The effect of heat treatment on the microstructure and the corrosion resistance of Zircaloy-4 in 450°c steam

The effect of beta treatment and the subsequent cold work and alpha annealing on the microstructure and corrosion resistance of Zircaloy-4 in 450°C steam was investigated. The distribution of second-phase particles in test specimens were found to be not uniform and the effect of cold work and alpha annealing was the growth and redistribution of second-phase particles. By using SEM-EDX, the particles were identified as Zr-Fe-Cr and Zr-Fe. One cycle of the cold work and alpha annealing process improved the uniform corrosion resistance but enhanced the nodular corrosion. The difference was explained by a nodular growth mechanism which was related to the distribution of second-phase particles, the build-up of hydrogen pressure, the weakening of oxide after rate transition, and crack propagation along grain boundaries.