含Nb微合金钢应变诱导析出的研究现状

简述了微合金钢中微量元素Nb的主要作用,回顾了应变诱导析出的研究方法及优缺点,阐明了变形奥氏体应变诱导析出相的种类,晶体结构,析出相的形成顺序、形貌和分布,分析了影响析出动力学的主要因素并简要介绍了应变诱导析出动力学模型的最新发展.     

热轧Nb-Ti-V钢应变诱导析出动力学的计算模型

以规则溶液亚点阵模型和经典型核长大理论为基础，计算了Nb-Ti-V复合微合金化钢的应变诱导析出动力学．计算所得的析出-时间-温度（PTT）曲线与采用等温应力松弛法所获得的实验结果基本符合。     

含铌微合金钢碳氮化物析出行为研究的现状及发展

综述了含铌微合金钢中铌的固溶与析出行为.着重阐述了控轧控冷过程中各工艺参数对含铌微合金钢中铌的碳氮化物析出行为的影响,涉及形变、温度、冷却速率及合金元素等对铌碳氮化物析出的作用;总结了含Nb微合金钢中碳氮化物的研究现状,并展望了其未来的发展.     

铌-钒微合金钢中碳氮化合物的析出特点

用三维原子探针分析了Nb—V微合金钢中析出相的特征,发现不同大小的析出团簇成分有较大的差异。结果表明：碳原子首先在位错等缺陷处偏聚,然后钒和铌原子依次向碳原子偏聚处聚集,先后形成V-C和V-Nb—C原子团簇,进而发展成（Nb,V）C复合相,并随着其进一步长大,成分出现不均匀。当合金中存在氮元素时,也会形成（Nb,V）（N,C）复合相。     

Nb微合金钢析出行为的热力学计算

以析出热力学为基础,对Fe-Nb-C-N系统中奥氏体／碳氮化物的热平衡过程,计算了不同温度下碳氮化物析出相的平衡摩尔分数、化学驱动力、各组元的原子分数及奥氏体组分等．结果表明,随着温度的降低,析出相的平衡摩尔分数增大,溶解在奥氏体中的各组元的摩尔分数降低,析出相的化学驱动力增大．在低温条件下,Nb和N元素巳基本析出．碳化物在析出物中所占的比例主要取决于钢的成分和温度．对于同一成分的钢种,这一比值随着温度的降低而增大．     

海洋大气环境下稀土及铌微合金钢的腐蚀行为研究

为给微合金钢的设计开发理论提供数据支撑,通过显微组织表征、干湿交替循环试验、中性盐雾试验和电化学分析等测试手段研究了稀土微合金钢和铌微合金钢在海洋大气环境中的腐蚀行为,对比分析了其耐腐蚀性能.结果表明:微合金钢的显微组织由铁素体和珠光体组成,并且铌微合金化有助于细化晶粒并能阻碍珠光体组织的形成.在腐蚀初期锈层的主要成分...     

铌钒微合金化对风电法兰用Q345E钢析出相的影响

采用Thermo-Calc热力学计算软件,对铌钒微合金化风电法兰用Q345E钢在400~1600℃存在的平衡析出相以及铌、钒在奥氏体相中的固溶规律进行了计算,并探讨了碳、氮、铌、钒元素含量变化对析出相的影响。结果表明:风电法兰用Q345E钢在400~1600℃存在的主要平衡析出相为MnS、AlN、MX#1(富含铌)、MX#2(富含钒)和M7C3相;MX#1相的主要组成元素为铌、碳、氮和少量的钒、铬,MX#2相的主要组成元素为钒、碳、铌、氮和少量的铬;MX#1相析出量和析出温度主要受钢中铌含量的影响,而受碳、氮、钒含量的影响不大。TEM分析表明,风电法兰用Q345E钢轧后析出相尺寸变化范围为几纳米到100纳米,大颗粒析出相为近似于立方形的富铌MX#1相,小颗粒析出相是球形或椭圆形的富钒MX#2相,这同热力学计算所得的MX#1相和MX#2相成分与析出温度基本吻合。     

