폐 강판으로부터 파분쇄에 의한 철분말의 제조 및 응용에 관한 연구

Abstract

Since the used steel plate of which the thickness is 200～300㎛ is rather thin, it is with ease to form the iron oxide/iron carbide layer into the inside in the atmosphere of oxidation/carburization and the powderization by milling is available as the oxide iron/carbide iron fragments obtained from this process has the inherent brittleness. In addition, manufacturing of the iron powder from the iron oxide/iron carbide powder, is also possible by the proper reduction/decarburization processes with respect to the combination of proper brittleness and ease of reduction/decarburization. In this study, carburization, oxidation, milling, decarburization and reduction behavior of the used steel plate was examined to produce the steel powder, iron oxide powder and iron powder with high added value by the dry-type way from the used steel plate of which the specific surface area is large. The type of oxides with time, the thickness of oxidation layer and the effect of vibration to increase oxidation rate were investigated in the atmosphere of oxygen. In addition, in order to obtain the pure iron powder from that iron oxide, the iron oxide was crushed below 100㎛ and then the reduction behavior with reduction temperature and time was investigated in fluidized-bed furnace. For this study, it was examined to produce the iron oxide powder and iron powder from the original thin plate state by carburization/decarburization and oxidation/reduction without melting the used steel plate and the results are as follows : 1) For the pre-treated used steel plate, the homogeneous hypereutectoid structure could be obtained by heating at 930℃ for 60 min in the atmosphere of air and propane gas. However, quenching after carburizing was needed to crush in vibratory mill and as milled for 5 min, about 60% of powders with 150㎛ of size was contained in the steel power particles, and the shape of particles was close to the plate. 2) For the steel powder, heating at 700℃ for 60 min in the atmosphere of H2O + H2 was required to remove the carbon that exists inside the steel power as a form of solutioned carbon or Fe3C, and porosity was not observed inside the produced iron powder. The apparent density(g/cm2), flow rate(s/50g), green density(g/cm3), space filling effect(%) and rattle value examined of decarburized powder were 3.42, 28.3, 6.67, 43.8 and 0.621, respectively. 3) When the steel can was oxidized at 930℃ with the amount of the air pre-heated at 400℃ being 10ℓ/min, the oxidation of used steel plate was mostly proper, and rotation of the retort during heating was required to produce the iron oxide with size of 2～3 cm. When the iron oxide was milled for 5 min in vibratory mill, the size distribution of iron oxide powder less than 100㎛ in size occupied 87% and the shape of particles was close to sphere. 4) For reduction condition of the proper flow, when flow rate was made 5ℓ/min and the used steel plate was maintained at 690℃ for 4 hour, the maximum reduction rate could be obtained and according to acid insoluble teat, reduction rate was 97%, and the microstructure of reduction powder showed sponge type of structure. 5) The apparent density(g/cm2), flow rate(s/50g), green density(g/cm3), space filling effect(%) and rattle value examined of reduction powder i.e. iron power were 1.91, 46.8, 5.90, 67.7 and 0.573, respectively. Compared with decarburized iron, it was revealed that the apparent density is reduced and flow rate is increased because lots of pores exist inside powder. 6) In the case of higher mixing ratio of pure iron and higher sintering temperature, surface and a part of interior are melted during sintering process, resulting in higher sintering density. In the case of lower mixing ratio of pure iron and lower sintering temperature, however, sintering density decreases while specific surface area increases. 7) Abrasive resistance and compressive strength are changed according to mixing ratio and sintering temperature; both abrasive resistance and compressive strength increase with increasing the mixing ratio of pure iron and sintering temperatue.