Investigations on the nanocrystallization of 40Cr using ultrasonic surface rolling processing

Ultrasonic surface rolling processing (USRP) was applied on quenched and tempered 40Cr. Microstructure observations of USRP specimen surface indicate that the processing can both get nano-structured layers, with grain size of 3–7 nm, and reduce the surface roughness to 0.05 μm. Life of the rolling processing tip is about 800 times longer than the fixed one, which makes the processing practical and economical. Tests of mechanical properties show that microhardness of USRP specimen surface was increased by 52.6%; residual compressive stress can reach −846 MPa. It has been determined by contrast wear test that USRP can reduce friction coefficient and improve the wear-resistant property.