L360管线钢热轧过程静态再结晶行为的研究

奥氏体再结晶行为是影响热轧钢带组织和力学性能的1个主要因素。在热模拟试验的基础上,采用应力松弛法和显微组织观察法,对含Nb和Ti的L360管线钢热轧过程奥氏体静态再结晶行为进行了研究,分析了应变、变形温度、应变速率、原始奥氏体晶粒尺寸对奥氏体静态再结晶的影响。利用线性回归分析,计算出试验钢静态再结晶激活能为203kJ;同时通过回归,得出试验钢热轧过程静态再结晶动力学方程。     

Numerical Simulation of Austenite Recrystallization in CSP Hot Rolled C-Mn Steel Strip

An integrated mathematical model is developed to predict the microstructure evolution of C-Mn steel during multipass hot rolling on the CSP production line,and the thermal evolution,the temperature distribution,the deformation,and the austenite recrystallization are simulated.The characteristics of austenite recrystallization of hot rolled C-Mn steel in the CSP process are also discussed.The simulation of the microstructure evolution of C-Mn steel ZJ510L during CSP multipass hot rolling indicates that dynamic recrystallization and metadynamic recrystallization may easily occur in the first few passes,where nonuniform recrystallization and inhomogeneous grain size microstructure may readily occur;during the last few passes,static recrystallization may occur dominantly,and the microstructure will become more homogeneous and partial recrystallization may occur at relatively low temperature.     

再结晶软化程度对C-Mn钢变形抗力的影响

利用带钢热连轧的实测条件研究了再结晶软化程度对C-Mn钢变形抗力的影响。结果表明，根据金属的再结晶规律得到的实质应变，比计算“残留应变率”法不但与实测更为接近，而且更符合理论结果；考虑再结晶软化程度对变形抗力的影响后使轧机负荷的预报精度得到明显提高；给出的C-Mn钢静态再结晶模型所得结果与实测符合得较好，从而为控制产品的组织性能提供了奥氏体再结晶的定量化依据。     

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Effect of double cold rolling on magnetic properties and microstructure of 3.98%Si-0.71%Al non-oriented silicon Steel Sheets cast by twin-roll thin strip casting process were investigated. The results show that the structure of the thin strip is equiaxed crystal, the recrystallization is complete and normalizing has lesser effect on microstructure. Using both cold rolled and double cold rolled process, the microstructure is equiaxed grain after final annealing. The average grain size of annealed sheet in double cold rolled specimen was smaller than single stage cold rolled sheet. Double cold rolling process is helpful for iron loss and magnetic flux density.     

Hot direct rolling in ferrite region in extra low-carbon steel

For the first time, hot direct rolling was applied in ferrite region in the mill and the resulting quality of the cold rolled and annealed sheet steel was as good as that hot direct rolled in austenite region with respect to microstructure and mechanical properties. In case of ferrite phase rolling, microstructure of the hot strip reveals abnormal grains and deformation bands in the grains, and elongation and r value are not so good as those rolled in the austenite phase. However, these abnormal grains left no traces and appeared to be equiaxed grains like the austenite phase rolled microstructure after 75 % cold rolling and continuous annealing at 830°C. This is attributed to the deformation bands which provide nucleation sites for recrystallization during annealing so that recrystallization occurs uniformly in the matrix. (111) texture was well developed and r value thus appeared high.     

国内外铁素体轧制的研究和应用

超薄热轧带钢(<1.2mm)的铁素体轧制(低温轧制)能显著节约能源和降低生产成本。当前迅速发展的薄板坯连铸连轧技术为铁素体轧制的发展与应用创造了良好的条件。已采用铁素体温轧工艺的钢板为低碳钢薄板和微合金化钢薄板。总结了铁素体轧制时流动应力,再结晶,轧后产品组织和性能的研究现状和铁素体轧制的应用情况。     

Effect of Lubrication during Hot Rolling on the Evolution of Through‐Thickness Textures in 18%Cr Ferritic Stainless Steel Sheet

Samples of a ferritic stainless steel sheet were hot‐rolled with and without application of lubrication. The effect of the different hot rolling processes on the evolution of texture and microstructure after hot rolling, cold rolling and subsequent recrystallization annealing was studied by means of macro and micro‐texture analysis and microstructure observations. After hot rolling, the sample rolled with lubrication displayed uniform rolling textures through the sheet thickness, while the sample rolled without lubrication showed shear textures in the outer layers of the sheet. The finite element method was employed to reveal the strain states during hot rolling with and without lubrication. The texture of the hot rolled sheet strongly influenced the formation of texture after cold rolling and final recrystallization and, therewith, planar anisotropy as well as the severity of ridging of the final gauge sheet. Hot rolling with lubrication was beneficial to the formation of strong recrystallization textures through the whole thickness layers leading to an enhanced planar anisotropy of the sheet. The recrystallized sheet hot‐rolled without lubrication displayed less severe ridging, however, which was attributed to a less frequent formation of orientation colonies in the outer thickness layers of the sheet.     

