Effect of low-frequency rotary electromagnetic-field on solidification structure of continuous casting austenitic stainless steel

To understand the solidification behavior of austenitic stainless steel in rotary electromagnetic-field, the influence of low-frequency rotary electromagnetic-field on solidification structure of austenitic stainless steel in horizontal continuous casting was investigated based on industrial experiments. The results show that the solidification structure of austenitic stainless steel can be remarkably refined, the central porosity and shrinkage cavity can be remarkably decreased, and the equiaxed grains zone are enlarged by means of application of appropriate low-frequency electromagnetic-field parameters. The industrial trials verify that the stirring intensity of austenitic stainless steel should be higher compared with that of plain carbon steel. Electromagnetic stirring affects the macrostructure even if the average magnetic flux density of the electromagnetic stirring reaches 90 mT (amplitude reaches 141 mT) with the frequency of 3-4 Hz. Due to a higher viscosity, rotating speed of molten stainless steel is 20%-30% lower than that of molten carbon steel in the same magnetic flux density.

Effect of electromagnetic stirring on solidification structure of austenitic stainless steel in horizontal continuous casting

An investigation on the influence of low frequency rotary electromagnetic stirring on solidification structure of austenitic stainless steel in horizontal continuous casting was experimentally conducted and carried out on an industrial trial basis. The results show that application of appropriate electromagnetic stirring parameters can obviously improve the macrostructure of austenitic stainless steel, in which both columnar and equiaxed grains can be greatly refined and shrinkage porosity or cavity zone along centerline can be remarkably decreased due to eliminating intracrystalline and enlarging equiaxed grains zone. The industrial trials verify that the electromagnetic stirring intensity of austenitic stainless steel should be higher than that of plain carbon steel. Electromagnetic stirring has somewhat affected the macrostructure of austenitic stainless steel even if the magnetic flux density of the electromagnetic stirring reaches 90 mT （amplitude reaches 141 mT ） in average at frequency f=3-4Hz, which provides a reference for the optimization of design and process parameters when applying the rotary electromagnetic stirrer.

Analysis of cracking phenomena in continuous casting of 1Cr13 stainless steel billets with final electromagnetic stirring

Solidification cracking that occurs during continuous casting of 1Cr13 stainless steel was investigated with and without final elec- tromagnetic stirring （F-EMS）. The results show that cracks initiates and propagates along the grain boundaries where the elements of carbon and sulfur are enriched. The final stirrer should be appropriately placed at a location that is 7.5 m away from the meniscus, and the appropri- ate thickness of the liquid core in the stirring zone is 50 ram. As a stirring current of 250 A is imposed, it can promote colurnnar-equiaxed transition, decrease the secondary dendrite arm spacing, and reduce the segregation of both carbon and sulfur. F-EMS can effectively de- crease the amount of cracks in 1Cr13 stainless steel.

Research on the trajectory of non-metal inclusions with the flow in the mold during the solidification of continuous casting slabs

By means of the numerical simulation method,the mathematical model of inclusions movement in the mold is established under the condition of austenitic and fen-itic stainless steel slab production. According to the simulation results, the main zones for inclusion particles accumulation were found and many factors that affected floating-up probability of inclusion particles were identified. These factors include the inclusion particle size, the casting speed and the slab width, etc. It is believed that the inclusion particle size is the key one among these factors.

奥钢联不锈钢连铸技术（VAINOX）的最新发展

描述奥钢联不锈钢连铸技术(VAINOX )的主要特点,并介绍一些应用实例和操作结果.

Numerical simulations of solidification and hot tearing for continuous casting of duplex stainless steel

Hot tearing is one of the major defects in continuous casting of steels, which severely limits the productivity of steelmaking processes. To further understand the defect, the problem of hot tearing in duplex stainless steel produced by a vertical continuous caster was investigated. A three-dimensional heat transfer and elastic-plastic model was developed based on the realistic roller layout in continuous slab casting, using ProCAST software. According to the hot tearing indicator criterion, the influence of operating parameters on the hot tearing susceptibility was evaluated. The results show that the surface temperature distribution is not sensitive to the superheat. The center of wide surface shell at the mold exit is the thinnest, and the thickness is about 10.52 mm at the superheat temperature of 40 -C. The hot tearing mainly concentrates on the slab solidification front and near the narrow face. However, corner cracks are prone to appear near the corner. With the increase in casting speed and the decrease in the cooling intensity in the secondary cooling zone, the solidification end point is rushed, which leads to the position of hot tearing lowering accordingly.

