Effect of carbide precipitation on the creep behavior of alloy 800HT in the temperature range 700 degrees C to 900 degrees C

The creep behavior of alloy 800HT was studied at 700 degrees C, 800 degrees C, and 900 degrees C under stresses ranging from 30 to 170 MPa. Samples that were tested in the as-quenched condition after solution treatment exhibited longer creep life than those that were averaged before testing. This difference in creep life was found to increase at lower creep stresses at a given temperature. This phenomenon is attributed to the precipitation of M(23)C(6) carbides during the early stages of creep, which strengthen the material by exerting threshold stresses on moving dislocations and thereby reducing the creep rate. A model is developed to describe the influence of carbide precipitation during creep on the behavior of the material under different creep temperatures and stresses. Comparison with the experimental results shows that the model gives accurate predictions of the creep behavior of the material in the range of stresses and temperatures used in the present study. In addition to its predictive value, the model is useful in understanding the factors that affect the creep behavior of materials when precipitation of hard phases is taking place during creep. The strengthening effect of particle precipitation during creep, as represented by the value of the threshold stress, is shown to be a complex function of the supersaturation of the matrix, the applied creep stress, and the test temperature.