【作者】 林莉；

【导师】 张俊善； 李喜孟；

【作者基本信息】 大连理工大学 ， 材料学， 2003， 博士

【摘要】 根据具有多种相结构合金钢不同热处理转变产物的组织特点，以及超声波在其中的传播规律，利用超声波速度、相对衰减系数以及功率谱分析三种方法，对三种钢（40Cr、38CrMoAl及GCr15SiMn）不同热处理（正火、淬火／退火、淬火+低温回火及淬火+高温回火）转变产物的显微组织进行了超声表征研究。比较了三种表征方法区分不同组织的灵敏度及特点，并提出了合金钢显微组织超声无损表征应遵循的多方法、多参量的原则。 利用TI-40N高精度超声波测厚仪，研究了超声波在不同钢种、不同热处理转变产物中的超声波速度C₁:38CrMoAl钢淬火组织C₁最小，淬火后在200℃～650℃范围内进行回火处理时，随回火温度的升高，C₁逐渐升高，HRC与C₁之间具有较好的相关性；正火组织的C₁介于淬火后中温回火及高温回火产物组织的C₁之间。40Cr钢不同显微组织C₁变化规律与38CrMoAl钢相似。GCr15SiMn钢淬火+低温回火组织的C₁远大于正火、退火及淬火+高温回火组织的C₁；正火、退火及淬火+高温回火组织的C₁比较接近。不同显微组织弹性模量的差异，可能是造成上述实验结果的主要原因。 在保证试样形状、尺寸、表面光洁度、系统参数设置、施加在探头上的压力以及耦合层厚度等测试条件一致的情况下，利用棒材圆柱面测衰减系数法，分别测定并比较上述不同热处理试样相对衰减系数的变化情况，得到的实验结果是：对于40Cr及38CrMoAl钢，α_低温回火＜α＿（淬火）＜α_高温回火＜α_正火；对于GCr15SiMn钢，α_低温回火＜α_退火＜α_高温回火＜α_正火；且随着频率的提高，衰减系数均呈现增加的趋势。研究表明，通过比较圆柱面法测得的相对衰减系数，能够对具有多种相结构的较大尺寸合金钢试样进行超声表征。该方法克服了绝对衰减系数测定法对实验条件要求极为苛刻、难以实现的不足，使得超声表征技术更接近工程条件、更具实用价值。 利用窄带信号频谱分析技术灵敏度高的突出优点，选取中心频率为1MHz的窄带超声信号，对上述不同热处理试样进行超声功率谱分析，发现不同热处理产物在功率谱主频率、谱峰特征（幅度、数量、分布）等方面，都存在不同程度的差异。由此提出，可以把超声波窄带功率谱技术用于多相结构合金钢显微组织的超声表征。 超声波速度、相对衰减系数及功率谱分析三种方法，各自独立；同时，三种方法区分不同组织的灵敏度不同，实验结果能够互为补充。38CrMoAl钢的淬火与淬火+低温回火组织，用声速法和主频率比较法都难以区分，最好的方法是比较功率谱谱峰特征（幅度、数量、分布）。而对于利用比较谱峰特征（幅度、数量、分布）无法区分的GCr15SiMn钢退火与正火组织，则可以利用相对衰减系数法进行比较。 分析三种方法的研究结果认为，对于合金钢这类具有多种相结构的材料，应综合运用多种方法、提取多个参量，从不同角度进行对比表征，才能得出全面可靠的结论。更多还原

【Abstract】 According to structural characteristics of multi-phased alloy steels and the properties of ultrasonic propagation, microstructures characterization with different heat treatment processes (normalizing, quenching/annealing, quenching plus low tempering, quenching plus high tempering) for three steels (40Cr, 38CrMoAl, GCrlSSiMn) was studied experimentally by using ultrasonic methods. Ultrasonic velocity, relative attenuation coefficient, and power spectral analyses were researched on the same samples respectively, on the basis of theory and experiment, the sensitivity and other characterizations of the three methods used to distinguish different microstructures were compared. The principle of multi-method and multi-parameter is suggested, which should be followed during characterizing microstructures of alloy steels by ultrasonic NOT method.Ultrasonic velocity (C,) of transformation products through different heat processes of three steels was measured by high-accuracy ultrasonic installation. The velocity of quenched microstructure of 38CrMoAl is the lowest, which gradually increases with increasing tempering temperature between 200癱 and 650癱 after quenching process. There is good correlation between HRC and C,. The velocity in normalizing structure is between the velocity in medium temperature and high temperature tempering production after quenching. The variation principle of wave velocity in different microstructures of 40Cr is similar with that of 38CrMoAl. The velocity in quenching and low temperature tempering structure of GCrlSSiMn is much lower than the velocity in normalizing, annealing and high temperature tempering structure. The difference in velocity among normalizing, annealing and high tempering structures are all approaching. The difference among the elasticity modulus of various microstructures is probably the main reason, which caused the experiment results above.Under the same experiment conditions, such as sample shape, size, surface roughness, establishment of testing system, pressure on the probe, and thickness of coupling medium, the variety of relative attenuation coefficient (or) in different heat treatment samples is measured and compared by measuring the attenuation obtained from the cylindrical surface of column. The result is as following: for 40Cr and 38CrMoAl, a MT<aZ MQ<a s<a P+F; for GCrlSSiMn, a MT<a ANNEA< s<a P+F; and a increased with the increasing of frequency. The study shows that using a obtained from cylindrical surface of column can characterize the alloy steel samples, which have complicated phase structure. This method overcomes the difficult and unrealizable experiment conditions that are used to measure the absolute attenuation coefficient and impels the technique of ultrasonic characterization to be more closed to the engineering requirements and more practical.Because of the good sensibility, ultrasonic narrow band signal analysis technique with1MHz central frequency was chosen to differentiate the heat treatment samples above-mentioned. There are obvious differences among heat treatment products in principal frequency, spectral peak’s quantity, amplitude and distribution. That is to say, the technique of ultrasonic narrow band power spectral can be applied to characterize the microstructures of multi-phased alloy steels.The three methods are independent, supplement mutually and proved each other because the sensibility of every method is different when used to distinguish different microstructures. For example, the quenching and quenching plus low tempered structure of 38CrMoAl are hard to be differentiated by velocity method and the principal frequency technique. It will be better if they are differentiated by the method of relative attenuation coefficient. Moreover, the best way is to compare the characteristic of spectral peaks in frequency domain.It could be concluded that, when microstructures of multi-phased alloy steels are ultrasonically characterized, the complete and reliable results could be drawn from many methods and parameters.更多还原