Hydrogen evolution of Cu precipitation 780 MPa grade steel HAZ with consideration of its cold cracking susceptibility

Abstract

The Cu precipitation 780 MPa grade steel has higher resistance to cold cracking than the conventional steels. To study this, we have investigated the hydrogen evolution characteristics of the Cu steel heat-affected zone (HAZ) by the thermal desorption spectroscopy method and compared with those of conventional 780 MPa steel HAZ. The thermal cycle tests were conducted to obtain the HAZ microstructures, and the peak temperatures were selected from 500 to 1400 °C at intervals of 100 °C. Hydrogen was then charged, and the hydrogen evolution curves were measured at a heating rate of 100 °C/h. The results show that the amounts of hydrogen released from the specimens whose peak temperatures of the thermal cycle tests were 1000 °C or higher are lower, while the results of the conventional steels have the opposite tendency. We numerically calculated the hydrogen evolution curves to determine physical constants, and using these constants, we also calculated the hydrogen concentration profiles of the y-groove weld cracking test and found that the hydrogen concentration of the Cu steel HAZ near the fusion line tends to become lower than those of the conventional steel HAZ. This phenomenon is considered one of the reasons for the higher cold cracking resistance of the Cu steel.