Study On Effect Of Vanadium And Titanium On Microstructure And Property Of 700MPa Grade Microalloy Seel

As one of the structure steel variety which have developed most rapidly and have the largest development potential in recent years, microalloy steel is main manufacture in modern iron and steel industry. Microalloy steel which the yield strength is 700MPa can be used for the lateral plate and framework of the container, etc. But the research on microalloy elements affecting steel performance is not deep enough and systemic enough in China, and the strength and plasticity of internal designing microalloy steel cannot reach international developing level. This paper designed microalloy steel which the yield strength is 700MPa, based on chemical composition of ultra-low carbon pure steel, by adding microalloy elements of V, Ti, Mn, Nb, etc. By vacuum induction melting experiments and controlled rolling and controlled cooling experiments in the laboratory, tension experiments, SEM morphologies of tension fracture of specimens analysis, composition and microstructures of microalloy steel analysis, this paper systemically researched effect of microalloy elements of V, Ti on structure property, finally made the main conclusions as follows.SEM morphologies of tension fracture of 700MPa microalloy steel at room temperature are dimple fracture characteristic; the diameter and depth of dimple increasing can improve the plasticity of test steel, but reduce the strength. The microstructures of 700MPa microalloy steel are basically composed of granular bainite and massive ferrite; the granular bainite in the proportion of test steel increasing can improve the strength of test steel, but reduce the plasticity.The other components in a similar situation, when V content in 0.03%～0.10% scope changes, the increasing of V content can prevent austenite grain growth and refined ferrite grain in 700MPa microalloy steel; the tensile strength of test steel increases from 680MPa to 700MPa, but the elongation falls from 19.0% to 18.6%.The other components in a similar situation, when Ti content in 0.02%～0.09% scope changes, the increasing of Ti content can prevent austenite grain growth and refined ferrite grain in 700MPa microalloy steel; the yield strength of test steel increases from 570MPa to 600MPa, and the tensile strength increases from 705MPa to 750MPa, but the elongation falls from 17.0% to 16.4%. When V, Ti, Mn, C, O and N content is differently controlled in 0.10%, 0.09%, 1.6%, 0.04%, 0.002% and 0.0009%, the strength and plasticity of preproduction 700MPa microalloy steel in the laboratory can reach the standard of performance that tensile strength is not less than 700MPa and elongation is not less than 17%.