Study On Strengthening And Toughening Mechanism Of Q890 High Strength Steel

The economic development allows the structural steel to be large and integrated,so more high-strength steel is used,which can save raw materials and also reduce the weight of the movement structural steel.However,structural steel also requires good ductility and toughness and weldability.This paper used Thermal Mechanical Control Processing(TMCP)and hot rolling + quenching and tempering process to develop high ductility and toughness Q890 steel.And microanalysis was used to study the microstructure evolution,mechanical properties and the influence of its strength and toughness,so that it can achieve the performance requirements of Q890 high-strength steel.In order to ensure that the elongation of the steel reaches more than 14.0%,the carbon content of the experimental steel was reduced in the smelting.After TMCP,the finished rolling temperature was at 900 ℃,and then the isothermal transformation was carried out in a salt bath at 520 ℃ to obtain the bainite.The tensile strength of the steel is 621 MPa and the elongation is 24.0%,which is a considerable difference from Q890 steel.The tensile strength of the sample after quenching and tempering is over 1038 MPa and the elongation is 14%,so the composition of the experimental steel was redesigned and a research of quenching and tempering process after hot rolling was performed.The optimum technology conditions for quenched and tempered processing is920 ℃/30 min+650 ℃/30 min,and the microstructure is tempered sorbite with many fine carbides.After hot rolling,the steel grains are fine with a certain amount of precipitates.Thus,there is tiny grain in the austenite by quenching and tempering at higher temperatures.The tempering processing plays a micro-alloying role after quenching,which makes a recovery and recrystallization of matrix grain fine and larger size of carbides with less amount.By fine-grain strengthening and precipitation strengthening,yield strength the steel is 1078 MPa,tensile strength is 1094 MPa,elongation is 14.5%,and-40 ℃ low-temperature impact is 151 J.In addition,following two cycles of quenching and tempering processing,the tensile strength of the steel is 1001 MPa,elongation is 16.5%,and-40 ℃ low-temperature impact is 135.5 J,which meets the performance requirements.