Microstructure And Mechanical Properties Control Of Ti-Microalloyed Steel Under Ultra Fast Cooling Conditions

Due to the increasingly severe problems of resource,energy consumption and environmental pollution,the new generation of steel production with low cost and high quality has been urgently needed in order to achieve the substantial development of the steel industry.The newly developed and widely used Ultra Fast Cooling(UFC)process has become one of the effective technique methods to produce hot rolled high strength steels with low cost and high quality.The thesis is based on the program"Control of Nano Precipitates in Low Carbon Steels under Ultra Fast Cooling(UFC)and Comprehensive Strengthening Mechanisms".In this program Ti was added into plain carbon steel,through the methods of varieties of experimental process,eventually exploring the way to achieve industrial production reduction,meanwhile,supplying products with good comprehensive properties.The main contents of this thesis are as follows:(1)The continuous cooling transformation behavior and rule of undercooled austenite microstructure evolution of 0.06%Ti-Microallyed steel were researched with MMS-200 thermal simulated test machine.The curve of continuous cooling transformation was drew with the way of thermal expansion and abserving the metallographic structure,analyzed the effect of the experimental steel on deformation?content of titanium and cooling rates.(2)Study of isothermal temperature on microstructure and microhardness of ferrite phase has been made by using isothermal quenching experiments of 0.06%Ti and 0.047%Ti steel.The range of nose temperature of "C" curve of the second phase precipitation was confirmed and microhardness of tested steel at different isothermal temperature.(3)The influence of ferrite phase transformation of steel and carbide precipitation on cooling rates and final cooling temperature and Ti content of steel has been investigated by means of different cooling processes thermal simulation experiments.(4)The effect mircostructure and properties of steel on cooling pattern and final cooling temperature by the means of hot rolling experiment of 0.06%Ti steel with UFC.The best UFC craft has been established.Combination properties of 0.06%Ti steel is better than 0.12%Ti steel.Reduction of Ti has been realized.Contribution of all the strengthening mechanism to yield strengh has been calculated.And the main strengthening mechanism of steel under UFC craft has been analyzed.Microstructure and the precipitation behavior of the second phase has been compared between surface and quarter of steel whose thickness is 30mm.