Study On Hot Deformation Behavior And Ferritic Rolling Of B250P P-added High Strength Steel

In this paper, the P-added high strength steel which is a production of Benxi Steel Group is researched. Its brand is B250P which belong to IF Steels (Interstitial Free Steel). B250P P-added high strength steel is developed by adding P, Si, Mn or other solution strengthening elements into traditional IF steels. It is well known that phosphorus is the low cost of solid solution strengthening elements. Because of the P-added high strength steel has three features that contain high forming performance, high strength and low cost, which in line with the auto manufacturing requirements of lightweight, high security and low cost, so that approved by the vast number of automobile manufacturers. Studies showed that ferritic rolled IF steels possessed{111}//RD texture type which is comparable with cold rolled IF steels, the strength of the{111}//RD texture largely determines the formability of the steel. Compared with the traditional cold rolling process, ferritic rolling not only simplifies the production process and reduces the production cost, but also has important theoretical significance and application value. However, the researches of P-added high strength steel hot deformation behavior and hot rolling process is relatively small.In this paper, the hot deformation behavior of B250P steel has been studied on the MMS-300thermal-simulation-testing machine. At the same time, we are analysis the thermal deformation microstructure in ferrite area of B250P steel; Its microstructure evolution has been observed by different kinds of microscope, such as EBSD, TEM and so on. Additionally, the process of ferritic rolled and annealed for B250P steel has been studied as well. The main work are shown as follows:(1) The phase transformation points from austenite to ferrite are measured by thermal expansion experiments.(2) Through the single channel compression experiment, draw the true stress-strain curve of B250P steel which under the conditions of different temperature and strain rate, and the effects of hot deformation parameters on flow stress of B250P steel are analyzed.(3) The hyperbolic sine constitutive equations have been established for both austenite and ferrite area by using the parameter of Zen-er-Holloman, and a6th order polynomial are applied to represent the compensation of strains to evaluate the values of the material constants and the hot deformation activation energy. The flow stress has been predicted by the above constitutive equations, which have a good accuracy.(4) The influence of hot deformation parameters on the microstructure of B250P steel at ferrite area is studied based on single-pass compression tests.(5) Through the ferrite rolling and annealing experiment, studied the annealing temperature and holding time how to influence the organization. Studied the open rolling temperature of B250P steel which on the ferrite area how to influence the organization, texture and mechanical properties when it been annealed.At the same time, the characteristic of morphology and distribution for precipitations has been discussed.(6) Compared with the properties of cold rolled B250P steel sheets, the sheets produced by ferritic rolled and annealed process can be achieved and have application prospect.