The Nb microstructural refinement in HR1000 – 1200TS automotive steels with different type of microstructures – impact on global and local formability

In the automotive industry, the use of hot-rolled steels with improved balance of strength and ductility ensures high cost-effectiveness, better fuel economy and passenger safety. High strength hot-rolled sheet steels with excellent combinations of strength and ductility as measured e.g. globally by the elongation to fracture or locally by the hole expansion test are used to increase for example the performance of various chassis parts. However, in the assembly, stamping operations such as drawing, stretching, bending, blanking, trimming, flanging produces various stress states to the formed steel parts and may initiate manufacturing defects either in subsequent processing steps or later in use. Therefore, microstructural features that improve the damage tolerance of the material are desirable.

The main objective as general point of view is to see the effect of different kind of microstructures in strength level 1000 – 1200 MPa on global and local formability, and to find optimal concept for producing over 1000 MPa steel with excellent stretch-flangeability properties for automotive applications.

The more specific aims of the project are as follows:

• To find chemistry that best suits for fully martensitic strip steel with 1000-1200 TS and high local formability
• To explore how alloying would benefit local and global formability in low and high temperature tempering scenarios
• To investigate the effect of the tempering temperature on formability properties
• To explore the possibility to produce over 1000 MPa ferritic steel with suitable formability properties
• To investigate the effects of galvanizing process in the making of 1000-1200 TS steel

Partners

SSAB Europe Oy, Companhia Brasileira de Metalurgia e Mineração (CBMM)