Structural composition and classification of cemented carbide

Cemented carbide is a material manufactured via powder metallurgy, consisting of one or more refractory metal carbides (e.g., tungsten carbide, titanium carbide) as the hard phase, bonded together by a metallic binder (e.g., cobalt, nickel, iron). For cutting tools, common carbides include WC, TiC, TaC, NbC, while typical binders are Co, Ni, Fe. The strength of cemented carbide primarily depends on cobalt content.

Owing to its exceptional properties: high strength, hardness, wear resistance, corrosion resistance, high-temperature stability, and low thermal expansion. It has become indispensable in industrial applications and is regarded as one of the most superior tool materials.

Cemented carbide is categorized in two main ways:

1）By Workpiece Material

2）By Chemical Composition

1. Classification by Workpiece Material (ISO Standard)

The International Organization for Standardization (ISO 513-1975(E)) classifies cutting tool cemented carbides into three categories:

P Class: Designed for machining steel, including cast steel.

K Class: Suitable for cast iron, non-ferrous metals, and non-metallic materials.

M Class: Used for machining steel (e.g., austenitic steel, manganese steel), cast iron, and non-ferrous metals.

2. Classification by Chemical Composition (Common in China)

Based on chemical composition and applications, cemented carbides are divided into three classes:

1）Tungsten-Cobalt (WC-Co) Alloys

l Hard phase: WC

l Binder phase: Co

l Designation: YG series (equivalent to ISO K Class).

2）Tungsten-Titanium-Cobalt (WC-TiC-Co) Alloys

l Hard phase: WC + TiC

l Binder phase: Co

l Designation: YT series (equivalent to ISO P Class).

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3）Tungsten-Titanium-Tantalum/Niobium-Cobalt (WC-TiC-TaC/NbC-Co) Alloys

l Hard phase: WC + TiC + TaC/NbC

l Binder phase: Co

l Designation: YW series (equivalent to ISO M Class).

Recent Developments in Cemented Carbide 

To meet evolving industrial demands, new varieties of cemented carbide have emerged:

1）Ultra-Fine Grain Cemented Carbide

Features: WC-Co alloys with average carbide grain size < 1 µm.

Advantages: Enhanced strength and wear resistance due to refined microstructure.

2）Surface-Coated Cemented Carbide

Structure: A few-micron-thick layer of high-hardness, wear-resistant compounds (e.g., TiC, TiN, Al₂O₃) deposited on a tough carbide substrate.

Benefits: Combines substrate toughness with surface hardness for extended tool life.

3）Steel-Bonded Cemented Carbide

Hard phase: WC or TiC.

Binder phase: High-speed steel or stainless steel (instead of Co/Ni/Mo).

Applications: Tools requiring both carbide-like hardness and steel-like machinability.

Summary:
Cemented carbide’s versatility stems from its tunable composition and microstructure. Traditional classifications (YG, YT, YW) address specific machining challenges, while modern innovations (ultra-fine grains, coatings, steel bonding) further expand its capabilities in precision engineering, high-speed cutting, and extreme environments.