X80管线钢热变形过程中再结晶行为及组织细化

利用Gleeble-1500D热模拟试验机研究了X80管线钢热轧过程中的再结晶行为及精轧过程中后四道次变形的再结晶特点与室温组织的关系.揭示了X80管线钢动态再结晶临界钢应变量与变形温度的关系,确定了奥氏体再结晶温度区和非再结晶温度区,所得到的技术要点对精轧过程轧制工艺制定细化奥氏体晶粒具有指导性,有助于X80管线钢获得细小均匀的室温组织.     

奥氏体晶粒尺寸对工艺参数的灵敏度方程及应用

为了便捷、准确地确定工艺参数对奥氏体晶粒尺寸的影响规律,考虑热加工工艺参数间的耦合关系,基于Hodgson再结晶模型建立奥氏体晶粒尺寸对工艺参数的灵敏度方程,探讨工艺参数对奥氏体晶粒尺寸的影响.研究表明:在单道次热加工过程中,变形速率、变形量、间隙时间、初始晶粒尺寸、间隙温度和变形温度灵敏度依次降低,工艺参数在不同的工艺过程中灵敏度不同;在多道次热加工过程中,工艺参数的灵敏度还与工艺参数所在道次和总道次数有关.H型钢开坯过程灵敏度分析结果表明,温度和后两个道次间隙时间是奥氏体晶粒尺寸的关键影响因素;降低温度并缩短间隙时间可以将H型钢开坯后的奥氏体晶粒尺寸减小26.2%.     

热模拟技术优化X80管线钢热轧工艺

用Gleeble 1500D热模拟实验机,对X80管线钢进行单道次双道次以及多道次压缩实验,找出动态再结晶的临界应变量和未再结晶区,在未再结晶区内优化精轧道次轧制工艺,通过抑制道次间的静态再结晶累积应变,在多道次轧制过程中使其在最后一道次超过临界应变量发生动态再结晶,从而避免晶粒大小不均并实现晶粒细化.     

基于45钢热变形中动态再结晶行为的本构模型

金属材料塑性变形应变积累量达到某一临界值后诱发的动态再结晶会降低流变应力,金属材料的再结晶临界条件及其动力学与形变条件密切相关。基于45钢形变温度在450~850℃,应变速率在0.1~30 s-1范围内的热模拟压缩试验数据,采用Poliak-Jonas法研究再结晶临界应变(εc)与形变条件参数Z之间的关系,以εc为应力应变曲线上的分界点,分别基于E-M方程和再结晶动力学,构建有、无动态再结晶发生时45钢变形的本构模型。结果表明模型预测值与试验结果吻合良好。     

ZrC粒子对低碳钢晶粒细化及力学性能的影响

在低碳低合金钢熔炼过程中加入平均径为0．5μm，体积分散为0．8％的ZrC粒子，研究了不同轧制变形量条件下的晶粒细化行为及力学性能，轧制变形过程中在ZrC粒子周围形成高位错密度和高晶格畸区，成为形为核心和再结晶核心，促进了高温奥氏体非自发再结晶细化奥氏体晶粒；由于奥氏体晶粒尺寸细化，奥氏体晶界面积增大，随着后进行的铁体相变的铁素体形核位置增多，从而大大细化了铁素体晶粒尺寸：轧制变形量与ZrC粒子体积分数存在一定的最佳配合才能对晶粒细有作用，本实验中轧制变形量为62％，ZrC粒子体积分数0．8％以及轧后水冷条件下，铁素体晶粒尺寸细化到9．8μm，屈服强度和抗拉强度明显提高，分别达到386．4MPa和522．1MPa；同时冲击吸收功（AKV＝118．5J）不降低且延伸率（δ5＝34．5％）有所提高，说明添加ZrC粒子粒子可促进晶粒细化。     

不同变形条件的HPS485wf钢动态再结晶仿真

为了揭示HPS485wf钢动态再结晶组织演变行为,在不同的单道次热压缩变形条件下,进行了该钢动态再结晶过程的CA仿真.结果表明:随着变形温度升高,动态再结晶的孕育期缩短、速度加快,平均晶粒尺寸增加;随着应变速率加快,动态再结晶的孕育期延长、速度减慢,平均晶粒尺寸减小.     

