SINTERING RATE OF CREEP CAVITIES IN HEAT RESISTING STEEL

Experimental measurements of kinetics of creep cavity elimination by a nnealing and compressive creep are reported for a 1.3Mn-0.5Mo-0.5Ni st eel. 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 sinteri ng rate calculation. The samples were then annealed for 800h at 550-70 0-degrees-C and compressively crept for 400h under 59-235 MPa and at 5 50-600-degrees-C to make the cavities shrink, and the creep cavity sin tering rates were monitored using the highly sensitive density measure ment technique. The results showed that sintering rates under compress ive creep are rapid and depend proportionally on compressive creep rat es, whereas annealing causes only slight sintering. Two models of diff usional and constrained cavity growth were applied for the calculation of sintering rate, and it was shown that the sintering rates calculat ed using the constrained cavity growth model coincides with the experi mental data. This coincidence means that the contraction in the neighb orhood of cavitied grain boundary due to the atom flow from grain boun dary 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 com pressive creep in the adjoining grains for progressive sintering.