Nb microalloy welded structural steel series has been developed to create a new system of high toughness and low cost with Nb microalloy structural steel with low carbon bainite type. Through union, on the basis of the deep research in the physical metallurgy principle, to develop a new medium temperature shift organization ultrafine new ideas and new technology, created a new generation of high performance low cost in China systems containing Nb micro alloyed steel. The yield strength of new steel under good toughness is 500 ~ 800MPa, with excellent comprehensive performance and weldability, which meet the requirements of low alloy consumption, energy saving and environmental protection.
Project USES the sharp drop in carbon and integrated micro alloying design, through the deformation induced nano precipitation strengthening, dislocation strengthening, medium temperature phase change control, especially the ultrafine organization to strengthen the development of a new generation of yield strength of 500 ~ 800 mpa grade low carbon bainite steel series, the new system involves updating and upgrading of thousand tons of low alloy steel in our country, to promote our country related industry chain development played an important role to the international advanced level. The main achievements include:
The new generation of steel has adopted a large carbon reduction design (0. 03% ~ 0. C) to ensure that no cementite is produced under normal cooling conditions, resulting in a low carbon bainite matrix with excellent plasticity and toughness. In the new steel reinforcement method, the alloying design of ultra-low carbon and multivariate microalloy is adopted. The reinforcement principle of steel is mainly used for the transformation of shear type, which can be used to retain a large number of dislocation of deformation in the phase change product. Using deformation inducement and promoting the dispersion of Nb, Ti and V, and the aging of a few nano-sized e-cu; It is more important to use the intersecting micron-sized bainite plate and the fine grain strengthening between submicron level. The three main intensification methods are selected reasonably, which ensures that the yield strength of the new generation of steel reaches 500 ~ 800MPa level and can be further developed to above 1000MPa level.
Ultrafine in order to achieve the temperature change in the organization, the formation of high strength, good comprehensive performance of the new generation steel series, the project created with independent intellectual property rights in our country, the realization of medium temperature shift organization of ultrafine relaxation precipitation - control phase change patent technology, and improve the actual control method of new processes.
In the industrialized mass production conditions, the use of innovative ideas and patent technology, through proper control the temperature of the relaxation phase process, relaxation process (including the start of the different thickness steel plate temperature of relaxation, relaxation time, temperature and cooling to accelerate cooling rate and final cooling temperature, etc.) in alloy under the condition of less than 1%, the total design of the steel yield strength is implemented doubled that of the 16 mn steel, and the impact toughness increased significantly.
