Distribution of macro-inclusions in low carbon aluminium-killed steel slabs

Macro-inclusions in low carbon, aluminium-killed steel slabs were characterised by step-machining within a 10?mm zone from the slab surface using an ASPEX automatic inclusion analyzer. Dendritic structures within the cross-section of slabs were examined. The results show that alumina clusters and alumina associated with bubbles are the dominant macro-inclusions. Along the slab width direction, macro-inclusions were mostly found at the slab centre because of the deeper hooks and freezing meniscus surrounding the submerged entry nozzle. In terms of slab thickness, inclusions were mainly concentrated within the zone 3.5–6?mm from the top of the slab surface, where the columnar dendrites showed a relatively small inclination angle, indicating small cross-flow velocities at the solidification front. The number density of macro-inclusions were strongly dependent on the washing effect produced by the flow velocity. High speed casting promotes this behaviour and improves the surface quality of the slabs.     

板坯连铸机二次冷却均匀性的分析与优化

针对某厂连铸板坯裂纹频繁出现的问题,结合连铸机的喷嘴布置特点,在测试分析铸机喷嘴的喷淋冷却特性的基础上,以Q235G钢为对象,考虑板坯宽度方向二冷水流密度分布状态,采用数值仿真方法模拟计算了200 mm×1350 mm连铸坯的凝固壳生长形貌及铸坯表面内弧温度分布.研究表明:板坯铸机二冷前期足辊段与零段原喷嘴布置及水流密...     

Determination of CC slab solidification using nail shooting technique

Abstract

The technology of nail shooting was improved and used to study the transverse shape of the solidified shell during steel continuous casting. Three locations across the slab width (1/2, 1/4 and 1/8) were measured by nail shooting and which indicated a larger solidification coefficient and longer liquid core in the slab at higher casting speeds. The solidified shell across the slab width direction was non-uniform due to uneven secondary spray cooling. The point of final solidification at locations 1/8 and 1/4 was much longer than the position between the slab centre and location 1/4, leading to a long solidification end of >2 m, which is poor for the application of dynamic soft reduction. A mathematical model was developed to simulate the growth of the solidified shell and which was in good agreement with the measurements measured by nail shooting. Based on the measurements and simulations, the water spray pattern was improved, making the solidified shell more uniform. Dynamic soft reduction was then optimised resulting in reduced centreline segregation.     

Three-dimensional analysis of molten steel flow in slab continuous casting mould with rotated ports in submerged entry nozzle

Abstract

The purpose of this study is to develop a three-dimensional (3D) analysis system capable of analysing the flow field of molten steel in the slab continuous casting mould with rotated ports in the submerged entry nozzle. The ultimate goal is to obtain the optimal design for the entry ports of the submerged nozzle, which can introduce favourable flow patterns to remove non-metallic inclusions and avoid entrapment of molten slag and casting powder to produce steel slab of high cleanliness. In this study, a computational fluid dynamics technique, Sola-Surf, is employed to conduct the 3D fluid flow analysis. The technique has the capability of treating fluid flow problems with a free surface that slightly vibrates. The slightly vibrating free surface presents fairly accurately the behaviour of the molten slag–casting powder layer in the continuous casting mould. The developed simulation system is then tested on a slab continuous casting mould to analyse the fluid flow behaviour of molten steel under various nozzle designs. The design conditions include submerged depth of the nozzle, tilted angle of the nozzle port, and rotated angle of the nozzle port. The results of the simulations show that of the various design factors rotation of the nozzle entry ports has the greatest effect on the flow pattern. It can prolong the residence time of the molten steel and stabilise the molten slag–casting powder layer, which is very favourable for obtaining continuous casting slag of high cleanliness.     

浸入式水口倾角对宽幅连铸结晶器内流动行为的影响

浸入式水口出口角度影响射流的动能损失,进而影响结晶器内的流动行为.建立了比例为1 ∶ 4的水模型,在模型拉速为0.425 m/min、水口浸入深度为40 mm的条件下,借助粒子图像测速技术研究了浸入式水口出口倾角为0°和+5°对宽幅连铸结晶器内流动行为的影响.结果表明,0°和+5°水口条件下,射流在模型内的流动方式有很...     

