Essential work of fracture and absorbed energy by Charpy impact test of TRIP780 1.5 mm thick sheet steel Kerbschlagarbeit und absorbierte Energie bei der Charpy-Schlagprüfung an 1,5 mm dickem Restaustenitstahlblech (HCT 780)

Abstract

Transformation-induced plasticity (TRIP) steels have been extensively studied concerning their mechanical performance under monotonic loading and conventional microstructural characterization. However, despite their pivotal role in various industries, particularly automotive, limited attention has been devoted to the fracture toughness of TRIP steels, especially in thin sheet forms. Given the increasing demand for materials with enhanced toughness, reliable and rapid alternative methods for measuring toughness are required. In this research, we evaluate the fracture toughness of TRIP780 steel, presented as 1.5 mm-thick sheets. The study analyzes its mechanical behavior using mechanical strength (tensile tests), toughness, and absorbed energy (essential work of fracture – EWF and Charpy impact tests). The microstructural characterization was performed using LePera chemical etchant and x-ray diffraction techniques, revealing a multi-phase structure comprising ferrite, bainite, and martensite/austenite constituents. The findings indicate that TRIP780 exhibits commendable ductility and energy absorption, with an essential work of fracture of 133.6 kJ/m². However, the impact test exhibited notable temperature sensitivity, as observed in the transition from ductile behavior at room temperature to brittle cleavage at -50 °C. Furthermore, discrepancies between our results and data reported in the literature suggest that the steel processing conditions strongly influence fracture behavior.