Mathematical model to simulate thermo-mechanical controlled processing in rod (or bar) rolling

This study presents a mathematical model for computing the thermo-mechanical parameters such as the strain and strain rate at a given pass and the temperature variation during rolling and cooling between inter-stands (pass), to assess the potential for developing “Thermo-Mechanical Controlled Process” technology in rod (or bar) rolling, which has been a well-known technical terminology in strip (or plate) rolling since the 1970s. The model has then been applied to a four-pass (oval-round or round-oval) bar rolling sequence for predicting the pass-by-pass AGS, by incorporating the equation for recrystallization behavior and AGS evolution being widely used in strip rolling. The predicted AGS was compared with those obtained from the hot torsion experiment. Results revealed the proposed model, coupled with the recrystallization behavior and AGS evolution model developed for strip (or plate) rolling, might be applied directly to rod (or bar) rolling. We also found that the recrystallization behavior during rod rolling was significantly influenced by the method for calculating the thermo-mechanical parameters, especially the strain.     

A new approach to predicting partial recrystallization in the multi-pass hot rolling process

An exploratory approach to handling partial recrystallization in multi-pass hot rolling where the heterogeneity of steel microstructures is inherent is presented. The proposed model is based on a modification of the conventional model in which the microstructure of deformed austenite at each pass is simply taken as homogeneous during the multi-pass rolling. The usefulness of the modified model is demonstrated by applying it to a four-pass oval-round (or round-oval) rod rolling sequence. The pass-by-pass recrystallized fraction and austenite grain size (AGS) computed from the modified model are compared with those from the conventional model. The result showed that in multi-pass rolling at higher rolling speed, the recrystallization behavior and evolution of the austenite grain size at a given pass was strongly influenced by the modeling method of the partial recrystallization attributed to microstructural heterogeneity.     

基于Deform高线粗轧奥氏体晶粒细化研究

本文结合GCr15再结晶模型, 根据轧线实际孔型参数、轧线布置与轧制程序, 采用刚塑性有限元法, 利用模拟软件Deform对轴承钢线材GCr15粗轧进行了三维有限元模拟, 分析总结了粗轧过程中轧件温度场、等效应变和应变速率的变化规律, 得出粗轧过程动态、亚动态和静态再结晶的百分数和对应晶粒尺寸, 揭示了轧件在粗轧过程中再结晶规律及奥氏体晶粒细化规律, 并且证实了初始晶粒尺寸对粗轧过程奥氏体晶粒细化的影响规律。     

Application of mathematical modeling in two-stage rolling of hot rolled wire rods

The no-recrystallization temperature (T_nr) is an important parameter in the design of two-stage rolling schedule to obtain finer grain size. T_nr was obtained both by continuous cooling compression testing and tension-compression testing. However, due to the limitations of experimental installation, both compressing testing and tension-compression testing have a scaling down of practical pass strain and strain rate in rolling mill. The mathematical model that calculates mean flow stress (MFS) can eliminate these limitations and the pass strain and strain applied in mathematical model are approximately equal to the mean value of that in wire-rod rolling mill. Therefore, mathematical calculation is a new method to determine T_nr and the predicted T_nr is similar to experimental results. Due to the high strain rate and short interpass time at the finishing strain of wire rods mills, mathematical modeling is also an effective method to simulate microstructure-evolution in wire rods rolling. An expert system was established to study the microstructure evolution in two-stage rolling through the obtained dynamic recrystallization (DRX) model combined with metadynamic recrystallization (MRX) and static recrystallization (SRX) model in literature. In the present work, it is simplified that the complete metadynamic recrystallization (MRX) is achieved when strain for deformation exceeds critical strain ɛ_c. It was found that strain accumulation played an important role in finishing rolling. The recrystallization behavior during finishing rolling stage was repeated by static and dynamic model. The predicted austenite grain size and mean flow stress at each pass are expected to provide guidance for appropriate rolling schedule design.     

