Surface Quality and Microstructure of Welded Joint of 12Cr1MoV Steel by Ultrasonic Peening

Abstract

Abstract The Ferrite heat-resistant steel 12Cr1MoV is extensively used for structural applications in thermal power plants due to its good strength, weldability and long-term stability. The components often undergo fatigue loading, which leads to premature failure. In most cases, fatigue cracks usually initiate from the surfaces of structural components. Hence, surface strengthening treatment is a necessary procedure to improve fatigue performance. In general, ultrasonic peening is treated as an important means of improving fatigue properties. In this study, the effect of ultrasonic peening on the microstructure evolution of 12Cr1MoV steel in service was investigated. Work hardened layer and plastic deformation layer with nanocrystals were generated in the 12Cr1MoV surface after ultrasonic peening treatment. The nanocrystallization process of grains was deeply discussed. The variation of fatigue notch coefficient under different ultrasonic peening parameters was analyzed in detail. The results show that ultrasonic peening can optimize the geometry of the weld toe and reduce the fatigue notch coefficient. In addition, after the UIT1 parameter treatment, the depth of ultrasonic peening on the base material can reach about 220 um, and after the UIT2 parameter treatment, the depth of impact on the base material can reach about 250 um. Compared with the original sample, the hardness of UIT1 increases by 20% and UIT2 increases by 26% at the depth of 0.1mm. Grains are refined to about 200 nm in the topmost surface after ultrasonic peening treatment. The mechanism of nanocrystallization is mainly due to dislocation motion.