Effects of Ultrasonic Impact Treatment Time on Surface Structure Refinement and Properties of 17CrNiMo6 Steel

Abstract

Ultrasonic impact treatment(UIT) was used for surface enhancement of 17CrNiMo6 steel. The effects of UIT time on the hardness, surface residual compressive stress and the surface structure refine ment were analyzed. Microstructure distribution of the structure refined layer was studied. The results show that, unprocessed material surface residual stress is about -223.7MPa, hardness is about 650HV, grain size is about 8-10μm. After UIT for 60s, surface residual compressive stress is about -463.4MPa, grain size is about 1-1.5μm within 5-10μm in depth, the depth of grain refined layer is about 250μm whereas. with UIT for 120s, surface residual compressive stress is about -587.2MPa, grain size is about 200-300nm within 5-10μm in depth, the depth of grain refined layer is about 250μm. Surface plastic deformation is greatly enhanced by ultrasonic impact treatment,high-density dislocation is produced under the high strain rate, high rotational speed and cyclic shear in large size gain, grain boundary density is greatly improved, and dislocation movement and grain rotation is accelerated.

Keywords

• ultrasonic impact treatment
• 17CrNiMo6 steel
• surface structure refinement
• microstructure