The cost and availability of high tensile strength steel has improved significantly over the past 15 years. What once were mild steel reinforcements in the A and B-Pillars are now routinely made out of boron steel, as shown here.
The typical steel “banana chart” shown here compares various steel grades. When reviewing the history of pillar material choices, there is a gap where advanced high-strength materials suddenly jumped to ultra high-strength steel such as boron. Part of this is due to new side-impact crash management needs where the high strength of boron steel helps meets the performance targets. Hot-formed steels also permit good shape and manageable spring back. While it is possible lesser grades could have met performance targets, the lack of forming properties and high spring back of HSLAs,
and DP materials or the high prices of CP and TRIP materials made boron an