热轧U型钢板桩精轧过程金属流动行为的有限元分析

针对热轧U型钢板桩(SY390BZ/%:0.23C、1.60Mn、0.44Si、0.18V,0.18Ti、0.05Nb)轧制过程中产生翘曲缺陷,采用有限元分析软件ABAQUS显式动力学算法,结合实验室试验测量参数,对钢板桩的精轧过程进行了仿真计算。在仿真计算的基础上,根据轧制平面内节点位移矢量分布情况,分析了轧件横向和纵向断面内金属流动规律。模拟结果显示轧件断面在孔型轧制的压下方向上存在零位移线,表明U型钢板桩轧制中坯料翼缘和锁口处在轧制压力方向上轧件内金属流动存在位移中性面,并伴有轧件锁口凸缘处金属流动过快,腹板处金属流动较慢而产生翘曲的现象。     

Preventing surface defects in the uncoiling of thin steel sheet

The formation of surface defects when annealed thin cold-rolled steel sheet is uncoiled for temper rolling is analyzed. The appearance of such defects is mainly due to adhesion and welding of the contacting surfaces of the turns in the coil. The influence of the strip thickness, surface roughness, temperature, properties of the metal, and other factors on the stress–state of the coil and the likelihood of surface defects is analyzed. Preventive measures are recommended.     

Analysis of secondary oxide-scale failure at entry into the roll gap

Both numerical analysis based on finite-element (FE) modeling and experimental evidence concerning the secondary oxide-scale failure at entry into the roll gap are presented and reviewed for a better understanding of events at the roll-workpiece interface, in turn, leading to better definition of the boundary conditions for process models. Attention is paid to the two limit modes leading to oxide-scale failure, which were observed earlier during tensile testing under rolling conditions. These are considered in relation to the temperature, the oxide-scale thickness, and other hot-rolling parameters. The mathematical model used for the analysis is composed of macro and micro parts, which allow for simulation of metal/scale flow, heat transfer, cracking of the oxide scale, as well as sliding along the oxide/metal interface and spallation of the scale from the metal surface. The different modes of oxide-scale failure were predicted, taking into account stress-directed diffusion, fracture and adhesion of the oxide scale, strain, strain rate, and temperature. Stalled hot-rolling tests under controlled conditions have been used to verify the types of oxide-scale failure and have shown good predictive capabilities of the model. The stock temperature and the oxide-scale thickness are important parameters, which, depending on other rolling conditions, may cause either through-thickness cracking of the scale at the entry or lead to entry of a nonfractured scale when the scale/metal interface is not strong enough to transmit the metal deformation.     

The Formation of Edge Cracks during Rolling of Metal Sheet

Many metals tend to develop edge cracks during hot and cold rolling. Edge cracks need to be removed by a trimming operation, and they may cause rupture of the sheet in the rolling mill. Hence, there is a strong motivation to understand the mechanisms of edge crack formation and to develop predictive tools for controlling the phenomenon. The present work explores the applicability of damage mechanics models to this problem. In conjunction with a plausible failure criterion the Gologanu‐Leblond model, which is based on non‐spherical ductile void growth, is able to predict edge cracking and the characteristic zigzag damage pattern on the edge of the rolled sheet. The experimental determination of the model parameters remains a challenging task, since the stress and strain history at the edge of a rolled sheet is substantially different from the situation in a tensile test, and also from that in other conventional laboratory tests.     

