Boron steels have phase transformation in hot stamping process, and the mechanical properties of hot stamped parts are determined by the microstructure generated by phase transformation. Cooling path has a significant effect on phase transformation and microstructure of the deformed parts; in order to obtain the tailored-customized mechanical properties, the relationship among cooling path, the phase transformation, and the corresponding microstructure must be investigated. In this paper, the dilatometric experiment with the cooling rate of 2, 10, and 50°C/s and various dwell temperatures was conducted to explore the influence of cooling path on the start and finish temperatures of phase transformations from austenite to ferrite, bainite, and martensite; lasting times of transformations; and final microstructures in hot stamping process. The controllable factors which influence the mechanical properties of hot stamped boron steel component were also determined. In addition, the metallographic and Vickers hardness experiments were conducted as well to confirm the analysis result of dilatometric experiment. The knowledge about the relationship of cooling path, phase transformation, microstructure, and mechanical property of the hot stamped parts helps the design of hot stamping process of the stamped parts with tailored-customized mechanical properties.

An effective approach was developed for identifying and correcting ocean-bottom seismometer (OBS) time errors through improving ambient noise cross-correlation function (NCCF) analysis and combination with other methods. Significant improvements were illustrated through analyzing data from a passive-source seismic experiment in the southwestern sub-basin of the South China Sea. A novel method was first developed that can effectively identify errors in the sampling frequency of the OBS instruments. The traditional NCCF method was then expanded by increasing the analyzed data spectrum from a single-frequency band to dual-frequency band pairs, thus doubling the number of available data points and substantially improving the time correction quality. For data with relatively low signal-to-noise ratios, the average time errors were reduced from the original average values of 60–80 ms by the conventional methods to <40  ms using the improved approaches. The new multistep procedure developed in this study has general applicability to analysis of other OBS experiments. The demonstrated significant improvements in the data quality are critical for advancing seismic tomography and other modern marine geophysical studies that require high accuracy in the OBS data.

During the indirect hot stamping process of boron steel, the pre-deformed component undergoes air cooling, one-side-contact cooling and both-side-contact cooling phases successively. The effects of pre-deformation and cooling rate on the phase transformation should be understood before conducting indirect hot stamping experiments of vehicle components. Uniaxial tensile tests of boron steel at RT were carried out to obtain specimens with different pre-strain levels. Then they were heated to 900°C according to the indirect hot stamping process and quenching tests were performed on them at different cooling rates. Metallographic observations were performed on the quenched specimens and their hardness was measured. The results show that the pre-strain at RT has little influence on the phase transformation of boron steel. This is due to the dislocation structure introduced by deformation at RT recovered during the heating process and it is good for the indirect hot stamping. Upper B-pillar parts were first cold pre-formed, and then were heated and hot stamped. The microstructure and hardness results at different locations on the indirect hot stamped components are demonstrated qualified.