Abstract
Experimental measurements of kinetics of creep cavity elimination by annealing and compressive creep are reported for a 1.3Mn-0.5Mo-0.5Ni steel. Samples of the steel were crept to implant creep cavities in the grain boundaries. The mean cavity size and spacing were obtained after measuring approximately 200 cavities and used for theoretical sintering rate calculation. The samples were then annealed for 800h at 550-700°C and compressively crept for 400h under 59-235 MPa and at 550-600°C to make the cavities shrink, and the creep cavity sintering rates were monitored using the highly sensitive density measurement technique.
The results showed that sintering rates under compressive creep are rapid and depend proportionally on compressive creep rates, whereas annealing causes only slight sintering. Two models of diffusional and constrained cavity growth were applied for the calculation of sintering rate, and it was shown that the sintering rates calculated using the constrained cavity growth model coincides with the experimental data. This coincidence means that the contraction in the neighborhood of cavitied grain boundary due to the atom flow from grain boundary to cavity surface during sintering is costrained by the adjoining grain, causes local tensile strain in the neighborhood, and decreases the sintering rate drived by surface energy of creep cavity. Therefor it was indicated that the local tensile strain must be removed by compressive creep in the adjoining grains for progressive sintering.
