Hydrogen effect on 2.25Cr–1Mo–0.25V bainitic steel under aging heat treatment

Abstract

In the present work, the mechanical properties and hydrogen interaction with microstructures obtained after thermal treatment of a 2.25Cr–1Mo–0.25V bainitic steel were investigated. The samples were heat-treated under two different conditions simulating shop-repairs and manufacturing procedures of reactors. The microstructures after each heat treatment showed MC, M2C, and M7C3 carbides, characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The hydrogen diffusivity values after the first permeation for both conditions were 4.2 × 10−11 m2s−1 and 8.6 × 10−11 m2 s−1, and the solubility was 7.4 molHm−3 and 5.3 molHm−3, showing the influence trapping in the behavior of permeation curves. The TDS results indicate that a greater hydrogen trapping capability can be achieved with one of the studied conditions. Tensile testing of the hydrogenated and heat-treated samples, showed that the number of heat treatment cycles has a strong influence on the loss of ductility, which is mainly due to carbide growth and coalescence.