Abstract
There are many studies on austenitic stainless steels with transformation induced plasticity (TRIP). Basically, in these steels, there is a significant increase in strength and toughness with the transformation of austenite to martensite. 304L steel finds extensive application in industry. Studies relating to martensitic transformation with plastic deformation are quite common. Many studies involve monotonic loading relating to the martensite formed. In practice, 304L steels are subject to distinct types of loading and possibly with stress concentrators. Thus, also in smaller quantities, it is possible to find in the literature studies involving cyclic loading with the TRIP effect. To contribute to the literature on the analysis of the TRIP effect on these steels, 304L steel samples with stress concentrators underwent interrupted monotonic tensile tests. Optical microscopy (OM) and x-ray diffraction (XRD) technique characterized the martensitic transformation. Other 304L steel samples with a stress concentrator underwent a low cycle fatigue test. The martensitic transformation, in this case, was possible to follow with the electron backscatter diffraction technique (EBSD). The samples after the interrupted monotonic tests show a high martensite volume fraction formed 1mm away from the notch (30% to 50%), due to the plastic deformation suffered. From 5.5mm of the notch, the samples again display a microstructure like that of the as-received (AR) sample. For the low cycle fatigue tested sample, the high concentration of deformation-induced martensite was within 15mm of the discontinuity. Approximately 0.5mm from the circular discontinuity, the sample again has a microstructure like the initial sample (IS).
Highlights
Austenitic stainless steels, within its class of stainless steels, are probably the most studied
Solid-state phase transformations in steels play an essential role in physical metallurgy. 304L austenitic stainless steel are metastable austenitic alloys that can undergo deformation-induced phase transformation (TRIP effect - transformation induced plasticity) (Mangonon & Thomas, 1970)
Xu and coauthors (Xu et al, 2012) analyzed the martensitic transformation induced by deformation in an AISI 304L subjected to cyclic tensile loading and unloading by in situ x-ray diffraction compared to conventional monotonic tensile loading
Summary
Austenitic stainless steels, within its class of stainless steels, are probably the most studied. Many studies involve monotonic loading related to the formed martensite (Galindo-Nava & Rivera-Díaz-del-Castillo, 2017; Palma-Elvira et al, 2019; Juho Talonen, 2007) These steels are subject to diverse types of loading, possibly with stress concentrators. Maier and coauthors (Maier, Schneeweiss, & Donth, 1993) investigated fatigue-induced martensitic phase transformation in an AISI 304L tested at low temperatures, -170°C and -70°C They observed that the martensite formation rate increased with decreasing temperature. Xu and coauthors (Xu et al, 2012) analyzed the martensitic transformation induced by deformation in an AISI 304L subjected to cyclic tensile loading and unloading by in situ x-ray diffraction compared to conventional monotonic tensile loading They concluded that the cyclic tensile loading and unloading increased the hardening and the deformation-induced martensite volume fraction compared to the traditional monotonic loading, increasing the TRIP effect. It was possible to follow the martensitic transformation with the electron backscatter diffraction technique (EBSD)
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