Study On Microstructure Control And Fire-resistance Mechanism Of Anti-seismic And Fire-resistant Constructional Steel

With the rapid development of economy and society,steel structure had attracted more and more attention from the market due to its high strength,light weight,convenient construction,environmental protection and so on.In the performance indicators of constructional steels,anti-seismic and fire-resistance were particularly important.In this paper,the anti-seismic and fire-resistance of constructional steels were analyzed and studied,and a variety of high-standard antiseismic and fire-resistant constructional steels were developed.The microstructure control and fire-resistance mechanism were analyzed and investigated,and then the variation law of Young's modulus at elevated temperatures was studied by using the first principle calculation.The research of microstruture control and fire-resistance mechanism provided theoretical support for the design of new anti-seismic and fireresistant constructional steels.The results show that only the terrace plane of the ferrite grain boundary in the rolled microstructure had element segregation.After tempering at 600?,the element segregation appeared on the whole grain boundary,but the enrichment degree of elements was weakened,and the composite precipitates containing of Mo,Ti,and V nucleated at the junction of the terrace plane and the step plane,which can effectively hinder the migration of grain boundaries.Mo can significantly reduce the annihilation rate of dislocations in bainite/martensite at elevated temperatures,and can significantly retard the degree of decrease in the boundary density of bainite/martensite at elevated temperatures,thereby increasing the fireresistance of steels composed of bainite/martensite.The interphase precipitation containing of Mo,Ti and V showed a B-N orientation relationship with the matrix.It was found that the lower ACC start temperature is,the greater the interphase precipitation density is.The special arrangement of interphase precipitation can effectively hinder the annihilation of dislocation at elevated temperatures,and interphase precipitation has superior thermal stability than supersaturated precipitation.Therefore,interphase precipitation can effectively improve the fire-resistance of steels.Since the boundary energy of the ?3 boundary was lower,the migration rate of the grain boundary was slower,and the experimental steel with higher ratio of the ?3 boundary had superior thermal stability.In the high-temperature fireresistance test,a large amount of alloy cementite nucleated at the lath boundary and the grain boundary in the bainite,resulting in the Young's modulus of the experimental steel with a higher volume fraction of bainite being significantly higher than that with lower volume fraction of bainite,which affected the fireresistance.The Young's modulus of the alloy cementite nucleated after replacing part of Cr and Mn atoms was basically equivalent to the matrix,and its Young's modulus decreased with temperature lower than the matrix.