Materials Transactions Online

Materials Transactions, Vol.57 No.12 (2016) pp.2097-2103
© 2016 The Japan Institute of Metals and Materials

Creep Rupture Strength for Weld Joint of 23Cr-45Ni-7W Alloy

Kyohei Nomura1, Keiji Kubushiro1, Hirokatsu Nakagawa2 and Yoshinori Murata3

1Research laboratory, Materials Development, IHI Corporation, Yokohama 235-8501, Japan
2Boiler Design Department, Energy System Center, Energy & Plant Operations, IHI Corporation, Tokyo 135-8710, Japan
3Department of Materials, Physics and Energy Engineering, Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan

The creep rupture strength and the degradation mechanism of 23Cr-43Ni-7W alloy weld joints were investigated using creep rupture tests and microstructure observation of the ruptured specimens. The creep rupture tests were conducted at 973, 1023, and 1073 K at stresses from 80 to 180 MPa. The creep strength of the weld joints was higher than that of the base metal. The ruptured area of every specimen was over 10 mm away from the bond line. The microcracks increased gradually up to 10 mm from the bond line, beyond which they suddenly increased. In the grains, traces of M23C6 were observed near the bond line, and the sizes of the M23C6 deposits increased further away from the bond line. But the size of the Laves phase was constant in every observed area. On the grain boundary, the grain boundary shielding ratio by precipitates was constant until 10 mm from the bond line, beyond which it decreased. These observations show that the creep strength near the bond line is higher than that of the base metal because of both precipitation strengthening in the grain and grain boundary.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 79 (2015) 348-355.

[doi:10.2320/matertrans.M2016242]

(Received 2016/06/30; Accepted 2016/09/05; Published 2016/11/25)

Keywords: advanced-ultra super critical (A-USC), HR6W, weld joints, creep strength, microstructure, heat-affected zone, precipitation strengthening, carbides, Laves-phase

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