Comparison of cracking sensitivity between high-permeability 1.5 wt% Si steel and 6.5 wt% Si steel in mushy zone

Abstract

Twin-roll thin strip casting process (SC) has been utilized in laboratory to fabricate typical high-permeability electrical steel (HPES) such as 1.5 wt% Si and 6.5 wt% Si steel with ideal crystallographic orientation and excellent permeability after a series of heat treatments. Whereas, there exists a problem associated to the cracking sensitivity in high temperature mushy zone, which further restricts the industrial application of SC to produce HPES. Mechanical behavior of 1.5 wt% Si and 6.5 wt% Si steels in high temperature mushy zone were comparatively studied by Gleeble-3800 physical simulation system under strain rate 3 s−1, systematically. The high temperature brittle region composed of zero strength temperature (ZST) and zero ductility temperature (ZDT) in the mushy zone were quantitatively determined, and the critical strain threshold associated to hot crack initiation in the brittle region were further evaluated following empirical model proposed by Y Won. Results show that the tensile strength and fracture ductility in the mushy zone are both closely associated with the varying volume fraction of network-shaped structure during solidification, and are decreased with decreasing solid fraction concerning studied 1.5 wt% Si and 6.5 wt% Si steels. The high temperature brittle region corresponding to the studied 1.5 wt% Si and 6.5 wt% Si steels in mushy zone are separately confirmed to be 1459 ~ 1465℃ and 1390 ~ 1427℃, and the thresholds of critical strain for hot cracks initiation in high temperature brittle region are calculated to be ~ 1.18% and ~ 0.24%, respectively. Considering from perspective of width of high temperature brittle region and critical strain threshold for hot crack initiation, the cracking sensitivity of 6.5 wt% Si steel in the mushy zone is more serious compared to 1.5 wt% Si steel.