Abstract
An investigation has been carried out to establish the effect of microstructures on the diffusivity and solubility of hydrogen in steels for prestressed concrete by means of the electrochemical permeation technique. The results obtained are as follows:
1) The diffusivity in PC steel-Type A is low when it has as quenched martensitic structure and low temperature tempered martensite. Then, it increases with increasing tempering temperature. The mixed structure of ferrite and lammellar pearlite gives a higher diffusivity than the tempered spheroidal pearlite. In the case of PC steel-Type B, the minimum diffusivity is obtained when the steel is tempered around 300°C, and the diffusivity increases with tempering temperature.
On the other hand, the solubility of hydrogen show an opposite tendency with respect to microstructures.
2) The hydrogen trapping in Type A steel occur predominantly at the lattice imperfections, such as dislocations and faults introduced by martensitic transformation, while those in Type B steel occur predominantly at the interface between the precipitated fine cementites and ferrite matrix.
3) The diffusivity does not depend on the cathodic current density but solubility of hydrogen increases up to a certain extent with cathodic current density for both steels, while the hydrogen permeation efficiency decreases with cathodic current density.
4) The activation energy for hydrogen diffusion in both type of the tempered pearlitic steels in the temperature range of 6 to 57°C is approximately 9.1kcal/mol. The heat of solution of hydrogen in both Type A and Type B steels also show the same value; about -13kcal/mol.
