Resistance Heating in XHV-Adequate Atmosphere

An Energy-Efficient Heating Process for Hot Stamping

authored by: Bernd Arno Behrens, Sven Hübner, Ulrich Holländer, André Langohr, Jörn Wehmeyer, Timo Fünfkirchler, Ehsan Farahmand Kahrizi, Lorenz Albracht
Abstract: Hot stamping is used to produce ultra-high-strength components that are used in the automotive industry. Typical applications can be found in the bumper area or in the A and B pillars. In the hot stamping process, a manganese-boron steel is first heated above the austenitisation temperature, usually 950 °C, and then formed and hardened in a water-cooled tool. At cooling rates of more than 27 K/s, a fully martensitic microstructure is established, whereby tensile strengths of more than 1500 MPa can be achieved. The sheets are usually heated in a roller hearth furnace for 8 to 10 minutes so that the aluminium silicon (AlSi) coating forms a sufficient intermetallic phase to prevent the sheet from scaling during heating. Since the heating of the sheets must be coordinated with the cycle time of the press, these roller hearth furnaces are up to 60 m long. Conductive heating provides an alternative here. Due to the very fast heating times of > 100 K/s, sheets can be heated up to 950 °C in less than 10 s in a space-saving manner. Due to the direct current flow through the sheet, 68 % of the energy can be saved compared to roller hearth furnaces. The heating time of 10 s is not sufficient for the common coatings to form a good bond with the sheet material. A new approach is conductive heating in an XHV-adequate atmosphere. The process gases nitrogen and silane reduce the oxygen content in the heating chamber to an XHV-adequate level, which means that uncoated sheets can also be heated without scale. By integrating coating nozzles into the heating chamber, the XHV (extremely high vacuum)-adequate environment and the heating energy can be used to coat the sheets. Within the scope of this research coatings adapted to the rapid heating are developed and tested for the forming temperatures by means of an integrated stretching device inside the chamber.
Organisation(s): Institute of Metal Forming and Metal Forming Machines
Institute of Materials Science
Type: Conference contribution
Pages: 126-132
No. of pages: 7
Publication date: 27.05.2024
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Mechanical Engineering, Mechanics of Materials, Metals and Alloys
Electronic version(s): https://doi.org/10.33313/512/A0603 (Access: Closed)
: Details in the research portal "Research@Leibniz University"

BibTeX

@inproceedings{72cbbac99bac4dccb4690d57b214eaab,
title = "Resistance Heating in XHV-Adequate Atmosphere: An Energy-Efficient Heating Process for Hot Stamping",
abstract = "Hot stamping is used to produce ultra-high-strength components that are used in the automotive industry. Typical applications can be found in the bumper area or in the A and B pillars. In the hot stamping process, a manganese-boron steel is first heated above the austenitisation temperature, usually 950 °C, and then formed and hardened in a water-cooled tool. At cooling rates of more than 27 K/s, a fully martensitic microstructure is established, whereby tensile strengths of more than 1500 MPa can be achieved. The sheets are usually heated in a roller hearth furnace for 8 to 10 minutes so that the aluminium silicon (AlSi) coating forms a sufficient intermetallic phase to prevent the sheet from scaling during heating. Since the heating of the sheets must be coordinated with the cycle time of the press, these roller hearth furnaces are up to 60 m long. Conductive heating provides an alternative here. Due to the very fast heating times of > 100 K/s, sheets can be heated up to 950 °C in less than 10 s in a space-saving manner. Due to the direct current flow through the sheet, 68 % of the energy can be saved compared to roller hearth furnaces. The heating time of 10 s is not sufficient for the common coatings to form a good bond with the sheet material. A new approach is conductive heating in an XHV-adequate atmosphere. The process gases nitrogen and silane reduce the oxygen content in the heating chamber to an XHV-adequate level, which means that uncoated sheets can also be heated without scale. By integrating coating nozzles into the heating chamber, the XHV (extremely high vacuum)-adequate environment and the heating energy can be used to coat the sheets. Within the scope of this research coatings adapted to the rapid heating are developed and tested for the forming temperatures by means of an integrated stretching device inside the chamber.",
author = "Behrens, {Bernd Arno} and Sven H{\"u}bner and Ulrich Holl{\"a}nder and Andr{\'e} Langohr and J{\"o}rn Wehmeyer and Timo F{\"u}nfkirchler and Kahrizi, {Ehsan Farahmand} and Lorenz Albracht",
note = "Publisher Copyright: {\textcopyright} CHS2 2024 . All rights reserved.; 9th International Conference on Hot Sheet Metal Forming of High-Performance Steel, CHS2 2024 ; Conference date: 27-05-2024 Through 29-05-2024",
year = "2024",
month = may,
day = "27",
doi = "10.33313/512/A0603",
language = "English",
pages = "126--132",
editor = "Daniel Casellas and Jens Hardell",
booktitle = "9th International Conference on Hot Sheet Metal Forming of High-Performance Steel",
publisher = "Association for Iron and Steel Technology, AISTECH",
}