Hydrogen in trapping states harmful and resistant to environmental degradation of high-strength steels

Abstract

This chapter intends to separate and extract the harmful and resistant trapping states of hydrogen in high-strength steels to the degradation, and clarify the trapping sites corresponding to the two hydrogen trapping states. The degree of the environmental degradation of mechanical properties is measured as a decrease in maximum stress and plastic elongation during the application of tensile stress by using the slow strain rate tensile (SSRT) technique. The 350°C specimen and 550°C-85%-specimen for SSRT tests are processed to 3 mm in diameter and 20 mm in gauge length. The 350°C-specimen is mounted on the SSRT test apparatus immediately after occluding peak 1 hydrogen. The 350°C occludes only the peak 1 hydrogen desorbed at the temperature of 120°C. The 550°C-85%-specimen occludes both peak 1 and peak 2 hydrogen desorbed at 120 and 370°C respectively. This difference in hydrogen desorption peaks is believed to be due to the trapping states of peak 1 and peak 2 hydrogen. The maximum stress and strain of the 350°C decreases with increasing immersion time. Decrease in the maximum stress and strain ceased after specimen immersion for 3 h.