Nb-Ti连铸坯热芯大压下轧制动态再结晶行为研究

采用热模拟单道次压缩实验,研究了Nb-Ti连铸坯热芯大压下轧制中动态再结晶行为及奥氏体晶粒转变规律。结果表明,变形温度越高,应变速率越低,发生动态再结晶的临界应变值越小,动态再结晶越充分。在变形温度1 350 ℃,继续增加应变至0.8和增加应变速率至10 s^-1,奥氏体晶粒尺寸并未得到进一步细化,反而较应变0.5和应变速率5 s^-1下的奥氏体晶粒更加粗大。这是因为高温粘塑性区的金属晶间粘性流动增加,位错增殖速度增大,在动态再结晶过程中会重新形成新的无畸变再结晶晶粒,这些新的无畸变晶粒的亚动态再结晶动力学极快,在较大驱动力下使奥氏体晶界快速迁移,从而使奥氏体发生一定程度的粗化。     

Nb-Ti连铸坯热芯大压下轧制动态再结晶行为研究

采用热模拟单道次压缩实验，研究了Nb-Ti连铸坯热芯大压下轧制中动态再结晶行为及奥氏体晶粒转变规律。结果表明，变形温度越高，应变速率越低，发生动态再结晶的临界应变值越小，动态再结晶越充分。在变形温度1 350 ℃，继续增加应变至0.8和增加应变速率至10 s^-1，奥氏体晶粒尺寸并未得到进一步细化，反而较应变0.5和应变速率5 s^-1下的奥氏体晶粒更加粗大。这是因为高温粘塑性区的金属晶间粘性流动增加，位错增殖速度增大，在动态再结晶过程中会重新形成新的无畸变再结晶晶粒，这些新的无畸变晶粒的亚动态再结晶动力学极快，在较大驱动力下使奥氏体晶界快速迁移，从而使奥氏体发生一定程度的粗化。     

皮尔格轧制AZ31镁合金管材微观组织预测

精准预测镁合金管材在皮尔格轧制变形过程中的晶粒演变,对控制镁合金管材的最终性能具有重要参考意义,本文结合AZ31镁合金管材在皮尔格轧机上的轧制实验,建立基于动态再结晶、静态再结晶、静态回复、晶粒粗化及晶粒拓扑变形的元胞自动机模型,并借助有限元计算得出的每道次轧制结果,与元胞自动机结合起来,得到镁合金管材在轧制过程中的晶粒演变的动态特征,发现晶粒在轧制过程中产生连续再结晶并细化,并最终进行实验验证。     

Investigation and Modeling of Austenite Grain Evolution for a Typical High-strength Low-alloy Steel during Soaking and Deformation Process

The final mechanical properties of components greatly depend on their grain size. It is necessary to study the grain evolution during different thermomechanical processes. In the study, the real-time austenite grain evolution of a high-strength low-alloy (HSLA) steel during the soaking process is investigated by in situ experiments. The effects of different deformation parameters on the dynamic recrystallization (DRX) kinetic behaviors are investigated by hot compression experiments. Based on the observations and statistics of the microstructures at different thermomechanical processes, a unified grain size model is established to evaluate the effects of soaking parameters and deformation parameters on the austenite grain evolution. Also, the DRX kinetic model and critical strain model are established, which can describe the effects of the soaking process on the DRX kinetics process well. The established grain size model and DRX kinetic model are compiled into the numerical simulation software using Fortran language. The austenite grain evolution of the material under different deformation conditions is simulated, which is consistent with the experimental results. It indicates that the established model is reliable, and can be used to simulate and predict the grain size during different thermomechanical processes accurately.     

Static recrystallization behavior of a martensitic heat-resistant stainless steel 403Nb

A static recrystallization behavior between the rolling passes of a martensitic heat-resistant stainless steel 403Nb has been studied by OM,TEM and double-hit thermo-mechanical simulator to explore the effects of deformation temperature,strain rate,strain and the prior austenite grain size. The results show that increases of deforma-tion temperature and strain rate and strain can promote the static recrystallization of 403Nb steel. Static recrystallization also proceeds faster when the prior austenite grain...     

