**Hot Forming of Ultra-Fine-Grained Multiphase Steel Products Using Press Hardening Combined with Quenching and Partitioning Process**

**Esa Pirkka Vuorinen 1,\*, Almila Gülfem Özügürler 1, John Christopher Ion 1, Katarina Eriksson 2, Mahesh Chandra Somani 3, Leo Pentti Karjalainen 3, Sébastien Allain <sup>4</sup> and Francisca Garcia Caballero <sup>5</sup>**


Received: 18 February 2019; Accepted: 18 March 2019; Published: 20 March 2019

**Abstract:** Hot forming combined with austempering and quenching and partitioning (QP) processes have been used to shape two cold rolled high silicon steel sheets into hat profiles. Thermal simulation on a Gleeble instrument was employed to optimize processing variables to achieve an optimum combination of strength and ductility in the final parts. Microstructures were characterized using optical and scanning electron microscopy and X-ray diffraction. Tensile strengths (*Rm*) of 1190 and 1350 MPa and elongations to fracture (*A*50mm) of 8.5 and 7.4%, were achieved for the two high-silicon steels having 0.15 and 0.26 wt % C, respectively. Preliminary results show that press hardening together with a QP heat treatment is an effective method of producing components with high strength and reasonable tensile ductility from low carbon containing steels that have the potential for carbide free bainite formation. The QP treatment resulted in faster austenite decomposition during partitioning in the steels in comparison with an austempering treatment.

**Keywords:** hot forming; multiphase steel; quenching and partitioning; austempering; Gleeble simulation; press hardening
