W1300无取向硅钢热变形行为的模拟分析

采用热模拟变形的方式在跨越奥氏体/铁素体转变的1100℃～800℃温度范围内观察了W1300无取向硅钢,在不同的模拟热轧变形流程中应力应变曲线的演变规律,并对比分析了热变形后的微观组织。研究表明,奥氏体区终轧之后相变得到的等轴铁素体组织难以再经加热粗化。铁素体区终轧后热轧组织的变形特征明显,内在的变形储存能可以推动高温卷取或常化退火过程中铁素体基体的静态再结晶,并获得粗大晶粒。铁素体与奥氏体变形抗力的明显差异会造成两相共存时热轧变形的不稳定性。     

钛合金热变形时的动态回复和再结晶

对于α+β及亚稳β钛合金,传统的轧制或锻造等热变形加工通常在α+β两相区和β单相区进行,在热变形过程中发生动态回复和动态再结晶.对β和α+β相区热变形组织的研究表明,变形早期动态回复形成的β亚晶界(小角度晶界),在进一步变形后变成大角度晶界.经过连续动态再结晶,晶界结构发生变化.但钛合金热变形过程中动态回复组织需要根据动态再结晶机制进行检验.     

AZ61镁合金热压缩变形组织研究

在gleeble 1500D热模拟试验机上以应变速率为0.01 s-1和1s-1,变形温度为350℃和400℃,对AZ61镁合金热压缩变形,并对变形试样显微组织进行了研究。结果表明:热变形过程中发生了不同程度的动态再结晶,得到不完全再结晶组织。变形温度和应变速率对再结晶程度、再结晶晶粒尺寸均匀性有明显影响;以较低的温度配合高的应变速率,热变形后发生再结晶晶粒均匀细小;变形温度高且应变速率高时,发生动态再结晶的区域变小,再结晶晶粒尺寸偏大且极不均匀,低温高速热变形有利于获得均匀细小的再结晶组织。     

抗大变形管线钢热影响区软化问题的研究

为了研究抗大变形管线钢热影响区出现软化区的具体原因,本文采用焊接热模拟实验研究了X80级抗大变形管线钢的焊接热循环过程,结合金相显微镜、扫描电镜、EBSD、透射电镜和冲击实验,分析了热影响区软化区的组织变化、晶体学特征和冲击韧性.结果表明:当母材组织为多边形铁素体+贝氏体时,焊接热影响区的软化区出现在峰值温度600~700℃的高温回火区,此时组织转变成硬度较低的粗大铁素体+回火贝氏体,并且回复过程加快,组织中亚结构的大幅度减少和位错密度的显著降低是产生软化区的主要原因;软化区的韧性较好,但是在800℃的临界区,M/A组元发生了聚集和粗化,并且大角度晶界比例降低,导致了韧性低谷的出现.     

微合金钢回温变形时的组织转变和铁素体动态再结晶行为

采用GLEEBLE 3800热模拟机进行回温变形热压缩实验,研究回温温度对微合金钢组织转变和铁素体动态再结晶行为的影响。利用金相显微镜、扫描电镜、透射电镜和背散射电子衍射观察实验钢的微观组织和晶粒取向,并对形变时的应力-应变曲线进行分析。结果表明:实验钢回温变形可获得超细晶组织,晶粒平均等效直径约2μm;在回温过程中变形发生动态回复形成亚晶组织,峰值温度变形发生铁素体动态再结晶形成超细晶粒;动态再结晶机制包括晶界迁移和亚晶的转动生长,回温到700℃和750℃时以前者为主,再结晶不充分,保留了条带状变形铁素体,800℃变形时,两者共同作用,形成均匀的等轴状超细晶组织;通过线性回归计算得到实验钢峰值温度变形时铁素体动态再结晶激活能Qd=250.18kJ/mol。     

Ti-IF钢铁素体区热变形行为研究和Zener-Hollomen参数方程的建立

利用单道次压缩变形,研究了变形温度、变形速率和变形程度对一种Ti-IF钢的奥氏体区、铁素体区和两相区的热变形行为的影响.在奥氏体区和铁素体区变形时,随变形温度的降低流变应力增加,而在两相区变形时,随变形温度的降低流变应力降低.Ti-IF钢的铁素体动态再结晶受变形温度的影响最大,在铁素体变形高温区可以发生动态再结晶,铁素体区变形高温区域的变形抗力显著降低.根据流变应力曲线,确定了Ti-IF钢Z-Hollomen参数方程.     

