Effect of irradiation on creep-fatigue interaction of DIN 1.4948 stainless steel plate and welds at 823 K

The effect of irradiation on creep-fatigue interaction has been studied for DIN 1.4948 plate material and welded joints tested at 823 K. Creep exposure lasted up to 4100 h prior to low cycle fatigue testing, which was carried out at a total strain range of 0.6% and a strain rate of 3x10-3s-1 at 823 K. Unirradiated plate shows a total damage factor, D, of about 1.0, unirradiated welded joints show a total damage factor of about 0.85. Irradiated plate and welded joints give total damage factors below 0.5, using reference times-to-rupture. The reduction by irradiation is caused by the easy creep crack development resulting from helium embrittlement early in creep life. When using the time-to-rupture for plate material in irradiated condition for the total damage factor calculation the bilinear ASME approach forms a lower boundary for our experimental results. Welded joints neither in reference nor in irradiated condition satisfy the linear or the bilinear approach. The experimentally determined total damage factors of welded remain below the ASME proposed even when taking the time-to-rupture in irradiated condition for the calculations. The accelerated creep crack growth in the heat affected zone near the root weld pass gives the main contribution to the reduction of D-value by irradiation. (author)