Research On Microstructure And Properties Of Low-cost High Strength And High Toughness Low Alloy Cast Steel

Along with cast steel production technology developing rapidly, development and applications of high-performance cast steel also become more and more widly. High-performance steel has unique superiority, with respect to strength and ductility, compared with traditional cast steel. Now, a part of raw materials is getting to rise in price, to reduce cost and improve performance, the cost of materials must be considering.This paper focuses on steel of ZG35SiMn, through orthogonal experimental designing elementary composition of low alloy steel, investigating its mechanical property, to analysis the elements and techenology for heating treatment process how to influen on its microscopic structure and property. Orthogonal experimental intuitive analysis and regression analysis are used to get optimum composition, and relationship between mechanical property and content of element. To combine the cost and demand on property, then, on the basis of orthogonal experimental, add rare earth and Nb to liquid steel, to research their influence on low alloy steel's performance and microstructure, and investigate the mechanism of action of rare earth and Nb on steel.The article has analysised what rare earth and Nb to exist in steel, and how oxide and sulphide to be produced, by thermodynamic calculation.Metallographic structure is analysised by the optical microscope and scanning electron microscope. It turned out that rare earth is not only with good functions deoxidation and desulfurization, but also controlling the morphology of inclusions. The rare earth and Nb both can promote fine grain size. It has anaysised the capability of nucleation based on Ce2O3 and NbC according to lattice misfit theory and classical electron theory, the result shows that Ce2O3 has the best remarkable capability of nucleation to 8-Fe, and medium toδ-Fe, while NbC has moderate capability of nucleation to 8-Fe and y-Fe. Ce2O3 and NbC to be phases of primary austenite and ferrite, and rare earth gathering to block grain boundary moving, are considered main mechanism of refined grains. Tensile and hardness has tested by universal tensile testing machine and Breinell tester. It shows that after adding 0.03%RE to steel, yield strength of it has increaseds from 525MPa to 535MPa while elongation of it has dropped from 18% to 16.6%. Based on the former, adding another 0.03%Nb to steel, yield strength of it has raised to 565MPa while elongation of it also has raised to 17%. So, it's proved that solution strengthening of RE become more effective and dispersive distribution of fine NbC particles separate more out when adding RE and Nb together. Low alloy steel can get well combination property as strengthening-toughening when RE and Nb are used for microalloyed steel.After adding RE and Nb to cast low alloy steel, yield strength of it has improved to 565MPa, and elongation of it improved to 17%. It comes true that strengthening-toughening is coordinated upgrade with low cost.