RH—KIP双重精炼工艺对钢中夹杂物的影响

本文讨论了RH-KIP双重精炼工艺对钢中夹杂物的影响。结果表明,无论采用RH→KIP还是KIP-RH处理工艺均能使钢液净化和夹杂物良好球化,但前一种工艺易使钢中产生较大颗粒夹杂物。     

VD低碱度渣对GCr15轴承钢夹杂物的影响

为了减轻铝脱氧GCr15轴承钢中B类和D类夹杂物的危害,开展了VD低碱度渣和正常碱度渣精炼的对比工业试验研究。结果显示,与正常碱度精炼渣相比,碱度为1.96的精炼渣可使连铸坯中塑性夹杂物比例由14.81%上升为40.65%;同时,全氧（T. O）含量由7.7 × 10^-6下降至4.9 × 10^-6,全铝（T.Al）和酸溶铝（Al_S）含量由279 × 10^-6、210 × 10^-6分别下降至80 × 10^-6、75 × 10^-6。热力学计算表明,低碱度精炼渣引起钢液中［Si］活度增大使复合夹杂中Al₂O₃（inc）含量下降,钢中酸溶铝（Al_S）含量落在与塑性夹杂物平衡对应的等铝浓度线范围内,理论计算与试验结果吻合。VD低碱度渣精炼有利于实现轴承钢夹杂物塑性化控制。     

Influence of thermal damage occurrence at microstructural scale on the thermomechanical behaviour of magnesia-spinel refractories

Many refractory materials exhibit high thermal shock resistance, which is often mostly due to their high flexibility. Understanding the microstructure key points allowing to develop a non-linear mechanical behaviour is of great relevance for future material improvements. The present work aims at optimising the processing of magnesia-spinel refractory materials close to industrial ones with simplified microstructures. The final goal is the investigation of the relationship existing between microstructure evolutions and induced thermomechanical properties. The thermal expansion mismatch which exists between the two phases (spinel inclusions and magnesia matrix) is expected to generate, during cooling, radial microcracks around the inclusions. The development of such microcracks network, closely related to the inclusions content, has been studied and the damage occurrence has been confirmed by several high temperature characterisation techniques. The influence of this thermal micro damage on the evolution of stress-strain law in tension of such materials has also been investigated.     

非金属夹杂物对等温淬火高硅铸钢力学性能的影响

钢中非金属夹杂物对材料力学性能的影响十分显著。本文利用图像分析技术 ,系统研究了非金属夹杂物对等温淬火高硅铸钢力学性能的影响。试验结果表明 :高硅铸钢的夹杂物主要为Si、Cr、Fe的氧化物 ;夹杂物平均尺寸、夹杂物面积百分数、夹杂物平均间距等参数均影响材料的力学性能 ;夹杂物平均尺寸大于 15μm、夹杂物面积百分数大于1%、夹杂物平均间距小于 2 5μm时 ,就会极大地影响高硅铸钢的抗拉强度和冲击韧性。     

钢的氧化物冶金技术

介绍了氧化物冶金技术的概念及发展现状,晶内铁素体的作用和形成机理,氧化物种类对晶内铁素体形成的影响及脱氧剂的选择;钢中氧浓度、凝固过程中冷却速度对氧化物夹杂尺寸和数量的影响。以钛脱氧钢为例,指出了有利于晶内针状铁素体形成的夹杂物尺寸、数量、奥氏体晶粒尺寸、氧浓度、铝浓度和氮浓度。     

Heat and mass transfer of a convective-stratified flow in a trough type tundish

Fluid flow, heat and mass transfer of liquid steel in a trough type tundish were physically and mathematically simulated using a water model. Flow structures were determined through particle image velocimetry (PIV) techniques. Under isothermal conditions fluid flow approaches that of a plug pattern. Non-isothermal conditions provoked long recirculating flows along the vessel and makes the flow to departure form the plug pattern. Buoyancy forces increased fluid velocities close to the bath surface and enhanced convection mass transfer of a tracer injected in the flow and the flotation of solid particles. Measured fluid velocity fields maintained an acceptable good agreement with mathematical simulations under isothermal and non-isothermal conditions.     

Impact of spinel forming systems (Fe-/Mg-/Mn-Al-O) as functional coating materials for carbon-bonded alumina filters on steel melt filtration

Since solid, non-metallic inclusions influence considerably the quality of casted steel products, carbon-bonded alumina foam filters are used in secondary metallurgical treatments to remove these particles from steel melts. In order to attain a significant improvement of the filtration process, five different carbonaceous spinel compounds from the Fe-/Mg-/Mn-Al-O systems are applied on carbon-bonded alumina filters in this study and investigated with regard of their filtration efficiency. However, these spinel compounds decompose partially during sintering at 1400?°C under reducing atmosphere, wherefore the resulting coatings contain not only spinel compounds, but also oxidic and metallic components. The subsequent interaction with molten steel leads to the development of multicrystal structures on the filter surface, which stem from interfacial reactions between coating materials, molten steel, and inclusions. As a result of this procedure, a reduction of almost 60% alumina inclusions is measured with the aid of an automatic SEM, whereby spinel compounds from the Fe-Mn-Al-O system achieve highest filtration efficiencies.     

27SiMn轧制表面裂纹缺陷原因分析

通过采用化学成分分析、光学显微镜、扫描电镜和能谱仪等分析手段对27SiMn轧制开坯表面出现的裂纹缺陷原因进行分析,结果表明;27SiMn轧制开坯表面出现大量的裂纹缺陷主要是由于钢锭表层夹杂物聚集形成夹杂物铁素体带状组织缺陷,轧制开坯产生表面裂纹。     

Dimensionless numbers for tundish modelling and the Guthrie number (Gu)

Abstract

Modelling the transport phenomena in tundishes has been a vast area of research for the last three decades. Many papers have been published and are available in the literature on this subject. The basics of modelling involve a similarity criterion between the model and the full scale prototype and are well documented in major textbooks. However, the similarity criteria are different for different cases. For example, for fluid flow in a tundish, the Re and Fr similarity is considered, whereas for heat transfer, the Pr and Pe number similarity should be considered. Numerous other examples can be cited. It is really important to know which similarity criteria should be used for a particular case. In this paper, a new dimensionless number Gu has been proposed when dealing with the modelling of inclusions separating out in a tundish. All dimensionless numbers can be represented as a ratio of two characteristic time scales, and this fact is highlighted in the present paper.