Chapter 165 Rare earths in steels

Abstract

Summary In this review, practical examples of improvements in the properties of steels achieved by rare earth additions, and the fundamentals to understand the cause of these improvements have been discussed. In spite of the progress so far in understanding the influence of rare earth additions on the physical, chemical and mechanical properties of steels, it is apparent that many questions remain unanswered. For example, although many reports revealed that the rare earth additions change the shape, size and composition of non-metallic inclusions formed in the steels and that they play a very important role in improving the various properties of steels, research is still not adequate. Thermodynamic data are still too scattered to accurately predict these characteristics of non-metallic inclusions and the conditions under which the shape, size and composition of inclusions are controlled. Data for the effects of rare earths on the surface and interfacial properties; surface tension, contact angle, etc., of steels, are also unsatisfactory. Precise solubilities of rare earths in molten and solid iron and steels are still not available. Studies are also required on the nucleation process of the non-metallic inclusions themselves in the steels. Knowledge of all of these is essential to understand the metallurgical process and the various properties of steels.