Physical simulation of hot deformation, and microstructural evolution for 42CrMo4 steel prior to direct quenching

 Direct quenching and tempering (DQ-T) of hot rolled steel section has been widely used in steel mill for the sake of improvement of mechanical properties and energy saving. Temperature history and microstructural evolution during hot-rolling plays a major role on the properties of direct quenched and tempered products. The mathematical and physical modeling of hot forming processes is becoming a very important tool for design and development of required products as well as to predict the microstructure and the properties of the components. These models were mostly applied to predict austenite grain size (AGS), dynamic, meta-dynamic and static recrystallization in the rods immediately after hot rolling and prior to DQ process. In this paper the hot compression tests were carried on 42CrMo4 steel in the temperature range of 900 - 1100°C and the strain rate range of 0.05 - 1 s- 1 in order to study the high temperature softening behavior of the steel. For the exact prediction of flow stress, the effective stress - effective strain curves were obtained from experiments under various conditions. On the basis of experimental results, the dynamic recrystallization fraction (DRX), AGS, hot deformation and activation energy behavior were investigated. It was found that the calculated results were in a good agreement with the experimental flow stress and microstructure of the steel for different conditions of hot deformation.     

Influence of a solution treatment on the evolution of through‐thickness texture gradients in dry cold rolled and recrystallized low carbon steel

The influence of a solution treatment on the evolution of through‐thickness texture gradients in a low carbon steel was studied. In order to intensify through‐thickness variations of the strain state, the samples were cold rolled dry, i.e. without lubrication. The evolution of the texture and the microstructure during rolling and recrystallization was tracked by X‐ray texture analysis and TEM microstructure investigations. The strain distribution during rolling was simulated for several layers of the rolled sheets by the finite element method. After the rolling deformation, a specimen taken directly from the hot band showed pronounced through‐thickness texture gradients, whereas the solution treated specimen showed a rather uniform rolling texture in all layers analyzed. Analysis of the friction behaviour between the different specimens and the roll material points to a much higher friction between the softer hot band and the rolls. This leads to stronger through‐thickness variations in the strain state and, thus, to the pronounced texture gradients observed. The texture gradients in the recrystallized samples reflected those of the as‐rolled sheets. In the center layer of the hot band specimen and in all layers of the solution treated specimen characteristic though notably weakened typical plane strain recrystallization textures formed; the textures in outer layers of the hot band sample were even almost random. These weak recrystallization textures could be attributed to the highly inhomogeneous as‐deformed microstructure.     

Physical Simulation of the Hot Direct Rolling of Steel

Thin slab casting and direct rolling technologies became important for hot strip production to increase the productivity, to lower the investment costs and to increase the energy efficiency. The main objective of our investigation is to gain a better understanding of the microstructural evolution starting from solidification through to the final hot rolled sheet. Small ingots were cast and direct rolled and reheated and rolled, using a thermomechanical testing machine. The differences in the recrystallization kinetics during both production routes were measured using double hit hot compression tests. In addition, multipass deformation trials were performed to reveal differences in the resulting microstructure and the grain size homogeneity. It was found, that the coarse initial microstructure before rolling become negligible after three rolling passes. This means that despite the simple and economical direct rolling similar mechanical strip properties can be obtained in comparison to conventional strip production routes.     

热轧Nb-Ti钢静态再结晶组织演变及模型研究

在热模拟实验的基础上，对Nb—Ti微合金钢热轧中微观组织的变化进行了分析，介绍了影响组织演变的主要因素及模拟实验方法，对静态再结晶行为和组织演变过程的数学模型进行了研究。研究表明，预报结果与实验结果吻合较好，这种理论处理方法可用来模拟静态再结晶行为。     

Recrystallization kinetics of an austenitic high-manganese steel subjected to severe plastic deformation

The evolution of the microstructure and the properties of an austenitic high-manganese steel subjected to severe deformation by cold rolling and subsequent recrystallization annealing is investigated. Cold rolling is accompanied by mechanical structural twinning and shear banding. The microhardness and microstructural analysis of annealed samples are used to study the recrystallization kinetics of the high-manganese steel. It is shown that large plastic deformation and subsequent annealing result in rapid development of recrystallization processes and the formation of an ultrafine-grained structure. A completely recrystallized structure with an average grain size of 0.64 μm forms after 30-min annealing at a temperature of 550°C. No significant structural changes are observed when the annealing time increases to 18 h, which indicates stability of the recrystallized microstructure. The steel cold rolled to 90% and annealed at 550°C for 30 min demonstrates very high strength properties: the yield strength and the tensile strength achieve 650 and 850MPa, respectively. The dependence of the strength properties of the steel on the grain size formed after rolling and recrystallization annealing is described by the Hall–Petch relation.     