Properties of TiAl sheet pack-rolled at temperatures below 1000°C

TiAl alloy specimens with microcrystalline (MC, grain size is 5 μm) and submicrocrystalline (SMC, grain size is 0.4 μm) structures were successfully pack-rolled to sheet with a thickness down to 0.4 mm in the temperature ranges of 800°C to 1000°C and 900°C to 1000°C, respectively. An 18/10 stainless steel was used as a rather inexpensive can material for pack-rolling. Unidirectional rolling and bidirectional cross-rolling were used. Because of a wider temperature range for pack rolling and a lower cost for production of the alloy preforms, the microcrystalline structure was found to be a better microstructural condition for the TiAl sheet rolling. The sheet produced by unidirectional rolling had an anisotropy of mechanical properties, i.e., strength was smaller and elongation larger in the rolling direction than in a transverse direction. The anisotropy decreased when the rolling temperature increased. The bidirectional rolling led to in-plane isotropic properties of the sheet. The produced sheet showed elongation of about 3 pct at room temperature, brittle-to-ductile transition in the temperature range of 750°C to 850°C, and superplastic behavior in the temperature range 900°C to 1000°C. This article is based on a presentation made in the symposium entitled “Fundamentals of Structural Intermetallics,” presented at the 2002 TMS Annual Meeting, February 21–27, 2002, in Seattle, Washington, under the auspices of the ASM and TMS Joint Committee on Mechanical Behavior of Materials.     

铜／钢双金属板异步轧制复合机理研究

研究了铜／钢双金属板异步轧制复合工艺对轧后界面形貌的影响,用电子探针分析了铜／钢复合板界面结合区成分的变化。轧制变形程度和退火温度是控制界面形貌的主要因素,异步轧制复合有不同于室温固相复合的结合机制。     

Production of thick 10XCHДΦ steel sheet of optimized composition for the construction industry

On the basis of newly developed steel, thick sheet for the construction industry may be produced, by smelting and casting, hot rolling, and subsequent heat treatment. In the oxygen-converter shop at OAO Magnitogorskii Metallurgicheskii Kombinat (MMK), a 370-t melt of steel is produced as a trial run. The metal is cast to slabs (thickness 300 mm), which are rolled on a 5000 mill to sheet (thickness 22–50 mm). A production technology for thick vanadium-steel sheet on the 5000 mill is developed: rolling with subsequent heat treatment (quenching + tempering); or controlled rolling with subsequent accelerated cooling to ensure the required strength class 390 and impact strength (KCU_?60, KCV_?20, KCA₂₀). The structure of the cast 10XCHДΦ steel sheet is investigated. Control tests of sheets used in the manufacture of metal structures for the Kazan football stadium confirm the high quality of the sheet.     

Fe-6.5%Si钢极薄带的试制

 为了研究Fe-6.5%Si钢极薄带的制备工艺,并获得良好的产品磁性能,以薄带铸轧试验机制备的6.5%Si钢铸带为原料,分别采用一次温轧法、二次温轧法和基于应变诱导无序(DID)原理的高硅钢室温冷轧3种工艺制备出厚度为0.1 mm的Fe-6.5%Si钢。分析结果显示,一次温轧法退火后以高强度γ织构为主,由于压下率达到90%,形变储能高,晶粒尺寸最大,铁损最低,同时磁感也最低;二次温轧的退火板除了γ织构外,还有较强的η织构,故其磁感值高于一次温轧法,该方法得到的6.5%Si钢薄带综合磁性能最优,但生产成本高,效率低;基于DID原理,对6.5%Si钢热轧板在温度为300～450 ℃、压下率为45%～65%的条件下进行温轧,实现了6.5%Si钢软化,随后可将6.5%Si钢室温冷轧至0.1 mm,此时温轧板和冷轧板内部有序相消失,基体变成无序态;室温冷轧板退火后晶粒更细,铁损略有升高。此外,室温冷轧可促进{111}<112>形变晶粒在冷轧剪切带中形核形成有利织构,因此磁感值得到更大提升;采用DID原理进行室温冷轧,效率较高,后续可通过优化退火工艺使其进一步降低铁损,该方法为薄带铸轧工艺批量生产磁性能优异的6.5%Si钢极薄带提供技术参考。     

Surface-crack formation in the two-phase region when rolling thick microalloyed-steel sheet

The formation of a surface defect (a lobed scab) in the final stage of large-diameter pipe production is analyzed. Surface microcracks are assumed to form in the rolling of thick sheet on account of problems in the two-phase region on rolling, with localization of the plastic strain, as well as the action of tensile stress in the surface layer and the attainment of limiting stress values. Physical modeling in the Gleeble system permits determination of the limiting stress (rupture strength) in rolling in the two-phase region, which depends on the temperature and is structure-sensitive. The limiting stress is determined by ferritic and bainitic transformation in the steel.     