细化母相奥氏体组织的研究

在Gleeble 1500热模拟机上以SS400钢为研究对象，采用冷加工＋α→γ逆相变等实验工艺，研究了此变形工艺对奥氏体再结晶行煌 影响以及细化母相奥氏体晶粒的方法，结果表明，由于低温大变形及快速升温同时有铁素体基体的回复，再结晶或奥氏体相变这三个相互竞争的过程发生，可得到晶粒尺寸为10－12um的奥氏体晶粒。     

AZ31镁合金动态再结晶临界应变和稳态应变

采用热拉伸实验测定AZ31镁合金的应力-应变曲线,依据加工硬化率理论,得到热变形过程中AZ31镁合金发生动态再结晶的临界应变和稳态应变,确定临界应变、稳态应变与塑性变形工艺参数的关系.结果表明:热变形温度和应变速率是影响AZ31镁合金动态再结晶的主要因素,提高变形温度和降低应变速率都有利于降低AZ31镁合金的临界应变和...     

316LN热变形行为及动态再结晶晶粒的演变规律

采用热压缩试验研究了316LN不锈钢在温度1250℃-900℃,应变速率0．005s^-1～0．5s^-1,变形程度50％条件下的变形行为和组织演变;分析了变形参数对应力-应变曲线的影响规律,计算获得了该钢热变形应力指数和激活能;并通过动态再结晶晶粒演变规律的研究,建立了该钢热变形动态再结晶图,以及动态再结晶晶粒演变规律模型。研究结果可为316LN不锈钢锻造过程晶粒细匀化的控制提供科学的依据。     

SPCC钢塑性变形中动态再结晶的数学模型与模拟分析

利用热模拟设备Gleeble-1500D,对SPCC钢在不同变形量下的真应力-应变曲线进行了测定,并结合微观组织观察,确定了SPCC钢动态再结晶的数学模型,研究并分析了变形参数对动态再结晶晶粒的影响.通过DEFORM有限元软件对SPCC钢的热压缩过程进行模拟计算.分析了不同变形条件对晶粒尺寸的影响.模拟计算结果很好地与实验结果相吻合,为进一步研究这种钢的动态再结晶提供了一定的参考依据.     

Microstructural Features During Strain Induced Ferrite Transformation in 08 and 20Mn Steels

The microstructure evolution during strain induced ferrite transformation was followed in thermal-simulation tests of clean 08 and 20Mn steels. The influences of carbon equivalence and initial austenite grain size on ferrite grain refinement and the volume frac- tion of ferrite during straining were inspected. The results revealed that the accelerating effect of ferrite transformation by strain was increased as the carbon equivalence decreased. However, finer ferrite grains were obtained at higher carbon content. At strain of -1 .5 ferrite grains less than 3 μm and 2 μm can be obtained in 08 and 20Mn steels respectively. Whereas the ferrite grain refinement in 08 steel was due to both effects of strain induced transformation and ferrite dynamic recrystallization, that in 20Mn was mainly due to st fain induced transformation. Heavy strain can produce fine ferrite grains in coarse austenite grained 08 steel, but it would lead to band microstructure in coarse austenite grained 20Mn.     

Ultra-fine ferrite grains obtained in the TSDR process

By careful design of rolling schedule,ultra-fine （～2μm） ferrite grains in a low carbon high niobium （0.09wt%Nb） microalloying steel with average austenite grain sizes above 800 μm can be achieved in the simulated thin slab direct rolling process. The 5-pass deformation was divided into two stages： the refinement of austenite through complete recrystallization and the refinement of ferrite through dynamic strain-induced transformation. The effects of Nb in solution and strain-induced NbCN precipitates on the ferrite transformation were also extensively discussed.     

Modeling of microstructural evolution during dynamic recrystallization in coarse Nb microalloyed austenite

The aim of the current study was to investigate the microstructural evolution during dynamic recrystallization in coarse Nb microalloyed austenite in thin slab direct rolling （TSDR） processing. A model was developed to predict the change of the austenite grain size during the dynamic recrystallization, by using the law of mixtures. The equations initially developed for partial static recrystallization were used for partial dynamic recrystallization, by adjusting the value of the constant. The results show that the change of the austenite grain size can be reasonably described by using the equations developed according to the law of mixtures.     

