Tailor Tempering and Hot-Spotting of Press Hardened Boron Steels

Abstract:

Hot forming processes are becoming a successful solution when complex geometrical components with high mechanical properties are desired. In fact, automotive structural components with tensile strengths higher than 1500MPa are being nowadays industrially produced. The technology is based on the forming and quenching of the sheet inside the forming tool using boron steels. Aiming at boosting the advantages of this technology, car manufacturers have started to demand structural components with different mechanical behavior areas in order to improve the impact response of the auto-motive passenger compartment: the so called tailor tempered components. The basic idea is to obtain final parts with different properties like it has been successfully done using tailored welded blanks. Although different solutions exist, one of the most common strategy is to use partially heated tooling, which influences the cooling of the sheet and consequently the local properties. At the present work, a special tooling with independent heated and cooled areas has been developed in order to evaluate the final properties achievable in the tailored tempering process. High and low conductivity alloys have been used to find the process limits and compare them to classical tool steels. Hardness values, Ultimate Tensile Stresses and microstructures are shown for different steels, tool temperatures and contact pressures. In the last part of the paper, the hot spotting results are presented. Different air gap diameters have been used to evaluate the possibility to create soft spots that will enable an easier cutting of geometrically accurate holes and a more suitable and ductile join between different components by using the spot welding.

• Periodical: Key Engineering Materials (Volumes 651-653)
• Pages: 789-795
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.651-653.789
• Online since: July 2015
• Authors: Lander Galdos*, Eneko Saenz de Argandoña, Joseba Mendiguren, Nuria Herrero, Rafael Ortubay, Xabier Agirretxe, José Miguel Martín
• Keywords: Boron Steels, Hot Spotting, Hot Stamping, Tailor Tempering

References

[1] H. Karbasian, A.E. Tekkaya, A review on hot stamping, Journal of Materials Processing Tech-nology 210 (2010) 2103–2118.

DOI: 10.1016/j.jmatprotec.2010.07.019

[2] Bardelcik, A., Salisbury, C., Winkler, S., Wells, M.A., Worswick, M.J., 2010, Effect of cooling rate on the high strain rate properties of boron steel, International Journal of Impact Engineering 37 (6), 694–702.

DOI: 10.1016/j.ijimpeng.2009.05.009

[3] Wilsius, J., Tavernier, B., Abou-Khalil, D., 2011, Experimental and numerical investigation of various hot stamped B-pillar concepts based on Usibor® 1500P, 3rd International Conference on Hot Sheet Metal Forming of High-Performance Steel, Kassel, Germany, 427–435.

[4] Stöhr, T., Lechler, J., Merklein, M., 2009, In-vestigations on different strategies for influencing the microstructural properties with respect to partial hot stamping, 2nd International Conference on Hot Sheet Metal Forming of High-Performance Steel, Lulea, Sweden, 273–281.

[5] Ghiotti, A., Borsetto, F., Bruschi, S., 2009, Investigation of the high strength steel Al–Si coat-ing during hot stamping operations, Key Engineer-ing Materials 410–411, 289–296.

DOI: 10.4028/www.scientific.net/kem.410-411.289

[6] George R., Bardelcik A., Worswick M.J., 2012, Hot forming of boron steels using heated and cooled tooling for tailored properties P, Journal of Materials Processing Technology 212, 2386– 2399.

DOI: 10.1016/j.jmatprotec.2012.06.028

[7] Tang B.T., Bruschi S., Ghiotti A., Bariani P.F., Numerical modelling of the tailored tempering process applied to 22MnB5 sheets, 2014, Finite Elements in Analysis and Design 81, 69–81.

DOI: 10.1016/j.finel.2013.11.009

[8] Mori K., Okuda Y., 2010, Tailor die quenching in hot stamping for producing ultra-high strength steel formed parts having strength distribution, CIRP Annals - Manufacturing Technology 59, 291–294.

DOI: 10.1016/j.cirp.2010.03.107