Molybdenum Compounds Formed on the Surface of Silicon Steel Slab

In an attempt to elucidate the mechanism by which the surface quality of steel products containing a small amount of Mo is noticeably improved, the precipitates formed on the surface of silicon steel slabs after coating with Mo compounds and the subsequent annealing under various atmospheres of N2, Ar and H2 gases have been investigated. Many fine spherical precipitates of O.05-10μm are formed on the surface of silicon steel slab after annealing under a H2 atmosphere, whereas agglomerated and complex precipitates are formed during slab annealing under N2 and Ar atmospheres. In the analyses of the precipitates by Electron Probe Micro Analysis (EPMA) and Energy Dispersive X-ray (EDX), Mo is detected together with the elements S, P, Se and Sb, which have very low solid solubilities in α-iron and the tendency to segregate to iron surface or to grain boundary. As Mo enhances the formation of precipitates consisting of Mo, S, P, Se and Sb on the surface of silicon steel slab and thereby scavenges the ferrite matrix and strengthens the grain boundary, it is considered that the slab annealing treatment after coating with Mo compounds will noticeably inhibit intergranular fracturing.