Effect Of Adding Nano SiC Particles On The Structure And Performance Of Q235 Steel

Iron and steel materials are still the most important materials used by man in the 21st century, which are optimal materials with high strength and toughness. One important way to increase the comprehensive mechanical properties of steel (i.e. strength, plasticity and toughness) is grain refining. Refining grain, improving the properties of steel and endlessly satisfying users'higher requirements for steel are the objectives that metallurgists always pursue.The second phase particles in steel have positive effect on the performance of steel. It is mainly presented in the following aspects: refining as-cast structure in the process of solidification, becoming the recrystallization nucleus during rolling and serving as a pinning particle to interfere grain growth. Most second phase particles in steel are generated in a way of precipitating from steel, so it is very difficult to control their sizes and distribution. Based on its positive effect on the performance of steel, the new method of adding ultra-fine particles into the melt is topic which is worth exploring very much.The demand on purity of molten steel isn′t quite high by adding ultra-fine particles into the melt, so the process is easy to control; moreover it has effect on inclusion refinement, original austenite crystal grain refinement and later processing processes. In this article low carbon steel Q235 is selected as the experimental material, through the way of pre-dispersing nano-particles, it studies the method of adding nano-sic particles into the melt and analyzes the thermodynamic stability of nano-sic particles in molten steel. Through Metallurgical analysis, SEM, TEM, XRD analysis and other experimental technologies, it studies the effect of adding different amount of nano sic particles on the grain size, microstructure, performance and steel inclusion of Q235 steel, and discusses its refinement mechanism.The results show that nano-sic particles can be added into high temperature melts through the method of pre-dispersing ultra-fine particles. The added nano-sic particles can become a nucleus of forming in the melt of Q235,and obviously refine as-cast structure, compared with the grain structure of the original steel, the cast grain structure of Q235 added with 5% nano-sic particles are refined 4.6 times; With the increase of sic content, pearlite content is gradually increased and the structure becomes more refined, uniform and compact; the thermodynamic calculation shows that a part of the added nano-sic melt in molten steel, some remained in molten steel. With the increase of the quantity of added nano-sic, the proportion of it melt in molten steel is tending to decline, when the quantity of added nano-sic is 1%, 3% and 5%, its proportions melt in molten steel are 45.39%, 15.43% and 9.43% respectively; before adding nano sic, the steel inclusions are mainly MnS, Al2O3 and Aluminosilicate. After adding sic, FeO, Lime silicate, Ferro silicate and Ferrocarbon compound appeared. The morphology of steel inclusions mainly includes spherical shape, bar shape and block. Thereinto, the morphology of MnS mainly includes spherical shape and irregular block; there is no abvious change in it after adding nano-sic particles, while the bar-shaped aluminosilicate, Ferro silicate and ferrocarbon compound can be transformed into blocks with the increase of nano-sic content; there is no obvious change in the respect of steel inclusion size; compared with the hardness of original Q235 steel, the hardness of strengthened Q235 is obviously increased, when the proportion of added nano-sic reaches 5%, the increase extent of micro-hardness is up to 147%.