Hydrogen in microalloyed steels

To understand and control hydrogen induced cracking and stress corrosion cr acking, the processes of hydrogen absorption, diffusion and trapping are of interest. Fundamentals of these processes are described and of the determi nation of permeation coefficient, diffusivity and solubility of H in iron a nd steels, using the electrochemical double cell. With this method trapping parameters are also obtained, i.e. numbers of traps and binding energies. Extended studies were conducted on hydrogen in ternary alloys Fe-Me-C or N (Me = Ti, Zr, V, Nb, Mo) and in pipeline steels. Flat traps with binding en ergies around -19kJ/mol H can be discerned from deep traps with binding ene rgies around -57kJ/mol H. As shown by constant extension rate tests with th e pipeline steels, only the mobile hydrogen in ideal solution and in the fl at traps is involved in hydrogen induced stress corrosion cracking, not the hydrogen tied up in deep traps.