basic-explanation-of-asymmetry.33951/

There is phenomenal information on this site. Getting a grasp on the jargon will help massively.

 

[Nemo]

Blades can be either symmetrical or asymmetrical.

Ideally you want a knife to cut straight but asymmetrical blades have a tendency to “steer” to the left or right on a gentle arc. But Asymmetry is cool when done correctly.

Almost all good knives are ground assymetrically, usually for a right hander. The thicker the knife, the more pronounced this is.

If you notice the knife steering, you should increase the sharpening angle on the side that the knife steers toward.

Single bevel knives are te ultimate in asymmetry. With these, you adapt your cutting technique to the steering. You don't sharpen these on the left side. Only very gentle deburring -by pushing only- on your finest stone (see Mr Broida's excellent videos on single bevel sharpenig).

 

[ojisan]

You might tell a clad knife is not properly heat treated (over heated) when the border of the core steel and the clad steel is unclear.

 

[osakajoe]

I wouldn’t read too much into users description of heat treatment. Most people don’t know what they are looking for or describing.

It usually takes sharpening hundreds of the same knives and steel to realize when the heat treat was improperly done.

Just take user reviews of heat treat with a grain of salt is what I’m saying.

 

[milkbaby]

If you're looking to buy knives, then I would focus on buying from brand/workshop or bladesmith/knifemaker with known good reputation. They will get the heat treatment done properly and grind the blade properly for the way they intend the knife to perform.

Some people consider there to be some kind of voodoo about heat treatment, but really it's just mostly science. Western knifemakers often use a computer controlled heat treating kiln/oven that takes the guesswork out of the heat treatment -- at least once they determine the best temperatures and times to achieve the properties they desire. If heat treatment is done a more traditional way by judging temperature by eye in an open forge, then there is an element of skill and experience involved. (Note that stainless steel are not HT this way because due to the higher temperatures and times necessary they will become heavily decarburized in an open oxidizing environment.)

The grind will help determine the way the knife interacts with different foods. There's no one right way to grind the knife, though as noted most traditional Japanese knives will be ground asymmetrically. While I believe there are benefits to that, I also do not believe all good knives must be asymmetrical. I also do not believe a perfectly even grind is necessary or even necessarily the best for a general purpose kitchen knife. It makes it easier for the end user to thin out their knife on stones and have it still look pretty, but I don't believe it's necessarily better performing except perhaps for certain specific tasks like katsuramuki (cutting a long thin sheet from daikon radish or cucumber).

 

[captaincaed]

I wouldn’t read too much into users description of heat treatment. Most people don’t know what they are looking for or describing.

It usually takes sharpening hundreds of the same knives and steel to realize when the heat treat was improperly done.

Just take user reviews of heat treat with a grain of salt is what I’m saying.

I hear a lot of anecdotal reports about "great heat treat" as well, but it's rarely any more detailed. I can imagine many cooks are thinking about acute edges with good edge retention - approaching it from the perspective of a few desirable end-user traits.

What is something you've noticed when a heat treatment seems "different" for one copy in a line of knives you have long-term experience with?

 

[Tristam Douglas]

I hear a lot of anecdotal reports about "great heat treat" as well, but it's rarely any more detailed. I can imagine many cooks are thinking about acute edges with good edge retention - approaching it from the perspective of a few desirable end-user traits.

What is something you've noticed when a heat treatment seems "different" for one copy in a line of knives you have long-term experience with?

Not so much with knives but I used to do a lot of vintage straight razor restoration. In my experience of trying to put together a matching 7 day set for myself they just did not all shave quite the same. Some took slightly better edges, but were less flexible and not able to conform to the shape of your face better, etc. I assumed because of the extreme thinness of the bevels any small differences in the mechanical properties of the steel were more obvious, especially when you consider a beard hair is as tough as a copper wire of the same diameter. If the type steal and grind were the same I concluded that it would have something to do with minor variations in HT.

I guess it was about 10 years ago and there was a flood of these NOS polak stainless wedge razors on the market. They were all originally made for use in hospitals before they moved over to disposable razors. (The scales were stainless too so they could go into an autoclave.) They were plentiful, cheap and a fantastic razor, provided you could find a "good one." The grinds were identical but the variation between quality of the edge and resulting shave could be huge. so buying one was somewhat of a gamble.

I have fallen into the trap of stating that my Denka has a great HT. What I should say is that it is a doddle to sharpen, takes a wicked edge that out lasts any other AS steels I have used by a significant margin.

 

[Tristam Douglas]

What I should have said that due to the extreme thinness of hollow grind razors is that controlling the temperature of the steel during the grinding could also play a huge role. I bet it is very difficult to do consistently.

 

[osakajoe]

What is something you've noticed when a heat treatment seems "different" for one copy in a line of knives you have long-term experience with?

An example would be a GIN3 stainless clad hand forged petty and santoku knife out of Takefu I sharpen a lot (about 100/month). This particular batch had the same issue.

After doing the rough grinding (bringing out the core) and thinning the asymmetrical grind down to the edge, you need to set an edge or micro bevel before going to the next water stone. Every time I tried to set the edge it would chip here and there a good 2mm. So called the forger and he said they were mistakenly thrown in with iron clad blue 2 knives.

