Influência do ciclo térmico de austêmpera no comportamento mecânico do aço alto C-Si-Mn-Cr com efeito TRIP

Abstract

The influence of austempering thermal cycle on the mechanical behavior of a 0.6%C-1.5%Si-0.8%Mn-0.77%Cr steel with TRIP effect was investigated. The thermal cycle consisted on heating the steel in the intercritical field at 800 ºC and in the austenitic field at 900 ºC, fast cooling down to 600 or 400 ºC, followed by austempering in these temperatures for 300 s. After austempering, the material was cooled with different rates down to room temperature. The mechanical properties were evaluated by tensile and hardness tests. The microstructure was evaluated using optical and scanning electron microscopy. The retained austenite and its carbon content were quantified with x-rays diffraction, whose results were associated with the parameters of the thermal cycle and microstructure. High levels of ductility, measured by reduction of area (50-70%), and tensile strength (1300-1400 MPa) were reached with austenitizing at 900°C, austempering at 400°C and fast cooling. The austenitetransformation to martensite during plastic deformation (TRIP effect) isresponsible for this combination of high strength and ductility.