双辊连铸不锈钢薄带凝固组织特点

 通过金相观察分析了同径双辊薄带连铸机上生产的奥氏体不锈钢薄带的凝固组织,结果表明：铸带凝固组织包括2个柱状晶区和1个等轴晶区,其等轴晶呈近球形或蔷薇形。与传统连铸板坯相比,其柱状晶区一次及二次枝晶的间距较小,等轴晶粒内部为非枝晶结构,其尺寸大约是连铸坯等轴晶的1/10,凝固组织更致密。     

双辊铸轧薄带钢裂纹形成原因分析

裂纹是影响双辊铸轧薄带钢质量的主要因素之一。分析了铸轧薄带钢裂纹的形成机理，并对形成裂纹的主要影响因素作了探讨与归纳。     

双辊薄带连铸技术状况的调查分析

调查了双辊薄带铸轧生产线的运行状况。整理出其工业化应用所需要的基础数据,如用于相关设计和决策的连浇时间、作业率等。给出了生产能力的算例。利用经典的传热凝固理论和经验对双辊连铸的关键参数进行界定,导出了辊缝d(铸带厚度)和辊径D、液位h和最大浇铸速度Vcm的关系。分析了铁辊和铜辊的差异。总结分析了双辊铸带宏观偏析有别于连铸坯的现象和机制。     

双辊铸轧薄带钢组织特点及其形成机理分析

通过对双辊铸轧熔池的特点和薄带在熔池中凝固变形过程的特点进行分析，探讨了不锈钢铸轧薄带的组织结构分布特点及其形成机理，并用结晶热力学做出了解释。     

Steel strips in the context of near net shape casting production

Following the replacement of ingots by continuously cast slabs the next logical step towards near net shape casting has been the development of thin slab casting machines. These are now beginning to match the quality and productivity levels possible with conventional machines. The next step in this evolution towards lower cost operation is high speed thin strip casting machines. The merits of twin roll casters versus belt casting machines for friction free casting of low carbon steels, suggest that a belt caster will be needed for achieving high productivities and associated cooling lengths required for the production of hot strip in the 5–20 mm thickness range.     

双辊薄带连铸生产不锈钢技术探讨

不锈钢是双辊薄带连铸工艺重点开发的钢种之一.综述了不锈钢的分类和性能特点,简要介绍了不锈钢的几种生产型式,详细讨论了双辊薄带连铸生产不锈钢的技术要点和难点.     

Thin Strip Casting of Steel with a Twin Roll Caster ‐ Correlation between Feeding System and Strip Quality

In twin roll casting, the strip surface must be of good quality, as the improvement by further rolling is limited. The strip surface is formed close to the pool surface, and thus it is very sensitive to pool turbulences. Good knowledge of the turbulences must be available. In this paper the pool behaviour is studied in a water model, and correlations to twin roll cast strip and its defects are evaluated.     

Advances in the Optimization of Thin Strip Cast Austenitic 304 Stainless Steel

This study is about the latest advances in the optimization of the microstructure and properties of thin strip cast austenitic stainless steel (AISI 304, 1.4301). Concerning the processing steps the relevance of different thin strip casting parameters, in‐line forming operations, and heat treatments for optimizing microstructure and properties have been studied. The microstructures obtained from the different processing strategies were analysed with respect to phase and grain structures including the grain boundary character distributions via EBSD microtexture measurements, the evolution of deformation‐induced martensite, the relationship between delta ferrite and martensite formation in austenite, and the texture evolution during in‐line deformation. It is observed that different process parameters lead to markedly different microstructures and profound differences in strip homogeneity. It is demonstrated that the properties of strip cast and in‐line hot rolled austenitic stainless steels are competitive to those obtained by conventional continuous casting and hot rolling. This means that the thin strip casting technique is not only competitive to conventional routes with respect to the properties of the material but also represents the most environmentally friendly, flexible, energy‐saving, and modern industrial technique to produce stainless steel strips.     

Twin roll strip casting of low carbon steels

Abstract

Strip casting of low carbon steels has been investigated using a laboratory twin roll machine with copper rolls. The following grades have been studied: a deep drawing low carbon (LC) steel, a LC steel with titanium addition, and a high strength low alloy (HSLA) grade. The casting behaviour of these steels has been examined, and the observed surface defects classified. Defects are most pronounced for the LC grade and significantly less for the HSLA steel and the LC steel with titanium addition. The as cast structure has been analysed. It can be modified by post-cast treatment, e.g. by normalisation or in line rolling. The mechanical properties of cold rolled and annealed strip materials and their textures are presented. Satisfactory sheet properties can be achieved both as hot band and as cold rolled sheet when adequate treatment steps are applied. Consequences for strip casting applications and future research are discussed.     

