C-Mn钢热轧带奥氏体再结晶晶粒尺寸的预测

在研究板带控轧控冷过程中钢中显微组织演变过程奥氏体再结晶、碳氮化合物析出、奥氏体相变和组织性能对应关系的物理冶金模型的基础上，通过Gleeble-1500热模拟机和计算机模拟计算得出成分(％)0．16C，0．06Si，1．30Mn钢在1173～1081K经7道次热变形后奥氏体晶粒尺寸为43μm，同时实测7道次变形后轧钢组织中奥氏体尺寸为38μm，相对误差13％。计算机模拟计算的奥氏体再结晶晶粒尺寸与实测结果吻合较好。     

热轧船板钢时奥氏体组织变化规律

奥氏体热变形时再结晶规律研究是制定合理控制轧制工艺的理论基础。在试验基础上就一般强度船板钢热变形时奥氏体再结晶百分数及晶粒尺寸与工艺参数的关系进行了研究。认为奥氏体再结晶百分数及晶粒尺寸在不同的温度区域有不同的变化规律，并借此讨论了制定控轧工艺时应注意的问题。     

X70管线钢热连轧过程奥氏体再结晶、晶粒尺寸和平均流变应力的预测

在考虑动态、亚动态再结晶及静态再结晶的基础上,建立了X70管线钢的物理冶金模型,并应用于板带钢热连轧过程奥氏体再结晶、晶粒尺寸和流变应力的预测.结果表明,在合理的温度和压下条件下,应变累积可导致在精轧过程出现动态 亚动态再结晶行为,促进奥氏体晶粒的进一步细化.终轧温度的降低可引起奥氏体晶粒的粗化和残余应变的显著提高.建立了考虑晶粒尺寸和残余应变影响的平均流变应力(MFS)的人工神经网络预测模型,大大提高了热连轧过程MFS预测精度.     

锅炉用碳素钢板控制轧制的研究

本文通过研究控制轧制对钢的组织和性能的影响,确定了控制轧制技术对20g钢板的适宜性。研究轧制道次及压下率对变形奥氏体的再结晶和晶粒大小的影响结果表明:热轧奥氏体晶粒是逐道细化的,但前两道轧制细化作用最大,随后道次细化作用逐渐减弱;在以20％的道次压下率轧制时,除第一、四道外,变形奥氏体都发生充分的再结晶,而在以10％的道次压下率轧制时,在所有道次中都只发生部分再结晶,20％的道次压下率要比10％为好。轧制道次及压下率对20g钢板轧后铁素体晶粒尺寸的影响规律表明:奥氏体再结晶区轧制的道次压下率及终轧温度是决定轧后铁素体晶粒大小的主要工艺参数。根据本实验结果拟定了适宜的轧制工艺参数。     

X80管线钢热变形过程再结晶规律研究

利用Gleeble2000热模拟试验机,研究X80管线钢单道次变形变形量对奥氏体再结晶及晶粒长大的影响。绘制了试验条件下X80管线钢变形量与奥氏体晶粒尺寸的关系曲线。结果表明:X80管线钢奥氏体晶粒尺寸随着道次变形量的提高,奥氏体晶粒平均晶粒尺寸逐渐减小,晶粒越来越细小均匀。结合设备及工艺条件,确定粗轧末道次压下率为25%。     

09MnVTiN钢再结晶奥氏体连续冷却转变的研究

本文利用Formastor-Press压力膨胀仪测试09MnVTiN钢热变形后再结晶奥氏体的连续冷却转变动力学曲线,并用金相法分析不同阶段淬火试样的组织。结果表明,再结晶控轧后,奥氏体区的冷却速度(1000～820℃)对再结晶奥氏体的晶粒尺寸和随后的连续冷却转变动力学都有影响。     

薄板坯连铸连轧流程钛微合金钢控制轧制技术

 重点阐述了薄板坯连铸连轧流程钛微合金钢的控制轧制模式及其机理。基于应力松弛试验和双道次压缩热模拟试验,研究分析了薄板坯连铸连轧钛微合金钢的奥氏体再结晶动力学。研究结果表明,轧前铸态粗大奥氏体组织经F1高温大压下后可实现完全静态再结晶;铸坯中固析TiN粒子可以有效阻止奥氏体再结晶晶粒的长大,实现再结晶区控轧。固溶钛的溶质拖曳作用以及形变诱导析出的TiC粒子对奥氏体再结晶具有抑制作用,可以阻止奥氏体再结晶的发生,实现未再结晶区控轧。     

