Effect of ultrasonic vibration and deep cryogenic treatment on the residual stress, mechanical properties and microstructures of HR-2 austenitic stainless steel

This study proposes a new aging treatment method, namely composite deep cryogenic treatment and ultrasonic vibration. Several different aging treatment methods were compared, including untreated, cryogenic treatment, ultrasonic vibration, and cryogenic treatment+ultrasonic vibration. The evolution of the microstructure, mechanical properties, stress relaxation mechanism, and strengthening mechanism of hydrogen resistant steel has been systematically revealed. The results showed that the specimen under cryogenic treatment and ultrasonic vibration had the highest hardness (98.3HRB) and exhibited a good match of high strength (423.46 MPa) and high elongation (46.51%). This is attributed to the reduction in grain size and the strengthening effect of precipitates. After cryogenic treatment and ultrasonic vibration, the surface residual stress and internal residual stress were well relaxed. Compared with no treatment, the surface residual stress and internal residual stress of the sample were reduced by 52% and 84% respectively after cryogenic treatment and ultrasonic vibration. The evolution of dislocations promotes the release of elastic potential energy, leading to stress relaxation. In addition, X-ray phase analysis shows that aging treatment will not cause phase transformation in hydrogen resistant steel.