The influence of boron on phase transformations during continuous cooling illustrated by unalloyed cast steels

This study investigates the influence of boron on phase transformations during continuous cooling of unalloyed cast steels. To achieve the research objective, cast steels with an appropriate chemical composition were designed and produced. One cast steel contained a micro-addition of 0.002% boron, while the other, with a similar chemical composition but without boron, served as the reference cast steel. The materials were subsequently subjected to dilatometric testing, on the basis of which Continuous Cooling Transformation (CCT) diagrams were developed. Microstructural analysis included examinations using light microscopy, as well as scanning and transmission electron microscopy. A Jominy end-quench test was also performed to assess hardenability. The test results were supplemented with discussion and conclusions. Based on the conducted studies, it can be concluded that, in the absence of alloying elements that enhance the effect of boron, the full potential of boron in improving hardenability is not realised. The benefits of its application are manifested mainly in the reduction of the critical cooling rate from over 300 to 262 °C/s, which occurs simultaneously with a decrease in the hardness of the resulting microstructures by approximately 70 HV5.