Tailoring Soft Local Zones in Quenched Blanks of the Steel 22MnB5 by Partial Pre-cooling with Compressed Air

authored by: Oleksandr Golovko, Max Henry Stolte, Kai Wölki, Sven Hübner, Bernd Arno Behrens, Hans Jürgen Maier, Florian Nürnberger
Abstract: The high-strength boron steel 22MnB5 steel is widely used for automotive lightweight constructions. A novel approach is promising to tailor strength and ductility in the hardened condition using locally pre-tempered sheets for the hot stamping process. It results in the formation of locally soft spots where mechanical joining is subsequently intended. A slow pre-cooling of the later joining zones with cooling rates below a certain critical cooling rate for obtaining a decreased strength in these regions is required. A tubular air cooling system suited for this task is presented and tested in a process where the subsequent quenching of the overall sheet is realized by rapid cooling in a water bath. Varying the air pressure and cooling duration allows controlling the size of the softened local spot in a wide range and still obtaining a bainitic microstructure. Using two-stage cooling with point jet nozzles and a subsequent hot stamping process with water-cooled dies resulted in a main sheet hardness of about 470 HV5 and of 260 HV5 in the pre-cooled spots, respectively.
Organisation(s): Institute of Materials Science
Institute of Metal Forming and Metal Forming Machines
Type: Article
Journal: Journal of Materials Engineering and Performance
Volume: 29
Pages: 4379-4389
No. of pages: 11
ISSN: 1059-9495
Publication date: 07.2020
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: General Materials Science, Mechanics of Materials, Mechanical Engineering
Electronic version(s): https://doi.org/10.1007/s11665-020-04916-5 (Access: Open)
: Details in the research portal "Research@Leibniz University"

BibTeX

@article{de6d6aa94c7947c3bc8dec3314cc9852,
title = "Tailoring Soft Local Zones in Quenched Blanks of the Steel 22MnB5 by Partial Pre-cooling with Compressed Air",
abstract = "The high-strength boron steel 22MnB5 steel is widely used for automotive lightweight constructions. A novel approach is promising to tailor strength and ductility in the hardened condition using locally pre-tempered sheets for the hot stamping process. It results in the formation of locally soft spots where mechanical joining is subsequently intended. A slow pre-cooling of the later joining zones with cooling rates below a certain critical cooling rate for obtaining a decreased strength in these regions is required. A tubular air cooling system suited for this task is presented and tested in a process where the subsequent quenching of the overall sheet is realized by rapid cooling in a water bath. Varying the air pressure and cooling duration allows controlling the size of the softened local spot in a wide range and still obtaining a bainitic microstructure. Using two-stage cooling with point jet nozzles and a subsequent hot stamping process with water-cooled dies resulted in a main sheet hardness of about 470 HV5 and of 260 HV5 in the pre-cooled spots, respectively.",
keywords = "air pre-cooling, press hardening, process-integrated heat treatment",
author = "Oleksandr Golovko and Stolte, {Max Henry} and Kai W{\"o}lki and Sven H{\"u}bner and Behrens, {Bernd Arno} and Maier, {Hans J{\"u}rgen} and Florian N{\"u}rnberger",
note = "Funding information: Open Access funding provided by Projekt DEAL. The presented data were obtained within the project “Production of areas with reduced strength in press-hardened components by means of a tempering station,” Project Number 313453754, granted by the German Research Foundation (DFG). The authors are thankful for the financial support.",
year = "2020",
month = jul,
doi = "10.1007/s11665-020-04916-5",
language = "English",
volume = "29",
pages = "4379--4389",
journal = "Journal of Materials Engineering and Performance",
issn = "1059-9495",
publisher = "Springer New York",
number = "7",
}