Layer Structure Analysis of Low-Carbon Steel Containing Rare Earth by High-Temperature Carburizing of Liquid Cast-Iron

The layer structure of low-carbon steel containing RE by high-temperature (T>1200 ℃) carburizing of liquid cast-iron was studied and the diffusion activation energy of carbon was calculated by metallographic microscpe, chemical analysis etc. The result shows that the technology of carburizing in liquid cast-iron can expedite caburization distinctly and changes the carburizing layer structure. The carburizing rate is 60～80 times of that of the traditional technology, and there is about 43% decrease in the activation energy compared with gas-carburization. In outer structure layer, cementite is formed simultaneously both on the crystal boundary reticularly and inside the crystal grains stripedly. In inner carburizing layer, there is undissolved blocky ferrite in reticular cementite. Besides, rare earth element can expedite carburization process.

碳纳米管/球墨铸铁复合材料制备及组织性能的研究

研究了利用消失模铸造工艺把碳纳米管加入到球墨铸铁铁液中,制备碳纳米管/球墨铸铁复合材料试样的工艺方法,并研究了不同CNTs含量对球墨铸铁显微组织及布氏硬度的影响。结果表明,采用含碳纳米管的消失模铸造工艺可以有效地把碳纳米管加入到铸铁中。随着CNTs的加入,球墨铸铁显微组织中的石墨球数增多,球径减小,铁素体含量、珠光体含量基本不变,布氏硬度增大;加入量过多时,会出现偏聚。

The influence of particle size on the thermal performance of coal and its derived char in a Union stove

For low-income communities in South Africa,coal is the most common solid fuel which is burnt in a variety of devices,including imbaulas and cast-iron stoves.The present work was conducted with the aim of determining the effect of the fuel particle size on the performance of coal,typically sourced in low-income households in townships in South Africa,and to subsequently compare the performance with a feed char of a common cast iron stove.Four fuel particle sizes of 15,20,30,and 40 mm,as well as a composite of the sizes were tested at 550C,against their untreated coal analogues to evaluate the thermal performance of each fuel.The thermal performance assessment metrics are ignition time,water boiling time,heat transfer and combustion efficiencies,while CO and CO_(2)emissions were measured for the calculations of CO/CO_(2)ratios.Ignition times were found to decrease from coals to chars and to decrease with increasing particle size.The effects of fuel type on the water boiling time were only observed in the later stages of the burn cycle,with the char boiling a 2 L batch of water in an average 24 min,while the coals reported an average boiling time of 20 min.Heat transfer efficiencies showed no significant variation with fuel type or particle size,with the average efficiency for the coals and that of the chars being around 66%.The fuels’performance was better gauged by the combustion efficiency,which was found to improve marginally from the coal fuels to the chars,and to increase with increasing particle size.Results from this testwork could contribute to the performance inventories from the combustion of domestic coal mined in South Africa in a typical cast iron stove which is used in informal settlements.

Study on Carburizing Kinetics of Low-carbon Steel at High-temperature and Short-term

In this paper, the carburizing kinetics of low-carbon steel at high-temperature and short-term in liquid cast-iron were studied by metallographic microscope, chemical analysis and so on, and the microstructure of carburized layer was also analyzed. The results show that the carburizing rate of low-carbon steel at high-temperature and short-term is so fast, and the microstructure of carburized layer possess higher carbon content, and cementite, pearlite and ferrite exist in carburized layer structure simultaneously. Besides, the kinetic equations of permeating layer forming have been presented, and the carburizing mechanism was preliminary discussed also.

The effect of particle size on the pollution reduction potential of a South African coal-derived low-smoke fuel

The coal combustion in cast-iron stoves leads to health hazards and air pollution.In this study the CO,SO2,NOx,PM and VOC emission concentrations were measured whilst combusting four fuel particle sizes(15,20,30,and 40 mm)as well as a composite of the sizes(all pre-devolatilized at a temperature of 550C)in a cast-iron stove.The results were compared to their raw coal analogues to evaluate the emission performance of each fuel type.Emission factors for NOx and SO2 were found to depend on the fuel nitrogen and sulphur contents in the coal and the combustion conditions used during pyrolysis.The PM,SO2 and VOC emissions show a strong dependence on the ash percentage and volatile matter yields,which both increased with increasing particle size.In addition,the PM,SO2 and VOC missions were found to only depend on particle size on a mechanistic level.The VOCs and PM emission factors are inversely correlated with particle size.The results from this study offer insight into the combustion environment in the Falkirk Union No 7 cast-iron stove as well as how this environment applies to low smoke fuels.The work contributes to the emission and performance inventories from South African domestic coal combustion in this stove used in informal settlements.