ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Regular Article
Carbonitride Dissolution and Austenite Grain Growth in a High Cr Ferritic Heat-resistant Steel
Xingang TaoJianfeng GuLizhan Han
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2014 Volume 54 Issue 7 Pages 1705-1714

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Abstract

Dissolution of carbonitrides and growth of austenite grain in X12CrMoWVNbN10-1-1 steel under various austenitizing conditions were investigated. The experimental results showed that the carbonitrides existing in after-forging heat treated state were mainly Cr23C6 and small amounts of NbN and Cr2N. However, Cr23C6 and Cr2N precipitates were dissolved completely after austenitization at 1070°C for 60 min or at 1200°C for 15 min, only the NbN particles left. The state of dissolution of NbN particles was also studied in detail as a function of austenitization holding time (tA) at different temperatures. Initially, the NbN particles dissolved with increasing tA at 1070°C. When tA reached over 360 min, the amount of NbN remained approximately constant. On the contrary, during the process of austenitization at 1010°C, no NbN particles dissolved into matrix. Starting from the fine and uniform grains, abnormal grain growth was observed after austenitizing at 1010°C for 960 min or at 1070°C for 180 min due to the heterogeneous distribution of NbN particles. The plot of grain size against tA indicated that the NbN particle with mean diameter of 117 nm and volume fraction of 3.1×10–4 would be sufficient to inhibit the austenite grain size effectively. Finally, the EBSD measurements demonstrated that the high energy grain boundaries whose misorientation range is 20–45° might be responsible for abnormal grain growth.

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© 2014 by The Iron and Steel Institute of Japan
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