INFLUENCE OF TITANIUM AND CARBON CONTENTS ON THE HYDROGEN TRAPPING OFMICROALLOYED STEELS

The presence of traps for hydrogen atoms influences the diffusivity an d solubility of hydrogen itself in steels. In the present work, permea tion measurements were carried out on hot-rolled microalloyed steels w ith different C and Ti contents in order to evaluate the number of irr eversible and reversible traps. The number per unit volume of irrevers ible traps was correlated to calculated volume fraction of Ti(C,N) pre cipitates. These results, combined with microstructural investigations by transmission electron microscopy (TEM), showed that the largest nu mber of irreversible traps was associated with steels having the large st volume fraction of fine and coherent Ti(C,N) precipitates. The reve rsible traps were associated with free Ti atoms, dislocations, and fer ritic grain boundaries. Theoretical calculations confirmed the hydroge n binding energy of Ti free atoms (-27.1 kJ/mol).