Research Of Aluminum Silicon Composite Layer On Heat Resistant Steel Grate By Cast-infiltration Method

The important component in sintering machine grate is vulnerable. Due to its large range of temperature changes in the working process and grate should not only bear the sinter material gravity the high-speed impact of powder and gas two-phase flow wear and tear but the atmosphere of CO,CO2,SO2and water vapor oxidation corrosion in the high temperature sintering process. So improving its useful life is always a key problem in the metallurgical enterprise. Through the traditional way of casting it is relatively difficult that the grate is resilient in the center and its. surface has good high temperature oxidation resistance and wear resistance. But the casting infiltration technology can solve this problem. Two different mental are combined and both their advantages can be played out.This subject aims to improve grate useful life using the cast-infiltration method to form an aluminum silicon composite layer on the heat resistant steel grate surface. The microstructure and hardness properties of cast-infiltration layer were studied by optical microscope (OM) scanning electron microscope (SEM) with electron dispersive spectrum (EDS) and micro hardness test. High temperature oxidation-resisting was also studied.The results show that aluminum silicon composite layers were successfully achieved by cast-infiltration method. When75ferrosilicon (referred as75Si-Fe) powder was selected as cast-penetrated agent75Si-Fe powder was poured into the silver paint and stirred well then the paint was coated on the mold.The optimized silicon content is50wt%and the average thickness of infiltration layer reaches lmm with superior quality. The as-cast microstructure of infiltrated layer is consisted with ferrite and fine carbides while the matrix is composed of ferrite and reticular structure carbides respectively. Most of the carbides are (Fe,Cr)3C and there may be a small amount (Fe,Cr)7C3in the composite layer as well. The hardness increased first and then decreased from the composite layer to the center. The highest hardness of fine carbides is1253HV. When the aluminum powder and75ferrosilicon powder were selected as cast-penetrated agent two kinds of alloy powder were poured into the silver paint and stirred well then the paint was coated on the mold. When the granularity of aluminum powder is200mesh the optimized weight ratio of aluminum to silicon is3:1.With the contents of Al increasing the composite layer becomes a whole. Point analysis of EDS results shows that the contents of Al and Si elements decreased from surfaced to the center. Micro hardness test results show that the micro hardness values of composite layer gradually reduced with the increase of Al content.The result of high-temperature oxidation resistance showed that the oxidation kinetics curves were in line with the parabolic law, oxidation increase quickly in the first25h of oxidation, but the oxidation rate gradually decreased along with the time and tended to be a constant in the end. If the cast filtration agents were200mesh aluminum powder and100-200mesh75Si-Fe powder and their mass ratio was3:1, the oxidation resistance would be the best, the oxidation rate was only0.1087g/m2·h. The oxidized morphology of the five groups of sample showed that with the increase of the content of alumina-silica, the casting surface quality increased and the oxidation film became more compact and the peeling was weakened.