Investigation into Hydrogen Diffusion and Susceptibility of Hydrogen Embrittlement of High Strength 0Cr16Ni5Mo Steel

High strength bolt steel 0Cr16Ni5Mo was charged with hydrogen by means of electrochemical technique to evaluate the hydrogen diffusion behavior. The bolt steels were investigated by a combination of electrochemical hydrogen permeation, thermal desorption spectroscopy (TDS), slow strain rate test (SSRT) and microstructure observation. The hydrogen concentration of both 10.9 grade (R-m=950 1 150 MPa) and 12.9 grade (R-m=1 150 1 250 MPa) bolt steels increases with increasing the hydrogen charging current densities and charging time. The 12.9 grade bolt steel has higher apparent diffusion coefficient than 10.9 grade steel, corresponding to the value of 4.7x10(-7) mm(2)/s. By means of TDS tests, the activation energies of the two experimental steels are 17.74 kJ/mol and 18.92 kJ/mol, respectively. The hydrogen traps of both grade bolt steels are dislocations and crystal lattice. The notch tensile strength of the steels is reduced with the hydrogen concentration carried out by SSRT. The fracture morphologies of the steels after hydrogen charging present ductile dimple and quasi-cleavage characteristic.