The key technologies of controlling low carbon steel as-cast strip surface quality

This article is try to explain or analyze the key technologies of controlling the surface quality of low carbon steel as cast strip through investigation of interface heat transfer between solidified shell and liquid steel.The one of the key technologies of controlling surface quality of low carbon steel as cast strip is through the casting roll surface texture in order to achieve the homogeneous solidification on the casting roll.Another is through forming a thin film on the casting roll surface in order to achieve a balance between rapid solidification and homogeneous solidification.This film formed between the twin roll and the molten steel can be controlled by adjusting the chemical composition and inclusion in liquid steel through controlling the amount of all[O]and free[O].     

不锈钢薄带双辊连铸设备的开发

开发了双辊薄带连铸设备和工艺，成功地连铸出厚３～５ｍｍ宽５８０ｍｍ的不锈钢带，简述了铸带的表面质量，铸带的机械性能和耐腐蚀性能。     

高硼不锈钢板的组织演化及制备工艺研究

采用常规“模铸”工艺制备的高硼不锈钢热加工性能差，而且成品板的强度较高但塑性差，难以进行再加工。针对这些难点，分别基于“模铸+复合轧制”以及“薄带连铸+热轧”工艺，成功制备出2. 1%（质量分数）B不锈钢板，研究了不同制备工艺对组织演化和力学性能的影响规律，并对热加工性能和塑性改善的机理进行了探讨。结果表明：与常规热轧相比，“复合轧制”能有效改善高硼不锈钢板的边裂，而且由于复合板包覆层对高硼不锈钢层具有几何约束的作用，成品板塑性显著改善，伸长率为15. 5%，是常规工艺所制备不锈钢板的2. 4倍；在（亚）快速凝固条件下，2. 1%B不锈钢铸带中硼化物的细微化和弥散化效果较为明显。热轧变形后，边部区域的硼化物的平均粒径小于3. 0μm，固溶处理后，薄板的室温伸长率为14. 1%。上述研究结果为难加工、塑性差的金属材料的制备工艺的开发提供了新的思路。     

薄带连铸304不锈钢凝固过程中生成的氧化物夹杂

 采用透射电镜(TEM)对双辊薄带连铸AISI304不锈钢凝固过程中生成的非金属夹杂物进行了研究,发现在薄带的晶界存在许多球型的微细氧化物夹杂,其成分主要是MnO Al2O3 SiO2类复合夹杂物,直径均小于1 μm,并采用数学模型对薄带连铸304不锈钢凝固过程中析出的氧化物夹杂的大小进行了计算,预测值与实验中观察到的结果吻合较好。与传统连铸相比,双辊薄带连铸AISI304不锈钢凝固过程中生成的非金属夹杂物数量增多,尺寸明显减小。     

Coupled Simulation of Flow and Thermal Field of Twin-Roll Strip Casting Process

The steel industry is moving ahead along the di-rection of low cost,short process,good quality andlow capital investment. Strip continuous castingwhich can directly cast a thin strip with thicknessless than 10 mm from molten metal and can elimi-nate the expansive and complex hot rolling,is ex-pected to reduce both the capital investment and thecost of production as compared with the convention-al continuous casting process. Among various pro-cesses under development,the twin- roll strip cast-i…     

Analysis and prevention of microcracking phenomenon occurring during strip casting of an AISI 304 stainless steel

This study was concerned with the effects of microstructural parameters on the microcracking phenomenon occurring during strip casting of an AISI 304 stainless steel. Detailed microstructural analyses of the microcracked regions showed that microcracks were formed mainly along tortoise-shell-shaped depressions and that their number and size were considerably reduced when strip casting was done right after a shot-blasting or pickling treatment of the casting roll surface. This microcracking phenomenon was closely related to the formation of a black oxide layer, which was mainly composed of manganese-rich oxides, on the roll surface. The black oxide layer acted as a barrier of thermal transfer between the rolls and melt, led to an increased gas gap and inhomogeneous solidification of cast strips, and, thus, played a role in forming both tortoise-shell—shaped depressions and microcracks on the strip surface. The installation of brush rolls behind the casting rolls was suggested as a method to prevent microcracks, because the brush rolls could continuously scrape off the black oxide layer affixed on the roll surface during strip casting.     

