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Title: Microstructure evolution during service exposure of two cast, heat-resisting stainless steels - HP-Nb modified and 20-32Nb

Abstract

The repair weldability of two types of heat-resistant austenitic stainless steel castings, HP-Nb modified alloys and 20-32Nb alloys, has been evaluated after extended service exposure of these materials at temperatures on the order of 815 deg. C (1500 deg. F). The initial part of this investigation has focused on characterization of the microstructure of these alloys after service exposure times of up to 12 years. Microstructure evolution from the as-cast condition to the service-exposed condition is described. In the as-cast condition, both eutectic NbC and Cr-rich M{sub 7}C{sub 3} carbides were observed in the HP-Nb alloys. In contrast, only eutectic NbC carbides were present in the as-cast 20-32Nb alloys due to a significantly higher atomic ratio of Nb/C as compared to the HP-Nb alloys. In the service-exposed condition, an Ni-Nb silicide and Cr-rich M{sub 23}C{sub 6} were identified in both alloys. The HP-Nb alloys exhibited a much higher total volume fraction of microconstituents than the 20-32Nb alloys and the M{sub 23}C{sub 6} phase was more prevalent than Ni-Nb silicide. In contrast, the Ni-Nb silicide was dominant in the service-exposed 20-32Nb alloys. This difference resulted in a significant increase in the repair welding liquation cracking susceptibility of the 20-32Nb service-exposed alloy.

Authors:
 [1]
  1. Industrial, Welding and Systems Engineering Department, The Ohio State University, 1248 Arthur E Adams Dr, Columbus, OH 43221 (United States)
Publication Date:
OSTI Identifier:
21140752
Resource Type:
Journal Article
Journal Name:
Materials Characterization
Additional Journal Information:
Journal Volume: 59; Journal Issue: 8; Other Information: DOI: 10.1016/j.matchar.2007.08.029; PII: S1044-5803(07)00310-5; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1044-5803
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AUSTENITIC STEELS; CRACKING; EUTECTICS; HEAT; MICROSTRUCTURE; NIOBIUM ALLOYS; NIOBIUM CARBIDES; SILICIDES; STAINLESS STEELS; TEMPERATURE RANGE 1000-4000 K; WELDABILITY; WELDING

Citation Formats

Shi, S., and Lippold, J C. Microstructure evolution during service exposure of two cast, heat-resisting stainless steels - HP-Nb modified and 20-32Nb. United States: N. p., 2008. Web. doi:10.1016/j.matchar.2007.08.029.
Shi, S., & Lippold, J C. Microstructure evolution during service exposure of two cast, heat-resisting stainless steels - HP-Nb modified and 20-32Nb. United States. doi:10.1016/j.matchar.2007.08.029.
Shi, S., and Lippold, J C. Fri . "Microstructure evolution during service exposure of two cast, heat-resisting stainless steels - HP-Nb modified and 20-32Nb". United States. doi:10.1016/j.matchar.2007.08.029.
@article{osti_21140752,
title = {Microstructure evolution during service exposure of two cast, heat-resisting stainless steels - HP-Nb modified and 20-32Nb},
author = {Shi, S. and Lippold, J C},
abstractNote = {The repair weldability of two types of heat-resistant austenitic stainless steel castings, HP-Nb modified alloys and 20-32Nb alloys, has been evaluated after extended service exposure of these materials at temperatures on the order of 815 deg. C (1500 deg. F). The initial part of this investigation has focused on characterization of the microstructure of these alloys after service exposure times of up to 12 years. Microstructure evolution from the as-cast condition to the service-exposed condition is described. In the as-cast condition, both eutectic NbC and Cr-rich M{sub 7}C{sub 3} carbides were observed in the HP-Nb alloys. In contrast, only eutectic NbC carbides were present in the as-cast 20-32Nb alloys due to a significantly higher atomic ratio of Nb/C as compared to the HP-Nb alloys. In the service-exposed condition, an Ni-Nb silicide and Cr-rich M{sub 23}C{sub 6} were identified in both alloys. The HP-Nb alloys exhibited a much higher total volume fraction of microconstituents than the 20-32Nb alloys and the M{sub 23}C{sub 6} phase was more prevalent than Ni-Nb silicide. In contrast, the Ni-Nb silicide was dominant in the service-exposed 20-32Nb alloys. This difference resulted in a significant increase in the repair welding liquation cracking susceptibility of the 20-32Nb service-exposed alloy.},
doi = {10.1016/j.matchar.2007.08.029},
journal = {Materials Characterization},
issn = {1044-5803},
number = 8,
volume = 59,
place = {United States},
year = {2008},
month = {8}
}