Hot Deformation Behavior of As-Cast 2101 Grade Lean Duplex Stainless Steel and the Associated Changes in Microstructure and Crystallographic Texture (original) (raw)
Related papers
2010
High temperature behavior of 2205 duplex stainless steel was studied by considering behavior of each constituent phase. The specimens were subjected to hot compression tests at temperatures of 800-1100°C and strain rates ranging from 0.001 to 1 s À1 at intervals of an order of magnitude. The flow stress analysis showed that hot working empirical constants are different at low and high temperatures. The strain rate sensitivity m was determined and found to change from 0.12 to 0.21 for a temperature rise from 800°C to 1100°C. The apparent activation energy Q was calculated as 554 and 310 kJ/mol for low and high temperature, respectively. The validity of constitutive equation of hyperbolic sine function was studied and stress exponent, n, was assessed to be 4.2. Assuming the hyperbolic sine function for determination of strain rate and application of the rule of mixture, the interaction coefficients of d-ferrite, P, and austenite, R, were estimated at different hot working regimes. It was found that the interaction coefficients are functions of Zener-Hollomon parameter Z and obey the formulas P = 1.4Z À0.08 and R = 0.76Z 0.005. Therefore, it was concluded that at low Z values d-ferrite almost accommodates strain and dynamic recovery is the prominent restoration process which may even inhibit dynamic recrystallization in austenite. Otherwise, at high Z, austenite controls the deformation mechanism of material and dynamic recrystallization leads in finer microstructure.
Microstructural Changes of a Construction Steel Caused by Hot Deformation
2013
A construction steel (shipbuilding strip) obtained by Advanced Thermomechanical Controlled Rolling Processes presents a room temperature banded ferrite-pearlite microstructure, and when superplastically deformed at 800°C with a strain rate of 5.85x10 s, the bands disappear as there is grain boundary sliding and grain cluster rotation. Nevertheless, the superplastic deformation does not imply a decrease in mechanical properties, as room temperature tests with strain rates of 1.46x10 s with the steel previously deformed in superplastic conditions (until a 110% of straining) result in similar mechanical data. If the steel is deformed at 750°C with low strain rates, cooling results in a microstructure formed only by ferrite and carbides (the pearlitic phase disappears). This behavior may be explained, from a thermodynamical point of view, by the effect of negative hydrostatic pressure during the tensile test and the pronounced ferriteand carbide-former capacity of Ti and Nb microalloyin...
Microstructure Evolution in Ferritic Stainless Steels during Large Strain Deformation
MATERIALS TRANSACTIONS, 2004
Deformation microstructures were studied in ferritic stainless steels during cold bar rolling and swaging to total true strains about 7. Two steels, i.e. Fe-22Cr-3Ni and Fe-18Cr-7Ni with coarse-grained ferritic and fine-grained martensitic initial microstructures, respectively, were selected as starting materials. Microstructure evolution in the both steels was characterized by the development of highly elongated (sub)grains aligned along the rolling/swaging axis. The transverse size of these (sub)grains in the Fe-22Cr-3Ni steel gradually decreased to about 0.1 mm with increasing the strain. On the other hand, the transverse (sub)grain size in the Fe-18Cr-7Ni steel decreased to its minimal value of 0.07 mm with straining to about 3 followed by a little coarsening under further working. The strengthening of worked steels that revealed by hardness tests correlated with the microstructure evolution. The hardness of the Fe-22Cr-3Ni steel increased with cold working within the studied strain range, while that of the Fe-18Cr-7Ni approached a saturation after fast work hardening at strains below 3, leading to an apparent steady-state behaviour. Development of strain-induced (sub)grain boundaries and internal stresses in the steels with different initial microstructures during severe deformation is discussed in some detail.
Mechanika
Duplex stainless steel samples were aged at low temperatures of the 300ºC and 400ºC for 3000, 5000 and 7000 hours. The changes at the micro-structure were fol-lowed during the annealing time using an optical micro s-copy and measurements of phase percentages. Nano-hardness was used in order to identify the phase responsi-ble for the increasing in the global hardness. The G phase precipitation and alpha’ phase due to spinodal decomposition was identified by transmission electron microscopy. It was detected that the micro-structural changes affect the global properties, remarkably the global hardness. TEM results showed that the chromium rich precipitation occurs mainly in the ferrite phases. The results also showed a clear difference between the kinetics of precipitation of the lower chromium content sample and the higher chromium sam-ple. The phenomena of precipitation and coalescence ofchromium rich phases must be related to the increasing and decreasing tendencies of hardness, res...
