High Temperature Plastic Deformation Behavior and Brittle Mechanism of S450EW Steel

Abstract

High-temperature tensile tests were conducted for high corrosion resistant weathering steel S450EW. The morphologies of fracture microstructures, dislocations and precipitates were investigated by field emission scanning electron microscopy and transmission electron microscopy. The high-temperature plastic deformation behavior and brittle mechanism of S450EW steel were also studied. The experimental results show that the ductility troughs appear at 700–850°C and 650–900°C when the strain rates are 3×10⁻³ and 1.5×10⁻² s⁻¹, respectively. With the increase of strain rates, the ductility trough moves to the lower temperature side. The hot ductility is best when the cooling rate is 5 °C/s before deformation at 750 °C and the area reduction rate reaches 60.56%. Fine second phase particles and inclusions precipitated before and during deformation provide effective core positions for microcracks or microvoids formation during deformation process. It is also easy to cause stress concentration which results in microcracks or microvoids between grains during deformation and ultimately causes damage along the grain boundaries. The precipitated particles inhibit austenite dynamic recrystallization and therefore enhance intergranular fracture along austenite grain boundaries. The deformation induced proeutectoid ferrite films distribute along the austenite grain boundaries hinder the dynamic recrystallization. The deformation concentrated on network ferrite films produces damage of grain boundaries.

Keywords

corrosion resistant steel / hot ductility / dynamic recrystallization / DIFT / brittle mechanism

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