OPTIMIZATION OF MICROSTRUCTURE OF THE LOW ALLOY STRUCTURAL STEEL USING RARE EARTH METAL (REM) ADDITION

摘要

A general trend in steelmaking industry is to increase strength, resistance to brittle fracture and fatigue properties of steel products at favorable price. Achieving fine-grained microstructure during austenite to ferrite transformation is a basic prerequisite to improve the mechanical properties. The desired transformation can be achieved in several ways one of which is the use of small nonmetallic inclusions as heterogenous nucleation sites during solidification of steel. A great attention is focused on this concept in recent years. Rare earth metals are suitable for the formation of small inclusions similarly as in the case of conventional microalloying elements such as niobium, titanium, vanadium and other. Rare earth metals have a high affinity to oxygen and sulfur. The paper deals with the optimization of microstructure of 42CrMo4 low alloy structural steel used for machine parts exposed to higher stresses. The steel was alloyed with cerium in the form of mischmetal to achive fine-grained microstructure. Operational experiment was proposed and realized in accordance with results of laboratory experiment.