Hydrogen Absorption and Desorption Behavior on Aluminum-Coated Hot-Stamped Boron Steel during Hot Press Forming and Automotive Manufacturing Processes

Abstract

Our study mainly focused on diffusible hydrogen in aluminum–silicon-coated hot-stamped boron steel during a hot press forming process and in pre-treatment sequential lines of the automotive manufacturing process using a thermal desorption spectroscopy (TDS) technique. First, in the hot stamping procedure, as the soaking time increased in the heating furnace at a specific dew point when austenitizing, a high concentration of diffusible hydrogen was absorbed into the hot-stamped boron steel. Based on the TDS analysis of hydrogen absorbed from hot stamping, the activation energy value of hydrogen trapping in 1.8 GPa grade steel is lower than that of 1.5 GPa grade steel. This means that diffusible hydrogen can be more easily diffused into defective sites of the microstructure at a higher level of the tensile strength grade. Second, in sequential pre-treatment lines of the automotive manufacturing process, additional hydrogen did not flow into the surface, and an electro-deposition process, including a baking procedure, was effective in removing diffusible hydrogen, which was similar to the residual hydrogen of the as-received state (i.e., initial cold rolled blank). Based on these results, the hydrogen absorption was facilitated during hot press forming, but the hydrogen was sequentially desorbed during automotive sequential lines on aluminum-coated hot-stamped steel parts.

Analysis of characteristic prediction of aluminized boron steel after the hot stamping process using an image color-based neural network

“…In this case, the heating time is assumed as 1/3 of the total heating time, as the time spent at the austenite phase is signi cant. The diffusion coe cient D is used (D = D 0 exp(-W/RT), where D 0 is 4.4×10 − 7 m/s 2 , W is the apparent activation energy of 37 KJ/mol) at high temperatures [26][27][28][29][30][31][32][33][34][35]. Additionally, taking into account that hydrogen diffuses for both sides of the 22MnB5 sheet, x is set to half of the sheet thickness, which is 1.6mm.…”

“…To analyze the diffusible hydrogen, the model validation was evaluated using the thermal desorption analysis (TDA) analysis [31,32]. TDA analysis was conducted by heating the sheet at approximately 20 ℃/min in the nitrogen atmosphere and analyzing the hydrogen desorption from the sheet in ppm/s units [31][32][33][34][35]. Figure 12 represents the hydrogen uptake of approximately 0.47 ppm based on the experimental center pillar vehicle part.…”

Minor Addition with Substantial Effect - New Aluminum-Silicon Coating for a Reliable Hot-Forming Process

“…After hot forming and cooling down to ambient temperature the alloyed Al-Fe-Si coating layers have only a low permeability for hydrogen effusion. Thus, sufficiently long desorption times need to be considered or, alternatively, a tempering process is required, in order to reduce the hydrogen content in the press-hardened component by degassing through the alloyed coating [5][6][7][8].…”