Martensite Formation and Recrystallization Behavior in 17Mn0.06C2Si3Al1Ni TRIP/TWIP Steel after Hot and Cold Rolling

Abstract

This work evaluates the evolution of the microstructure and its influence on the mechanical behavior of steel containing 17% Mn, 0.06% C, 2% Si, 3% Al, and 1% Ni after hot rolling at 1070°C, cold rolling with 44% reduction, and annealing at 700°C for different time periods. The resultant athermal, strain-induced martensite and austenite grains were analyzed by optical and scanning electron microscopy (SEM). The volume fractions of the g, e, and α’ phases of martensite were confirmed by X-ray diffraction, dilatometry, and SEM-electron backscatter diffraction (EBSD) techniques. It was found that cold reduction results in the formation of more a’ martensite. The Vickers microhardness values were higher for the cold-rolled condition and lower for recrystallized samples, as expected. However, this reduction is counterbalanced by the formation of athermal e and a’ martensite during the cooling process. The sizes of the recrystallized grains change exponentially during their growth and remain within 1–3 mm. The yield and tensile strength of the hot-rolled steel reach values close to 250 and 800 MPa, respectively, with a total elongation of 40%, which demonstrates the high work-hardening rate of the steel.

Formation of epsilon martensite by high-pressure torsion in a TRIP steel

“…It was shown in earlier work that this is observed in the stress-strain curves of the material used in these experiments without HPT processing [23]. Thus, these experiments showed that the flow stress increased from ~200…”

“…However, the transformation is expected to be complete at low values of straining at room temperature leading to an almost complete α' microstructure. It is interesting to note that a similar alloy was subjected to cold rolling and it was found that a 44% thickness reduction gave ~78% of α' phase [23] whereas a 90% thickness reduction led to ~98.5% of α'. The present results…”

“…where σ is the material average flow stress in MPa (σ = 800 MPa [23]) and ω is the rotation rate in rad/s (ω ≈ 0.10 rad/s). Thus, a maximum temperature rise of ~40 ºC is expected during HPT processing which is in agreement with the experimentally observed temperature rise in pure iron with a similar flow stress [24].…”

Martensite reversion and texture formation in 17Mn-0.06C TRIP/TWIP steel after hot cold rolling and annealing

“…In order to be able to predict the deformation mechanisms of the various heat treated samples, their SFE values were estimated using the model proposed by Dumay et al [4]. The value obtained was 14.5 mJ m −2 [23,24], which indicates the occurrence of martensitic transformation as a plastic deformation mechanism, as well as mechanical twinning and dislocations slip. Dilatometric results demonstrate that the martensite phase occurs in steel samples subjected to deformation, that is strain induced mode and having a low SFE.…”

“…The samples were first etched with nital (10%) and then with Klemm's I etchant [23,24]. For the Scanning electron microscopy (SEM) measurements, the samples were etched with Villela etchant.…”