Inclusions in 9SMn28 free-cutting steel during directional solidification process

The 9SMn28 free-cutting steel samples were prepared under different with drawal velocity using Bridgman zone melting directional solidification apparatus. The inclusions and dendrites of which were observed by OM (optical microscope), SEM (scanning electron microscope) and EPMA (electron probe microanalyzer) were calculated and analyzed by applying solidification theory. The results show that the inclusions are mainly manganese sulfides and gathered in the space among dendrites arms in 9SMn28 steel ingots. Manganese-sulfide inclusions are almost spherical,as a small amount of elliptoid and rod-like inclusions are found around the secondary dendrite arms. And the size of inclusions decreases with increasing the with drawal velocity. The calculation result of secondary dendrite arm spacing is in agreement with that of the test, which both decreases as withdrawal velocity increases.