DANIELI concepts and experiences in thin slab casting and rolling technology for HRC production—the evolution of a winning process route to face increasing market requirements

The direct rolling process for hot strip production,where the thin slab caster is connected directly to the mill,has gained market share rapidly because of its remarkable advantages in terms of energy savings and investment cost over the conventional hot strip mills. However,the unquestionable advantages of the first-generation applications of this plant concept also entail significant limitations both in productivity and steel grades that can be produced. Since his first pioneering applications,Danieli considered strategic the development of new technical solutions specifically conceived to overcome these limitations with the goal of increasing plant production volumes and enlarging steel grade product mix,in order to cover the gap between "Conventional mill" and "Thin slab casting and rolling" process routes. In order to reach this goal,Danieli has developed a complete portfolio of plant lay outs adopting Thin Slab Casting and Rolling technologies,each of them conceived to guarantee the optimal CAPEX and OPEX parameters in fitting with market requirements our Customer intend to target.in terms of productivity,steel grades and coil dimension product mix. Danieli TSR(Thin Slab Rolling) fTSR(flexible Thins Slab Rolling) QSP(Quality Strip Production) and ETR(Extra Thin Rolling) plant configurations are analyzed in this paper. With this diversified approach,Danieli solutions are most appropriate answers to thin slab casting and rolling to produce hot rolled coils with superior quality and an extremely diversified range of steel grades. Already,this approach has allowed Danieli plants to:①exceed the threshold production of 3.0 Mt/a with 2 casting strands in operation as done in Tangshan Iron and Steel plant in P.R.China since 2005;②expand the product mix to include virtually all the steel grades used for flat product applications,including the most demanding ones,such as peritectic(in Essar Algoma Canada and Benxi Iron and Steel,China),micro-alloyed,and silicon steels,for the most sophisticated applications,such as automotive and pipe manufacturing,including Arctic applications,(as done in OMK plant in Russia);③extend the range of final strip thicknesses to include ultra thin gauges,down to 0.8 mm(as in Ezz Flat Steel,in Egypt).

Slab Storage Calculation Method for Continuous Casting-Hot Rolling

Based on load-oriented manufacturing control theory,different combining modes and slab storage calculation method for continuous casting and hot rolling were discussed.The buffer capacity index of continuous casting-rolling was introduced,and the reasonable slab storage under different combining modes was calculated with buffer capacity index of 120.00 hfor CCR,79.20 hfor HCR,19.68 hfor DHCR and 3.84 hfor DR.Thin slab is 1.20 h,and the strip is zero.Theory gist was provided for steel enterprise to decrease storage.

Characteristics evolution of 6009/7050 bimetal slab prepared by direct-chill casting process

6009/7050 alloy bimetal slab was prepared by a direct-chill (DC) casting process. Homogenizing annealing, hot rolling and T6 treatment were successively performed and their effects on microstructure and properties of the slab were studied. The results reveal that the average diffusion layer thickness of as-cast slab, determined by interdiffusion of elements Zn, Cu, Mg and Si, was about 400 μm. Excellent metallurgical bonding was achieved because all tensile samples fractured on the softer 6009 alloy side after homogenizing annealing. After homogenizing annealing plus rolling, the average diffusion layer thickness decreased to 100 μm, while the network structure of 7050 alloy side transformed to dispersive nubby structure. Furthermore, subsequent T6 treatment resulted in diffusion layer thickness up to 200 μm and an obvious increase of the Vickers hardness for both 7050 and 6009 sides. The layered structure of the as-cast 6009/7050 bimetal is retained after hot rolling and T6 treatment.

STUDY OF DYNAMIC RECRYSTALLIZATION OF LOW CARBON STEEL IN THIN SLAB CONTINUOUS ROLLING PROCESS

Combined with the technological characteristics of thin slab continuous rolling process （TSCR）, dynamic recrystallization of an extremely coarse austenite of low carbon steel is studied by Thermecmaster-Z hot simulator. By the analysis of true stress-strain curves and the observation of microstructures at different deformation stages, the critical stress and critical strain are determined under different deformation conditions. The effect of Z parameter on dynamic recrystallization of coarse austenite is studied. The microstructure evolution in real production is also discussed.

Texture of Hot Rolled Strip for Fe-3Si Steel Produced by Thin Slab Casting and Rolling

Fe-3Si steel strip was produced by thin slab casting and rolling （TSCR） process in the laboratory. The microstructure and texture of hot rolled strip by different total reduction and rolling schedules were observed through EBSD technique and X-ray diffraction method. The rule of texture density for the a,ε and γ fibers was analyzed. When the total reduction was increased from 82.9% to 97.1%, the gradient of microstrueture and texture for A steel surface layer and center layer was found, {001}〈110〉 texture had higher intensity, and {001}〈110〉texture was changed to { 110 } 〈 001 〉 and { 112 } 〈 111 〉. The texture distribution with different reduction schedules for B steel was basically similar, but the Goss texture orientation density and volume fraction for B steel were higher, the hot rolling reduction schedule of C1 was effective for the formation of Goss texture. The research work was useful theoretical basis and reference data to develop electrical steel by thin slab continuous casting and direct rolling technology.