浇铸参数对结晶器液面波动影响及其工业应用

 板坯连铸结晶器液面的波动行为是结晶器内钢液流动、结晶器自身振动以及辊子挤压铸坯内部未凝固的钢液造成液面波动综合作用的结果。结晶器液位波动的稳定性对板坯连铸过程的卷渣行为有直接影响。在工业板坯连铸生产实践中,一般在结晶器某一区域(比如结晶器中部)利用放射源或涡流传感器检测液位波动来代表该工况下的整体波动水平。利用三维气液两相流动的数学模型研究了浇铸参数对结晶器液位轮廓的影响,浇铸参数包括拉速、吹氩流量、浸入式水口出口角度和浇铸断面。研究结果表明,结晶器不同宽度位置的波动幅值差异较大,且与工艺参数密切相关。液面的波峰与波谷之差随着拉速的增加在窄面附近逐渐增大,随着吹氩流量的增加在水口附近逐渐增大。在水口出口角度15°条件下,水口和窄面附近的液位波动均较大,而在水口出口角度45°条件下,仅在水口附近存在较大的液位波动。研究结果表明,使用板坯连铸常规的15°浸入式水口,当铸坯宽度大于800 mm时,结晶器液面检测需要在水口和窄面附近同时布置液位检测设备,以便更全面反应结晶器的真实液面行为,使液面波动对轧板表面质量指导性增强,有效提高连铸工艺的控制水平。如使用45°浸入式水口可以继续沿用原有的液位检测布置。     

Development of mould fluxes based on lime–alumina slag system for casting high aluminium TRIP steel

Abstract

With excellent strength and ductility properties, transformation induced plasticity (TRIP) steels are superior to ordinary commercial steels and have great application potential in the automobile industry. However, the continuous casting of TRIP steels is associated with challenges owing to its high aluminium content, approximately 0?5–1?8%. The reaction of aluminium near the steel/slag interface continuously changes the basicity of conventional lime–silica based mould fluxes causing variation in the flux physical properties between the solidifying shell and mould wall. Therefore, the heat transfer process is unstable and the surface quality of the as-cast slab is not guaranteed.

To reduce the reactivity of aluminium in TRIP steel during casting, it is suggested to replace the lime–silica based fluxes with a lime–alumina based mould flux, based on laboratory measurements and industrial trials.

The trials showed great improvement in the slab surface quality and no depression defect was noticed so far.     

大方坯径向水口旋流效应及其对凝固的影响

通过改变水口侧孔钢水流动方向可以控制结晶器内钢水流动与换热。采用流体动力学与凝固模拟方法对比研究了浸入式四分径向水口不同出流方向对大方坯连铸结晶器内流动、传热和凝固行为的影响。结果表明,侧孔方向对浇注过程结晶器内钢水的流动与凝固行为有显著影响。当水口侧孔水平旋转角度为30°时,结晶器内形成较好的水平旋流,可以有效降低侧孔出流钢水对坯壳的冲刷作用,并有利于结晶器内自由液面过热度的提高。比较不同侧孔出流角度发现,利用普通径向四分水口在一定安装角度下的旋流效应不仅对于初生坯壳的均匀生长以及自由液面的冶金效果产生有利影响,还可能在不改变水口结构条件下获得类似结晶器电磁搅拌的旋流效应。     

Optimal control of secondary cooling for medium thickness slab continuous casting

Abstract

A software to simulate the solidification, heat transfer and water flowrate distribution in slab continuous casting was developed by establishing a mathematical model for the heat transfer and solidification in medium thickness slab casting. This model was validated by pin shooting and surface temperature measurement experiments. A reasonable target surface control temperature was found by testing the high temperature mechanical properties of Nb bearing ship plate steel, and then the water flowrate of each loop of the secondary cooling zone was determined by the software. The influence of uneven secondary cooling in the slab width direction on the quality of the slab was also investigated, which provided data for the optimisation of the secondary cooling of the slab caster. On the basis of the above research, an optimisation scheme for a secondary cooling system was proposed. Experimental results showed that the quality of the slab was significantly improved after optimisation. The centreline macrosegregation was reduced, and the ratio of equiaxed grains was increased by 3·18%. In addition, the transverse cracking of the slab was almost eliminated.     

The oriented growth of precipitates on dislocations in Al-Zn-Mg—part I. Experimental observations

The weak-beam transmission electron microscope technique was employed to examine the precipitation of η phase laths on dislocation lines in Al-3.87 wt.% Zn-1.79 wt.% Mg. The use of this technique allowed the observation of fine-scale particles which were still in intimate contact with their catalyzing dislocations, and so would presumably most strongly reflect the role of dislocations during particle growth.The lath-like particles generally formed with their long axes (preferred growth directions) in the dislocation glide planes and parallel to the 〈110〉 matrix directions closest to the estimated initial orientations of the catalyzing defects. During these early stages of growth, the randomly oriented dislocations maintained contiguity with the lengthening particles by bending in their glide planes to accommodate the preferred growth directions of the particles. The misorientation angle between the 〈110〉 growth direction of a lath and the initial orientation of its associated dislocation was found to affect the particle growth kinetics: Laths growing at larger misorientation angles were found to be significantly shorter than those growing at smaller angles for the same aging time.     

