Effect of tempering time on microstructure and properties of BS960E steel after rapid heating and quenching
Effect of tempering time on microstructure and properties of BS960E steel after rapid heating and quenching was studied by means of optical microscope,scanning electron microscopy,electron backscatter diffraction technique,energy dispersive spectroscopy analysis and X-ray diffraction.The results show that the microstructure of the BS960E steel after quenching is lath martensite,the average grain size of prior austenite is 5.69 μm,and the dislocation density is 4.02281 ×1015 cm-2.With the increase of tempering time,the martensitic lath structure gradually decomposes,some lath structures still exist after tempering for 2 min,the effective grain size(martensite lath block)is 2.47 μm,and the dislocation density sharply decreases to 9.48079 ×1014 cm-2.When tempering for 15 and 30 min,the martensite lath begins to coarsen,and the proportion of small angle grain boundary density decreases.At this time,the effective grain sizes are 2.57 and 2.59 μm,respectively,and the dislocation densities are 7.80957× 1014 and 6.75406× 1014 cm-2,respectively.When tempering for 60 min,martensite lath and block merge obviously,the density and proportion of large angle grain boundaries decrease,the effective grain size increases to 2.99 μm,and the dislocation density decreases to 5.19655× 1014 cm-2.The precipitation of carbides can be divided into three types:prior austenite grain boundary precipitation,martensite lath block boundary precipitation and intragranular precipitation.With the increase of tempering time,the tensile strength and yield strength of the BS960E steel gradually decrease,while the elongation increases.When the tempering time reaches 60 min,the coarse precipitated carbides lead to a decrease in the elongation.Taking into account the comprehensive mechanical properties of the BS960E steel after rapid heating and quenching,the optimal tempering time is 2 min.
NETL
NSTL
万方数据
