Dissolution Behavior of Delta Ferrites in Martensitic Heat-resistant Steel for Ultra Supercritical Units Blades

The dissolution behavior of delta ferrites in martensitic heat-resistant steel was studied. And the reason why the dissolution rate of delta ferrites decreased with dissolution time was discussed. The experimental results show that the chemical compositions of delta ferrites negligibly change with dissolution time. The decrease of dissolution rate of delta ferrites with dissolution time should be attributed to the change of shape and distribution of delta ferrites. The shape of delta ferrites tends to transfer from polygon to sphere with dissolution time, causing the decrease of specific surface area of delta ferrites. The distribution position of delta ferrites tends to transfer from boundaries of austenite grains to interior of austenite grains with dissolution time, decreasing the diffusion coefficient of alloy atoms. Both them decrease the dissolution rate of delta ferrites.