Recrystallization of High Carbon Steel during High Strain Rate

The recrystallization of high carbon steel during high temperature and high speed rolling has been studied by analyzing the Stress-strain curves and the austenite grain size. Isothermal multi-pass hot compression at high strain rate was carried out by Gleeble-2000. The austenite grain size was measured by IBAS image analysis system. The results show that static recrystallization occurred at interpass time Under pre-finish rolling, and at the finish rolling stage, due to the brief interpass time, static recrystallization can not be found.     

微碳钢铁素体区热轧试验研究

在连铸连轧生产线采用铁素体轧制技术制备微碳钢热轧薄板,并对所制备薄板的组织、性能及织构进行分析。结果表明：铁素体轧制微碳钢热轧薄板的组织为完全再结晶铁素体,平均晶粒尺寸50 m左右。相对于常规奥氏体轧制,铁素体轧制薄板的屈服强度和抗拉强度分别下降了21%和6%,延伸率略有下降。热轧薄板的塑性应变比值为0.4,明显低于常规奥氏体轧制。薄板中存在较强的{001}织构是导致值较低的主要原因。     

多道次热轧形变中混晶的细化规律研究

本文用定量金相的方法研究了多道次热轧形变条件下混晶奥氏体的细化规律。研究结果表明:形变在高温再结晶区进行时,起始奥氏体大晶粒或未再结晶晶粒明显细化,而小晶粒细化缓慢;形变在部分再结晶区进行时,主要是小晶粒或已再结晶晶粒细化,随温度下降,起始奥氏体大晶粒或未再结晶晶粒变得更难实现再结晶细化。此外,还研究讨论了产生上述结果的原因。     

Effect of deformation and cooling rate on the transformation behavior and microstructure of X70 steels

The effects of the deformation in the non-recrystallization region of austenite and the cooling rate on the transformation behavior and microstructure of low-carbon low-alloy steel for pipeline application were studied on the thermal-mechanical simulator Gleeble-1500. It was shown that an increase in deformation amount can greatly increase the nucleation site of ferrite when deformed in the non-recrystallization region of austenite, and an increase in nucleation ratio can greatly refine grains. When the cooling rate is accelerated, the driving force of nucleation is increased and the nucleation rate also improves. Ultra-refine grains can be obtained by controlled rolling. The high density of ferrite nucleus, which forms along the austenite grain boundary, twin interface, and deforma- tion band are introduced in the matrix of austenite by the control of hot rolling, after which the microstructure can be refined. It was found that the acicular ferrite has a very fine sub-structure, high dislocation density, and a thin slab with ultra-fine grains. Small M/A islands and cementite are precipitated on the matrix of the slabs by the analysis technique of TEM and SEM.     

大棒材热轧工艺的数值模拟

大棒材轧制属于高温大变形塑性成形过程,为了研究轧制过程中轧件温度场、应变场及微观组织演变的规律,在热模拟实验的基础上建立了大棒材初轧道次热-力-组织耦合的有限元模拟模型。模拟结果显示,轧制过程中轧件由于发生再结晶使晶粒得到细化,初轧完成后,轧件平均晶粒尺寸由芯部到表层逐渐减小;由于大棒材初轧过程中轧件芯部变形量较小,不利于轧件芯部孔隙性缺陷的压实,因此提高热轧连铸坯的芯部致密度是改善大棒材芯部质量的重要措施之一。     

Grain refinement of low carbon steel produced by CSP process

In comparison with conventional production for hot strips, compact strip production (CSP) brings about some new micro-structural phenomena. Investigations were carried out to clarify the grain refinement mechanism of low carbon steel strips produced by the EAF-CSP process. Samples, obtained from the same rolling stock during continuous rolling, were examined through SEM,TEM and XEDS. Thin slabs have a dominant columnar structure and the spacing of the secondary dendrite arms ranges from 90 to ～125 μm. The average grain sizes for the central area of the samples from the 1st to 6th pass are 41.6, 25.2, 21.4, 20.2, 13.1, 6.7 μm,respectively. Large number of nanometer oxide and sulfide have been found in the low carbon steel produced by the CSP process.The grain refinement mechanism can be summarized as follows: finer solidification structure of the thin slab; austenite recrystalliza-tion at higher temperature and stain accumulation at lower temperature caused by the great reduction of single rolling pass during continuous rolling; nano-scaled precipitates of sulfide and oxide which drag grain boundaries of austenite or ferrite to prevent the grain coarsening.