Effect of carbon content on strength and toughness of deposited metal for 1000 MPa-grade high-strength welding wire

Abstract

The microstructure and mechanical properties of the deposited metal of 1000 MPa-grade marine steel welding wire were observed and tested using characterization methods such as OM, SEM, TEM, XRD, and EBSD. The influence of carbon content (0.061–0.080 wt%) on the structure of the deposited metal was examined, with the strengthening and toughening mechanisms of the deposited metal elucidated. The results indicated that the deposited metal structure primarily consisted of lath bainite, martensite, and a small amount of retained austenite as the carbon content increased from 0.061 wt% to 0.080 wt%; the proportion of martensite increases, while bainite and retained austenite decrease. Additionally, the lath morphology changes from “interwoven” to “parallel.” The yield strength of the deposited metal increases from 915 MPa to 1007 MPa, while the impact energy at −50 ℃ decreases from 120 J to 59 J. The increase in martensite proportion contributed to the enhanced strength of the deposited metal. Solid solution and dislocation strengthening are the primary strengthening methods. The observation of the impact fracture section revealed that the bainite was segmented and refined. In contrast, the “intertwined” morphology of plate-striped bainite/martensite and high-angle grain boundaries hinders crack propagation, thereby improving the low-temperature impact toughness.