Effect of Heat Treatment on Hydrogen Diffusion Behavior of Process Pipe Steel

Abstract

The influence of heat treatment on the HIC susceptibility in process pipe steel was investigated with respect to the hydrogen diffusion behavior by employing the electrochemical permeation technique. This study clearly shows that, contrary to other microstructures, in acicular ferrite, iron carbide (Fe3C) particles are newly precipitated mostly along the grain boundaries by the simulated PWHT conducted at 620 degrees C for one hour. In addition, a decrease in hydrogen diffusivity attributed to the hydrogen trapping effect by the Fe3C leads to an increase in apparent solubility. As a result, heat-treated process pipe steel is more susceptible to HIC.