A Simple Model for Conventional Hot Rolling of Sheet Materials

Temperature transients during the bare hot rolling of sheet materials have been modeled using a simple one-dimensional, finite-difference heat-transfer approach. The model addresses heat losses associated with (1) the transfer of the sheet from the reheat furnace to the rolling mill and (2) the actual rolling operation itself. The former step comprises heat losses primarily through radiation and the latter through chilling of the hot workpiece in contact with the cooler rolls. The principal output of the model is the temperature field through the thickness of the sheet. The usefulness of the model was gaged through an investigation of the effect of temperature transients on the hot-rolling behavior of Ti-6Al-4V sheet. Specifically, the effect of temperature transients on rolling pressure and development of nonuniform microstructure was determined. Over the entire temperature range studied, the rolling pressure for Ti-6Al-4V was found to be dependent only on the average temperature of the workpiece within the roll gap, irrespective of metastable phase transformations that may have accompanied the deformation process itself. The one-dimensional heat-transfer model was also successful in explaining the occurrence of the nonuniform microstructures produced during rolling at nominal (furnace) temperatures near the beta transus.     

铝合金钎焊板(箔)热轧复合工艺研究

揭示基体金属和焊层金属在热轧时的复合机理及成形规律，根据金属轧制过程中的变形规律，研究了热轧过程中及冷轧过程中包覆层的厚比变化规律，研究了铝合金钎焊板(箔)热轧复合工艺，开发出满足使用要求的铝合金钎焊板(箔)。     

废钢-电弧炉流程和铁水+废钢-电弧炉流程工序能耗的数学模拟

在物料平衡和热平衡模型的基础上,结合相关工艺参数,分别建立了废钢-电弧炉-连铸-连轧流程(废钢-电弧炉流程)和铁水+废钢-电弧炉-连铸-连轧流程(混合流程)的工序能耗的计算模型;分析了模型中几个重要参数对工序能耗的影响。结果表明,电弧炉热装铁水33％的混合流程的工序能耗较废钢-电弧炉的工序能耗降低43.72 kg_标煤/t_铜,但流程总能耗约增加1/3。     

IF钢冷轧退火板中第二相粒子分析与研究

采用CSP工艺生产的IF冷轧钢板,分析了热轧卷取温度、冷轧压下率、退火温度及保温时间对退火板中第二相粒子的影响。结果表明,提高卷曲温度、增大冷轧压下率,提高退火温度、延长保温时间均促进退火板中第二相粒子Ti(CN)与FeTiP聚集并复合生长,有利于{111}织构的发展。     

基于热轧全流程氧化铁皮控制的耐蚀性工艺

 针对热轧生产流程实际工况,系统研究了热轧、卷取阶段的三次氧化铁皮演变规律,旨在不增加生产成本的前提下,通过调整热轧生产工艺控制氧化铁皮结构,利用热轧后生成的氧化铁皮作为防护屏障,提高钢材耐蚀性能。结果表明,在不同轧制温度下,三次氧化铁皮结构从外到里分别为Fe₂O₃、Fe₃O₄和FeO,由于FeO中的阳离子空位密度大,导致其比例最大,并且随着轧制温度增加,氧化铁皮中的FeO层厚度逐渐增厚,并且其比例也逐渐增加。通过模拟连续冷却试验发现氧化铁皮结构转变关系呈现出“C”曲线的形式。在450～550 ℃温度范围内卷取时,FeO发生共析反应程度达到峰值,同时可以看出在高温下卷取可以有效抑制共析转变的发生。通过大量的试验研究表明,获得以先共析Fe₃O₄为主的完整氧化铁皮的结构类型,是有效提高热轧钢材耐蚀性的主要控制方向。因此在国内某钢厂热连轧生产线进行了基于氧化铁皮控制的耐蚀性工艺试轧试验和盐雾试验,结果表明,氧化铁皮完整致密,并且其结构类型主要为先共析Fe₃O₄,因此利用轧制工艺调整改变钢板表面氧化皮结构,钢材耐蚀性能得到显著提高。     

