Effect Of Hot Rolling Reduction On Microstructure And Mechanical Properties In Hot Rolled High-strength Strip

The vigorous development of industry has created a great demand for environment-friendlymaterial. And hot rolled strip with improved strength and ductility and good formability has beenselected as one of the most promising candidates for cold rolled sheet in order to maximizeenergy conservation as well as minimize gas emissions.Firstly, an appropriate chemical composition with low carbon and titanium contents wasdesigned, and then5hot rolled strips with rolling reduction ranged from95.5%to97.5%wereprepared through controlling rolling and controlling cooling process in Compact Strip Productionline in the present work. Then96.5%and97%hot rolled strips exhibited superior mechanicalperformance due to the comprehensive effect of grain refinement and precipitation strengthening.In addition, it turned out that the experimental hot rolled strips reached the leading level of yieldstrength under the same thickness condition in the world, of which yield strength is in excess of730MPa.Secondly, the microstructure observation of experimental hot rolled strips showed thatferrite grain refinement can be obtained by increasing the hot rolling reduction, and that the sizeof precipitates can be obviously fined when increasing the hot rolling reduction from95.5%to97%, while it enlarged slightly when the cumulative reduction ratio reached97.5%. Meanwhile,the orientation of ferrite grain was mainly {012},{011},{112} and {221} parallel to the rollingplane when ferrite nucleated in the precipitates, by which the strength enhancement of ferritegrain can be achieved.Finally, the Charpy-V impact toughness of5hot rolled strips was investigated in thetemperature ranged from room temperature to-196°C. And the experimental hot rolled stripsshowed a marked decrease in ductile-brittle transition temperature with increasing rollingreduction. Furthermore, the impact toughness of97%and97.5%hot rolled strips alwaysremained a high level as temperature decreased. The enhanced impact toughness was attributedto the fine grain and dispersed second phase particles. Also, a new model for estimation of themicro-toughness in ductile fracture was presented,which was a reasonable result with the experimental measuring values.