Development of an Ultrafine Grained Ferrite in a Low C-Mn Steel Intensely Deformed under Hot Torsion
In the last years, several studies concerning ultra refinement of ferrite grains have been conducted using different experimental techniques (ECAP, ARB, HPT). The aim of all investigations was to provide an optmized relationship between mechanical properties and microstructure of steels. The present work, likewise, deals with strain induced dynamic transformation of ferrite. Samples of low C-Mn steel were intensely deformed in hot torsion aiming at the production of ultrafine grains of ferrite thereby enhancing the mechanical properties when compared to hot rolled products. After soaking during 5min at 900°C, the samples were quenched and then reheated and submitted to hot torsion deformation at temperatures of 700 and 740°C. The torsion schedule consisted of 7 isothermal passes leading to a total strain of ≈1, generating an ultrafine microstructure with grain sizes of the order of 1µm. The shape of stress-strain curves so obtained suggested that ferrite refinement occurred by dynamic recrystallization. The various constituents present in the microstructure as well as ferrite grain size and morphology were examined by optical and scanning electron microscopy. Microhardness tests were performed to evaluate mechanical properties.
B. Bacroix, J.H. Driver, R. Le Gall, Cl. Maurice, R. Penelle, H. Réglé and L. Tabourot
G. Azevedo et al., "Development of an Ultrafine Grained Ferrite in a Low C-Mn Steel Intensely Deformed under Hot Torsion", Materials Science Forum, Vols. 467-470, pp. 1271-1276, 2004