Microstructural changes occurred during hot-deformation of SDSS F55 (super-duplex stainless steel) alloy (original) (raw)
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Microstructure Evolution during Hot Deformation of UNS S32750 Super-Duplex Stainless Steel Alloy
Materials, 2021
The present paper analyzes UNS S32750 Super-Duplex Stainless Steel hot deformation behavior during processing by upsetting. The objective of this paper is to determine the optimum range of deformation temperatures, considering that both austenite and ferrite have different deformation behaviors due to their different morphology, physical, and mechanical properties. Because the capability of plastic deformation accommodation of ferrite is reduced when compared to austenite, side cracks and fissures can form during the hot deformation process. Consequently, it is important to find the optimum conditions of deformation of this type of stainless steel to establish the best processing parameters without deteriorating the material. The experimental program involved the application of hot deformation by the upsetting method on a series of samples between 1000 °C and 1275 °C, with a total degree of deformation of 30%. The resultant samples were examined by SEM-EBSD to establish and analyze ...
Evaluation of Hot Deformation Behaviour of UNS S32750 Super Duplex Stainless Steel (SDSS) Alloy
Metals, 2020
The super-duplex stainless steel UNS S32750 consists of two main phases, austenite and ferrite, which differ not only by their morphology, physical, and mechanical properties, but also by their deformation behaviour. A heterogenous deformation can be obtained during thermomechanical processing, generating internal stresses and sometimes fissures or cracks on sample lateral surfaces, due to ferrite’s phase lower potential of plastic deformation accommodation in comparison with austenite phase. The research objective is to determine the optimum range of the applied deformation degree, during hot deformation processing by upsetting of the super-duplex steel (SDSS) UNS S32750. In the experimental program several samples were hot deformed by upsetting, by applying a deformation degree between 5–50%, at 1050 °C and 1300 °C. The most representative hot-deformed samples were selected and analysed by scanning electron microscope-Electron Backscatter Diffraction (SEM-EBSD), to determine the m...
Metals
In this present study, the influence of isothermal aging temperature and duration on microstructural and mechanical properties of a hot-deformed UNS S32750 super duplex stainless steel (SDSS) alloy was investigated by SEM-EBSD (scanning electron microscopy-electron backscatter diffraction) and tensile testing techniques. An isothermal aging treatment, at temperatures between 400 and 600 °C and treatment duration between 3 and 120 h, was applied to a commercial UNS S32750 SDSS alloy. Microstructural characteristics of all thermomechanical (TM) processed states, such as distribution and morphology of constituent phases, grain’s modal orientation (MO), and obtained mechanical properties were analysed correlated with the TM processing conditions. The obtained experimental results show that the constituent phases, in all TM processed states, are represented by elongated γ-phase grains within the δ-phase matrix. The R-phase was observed in the case of aging treatment performed at 600 °C f...
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.
On the High Temperature Deformation Behaviour of 2507 Super Duplex Stainless Steel
Journal of Materials Engineering and Performance, 2017
High temperature deformation behaviour of 2507 super duplex stainless steel was investigated by conducting isothermal hot compression tests. The dominant restoration processes in ferrite and austenite phases present in the material were found to be distinct. The possible causes for these differences are discussed. Based on the dynamic materials model, processing map was developed to identify the optimum processing parameters. The microstructural mechanisms operating in the material were identified. A unified strain-compensated constitutive equation was established to describe the high temperature deformation behaviour of the material under the identified processing conditions. Standard statistical parameter such as correlation coefficient has been used to validate the established equation.
Metallurgical and Materials Transactions A, 2016
The hot deformation behavior of 2101 grade lean duplex stainless steel (DSS, containing~5 wt pct Mn,~0.2 wt pct N, and~1.4 wt pct Ni) and associated microstructural changes within d-ferrite and austenite (c) phases were investigated by hot-compression testing in a GLEEBLE 3500 simulator over a range of deformation temperatures, T def [1073 K to 1373 K (800°C to 1100°C)], and applied strains, e (0.25 to 0.80), at a constant true strain rate of 1/s. The microstructural softening inside c was dictated by discontinuous dynamic recrystallization (DDRX) at a higher T def [1273 K to 1373 K (1000°C to 1100°C)], while the same was dictated by continuous dynamic recrystallization (CDRX) at a lower T def (1173 K (900°C)]. Dynamic recovery (DRV) and CDRX dominated the softening inside d-ferrite at T def ‡ 1173 K (900°C). The dynamic recrystallization (DRX) inside d and c could not take place upon deformation at 1073 K (800°C). The average flow stress level increased 2 to 3 times as the T def dropped from 1273 to 1173 K (1000°C to 900°C) and finally to 1073 K (800°C). The average microhardness values taken from d-ferrite and c regions of the deformed samples showed a different trend. At T def of 1373 K (1100°C), microhardness decreased with the increase in strain, while at T def of 1173 K (900°C), microhardness increased with the increase in strain. The microstructural changes and hardness variation within individual phases of hot-deformed samples are explained in view of the chemical composition of the steel and deformation parameters (T def and e).