C-Mn钢窄带热轧时的再结晶软化规律

针对唐山钢铁有限责任公司带钢厂的生产实际,借助理论与实验结果,研究了C-Mn钢热轧过程中各道次奥氏体的再结晶规律,计算结果与实测结果吻合较好,说明给出的组合模型用于窄带热轧的生产是可行的,它为在生产中控制与预报带钢的组织性能提供了奥氏体再结晶的定量化基础,并为再结晶软化不充分时的力能计算提供了修正依据.     

轧制方式对钢板低温韧性的影响

研究了实施再结晶区控轧控冷工艺和未再结果区控轧工艺对产品低温冲击韧性的影响,指出采用未再结晶区控轧工艺产品的韧脆性转变温度较低,并通过实验室实验说明控制轧制后的冷却工艺参数对冲击性能的影响。     

冷轧高强集装箱板轧制稳定性控制技术

 冷轧高强集装箱板由于其屈服强度、成形性能及尺寸精度的要求,对冷轧轧制稳定性和板形控制提出极大挑战。针对某钢厂薄规格冷轧高强集装箱板生产过程存在的肋浪和边裂情况进行分析,采用试验方法研究了热轧带钢库区冷却过程对钢卷温度及性能均匀性的影响,利用数值模拟的方法研究了该钢种在UCM机型冷轧轧制过程中带材变形特征,揭示了带材浪形和边裂的并发机理,同时分析了不同工艺对带钢变形均匀性的影响规律。结合理论及仿真分析,提出了针对热卷性能均匀性及酸轧轧制稳定性的优化方案,改进后冷轧板形质量明显提高,带材边裂缺陷完全消除,冷轧高强集装箱板的轧制稳定性及产品质量均得到大幅提升。     

轧制条件对冷轧无取向硅钢织构的影响

除钢质的纯净度、夹杂物聚集程度、再结晶组织外 ,织构分布和各组分强度对冷轧无取向硅钢的磁性能 磁感应强度和铁损亦具有显著的影响。从基础理论方面讨论了冷轧无取向硅钢的热轧、终轧温度和层流冷却条件对轧件织构形成的影响及冷轧压下率和冷轧轧制形状参数对其再结晶织构的影响.     

调质钢棒材组织性能预报软件的开发和应用

 介绍了调质钢棒材组织性能预报软件的开发和应用情况，模拟了从轧制到调质整个工艺过程中的温度场、轧制负荷、组织性能、热处理效果等。轧制负荷的计算研究中，考虑了奥氏体再结晶软化不充分对轧制负荷的影响。温度场的计算中，实现了VB和ANSYS之间的相互调用，相变量化分析计算中充分考虑了影响CCT曲线位置的因素，并对CCT曲线进行解析化处理，有效提高了组织转变的预报精度。软件的实际应用表明，无论是热轧态还是调质态，组织性能的预报值均与现场实测值基本相符，对改善产品的组织性能，提高产品合格率，具有重要的参考价值。     

薄板坯连铸连轧钢的组织性能综合控制理论及应用

在对国内外薄板坯连铸连轧工艺及产品开发现状及发展趋势分析的基础上,通过大量的试验研究提出了连铸连轧组织性能综合控制的概念,对钢中夹杂物超细化,锰和硫的控制,热连轧过程中的再结晶、组织细化及沉淀析出,层流冷却过程特征及对组织性能的影响以及柔性轧制工艺控制进行了研究分析,给出了通过组织性能综合控制得到的高性能低碳高强钢板（HSLC）在汽车上应用的实例。     

Recrystallization Behavior Design for Controlling Grain Size in Strip Rolling Process

To promote effectively dynamic recrystallization and obtain a homogeneous distribution of ultrafine grain size in strip finish rolling process,the behavior of static and dynamic recrystallization must be appropriately designed to provide an ultrafine austenite microstructure without mixed grain size.The design of rolling schedule was analyzed based on the control of the recrystallization behavior to achieve ultrafine grain size in the strip rolling process of niobium microalloyed steel.The experimental simulations were presented to validate the twice dynamic recrystallization design to achieve ultrafine grain size control.     

Deformation processes in hot worked copper and α brass

The generation of the fine grained, dynamically recrystallized microstructure has been studied in hot rolled copper and α brasses and in 70:30 brass deformed by hot torsion. The new grains, which developed preferentially at grain boundaries and inhomogeneities of deformation, contained none of the deformation features present in unrecrystallized parts of the microstructure. This observation is contrary to theories of dynamic recrystallization which imply that the microstructure contains a spectrum of grains ranging from just recrystallized to severely deformed. Texture studies showed cold rolled textures at low rolling temperatures but in the case of copper the texture became quite flat after rolling at 350 and 425 °C. Flat textures were associated with a minimum grain size. At higher rolling temperatures the textures were again typical of cold rolled material. It is suggested that while normal slip processes are operating at all temperatures there is an additional contribution from grain boundary deformation processes associated with fine grained microstructures. Such processes would account for the absence of normal deformation features from dynamically recrystallized microstructures.