Increasing the energy absorption capacity of structural components made of low alloy steel by combining strain hardening and local heat treatment

Modern high and ultra-high strength steels often require extensive alloy concepts and complex processing routes. To tailor the properties of low alloy steel accordingly, strain hardening combined with a subsequent local heat treatment presents a promising alternative. As a result, the final annealing step of the whole steel strip after cold rolling can be omitted. This process combination can be used to locally increase the formability of semi-finished parts as well as to improve the functionality of final parts. In this work, local heat treatment strategies are applied to increase the energy absorption capacity of a structural component. A high strength low alloy steel is strain hardened by cold rolling and heat-treated locally via laser irradiation. To identify suitable parameters for the laser heat treatment, the material is subjected to a short time heat treatment followed by a tensile test in a dilatometer. The determined mechanical properties are used for an FE study of a crash test. The FE model is used to develop potential local heat treatment strategies and to evaluate their crashworthiness. To validate the model, the developed heat treatment strategies are applied on real crash boxes. In dynamic impact tests, it is shown that the combination of strain hardening and local heat treatment can be used to improve the energy absorption capacity compared to a globally heat-treated crash box and to control the crash behaviour of structural components.