General Types Of High Speed Steel And Effects of Alloying elements on HSS :

There are four general types of High Speed Steel ,

1. 18-4-1 High Speed Steel :

This Steel, containing 18 per cent tungsten , 4 per cent chromium, and 1 per cent vanadium with about 0.75 per cent carbon is considered to be one of the best of all-purpose tool steels. This steel is extensively used for lathe, planer and shaper tools, drills and milling cutters.

2. Cobalt High Speed Steel :

This is known as super high speed steel. Normally cobalt is added from 5 to 8 per cent to increase better hot hardness and wear resistance than 18-4-1 type. One analysis of cobalt high speed steel contains 20 per cent tungsten, 4 per cent chromium, 2 per cent vanadium and 12 per cent cobalt.

3. Vanadium High Speed Steel :

This steel contains 0.70 per cent carbon and more than 1 per cent vanadium. High Vanadium with carbon high speed steel is superior to 18:4:1 type for difficult - to - machine materials. This has excellent abrasive resistance.

4. Molybdenum High-Speed Steel :

This Steel containing 6 per cent molybdenum , 6 per cent tungsten, 4 per cent chromium, and 2 per cent vanadium have excellent toughness and cutting ability

Effect of Alloying Elements on HSS :

Carbon produces carbides and a hardenable matrix. Melting point is decreased with increase in carbon content. A low carbon content increases the impact strength but reduces the matrix hardness.

Chromium reduces tendency to scaling. It is mainly present in ferrite matrix and is largely responsible for the sir hardening of HSS.

Vanadium increases the abrasion resistance, cutting quality of the tools and the tendency to air hardening.

Tungsten provides hot hardness by forming carbides and form - stability.

Molybdenum increases hardenability , while

Cobalt improves hot hardness and makes the cutting tool more wear resistant.

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