高温轧制对AZ31B镁合金组织和性能的影响

研究了高温轧制工艺对AZ31B镁合金微观组织、织构以及性能的影响规律.在轧制状态下,随着轧制温度从450℃升高至525℃,合金组织内部动态再结晶逐渐增多,孪晶数量不断减少,同时组织的均匀性也得到了改善,基面织构强度也呈下降的趋势.经350℃保温60min退火之后,合金板材内部发生了完全再结晶,孪晶组织消失,显微组织更均...     

中厚板表面片状开裂原因分析及控制

针对中厚板表面片状开裂缺陷,采用光学显微镜及扫描电镜等设备对缺陷进行分析验证。结果表明,开裂的原因是扇形段辊子上铜制的轴承保持架破损压入铸坯,在轧制过程中造成开裂并扩散;而轴承破损主要是由于高温环境下设备冷却及润滑不良,通过更改轴承材质、改善轴承润滑油路、冷却水路等措施,片状开裂缺陷得到有效控制。     

SP定宽轧制板形侧弯机理与策略

针对热轧SP定宽轧制的板形侧弯问题,经分析指出:板坯两侧温差造成金属塑性变形抗力大小不相等,从而使金属变形速度不同,变形速度快则相同时间内移动的金属量多,最终使变形快的一侧向变形慢的一侧弯曲是板形侧弯的形成机理.以宝铜分公司热轧厂1580mm机组的SP定宽机为研究对象,通过板坯温差检测、数据分析和板形结果对比,验证了板坯温差造成板形侧弯的机理.最后,通过实施一系列的减小板坯两侧温差的改进措施,使1580mm热轧SP定宽轧制板形侧弯得到了有效控制.     

热连轧低合金钢边部横裂形成原因分析

通过采集现场过程数据,从温度、成分、相变、晶粒形貌、轧制变形应力等方面对低合金钢Q355B宽规格钢板在热连轧过程中产生边部横向裂纹缺陷的原因进行机理分析.结果 表明,宽规格低合金钢边部横向裂纹产生原因与板坯宽度方向温度均匀性相关,边部局部温度过低导致两相区和非再结晶区域轧制,边裂区晶粒度尺寸和形貌与正常区有明显差异,从...     

Oblique and Herringbone Buckling Analysis of Steel Strip by Spline FEM

 The tilted waves in steel strip during rolling and leveling of sheet metal can be classified into two different types of buckling, oblique and herringbone buckling, respectively. Numerical considerations of oblique and herringbone buckling phenomena are dealt with by the spline finite element method (FEM). It is pointed out that the shear stress due to residual strains caused by the rolling process or applied non-uniform loading is the main reason of oblique and herringbone buckle. According to the analysis of stress distribution in plane, the appropriate initial strain patterns are adopted and the corresponding buckling modes are calculated by the spline FEM. The developed numerical model provides an estimation of buckling critical load and wave configuration.     

温轧工艺对Fe-6.5％Si薄板织构的影响

高硅钢具有优异的软磁性能,是中高频电机铁心的理想材料。采用双辊连铸-热轧-温轧-退火工艺,制备了厚度为 0.30 mm的6.5 %Si薄板。利用X射线衍射仪和磁性测量,研究了不同温轧工艺对6.5 %Si薄板轧制及退火织构、最终磁性能的影响。结果表明,温轧温度越低,越有利于温轧板心部形成{001}〈0vw〉织构,600 ℃和500 ℃轧制的试样经退火后主要是γ织构,而400 ℃轧制的试样退火后则同时含有γ织构及强度较高的η织构,其对应的磁感值高;同样的温轧温度,二次轧制的温轧板中并未形成{001}〈0vw〉织构,且试样经退火后也没有形成η织构,其磁感比一次轧制的试样低。因此,低温一次轧制,有利于试样在退火过程中形成有利的η织构而提高磁感。