Abstract
Safety-relevant components in automobiles require materials that combine high strength with sufficient residual ductility and high-energy absorption. A graded thermo-mechanical treatment of the press-hardening steel 22MnB5 with graded microstructure can provide a material with such properties. Different austenitization temperatures, cooling and forming conditions within a sheet part lead to the development of microstructures with mixed phase compositions. To determine the resulting phase contents in such graded processed parts, a large number of dilatometric tests are usually required. With a non-contact characterization method, it is possible to detect local phase transformations on an inhomogeneously treated flat steel specimen. For press-hardening steel after heat treatment and thermo-mechanical processing, correlations between austenitization temperature, hot deformation strain, microstructure, and hardness are established.
Highlights
DUE to their advantageous specific properties such as a high strength combined with a sufficient residual deformability and a high-energy absorption in the event of a crash, press-hardened components find increasing use in the automotive industry.[1]
For the green curves, which represent the cooling curve and the Duy/ DT curve for an austenitization temperature of 800 °C, the bainite start temperature (Bs) was at 659 °C and the martensite start temperature (Ms) at 437 °C; martensitic transformation (Mf) amounted to 267 °C
At a cooling rate of about 23 K/s, the resulting microstructure should consist of martensite and bainite, with a high proportion of martensite according to Reference 3
Summary
DUE to their advantageous specific properties such as a high strength combined with a sufficient residual deformability and a high-energy absorption in the event of a crash, press-hardened components find increasing use in the automotive industry.[1] The martensitic microstructure of a press-hardened part, which reaches tensile strengths of up to 1500 MPa, develops during the simultaneous forming and quenching in cooled dies.[2] While a cooling rate above the critical rate of 25 K/s is required for the formation of a fully martensitic microstructure according to the continuous cooling transformation (CCT) diagram of 22MnB5, softer phases such as ferrite, perlite, and bainite are formed at lower cooling rates.[3] The formation of these phases is influenced by hot deformation, whereby a shift of the ferritic and bainitic area to shorter times has been observed at a hot deformation degree of 20 or 40 pct.[4,5,6] A specific adjustment of a mixed microstructure can produce a material with both high strength and elongation, for which phase compositions of martensite and bainite or martensite and ferrite are favorable.[7].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
