Nb-Ti微合金钢连续冷却相变的研究

利用Gleeble-2000热模拟实验机,测定了Nb-Ti微合金钢变形奥氏体的CCT曲线,研究了冷却速度对连续冷却相变及显微组织的影响,利用碳萃取复型法对第二相析出物进行了分析。结果表明,随冷却速度提高,Nb-Ti微合金钢相变温度降低,组织细化,铁素体的形貌从多边形逐渐向针状转变;随冷却速度的增加,第二相析出物增多且变得细小。     

V-Ti微合金钢形变奥氏体的连续冷却相变研究

采用热力模拟实验技术、OM、SEM及TEM,并结合宏观硬度测试,研究了V-Ti微合金钢形变奥氏体的连续冷却相变和组织演变规律,建立了实验钢连续冷却转变曲线,并探讨了第二相的析出行为。结果表明,不同冷速下,实验钢获得了不同的微观组织,同时第二相的形貌、尺寸也发生了变化。     

一种含Nb、Ti微合金钢的连续冷却相变行为

利用MMS -200热模拟试验机对试验钢进行不同变形条件下的连续冷却转变试验.针对不同的冷却速度,采用热膨胀法结合金相法测定试验钢在连续冷却转变中的相变温度,利用光学显微镜及扫描电镜观察试样的显微组织,并测定珠光体的含量,进而绘制出试验钢在变形和未变形条件下的连续冷却转变(CCT)曲线,从而得出不同变形工艺对微合金钢连续冷却转变行为和显微组织的影响规律.     

碳含量及晶粒尺寸对微合金钢激活能的影响

通过对3种常用应力函数的回归计算，认为双曲正弦函数的回归精度最高。以此为基础，确定了11种分别含Mo、Ti、V、Nb钢的激活能，进而建立了激活能与材料化学成分、原始晶粒尺寸关系的BP网络模型。并得出表观激活能随钢中碳含量增大而增大，随原始晶粒尺寸的增大而减小的结论。     

含硼微合金钢奥氏体晶粒尺寸神经网络模型

以Gleeble1500热模拟机试验数据为基础，建立了含硼微合金钢高温奥氏体晶粒尺寸与热加工工艺参数的回归统计及BP网络模型，结果表明：ＢＰ网络模型具有较高的预报精度。     

亚共析钢复相组织中铁素体晶粒尺寸测定方法

亚共析钢复相组织主相的晶粒尺寸主要采用金相法和扫描电镜 EBSD 法。其中,金相法可以测量晶粒尺寸并对其评级,定量测量过程需要手动完成;扫描电镜 EBSD 法可对经过电解抛光的试样进行晶粒尺寸的自动测量,借助两相花样质量的差异,实现对铁素体+珠光体复相组织中铁素体晶粒的自动统计。     

Ti微合金钢热变形后连续冷却相变及第二相析出行为

采用热力模拟试验技术、金相显微镜(OM)、扫描电镜(SEM)及透射电镜(TEM),并结合宏观硬度测试,研究了钛微合金钢形变奥氏体的连续冷却相变和组织演变规律,建立了试验钢连续冷却转变曲线,探讨了不同冷速对第二相析出的影响。结果表明,不同冷速下,试验钢获得了不同的微观组织,随冷速增加,第二相析出量增多,尺寸更细小,但冷速过高,析出被抑制。     

钼、铬对低碳铌钛微合金钢连续冷却转变行为的影响

 为研究合金元素钼、铬对低碳铌钛微合金钢连续冷却转变行为的影响,采用Gleeble-3800热模拟试验机和热膨胀试验方法,测定了钼、铬含量不同的3种低碳铌钛成分微合金钢在不同冷却速度下的相变点,采用光学显微镜及扫描电子显微镜观察了其转变产物的微观组织,同时结合维氏硬度测试,绘制了动态CCT曲线。结果表明,钼和铬均降低奥氏体向针状铁素体转变的相变温度,并且在冷速大于1℃/s时,钼比铬的作用效果更加明显。钼、铬均能抑制先共析铁素体和珠光体的转变,扩大针状铁素体形成冷速范围,并能够显著细化组织。     

含钛微合金钢连续冷却转变的研究

利用Gleeble-1500热模拟实验机研究了不同钛含量对微合金钢连续冷却转变的影响,用热膨胀法建立了静态和动态条件下的连续冷却转变曲线(CCT),为含钛微合金钢制定合理的控冷控轧工艺提供了依据。研究表明,在较宽的冷却速度范围内(2—20℃／s)都有贝氏体组织生成;随含钛量增加,γ-α相变点上移,扩大了先共析铁素体形成的冷却速度区间;在动态条件下出现了只有多边形先共析铁素体和珠光体的组织。     

连续冷却过程中铁素体相变温度的模拟

以传统的形核理论为基础,考虑了变形的影响,研究了奥氏体-铁素体相变的等温相变孕育期,采用Scheil的可加性法则计算了SS400钢在变形和未变形条件下的铁素体相变实际转变温度（Ar3）,并与实测值进行了对比,结果表明：计算的Ar3与实测的Ar3吻合良好,从而进一步表明该相变孕育期模型的准确性．     

Grain Size Prediction after Continuous Cooling Transformation from Deformed Austenite to Ferrite

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C Mn Nb钢在控轧控冷条件下相变后铁素体晶粒尺寸的预测

