Abstract
The effect of γ-HCR conditions on microstructures and mechanical prorerties of Si-Mn, Nb and Ti bearing steels were investigated. Here, γ-HCR is defined as hot charge rolling in which casted slab is charged into furnace at austenite(γ) state. The results are summarized as follows.
(1) Si-Mn steel produced by γ-HCR and cold charge rolling has almost the same mechanical properties. On the contrary, Nb and Ti bearing steels produced by γ-HCR has significantly mixed grain size structure and low toughness.
(2) The increase in charging temperature, increase in heating temperature and reduction of heating time in γ-HCR process lead to increase in strength and microstructural refinement in Nb and Ti bearing steels.
(3) Increase in rolling start temperature in γ-HCR process leads to microstructural refinement and improvement of toughness in Nb and Ti bearing steels.
(4) The amount of precipitates prior to rolling decreases in accordance with the change on γ-HCR conditions as mentioned in (2). Precipitates prior to rolling retard the recrystallization of as-casted coarse grain. From these results, (2) was explained.
(5) In the case of applying γ-HCR process to micro-alloyed steel plates, it is important to charge the slab at high temperature, beet for short time and start rolling from the temperature above 1100°C with high one pass reduction such as 20%/pass.