Influence of Sulfur Content on Penetration Depth in TIG Welding for High Manganese Stainless Steels

TIG welding of high manganese stainless steels was conducted with different sulfur contents of 5 and 20 ppm. The penetration depth of the welding bead clearly increased even when the sulfur content of the sample was only very slightly increased from 5 to 20 ppm. In situ observation of the surface of the molten pool revealed that the increase in penetration depth of the welding bead could be attributed to an elevation of the average temperature at the center of the molten pool from 2070 to 2200 K due to the generation of an inward fluid flow in the pool. The results of precise measurements of the surface tension of molten high manganese stainless steels using the electromagnetic levitation (EML) technique, thoroughly explained that the inward flow in the molten pool of the sample containing a sulfur content of 20 ppm was induced by Marangoni convection driven by the boomerang shape temperature dependence of the surface tension of the molten sample. The experimental results of the variations in the temperature distribution and the fluid flow direction in the molten pool depending on the sulfur content were reproduced well by a numerical calculation considering the four dominant driving forces of plasma jet, buoyancy, electromagnetic forces, and Marangoni convection, which indicated that the fluid flow direction was dominantly controlled by Marangoni convection.

     

水口扩张角对230mm x 1300 mm板坯结晶器流场及氩气泡行为的影响

利用离散相模型研究水口扩张角（0~12°）对230mm×1300 mm板坯结晶器流场及氩气泡行为影响。并用水模型实验进行了验证。结果表明,扩张角增大,能显著减小注流冲击深度及氩气泡在自由液面上浮区域;尤其当扩张角为9°时,结晶器流场较好,自由液面波动较小,有利于夹杂物去除及减轻界面卷渣几率。双流230mm板坯连铸工业性试验表明,安装扩张角9°的水口一流铸坯较安装无扩张角水口的另一流铸坯表面夹渣发生率降低了5.9%~14.8%。     

CSP热轧过程中夹杂物周围孔洞的演变

借助于动态显式有限元软件ABAQUS/Explicit,模拟了CSP热轧过程中,板坯厚度方向上不同位置处直径为50μm的Al2O3夹杂物周围孔洞的形成和演变过程。结果表明,对于不同位置处的Al2O3夹杂物,在它们沿轧制方向的前、后部位都形成了孔洞,但前孔洞面积大于后孔洞面积;夹杂物越靠近板坯表面,形成的孔洞越大;热轧过程中,孔洞的演变是一个"愈合—长大—愈合"的动态过程;随着道次的增加,夹杂物前、后孔洞在轧制方向上的投影长度变化与面积变化趋势相一致,而与孔洞尖端夹角的变化趋势恰好相反;孔洞在热轧过程中发生转动,导致前孔洞尖端朝着带钢表面扩展。模拟结果有助于揭示夹杂物周围孔洞与表面缺陷的关系,并为实际生产提供理论指导。     

Growth direction of columnar crystals solidified in flowing melt

Aluminum-copper alloys containing 0.5–8.8 wt% Cu were unidirectionally solidified. Columnar crystals were grown in flowing melts at flow rates ranging from 4 to 90 cm/s, and the deflection angle of the crystal growth direction in the upstream direction was measured as functions of flow rate and copper content. The columnar crystals originated from nuclei or solid particles with the most suitable crystallographic orientation for growing in flowing melt. The growth direction of the columnar dendrites was nearly equal to that of the columnar grains comprising the columnar dendrites. The deflection angle for the columnar grains increased only slightly with an increase in flow rate or copper content within the ranges investigated, while the inclination angle of the growth direction of columnar dendrites from the [100] direction increased with an increase in flow rate and with a decrease in copper content.     

Trunk muscle activation and cocontraction while resisting applied moments in a twisted posture

Previous studies of twisting have revealed substantial cocontraction of agonist and antagonist muscles within the torso when torsional moments are generated. The objective of the current study was to quantify the activations and cocontraction of eight trunk muscles as subjects maintained an axially rotated trunk posture and resisted external applied bending moments. Ten subjects twisted their torsos 25 degrees to the right (clockwise) and resisted 20 and 40 Nm bending moments from 12 directions. The moment directions were in a transverse plane and labelled clockwise as viewed from above, ranging from 0 degrees (mid-saggital, anterior) to 330 degrees, in 30 degrees increments. RMS EMG amplitude data were collected using surface electrodes and normalized to maximal voluntary contractions. Significant changes were observed in the muscle responses due to the interaction of the moment direction and moment magnitude for six of the eight muscles tested. Comparison of the present data with that collected previously in neutral postures indicated: (1) a large increase in the activation levels of the right erector spinae and the left external oblique muscles; and (2) a counter-clockwise shift in the moment direction at which the peak activation of these same muscles occurs. Analysis of the relative activation levels (RALs), constructed from the NEMG data to quantify the cocontraction, indicated that the changes in cocontraction were more robust in response to changes in the bending moment's direction as opposed to changes in bending moment's magnitude.     

