Abstract:The effects of ultrasonic treatment (UST) on the solidification microstructure of a 35CrMo steel cast ingot were investigated. To avoid the erosion of a high-temperature melt, a T-shaped ultrasonic waveguide unit was used to introduce ultrasonic vibrations into a 35CrMo steel die casting melt. The experimental results show that the microstructure of the ingot was refined by ultrasonic treatment. While the microstructure of untreated 35CrMo steel is coarse dendritic grains, after the introduction of ultrasonic treatment, the solidification microstructure transforms from coarse dendritic to equiaxed grains, and the dendrites are also refined. Samples from different positions of the ingots were subjected to different ultrasonic effects, and the effects on grain refinement also varied due to the severe attenuation of the ultrasound in the melt. The mechanisms of grain refinement using ultrasonic treatment for 35CrMo steel melt are presented.
Abstract. Effects of different power ultrasonic on microstructure and mechanical properties of 35CrMo steel casting were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and hardness testing. A self-developed experiment apparatus was used for the propagation of ultrasonic vibration into the 35CrMo steel melt to carry out ultrasonic treatment. The experimental results showed that compared to the traditional casting, ultrasonic treatment can obviously change the solidification microstructure of 35CrMo steel, which is changed from coarse dendrites to fined dendrites or equiaxed grains. With the increase of ultrasonic power, equiaxed crystal is remarkably refined and its area is broadened. The micro porosity percentage of ingot casting decreases significantly and the porosity defects can be suppressed under ultrasonic treatment. The mechanical properties of 35CrMo steel ingot after heat treatment were enhanced by ultrasonic treatment: the maximum tensile strength is improved by 8.4% and the maximum elongation increased by 1.5 times. IntroductionThe traditional methods of casting to produce large size ingots are easy to produce macro and micro defects such as coarse grains, composition segregation and porosity. The microstructure of ingots could not be controlled precisely. Ultrasonic assisted casting is a new type of solidification method developed for the manufacture of high performance aluminum and magnesium alloys recently. Ultrasonic energy is used to control the grain shape, grain orientation and precipitate state in the solidification process of light alloy. According to the literature [1] and literature [2], scientists found that the solidification process of AZ91 magnesium alloy could be refined obviously by introducing ultrasonic wave in the casting processing. The microstructure of 7050 and 7085 aluminum alloy could be refined and the second phase could be ameliorated by ultrasonic treatment. Literature [3][4] reported the possible use of ultrasonic for the degassing of aluminum alloy melt. Literature [5] studied that the microstructure of Al-Si alloy was refined by high intensity ultrasonic and the Si phase distributed more evenly. Literature [6] reported that mechanical properties of AlSi9Cu3 alloy was enhanced by ultrasonic melt treatment.However, most of the researches on ultrasonic processing technology focused on the nonferrous metals, or the technology of ultrasonic treatment could only be used to deal with small size steel
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