The .10 Crni5mo Steel Special Plate Organization And Performance Relationship Research

For the production of quenching and tempering super-thick plate, center segregation exist in the casting process, deformation concentrated in the upper and lower surfaces in the rolling process, led to percent reduction of center position insufficient and quenching is not complete in quenching and tempering process, resulted in microstructure and performance is inhomogeneous in thick direction, so the overall performance of steel plate were effected. Good strength and toughness match of quenching and tempering super-thick plate with high strength and high toughness is required, production process is very difficult. Production of quenched and tempered high strength and toughness super-thick steel plate has great technical difficulty. In this paper, comprehensive properties of 120mm super-thick steel plate were carried out in 10CrNi5Mo steel, mechanical properties and microstructure of surface,1/4T, and center in different parts in different parts were key studies. The test results indicate that martensite/bainite mixed structure of 1/4T and center position improve the strength and toughness, significantly lower ductile-brittle transition temperature of steel. According to special production process characteristics of thick plate, quenching cooling process of different positions was simulated in the lab, heat treatment was carried out, the relationship between heat treatment process, organization and mechanical properties was examined in detail. On this basis, strengthening and toughening mechanism of martensite/bainite mixed structure was in-depth study. The block size is "the effective grain size" for controlling toughness was first introduced in quenching and tempering super-thick plate, which provides theoretical basis and guidance for industrial production, innovative in technology.Quenching process of 120mm super-thick plate in industrial production, the surface to be a typical lath martensite structure, but the center position obtained lath martensite/bainite mixed structure; Various parts of the surface to the center small changes in the strength and plasticity, but the plate center much better than the surface of low-temperature toughness, ductile-brittle transition temperature is considerably lower than the surface. As the experimental temperature of the lower, the impact energy of plate surface decreased rapidly, In experimental temperature of-84℃, the impact energy of plate center reached 138J, while surface is only 30J; Ductile-brittle transition temperature of steel center is-100℃, while surface is only-60℃. A comprehensive analysis of experimental results show that differences of microstructure in surface and center position are the reason why center for low-temperature toughness of steel is superior to the surface.Quenching cooling process simulation experiment of super-thick was carried out in the lab, the steel was heated to 1200℃, then water quenched, oil quenched, rapid air cooled, cooled by sand covering respectively, different ratios of the martensite/bainite mixed structure were obtained. As the cooling rate decreases, a gradual increase in bainite content, the tensile strength increased slightly, yield strength decreased to a lesser extent, when the bainite content reached 86%, the yield strength only reduce around 60MPa. However, the impact work changes significantly. When the amount of bainite is 76%, the touehness is in best condition, the impact work is 160J at-20℃. And it is the worst with water cooline for single martensite, the impact work is only 12.5J at-20℃. On this basis, fine structure of lath martensite/bainite mixed structure was in-depth analysis by means of optical microscope(OM), scanning electron microscopy(SEM), electron backscatter diffraction(EBSD) and transmission electron microscopy(TEM). The test results indicate that toughness of experimental steel is enhanced along with the decreasing of the packet and block size under the condition of the same prior austenite grain size mixed with different ratios of martensite and bainite, while the lath width is about 0.38μm. The calculation shows that both the packet and block boundaries have the same hindering effect on crack extension. Furthermore, the effect of the block width on impact energy is much larger than the packet. Therefore, the block can be used as micro-structural substructure to affect the toughness in low carbon martensite steels, which means that the block size is "the effective grain size" for controlling toughness.Lath martensite/bainite mixed structure partition and fine mechanism was in-depth analysis by means of color metallography technology. Super-thick plate quenching cooling process, cooling rate of plate in different parts is varied significantly. Cooling rate below the critical cooling rate in center position, formation of a small amount of lath bainite, segmentation of the prior austenite grain. When temperature further reduce, divided and refined prior austenite grain occurs the martensitic transformation, packet smaller size, in a packet, martensite block and bainite block parallel to each other, and emergence of alternate, which played a role of partition and fine the prior austenite grain size, which means that "the effective grain size" for controlling toughness in center position is smaller than surface, so it leads to industrial production super-thick plate center position have been an excellent low-temperature toughness in 10CrNi5Mo steel.