How do you evaluate the heat treatment of a knife?

[Carbon-]

I originally posted this over in the General Knife Discussion but didn't get a suitable answer and figured you guys might be able to help me out. I am not a knifemaker but just an average Joe who likes his knives. Hopefully you folks can help me out.

We all know that when it comes down to steels and their properties, the heat treatment is an incredibly important factor that ultimately determines how a given knife or steel will perform. Rowen's 1095, Buck's 440C, Cold Steel's AUS-8, Swamp Rat's SR-101, etc. are all well known for having perfected their heat treatment process and wringing every bit of performance out of their respective steels. I'm sure most of us have also experienced steels that have let us down and not lived up to their reputations because they weren't treated properly.

My question is, how do you evaluate a heat treatment? Let's say you're given a random knife in a particular steel; how do you determine if it was treated right? Is there any way to tell without using it? Is it related to ease of sharpening? Toughness? The Rockwell hardness? What are Rowen and Busse doing that other companies are not, and how do they figure it out? This is something I've always been curious about.

 

[Jonathans]

Carbon,
I am just a beginning as a maker, and I am sure there are others in this forum that will have a much more technical answer for you. However I test my blades for Rockwell C hardness to make sure that my targeted hardness was achieved. Target hardness for me is determined by the ultimate use of a particular blade. A chopper for instance might have a hardness of 56-58c so it does not chip when used hard, while a fine slicer might have a hardness of 62 c to retain its sharpness as long as possible and chipping from chopping is not a concern. Some steels will allow a combination of hard use and a hard Rockwell number if it was ground accordingly. A lot of what I see out there from the brand name manufacturers IMO is often a marketing strategy, while whether or not a blade is a performer is in reality determined by real life usage.
I hope this answers your question some.

 

[Bo T]

In my opinion, it is really difficult. While you can visually determine the finish, it is nigh on impossible to tell if the heat treatment was optimal on any single knife. Even determining the hardness will create a mar on the blade. Many makers will break blades or test coupons to determine the grain size. Martensite vs bainite vs austenite - a similar situation. Many have written that it boils down to the reputation of the maker and performance tests of their respective blades.

 

[stezann]

The matter is way more complicated than just the steel's hardness, and telling "optimal" is out of the game in terms of in-house evaluation.
But we most certainly just use the knives and see if the edge is stable enough to perform its intended tasks, it's as simple as that.
So let's just leave all the heat treatment claims to the companies and we just see if the edge is able to cut up to the expectations with a proper geometry.

 

[Matt Rochester]

As someone who does my own heat treat I have also wondered this. I am under the impression, and could be wrong, that if you hit your targeted hardness using the correct temper then your heat treat is correct. As for how to evaluate a finished knife I would say that you will have to test the edge holding ability and toughness. Like said above this depends on the type of knife and what the hardness is claimed to be. I will be staying tuned for more/better answers.

 

[Stacy E. Apelt - Bladesmith]

The way to evaluate a HT that you have no specs on vary, but the main method is to test it.

If you can do a Rockwell test, that is great, but it only tells part of the story. Any hardness above Rc56 is probably fine for the majority of knives.
Hardness if like a gal with a great figure and beautiful face. It may seem wonderful and then she says or does something to show that there is nothing inside that works with the good looking outside. If you go only with the first impression you may regret it later. You need to look deeper into the blade/gal.

It is how the edge holds up that really matters. Do an edge flex test ( brass rod test) for chipping and rolling. If it chips, the blade is too hard for the edge . Since you can't change the temper, you have to increase the edge angle. If it rolls, the HT is too soft and there isn't much you can do about it but return the knife.

If the edge does well on the edge flex test, test for durability. Start with soft wood and carve up the side of a 2X4. If the blade is big enough, chop on it. Examine the edge for any damage or rolling. If it is good, try carving on some oak. Chopping oak would only be a usable test for a heavy duty blade.

Obviously, chopping on wood with a kitchen slicer is a useless test. Cut things that simulate lots of use on things the knife is meant to cut. Cutting cardboard is a good test for a kitchen knife. Cutting up a box into strips is like using the knife in the kitchen for a day.

If the edge lasts fairly well on these tests, the HT is sufficient for the task the knife is made to do.
This type testing is like taking that gal in the first example hunting and finding out that she not only can shoot her own deer, but she can skin it and cook a wonderful stew as well. That is a truly good gal/knife. Even if the gal has a bit less figure than a supermodel, the things you found out on the hunting trip show she is a far better companion.
Knives are actually simple to determine the good from the bad.

 

[Stacy E. Apelt - Bladesmith]

The way to evaluate a HT that you have no specs on vary, but the main method is to test it.

If you can do a Rockwell test, that is great, but it only tells part of the story. Any hardness above Rc56 is probably fine for the majority of knives.
Hardness if like a gal with a great figure and beautiful face. It may seem wonderful and then she says or does something to show that there is nothing inside that works with the good looking outside. If you go only with the first impression you may regret it later. You need to look deeper into the blade/gal.

It is how the edge holds up that really matters. Do an edge flex test ( brass rod test) for chipping and rolling. If it chips, the blade is too hard for the edge . Since you can't change the temper, you have to increase the edge angle. If it rolls, the HT is too soft and there isn't much you can do about it but return the knife.

If the edge does well on the edge flex test, test for durability. Start with soft wood and carve up the side of a 2X4. If the blade is big enough, chop on it. Examine the edge for any damage or rolling. If it is good, try carving on some oak. Chopping oak would only be a usable test for a heavy duty blade.

Obviously, chopping on wood with a kitchen slicer is a useless test. Cut things that simulate lots of use on things the knife is meant to cut. Cutting cardboard is a good test for a kitchen knife. Cutting up a box into strips is like using the knife in the kitchen for a day.

If the edge lasts fairly well on these tests, the HT is sufficient for the task the knife is made to do.
This type testing is like taking that gal in the first example hunting and finding out that she not only can shoot her own deer, but she can skin it and cook a wonderful stew as well. That is a truly good gal/knife. Even if the gal has a bit less figure than a supermodel, the things you found out on the hunting trip show she is a far better companion.
Knives are actually simple to determine the good from the bad.