Effect Of Titanium Microalloying And Heat Treatments On The Microstructure And Mechanical Properties Of Low Carbon High Strength Steels

Good mechanical properties of low-carbon high-strength steels is often required because of the special application environment and conditions.Micro-alloying of low-carbon high-strength steel combined with a certain heat treatment process can effectively improve the mechanical property of the materials.It is of great significance to analyse the effect and the mechanism of titanium micro-alloying and heat treatment on the structure and properties of low-carbon high-strength steels,which can improve the properties and expanding the application of the materials.This paper mainly studies the influence of titanium microalloying and solution heat treatment on the microstructure and mechanical properties of low-carbon high-strength steel,and the effect of precipitated particles on the growth of the prior austenite grain size as well as the strengthening mechanism were analyzed and discussed.The thermodynamic and kinetic behavior of the low-carbon high-strength steel was simulated and analyzed through the JMatPro software.As the content of titanium increases,the content and the precipitation temperature of the Ti（C,N）precipitation in the equilibrium phase composition of low-carbon high-strength steel gradually increase,while the precipitation content and the precipitation temperature of the M₂₃C₆ decrease.Increasing the content of titanium will promote the ferrite transformation during the isothermal cooling transformation and the formation of martensite during the continuous cooling transformation of the low-carbon high-strength steel;however,the change in titanium content will not change the Ac₃ temperature of low-carbon high-strength steel.To analyze the effect of titanium content and solution temperature on the microstructure of low carbon high strength steel,the low-carbon high-strength steel was added with different contents of titanium and solution treated at different temperatures for 30 minutes,The microstructure of the low-carbon high-strength steel is mainly lath martensite.The increase in the content of titanium does not change the phase composition at the room temperature of low-carbon high-strength steel;with the increase of titanium content,the size of the prior austenite grains of the material decreases.And when the titanium content reaches 0.05 wt%,the prior austenite grains are the finest.As the titanium content continues to increase,the degree of refinement of the prior austenite grains decreases,but compared with the sample without Ti addition,the size of the prior austenite grains are finer.The solution treatment will not change the phase composition of the low-carbon high-strength steel;as the solution temperature increases,the prior austenite grain size of the material grows slightly,and the boundaries of the martensite lath gradually blur.The mechanical properties of low-carbon high-strength steels with different titanium contents and different solution treatment processes were tested.Increasing the content of titanium,the strength and hardness of the low-carbon high-strength steel are increased,the plasticity is reduced,and the yield strength ratio is increased;when the content of titanium reaches 0.05 wt%,the mechanical properties of low-carbon high-strength steel are the optimal.Continue to increase the content of titanium,the mechanical properties of the steel decrease,but compared with the steel without titanium microalloying,the properties are better.When the solution treatment is performed in the temperature range of 850℃～900℃,for every 25℃increase in solution temperature,the strength of the material increases by about 50 MPa～100 MPa,and the yield ratio of the material decreases.Combined with the content of Chapter 4 and Chapter 5,the influence of the precipitation on the grain growth behavior of the titanium-containing low-carbon high-strength steel is analyzed,and the strengthening mechanism of the steel with titanium microalloyed is discussed.In titanium microalloyed low-carbon high-strength steel,the Ti C particles and Ti N particles can refine the grain and inhibit the growth of the priorl austenite grains,but the inhibition effect of Ti C particles is stronger;when the Ti C particles cannot be precipitated,the grain growth tendency of the steel is obvious.For titanium microalloyed low-carbon high-strength steel,its high strength is mainly the result of the synergistic effect of solid solution strengthening,fine grain strengthening,precipitation strengthening and dislocation strengthening..