The Effect of High Boron Additions on the Microstructure of Cast Steel

This study summarizes research into the effect of high boron additions on the microstructure of cast steel under the certain carbon (0.42 C wt.%) and chromium (11.65 Cr wt.%) content. Varying amounts of boron between 0.48 - 4.75 wt.% was added into steel melt. The boron analysis of the alloys was conducted by wet chemical analysis. The microstructure of the specimens was characterized with optical microscope, Scanning Electron Microscope with Energy Dispersive X-Ray Analysis (SEM/EDX) and X-Ray Diffraction (X-RD). The experimental results showed that high boron steel was successfully produced by sand casting with high casting yield. The microstructure of boron alloyed high chromium cast steel consists of three dimensional networks of M2B borides surrounding the martensitic matrix in as cast condition. Under the certain carbon and chromium content, boron carbide volume fraction is directly depended on the boron additions. Due to the high amount of chromium and boron, carbides and borides were embedded in each other in all additions. In the specimens having less than 2.44 B wt.%, carbide/boride structure was fishbone type with dendritic distribution over the matrix whereas rod/needle like structure with randomly distribute was observed in specimens having 2.44 - 4.75 B wt.%. In all specimens containing boron, M2B and M7 (C, B)5 type carbides/boride peaks were detected by X-RD analysis.