Hydrogen Permeation Behaviors of Microalloyed TRIP-assisted Annealed Martensitic Steels

In this paper a serials of TRIP-assisted annealed martensitic（TAM） steels had been obtained through niobium,vanadium and/or titanium microalloying additions into a base chemistry of 0.2%C-1.5%Si-2.0%Mn,and a complex heat cycles of double quenching+tempering processes.From the hydroden charging curves microalloyed precipitates have significant effects on delaying/retaining the hydrogen diffusion through steel matrixs.Hydrogen charging test results indicates that when microallying additions are at silimar level,Nb microalloying steel has the lowest apparent hydrogen diffusive index D_a=0.716×10^-7 cm²/s,Ti steel with moderate D_a=1.136×10^-7 cm²/s,while value is 2.647×10^-7 cm²/s for 0.052%V steel.However,all these values are far lower than that of refered steel with its D_a=4.215×10^-7 cm²/s.For V-microalloyed steels,the SSRT results show that the hydrogen induced ductility loss ID is 76.2% for 0.2%V steel,compared with 86.5% for V-free steel.The trapping mechanism of the steel containing different V contents is analyzed by means of TDS and TEM observation.It is found that the steel containing 0.2%V can create much more traps and higher activationenergy for hydrogen trapping compared with V-free steel,which is due to VC as hydrogen traps capturing hydrogen.The relationship between hydrogen diffusion and hydrogen trapping mechanism is discussed in details.