Microstructure and properties characterization of a Ti-Nb high strength micro alloyed steel for cold forming
Bruno Bastos da Silva Murad; Angelo Fernando Padilha
Abstract
Driven by new market demands, environmental regulations and an ever-increasing pressure for lower weight and carbon footprint reduction in vehicles and transportation industry, suppliers have been pushed to develop new solutions which often translate themselves into more resistant, thinner, and wider hot and cold rolled steel products for downstream forming. In such applications, cracking during flanging operations is the major restriction in the use of an advanced high strength steels and a good stretch-flangeability is an essential property for complex press formed parts such as chassis, suspension arms, semi-trailers, and agricultural components. This paper consists of a wide and logical microstructural and properties characterization of a hot rolled Ti-Nb micro alloyed steel for cold forming, whose simulations via ThermoCalc predicted a final BCC structure with small amounts of cementite with additional FCC carbides. CCT and TTT diagrams also simulated via JMatPro suggested a final microstructure of ferrite α, what was later confirmed by X ray diffraction. Both optical and scanning electronic microscopy confirmed the presence of ferrite α, cementite, and the niobium and/or titanium enriched precipitates predicted in earlier simulations. Finally, yield and tensile strengths of 790 and 815 MPa, respectively, in longitudinal direction, and total elongation until fracture of 17% plus the absence of cracks in bending tests confirmed that sampled material meets all requirements for grades S650MC and S700MC stated in EN1019-2.
Keywords
Referências
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Submetido em:
18/07/2024
Aceito em:
06/02/2025
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