高强韧及延伸性能耐磨钢NM600关键技术研发与应用

采用Gleeble-3500 热模拟试验机对超高强耐磨钢NM600 进行试验,研究第1 轧程控轧压下率与原始奥氏体晶粒尺寸的关系.结果表明:当单道次压下率范围在15％～25％时,板坯表面和心部同时发生充分的动态再结晶,得到细小原始奥氏体晶粒.根据耐磨钢NM600 奥氏体连续冷却转变曲线,设定轧后空冷驰豫开始温度Ac3+...     

碳锰钢压缩过程中非均匀应变与再结晶之间关系的研究

采用有限元方法模拟了热模拟试验的变形过程,分析了热模拟变形过程中的非均匀应变对奥氏体动态再结晶及晶粒尺寸的影响.结果表明,在等效应变最大的区域,奥氏体动态再结晶并非最完全,而剪应变对动态再结晶的影响则较大,在剪应变最大的区域,再结晶最完全,晶粒最细小.在试验所设定的最大变形量为62%的变形条件下,等效应变对晶粒细化的影响存在一个临界值,当等效应变大于0.96时,不完全动态再结晶区域的奥氏体晶粒得不到进一步细化,而随着剪应变的增加,奥氏体晶粒不断细化,可见剪应变对奥氏体晶粒尺寸的影响更大.因此,用等效应变等于实际应变处的晶粒尺寸来考察实际晶粒尺寸的方法,存在着不合理性.     

V-Ti-N微合金钢的再结晶控轧与控冷

本文提出了一个称为再结晶控轧的新控轧方案及相应的合金化原则。再结晶控轧不要求分段轧制及在奥氏体未再结晶温度区轧制,从而避免了常规控轧所具有的两个主要缺点,即生产率较低及需要强力轧机。 对0.13V—0.017Ti微合金钢的研究表明,钒钛系微合金钢具有高的奥氏体晶粒粗化温度,低的奥氏体再结晶温度以及热变形后小的晶粒粗化速度。此外,这种微合金钢还表现出足够的过冷能力和铁素体内碳氮化合物析出硬化能力。这些特性使得钒钛微合金钢特别适于实施再结晶控轧。     

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.     

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.     

The thermal and metallurgical state of steel strip during hot rolling: Part III. Microstructural evolution

A mathematical model has been developed to compute the changes in the austenite grain size during rolling in a hot-strip mill. The heat-transfer model described in the first of this series of papers has been employed to calculate the temperature distribution through the thickness which serves as a basis for the microstructure model. Single-and double-hit compression tests have been conducted at temperatures of 900 °C, 850°C, 950 °C, and 875 °C on 0.34 and 0.05 pct carbon steels to determine the degree of recrystallization by metallographic evaluation of quenched samples and by measuring the magnitude of fractional softening. The Institut de Recherches de la Sidérurgie Francaise, (IRSID) Saint Germain-en-Laye, France equation has been found to yield the best characterization of the observed recrystallization kinetics. The equations representing static recrystallization kinetics, recrystallized grain size, and grain growth kinetics have been incorporated in the model. The principle of additivity has been invoked to permit application of the isothermal recrystallization data to the nonisothermal cooling conditions. The model has been validated by comparing predicted austenite grain sizes with measurements made on samples quenched after one to four passes of rolling on the CANMET pilot mill. The austenite grain size evolution during rolling of a 0.34 pct carbon steel on Stelco’s Lake Erie Works (LEW) hot-strip mill has been computed with the aid of the model. The grain size decreased from an initial value of 180μm to 35μm in the first pass due to the high reduction of 46 pct. The changes in austenite grain size in subsequent passes were found to be small in comparison because of the lower per pass reductions. It has been shown that the equation employed to represent grain growth kinetics in the interstand region has a significant influence on the computed final grain size. Altering the rolling schedule had a negligible influence on the final grain size for a given finished gage. A 200°C increase in entry temperature to the mill resulted in a 20μm increase in final grain size, which is significant. This can be attributed to increased grain growth at the higher temperature. Formerly Graduate Student, The Centre for Metallurgical Process Engineering, The University of British Columbia Metallurgical transactions a     