Characteristics of SEN clogging and adhesive behavior of oxide inclusion during continuous casting of Ti-stabilized ultra-pure ferritic stainless steels

Submerged entry nozzle(SEN)clogging during continuous casting of Ti-stabilized ultra-pure ferritic stainless(Ti-UPFS)steels was systematically investigated via cross-sectional analysis and acid dissolution treatment.The SEN deposit profile was characterized as occurring in three major layers:(1)an eroded refractory layer;(2)an initial adhesive layer comprised an Al_(2)O_(3)-ZrO_(2) composite sub-layer and a dense Al_(2)O_(3)-based deposit sub-layer;and(3)a porous multiphase deposit layer mainly consisting of MgO·Al_(2)O_(3),CaO-Al_(2)O_(3),and CaO-TiOx.The MgO·Al_(2)O_(3)-rich inclusions did not adhere directly to the eroded refractory but were entrapped during the deposit growth.Results of inclusion characterization in the tundish revealed that the MgO·Al2O3-rich particles present in the tundish served as the primary source of clogging deposits.Furthermore,a novel cavity-induced adhesion model by circular approximation was established to explain the effects of complex inclusion characteristics and refractory material type on adhesion force.A high number of small MgO·Al_(2)O_(3) inclusions were expected to accelerate the buildup of clogging deposits.Improving the modification of MgO·Al_(2)O_(3)-rich inclusions in the size range of 2-4μm by Ca treatment was crucial to minimizing the risk of SEN clogging during the continuous casting of Ti-UPFS steels.

Design of a submerged entry nozzle for optimizing continuous casting of stainless steel slab

To solve slag entrapment and casting slab defects in the process of stainless steel continuous casting,submerged entry nozzle(SEN)for slab casters operating at casting speed of 1 m/min was developed based on 3D numerical simulation and water modeling experiments by controlling the outlet shape and angle of original SEN with oval and 15°angle outlet under current industrial use.Mathematical simulations of fluid velocity at outlets with different shapes and angles of SENs have been carried out.The results showed that oval outlet with 5°and 15°angle led to asymmetric rotating flow pattern at outlet,as well as square outlet with 15°angle,but symmetric flow pattern formed at square outlet with 5°angle.The effect of these SENs on meniscus stability,flow field and slag entrapment behavior of stainless steel slab casting mold was further studied by water modeling experiments.The results showed that difficult floating fine droplets formed when the angle of outlet was 15°under the dual effect of vortex convection and shear force due to the strong swirling flow from outlet and rotating flow of outlet.However,outlet with 5°angle could lead to the formation of larger slag droplets,while the oval outlet with 5°angle could result in the scour to the mold wall.Thus,the square outlet with 5°angle was a relatively ideal solution for the submerged entry nozzle from the aspects of the stability of the mold and the slag entrapment behavior.After the design of a new SEN according to the experimental result,the solidification structure of continuous casting slab was obviously improved by industrial test.

SIMULATION OF THE TWIN ROLL STAINLESS STRIP CASTING PROCESS

The position of the solidification completed temperature of twin roll stainless strip casting process is very important to the quality of the casting strip. In order to control this position, the solidification completed temperature should be known at first. The present paper first simulated dendritic microsegregation under conditions of twin roll stainless strip casting, and got the relationship between the temperature and the solid fraction of the mush zone. The temperatures such as ZDT (equal to the solidification completed temperature) and LIT (liquid impenetrable temperature), et al., also can be found from this relationship. Then by using the turbulent model, the flow and thermal fields of the pool of the twin roll stainless strip casting and the speed and temperature fields of different casting speeds were given and also explained. The simulation results are coincident with the experimental results. Combined with the results of these simulations, the appropriated casting speed was found.

