"The Effect of Precipitates Control & Grain Boundary Strengthening in Ultra-Low Carbon Steels "

by "Lin Hsu, Po-Yu Chen, Ming-Chin Tsai, Hsin-Yi Lee, I-Ching Hsiao "

Publisher - "China Steel Corporation, Kaohsiung, Taiwan(R.O.C). "

Category - Engineering & IT

"Ultra-low carbon (ULC) steels are well-known for superior formability but relatively low strength due to a lack of strong solid solution hardening by carbon solutes. The common strengthening mechanisms of ULC steels are thus suggested to be precipitation strengthening and grain size effect. In this study, we investigated the effect of grain boundary strengthening in ULC steels by controlling the morphology of precipitates through various heating conditions. The evolution of size and distribution of these precipitates in each stage were explored to estimate the pinning effect which can not only refine the grain size but also improve the performed strength. The results showed that in slab stage different types of precipitates including MnS, TiN and AlN often aggregate with each other. When the slab was reheated to 1100°C, the aggregated precipitates maintained the same morphology at the slab stage and the consequent grain size of hot-rolled sheet was coarse. On the other hand, as the slab was reheated to 1250°C, those precipitates dissolved but re-precipitated during the following hot rolling process. In the latter condition, those precipitates were dispersed separately and performed as effective obstacles for grain growth which leading to significant grain refinement hardening. "

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