带状组织对微合金钢应变局部化及应变强化行为的影响

目的 研究不同加载方向下带状结构对微合金钢塑性变形及应变强化行为的影响。方法 将X80管线钢加热到1200 ℃后分别进行炉冷和空冷热处理,得到多边形铁素体/退化珠光体和粗/细铁素体晶粒带状组织以用于实验研究。将单轴微拉伸实验和数字图像相关方法相结合,通过零变形实验分析系统精度,获取RD、45°和TD取向带状组织试样的拉伸变形规律。同时,在DIC全场变形测量结果与实验数据统计分析结果的基础上,提出了可描述应变强化程度的参量K_f,用于对比和分析不同加载方向下带状结构对应变强化行为的影响。结果 零变形实验中位移平均值和标准差的最大值分别为0.004 pixels和0.006 pixels,系统精度较高。加载方向会影响带状组织的塑性变形演化情况,45°试样中产生了明显与带状取向一致的应变分布特征。在相同应力下45°试样首先达到了较大的应变强化程度,其抗变形能力最低。结论 不均匀带状组织对局部变形的影响程度与2个组成带的力学性能差异有直接联系,参量K_f可在一定程度上描述应变局部化引起的各向异性特征。     

硼微合金化镍基合金的晶界偏聚析出行为

针对20多年来镍基合金中硼微合金化的研究,介绍了微量硼在其晶界上的偏聚析出机制,重点综述并讨论了微量硼在晶界上的偏聚析出行为。     

Influence of RPC Parameters on the Precipitation of Nb in Microalloyed Steel

Thermo-simulation test, metallographic analysis, measurement of hardness, TEM(including diffraction contrast technique and nano-beam anylasis)along with calculating software of Metlab, etc. were used to study the influence of RPC parameters(relaxation time, aging time)on the precipitation of Nb in microalloyed steel. Following work was undertaken in this study:Strain-induced precipitation in Nb-bearing multi-microalloyed steel was monitered and analyzed. The interaction between dislocation evolution and precipitates in deformed austenite was directly observed(an Fe-Ni-Nb alloy was employed to simulate austenite in steel). The(a low carbon microalloyed steel only by Nb was adopted)effect of relaxation of deformed austenite on aging behavior occurring in bainite was investigated. Finally, the thermal stability and variation of composition of carbonitride precipitates during dissolving process in Nb-Ti microalloyed steel were alsodetected. These results indicate:(1)During the stress relaxation, the process of precipitation happened in deformed austenite of multi-microalloyed steel can be divided into three stages, i. e. nucleation, growth and coarsening. In the final stage of relaxation, Mo atoms would enter the lattice of(Nb,Ti)(C,N)precipitates and its concentration in the precipitates increases with the relaxation time.(2)In the earlier stage of relaxation, the dislocations in deformed austenite demonstrate twisted and distribute randomly. The precipitates have the tendency to occur along those dispersed dislocations. The dilocation cells would form gradually with the relaxing time prolonged and would become more stable by the subsequent precipitates formed on them in the later relaxation period. The paralleled dislocations in dislocation cells exhibit the same Burgers vector. The dislocations get rid of pinning by the bypassing mechanism.(3)When the samples are reheated to hold isothermally at 525℃,which are relaxed for different time in deformed austenite followed by accelerated cooling, their microstructures evolve very slowly with the aging time but two hardness peaks can be found one each hardness-time curves. The position of hardness peaks nearly raimains unchanged while their height varies obviously with the relaxation time. In no relaxtion samples, only one hardness peak could be observed. During the process of aging at 525℃, The growth and coarsening of as-existed strain-induced precipitates formed in deformed austenite contribute to formation of the first hardness peaks. While the second hardness peaks result from the further precipitates which nucleate in a phase after γ→α transformation(after aging for about 10 hours).(4)It was found that the precipitates formed during solidification are monophase(Ti,Nb)(C.N)rather than TiN enclosed with NbC. With addition of Ti to the steel, the thermal stability of the carbonitrides would enhance remarkably.     

Ti,Nb和W复合强化超纯铁索体不锈钢的高温析出行为

为提高汽车尾气排放系统中高温端排气歧管等所用铁素体不锈钢的综合性能,采用真空熔炼制备Ti,Nb和W复合强化的超纯铁素体不锈钢(不含Ni),并利用硬度和力学性能测试、场发射扫描电子显微镜和透射电子显微镜分析研究固溶态材料在550,600℃和700℃的时效硬化规律、拉伸性能以及时效析出行为.600℃时效40h之后材料力学性能达到最佳值,在晶粒内部和晶界区域弥散分布着两种形态的纳米析出相,一种是呈不规则颗粒状的(Ti,Nb)C,另一种是呈长条状的Laves相Fe2(Nb,W);这两种析出相与铁素体基体均存在固定的晶体学取向关系,即[011]Fe∥[011](Ti,Nb)c和(0(-1)1)Fe∥(200)(Ti,Nb)C(晶面偏差约3°)以及[011]Fe∥[0001]Fe2(Nb,w)和(200)Fe∥(01(-1)0)Fe2(Nb,w)(晶面偏差4°～5°).随时效温度提高,析出相的尺寸增大,且析出相由(Ti,Nb)C逐渐转变为Fe2 (Nb,W).     