Metals
An in situ scanning electron microscope (SEM) study was conducted on a super duplex stainless steel (SDSS) containing 0%, 5% and 10% σ-phase. The material was heat treated at 850°C for 12 min and 15 min, respectively, to achieve the different amounts of σ-phase. The specimens were investigated at room temperature and at −40°C. The microstructure evolution during the deformation process was recorded using electron backscatter diffraction (EBSD) at different strain levels. Both σ-phase and χ-phase were observed along the grain boundaries in the microstructure in all heat treated specimens. Cracks started to form after 3-4% strain and were always oriented perpendicular to the tensile direction. After the cracks formed, they were initially arrested by the matrix. At later stages of the deformation process, cracks in larger σ-phase constituents started to coalesce. When the tensile test was conducted at −40°C, the ductility increased for the specimen without σ-phase, but with σ-phase present, the ductility was slightly reduced. With larger amounts of σ-phase present, however, an increase in tensile strength was also observed. With χ-phase present along the grain boundaries, a reduction of tensile strength was observed. This reduction seems to be related to χ-phase precipitating at the grain boundaries, creating imperfections, but not contributing towards the increase in strength. Compared to the effect of σ-phase, the low temperature is not as influential on the materials performance.
Hot deformation of duplex stainless steels
Journal of Materials Processing Technology, 2003
Duplex stainless steels (DSSs) have become established materials, successfully employed in many industrial applications. Their combination of mechanical properties and corrosion resistance is particularly appreciated in the petrochemical field. Hot deformation of these two-phase materials is still a critical point because the different mechanical response of austenite and ferrite often leads to the formation of edge cracks. In the present research, two DSSs with different nitrogen contents, i.e. EN 1.4462 and EN 1.4410, have been subjected to uniaxial hot compression tests in a wide range of temperatures and strain rates. The microstructural changes produced as a consequence of the distinct test conditions have been analyzed by means of optical and electron microscopy. The characteristics of high temperature plastic flow of both DSSs are interpreted in terms of the classical hyperbolic sine equation. The results are finally discussed considering the intrinsic two-phase nature of the materials studied.
JOM, 2017
The microstructural changes induced by solution treatment of an industrial forged F53 Super Duplex Stainless Steel alloy were studied, in order to emphasize how component phases are influenced by heat treatment temperature and duration. The solution treatment was done at a temperature of 1100°C, with variable holding times: 0.6 ks (10 min), 3.6 ks (60 min) and 10.8 ks (180 min). Scanning electron microscopy-electron backscattered diffraction was used as main characterization technique, to obtain and analyse data referring to microstructural features, such as: nature and morphology of constituent phases, average grain-size and grain misorientation. It was shown that in all studied cases the microstructure consisted of a mixture of about 45% d-Fe (ferrite) and 55% c-Fe (austenite). Besides d-Fe and c-Fe phases, other phases were also identified, such as s-phase (chromium-iron carbide), rphase (chromium-iron) and d-(Cr-Fe) (ferrite).
Influence of annealing temperature on deformation behavior of 329LA lean duplex stainless steel
Materials Science and Engineering: A, 2017
Tensile behavior of a 329LA lean duplex stainless steel at room temperature is investigated after annealing at different temperatures. The austenite composition and thereby, its stability depend on the annealing temperature. For recrystallized alloys, austenite stability increases with the annealing temperature. Therefore, martensitic transformation is effectively suppressed during cooling and deformation, which results in low tensile strength and strain hardening rate, when the steel is annealed at higher temperature. Accordingly, transformation-induced plasticity is more pronounced in alloys annealed at lower temperature. During deformation, α′-martensite forms with a blocky morphology with the absence of the deformation bands indexed as an hcp phase. Thus, it is suggested that austenite directly transforms to α′-martensite during deformation rather than via the deformation bands due to a relatively high driving force for α′-martensite transformation in the present alloy. The chemical composition of a 329LA lean DSS used in this study is Fe-0.17N-0.02C-20.5Cr-2.0Ni-1.8Mn-0.7Cu-0.6Mo-0.5Si (wt%). A 4.0 mm thick hot-rolled plate was cold-rolled to 1.0 mm in thickness.