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Vol.49, No.3, 203 ~ 211, 2011
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| Title |
| Effect of Fine Copper Sulfides on the High Cycle Fatigue Properties of Bake Hardening Steels for Automotive |
| 강성규 Seong Geu Kang , 김진용 Jin Yong Kim , 최일동 Il Dong Choi , 이승복 Sung Bok Lee , 홍문희 Moon Hi Hong |
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| Abstract |
| Bake hardening steels have to resist strain aging to prevent the yield strength increment and stretcher strain during press process and to enhance the bake hardenability during baking process after painting. The bake hardening steels need to control the solute carbon and the solute nitrogen to improve the bake hardenability. Ti and/or Nb alloying for nitride and carbide precipitation and low carbon content below 0.003% are used to solve strain aging and formability problem for automotive materials. However, in the present study, the effect of micro-precipitation of copper sulfide on the bake hardenability and fatigue properties of extremely low carbon steel has been investigated. The bake hardenability of Cu-alloyed bake hardening (Cu-BH) steel was slightly higher (5 MPa) than that of Nb-alloyed bake hardening (Nb-BH) steel, but the fatigue limit of Cu-BH steel was far higher (45 MPa) than that of Nb-BH steel. All samples showed the ductile fracture behavior and some samples revealed distinct fatigue stages, such as crack initiation, stable crack growth and unstable crack growth. |
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| Key Words |
| metals, annealing, fatigue, transmission electron microscopy, TEM, BH steel |
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