吹氩板坯结晶器水模型实验研究

采用1：2.5的相似比,以1 500 mm×280 mm断面的结晶器为原型建立水模型,试验研究了在吹氩条件下拉速,水口倾角、吹气量和浸入深度对液面波动的影响,并分析了在试验条件下的卷渣行为,研究结果表明在吹氩条件下主要存在气泡群冲击卷渣和类漩涡卷渣两种方式。     

Dendrite growth directions in aluminum-zinc alloys

The dendrite growth directions in fcc aluminum-zinc alloys have been measured by electron backscattered diffraction (EBSD) as a function of the zinc concentration,c _o . In specimens produced by directional or Bridgman solidification, 〈100〉 dendrites were observed up to 25 wt pct Zn, whereas, above 60 wt pct, the dendrite growth direction was clearly 〈110〉. In between these two concentrations, the angle, φ(c _o ), between 〈100〉 and the 〈hk0〉 dendrite growth direction, varied continuously between 0 and 45 deg asc _o increased. Following an analysis of growth directions suggested by Karma but restricted to two dimensions in a (001) plane,^[1] this angle was fitted with a function ¼ arcos (?η₄/4η₈), where η₄(c _o ) cos (4φ) and η₈(c _o ) cos (8φ) are the first two contributions to the solid-liquid interfacial stiffness anisotropy in a (001) plane. This analysis also gives a qualitative explanation to textured seaweed structures observed aroundc _o ≈ 25 and 60 wt pct. These findings are discussed in light of recent measurements of the weak interfacial solid-liquid energy anisotropy of aluminum^[2,3] and of dendrite growth directions in hcp Zn-Al alloys.^[4]     

板坯连铸结晶器内钢液表面流速的水模型研究

以承德钢铁厂板坯连铸结晶器为原型,采用1∶1的水模型进行试验,研究了拉速、浸入式水口出口角度、水口浸入深度、水口底面结构及结晶器断面宽度等工艺参数对板坯结晶器内表面流速的影响。结果表明:拉速对表面流速的影响最大,随着拉速的提高,结晶器内钢液表面流速明显增大,当断面宽度为1 650 mm,拉速由0.7 m/min提高到1.4 m/min,表面流速由0.04 m/s提高到0.1 m/s;波浪面结构的浸入式水口表面流速效果最优。     

Influence of production parameters on surface energy of tinplate

Abstract

The surface energies of commercially produced tinplate samples have been characterised. The surface energies were determined using contact angle measurements by both a single liquid analysis and a multiliquid analysis using mixtures of water and diacetone alcohol. The single liquid method should be treated with caution as the results are significantly affected by choice of liquid. The multifluid methods are more accurate and reliable, and the optimum methodology for surface energy measurements was developed. The surface energies of the tinplate substrates were in the range of 30 to 35 mJ m^?2, about one third of which was polar in nature. The substrate variables assessed included levels of lubricating oil, chromium passivation, tin, iron–tin alloy and tin oxide as well as surface roughness. A multiparameter analysis showed that the levels of lubricating oil and tin oxide were most significant in determining the surface energy.     

Optimisation of pinch roll load in thin slab continuous casting

Abstract

An analytical model has been developed to investigate the optimum pinch roll load and resulting slab thickness reduction during the continuous casting of a steel, constant thickness, thin slab in a vertical type machine. The pinch roll unit consists of two driven pinch roll sets, which support the solidified hot slab weight and take up the reaction forces owing to slab bending. Optimum conditions prevail when the pinch roll load required to support the slab weight is equally shared by the two pinch roll sets and has the minimum value allowing proper control of the slab speed. The model has been validated by being applied to an existing industrial case of thin slab continuous casting of plain low carbon steel. The effects of pinch roll radius, slab thickness, casting speed, slab temperature and the material carbon percentage on minimum pinch roll load and slab thickness reduction ratio have been investigated. Expressions have been obtained for the optimum pinch roll load and slab thickness reduction ratio related to the prevailing process parameters, which the plant operator can directly apply to determine the optimum pressure setting for the hydraulic cylinders fitted to the movable roll ends. The bending roll load is shown to be small compared with the pinch roll load.