The key metallurgy for improving long-term creep strength of base metal and welded joints at 650oC is presented for martensitic 9Cr steel with emphasis on microstructure stabilization near prior austenite grain boundaries by boron. Boron stabilizes fine distributions of M23C6 carbides along prior austenite grain boundaries in a 9Cr-3W-3Co-0.2V-0.05Nb steel for up to long times during exposure at 650oC, which increases the creep strength at low stresses and long times. The addition of boron and nitrogen without any formation of boron nitrides during normalising heat treatment exhibits not only much higher creep rupture strength of base metal than conventional martensitic steels Gr.91, Gr.92 and Gr.122 but also substantially no Type IV fracture in welded joints at 650oC. This is a new martensitic 9Cr steel MARBN (martensitic 9Cr steel strengthened by boron and MX nitrides), which contains 120 to 150 ppm boron and 60 to 90 ppm nitrogen.
Fujio Abe is a Research Fellow at the National Institute for Materials Science (NIMS), Japan. He received his B.E. degree from Iwate University and his M.E. and D.E. degrees from Tohoku University. He has been working at the National Institute for Materials Science (formerly, National Research Institute for Metals) since 1978. His main field is creep strength and microstructure of heat-resistant steels and alloys at elevated temperature. After retirement from NIMS at the end of March 2010 (60 years old), he was re-employed at the beginning of April 2010 as a Senior Scientist (Research Fellow). He is still continuing his research activities at NIMS. He was awarded the August-Thum Commemoration Medal from Darmstadt University of Technology, Germany in 2005 and the Carl von Bach Commemoration Medal from MPA Stuttgart, Germany in 2014. He was also awarded several academic achievement medals by the Iron and Steel Institute of Japan and the Japan Institute of Metals.
DATE: Friday, 14 October 2016
VENUE: MSG-025 MSSI Building Extension
TEA/COFFEE WILL BE AVAILABLE AT 11h45
For further information, please contact: email@example.com