Patent ID: 8852367

Claim:
A method of producing high-strength hollow bodies from multiphase martensitic steels, where the production includes a heating process, a forming process and a cooling process, comprising the steps of: heating a body of hollow steel stock to about an austenitic temperature of the steel material from which the body of hollow steel stock is made; converting the body of hollow steel stock by deformation of the body of hollow steel stock in a forming device into a hollow body having a final shape; initially cooling the hollow body having the final shape in an initial cooling device after the converting step in such a way that the steel material comprising the hollow body having a final shape and having an original austenite microstructure refined by deformation introduced during the converting step is initially cooled down to a temperature between the temperature at which martensite begins to form and the temperature at which martensite formation is finished, such that incomplete transformation of austenite to martensite takes place and part of austenite remains in a meatastable state, to yield an initially cooled hollow body comprising retained austenite; immediately after the initial cooling down to the temperature between the temperature at which martensite begins to form and the temperature at which martensite formation is finished, annealing the initially cooled hollow body in an annealing device at a temperature above the initial cooling temperature, whereby retained austenite stabilization is performed in the annealing device by diffusion-based carbon partitioning within the material of the initially cooled hollow body to yield an annealed hollow body; and finally cooling the annealed hollow body to ambient temperature in a final cooling device after the annealing step has finished the retained austenite stabilization, to yield a hollow body having increased residual ductility.