Short-time heat treatment of press hardened steel for laser assisted clinching

Abstract

Clinching of high strength steels is currently difficult due to their relative low ductility. Hence a new method has been developed to clinch these steel grades. This could be achieved by heating the sheets locally at the joint by a laser during the clinching process. The short-time tempering behaviour of the press hardened steel 22MnB5 has been investigated by dilatometry respectively calorimetry experiments. Different stages of the tempering process have been identified depending on heating rates up to 1000 K s⁻¹. Characteristic tempering reactions were shifted to higher temperatures with increasing heating rate. Based on these results, suitable short-time heat treatment parameters have been selected and transferred to the clinching process. Thereby the press hardened steel 22MnB5 has been successfully clinched with laser assistance for the very first time. The laser assisted clinched joint has been characterised by metallographic analysis and hardness testing. It could be shown, that in the clinching joint only a slight strength loss occurs due to the introduced laser heat.

Keywords:

• Press hardened steel
• 22MnB5
• Tempering
• Dilatometry
• Calorimetry
• Laser assisted clinching

Acknowledgement

The authors gratefully acknowledge funding of this work by the Deutsche Forschungsgemeinschaft, project KE616/19-1 and FU307/9-1, in the framework of the Priority Program 1640 ‘Joining by Plastic Deformation’.