TITANIUM NITRIDE INCLUSIONS IN Ti-STABILIZED STAINLESS STEEL

TiN inchusions are the major inclusions in Ti-stabilized stainless steels.The quantity and dis- tribution of the TiN inclusions depend on the casting process closely.TiN inclusions in molten steel can float up and grow up gradually during huoying.The sequence of the formation of in- clusions in the steel is oxides,nitrides and sulphides.

409L不锈钢连铸坯表层夹杂物试验研究

为研究409L不锈钢连铸坯表层夹杂物形貌、分布及类别,取样后逐次研磨1 mm后进行夹杂物检测,并将检测结果进行对比分析。发现夹杂物分布呈随机性分布特征、尺寸主要集中在2~5μm,在空间分布上呈现随着深度的增加夹杂物数量呈现递减、中间位置夹杂物数量较两端少、内弧侧数量略高于外弧侧的特征,连铸坯表层夹杂物主要为12CaO-7Al_(2)O_(3)及一定比例的氧化物及少量其他类别夹杂物。

铁素体不锈钢430连续铸造板坯成形合理工艺参数的研究

目的以某钢厂板厚为180~220 mm的铁素体不锈钢430连铸板坯为对象,研究合理的板坯连铸工艺参数,以提高不锈钢430连铸坯的等轴晶率,强化铸坯质量。方法通过高温拉伸试验、结晶器凝固冷却温度分析以及电磁搅拌磁感应强度模拟,探讨了液体加热温度、结晶器冷却水参数及电磁搅拌参数等工艺参数对连铸坯质量的影响规律。结果高温拉伸试验结果表明,430不锈钢在不同温度下的应力-应变曲线都是典型的塑性拉伸曲线,当温度超过1000℃后,抗拉强度显著减小;在结晶器宽面水量3400 L/min、窄面水量400 L/min的参数条件下,结晶器宽面及窄面铜板温度均匀,满足铸坯成形要求;在扇形1段第6^(#)和7^(#)辊位并列增加电磁搅拌辊后,430不锈钢铸坯电磁场分布合理且铸坯中心磁感应强度最大,为0.104 T,平均磁感应强度为0.09 T,显著提升了液相穴内钢水的流动性。结论在结晶器宽面水量为3400 L/min、窄面水量为400 L/min条件下,在连铸机扇形1段第6^(#)和7^(#)辊位并列增加电磁搅拌辊后,对430不锈钢进行连续铸造工业试验,铁素体不锈钢430板坯等轴晶率达到62.5%,裂纹发生率降低。

可控移动式顶抽除尘罩系统在不锈钢连铸切割中的应用

为解决不锈钢铸坯在线切割时产生的金属粉尘污染工作环境的问题,设计并制作了一套可控移动式顶抽除尘罩系统,在保证除尘效果的前提下,有效实施对切割区域的散热,保证切割机和辊道系统的正常使用。

304不锈钢No.1表面黑带缺陷研究与控制实践

针对304奥氏体不锈钢No.1表面的黑带缺陷,使用SEM及EDS进行了微观形貌及成分分析,结合结晶器内流场行为,明确了该缺陷的来源为渣钢卷混。在304不锈钢生产实践中,通过在连铸工序控制浸入式水口选型、限定水口插入深度、稳定拉坯速度等措施稳定了钢液浇铸过程中结晶器内的液面,有效降低了卷渣几率;并在后续工序中加强了铸坯表面质量检验、优化了除鳞工艺等,进一步降低了黑带缺陷整体降级率。最终,304不锈钢No.1黑带缺陷发生率整体由改善前的15.0%降低至3.0%以下。

含钛不锈钢连铸浸入式水口结瘤的研究

为了解决含钛不锈钢连铸过程中浸入式水口的结瘤问题,采用扫描电镜和 X射线微区衍射等方法分析了AISI 321不锈钢连铸水口结瘤物的物相,探讨了浸入式水口的结瘤机理。结果表明:水口结瘤物中的物相主要有CaO·TiO2 -MgO·Al2O3 和金属,其中CaO·TiO2- MgO·Al2O3 主要来自于钢液中的夹杂物。喂钛线后吹氩搅拌过强使钢液面裸露和浇铸时的二次氧化会显著增加钢中CaO·TiO2- MgO·Al2O3 双相夹杂物的数量,导致结瘤层明显变厚。冶炼过程中采用低铝硅铁(ωAl=0 05%)还原,且不加铝、Ca- Si脱氧,或者在加 Ca Si后通过喂钛线前的吹氩弱搅拌尽可能排除钢中CaO- SiO2、CaO- SiO2 Al2O3 等夹杂物,严格控制二次氧化,可使喂入钛线后钢中CaO·TiO ·Al O 双相夹杂物数量明显减少,从而改善水口结瘤现象。

