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| Microstructure，mechanical properties and strengthening #br#
mechanism of Ti microalloyed high strength steel |
| YANG Yuebiao1，2，DENG Shen2，FAN Lei2，ZHAO Zhengzhi1，#br#
YUAN Qinpan2，LUO Jing2 |
(1. Collaborative Innovation Center of Steel Technology， University of Science and Technology Beijing，
Beijing 100083， Beijing， China；2. Technical Center， Guangxi Liuzhou Iron and Steel Group
Company Limited， Liuzhou 545002， Guangxi， China) |
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Abstract In order to study the microstructure，mechanical properties，characteristics and precipitation behavior of the secondphase precipitate as well as strengthening mechanism of Ti microalloyed high strength steel for automobile carriage，which were systematically investigated by means of the optical microscope，scanning electron microscope，transmission electron microscope and tensile testing machine combined with thermodynamic calculation. The results show that the microstructure of the experimental steel is mainly composed of polygonal ferrite+acicular ferrite+a small amount of sorbite，and the average effective grain size is about 3.5 μm. There are a large amount of spherical TiC and a small amount of irregularshape Ti4C2S2 and square TiN precipitates in steel. The precipitation sequence is TiN→Ti4C2S2→TiC. The precipitation strengthening effect of TiC is the most remarkable for the secondphase precipitates，and the precipitation strengthening effects of TiN and Ti4C2S2 are very weak. The contribution order of all strengthening methods to the strength of experimental steel is as follow：fine grain strengthening>precipitation strengthening>dislocation strengthening>solid solution strengthening>lattice strengthening，in which the strengthening effects of fine grain strengthening and precipitation strengthening are the most significant，and the contribution to yield strength is more than 50%.
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