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Common hard alloys

Hard alloy is a composite material made by powder metallurgy process using refractory metal carbides (mainly tungsten carbide WC) and metal binders (mainly cobalt Co). It has extremely high hardness, wear resistance, red hardness, and certain impact toughness, and is a key material for manufacturing cutting tools, molds, mining tools, wear-resistant parts, and so on.

1. Core concepts

1.1 Ingredient basis

Tungsten carbide (WC) provides extremely high hardness and wear resistance. The higher the content, the better the hardness, wear resistance, and red hardness, but the toughness decreases.

Cobalt (Co) serves as a binder to bond WC particles together. The higher the content, the better the toughness, but the hardness and wear resistance decrease.

Other carbides such as titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), etc. Adding TiC/TaC/NbC can significantly improve the alloy's red hardness, oxidation resistance, and resistance to crescent wear (especially suitable for processing steel), but it will reduce its thermal conductivity and toughness.

1.2. Main classification (based on ingredients and applications)

WC Co alloys (YG type) are mainly composed of WC and Co. Good toughness, good thermal conductivity, good impact resistance, but relatively poor red hardness. Mainly used for processing cast iron, non-ferrous metals and their alloys, non-metallic materials, as well as wear-resistant parts, impact drills, etc.

WC TiC Co alloy (YT type) is made by adding TiC on the basis of WC Co. Red hardness, oxidation resistance, and wear resistance (especially resistance to crescent wear) have been improved, making it suitable for processing steel. But its toughness, thermal conductivity, and impact resistance are lower than YG class.

WC TiC TaC (NbC) - Co alloys (YW type) add TaC and/or NbC on the basis of YT type. It has better comprehensive performance, stronger universality, and good red hardness, toughness, and wear resistance. It can process both steel, cast iron, and non-ferrous metals, hence it is known as the "universal alloy".

Coated hard alloys are coated with one or more layers of extremely hard, wear-resistant, and high-temperature resistant thin films (such as TiC, TiN, Al ₂ O3, TiAlN, TiCN, etc.) on tough substrates (usually fine-grained or ultrafine grained WC Co or alloys with small amounts of other carbides added) through CVD or PVD processes. Coating significantly improves surface hardness, wear resistance, and service life, and is the mainstream of modern cutting tools.

The WC grain size of ultrafine/nanocrystalline hard alloys is very small (usually below 0.5 μ m). Has extremely high hardness and strength ("double high"), while maintaining good toughness. Suitable for precision machining, processing of difficult to machine materials, and micro cutting tools.

2. Comparison table of commonly used grades, compositions, and performance applications (mainly based on Chinese GB grades, with ISO application classification included)

3. Important note

3.1. Differences in brand system

Different countries and manufacturers have their own brand systems (such as Chinese GB, international ISO, American ANSI, Japanese JIS, and manufacturers such as Sandvik, Kennametal, Iscar, etc.). The above table is mainly based on Chinese GB grades. In practical applications, ISO's application classification (P/M/K) is more commonly used as a preliminary basis for material selection.

3.2. Composition range

The range of ingredients in the table is typical, and specific grades may have more precise formulas and trace additives (such as Cr ∝ C ₂ to inhibit grain growth). There may be slight differences in performance among different manufacturers or batches of the same brand.

3.3. Performance indicators

Density, hardness, and flexural strength are basic performance indicators. In practical applications, comprehensive properties such as wear resistance, toughness, red hardness, thermal conductivity, thermal shock resistance, and resistance to crescent wear are more critical, and these properties are closely related to composition, grain size, and manufacturing process.

3.4. Selection criteria

Choosing a hard alloy grade is a comprehensive process that requires consideration of:

Processed materials: material type (steel, cast iron, stainless steel, non-ferrous metals, high-temperature alloys, non-metallic, etc.), hardness, strength, work hardening tendency, etc.

Processing types: turning, milling, drilling, planing, tapping, etc.

Processing conditions: rough machining, semi precision machining, precision machining; Continuous cutting, intermittent cutting; Cutting speed, feed rate, and back cutting amount; Cooling conditions, etc.

Requirements for cutting tools: focus more on wear resistance (high hardness grades) or resistance to damage (high toughness grades).

Cost: The cost of grades containing TiC/TaC/NbC and coating grades is higher.

Development trend: Coated hard alloys and ultrafine/nanocrystalline hard alloys are the mainstream directions of current development, which significantly improve the comprehensive performance and processing efficiency of hard alloys. Gradient structures and new bonding phases (such as Ni, Fe, NiCo, etc.) are also research hotspots.

In summary, understanding commonly used hard alloy grades and their corresponding compositions, performance characteristics, and application ranges is the basis for selecting cutting tools and wear-resistant parts reasonably. In practical work, referring to the detailed material selection guide provided by the tool manufacturer based on specific machining objects and working conditions is the most reliable approach.