Knife Steel 101

Here's a nice rundown of the various materials used to make cutter knives, along with some lively discussion. November 27, 2007

I have been working at a moulder for a while now and I only use M2 high speed steel. I buy it from various sources and have found that sometimes it doesn’t seem to last as long. I have been told that there are better knife steels than M2 and I would like to know what your favorites are and why. Also, for you tooling guys lurking out there, what are the differences between the different steels?

Forum Responses
(Solid Wood Machining Forum)
From contributor T:
I will start with the lowest grade and move up. If I miss a few types, forgive me, as it seems everyone has their own special grades and product names.

D2 HCHC - This grade has an average Rockwell hardness of 58Rc. It has a high carbon and chrome content, making it very chemical resistant. This is good for materials like redwood and cedar. This steel is good for softwoods and short runs in hardwoods.

AKM - This grade has an average Rockwell hardness of 62Rc. This material is a semi-high speed steel. It offers good wear resistance that is suitable for short runs.

M2 HSS - This grade has an average Rockwell hardness of 63Rc. It offers about 25% longer run life than D2 due to the addition on tungsten and moly. It handles heat better and is great for long runs in softwoods and hardwoods.

T1 HSS - This grade has an average Rockwell hardness of 63Rc. It offers about 20% longer run like than M2 due to a high tungsten content. It offers a better resistance to abrasive glue lines and is great for running hardwoods. It is also great for running softwoods where the ultimate cutting life is wanted at a reasonable price.

M3 HSS - I do not know the Rockwell of this grade. This grade contains additional carbon, vanadium, and molybdenum. According to the manufacturer of this grade of high speed steel, it can provide better finishes and longer runs in certain applications.

V3 HSS - This grade has an average Rockwell hardness of 66Rc. This long wear life high speed steel gets its properties from high levels of vanadium and cobalt.

Black Nitride HSS - This grade has an average Rockwell hardness of 72Rc. This grade of high speed steel is a case hardened M2 that produces extra long run times. It is equivalent to Opti® but costs less. It is supplied with a black oxide coating.

Opti® - This grade has an average Rockwell hardness of 78Rc. This knife steel is “specially treated” to produce an ultra hard surface. It offers a 50% increase in life over standard M2.

M42 HSS - This grade has an average Rockwell hardness of 66Rc. This high grade high speed steel contains large amounts of cobalt and tungsten. It was originally engineered to cut high grade aluminum alloys in the aircraft industry. It is inlayed into a steel backer. This steel performs remarkably well in woods with reported increases in life of up to 8 times over M2.

RW-90 HSS - This grade has an average Rockwell hardness of 72Rc. This knife steel is a V3 that is coated on its face with a mixture of chrome and 1,500 grit diamond powder. It is advertised as the longest wearing high speed steel in the industry.

Carbide - This material has an average Rockwell hardness of 89+Rc. Carbide knives offer over 1000% longer run times than T1. It is available in brazed material and as Knife-Lock systems. Carbide is used in problem hardwoods such as teak, maple, and hickory as well as engineered woods.

From contributor J:
I prefer M3+. I have tried other types and always come back. It grinds nice and as long as you don't burn the edge while grinding, it lasts for thousands of lineal feet even on hard maple (non-jointed) before regrinding. As long as you don't hit a staple, that is.

From contributor R:
My favorites are the Black Nitride and Opti. My customers like them the best because of the run time between sharpenings.

From contributor S:
There are many differences that will effect the life of your knife steel. Some steel is blanchard ground - you can see radial lines in the face of it. At each point where these lines meet the cutting edge of the tool, there is a greater chance for it to knick. The steel we use is all surface ground, eliminating the radial lines and reducing the frequency of knicks.

From contributor J:
Contributor S, we machine wood, not airplane parts. Could you post test results to prove your theory on the two different ground ways? I don't mean to be rude, but I have seen this sales pitch way too often to new people coming into the moulder industry.

From contributor S:
Our research and development team has extensively tested many types of tool steel over the last 20 years. We offer both blanchard and surface ground steel, but we recommend using surface ground to extend the time between regrinds. Due to agreements with our testing partners, test data is currently not available for public distribution.

From contributor D:
Getting back to the original question on why the steel may not last as long at times... One of the keys to a good bar of knife steel is the heat treat. Consistently hardened knife steel should perform the same. Variations in the hardness both within the same bar and from bar to bar will obviously impact life. Contributors have provided very good information on the various types of steel, but consistent bar to bar performance comes down to a good quality base material and a controlled heat treat process.