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In this study, strong {0002} textured (or strong ND//<0002> textured) AZ31 Mg alloy sheets were prepared. These AZ31 Mg alloy sheets were cut along the angles of 0, 12.5, 25, 30 and 37.5 degrees to the rolling direction or {0002} texture. Prepared samples with different angles to the rolling direction were rolled at room temperature and after subsequent heat treatment, the bendability, ultimate tensile stress, elongation and texture are investigated using the 3-points bending tester, tensile tester and x-ray diffractometer, respectively. The specimen having along the angles of 0 degree to the rolling direction shows the highest load and 45 degrees specimen shows the highest displacement among any other specimens in the bending test. The specimen having along the angles of 12.5 and 25 degrees to the rolling direction shows highest elongation and of 0 degree specimen shows the highest ultimate tensile stress among any other specimens after cold rolling and subsequent heat treatment at 150°C for 30 minutes in bending test.

The emphasis on passenger safety and fuel efficiency has led to a significant increase in the usage of hot stamped boron steels in automobile applications due to their high strength-to-weight ratio. The most common applications of boron steels in vehicles are as structural reinforcements used to resist the impact deformation. The performance of the parts to resist side impact deformation mainly depends on the cold bending property of the material. This paper presents the approach by optimizing the amount of Nb micro alloying in the boron steel to improve its toughness. The results show that the bendability of boron steel can be significantly improved due to the original austenite grain size of the material is refined by adding an appropriate amount of Nb micro alloying.

Press hardening steel (PHS) of 1500MPa grade has been widely used in the car body structure of modern vehicles today. The global trend for light-weighting and safety will drive OEMs to further increase the strength of car body structure in the future. This has given steel industry momentum to develop new advanced high strength steels (AHSS) including PH1800 or even PH2000. The conventional steel grade of PH1500 is based on the Mn-B concept (22MnB5). For the new grade of PH1800, basically only carbon content needs to be increased from 0.22 (PH1500) to 0.32% to reach 1800MPa strength after press hardening. However, due to higher strength related to higher carbon content, PH1800 has lower fracture resistance under impact load, especially at lower temperature or under the influence of hydrogen embrittlement. The delayed cracking due to hydrogen embrittlement is the major concern for OEMs to use high strength PHS currently. Therefore, the development of PH1800 should be focused on the improvement of resistance to hydrogen embrittlement which requires the fundamental changes in alloying design and process optimization compared to conventional PH1500. This paper will highlight the alloying design and process strategy for the new steel grade of PH1800 with the target to improve the crash performance by increasing the fracture resistance under impact load or during bending deformation, especially the resistance to hydrogen induced delayed cracking. The key solution is to achieve the optimum steel microstructure characterized by clean steel matrix with less inclusions and large particles, refined martensite substructure with high share of high angle grain boundary, high homogeneity with less or no banding structure and finely-dispersed precipitates of NbC as hydrogen traps. Based on the experiences gained from development of Nb alloyed PH1500, the new alloying design and process strategy for PH1800 will be discussed.

The global reduction of CO₂ emission generated by cars is a major challenge of the 21st century. The lightweighting of automotive structures is mandatory to achieve the ambitious environmental targets. The use of high strength steels in the car design, and especially, Press Hardened Steels (PHS) with tensile strength higher than 1000MPa, is one the most cost-efficient way to help the car makers to keep excellent crash behavior on mass saving body-in-white structures. The 2nd generation of PHS recently developed at ArcelorMittal is being deployed worldwide with Usibor^®2000 and Ductibor^®1000. These new grades demonstrate that CMnB metallurgies, commonly used in hot stamping, must be optimized to offer steel solutions with suitable properties for anti-intrusion and energy absorption parts. As a key metallurgical feature of these martensitic steels, a good control of inclusions and precipitations is necessary to improve the crash ductility. Among different factors influencing the bending properties of the martensitic microstructure, the present paper focuses on the effect of cleanliness of advanced steels for press hardening. The characteristics of the particles formed in the earlier stage of the steelmaking production are linked to the final In-Use Properties of the PHS. The type of particles and its geometry, such as cubic TiN, spherical complex oxides or disk-like manganese sulfides plays a different role in the crack initiation and crack propagation mechanisms. A high density of large inclusions is to be avoided as they act as local heterogeneities in the microstructure which can be detrimental to achieve a good crash performance. Particles close to the surface are even more damaging than particles localized in mid thickness. As an indirect effect, grain size refinement induced by precipitation of micro-alloying elements (Ti, Nb, V) also contributes to the achievement of a fine martensite which is essential to obtain a PHS grade with superior crash ductility. All these aspects have been integrated in the metallurgical design of Usibor^®2000 and Ductibor^®1000 and contribute to the remarkable and robust performances of these new PHS products.

In this study, strong {0002} textured (or strong ND//<0002> textured) AZ31 Mg alloy sheets were prepared. These AZ31 Mg alloy sheets were cut along the angles of 0, 12.5, 25, 30 and 37.5 degrees to the rolling direction or {0002} texture. Prepared samples with different angles to the rolling direction were rolled at room temperature and after subsequent heat treatment, the bendability, ultimate tensile stress, elongation and texture are investigated using the 3-points bending tester, tensile tester and x-ray diffractometer, respectively. The specimen having along the angles of 0 degree to the rolling direction shows the highest load and 45 degrees specimen shows the highest displacement among any other specimens in the bending test. The specimen having along the angles of 12.5 and 25 degrees to the rolling direction shows highest elongation and of 0 degree specimen shows the highest ultimate tensile stress among any other specimens after cold rolling and subsequent heat treatment at 150°C for 30 minutes in bending test.