Mechanical and Microstructural Analyses of Advanced High-strength Steels

The microstructure and fracture behaviour of two advanced high-strength steels designed for automotive components were studied. The steels were produced by the thin-strip continuous casting and hot rolling route. Samples from both steels were cut along three directions corresponding to 0 degrees, 45 degrees and 90 degrees inclination concerning rolling and were tested in tension. Microstructural observations were conducted by light optical and scanning electron microscopy; selected samples were prepared for their electron backscattered analyses. The fracture surfaces of the tension samples were observed by scanning electron microscopy in which different morphologies were observed, such as blisters and in one steel, delamination fissures; TiN particles were present within the fracture surfaces. Electron backscattered diffraction analyses assume that ferrite is formed from recrystallized austenite in both steels. Solidification and solid-transformation analyses were conducted to clarify the role of the various microstructural constituents in the steels.