| Title |
Effect of the solidification Rate and Deformation Condition on the Micro - Structures in 12 % Chromium Rotor Steel |
| Authors |
강석봉(Suk Bong Kang); 최재영(Jae Young Choi); 이래성(Nae Sung Lee) |
| Abstract |
The influence of solidification rates on the morphology and distribution of δ-ferrite and eutectic niobium carbides was studied using Bridgman-type unidirectional solidification apparatus in order to simulate the solidification pattern of a large-scale ingot of 12% chromium rotor steel. The volume fractions of the δ ferrite contained in the specimens solidified with the withdrawal speeds of 225 ㎜/hr, 45 ㎜/hr, and 4.5 ㎜/hr were measured to be 7%, 5%, and 30% respectively. δ-ferrite was finely distributed in the case of the withdrawal speeds of 225 ㎜/hr and 45 ㎜/hr, but the distribution was coarse network type in the case of the withdrawal speed of 4.5 ㎜/hr. When hot compressive working was applied in temperatures from 950℃ to 1250℃, 3-ferrite was transformed into carbides and austenite at the interface of δ-ferrite with the matrix. Subsequent heat treat melts result in a complete annihilation of δ-ferrite in the case of fast withdrawal speeds, but result in only a partial annihilation in the ca -e of the slow withdrawal speed, 4.5 ㎜/hr. |