In automotive design, higher safety requirements, lower weight
and CO₂ emissions, and compact design, all speak for the use of
ultra-high-strength steels. But still today there is a lot of
caution when such steels are used, due to presumed lack of
formability and the ductility in the material after forming. In the
current paper, a design in the ultra-high-strength steel Docol 1200
M will be shown, which clearly shows the potential in terms of
safety and compact design when using such steels, but also the
formability and ability to withstand deformations in a crash
situation of the steel involved.
The application is an inflatable side impact beam for a
passenger vehicle. The inflatable side impact beam is a compact
module made of thin-walled metal and pyrotechnics comparable to the
ones used for airbag application.
Within a few milliseconds, inflation causes thin-walled metal to
deform/expand and the pressure to increase up to 20 bar inside the
structure.
Larger cross-section beam provides then similar or higher impact
performance and increased protection of occupant with lower
weight.
The material used for the structure is Docol 1200 M, an
ultra-high-strength cold-rolled martensitic steel. The steel, which
is delivered in quenched condition, has a minimum tensile strength
of 1200 MPa, and is cold formed to the structure shown in picture
below. The part was formed to the final shape in two forming steps,
after which it was assembled with the bottom part with the
pyrotechnics inside. Details of the forming process are given in
the paper.
The application shows the possibilities which exist when new
thinking is combined with new, ultra-high-strength steel
grades.