Abstract
This article investigates the effect of niobium-vanadium composite microalloying on the extreme tip cold bending property of hot press forming steel. The extreme tip cold bending angle and the bending deformation curves of hot press forming steel with different alloy compositions were measured by using of VDA 238-100 method and standard. The initiation work of the crack during bending deformation were defined and calculated based on the measured bending deformation curves. The microstructure, the size of martensite lath bundles and austenite grains in different samples were observed and measured with using SEM and EBSD. Based on the measured and calculated crack initiation work and the maximum bending load, the mechanism of composite microalloying improving the strength, toughness and cold bending angle of hot press forming steel was elucidated. The observation results of EBSD on the microstructure changes during cold bending deformation of samples with different compositions further elucidated the influence of niobium-vanadium composite microalloying on the extreme tip cold bending property of hot press forming steel. It was found that niobium-vanadium composite microalloying can optimize the quenching property of steel, improve the uniformity and consistency of the microstructure after hot forming, and refine the austenite grains and martensite lath bundles of the steel. These all increase the coordination during sample deformation, thereby improving the strength and toughness of the steel, and enhancing the extreme tip cold bending property of hot press forming steel.
