Microstructure and properties of SPHD hot strips with boron produced by CSP technology

B-contained (0.004% -0.006%) and B-free SPHD hot strips produced by CSP process were chosen as experimental materials. The mechanical properties, microstructure, precipitates, dislocation density and grain orientation of the two different kinds of specimens were analyzed by tensile tests, metallographic observations, SEM analysis, TEM and EBSD observations. The results showed that the addition of micro-alloying element B into SPHD hot strips made ferrite grains evidently coarse, large precipitates were found, the dislocation density decreased, and all these caused the yield strength to reduce. The crystallographic orientation was analyzed and observed by EBSD. The orientations among neighboring grains both of the B-contained and B-free steel were mainly large angle grain boundaries, however, a great deal of subgrains were found in the B-free steel.