低Ni型LNG钢的热变形行为及力学性能

通过单道次、双道次压缩试验,研究了低Ni型LNG钢的高温奥氏体动态再结晶及静态再结晶行为,并采用两阶段控制轧制及超快速冷却技术进行不同轧制工艺下的热轧试验,通过热模拟及热轧试验研究了低Ni型LNG钢的热变形行为及力学性能。结果表明,在高温(1000~1050 ℃)、低应变速率(0.1~0.5 s^-1)下奥氏体容易发生动态再结晶,确定了发生再结晶的临界条件,并建立了动态再结晶动力学模型。试验钢在较高温度(800~1050 ℃)、较长道次间隔时间(60 s)下静态软化现象明显,容易发生静态再结晶。依据热模拟试验结果制定热轧试验工艺,通过控制精轧开轧温度和终轧温度调控高温奥氏体再结晶行为,从而细化晶粒,改善低Ni钢的冲击性能。精轧开轧温度920 ℃、终轧温度770 ℃时,低Ni钢的低温冲击吸收能量为180.1 J,屈服强度为595.1 MPa,抗拉强度为717.8 MPa。     

核电用304不锈钢静态再结晶模型的建立

利用Gleeble-1 500 D热力模拟试验机,对304不锈钢进行了热压缩模拟试验。研究了变形温度在950℃~1 200℃之间,变形速率为1×10-3 s-1、1×10-2 s-1、1×10-1 s-1,变形量为50%的变形行为及组织特征,建立了304钢的静态再结晶晶粒尺寸模型。结果表明：变形量、变形温度、应变速率因素的影响较大;应变量越大,变形温度越低,应变速率越高,晶粒越细;304钢静态再结晶晶粒尺寸模型的建立为大锻件静态再结晶数值模拟分析提供了可靠的判据。     

AG700L钢亚动态再结晶行为研究

AG700L钢主要应用于汽车大梁等重要承重结构件。通过在Gleeble-3800热模拟试验机上采用双道次压缩试验,研究了AG700L钢在应变速率为0.01～2 s^-1、变形温度为950～1 050℃、道次间隔时间为10～120 s不同条件下的亚动态再结晶行为。结果表明：AG700L钢道次间隔内亚动态再结晶行为受变形温度、应变速率和道次间隔时间的影响显著;随变形温度的升高,亚动态再结晶体积分数先缓慢增加,然后迅速增加;随应变速率的增加,亚动态再结晶体积分数先迅速增加,然后趋于平稳;随道次间隔时间的增加,亚动态再结晶体积分数明显增加。随变形温度的升高、应变速率的增加以及道次间隔时间的延长,变形后AG700L钢的晶粒尺寸显著增加,组织变得更加均匀。同时,建立了AG700L钢的亚动态再结晶动力学模型,为其实际生产轧制工艺的制定与优化提供了依据。     

高强低合金T510L的热模拟工艺研究

本文结合唐钢FTSR生产线的实际生产工艺参数,利用Gleeble3500C热模拟机,分别研究了单道次不同变形温度、变形速率(50%压下率)对高强低合金T510L钢变形抗力和奥氏体微观组织演变的影响及两道次(R1→R2)连续变形后奥氏体微观组织演变。实验表明通过高温大压下量的变形,完全可使该钢种充分发生动态再结晶,细化奥氏体晶粒度。     

Incoloy825合金热变形过程中的本构模型和特殊晶界演变

采用原始JC模型、修正JC模型和应变补偿Arrhenius方程，描述了Incoloy825合金在不同温度（950～1150 °C）和应变速率（1~10 s^-1）下经摩擦和温升修正后的应力-应变曲线。结果表明，修正后曲线具有明显的动态再结晶特征。与原始JC模型和修正的JC模型相比，Arrhenius应变补偿模型更适合于描述Incoloy825合金热变形过程中的应力应变行为。温度和应变速率对特殊晶界的演变有显著影响。特殊晶界长度分数与动态再结晶分数呈正相关。与冷轧后退火处理工艺相比，热变形工艺调控的特殊晶界长度分数较低，热变形工艺不适合用来调整特殊晶界分数，其原因是在热变形过程中动态再结晶的大量形核造成较小的晶粒团簇。     

14Cr1MoR钢控轧和直接淬火工艺研究

研究控制轧制和直接淬火相结合生产14Cr1MoR压力容器钢的工艺.结果表明奥氏体再结晶区变形时,单道次变形量越大则再结晶进行得越充分,再结晶后的晶粒就越细.奥氏体未再结晶区总变形量增大则奥氏体晶粒内形变区域增多,从而使马氏体形核点增多,淬火后得到细板条马氏体组织.该钢种控轧后有足够高的温度进行直接淬火,经高温回火得到细小回火索氏体,机械性能优良.     

