13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- Figure 1. Comparison of creep crack growth path, Vickers hardness and stress tri-axiality for weldment of P92 and tempering for 2hr, was prepared as a base metal (BM). The chemical composition is shown in Table 1. The welded joint (WM) was fabricated using multi-layer gas tungsten arc (GTA) welding with single bevel of 20° [4]. Welding consumable used for GTA welding was matching filler wire developed recently for welding this class of steel [5]. Finally, the post weld heat treatment (PWHT) was carried out at 1013K for 4hr. The process parameters of multi-layer GTA welding are given in Table 2 [4]. The specimen used was manufactured into a circular notched round bar specimen, as shown in Fig. 2. For the welded joint specimen, two kinds of specimen with variation in the notch location such as one located in the middle part of HAZ and the other in the interface of fine-grained HAZ and base metal in the region of HAZ were prepared, as shown in Fig. 2. Creep crack growth tests were performed using a lever arm creep testing machine of Type RT-30 manufactured by TOSHIN KOGYO. The test temperatures were kept at a specified temperature with the precision of ±2°C. The experimental conditions are shown in figures of experimental results. The crack length was measured by electrical potential method [6-8]. The creep crack growth tests were conducted based on ASTM E1457-07 [9] and JSPS standards [10]. 3. Characteristics of creep crack length and deformation The relationship between creep crack length Δa and non-dimensional time t/tf of each specimen for weldment is shown in Fig. 3. The relationship between load line displacement Δδ and non-dimensional time t/tf of them is shown in Fig. 4, where t and tf are the current time of load application and the life of creep crack growth for each specimen. From the creep crack initiation and growth tests, fracture lives for both specimens such as one located in the middle part of HAZ and the other in the interface of BM and fine-grained HAZ in the region of HAZ are the same and the characteristics of creep crack growth show the similar, as shown in Fig. 3. From these results mentioned above, even though notch was located in the lower hardness region, creep crack growth was found not to be immediately accelerated. This shows the possible presence of an incubation time of creep crack growth even if the notch was located in the interface between base metal and fine-grained HAZ in the region of HAZ, which corresponds to the region of minimum hardness. However, specimen with the notch located in the interface between base metal and fine-grained HAZ in the region of HAZ shows the ability to deform.
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