 基于相变动力学和热力学原理，讨论了椭球形铁素体晶核在奥氏体晶界形核及长大的动力学，在模型中引入变形和冷却的作用，提出了预测C Mn Nb钢经控轧控冷后铁素体晶粒尺寸的方法。用该方法进行的计算机模拟结果和实验结果吻合良好，表明这种方法可用来模拟该相变过程。     

Grain Growth of Deformation Induced Ferrite in V Microalloyed Low Carbon Steel During Controlled Cooling Process

The effect of vanadium on the DIFT (Deformation Induced Ferrite Transformation) microstructure coarsening in low carbon steel during the continuous cooling processes and isothermal processes at different temperatures were investigated using thermo-simulator.The results showed that the steel containing a small amount of vanadium had the similar velocity of grain growth with the vanadium free steel during the continuous cooling process,but a lower velocity of grain growth than that of vanadium free steel during isothermal processes at high temperatures.On the other hand,the vanadium remarkably inhibited grain growth in the steel containing a high amount of vanadium during both the continuous cooling and isothermal processes.Vanadium dissolved in matrix is indicated as an important factor on restraining grain growth through estimating the driving force of normal grain growth and the resistance of precipitation particles of vanadium on grain growth.The influencing mechanism of vanadium dissolved in matrix on the grain growth during the controlled cooling process is discussed.     

热轧管线钢冷却过程相变预测模型

为能够精确模拟管线钢连续冷却过程中组织演变行为,建立了一种包括相变潜热模型、温度场模型和相变体积分数模型在内的数学耦合模型,深入研究了含碳量和冷却速度对相变潜热的影响,以及相变潜热对冷却过程中温度分布的影响.将耦合模型的计算值与实验数据进行对比,两者吻合较好,且耦合模型的计算结果与普通相变模型计算结果相比更加精确,证明了该耦合模型能够准确预测X80管线钢冷却过程中的组织演变.     

控轧控冷工艺条件下Nb—V钢碳氮化物的析出行为

本文通过热模拟实验和电子显微技术等方法,系统地研究了控轧控冷对铌钒钛复合微合金化低碳热轧钢板的铌、钒、钛碳氧化物的析出行为的影响,研究结果对开发高强度船体用钢板具有参考价值。通过研究表明,在奥氏体区和铁素体区都用Ni(C,N）析出,对Nb、V的析出起了诱导作用,并与Nb、V形成复杂的碳氮化物。在铁素体中主要以基体均匀沉淀析出和位错沉淀析出。     

冷却速率对高铌微合金钢组织的影响

 采用热模拟和组织显微分析方法研究了不同冷却速率对高铌微合金钢组织的影响。结果表明，铌含量高有利于在极低的冷却速率下获得针状铁素体组织，提高冷却速率则能进一步促进针状铁素体转变，并使铁素体板条得到细化。同时，固溶铌有利于针状铁素体的形成，而铌的沉淀析出则不利于针状铁素体的获得。     

Effect of Cooling Patterns on Microstructure and Mechanical Properties of Hot-Rolled Nb Microalloyed Multiphase Steel Plates

 The effect of the run-out table cooling patterns on the microstructure and mechanical properties of Nb microalloyed steel plates was investigated by hot rolling experiment. The results showed that the mixed microstructure containing ferrite, bainite and significant amounts of retained austenite can be obtained through three kinds of cooling patterns on the run-out table under the same hot rolling condition. Three kinds of cooling patterns possess different austenite transformation kinetics, which leads to variations in microconstituent characteristics. The yield strength increases, the tensile strength decreases and the total elongation tends to increase as the cooling patterns Ⅰ, Ⅱ and Ⅲ were applied respectively. The yield strength, the total elongation and the product of tensile strength and ductility reach the maximum values (547 MPa, 37.2% and 28384 MPa·%, respectively) for the steel plate processed by cooling pattern Ⅲ.     

晶内铁素体型高强韧性微合金非调质钢的进展

晶内铁素体型微合金非调质钢成分一般为(%):0.2～0.4C,0.2～0.8Si,1.0～1.7Mn,0.05~ 0.15V,采用再结晶锻造或轧制、控制相变区间冷却速率以促进形成细小弥散的晶内铁素体组织是提高铁素体 -珠光体型微合金非调质钢强韧性的重要手段。选择合适的脱氧工艺,获得一定组成的细小、弥散的氧化物, 使之成为MnS、VN和V4C₃ 等的析出核心,利于晶内铁素体析出的氧化物冶金是近来提高该钢强韧性的重要 进展。介绍了国内外晶内铁素体型微合金非调质钢的化学成分和生产工艺,并分析了晶内铁素体形成机理。     

Influence of Vanadium on Grain Growth of Deformation Induced Ferrite in Low Carbon Steel during Continuous Cooling Process

The effects of vanadium on the deformation induced ferrite transformation (DIFT) in low carbon steel during heavy deformation at the temperature slightly higher than Ar₃ and on the coarsening of DIFT microstructure during the continuous cooling processes after deformation were investigated using a thermo‐simulator. The results show that vanadium has little effect on the volume fraction of DIFT microstructure under heavy deformation, whereas the deformation induced ferrite (DIF) grains are refined with increasing vanadium content. The steel containing a small amount of vanadium exhibits similar velocity of grain growth compared to vanadium free steel, while the vanadium remarkably inhibits grain growth in a steel containing a high amount of vanadium during the continuous cooling process. The diffusion activation energy of grain boundaries for all the tested steels is calculated and the influencing mechanism of vanadium on the grain growth during the continuous cooling process is discussed.