Microstructure and temperature monitoring during the hot rolling of AZ31

This study details the microstructural evolution during hot rolling of AZ31 alloy sheet using a pilot-scale rolling mill. The aim is to understand the deformation mechanisms leading to grain refinement under industrial processing conditions and to design and optimize the hot rolling schedule for AZ31 in order to produce sheet with a fine and homogeneous microstructure. The study examined three different hot rolling temperatures, 350, 400, and 450°C, and two rolling speeds, 20 and 50 rpm. A total thickness reduction of 67% was obtained using multiple passes, with reductions of either 15% or 30% per pass. It was found that the microstructure of the AZ31 alloy was sensitive to the rolling temperature, the reduction (i.e., strain) per pass and the rolling speed (i.e., strain rate). The results show that the large cast grain structure is broken down by segmentation of the cast grain through localized deformation in twin bands, where dynamic recrystallization occurs in these bands as well as at the grain boundaries (necklacing).     

MODELING OF CONTROLLED THERMO-MECHANICAL PROCESSING OF TUBES FOR ENHANCED MANUFACTURING AND PERFORMANCE

1.IntroductionApproximately15milliontonsofsteeltubeandpipeproductsareconsumedintheUnitedStatesannually.Mechanicaltubesarethefeedstocksusedinthemanufactureofrollingelementbearings,hydrauliccylinders,alldagreatvarietyofpowertransmissioncomponents.Steeltubesarealsoemployedinthedrillstringsforoilandnaturalgasexplorationandrecovery.Steelpipesareusedinthetransportofgas,oilandotherfluids.ControlledThermal--MechanicalProcessing(CTMP)involvesprecisecontroloftemperature,mechanicaldeformation,andmicr…     

Hastelloy C276高温合金热加工微观组织演化元胞自动机模拟

采用Gleeble热模拟试验机对Ni-Cr-Mo系高温合金Hastelloy C276进行单道次和双道次热压缩试验,获得了不同热变形条件下的流变应力曲线和微观组织,在此基础上回归了该合金热变形物理冶金模型及参数,进而构建了微观组织拓扑演化的元胞自动机模型。结果表明:Hastelloy C276高温合金在高温热压缩过程中易发生动态再结晶,当动态再结晶不完全时,在热压缩保温或道次间歇内,再结晶晶粒将进一步快速生长而发生亚动态再结晶。Hastelloy C276高温合金再结晶行为对变形温度、变形速率、应变量等工艺参数敏感;构建的元胞自动机模型,集成计算了热压缩和道次间歇过程中的位错密度、再结晶形核及晶界迁移等,可有效表征多工艺参数下Hastelloy C276高温合金热压缩过程中的微观组织拓扑结构演化和应力-应变响应。     

微合金元素Nb对高碳合金钢动态再结晶行为的影响

为研究微合金元素Nb对高碳合金钢动态再结晶行为的影响,利用Gleeble-3500热模拟试验机进行单道次压缩试验,测定了高碳合金钢在变形温度为950~1150 ℃、应变速率为0.01~5 s^-1的流变应力曲线,利用Zeiss光学显微镜观察了奥氏体动态再结晶晶粒形态,通过回归计算获得了相应的再结晶激活能,建立了热变形方程。结果表明:较高的变形温度和较低的应变速率有利于含铌高碳合金钢发生动态再结晶;含铌高碳合金钢的动态再结晶晶粒尺寸随着变形温度的升高而增大,当变形温度为1050 ℃时,含铌高碳合金钢已大量出现动态再结晶晶粒;0.040%铌加入到高碳合金钢中,在应变速率为0.1 s^-1,变形温度为1150 ℃时推迟了钢的动态再结晶开始时间约2.23 s,动态再结晶形变激活能增加了52.26 kJ/mol。     

GH738合金冷变形及中间退火再结晶行为研究

通过光学显微镜、扫描电镜、电子背散射衍射、显微硬度计等手段,系统研究了GH738合金不同冷轧变形量后中间退火组织演变规律。研究表明:变形量是影响加工硬化的主要因素;经过不同冷轧变形后,1000℃退火奥氏体未发生再结晶;在1040～1080℃进行退火处理,可得到均匀细小的等轴晶。建立了GH738合金冷加工本构方程和再结晶晶粒长大方程。