热变形参数对3003铝合金显微组织及硬度的影响

采用Gleeble-1500热模拟试验机对经高效熔体处理的3003铝合金进行变形温度为300℃～500℃,应变速率为0.01～10.0 s-1的等温压缩实验,建立了动态再结晶平均晶粒尺寸与变形温度和应变速率的三维关系图.通过显微维氏硬度测试表明,3003铝合金热变形后的显微硬度随应变速率的增大和变形温度的升高而降低,且显微维氏硬度随动态再结晶平均晶粒尺寸的减小而增大.TEM形貌像表明,当变形温度T≥400℃,应变速率.ε≥1.0 s-1时,合金中粗大的AlMnFe和AlMnSi第二相在铝基体中不均匀分布,在动态再结晶过程中起到了粒子促进形核作用.显微维氏硬度的变化与微观组织观察结果一致.     

2205和2507双相不锈钢双道次热压缩条件下的微观组织演变及变形行为

对DSS2205和SDSS2507进行1000~1200℃的双道次热压缩实验,以研究热变形道次间隔过程中双相不锈钢的微观组织演变及其对合金后续变形行为的影响。结果表明:较高的变形温度(1200℃)不利于奥氏体稳定。随着保温时间的延长,γ→δ相变使得奥氏体占比逐渐降低,亚稳铁素体再结晶晶粒明显长大,合金第二道次热变形时的流变应力水平逐渐降低。在较低的变形温度下(1000℃),δ→γ相变占据主导,保温时间的延长促使铁素体晶界处形成大量的块状奥氏体相,抑制了铁素体再结晶晶粒长大。合金在第二道次热压缩变形时,块状奥氏体相的形成致使铁素体内大量位错发生缠结,并聚集在奥氏体/铁素体相界面处。对比DSS2205和SDSS2507较低温度下的微观组织演变过程可知,双相不锈钢第二道次变形抗力的提高主要与保温过程中铁素体内块状奥氏体相的形成有关。     

金属热变形微观组织精密控制的研究进展

大多数承力关键金属构件在其生产过程中均需经历热变形工步。探讨了典型金属结构材料热变形中3种主要动态再结晶机制的流变行为、微观组织演变特征,并对热变形间隔及热变形后的亚动态再结晶行为进行分析,提出了相应的微观组织控制策略。讨论了第二相颗粒对热变形微观组织演变的影响以及通过第二相颗粒实现微观组织控制的方法。对在热变形中及热变形后冷却过程中会发生相变材料的热变形微观组织演变规律进行了分析。分析热变形过程中的微观组织演变规律,并建立相应的数值模型是实现微观组织精密控制的有效途径,因此简要讨论了不同微观组织演变数值模型的特点及适用性。综合考虑动态再结晶、亚动态再结晶的演变过程以及第二相颗粒和相变的影响规律,并结合基于物理冶金基础理论微观组织演变数值模型是实现热变形微观组织精密控制的必由之路。     

冷却工艺对20CrMnTi组织转变与硬度的影响

探索合理的轧后冷却工艺制度对降低热轧齿轮钢棒材冷后硬度具有重要的指导意义.本文通过热模拟试验机进行冷却工艺试验,研究了单道次变形后不同冷却速度和不同终冷温度对齿轮钢20CrMnTi组织转变与硬度的影响.研究结果表明：在快冷速(10, 50 ℃/s)条件下,再结晶晶粒长大受到抑制,奥氏体晶粒细化,晶界面积增大,铁素体形核质点增多; 当终冷温度升高时,高温区铁素体相变时间增加,冷后组织中铁素体体积分数增大,硬度值降低.在终冷温度850 ℃时铁素体体积分数达到最大值58%,硬度值相应降低为264HV.在慢冷速(0.1 ℃/s)条件下,再结晶晶粒长大明显,铁素体形核质点减少,但随着终冷温度降低,两相区中C元素扩散时间延长,铁素体形核长大时间增加,冷后组织中铁素体体积分数增大,硬度值降低.在终冷温度760 ℃时铁素体体积分数达到最大值48%,相应硬度降低为最小值240HV.在1 ℃/s条件下,终冷温度对铁素体体积分数及硬度影响较小,铁素体体积分数和硬度分别在34%±4%和(282±5)HV范围内波动.     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

水三相点复现的不确定度评定

水三相点是开尔文热力学温度的唯一基准点，也是ITS-90国际温标重要的定义固定点。因此，水三相点不确定度分析对整个温标的建立、温度量值传递起着至关重要的作用。近3年来，中国计量科学研究院研制出一系列高质量的水三相点容器，加强了水三相点的研究，为不确定度的分析提供了更为可靠的实验依据。同时，不确定度的分析也是客观评价新研制容器性能的一个重要指标。因此，根据实验结果对新研制容器所复现的水三相点进行了不确定度评定。评定结果表明，其扩展不确定度为0．16mK(k=2．69，P=0．99)。