低碳钢热变形奥氏体的再结晶行为

对热变形奥氏体的再结晶动力学和微观组织演变进行了模拟计算,对晶粒尺寸的模拟值和实测值作了比较,分析了化学成分对动态再结晶率的影响以及残余应变与变形温度的关系.结果表明:在温度较高、应变速率较低的条件下容易发生动态再结晶,随着变形温度的降低,发生动态再结晶的几率减小,而静态再结晶在前几道次进行得比较充分,随后进行得不充分,增加碳和锰的含量可以促进动态再结晶的发生,残余应变随变形温度的降低而增大,晶粒尺寸的模拟值和实测值吻合较好,表明所选用的模型有一定的参考价值.     

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。     

Changes in the austenite grain structure of microalloyed plate steels due to multiple hot deformation

Simulating processes during roughing passes with the plane strain compression test, the influence of soaking temperature, initial grain size, deformation temperature and strain on the grain size of austenite after static recrystallization in the course of multiple deformation schedules is investigated for three microalloyed steels. The temperature region of a completely recrystallizing austenite was found to depend on the soaking temperature as a result of the change in the initial solute concentration. Temperature and strain of the last deformation/recrystallization steps in a roughing schedule control the intermediate austenite structure before the finishing passes without any significant effect of the initial grain size.     

Grain Refinement of Nb Steels by Control of Recrystallization during Hot Rolling

Control rolling of Nb-bearing steels is employed to produce the uniform fine-grained product needed to meet the most stringent strength and toughness specifications. To produce such structures consistently requires a thorough understanding of the effects of compositional and process variables on austenite grain refinement at every stage of the hot rolling process. These effects were examined by means of a laboratory simulation of plate rolling. It was found that limiting the reheated grain size to about 100 μm (by lowering the reheat temperature or by adding Ti to the steel) is essential to assure complete recrystallization and refinement of the initial grain structure without an excessive amount of reduction at high temperatures. Because of the slow cooling rate at the slab center, this initial breakdown stage of rolling must be followed by a hold to allow the slab to cool to the lowest temperature at which recrystallization during rolling will be complete. This procedure will assure that the second roughing stage will produce the finest and most uniform recrystallized structure possible. This structure transforms to a very uniform ferrite-pearlite with a grain size of 10 to 15 μm. If, however, the fine recrystallized austenite is further rolled below the recrystallization temperature (control rolled) it will produce flattened austenite grains that transform to ultra-fine ferrite 4 to 6 μm in diameter. The uniformity of the final structure depends critically on the state of the austenite prior to grain flattening. The austenite must be completely recrystallized, since partially recrystallized regions produce duplex ferrite. Two attempts to change the control-rolling temperature range by modifying composition were unsuccessful. Increasing the Nb content from 0.05 to 0.10 to promote higher-temperature precipitation and boundary pinning did not raise the temperature at which grain flattening began. The addition of Ti to a Nb steel to remove soluble nitrogen and thereby prevent formation of NbCN in favor of the lower-temperature NbC did not promote recrystallization to lower temperatures.     

特厚板温度梯度轧制有限元模拟与实验研究

针对特厚板再结晶型轧制,板坯中心难以变形导致心部晶粒粗大的问题,使用Q345B钢,采用有限元方法建立了特厚板轧制的仿真模型,以研究在特厚板轧制过程中引入厚度方向上的温度梯度对钢板心部应变的影响,并与传统均温轧制进行对比,预测了两种温度场条件下奥氏体再结晶的晶粒尺寸.采用大试样平面应变实验对模拟结果进行验证.研究结果表明,温度梯度轧制有利于增加坯料心部应变量,最大增加了61.35%.计算和实验结果显示温度梯度轧制可以减小特厚板心部晶粒尺寸,晶粒度级别提高了一个等级,说明该工艺对提高特厚板中心区域性能有利.