Materials Research, 2000
Two types of duplex stainless steels were deformed by torsion at a temperature range of 900 to 1200 °C and strain rate of 1.0 s -1 and their final microstructures were observed. The austenite volume fraction of steel A (26.5Cr -4.9Ni -1.6Mo) is approximately 25% at room temperature, after conventional annealing, while that of steel B (24Cr -7.5Ni -2.3Mo) is around 55%. Experimental data show that steel A is ductile at high temperatures and displays low ductility at low temperatures, while steel B has low ductility in the entire range of temperatures studied. At high temperatures, steel A is essentially ferritic and shows dynamic recrystallized grains after deformation. When steel A is strained at low temperatures and displays low austenite volume fraction, microstructural observations indicate that failure is triggered by grain boundary sliding due to the formation of an austenite net structure at the ferrite grain boundaries. At intermediate volume fraction, when austenite forms a dispersed second-phase in steels A and B, failure begins at the ferrite/ferrite boundaries since some of the new ferrite grains may become immobilized by the austenite particles. When steel B is strained at volume fraction of around 50% of austenite and both phases percolate the microstructure, failure occurs after low straining as a consequence of the different plastic behaviors of each of the phases. The failure characteristics of both steels are correlated not only with the volume fraction of austenite but also with its distribution within the ferrite matrix, which limits attainable strain without failure.
Marion Calcagnotto, Yoshitaka Adachi, Dirk Ponge, Dierk Raabe, Acta Materialia 59 (2011) 658–670
Three ferrite/martensite dual-phase steels varying in the ferrite grain size (12.4, 2.4 and 1.2 um) but with the same martensite content (30 vol.%) were produced by large-strain warm deformation at different deformation temperatures, followed by intercritical annealing. Their mechanical properties were compared, and the response of the ultrafine-grained steel (1.2 um) to aging at 170°C was investigated. The deformation and fracture mechanisms were studied based on microstructure observations using scanning electron microscopy and electron backscatter diffraction. Grain refinement leads to an increase in both yield strength and tensile strength, whereas uniform elongation and total elongation are less affected. This can be partly explained by the increase in the initial strain-hardening rate. Moreover, the stress/strain partitioning characteristics between ferrite and martensite change due to grain refinement, leading to enhanced martensite plasticity and better interface cohesion. Grain refinement further promotes ductile fracture mechanisms, which is a result of the improved fracture toughness of martensite. The aging treatment leads to a strong increase in yield strength and improves the uniform and total elongation. These effects are attributed to dislocation locking due to the formation of Cottrell atmospheres and relaxation of internal stresses, as well as to the reduction in the interstitial carbon content in ferrite and tempering effects in martensite.
Effect of Strain Rate on the Microstructure of Warm-Deformed Ultrafined Medium-Carbon Steel
2018
In this study, medium-carbon steel was subjected to warm deformation experiments on a Gleeble 3500 thermosimulator machine at temperatures of 550°C and 650°C and strain rates of 0.001 s–1 to 1 s–1. The warm deformation behavior of martensite and the effects of strain rate on the microstructure of ultrafine grained medium-carbon steel were investigated. The precipitation behavior of Fe3C during deformation was analyzed and the results showed that recrystallization occurred at a low strain rate. The average ultrafine ferrite grains of 500 ± 58 nm were fabricated at 550°C and a strain rate of 0.001 s–1. In addition, the size of Fe3C particles in the ferrite grains did not show any apparent change, while that of the Fe3C particles at the grain boundaries was mainly affected by the deformation temperature. The size of Fe3C particles increased with the increasing deformation temperature, while the strain rate had no significant effect on Fe3C particles. Moreover, the grain size of recryst...
ISIJ International, 2014
With the ultimate target of improving the deep drawability of a dual-stabilized 21%Cr ferritic stainless steel, the evolution of the flow stress, microstructure, texture, dislocation structures and precipitation during multi-pass hot deformation were studied. Plane strain compression in three passes with 0.4-0.5 pass strains and 20 s inter-pass times was employed together with scanning electron microscopy combined with electron backscatter diffraction (SEM-EBSD) and transmission electron microscopy (TEM). The temperature of the final pass was varied between 1 223 K and 923 K and the final cooling took place either by water quenching to room temperature or water cooling to 923 K followed by cooling at 0.33 K/s to room temperature. At 1 223 K, static recrystallization was almost complete during the 20 s inter-pass times and this randomized the texture. When the deformation temperature was lowered to 1 073 K or 923 K, in-grain shear bands were formed in the grains belonging to the γ fibre. The deformation temperature of the third pass had only a minor effect on the deformation texture intensity maxima. The final dislocation structure was not changed by the cooling rate from 923 K, but slow cooling enabled precipitation to occur. The results indicate that although the deformation conditions affect the deformed microstructures and dislocation structures, the effect of the deformation temperature on the texture was insignificant.
Microstructure of EK-181 ferritic-martensitic steel after heat treatment under various conditions
Technical Physics, 2012
The effect of heat treatment conditions on the microstructure and phase composition of a low activated high temperature ferritic-martensitic EK 181 steel (Fe-12Cr-2W-V-Ta-Ba) is studied. Addi tional thermal cycling about the austenite-martensite phase transition temperature between quenching and tempering hinders the formation of fine interstitial phases, decreases the phase transformation induced hard ening intensity, retards the formation of a substructure with continuous misorientations, and decreases the brittle-ductile transition temperature.