Precipitation Control of Sigma Phase in Austenitic Heat-resistant Steels

2014 Fiscal Year Final Research Report

• Project/Area Number: 25630300
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Structural/Functional materials
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: TAKEYAMA Masao 東京工業大学, 理工学研究科, 教授 (30251622)
• Project Period (FY): 2013-04-01 – 2015-03-31
• Keywords: 相平衡 / 粒界析出 / tP30 / 相安定性 / Fe-Ni-Cr-Mo / Fe-Ni-Cr-Mn / 合金設計 / 固溶軟化

Outline of Final Research Achievements

Phase stability, phase equilibria and the precipitation behavior of σ phase, which has been considered as a detrimental phase, in carbon free Fe-Cr-Ni austenitic heat resistant steels have been examined, in order to seek its new possibilities as a strengthening spices. The stability of the σ phase in Fe-Cr-Ni ternary system increases by the addition of Mo and Mn. Especially, the thermodynamically stable σ phase increase by 300K by Mo addition. Proposed steels designed by newly created database revealed a unique microstructure having 90 % of the grain boundaries of the total grain boundaries are covered by the σ phase after prolonged aging at 1073 K. This result shows a possibility to have a excellent creep rupture strength of the steels by grain-boundary precipitation strengthening. In addition, the σ phase shows solid solution softening by the elements in solution, indicating that alloying can change the nature of σ phase.

Free Research Field

構造材料設計学