Had to send the all the knife blanks to a heat treatment processing plant we trust in order to do heat treat again at the correct temperatures. We now request all our forged stainless steel knife blanks from Takefu without the heat treat so we can send it to our trusted heat treatment sources.

 

[CiderBear]

Thank you everyone for the good discussions! Keep em coming

 

[HSC /// Knives]

I wouldn’t read too much into users description of heat treatment. Most people don’t know what they are looking for or describing.

It usually takes sharpening hundreds of the same knives and steel to realize when the heat treat was improperly done.

Just take user reviews of heat treat with a grain of salt is what I’m saying.

well said, absolutely agree with you on this one,
I digress but the same could be said here of the concept of "fit and finish"...
I see that term here alot and the person is talking about a simple kitchen knife with a simple handle, I mean it's not like we are talking an interframe slipjoint folder or quillon dagger...

 

[Barclid]

I wouldn’t read too much into users description of heat treatment. Most people don’t know what they are looking for or describing.

It usually takes sharpening hundreds of the same knives and steel to realize when the heat treat was improperly done.

Just take user reviews of heat treat with a grain of salt is what I’m saying.

There's definitely a certain mystique that people like to attribute to "good heat treat" versus "poor heat treat" and people like to convince themselves they can discern fine detailed differences between two. Generally when I talk about poor heat treatment, it's when a knife is crumbling or chipping at similar edge geometry that I have sharpened multiple other knives at, in the same steel. Not nearly the same volume or consistency as you're doing, but there's a definite difference. Most notable (recent) personal experience being a TF Denka I was sharpening for @Darren Perkell crumbling at the heel at the same thickness behind the edge as the rest of the knife, which was totally fine.

 

[CiderBear]

Say, between a Watanabe/ Toyama B2 knife, and another budget B2, how could one tell if the heat treatment from the former is better?

 

[Tristam Douglas]

Most notable (recent) personal experience being a TF Denka I was sharpening for @Darren Perkell crumbling at the heel at the same thickness behind the edge as the rest of the knife, which was totally fine.

Interesting.

Any idea if inconsistencies in HT are more prominent at the tips and heels or on the belly?

 

[labor of love]

My question is: how do you tell if a knife has good heat treatment?
-OP

This thread went in a funny direction because I don’t think your question was precise enough.
You could try 30 different knives from different makers made from the same steel. But will they all perform the same? Unlikely.
Good and Bad isn’t really what most people are discussing here. Preferences for certain edge characteristics is what the discussion is about.
“Good heat treat” most often means the edge performs in a way the user finds to be optimized. It’s all opinion. Also, it seems pointless to participate in a forum if people can’t stand hearing other people’s opinions.

 

[CiderBear]

@labor of love:thank you for your comment. If I somehow came off as not willing to listen to others' opinions in my responses, I apologize. I would not apologize for the imprecise question, however, because I truly had no idea, and since I saw the concept thrown around a lot, I wanted to ask.

 

[labor of love]

Comment wasnt directed at you or anyone else specifically.
You have nothing to apologize for. I’m just trying to help you.

 

[CiderBear]

Thank you! You seem to have tried every knife I'm interested in (based on your forum posts) , so I would love to pick your brain (through pm) on some stuff if that's ok

 

[labor of love]

Yeah. Let’s do it. I love to chit chat.

 

[labor of love]

Why is ch!t censored? Lol

 

[dwalker]

Chit! Apparently so.

 

[Nemo]

In my limited experience (which pales in comparison to, for example, @osakajoe 's), "a good heat treatment" can be used to describe any the following features (often in combination, but there are tradeoffs between some of these):

1) Good sharpening feel and feedback (for me, it's especially about steels which feel smooth or creamy to sharpen and steels which give feedback about when you are sharpening the edge).
2) Ease of sharpening (how quickly/ easily can you grind the steel)
3) Ease of deburring.
4) Ability to hold a fine polish.
5) A steel which feels hard on the stones (which may be seen as giving poor feedback to some People).
6) Long edge retention.
7) Good edge stability (will hold a fine edge).
8) Adequate toughness.

I'm guessing that a fine grain structure probably contributes to ease of sharpening, sharpening feel and feedback, ability to hold a polish, toughness and possibly ease of deburring.

A high hardness contributes to edge retention (but probably less than the carbide structure), edge stability and a hard feel on the stones. Probably also to ease of deburring. It may or may not affect sharpening feel (there is probably a hardness sweet spot as very soft steels can feel gummy), toughness (once again, there are sweet spots) and ease of sharpening.

A good carbide structure probably contributes to the feel of hardness on the stones and is important for edge retention but may reduce edge stability (depending on carbide size). It probably affects toughness but I suspect in a complex manner.

Note that there is some degree of tradoff between a fine grain structure, carbide structure and probably hardness in the heat treatment process. A good heat treament is probably about finding an acceptable tradeoff between these which meets the intended charecteristics of the knife.

 

[Tristam Douglas]

I agree with Nemo on this GHT is very broad term.

No edge is perfect there always compromises to be made.

Murray Carter has an interesting video on YouTube where he discusses the differences between White and Blue steel. He talks about how through experimentation he proved theat the skill of the smith was key. well worth 8mins of anyone's time.