| The development and research of micro-alloyed high strength steel has been paid more and more attention by domestic and foreign researchers.Fine gain strengthening and precipitation strengthening,which are the main ways to improve the mechanical properties,has been used in the development and production of micro-alloyed high strength steel.So,how to fully use the role of micro-alloying elements in gain refinement and precipitation is the key problem of TMCP development.In this paper,the effects of different process conditions on the precipitation behavior of Ti-Nb-Mo hot rolled high strength steel was studied by thermal simulation experiment.Provide experimental guidance for actual process production.Specific contents as follows:?1?The precipitate absolutely dissolution temperatures of Ti?C,N?,Nb?C,N?,V?C,N?were 1990?,1130?,820?respectively through thermodynamic calculation.And draw the relevant solid solubility curve.The precipitation of Ti?C,N?in the high temperature stage of the experimental steel was calculated by Thermo-Calc thermodynamics software.The Ti?C,N?particles hardly contained Nb,V,Mo alloy elements,low temperature ferrite/bainite is mainly precipitated with?Ti,Nb?C,and the precipitated phase contains a small amount of V and Mo.?2?The effects of different cooling rates on the transformation and precipitation behavior of experimental steels after hot rolling deformation was studied by thermal simulation experiment.The results showed that the bainite transformation occurs mainly with the increase of the cooling rates.The morphology of the bainite was complicated by the GB and LB,and with the increase of the cooling rates,The proportion of different forms of bainite was different.For Ti-Nb-Mo-containing micro-alloyed steels,the slow cooling process prior to coiling can promote the precipitation of fine carbides in the steel,and the precipitation strengthening effect was improved.In addition,four types of precipitated particles can be observed in the matrix.One is the size of the large TiN particles;One is?Ti,Nb?C particles,but the central and external chemical is not consistent,?Ti,Nb?C is TiN as core of the epitaxial growth;the other is Ti4C2S2 particles;and most of the smaller size?Ti,Nb,Mo?C precipitation particles,was chain or dispersed distribution.?3?The effects of isothermal temperature on the microstructure and precipitation behavior were investigated by isothermal quenching experiments.With the increase of isothermal temperature,the grain size of ferrite decreases gradually.The size of precipitates was mainly distributes from 6nm to 12nm,and the number of precipitates was more.The microhardness of experimental steel showed that the effect of the second phase particles on the microhardness was obvious.The contribution of precipitation to yield strength was calculated at theoretical temperature of 550?,600?and 650?,which were 203.1MPa,230.82MPa and 145.14MPa respectively. |
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