D. Jandova, J. Kasl, V. Kanta

Trial weld joints of creep resistant steels (grade P22, P91 and P92) underwent creep testing in temperature range from 525 to 650 °C and stress range from 40 to 240 MPa. Filler metals of the dissimilar weld joint of P91 and P22 steel were on the base of low alloyed P22 steel. Creep strength was evaluated in dependence on Larson-Miller parameter. Fractography and extended metallography including SEM, STEM and EDX microanalysis were carried out. Causes of creep failure occurrence in specific regions of weld joints were elucidated on the base of different precipitation reactions and structure recovery in individual zones of weldment. Type I and II cracking occurred in similar weld joint of P91 steel pipes and dissimilar weld joint of P91 and P22 steel pipes; in the dissimilar weld at low stresses and relatively high temperatures, while in similar weld at high stresses and low temperatures. Dissimilar weld joint ruptured in low alloyed base material after creep at high stresses and low temperatures. Type IV cracking of similar pipe P91 steel weld joint was observed at high stresses and low temperatures. Type IV fractures of similar pipe P92 steel weld joint and similar cast P91 steel weld joint occurred within almost the whole stress and temperature ranges. One exception of failure concentration in the weld metal was detected in the cast steel weld joint after creep at the highest temperature and under the lowest stress. This was caused by precipitation of coarse Laves phase particles on the surface of small oxide inclusions.

Creep strength

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