Influence of technological factors on formation process of bimetallic castings

The analysis of the modern state of wear-resistant metallic material production showed that one of the promising directions for improving their quality is the use of bimetallic steel-cast iron castings, which have a complex of properties differentiated over the volume and surface of the products. However, the problem of obtaining a high-quality joint of the steel base and the working cast iron layers is not completely solved at present. So, the research aims to determine the quality criterion of a good diffusion joint and to study the selected technological factor influence on the formation process of bimetallic castings using the developed mathematical model. The paper examines the effect of the steel base temperature at liquid cast iron pouring over it, the temperature of pouring cast iron, as well as the ratio of liquid cast iron mass to the unit surface of the steel base on the contact surface temperature as selected quality criteria, and the structure of the transition diffusion layer of bimetallic castings. It was determined that a high-quality joint is realized when this temperature is larger than the solidus temperature of the cast iron. Moreover, the results of the mathematical model application showed maximum contribution of the liquid cast iron mass/steel unit surface ratio, less effect of the pouring iron temperature and minimum influence of the solidified steel base temperature onto the quality criteria. The metallographic analysis established the diffusion joint formation in the transition steel-cast iron layer consisting of pearlite on the side of the steel base and without the carbide matrix area on the side of the working iron layer. The results obtained are of great importance for the designing bimetallic machine parts worked under intensive wear conditions.