Performance Optimization And Fracture Behaviors Of The High Strength Bainitic Finish-rolled Steel Bar

Recently, high strength bainitic finish-rolled steel bar is widely used in the field of industry, such as large-scale hydropower projects, civil construction of continuous beam and large frame structure. It also has a wide range of applications in roads, railways and bridge engineering, etc. It has advantages for its excellent performance in service location of connection and the anchoring. The outstanding safety and reliability of bainite reinforced bar can effectively reduce weight of components. The experiment steel in this research is mainly based on the Mn-Si-Cr series bainite steel, which can be obtained by air-cooling process by actual production. As a kind of a bainite/martensite (B/M) multiphase steel, microstructure in the steel is composed of bainite, martensite and some retained austenite. As cheap alloy elements, the addition of manganese, silicon and chromium makes sure the low cost within high properties in the steel. The simple production process has significances to energy saving and environmental protection. This makes the steel production process is simple and energy saving.There were some problems in PSB830 bainite steel reinforced, and the prominent issue is the shortage of low yield strength and elongation. In order to improve yield strength and elongation of the steel, different kinds of inclusions in the steels and their effects on the fracture behavior are investigated in this research. After fine-tuning for several times, we have obtained the optimization heat treatment process with appropriate composition by fine controlling inclusions was make the mechanical stability of the bainite steel is greatly increased. The process of controlling the inclusions in the steel bar can provide guiding significance for metallurgical quality, which is necessary for industrialized production of the bainitic bars.The size, type, distribution and other factors of non-metallic inclusions in steels all affect the mechanical properties of steel, while the effects of those factors on the fracture behavior are still unclear. Analysis work has been done on the size, type, distribution on inclusions in steel bar. Basis on the conclusions, different role of inclusions on the micro crack nucleation mechanism was studied. Under the changing true stress we compared sensitivity of the different B/M multiphase steels for inclusions, and inclusion critical dimension for the micro-crack nucleation. We can conclude that the improvement of the metallurgical quality can reduced the size, quantity and the most harmful inclusions species in steel, in which way crack nucleation on inclusions and collision of crack growing up can be reduced. With the true stress increasing, the area of a single cracking inclusion will be decreases. It was also found that through homogenization heat treatment, inclusions sensitivity will be decreases for B/M multiphase steels and the harm for inclusion induce crack initiation and growth also reduced.