Study On Carbon Steel/Hypereutectic High Chromium Cast Iron Prepared By Centrifugal Casting-Hot Rolling Process

Metal wear-resisting plates are the most important parts used in the conditions of machinery, metallurgy, mining and other industries which are under the dual role of impact and abrasion. Consequently, it needs higher requirements in the ways of wear resistance and impact resistance. Hypereutectic high chromium cast iron (HCCI) is one of the excellent wear resistant materials, but the low impact toughness is a fatal defect due to the existence of hard and consecutive carbides in the matrix. At present, most of the high chromium iron/low carbon steel wear composite plates were prepared through surface welding process, with the advantages that the hardness of wear-resisting coatings is high, and matrix materials has good processing performances. But because of its high welding stress, the coatings would easily crack when used, which reduce the service reliability and life expectancy. Focused on the brittleness of hypereutectic high chromium cast iron, a novel preparation of carbon steel/hypereutectic high chromium cast iron with high performance is put forward in this work:a sandwich structured casting blank containing hypereutectic high chromium cast iron (HCCI)core and Q235steel claddings was fabricated by centrifugal casting, then hot rolled into composite plate. Main conclusions are drawn in this thesis as follows:Through orderly pouring each liquid material with the mold rotating speed of850r/min,900r/min,1000r/min and the pouring time intervals of10-15s and55-60s, microstructures of HCCI and Q235steel in the casting blank distinct clearly and transit continuously near the interfaces. HCCI and Q235steel achieved metallurgical bonding, the bonding strength is392MPa, which is higher than the tensile strength of both carbon steel (376MPa) and high chromium cast iron (117MPa), respectively.Through stress simulations and rolling tests of hot rolling process, the hot-rolled composite plate can get good rolling qualities at1170℃, under different rolling rates. Due to the high bonding strength of the interface which has certain constraints on the core high chromium cast iron, high chromium cast iron is under low stress and deform uniformly in the rolling process. After hot-rolled, interface appeared lean carbon ferrite area with good plasticity, which means that the interface of the composite relieves the stress on high chromium cast iron layer. Interface under different rolling processes cannot get destroyed since the interface stress is less than the bonding strength of each material.Through physical simulation test at Gleeble thermal simulation tester and microstructures observation, in the deformation conditions of1142℃-1170℃, strain rate0.4-1.0s-1, high chromium cast iron composite layer can obtain recrystallization in microstructures.Thermal simulation and stress simulation results have good consistency, at1170℃, the strain rate of1.0s-1, each pass deformation of10%, the composite plate can obtain better forming quality, as well as high chromium cast iron layer is able to obtain the martensite.After rolling, the composite material can obtain the best mechanical properties by1000℃quenching heat treatment, which show that the hardness of high chromium cast iron layer is HRC68.5and the overall impact toughness is11.0J/cm2, which is3.5times compared with the composite materials before being rolled. The average wear weightlessness during each30min is24.4mg, which is2.3times than unrolled hypereutectic high chromium cast iron.The carbides in high chromium cast iron layer were broken and dissolution in effect of the rolling force during hot rolling process. On the longitudinal direction the broken of carbides is mainly caused by the effect of the shear stress, well it is mainly caused by the effect of friction force on cross section direction. The mechanism of carbides refinement can take a conclusion as follows:local dissolution of carbides, the groove formed at defects and the dissolution aggravated, then the grooves deepen and the least cross section of carbide appeared, after that the carbide broken by tensile, at last, the carbide dissolution.With microstructure and properties comparison of the composite prepared by surface welding and centrifugal casting-hot rolling processes, the wear weightlessness of the composite prepared by surface welding are higher than that prepared by centrifugal casting-hot rolling process. The wear weightlessness of the composite prepared by surface welding is lower when the welding line energy is higher, but the welding stress is larger, the coating will easily peeled off in the process of wear and tea. Centrifugal casting-hot rolling composite process has a relatively good mechanical properties.