Refinement Of Structures And Improvement Of Mechanical Properties For Low-Alloy Bainite Steels

Now, the industry of steel is confronted with the condition that the strength of steels is enhanced greatly, but the toughness is not improved much. In order to solve this inconsistency, this paper has done many experiments and researches. Through judiciously using the silicon, manganese and nickel as alloying elements and effectively controlling transformation temperature, cooling rate and tempering parameters for a series of low carbon ultra-high strength bainite steels (LCUHSBS), we get a new type of steel that has the excellent combination of strength and toughness.The microstructure and the gain size is analyzed and measured by AFM,SEM,TEM, HRTEM. The volume fraction of A_R was determined by the X-ray diffraction and magnetic analysis for obtaining the smaller measurement error. The stretch strain and impact energy absorption were measured with an AG-25 TA universal testing machine and a JB-30B impact testing apparatus, respectively. Reaults show:(1) Through judiciously using the silicon, manganese and nickel as the alloying elements and effectively selecting the transformation temperature, cooling and tempering techniques for a series of dow alloy ultra-high strength bainitic steels (UHSBS), not only is the carbon content of BF supersaturate, but also the microstructure of UHSBS has been obviously refined means of the dislocation motion during the continuous cooling and tempering.(2)Add silicon to the UHSBS as the alloying elements and control its quantity, the separating of the cementite will be totally restrained and it is beneficial to the enhancement of the toughness.(3)Through effectively selecting the transformation temperature, cooling and tempering techniques for a series of UHSBS, the sub-grain is refined to 18nm or smaller and the boundary between ferrite and A_R grows. For this, the strength increases 300MPa.(4)Not only is the carbon content of BF supersaturate, but also the microstructure of UHSBS has been obviously refined means of the dislocation motion during the continuous cooling and tempering. This is result that the obdurability of UHSBS is better.(5)The stress is eliminated by effectively selecting the transformation temperature, cooling and tempering techniques and the stability of A_R is improved by increasing its carbon content. Compared with the martensite steel with the same strengh, the impact...