Effect of Ultrasonic Treatment on the Solidification Microstructure of GCr15 Bearing Steel

Abstract

Ultrasonic treatment with various powers is introduced to liquid steel from the side wall of a mold during GCr15 steel solidification, and the effect of ultrasonic on the microstructure and properties of GCr15 steel is investigated. Results show that the columnar grains in the GCr15 steel are coarse and that the microstructure is inhomogeneous when ultrasonic is not applied on the liquid steel. A suitable power ultrasonic leads to the appearance of a large number of equiaxed grains and increases the uniformity of the microstructure. The segregation of alloy elements gradually decreases as the power increases from 0 W to 500 W. The maximum segregations of carbon and silicon decrease from 2.541 to 1.129 and 2.861 to 1.196, respectively. Given a power of 500 W, the statistical segregations of carbon and silicon decrease from 0.0964 to 0.0693 and 0.1152 to 0.1075, respectively. A further increase in ultrasonic power is not conducive for improving the element segregation. Ultrasonic treatment can remarkably refine the size of carbide and increase the uniformity of its distribution. When the powers are 0 W, 300 W, 500 W, 700 W, and 1,000 W, the average sizes of carbide are 14.63 μm, 2.96 μm, 3.05 μm, 3.72 μm, and 7.83 μm, respectively. The tensile strength, yield strength, and ductility and reduction of the area of the GCr15 bearing steel are correspondingly improved to varying degrees.

Keywords

• bearing steel
• ultrasonic
• element segregation
• carbide
• mechanical properties
• 64.70.kd