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The effect of the aЈ-strain induced martensite on the austenitic stainless steel grain size reduction is analyzed. Rolling with a 80 % reduction factor at 200°C and at 20°C resulted respectively in a heavily deformed austenite and a mixed deformed austenite with aЈ-martensite bands. Further annealing treatments were carried out in the range of 20-880°C. Fine grains of about 1 mm can be obtained in the metastable austenitic stainless steel by a repetitive cold rolling and annealing thermomechanical process. In this case, reversion mechanism from deformation induced martensite aЈ to austenite g is responsible for grain refining. Nonconventional warm rolling and annealing process can also lead to fine grains of 2 mm without a reversion stage and as a result of recrystallization process of the strain-hardened austenite. The cold rolling route gives rise to a bimodal grain size distribution with a "lamellar" structure resembling to a "composite" material.

Grain refinement of metallic alloys is well known as a mechanism to improve mechanical properties (high strength and high toughness). In recent decades, attention has been paid to the elaboration of ultra-fine grained materials from processes involving severe plastic deformation (SPD) [1][2][3][4][5] and an appropriate heat treatment. For example, high pressure torsion (HTP), equal channel angular pressing (ECAP) and accumulative roll-bonding (ARB) are processes that have been successfully applied to a wide range of metallic alloys (copper, aluminium, invar alloy, IF steels, Ni alloys stainless steels, etc.). Grain refinement in stainless steels, especially in the austenitic class, would make the latter very attractive for a large range of applications because they could exhibit very high corrosion resistance with very high mechanical strength but limited elongation. [6] Among all the metallic alloys considered for investigations aimed at reducing the grain size, austenitic stainless steels also differ from the others by the possibility of exhibiting a phase transformation during plastic deformation. Nevertheless, the mechanical behavior -including the cyclic responsehas to be analyzed because only a few studies have been devoted to fatigue of fine-grained materials, especially in terms of phase stability under cyclic deformation in correlation with texture and grain size.This article discusses the dependence of the martensitic transformation feature with the grain size and with the texture of an austenitic stainless steel subjected to cyclic plasticity. Experimental SetupThe metastable austenitic stainless steel (chemical composition given in Table 1) was provided in the form of a hot-rolled and annealed steel sheet. Grain size control was achieved by the hard cold rolling (HCR) process followed by subsequent annealing. The as-received sheets were first cold rolled to a reduction of 80% down to 1 mm in final thickness. Second, they were annealed at two different temperatures in order to obtain fine (2 mm) and coarse (20 mm) grained microstructures. Details of the thermomechanical processes are presented elsewhere. [7] Flat specimens with a gauge length of 15 mm and a gauge width of 8 mm were machined by electrospark erosion with COMMUNICATION [**] This research was carried out within the framework of the PhD thesis of S. Brochet. The authors warmly thank ARCELOR and ADEME for their financial support.The influence of grain size and texture on microstructural changes occurring during low-cycle fatigue of an austenitic stainless steel are investigated (grain size of 2 and 20 mm). All the materials exhibited a strong secondary hardening at high strain range as a result of a fatigue-induced martensitic transformation. a 0 martensite is found to nucleate in austenitic grains containing a high density of dislocations but not at slip band intersections, as is usually reported for austenitic stainless steels.Considering the unstable composition of the steel studied and the decrease of the grain size, dislocations structu...