Effect of content of impurites and PWHT conditions on creep embrittlement cracking of Cr-Mo steels

摘要

Creep embrittlement cracking was examined with regard to 1Cr- 1/2 Mo and 1.25 Cr- 1/2 Mo steels used in four actual reactors. Cracks were found in three reactors. Intergranular cracks were developed through coarse grain of welding heat affectedzones in the above equipment (HAZ materials). Also, cracking tends to occur in materials containing high impurity elements and depends on PWHT conditions. A SERT test (strain rate 1 % / h ) was conducted to evaluate creep embrittlement sensitivity.It was clarified the limit of creep embrittlement damage could be arranged satisfactorily by means of PWHT conditions, impurity content and grain size. From the results obtained, it is presumed that creep embrittlement cracking can be reduced due todecrease of grain strength by increasing of PWHT temperature and holding time even when the material contains higher degree of impurities.