*2.1. Materials*

Figure 1a shows that the function of the center pillar during a side crash. Generally, the HPF center pillar has a low elongation of less than 5%, so collision toughness is not satisfied. In addition, the stiffness of the center pillar in the top region is not sufficient against intrusion resistance. The PS technique provides ductility to the HPF center pillar and, PW strengthens the stiffness of the HPF center pillar to improve collision characteristics, such as energy absorption and intrusion resistance.

**Figure 1.** (**a**) Function of the center pillar during a side crash. (**b**) Four kinds center pillars [20].

In this study, a 22MnB5 boron steel sheet was used for the HPF center pillar and PW. The PS region was controlled by a cartridge heater during manufacturing of the HPF center pillar [20]. Table 1 shows the material properties of 22MnB5 (HPF) and 22MnB5 (PS). The thicknesses of the HPF center pillar and PW were both 1.2 mm. To evaluate the effect of PW and PS on energy distribution and intrusion resistance, a side crash simulation was performed with four kinds of the center pillar, as shown in Figure 1b.


**Table 1.** Material properties of 22MnB5 (HPF) and 22MnB5 (PS) [20].
