|
Vol.44, No.2, 77 ~ 84, 2006
|
| Title |
| The Effect of Boron on the Microstructure and High Temperature Tensile Strength of 9Cr-1.5Mo Ferritic Steels |
| 홍석우 Suk Woo Hong , 송상민 Sang Min Song , 정우상 Woo Sang Jung , 정순효 Soon Hyo Chung , 권숙인 Sook In Kwun |
|
|
|
| Abstract |
| Effects of boron on the microstructure and high temperature tensile strength of 9Cr-1.5Mo ferritic steels were investigated. Three alloys having different boron content were manufactured by vacuum induction melting and electro-slag remelting. Boron was segregated in prior austenite grain boundary during normalizing treatment. And this boron were slowly diffused into the grain interior during tempering and aging at 700℃. Major precipitates in these ferritic steels are M23C6 and MX. However, FeMo2B2 was also precipitated in alloy containing 196 ppm. boron. FeMO2B2 phase was formed at prior austenite grain boundary and martensite lath boundary after 1,000 hours aging at 700℃. It was expected that the formation of FeMO2B2 are closely related to the redistribution of boron atoms. The growth rate of FeMO2B2 was higher than those of M23C6 and MX phase. The tensile strength in 9Cr-1.5Mo ferritic steels were increased by increase of boron contents in tempered condition. However, the tensile strength for alloy containing 196 ppm. boron was lower than that for alloy containing 144 ppm. boron after 3,000 hours aging at 700℃. This is due to the formation of FeMO2B2 and its rapid growth rate in alloy containing 196 ppm. boron. |
|
|
| Key Words |
| 9Cr-1.5Mo ferritic steels, Precipitation behavior, Boron effect, FeMo2B2 phase, Tensile strength |
|
|
 |
|
