*3.3. Characterization*

Microstructural examinations were performed using light optical microscopy (LOM) (Olympus Vanox-T AH-2, Tokyo, Japan) and scanning electron microscopy (SEM) (JEOL JSM 6064LV, Tokyo, Japan). X-ray diffraction (XRD) (Siemens D5000 PANalytical Empyrean diffractometer, Munich, Germany) measurements were made with monochromatic CuKα radiation (40 kV and 45 mA). Rietweld analysis was used to establish the volume fraction of austenite present in the microstructures of the hat profiles.

Vickers hardness was measured on the Gleeble specimens using a load of 5 N. A load of 20 N was used for the hat profiles in which the hardness was determined at 5 positions—on the top, side walls 1 and 2, and flanges 1 and 2—as shown in Figure 2.

**Figure 2.** Schematic view of the hat shaped profile, after press hardening operation.

Tensile tests were carried out according to the standard EN ISO 6892-1:2009. One test specimen was laser cut from the top surface of each press hardened hat shaped profile. Reference measurements were performed on isothermally heat-treated samples for both steels but with a shorter gauge length of 25 mm instead of 50 mm because of the limited amount of material available. Steel CR1 was soaked at 400 ◦C for 15 min and steel CR3 at 350 ◦C for 30 min following austenitization at 890 ◦C for 100 s. In principle this temperature does not imply complete austenitization of steel CR1, as the *Ac*<sup>3</sup> temperature was determined to be 895 ◦C: Electron microscopy of a sample quenched from 890 ◦C confirmed the presence of a minute quantity of intercritical ferrite.
