Cutting Tool Materials: High Carbon Steel, High Speed Steel, Cemented Carbides, Stellite, Ceramics, Diamond

Cutting Tool Materials

The following materials are commonly used for manufacturing the cutting tools, selection of a particular material will depend on the type of service it is expected to perform.

1. High Carbon Steel: 

Plain carbon steels having a carbon percentage as high as 1.5% are in common use as tool materials for general class of work. For high production work they are not considered as they are not able to withstand very high temperature, hence they can’t be used at high speeds. 

The required hardness is lost by them at temperature 200- 250 0C. They are also not highly wear resistant. They are used mainly for hand tools as they are less costly, easily forgeable and easy to heat treat.

High carbon medium alloy steels are more effective than plain high carbon steels. These steels in additions to carbon content are provided better hot hardness, higher impact resistance, higher wear resistance by adding small amount of Tungsten, Chromium, Molybdenum, Vanadium etc. Which improves the performance and able to operate temperatures of 3500C.

2. High Speed Steel: 

It is a special alloy-steel containing the alloying elements like Tungsten, Chromium, Vanadium, Cobalt and Molybdenum up to 25%. 

These alloying elements increase its strength, toughness, wear resistance, cutting ability and retains it’s hardness at elevated temperature of 5500-6000on account of these added properties the high speed steel tools are capable of operating at 2 to 3 times higher cutting speeds than high carbon steel tools.

The most commonly used high speed steel has composition alloying elements as 18-4-1 i.e. 18%W, 4%Cr, and 1%V.

3. Cemented Carbides: 

These Carbides are formed by the mixture of Tungsten, Titanium with Carbon. The carbides in the powder form are mixed with Cobalt which acts as binder. 

The mixture with powder metallurgy process, sintered at high pressures of 1500kg/sq cm to 4000kg/sq cm and temperatures of above 15000is shaped in to desired forms of tips. 

These Carbide tips are then brazed or fastened mechanically to the shank made of medium Carbon steel. These cemented carbides possess a very high degree of hardness and wear resistance. 

They are able to retain this hardness at temperature up to 10000with the result, the tools tipped with cemented carbide tips are capable of operating at speeds 5 to 6 times higher than those of high speeds.

4. Stellite: 

It is a non ferrous alloy mainly of Cobalt, Tungsten and Chromium. Other elements added in varying proportions are Tantalum, Molybdenum and Boron. It has good shock and wear resistance and retains its hardness at a red heat up to 9200C

It is used for machining materials like hard bronzes, cast and malleable Iron etc. 

Tools made of Stellite are capable of operating at speed up to 2 times more than those of common high speed steel tools. Only grinding can be used for machining it effectively.

A satellite may contain 40-50% Co, 15-35%Cr, 12-25%W and 1-4%Carbon.

5. Ceramics: 

The introduction of ceramic material as a cutting tool material is a latest development in the field of tool metallurgy. It mainly consists of Aluminum oxide which is comparatively much cheaper than any of the chief constituents of cemented Carbides. Boron nitrides in powdered form are added and mixed with Aluminum oxide powder and sintered together at a temperature of 17000C. They are then compacted in to different tip shapes. 

Tools made of ceramic material are capable of withstanding high temperatures, without loosing their hardness up to 12000C. They are much more wear resistant than cemented carbide tools. They are more brittle and low resistance to bending. They can’t be used for rough machining work and mainly used for finishing operations. 

They are capable of removing 4 times more material than Tungsten carbide tools and 2-3 times high cutting speeds under similar conditions. 

No coolant is needed while machining with ceramic tools.

6. Diamond: 

It is the hardest material known and used as cutting tool material. It is brittle and low resistance to shock but it is highly wear resistant. Diamonds are used for only light cuts on materials like Bakelite, Carbon, Plastics, Aluminum and Brass etc. Because of low co efficient of friction they produce a high grade of surface finish. Because of high cost only limited use in tool industry.

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