Effect of Ultrasonic Melt Treatment on Microstructure and Mechanical Properties of 35CrMo Steel Casting

Abstract

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

Effect of Ultrasonic-Assisted Casting on Hot Deformation Mechanism and Microstructure of 35CrMo Steel Ingot

“…In recent years, ultrasonic waves had been widely used in the field of casting because of their cavitation and acoustic flow effect, which refined the solidified structure and avoided pores and inclusions [ 5 , 6 , 7 ]. Shi et al [ 8 , 9 ] showed that the introduction of ultrasonic wave in the casting process of 35CrMo steel makes the microstructure change from coarse dendrites to fine dendrites or equi-axed grains and more pronounced grain refinement observed with increasing ultrasonic power. Liu et al [ 10 ] introduced ultrasonic waves into the casting process of AZ91 magnesium alloy and found that fine and uniform non-dendritic structure was obtained under the action of ultrasonic cavitation and flow, and the material exhibited strong yield strength.…”