Study on the modification of inclusions by Ca treatment in GCr18Mo bearing steel

The effect of Ca treatment on the modification of inclusions in Al-killed GCr18Mo bearing steel was studied and a thermodynamic and kinetic model was established.The experimental results showed that oxygen content in the steel could be reduced from 120ug/g to the range 5.5-21.6ug/g by Al-Ca complex deoxidization at 1873 K.An appropriate increase in Ca/Al mass ratio is beneficial to reduce the total oxygen content in steel.When the content of dissolved aluminum was in the range of 0.03%-0.3%,w让h the increase of Ca/Al mass ratio from 0.8-1.6 to 2.4-3.2,the number of inclusions per unit area significantly reduced.In addition,the main types of inclusions were modified from large-sized Al2O3 clusters to plastic or semiplastic liquid phase calcium aluminates.The experimental results matched well with the thermodynamic analysis.

Recovery of rare earth elements from permanent magnet scraps by pyrometallurgical process

In order to recover valuable rare earth elements from Nd-Fe-B permanent magnet scraps, a high-temperature pyrometallurgical process was developed in this work. The magnet scraps were first pulverized and oxidized at 1000℃ in normal atmosphere. The oxidized mixtures were then selectively reduced by carbon in the temperature range of 1400-1550℃. In this way, the rare earth elements were extracted to the form of oxides, whereas Fe and B were separated to metal phase. For improving the purity of rare earth oxides, the effects of temperature and reaction time on the reduction of B_(2)O_(3) in oxide phase were investigated. It is found that increasing reaction temperature and extending reaction time will help the reduction of B_(2)O_(3) contents in rare earth oxide phase. Almost all rare earth elements can be enriched in the oxide phase with the highest purity of 95 %.

Investigation on the application of reformed coke oven gas in direct reduction iron production with a mathematical model

To investigate the application of reformed coke oven gas （COG） in producing the direct reduction iron （DRI）, we simulated a countercurrent gas solid moving bed reactor in which the iron ore pellet was reduced by reformed COG. An ordinary differential equation （ODE） was set based on the unreacted shrinking core model considering both mass and energy balances of the reactor. The concentration and temperature profiles of all species within the reactor were obtained by solving the ODE sys tem. The solid conversion and gas utilization were studied by changing gas flow rate, solid flow rate, reactor length, and the ratio of O/CHa to guide the practical application of COG in DRI production. Model results showed that COG was suitable for the DRI production. In order to meet the requirement of the industrial production, the minimum gas flow rate was set as 130,000 Nm3/h, and the maximum production was 90 t/h. The reactor length and the mole ratio x（O）： x（CH4） were depended on the actual industrial situations.