Effect of bismuth content on the microstructure and properties of free cutting steels
The bismuth-containing free-cutting steel served as an environment-friendly material has a broad application prospect.Bismuth was alloyed by preparing bismuth ferromanganese alloy,which was then added to the molten steel in the process of vacuum induction melting.After casting the melt and hot rolling,three kinds of bismuth-containing free cutting steels were obtained.The effect of bis-muth content on the second phase,mechanical properties and cutting properties of steels was studied.With the increase of bismuth content from 0.013％to 0.069％,the size of MnS decreased by about 45％and the shape changed from rod to ball.The yield strength,the hardness of matrix and second phase,and the impact energy of the steels decreased.The tensile strength increased slightly,and the elongation of the experimental steel increased greatly.The comprehensive mechanical properties of the steel de-creased slightly.The results of cutting experiments showed that with the increase of bismuth content,the wear of milling tools decreased significantly;the surface flatness and smoothness of the steels in-creased;the chip shapes changed from long strip to short spiral;the chip breakage degree was greater;and the cutting performance was significantly improved.
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