薄带连铸技术发展现状与展望

双辊薄带钢连铸也称薄带连续铸轧,是以液态金属为原料,以两个转动方向相反的铸辊为结晶器．用液态金属直接生产薄带钢的新技术。该技术受到了世界上各工业发达国家的高度重视,并投入大量的财力和人力进行积极的技术开发和理论研究工作,取得了令人瞩目的新进展,已有多条试验线和半工业生产线接近工业化生产的水平。本文介绍了国外几个接近工业化生产的双辊薄带钢铸轧机组的发展概况、国内薄带连铸技术的研究现状以及双辊薄带技术展望。     

Development of laboratory scale thin strip caster and investigation of direct casting of AISI 304 stainless steel

Abstract

An unequal diameter (1 : 3), two roll thin strip casting machine has been designed and fabricated for investigation of the direct casting of thin strip on a laboratory scale. The system consists of a preheatable shallow tundish with online heating facility, water cooled rotating rolls (chill and auxiliary) for solidification of the liquid metal, and a stripper assembly. The machine has a variable speed. Roll gap setting and roll pressure adjustment are two important features of the machine. It is also possible to vary the placement angle of the auxiliary roll with respect to the chill roll. A heat transfer model was developed, based on experimental casting results. Experiments were conducted using AISI 304 grade stainless steel. Up to 100 kg of steel was cast without interruption into strips of widths 100 and 200 mm and thickness varying between 1 and 2 mm. Some of the process parameters affecting the quality of the strip were identified.     

Physical and Numerical Simulation of Fluid Flow and Solidification at the Twin‐Roll Strip Casting Process

The fluid flow in a twin‐roll strip caster is investigated by physical and numerical simulation on a 1:1‐scale water model. A laser‐optical measurement technique (Laser Doppler Anemometry ‐ LDA) is used to validate the numerical results for the water flow. The numerical simulations are then transferred to the melt flow in the strip caster. The investigations are focused on different SEN concepts (submerged entry nozzle), a single‐nozzle system with two outlet ports and a double‐nozzle system with one outlet port each. The Influence of these concepts on the velocity, turbulence, and temperature distribution inside the liquid pool between the casting rolls and on the solidification and growth of the strip shells are investigated by numerical simulations (Computational Fluid Dynamics ‐ CFD). The non‐isothermal melt flow is calculated considering the solidification enthalpy as well as the behaviour of the solidifying melt. In addition to the numerical simulations of the melt flow inside the pool the temperature distribution in the cast strip is simulated. The SEN concept directly correlates with the temperature distribution Inside the strip. Furthermore, the surface temperature of the strip below the outlet of the roll gap is measured using a line‐scanner and is compared with the CFD simulation. In order to simulate the shape of the free surface in the liquid pool, CFD simulations of the water flow in the physical model are carried out using a Volume of Fluid model (VoF). This two‐phase model is able to reproduce free surface waves.     

Analysis and prevention of cracking during strip casting of AISI 304 stainless steel

In this study, a microstructural investigation was conducted on the cracking phenomenon occurring during strip casting of an AISI 304 stainless steel. Detailed microstructural analyses of the cracked regions showed that most of the cracks were deep, sharp, and parallel to the casting direction. They initiated at the tip of dendrites and propagated along the segregated liquid films between primary dendrites, indicating that they were typical solidification cracks. This cracking phenomenon was closely related to the inhomogeneous solidification of cast strips, represented by depressions, i.e., uneven and somewhat concave areas on the strip surface. The depressions, which were unavoidable in flat rolls due to the presence of a gas gap between the roll and the cast strip, were finely and evenly distributed over the cast strip surface by intentionally providing homogeneous roughness on the roll surface; then, the number and size of cracks were considerably reduced. In addition, the nitrogen gas atmosphere, which retained high solubility in the melt during cooling and good wettability with the roll surface, was successfully used to prevent cracking, because the thickness of the gas gap was minimized.     

Physical Simulation of Nozzle Electromagnetic Brake in Twin‐Roll Strip Casting

This paper presents the Nozzle Electromagnetic Brake (N‐EMBR) technology for twin‐roll strip continuous casting. N‐EMBR consists of imposing a stationary magnetic field coupled with direct current inside the nozzle to control the flow and suppress the free surface fluctuation. A low melting point metal model was set up to examine the magnetic field and additional current effect on the velocity near the meniscus and free surface fluctuation. The experimental results showed that the velocity near the meniscus, the amplitude and main frequency of the free surface fluctuation were all decreased with the N‐EMBR technology. It was found that the N‐EMBR technique can be applied successfully in twin‐roll strip casting to suppress the flow near the meniscus and free fluctuation.