The investigations deal with processes leading to local effects of strengthening in multiphase steels, being characterized by good formability, continuous yielding, high strength and a strong bake hardening and ageing effect. Dual phase and complex phase steels are under investigation to examine the effect of thermo-mechanical processing parameters on local ageing ability and its use for designed properties. For this purpose local heat treatment by laser are studied, as well as stability of local ageing on the adjusted strength. A remarkable increase of the hardness in the heat treated zone was observed. Stability of the local strengthening effect could be confirmed. Partial heat treatment of multiphase steels by laser can open a new field of application for the local use of the strengthening effect to influence only relevant areas, thus giving potential for energy saving.