Effect of welding conditions and martensite-austenite (MA) constituents on CTOD in 690 MPa high-strength heavy plate steel

This article analyzes the influence of martensite-austenite (MA) constituents on the crack tip opening displacement (CTOD) values of high-strength heavy plates with a thickness of 210 mm under varying welding conditions. Firstly, quenching and tempering treatments significantly improved the segregation of elements in the steel, resulting in minimal differences in microstructure and mechanical properties throughout the thickness. The results indicated that the CTOD values at −10 °C for the base material, steel with heat inputs of 10 kJ/cm and 30 kJ/cm, and post-weld heat treatment (PWHT) steel with heat inputs of 30 kJ/cm were 1.37 mm, 0.12 mm, 0.09 mm, and 0.39 mm, respectively. The study revealed a high concentration of carbon atoms at the boundary of the MA constituent. PWHT enhances the CTOD value of steel by promoting the shrinkage and spheroidization of MA constituents. Observations indicate that the slip system of the microstructure near the secondary crack needs to be adjusted to {110}<111> to accommodate deformation caused by the influence of MA constituents. The accumulation of dislocations near the MA constituent results in differences in geometrically necessary dislocation (GND) density between the {110}<111> and {112}<111> slip systems. Additionally, the measured elastic modulus ( E ) and intrinsic hardness ( H 0 ) were 305 GPa and 4.21 GPa for the MA constituents, and 234 GPa and 3.3 GPa for the matrix, respectively. By integrating the Crafft, Dewsnap, and elastic-plastic fracture mechanics (EPFM) models, the CTOD value exhibits a linear relationship with the average distance between MA constituents.