| The development of the600-700MPa hot rolled Micro-alloy steel in our country is relatively late, there are some deficiencies in production of hot rolled Micro-alloy steel for automobile structure, such as high cost, complex process, unstable microstructure and properties and so on.The objects of this thesis are development a low-cost micro-alloyed Nb-Ti alloy steels, use two different components of the Department of Nb-Ti steel experiments conducted research and development. The main works and research results of this thesis are as follows:(1) Department of micro-Nb-Ti alloyed steels which content of0.024%Ti combined with Ultra-Fast Cooling, can be used for the development of automobile beam steel; Department of micro-Nb-Ti alloyed steels which content of0.10%Ti, could give full play to fine grain refinement and precipitation strengthening, can be used for the development of micro-alloy high strength steel.(2) Investigated the effects of various process parameters on microstructure evolution and mechanical properties witch goal is to develop automobile beam steel. The thermal simulation experimental results show that:The organization is F+P when the deformation temperature is900℃and the fast cooling temperature is about650℃, the ferrite grain size is about4～5μm, when the fast cooling temperature is below550℃, organizations are mainly Bainite. Hot rolling Experimental results show that:the final rolling temperature at about860～910℃, after ultrafast cold temperature is about600～660℃, the cooling temperature is about580～630℃, able to obtain good performance micro-alloyed automobile beam steel.(3) Investigated the effects of various process parameters on microstructure evolution and mechanical properties witch goal is to develop high-strength steel. The thermal simulation Experimental results showed that:The organization is F+P when the deformation temperature is about900℃and the After ultrafast cold temperature is about650℃, pearlite uniformly distributed in the ferrite grain boundary. Hot rolling experimental results show that:The final rolling temperature at about870～930℃, after ultrafast cold temperature is about660～675℃, the cooling temperature is about630～650℃, after the heat treatment by a certain time, in micro-Nb-Ti alloyed steels which content of0.10%Ti, Ti element mainly in the form of TiC precipitates, precipitates was fine and dispersed, has excellent precipitation effect.(4) Microstructure and mechanical properties of test steels with the UFC+Ultra-Fast cooling strategies were researched through hot rolling experiment at laboratory, The results showed that:The microstructure and properties of Nb-low Ti steel was excellent under the best of rolling and cooling process parameters, can be used for the development of automobile beam steel. The microstructure and properties of Nb-high Ti steel was excellent through make full use of ultra fast cooling system, can be used for the development of micro-alloy high strength steel. |
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