Research On The Microstructure And Properties Of High Chromium Cast Iron Used On Furnace Liner

Maximization and high efficiency of furnace make bell-less top to be the development of modern charging system of furnace. Bell-less top mainly consists of receiving hopper, gas seal box, central throat and distributing chute, and their different working conditions decide the difference of materials used for them. At present, service lives of furnace liners are not long enough and the maintenance is not in one downtime, which leads to high downtime percentage and tremendous economic loss. Materials used on furnace liner contain high manganese steel, steels surface welding or mosaic cemented carbide and high chromium cast iron, and high chromium cast iron exhibits the highest performance price ratio and owns wide application prospect. This topic started with chemical compositions and heat treatment of Cr26 cast iron, researched modification of Y-RE to Cr26 cast iron and studied the relation of compositon, microstructure and properties of new material used on furnace liner.The orthogonal experimental method was employed in this work to research the law of effect of Mo, Ni and Cu on the as cast microstructure and mechanical properties of Cr26 cast iron that used on the furnace liner. Based on the data of the impact toughness and macrohardness, the optimization about the composition was carried on. The results show that, interaction of two alloy elements to impact toughness was significate than that of any one alloy element, and effect order is Mo+Cu>Ni>Ni+Cu >Mo+Ni>Mo>Cu. The best as-cast mechanical properties, which are HRC 55.5 and 7.4 J·cm-2 can be obtained when the composition is 0.6wt.%Mo,0.7wt.%Ni and 1.0wt.%Cu, and the corresponding microstructure contains hexagonal M7C3 primary carbides, eutectic M7C3 carbides and austenite.The orthogonal test was also employed to analysis the effect of quenching temperature, quenching soaking time, tempering temperature on the microstructure and mechanical properties of Cr26Mo0.6Ni0.7Cu1.0 cast iron, who owns the best as-cast mechanical properties, and the three parameters were optimized. The results show that, as the quenching temperature rising, the quenching hardness gets higher; however, as the quenching soaking time prolonging, the quenching hardness presents a trend of rise first then fall. Effect order of the three factors to impact toughness is quenching temperature+quenching soaking time> quenching temperature> tempering temperature> quenching soaking time. The optimum heat treatment was 1000℃×2h, strong wind cooling+260℃×2h, air cooling. After this kind of heat treatment, the hardness can reach HRC59.5 and the impact toughness 8.0 J·cm-2 and the corresponding microstructure consist of martensite, M7C3carbide, secondary carbide and retained austenite.Modification effect of Y-RE to microstructure and mechanical properties of Cr26Mo0.6Ni0.7Cu 1.0 cast iron was studied in this work, the results show that, When the content of Y-RE rises to 0.15wt.% from 0, morphology of carbides changes into thin rod shape from crude stripy, and exhibits dispersive distribution, after heat treatment, mechanical properties can reach HRC61.6 and the impact toughness 7.4J·cm-2, and the corresponding microstructure consists of martensite, M7C3carbide, secondary carbide and retained austenite; When the content rises to 0.3wt.%, morphology of carbides changes into rude stipy and network-like, which results in the lower impact toughness.