TY - JOUR

T1 - Tailoring Soft Local Zones in Quenched Blanks of the Steel 22MnB5 by Partial Pre-cooling with Compressed Air

AU - Golovko, Oleksandr

AU - Stolte, Max Henry

AU - Wölki, Kai

AU - Hübner, Sven

AU - Behrens, Bernd Arno

AU - Maier, Hans Jürgen

AU - Nürnberger, Florian

N1 - 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.

PY - 2020/7

Y1 - 2020/7

N2 - 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.

AB - 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.

KW - air pre-cooling

KW - press hardening

KW - process-integrated heat treatment

UR - http://www.scopus.com/inward/record.url?scp=85087341541&partnerID=8YFLogxK

U2 - 10.1007/s11665-020-04916-5

DO - 10.1007/s11665-020-04916-5

M3 - Article

AN - SCOPUS:85087341541

VL - 29

SP - 4379

EP - 4389

JO - Journal of Materials Engineering and Performance

JF - Journal of Materials Engineering and Performance

SN - 1059-9495

IS - 7

ER -