Abstract: Hydrogen (H) was charged into SA508-3 steel by high-pressure thermal charging method. The J-integral method was used to compare the fracture toughness of the H-charged and uncharged SA508-3 steels at different loading rates, and the effect of H on the fracture toughness of SA508-3 steel was investigated. The results indicate that at the same loading rate, the fracture toughness of the H-charged SA508-3 steel is obviously lower than that of the uncharged, and the fracture of the H-charged steel shows a mixing of ductile and brittle morphologies. With the decrease of loading rate, the loss of fracture toughness increases, the area of quasi-cleavage increases, and the brittleness increases. Under the action of three-direction stress, the interaction energy between H and hydrostatic stress is greater than that between H and mobile dislocation, and the hydrostatic stress is easier to capture H. In the process of fracture toughness test of SA508-3 steel, the three-direction stress can induce and promote H to enrich at the interface between the carbide and the matrix at the crack tip, thus reducing the bond strength between the carbide and the matrix and weakening the ability to hinder crack growth, so the fracture toughness of steel decreases after H charging. With the decrease of loading rate and the increase of the time of three-direction stress acting on the crack tip, the concentration of H at the carbide/matrix interface increases, the hydrogen pressure increases, so the crack growth is promoted and the brittleness of the steel increases, and the fracture toughness loss increases.

Key words: SA508-3 steel, loading rate, hydrogen, fracture toughness