In the last years, since nickel price increased, another series of austenitic stainless steel with less amount of nickel has emerged: the series 200. The AISI 201 stainless steel has been used where intermediated corrosion resistance is needed. In this work, the formation of straininduced martensite and its reversion in an AISI 201 austenitic stainless steel were studied. The material was characterized in terms of microstructure and then cold rolled up to 20, 40 and 60% of thickness reduction. For all degree of reduction, samples were annealed at several temperatures o C) for 1 hour. Additional samples taken from the 60% cold-rolled material were also annealed at several temperatures (200-800 o C) for several times (5-180minutes). The microstructural evolution during cold rolling and annealing was evaluated using microhardness Vikers testing, light optical microscopy, scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction, X-Ray diffraction and magnetization measurements. Phase predictions were also performed using software Thermocalc©. It was observed that the as-received material was not fully austenitic. It has a small fraction of -ferrite within its matrix. The amount of ferromagnetic phase (martensite) increases with increasing deformation. For small deformation (20%), there is a peak in the coercive field of the material (Hc). As deformation increases, Hc values decrease. It was also observed that the martensite reversion takes place at 500-700 o C. The behavior of the material is in accordance with what has been reported in the literature for the 300 series. However, only few works have been reported concerning AISI 201 stainless steel and its magnetic properties. In this work, magnetic measurements were also carried out during annealing (in situ condition). The obtained parameters from the in situ magnetic measurements were compared to those ones obtained from the isothermally annealed samples.
INTRODUÇÃOAços inoxidáveis austeníticos são amplamente utilizados em aplicações que envolvem alta resistência à corrosão, alta resistência mecânica e boa ductilidade. Em consequência da deformação plástica, além de intensa multiplicação de discordâncias, aços inoxidáveis austeníticos apresentam a formação de falhas de empilhamento, martensita induzida por deformação ( ') e maclas de deformação (LO et al., 2009;PADILHA et al., 2003).Com relação à martensita induzida por deformação, dois tipos distintos podem ser formados:a martensita ε (HC) e a martensita α' (CCC) (MERTINGER et al., 2008). Assim como a fase austenítica, a martensita ε é paramagnética, enquanto que a martensita α' é ferromagnética (MERTINGER et al., 2008). As técnicas comumente utilizadas para a quantificação do teor de martensita induzida por deformação são a difração de raios X e as medidas magnéticas.Já que a martensita α' é ferromagnética, a fração dessa fase martensítica presente no aço é proporcional à magnetização de saturação (Ms) da amostra (TAVARES et al., 2000). Além A microestrutura de...