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

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Original languageEnglish
Pages (from-to)4379-4389
Number of pages11
JournalJournal of Materials Engineering and Performance
Volume29
Issue number7
Publication statusPublished - Jul 2020

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

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Tailoring Soft Local Zones in Quenched Blanks of the Steel 22MnB5 by Partial Pre-cooling with Compressed Air. / Golovko, Oleksandr; Stolte, Max Henry; Wölki, Kai et al.
In: Journal of Materials Engineering and Performance, Vol. 29, No. 7, 07.2020, p. 4379-4389.

Research output: Contribution to journalArticleResearchpeer review

Golovko O, Stolte MH, Wölki K, Hübner S, Behrens BA, Maier HJ et al. Tailoring Soft Local Zones in Quenched Blanks of the Steel 22MnB5 by Partial Pre-cooling with Compressed Air. Journal of Materials Engineering and Performance. 2020 Jul;29(7):4379-4389. doi: 10.1007/s11665-020-04916-5
Golovko, Oleksandr ; Stolte, Max Henry ; Wölki, Kai et al. / Tailoring Soft Local Zones in Quenched Blanks of the Steel 22MnB5 by Partial Pre-cooling with Compressed Air. In: Journal of Materials Engineering and Performance. 2020 ; Vol. 29, No. 7. pp. 4379-4389.
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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.",
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