Report on NIMS-MPA Workshop

"NIMS-MPA Workshop on Long-term Strength and Reliability of High Cr Ferritic Creep Resistant Steels", co-hosted by our center and the Materials Information Technology Station: MITS †1, was held on Wednesday, March 17, 2004 in Conference Room 1 at the Sengen site of NIMS.

In October 2002, our center and MITS signed the Memorandum of Understanding with the State Materials Testing Institute at Stuttgart University in Germany (Staatliche Materialprüfungsanstalt: MPA †2) (November 2002 issue of NIMS NOW) with the purpose of promoting joint research regarding the assessment of the reliability and strength of structural materials. Since then, NIMS and MPA have hosted workshops alternatively to exchange information, with this one being the fourth workshop. At this workshop, there were 4 presentations from both NIMS and MPA, 2 each from Japanese and European industries, and a special lecture by Emeritus Professor Toshio Fujita from the University of Tokyo. In addition to NIMS and MPA, many active creep resistant steel researchers from all over the world including approximately 70 participants from Japan, Germany, Italy, Denmark, Finland, The United States, and Korea, came and took part in the active discussions.

At this workshop, opinions were exchanged on the main theme of “an assessment of long-term strength of high Cr ferritic creep resistant steel”. The modified 9Cr-1Mo steel which was developed in the United States during the early 1980’s and the modern 9-12% Cr ferritic steel (ASME P92, P122) which was later developed had better long-term creep strength than the existing ferritic creep resistant steels of that time. They contributed greatly towards improving the energy efficiency of thermal power generation plants and have been utilized as a high temperature structural component for more than 10 years. Therefore, the life extension and maintaining the reliability of the plants used beyond its original design life based on the precision life assessment have become important technological subjects. The low-stress and long-term creep strength, creep fatigue and microstructural degradation, several types of modeling and a prediction method of creep life or deformation behavior based on the optimization of some parameters of the high Cr ferritic creep resistant steel, such as the modified 9Cr-1Mo steel were discussed at this workshop. Strength evaluation of a welded joint, creep damage under multiaxial loading condition, an internal pressure creep test and life assessment of the components used in the plants for long term, and the mechanical strength of the full size components were also mentioned. Furthermore, the effects of heat treatment condition, chemical composition, and microstructure on the creep strength were summarized to come up with a guideline for designing materials with a much higher strength.

The extremely high potential that NIMS maintains, especially on the assessment of long term creep property and the design and development of heat resistant steel were verified at this workshop; however, there seemed to be a lot of points that could be learned from the researchers at MPA and Europe regarding the theoretical analysis based on the basic science of high temperature strength and the establishment of a prediction method for creep deformation.

 At the end of the workshop, Professor Toshio Fujita was asked to look back at his research career spanning a period of 50 years, which also outlined the history on the development of high Cr ferritic creep resistant steels. The workshop concluded with the professor’s words of encouragement that had a strong effect on us with an expectation towards the future development on the research on heat resistant steels.

To solve the energy and environmental problems, the high efficiency of thermal power plants has become an important topic throughout the world. The research on the development of heat resistant materials including high Cr ferritic steels is very active, especially in Japan and Europe, and it will become necessary for NIMS and MPA which constitute the core in this research, to promote the research in this field vigorously through collaborating in future workshops and by working hard within their respective institutes.

 (Heat Resistant Design Group, Yoshiaki Toda)

†1　Materials Information Technology Station  http://www.nims.go.jp/mits/english/E_index.htm
†2　Staatliche Materialprüfungsanstalt Stuttgart  http://www.mpa.uni-stuttgart.de/mpa_de/
†3　NIMS NOW 2002, vol. 11  http://www.nims.go.jp/jpn/news/nimsnow/2002-11/ (in Japanese)

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