| Summary: | 碩士 === 高苑科技大學 === 機械與自動化工程研究所 === 102 === With the increasing requirements of fastener products, to develop new materials or improve heat treatment technique become the key of industrial upgrading.Nowadays, high tensile strength bolts are heat treated (quenching and tempering) to achieve the desired mechanical property, such as hardness、strength、toughness、fatigue resistance、wear resistance etc. As we all know, ultrasound is one of widely used nondestructive inspection technique. Based on the characteristic of wave transmission, the grain boundary caused the refraction, diffraction and scattering results of ultrasonic velocity and attenuation. In this study, the 1045 medium steel is heat treated with different heating temperatures and then water quenched. the relationship between grain size and both ultrasonic velocity and attenuation and mechanical property (hardness) is determined by two ultrasonic probes (5MHz and 10MHz). The experimental results show that 1) the quenching temperature is higher, the average grain size smaller 2) the smaller average grain size, the higher hardness measured 3) the higher hardness, the faster acoustic velocity, but the attenuation rate is slower 4) the smaller average grain size, the faster acoustic velocity, but the attenuation rate is slower 5) the higher the frequency of the probe, the impact of the scattering effect is more obvious, The above results can be used as another non-destructive testing reference in quenching process in fastener industry.
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