Microstructure,texture and precipitates of grain-oriented silicon steel produced by thin slab casting and rolling process

A grain-oriented silicon steel strip with AlN as main inhibitor was produced by thin slab casting and rolling（TSCR）process.The microstructure,texture and precipitates of the hot-rolled strip were investigated by use of optical microscope（OM）,X-ray diffractometer,transmission electron microscope（TEM）and energy dispersive spectroscope（EDS）.The result shows that the microstructure and texture exhibit a through-thickness gradient similar to that of the hot-rolled strip produced by conventional high-temperature slab-reheating process;the preferred orientation varies from {110}〈001〉in the surface layer to{001}〈110〉in the center layer,and the Goss texture with a maximum intensity mainly concentrates on the surface layer.In addition,some other texture components,for example rotated Goss texture,form in the 1/4thickness layer,which are not observed in the hotrolled strip produced by conventional high-temperature slab-reheating process.The precipitates in the hot-rolled strip are mainly（Mn,Cu）S and AlN compound particles with dimension of 100-200 nm,and the fine precipitates are significantly less than that in the hot-rolled strip produced by conventional high-temperature slab-reheating process.Moreover,the areal density of the fine precipitates in the center layer is more than that in the surface layer.

Texture of Cold Rolled Strip of Fe-3Si Steel Produced by Thin Slab Casting and Rolling

The hot rolled strip of Fe-3Si steel was experimentally produced by thin slab casting and rolling（TSCR） process in the laboratory.The texture evolution rule was investigated during hot rolling and cold rolling.The texture distribution of cold rolled strips with four kinds of cold rolling reduction schedules was observed through X-ray diffraction method,and the orientation density variation of 1/16 layer,1/8 layer,1/4 layer,and 1/2 layer in thickness was analyzed.The cold rolled texture of steel A with four kinds of cold rolling reduction schedules was mainly composed of α and γ fibers.Cold rolling reduction ratio of 70% was more beneficial for obtaining more γ fibers.The γ fiber texture orientation density of {111}01-1 and {111}1-1-2 was the largest on the 1/8 layer and 1/4 layer and the least on the 1/16 layer and 1/2 layer for steel B.The texture orientation density of {001}-{223}11-0 in the α fibers for steel C was increased,but the texture orientation density of {332}-{110}11-0 was low.

TSCR流程生产钛微合金化高强耐候钢中的析出物

运用电子显微镜和化学相分析等多种实验手段研究了Ti微合金化高强耐候钢中的析出物,并在热力学计算的基础上分析了其析出过程.结果表明:钢中主要存在TiC,TiCN,Ti4C2S2,Ti N等析出物,连轧前Ti N的析出过程已基本完成;大量纳米尺寸的TiC球形析出物粒子在铁素体的位错线上分布;Ti含量增加改变了MC相的粒度分布,小尺寸粒子的体积分数显著增加,增强了沉淀强化的效果.

TSCR工艺生产Ti-IF钢中第二相粒子析出行为的模拟研究

研究了模拟薄板坯连铸连轧工艺(Thin Slab Casting and Rolling)生产Ti-IF钢的析出行为。利用透射电镜分析了铸坯连续快速冷却及热连轧过程Ti-IF钢中第二相粒子的析出行为特征,将TiS,Ti4C2S2等析出粒子的尺寸、分布及数量分别与传统工艺的析出物进行了分析比较。结果表明,TSCR生产的Ti-IF钢析出物比传统工艺更为粗大,且发现有较粗大的TiC和Ti4C2S2的复合析出物。

TSCR热轧工艺对3.2%Si无取向硅钢组织性能的影响

研究了薄板坯连铸连轧流程(TSCR)条件下热轧工艺对3.2%Si-0.7%Al无取向硅钢组织、织构演变及磁性能的影响规律。结果表明,提高均热温度和热轧温度有助于获得粗大的变形组织和强烈的{001}〈110〉织构,进而对后续的组织、织构演变进程及磁性能产生有利的遗传影响。与低温均热和低温热轧相比,高温均热和高温热轧得到的最终成品板的再结晶晶粒较粗大,λ纤维再结晶织构较强而γ纤维再结晶织构较弱,磁感应强度较高。

TSCR生产低碳铝镇静钢薄带软化机理研究

通过实验室模拟薄板坯连铸连轧（TSCR）流程生产低碳铝镇静钢热轧钢带,分析了硼的质量分数为（10～50）×10^-6的热轧钢带的组织、析出物的特点及性能变化.结果表明：钢中加入硼的质量分数为（10～50）×10^-6的热轧钢带晶粒度达到7～8级,平均晶粒尺寸达到25μm,屈服强度降至231 MPa,与不加硼钢相比,屈服强度降低了94 MPa.

