Tool steel knife blades introduction
In the following article, we are going make an overview about different tool steels, which are used for tool steel knife blades. Many knife enthusiast and experts already know and enjoy advantages of knives with blades made of tool steels. We are going to explain what tool steels are, what are their advantages and disadvantages, their categorization, for which purpose they are designed and why some stainless steels are labelled as stainless steels. We are also going to present the most common tool steel used for knife blade and which knife companies are producing knives with tool steel blades. Maybe also knife experts will find some new information about tool steel blades.
About tool steels
We all know that some material can be cut only with a harder material. In production technologies they need for steel cutting and other mechanical treatments a material, which is harder than the conventional steel. For that purpose they used a tool steel.
Tool steels are basically alloy or carbon steel with mechanical properties demanded for cutting conventional steel.
Tool steels used for knife blades
Knife craftsman and designer also find out the advantages of tool steels and started to use them for knife blades. Probably there is no need to put out that due to really high hardness of the tool steels, they demanded only the most experiments knife craftsman’s for production. Tools steels required special heat treatment.
The main characteristics of tool steels:
- High hardness
- Semi-stainless
- Very high toughness
- Great cutting edge holds ability
- Excellent abrasion resistance
Tool steel blades are due to their properties suitable for outdoor, every-day carry and tactical knives. Tool steels are semi-stainless steels, which mean that they can be without any problems used for above written purposes. In comparison with stainless steel blades, tool steel blade are tougher, have higher surface hardness, stiffness, abrasion resistance and high ability to hold sharp edge.
However, they cannot be used e.g. for kitchen or hunting knives, where only high corrosion resistant stainless steels can be used.
Tool steel blades surface finish
Most common surface finishes of blades made of tool steels are bead-blasted, stone-washed or coated surface.
AISI D2 is one of most widely used tools steels for knife blades. AISI D2 is characterized as high-carbon high-chromium steel and also labeled as W.-Nr. 1.2379. The main characteristics of AISI D2 tool steel are:
- Distinctive toughness and shock-resistance
- High strength and stiffness
- Excellent edge hold ability
- Great wear and abrasion resistance
- Good corrosion resistance due to high chromium content – semi-stainless steel
| Alloy material | C | Si | Mn | Cr | Mo | V |
| Content % | 1.55 | 0.3 | 0.4 | 11.8 | 0.8 | 0.8 |
Most commonly AISI D2 tool steel blades are hardened up to surface hardness of 62 HRC. The following chart shows the main mechanical properties of AISI D2 tool steel hardened to 62 HRC at 20°C (the most common temperature for knife use)
| Density kg/m3 | 7700 |
| Elasticity modulus MPa | 210000 |
| Compressive yield strength, Rc0.2 | 2200 |
| Specific heat J/kg °C | 460 |
The knife manufactures who commonly uses AISI D2 tool steel:
- Viper by Tecnocut
- Pohl Force
- LionSteel
CPM Tool steel blades
CPM Crucible Particle Metallurgy is a process of high-speed tool steels and high alloy steels production; produced by company Crucible Industries LLC.
The main characteristic of CPM process is very homogenous steel of high quality with great toughness and grindability compare to other steel production processes.
Comparison between CPM Steel and Conventional steel (source: Crucible Industries LLC CPM® S35VN™ Data Sheet)
CPM S35VN
CPM S35VN is a martensitic tool steel. Due to high corrosion resistance it is labeled as stainless steel; but due to its mechanical properties and purpose of knife use, it is characterized as a tool steel. For knife blades is used by Italian knife company Maserin.
| Vanadium % | Niobium % | Chromium % | Total % | |
| CPM S35VN | 3.0 | 0.5 | 10.5 | 14.0 |
| CPM S30V | 4.0 | 10.5 | 14.5 | |
| 440 C | 0.0 | 12.0 | 12.0 | |
| 154 CM | 0.0 | 17.5 | 17.5 | |
| CPM S90V | 9.0 | 11.0 | 20.0 |
CPM M4
CPM M4 is a high performance tool steel manufactured with Crucible Particle Metallurgy CPM process by Crucible. It is used for premium, custom, high end blades and is definitely one of the best tool steel used for knives.
The main features of CPM M4 tool steel are (source : Crucible Industries LLC, General Information)
- High deformation resistance (higher than A2, M2 or D2)
- Surface hardness of 63/64 HRC
- Better wear resistance even than M2 or D2
CPM M4 tool steel is used also for Spyderco knives.
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