Research on the crack mechanism of electrodes for a high-alloyed martensitic valve steel

Abstract

The crack mechanism of electrodes for 9Cr18Mo martensitic valve steel has been analyzed in detail through calculation of phase diagram, in situ observation of high temperature microscope, thermal simulation of elevated-temperature tensile tests and estimation of steel melt solidifying time in the steel mold. The reason of cracks appearing on the surface of electrodes was given follows. There existed a certain amount of porosity in the center of electrodes. After casting completion, mold cooling time of the electrode was relatively short. Temperature of the electrodes was still kept in the temperature range of poor plasticity. When demolding, the cracks were easy to initiate near the porosity under the external mechanical stress. Martensitic transformation occurred during the course of air cooling after medium temperature annealing. The stress of phase transformation thus stimulated the propagation of cracks.