TSCR流程Ti微合金化超高强钢的第二相析出行为研究

利用Gleeble-1500D模拟机进行了Ti微合金钢的热模拟试验,研究了其在薄板坯连铸连轧(TSCR)流程下Ti(C,N)沉淀析出行为。结果表明,Ti微合金钢在TSCR流程中存在两类含Ti析出物:正方形的或矩形的TiN和球形或不规则形状TiC。TiN析出物主要在连铸凝固前钢液中和铸坯均匀化加热时析出,在连轧时起到抑制动态再结晶晶粒生长的作用;而TiC析出物主要是在连轧和卷取时析出,对Ti微合金钢起沉淀强化作用。为了提高Ti微合金钢沉淀强化效果,应在TSCR流程中增加TiC的体积分数和减小TiC的尺寸。

TSCR工艺参数对Fe-3%Si钢带显微组织的影响

在实验室模拟薄板坯连铸连轧(TSCR)生产Fe-3%Si钢带,研究薄板坯连铸连轧不同工艺参数对Fe-3%Si钢带热轧和常化显微组织的影响.结果表明,TSCR工艺生产的Fe-3%Si钢带热轧显微组织沿板厚方向呈现组织不均匀性,1 200℃保温20 min,前两道压下量较大、道次递减的显微组织过渡层再结晶晶粒数较多且相对均匀细小,没有中心层拉长的条带组织,有利于二次再结晶的完善.显微组织平均晶粒尺寸与传统流程热轧平均晶粒尺寸相差1.5μm,具有几乎相同的位错形貌,头部和中部显微组织差别都很小.热轧显微组织质量决定了常化后显微组织的质量.

TSCR热轧工艺参数对Fe-3%Si钢带织构的影响

在实验室模拟薄板坯连铸连轧生产Fe-3%Si钢带,从宏观和微观的角度研究了TSCR热轧工艺参数对Fe-3%Si钢带织构形成的影响。结果表明,实验几种热轧工艺制度,热轧板沿板厚方向均呈现织构的不均匀性,表面附近主要有〈101〉//ND,中心层主要有〈001〉//ND。不同工艺热带次表层织构组分基本相同,有{110}〈001〉Goss织构、{110}〈112〉brass织构和S织构,只是强度有所区别。铸坯以表面温度≥1000℃入加热炉,保温1200℃,保温20min,压下制度为70→42→22→12→7→4→2.5→2的试样,其次表层各织构组分及体积百分含量与传统工艺生产Hi-B钢的结果最接近。

TSCR生产IF钢相变及组织演变规律研究

采用热模拟方法研究了薄板坯连铸连轧工艺生产无间隙原子钢的动态及静态相变规律,绘制其动态与静态连续冷却转变曲线;并比较分析薄板坯连铸连轧工艺下无间隙原子钢在变形及不变形条件下的相变温度及组织演变规律。

FTSR薄板坯连铸连轧生产无取向硅钢实践

对本钢采用FTSR形式薄板坯连铸连轧产线开发无取向硅钢进行介绍,可实现节能降碳达30%。采用1100℃以下的板坯低温加热工艺技术,实现了节约能源和减少排放,并有效控制第二相粒子的固溶和析出;制定合理的热轧工艺,通过高温终轧和卷取,保证了热轧卷发生再结晶的驱动力,形成更多对电磁性能有利的织构。生产的无取向硅钢电磁性能优良,板型良好。

TSCR流程生产无取向电工钢的冷轧变形抗力模型

利用MTS880、WE-300拉伸试验机对采用TSCR流程生产的3种不同Si+Al含量的无取向电工钢冷轧变形抗力进行了研究,分析了可逆轧制和连轧过程生产方法对变形抗力的影响,并通过试验数据建立了变形抗力数学模型,并对模型判定系数分析和回归计算结果与实际测试结果进行比较,结果表明此模型具有良好的曲线拟合特性。

连铸机扇形段控制模式的转换

本钢炼钢厂6#板坯连铸机扇形段控制模式分为收缩辊缝和扇形段轻压下控制技术两种模式。本文分析了板坯铸机在两种控制模式转换过程中,铸机拉矫力过大造成拉不动板坯,严重时发生冻坯事故的原因及解决办法,通过优化扇形段控制过程,解决了两种控制模式转换时发生问题的现象。

TSCR工艺生产30CrMo热轧带钢的实践

针对薄板坯连铸连轧流程的工艺特点,通过合理的成分设计和生产工艺优化,有效解决了脱碳和铸坯裂纹等关键技术问题,开发出了高品质的合金结构钢30CrMo热轧带钢,产品组织为细小均匀的铁素体+珠光体,夹杂物尺寸在5μm以下的占98%以上,且球化较好;带钢抗拉强度为795～950MPa,伸长率为15%～21%;带钢厚度公差控制在±25μm以内,平直度控制在±10I以内。

Shape Discrimination Analysis of Rolled Strip Based on Strip Element Method

Based on load-oriented manufacturing control theory, different combining modes and slab storage calculation method for continuous casting and hot rolling were discussed. The buffer capacity index of continuous casting-rolling was introduced, and the reasonable slab storage under different combining modes was calculated with buffer capacity index of 120.00 h for CCR, 79.20 h for HCR, 19.68 h for DHCR and 3.84 h for DR. Thin slab is 1.20 h, and the strip is zero. Theory gist was provided for steel enterprise to decrease storage.