Carbide Size and Distribution and Their Effect on the Performance of High-Speed Steel Tools

Summary

Heat treatment of tools, composition and structure of high-speed-steel are important metallurgical factors influencing the performance of cutting tools. The effect of chemical composition and heat treatment on the cutting performance is now known, but the effect of structure on the behaviour of high-speed-steel tools during machining is not sufficiently known at present.

This study is an attempt to explain the influence of the size of carbides and their distribution in the steel matrix on the tool life of high-speed-steel tools. The study evaluates three different structures of commercial high-speed-steel 18–4–1 type (AISI type Ti) bar stocks of 50 mm (2 in.) diameter. The size of carbides and their distribution were determined quantitatively on a Quantimet instrument and qualitatively on a metallographic microscope. Grain size, heat treated hardness and distortion were determined before the evaluation of tool life. Tool life has been estimated for turning and face milling.

The performed tests show that the carbide size distribution is the most important factor to influence the character of steel and tool life. Coarse carbide particles in matrix unfavourably influence mainly the grain size, toughness and increase variation in tool life. The influence of distribution of carbides proved to be less important than their sizes when tested.