Reversed Microstructures and Tensile Properties after Various Cold Rolling Reductions in AISI 301LN Steel

Abstract

Heavy cold rolling is generally required for efficient grain size refinement in the martensitic reversion process, which is, however, not desirable in practical processing. In the present work, the influence of cold rolling reductions of 32%, 45% and 63% on the microstructure evolution and mechanical properties of a metastable austenitic AISI 301LN type steel were investigated in detail adopting scanning electron microscopy with the electron backscatter diffraction method and mechanical testing. A completely austenitic microstructure and a partially reversed counterpart were created. It was found that the fraction of grains with a size of 3 µm or larger, called medium-sized grains, increased with decreasing the prior cold rolling reduction. These grains are formed mainly from the shear-reversed austenite, transformed from slightly-deformed martensite, by gradual evolution of subgrains to grains. However, in spite of significant amounts of medium-sized grains, the tensile properties after the 32% or 45% cold rolling reductions were practically equal to those after the 63% reduction. The austenite stability against the formation of deformation-induced martensite in subsequent straining was reduced by lowering the cold rolling reduction, due to the larger grain size of medium-sized grains and the shift of their orientation towards {211} <uvw>.

Deformation-induced martensite in austenitic stainless steels: A review

“…It is possible that some deformed retained austenite (RA) remain in the microstructure as shown in Fig. 12, which affects the microstructural evolution during annealing stage [3,45,47,104,106,111,161,[193][194][195][196][197][198][199]. Moreover, the deformationinduced martensite forms gradually and will be inevitably deformed to different degrees, which also has an influence on microstructure heterogeneity and thereby on the mechanical properties [2,53].…”

“…Regarding the metastability in Fe-Cr-Ni alloys, when Ni + 0.35Cr < 16 wt%, it has been reported that over 90 vol% α'-martensite forms by 90% cold rolling at room temperature [40]. Promisingly, for instance for a 301LN grade, cold-rolling reductions as low as 35-52% seemed to result in excellent strength-ductility combinations, even though the grain size refinement was not most efficient and the obtained grain size was not uniform [2,196,197].…”

“…An interesting observation is the plastic instability related to the Lüders or Portevin-Le Chatelier bands formation in UFG ASSs [2,5,7,58,197]. It has been reported that the discontinuous yielding became more pronounced with decreasing grain size so that the Lüders strain disappeared when the grain size was larger than ~ 1 μm [2,5,197]. Distinct Lüders-like deformation has been found recently in the steels having austenite matrix or retained austenite, where the Lüders elongation usually accounted for more than half of the total elongation of the materials.…”

Cyclic deformation behaviour and stability of grain-refined 301LN austenitic stainless structure

“…The choice of proper parameters of this thermomechanical treatment, namely the level of cold deformation and temperature and time of reversion annealing can lead up to ultrafinegrained (UFG) microstructure with an excellent combination of high strength and good ductility -see e.g. [2][3][4][5][6][7][8][9][10][11][12].…”

Strain‐Induced Martensite and Reverse Transformation in 2304 Lean Duplex Stainless Steel and its Influence on Mechanical Behavior

“…Weidner et al reported a similar orientation in high‐alloy metastable austenitic CrMnNi steel with different nickel contents for cold rolling of less than 70%. A recent study by Järvenpää et al illustrated that the {110}<112> Brass component is the most resistant to a transform in martensite, whereas grains with an orientation between {100}<uvw> and {111}<uvw> show the first α ′‐martensite after a 7% tensile strain.…”