Melting and floating processes of inorganic materials in molten steel:Visualization physical simulation and mathematical modelling

It has been demonstrated that heat absorption method by using the inorganic material rod to cool the molten steel can significantly reduce the macrosegregation level of the large steel ingot.However,owing to the opacity of the molten steel,the physical mechanism of the heat absorption method is not clear.In this work,a transparent hydraulic physical model with water and paraffin wax was built to simulate the melting and floating processes of inorganic materials in the molten steel.A mathematical simulation was also carried out to analyze the connection between the actual ingot and the physical model.Results show that it is feasible to simulate the molten steel and inorganic materials with water and paraffin wax.With the help of the physical model,the process of the melting of paraffin wax and its floating to the surface of water were clearly observed,during which the temperature of water at some characteristic positions in the mold was recorded.The visualization findings demonstrate that the melting and floating processes of paraffin wax can help to bring the heat from the center of the mold to the top surface more quickly,which reduces the superheat and significantly accelerates the cooling rate of water.The experimental results show that for the water with a certain superheat,the use of a larger mass of paraffin wax can accelerate the cooling of the water,but there is a risk of incomplete melting of the paraffin wax.A higher superheat of water will lead to a quicker melting rate for a given mass of paraffin wax,while a lower superheat leads to the incomplete melting of paraffin wax as well.

合并消化系统症状系统性红斑狼疮的危险因素分析及风险评估模型

目的研究合并消化系统症状的系统性红斑狼疮(SLE)的临床特征及危险因素,建立风险评估模型,为诊断及预防该病提供参考依据。方法收集2012年8月-2017年8月广西医科大学第一附属医院及广西医科大学第二附属医院首次诊断并住院治疗的307例SLE患者的临床资料,并对患者的临床资料进行回顾性分析。结果 307例SLE患者中61例(19.9%)合并消化系统症状,多表现为腹痛、恶心、呕吐、腹泻。合并消化系统症状SLE患者出现血液系统损害、多浆膜炎、肾盂输尿管扩张的概率高于未合并消化系统症状患者(P<0.05)。且白蛋白(Alb)、补体C3、血小板(PLT)降低,以及C反应蛋白(CRP)、天门冬氨酸转氨酶(AST)、丙氨酸转氨酶(ALT)、碱性磷酸酶(ALP)、谷氨酰转肽酶(GGT)升高与合并消化系统症状相关(P<0.05)。多因素Logistic回归分析结果显示,血液系统损害、多浆膜炎、Alb降低,以及ALT升高为合并消化系统症状的独立危险因素。对构建的风险评估模型的预测能力研究发现:模型预测的敏感性为70.0%,特异性为92.1%,总正确率为87.5%。结论消化系统症状是SLE常见的临床表现,合并消化系统症状的SLE患者住院时间长,临床表现多种多样,影像学表现多为非特异性。血液系统损害、多浆膜炎、Alb降低、ALT升高作为独立危险因素可用于SLE合并消化系统症状风险评估模型的建立。

Influence of mechanical reduction amount on internal quality of continuous casting billets by thermal and numerical simulation

With establishment of thermal and numerical simulation models,the influence of reduction amount on solidification structure,segregation and shrinkage porosity of continuous casting(CC)billets was investigated.The thermal–mechanical coupled simulation results indicated that with an increase in reduction amount,the temperature in the central area decreases,and the reduction efficiency firstly increases and then decreases,reaching the maximum value at reduction amount of 6 mm.Metallographic analysis showed that increasing the reduction amount is beneficial for the refinement of central solidification structure.Moreover,the internal cracks are more likely to appear at higher reduction efficiency.The X-ray computerized tomography results revealed that a higher reduction amount can significantly reduce the volume fraction and equivalent diameter of the central shrinkage porosities of CC billets and increase the sphericity of them.Simultaneously,the macrosegregation of carbon along the central line is improved as the reduction amount increases;while the reduction amount exceeds 8 mm,the segregation degree will not change any more.

Effect of final electromagnetic stirring on solidification microstructure of GCr15 bearing steel in simulated continuous casting

The effect of final electromagnetic stirring on the solidification structure,element segregation,and carbides of GCrl5 bearing steel was investigated.The experiment of continuous casting of the steel was carried out by using a continuous casting physical simulation apparatus with the final electromagnetic stirring.The liquid core profile was revealed by the pour-out method during the solidification process.Eight ingots were produced under different electromagnetic stirring parameters for comparison.The results show that,at the final stage of solidification,intense electromagnetic stirring exacerbates the central carbon segregation,resulting in more serious precipitation of the primary carbides.It is also found that the carbides in the segregation area are dominantly M3C type,together with a small amount of M7C3-type and M3C2-type carbides.In this physical simulation model,the optimal stirring parameters to obtain a fine and homogeneous structure are the liquid pool width of 15 mm,current intensity of 150 A,and stirring frequency of 5 Hz.