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In order to further control the springback of advanced high-strength steel in stamping,a method to reduce the bending springback by increasing the variable closing pressure (VCP) through servo hydraulic equipment without increasing the material forming margin was proposed. For U-shaped benchmark parts of 1 180 MPa dual-phase (DP1180) steel formed by stamping, the feasibility of increasing VCP to control springback was analyzed by using the finite element method, and the mechanism of increasing VCP to reduce springback was studied from the perspective of residual stress and dislocation. The results show that the proposed method can reduce the residual stress and the dislocation density of the formed material, thus increasing the inelastic recovery and achieving the effect of reducing the springback angle of the target part by 22.3%. Because this method is only applied at the end of part forming, which does not affect the plastic flow in the material forming process, there is no need to increase the additional material forming ability and shaping process, which can be applied to actual industry without changing the production rhythm, and has a broad application prospect.

A self-developed strip-type high-temperature friction and wear test device was used to simulate the high-temperature friction process of uncoated 22MnB5 boron steel under actual hot stamping conditions. The mold was preheated to simulate the temperature increase of the die in the hot stamping process. The effects of mold temperature on the friction behavior and mechanism of uncoated boron steel were studied by using the friction coefficient test, surface wear morphology observation, and cross-section and matrix structure chart of hot stamping boron steel. The results show that the friction coefficient between the uncoated boron steel and the H13 steel is basically stable at 0.5 when the temperature of the mold is low, and the wear mechanism is mainly classified to abrasive wear and adhesive wear. Besides, when the mold temperature exceeds 100 ℃,the friction coefficient of the uncoated boron steel decreases from 0.474 to 0.414 with an increase of temperature from 150 ℃ to 200 ℃,inferring that the adhesive wear is weakened. The Vickers hardness of the boron steel matrix is approximately close to 430 from room temperature to 100 ℃. Moreover, with the temperature further rising to 150 ℃ and 200 ℃,the hardness decreases to 413.5 and 399.7 respectively, which indicates that the mold temperature has a significant effect on the mechanical behavior of formed parts.

The effect of a Cu addition on the corrosion behavior of 304 austenitic stainless steel in a solution was elaborately investigated through salt spray tests, FeCl3 immersion tests and characterization analyses. The corrosion behavior was further analyzed by optical microscopy, scanning electron microscopy, inductively coupled plasma mass spectrometry and an X-ray photoelectron spectroscopy analysis. 304Cu showed a higher corrosion resistance than 304 after the salt spray tests in a 5 wt.% NaCl solution for 168 h; the beneficial effect of Cu was not obvious after exposure for 480 h. Penetrating (stripped morphology in 304 and fishbone morphology in 304Cu) and non-penetrating dish-shaped pits were both observed on 304 and 304Cu after immersion in a 6 wt.% FeCl3 solution for 72 h; the corrosion rates of 304Cu were much higher than 304. Cu and Cu2+ were the main existing forms in the as-received 304Cu and Cu+ formed with the corrosion in chloride solutions. The results indicated a good corrosion resistance of 304Cu in service. The use of steel in an aggressive environment for a long exposure time should be cautiously considered. [ABSTRACT FROM AUTHOR]