不锈钢连铸坯表面缺陷与对策

针对不锈钢中镍、铬、钛等合金元素的作用,分析了不锈钢的组成、凝固特征、高温热性能、力学性能与普碳钢的差异以及不锈钢连铸坯表面凹陷、裂纹、夹渣等表面缺陷产生的机理。重点阐述了钢水洁净度、浇铸温度、保护渣性能、结晶器振动以及液面控制等连铸工艺对表面质量的影响。结合Ocr18Ni9、2cr13以及钛不锈钢实际生产情况,提出解决铸坯表面凹陷、裂纹、夹渣及不易除掉的深振痕等缺陷的措施与对策。

316不锈钢板坯连铸结晶器内坯壳厚度模拟

为研究连铸过程中高温区δ铁素体含量对凝固传热的影响,采用商业有限元软件ANSYS,利用单元生死技术,对316不锈钢板坯的浇注过程进行了模拟。采用2-D模型,分别计算了δ铁素体含量为0、25%、50%、75%及100%时坯壳出口温度、坯壳厚度及表面温度的变化,探讨了坯壳生长及厚度变化规律。结果表明,随着δ铁素体含量升高,坯壳出口温度升高,表面温度变化剧烈,坯壳的出口厚度减薄。

304和321不锈钢连铸水口结瘤的不同机理

分析了304和321不锈钢连铸水口结瘤物的物相,探讨了结瘤机理.结果表明,304水口结瘤物主要由Al2O3,MgO·Al2O3和少量细小的金属颗粒构成,结瘤层较薄,对正常浇铸的影响不显著,控制钢中Al<0.01％,可改善其结瘤.321连铸水口结瘤有TiN和CaO·TiO2两种类型:TiN型结瘤物主要由TiN和少量金属组成,控制措施是保持钢中钛氮积小于3.5,Al<0.01％;CaO·TiO2型结瘤物由CaO·TiO2-MgO·Al2O3和大量金属构成,尽可能减少钢中CaO·TiO2-MgO·Al2O3双相夹杂物的数量和避免二次氧化,可改善CaO·TiO2型结瘤,适当提高浇铸温度可缓解CaO·TiO2型结瘤.

不锈钢连续定向凝固的试验研究

用电渣感应连续定向凝固方法 ,对不锈钢的连续定向凝固进行了试验研究。结果表明 ,用该法可稳定地进行不锈钢的连续定向凝固 ,是实现高熔点黑色金属连续定向凝固最有前途的方法之一。

不锈钢连铸板坯横截面夹杂物的原位统计分布分析

采用原位统计分布分析表征技术对电磁搅拌工艺条件下生产的不锈钢连铸板坯样品横截面进行取样分析,对铸坯横截面1/4处(宽度方向)沿厚度方向的全尺寸范围、中心部位及白亮带处的铝系夹杂物含量、组成、数量、粒度分布进行解析。试验表明,由电磁搅拌产生的白亮带中C、Ti、Si各元素分布呈负偏析,其位置与低倍组织形貌中白亮带位置准确对应,Al和Ca在白亮带富集呈严重正偏析;白亮带区铝系夹杂物总量较中部区域略多,且白亮带区AlCa夹杂比例略高,而中部区域Al-O夹杂比例略高;白亮带中铝系夹杂物小颗粒比例略大,而中部区域大颗粒略多;Ca夹杂最大粒度位于白亮带,而Al夹杂最大粒度位于中部区域。采用扫描电镜结合能谱分析,验证了铸坯横截面"全尺寸"原位统计分布分析表征结果的正确性。研究表明,与扫描电镜等微观分析技术相结合,可实现原位统计分布分析对指定部位夹杂形貌的解析。