Solid carbide cutting material

Solid carbides are composites produced through sintering.

They consist of a soft metallic binder phase made of cobalt embedded with hard carbide titanium, tungsten, tantalum carbide or titanium nitride. The hardness and toughness depends on a carbide composition of 1-10 µm and the soft binder, which is normally a volume fraction of up to 20%, whereby more binders make the cutting edge softer and tougher [6].

The hot hardness of approximately 1,000 °C depends entirely on the binder phase as it has the lowest melting point. They are mostly in the form of indexable inserts, but they are also available as solid carbide tools or soldered carbide inserts on steel tool bodies.

Carbides with tungsten carbide (HW) have high wear resistance and are characterized by their extreme toughness. They are divided into titanium carbon-free and titanium carbide-containing cutting material. The former are based on tungsten carbide and are extremely tough, allowing them to withstand high mechanical stress. The hot hardness is slightly lower than is the case for the titanium carbide-containing versions, which contain up to 60% titanium carbide in addition to tungsten carbide. This increases the hardness additionally and these materials have better resistance to the tendency of wearing of the machining chip. Furthermore, the oxidation resistance increases with higher cutting temperatures.

The grain size of the carbide also has a critical influence on the properties and thus micro-grain carbides (HF) were developed on the basis of tungsten carbide and cobalt. They are also referred to as ultra-fine grained carbides depending on the grain size. The grain size moves within the range of 0,2–1 µm thereby achieving properties that oppose one another in normal carbide [6]. This increases the hardness and bending strength without changing the binder phase, which makes the cutting material especially suitable for dynamically demanding machining work such as occurs during cutting interruptions.

With micro-grain carbide tools, difficult-to-machine materials such as hardened steel can also be machined. By hard material coating of tools, as is the case with the majority of carbide tools today, the wear resistance can be increased while the same tough carrier is retained. This is done by applying several titanium carbide hard material coatings, titanium nitride, titanium carbon nitride, aluminium oxide, titanium aluminium nitride, chrome nitride or zirconium carbon nitride in PVD-, CVD or PACVD procedures [2]. We prefer to apply the CVD procedure, which distinguishes itself through process temperatures between 850 °C and 1000 °C. The multi-layer coatings are applied almost exclusively with a total thickness of up to 25 µm [8]. The advantage between coated and uncoated carbide inserts is the higher tool life or respectively the higher achievable cutting speed. Coatings also widen the range of application of a carbide grade (grade adjustment).