Microstructure and Properties of Ti-Mo Microalloyed Steel with Different Ti Contents
Microalloyed steel is based on low-carbon steel or ultra-low-carbon steel.By adding small amount alloying elements,a large number of nano-scale precipitated particles are formed inside the steel during the austenite/ferrite transformation,which enhances the mechanical properties of the steel.As a microalloying element widely used in steel,Ti is easy to form TiC and TiN with carbon and nitrogen.TiC and TiN particles in steel can play a role in grain refinement and precipitation strengthening by inhibiting grain growth,pinning dislocations at high temperatures or during rolling.At the same time,the price of Ti element is low,which can reduce the cost of materials and improve economic benefits.The addition of Mo element to Ti microalloyed steel can form(Ti,Mo)C particles inside the steel,which has an excellent ability to resist grain coarsening.Meanwhile,it can inhibit the nucleation and growth of TiC particles,and promote precipitation strengthening and fine grain strengthening.Ti-Mo microalloyed steel has attracted wide attention due to its high strength,good weldability,and formability,and has a wide field of applications with good prospects.However,in a state of high strength,the problem of a high yield ratio remains to be solved.Therefore,reducing the yield ratio is of great significance to improve the formability of the material and the safety performance during use.In this paper,eight kinds of Ti-Mo microalloyed steels with different Ti contents in a hot rolled state were taken as the research object.The microstructure and mechanical properties of the steels were tested by optical microscope(OM),tensile testing machine and impact tester.The effects of Ti content on the microstructure,tensile strength,yield strength,elongation,and impact toughness of the tested steels were systematically analyzed,based on the observation results and test data.Using the calculation formula of the comprehensive strengthening mechanism of steel,combined with the solid solubility amount of each element,ferrite grain size,effective Ti content,and other factors in the steel,the solid solution strengthening amount,fine grain strengthening amount,and precipitation strengthening amount of the tested steel were determined.The yield strength value was calculated by the formula of the addition rule,which was in good agreement with the measured value of the actual yield strength.The strengthening mechanism of Ti-Mo microalloyed steel was clarified,and the influencing factors of yield ratio were discussed from two aspects of strengthening mechanism and phase composition,which could provide a reference for further optimization of mechanical properties of Ti-Mo microalloyed steel.The results showed that with the increase of Ti content,the amount of ferrite and pearlite decreased gradually,and the amount of bainite increased gradually,in addition,the change was more obvious when Ti content was higher than 0.1％.When Ti content of the steel was 0.012％～0.16％,with the increase of Ti content,the tensile strength and yield strength of the steel gradually increased,while the ferrite grain size gradually decreased.At the same time,the plasticity and toughness gradually decreased and then tended to be stable.When Ti content was further increased to 0.21％,the ferrite grain size began to increase,while the tensile strength and yield strength began to decrease.When Ti content was 0～0.026％,the strengthening mode of the steel was mainly fine grain strengthening and solid solution strengthening,and with the increase of Ti content,the main strengthening increment was fine grain strengthening.When Ti content was 0.040％～0.21％,the strengthening mode of the steel began to be dominated by fine grain strengthening and precipitation strengthening,and with the increase of Ti content,the amount of precipitation strengthening gradually increased.The amount of fine grain strengthening gradually increased with the increase of Ti content of 0～0.16％,and decreased with the increase of Ti content of 0.16％～0.21％.The strengthening method was one of the important factors affecting the yield ratio.In Ti-Mo microalloyed steel,solid solution strengthening could reduce the yield ratio,while fine grain strengthening and precipitation strengthening could increase the yield ratio.The ratio of soft phase and hard phase in the steel was another factor affecting the yield ratio of the tested steel.The soft phase affected the yield strength of the steel,and the hard phase affected the tensile strength.To obtain Ti-Mo microalloyed steel with a low yield ratio under the condition of maintaining high strength,the proportion of ferrite and bainite in the steel could be appropriately controlled.Under the experimental conditions,when Ti content was 0.11％,the steel with excellent comprehensive mechanical properties could be obtained,whose yield strength was 482 MPa,tensile strength was 647 MPa,and the yield ratio was 0.7456.
Ti contentTi-Mo microalloyed steelelongationstrengtheningyield ratio
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NSTL
万方数据