Effect of Strain Rate on the Ferrite Grain Refinement in a Low Carbon Nb-Ti Microalloyed Steel during Low Temperature Deformation

1. IntroductionThe thermomechanical controlled processing(TMCP) of microalloyed steels has been employed fosome times in the production of plates and sheet material to optimize mechanical properties. The centrafeature of thermomechanically processed steel is the ul-trafine grain size in the final product. Therefore, theferrite grain refinement of structural steels has attractedconsiderable interest from engineering scientists due toits unique role of increasing both strength and toughnessDem…     

Mathematical Modelling of Carbonitride Precipitation during Hot Working in Nb Microalloyed Steels

Based on thermodynamics and kinetics, precipitation behavior of microalloyed steels was analyzed. Deformation greatly promotes isothermal carbonitride precipitation and makes C-curve shift leftwards. The position and shape of C-curve also depend on the content of Nb and N. C-curve shifts leftwards a little when N content increases and the nose temperature is raised with increasing Nb content. Deformation shortened precipitation start time during continuous cooling, raised precipitation start temperature, accelerated precipitation kinetics of carbonitrides. With decreasing the finishing temperature and coiling temperature, the precipitates volume fraction increases and strength increment is raised during hot rolling. The simulated results are in agreement with experiment results.     

高速钢高温形变诱发析出的研究

本文探讨了高速钢在高温形变过程中碳化物析出的行为及奥氏体组织状态对析出的影响。用透射电镜和扫描电镜分析了不同热处理状态奥氏体的组织结构,分析了高温形变过程中碳化物析出的部位,颗粒尺寸及形态。试验表明, 碳化物主要在奥氏体的缺陷处呈点状和点列状析出,大小为20mμ。处于回复状态的奥氏体缺陷诱发碳化物析出,析出碳化物钉札缺陷阻止再结晶进行。当再结晶驱动力较大时,由于动态再结晶充分发展,使缺陷大量消除,碳化物析出显著地减少。     

Nb-Ti微合金高强钢动态再结晶动力学及临界条件

在Gleeble-3500 热模拟试验机上对Nb-Ti微合金高强钢进行了热模拟压缩试验,研究了其在变形温度为900~1 100 ℃、应变速率为0. 01~5 s-1 、最大变形量为70%条件下的动态再结晶行为。对流变曲线的分析及微观组织观察结果表明,低温高应变速率下流变曲线未显现出典型动态再结晶特征,但此条件下已发生动态再结晶。使用双曲正弦形Arrhenius关系计算的Nb-Ti微合金钢变形激活能为404 kJ/mol。利用加工硬化原理和Cingara-McQueen模型确定了动态再结晶初始临界应力和应变,分析了由Cingara-McQueen模型计算临界应力值偏高的原因,建立了临界应力、应变和Z参数之间的定量关系,得到了动态再结晶临界应力和应变方程:σ_c=0.335Z0.144,εc=0.005 9Z0.079。通过对θ-ε曲线进行分析,建立了最大软化速率处应变(εm)和变形条件的关系。在此基础上使用Avrami型动态再结晶动力学模型计算了不同变形条件下的再结晶体积分数,结果表明此模型可准确预测Nb-Ti微合金高强钢动力学。     

应变率对05Cr17Ni4Cu4Nb钢拉伸性能的影响

采用万能材料试验机和旋转盘冲击拉伸装置对05Cr17Ni4Cu4Nb钢进行了不同应变率的拉伸实验研究,获得了05Cr17Ni4Cu4Nb钢沿轧制方向和垂直于轧制方向在应变率为10-2/s~103/s范围内的应力应变曲线,分析了应变率对05Cr17Ni4Cu4Nb钢屈服应力的影响规律。结果表明,05Cr17Ni4Cu4Nb钢在两个方向的弹性模量和拉伸强度几乎相当,但沿轧制方向的断裂强度和断裂延伸率较高,05Cr17Ni4Cu4Nb钢沿轧制方向和垂直于轧制方向的屈服应力均随应变率升高而增大,但变化趋势不同。根据实验结果,拟合得到了05Cr17Ni4Cu4Nb钢不同方向屈服应力与应变率变化关系的方程。