Investigation on surface integrity and process parameter optimisation of carburised 18CrNiMo7-6 steel by induction-heating-assisted ultrasonic surface rolling process

The purpose of induction-heating-assisted ultrasonic surface rolling process is to introduce the temperature field into the ultrasonic surface strengthening process of materials and use the influence of heating temperature on the mechanical properties and microstructure of the material so that a surface-modified layer with improved performance can be obtained. Many studies on the ultrasonic surface rolling process have been conducted at room temperature. In this study, the effect of temperature on the surface integrity of carburised 18CrNiMo7-6 steel after ultrasonic surface rolling process was studied by induction heating. Compared with the result of ultrasonic surface rolling process at room temperature, below 250(degrees)C, with the increase of heating temperature, the residual compressive stress and residual compressive stress depth of the sample increase continuously. The maximum surface residual compressive stress and residual compressive stress depth can be obtained at 250 C-degrees, the surface residual compressive stress increases by 29%, and the residual compressive stress depth increases from 1700 to 2450 mu m. The surface hardness of the sample also shows an increasing trend when the heating temperature is from 100 to 250 C-degrees, and the hardness influence layer increases with the increase of heating temperature. The minimum surface roughness can be obtained by ultrasonic surface rolling process at 100 C-degrees. In addition, the induction-heating-assisted ultrasonic surface rolling process parameters are optimised by grey correlation analysis method, and the optimum process parameters to achieve the best surface integrity are obtained as follows: static pressure of 400 N, rotation speed of 50 r/min, feed rate of 0.04 mm/r, and heating temperature of 250 C-degrees. The order of significance of influence on surface integrity is static pressure > rotation speed > feed rate >heating temperature. The conclusion has a certain guiding significance for the anti-fatigue manufacturing of materials.