13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Creep Crack Initiation and Growth Behavior in Weldments of high Cr steels Ryuji Sugiura 1,*, A. Toshimitsu Yokobori, Jr. 1, Kazuto Sato 1, Masaaki Tabuchi 2 Kenichi Kobayashi 3, Masataka Yatomi 4, Kamran Nikbin 5 1 Graduate School of Engineering, Tohoku University, Japan 2 NIMS, Japan 3 Chiba University, Japan 4 IHI Co., Ltd, Japan 5 Imperial College, London, UK * Corresponding author: sugiura@md.mech.tohoku.ac.jp Abstract W added high Cr ferritic heat-resistant steels have been developed as a boiler material. Most of boiler component structures are mainly fabricated by welding which are likely to the regions of crack initiation and propagation. However, the method of predicting the life of creep crack initiation and growth have not been clearly established for weldments of high Cr ferritic heat resistant material due to many factors such as the variation in micro-structures and the residual stress caused by welding and thermal cycles. In the present study, the experiments of creep crack growth using a circular notched round bar specimen with variation of notch location in HAZ were conducted and the characteristics of creep crack growth rate and creep crack initiation life were summarized in terms of Q* parameter, which has been proposed as fracture mechanics parameter to describe creep crack growth rate. Keywords Creep crack initiation, Creep crack growth, Weldment, High Cr steel, C* parameter, Q* parameter. 1. Introduction The W added high Cr ferritic heat-resistant steels have been developed as a boiler material. Most of boiler component structures are mainly fabricated by welding which are likely to the regions of crack initiation and propagation. However, the method of predicting the life of creep crack initiation and growth have not been clearly established for weldments of high Cr ferritic heat resistant material due to many factors such as the variation in micro-structures and the residual stresses caused by welding and thermal cycles. In the previous work, we have reported that creep crack grows initially in the oblique direction to the direction of initial notch with 45 degree as it approaches the site of minimum hardness region near the boundary between base metal (BM) and heat affected zone (HAZ) [1-3], as shown in Fig. 1, by conducting the tests using a C(T) specimen for P92 weldment. Correspondingly, the site of maximum value of stress multiaxiality shifts to the site of minimum hardness. This process was defined as the incubation process of creep crack growth. Therefore, we suggested that in order to predict the fracture life for weldment, it is important to clarify the incubation process and path on a structural mechanical basis in order correctly determine the incubation time of creep crack growth. In the present study, more detailed experiments of creep crack growth using a circular notched round bar specimen with variation of notch location in HAZ were conducted and the characteristics of creep crack growth rate and creep crack initiation life were summarized in terms of Q* parameter, which has been proposed as fracture mechanics parameter to describe creep crack growth rate. The present work is closely concerned with the Japanese result for the VAMAS Project and JSPS 129 Committee. 2. Creep crack growth test procedures The material used is W-added 9%Cr ferritic heat-resistant steel (ASME Code Case 2179, ASTM A335 P92) and its plate of 31 mm thickness, which was subjected to normalizing at 1343K for 2hr
RkJQdWJsaXNoZXIy MjM0NDE=