Phase Transformations in Cast Superaustenitic Stainless Steels (original) (raw)
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Phase Transformations on ASTM a 744 Gr. CN3MN Superaustenitic Stainless Steel after Heat Treatment
Defect and Diffusion Forum, 2011
The superaustenitic stainless steel ASTM A 744 Gr. CN3MN (22Cr-25Ni-7Mo-0.2N) has as mainly characteristic high corrosion resistance in severe environment. As the corrosion resistance depends on the microstructure, it was investigated the phase transformations after a solution treatment at 1200°C. Thermocalc calculation for 53Fe-25Ni-22Cr alloy indicates austenitic phase between 1300 and 800°C and austenite + sigma phase below 800°C. The as-cast steel studied presented 2.7 % of precipitates volume fraction and the precipitates were located on the grain boundaries and inside the austenitic grains. X-ray diffraction confirmed the presence of sigma phase in as-cast sample. Scanning electron microscopy showed that the level of Cr and Mo was higher in the precipitates than in the austenitic matrix and the Ni content was higher in matrix compared to precipitates. After heating at 1200°C during 90 minutes, the precipitate volume fraction was reduced to 2.1 % and the grain boundaries precip...
Thermal and mechanical treatments effects on phase transformation in duplex stainless steels
This paper concerns the phase transformation induced by heat treatment and cold rolling in duplex stainless steels with different compositions. In the 2205 and 2507 grades, during the isothermal heat treatments, chi-phase precipitates as small particles at the ferrite/austenite boundaries, followed by sigma precipitation. At the lowest temperature the kinetic of chi-phase is favoured, with the increasing of time and temperature a progressive transformation of chi to sigma occurs and the kinetic of sigma is favoured. During continuous cooling, the chi -phase appears at the lowest cooling rates. In the low Ni grades (2101 and 2304) the grain boundaries precipitation of chromium nitrides were detected, but no sigma and chi. In 2101 the austenite transforms to martensite both after cold rolling and quenching
Materials Science Forum, 2010
This paper concerns the phase transformation induced by heat treatment and cold rolling in four duplex stainless steel. In 2205 and 2507 , during the isothermal heat treatments, chi-phase precipitates as small particles at the ferrite/austenite boundaries, followed by sigma precipitation. At the lowest temperature the formation kinetic of chi-phase is favoured, with the increasing of time and temperature a progressive transformation of chi to sigma occurs and the kinetic of sigma is favoured. During continuous cooling, the chi -phase appears at low cooling rates. In low Ni grades the grain boundaries precipitation of chromium nitrides were detected , but no sigma and chi. In 2101 the austenite transforms to martensite both after cold rolling and quenching
Journal of Materials Engineering and Performance
The importance of duplex stainless steel in the global steel industries takes from its application because of its utilization in the environment, the paper industries, and pipelines and reactions champers found in the gas, oil, and chemicals industries. This research investigates the effect of various heat treatment cycles on the intermetallic compound precipitation and different constituents' evolution of the AISI 329 steel. Also, this investigation aims at exploring the relationship of the microstructure evolution at various heat treatment cycles and its effect on the tensile properties of selected steel. The phase transformation studies were conducted theoretically utilizing the JMatPro program and experimentally employing differential scanning calorimetry tests and dilatation; the obtained microstructure was inspected by exploiting a light metallographic microscope, a field-emission scanning electron microscope, and x-ray diffraction. The results illustrated that the microst...
Investigation on Solid-State Phase Transformations in a 2510 Duplex Stainless Steel Grade
Metals
Duplex and Super Duplex Stainless Steels are very prone to secondary phases formation related to ferrite decomposition at high temperatures. In the present paper the results on secondary phase precipitation in a 2510 Duplex Stainless Steel, heat-treated in the temperature range 850–1050 °C for 3–30 min are presented. The precipitation starts at grain boundaries with a consistent ferrite transformation for very short times. The noses of the Time–Temperature–Precipitation (TTP) curves are at 1000 °C for σ-phase and at 900 °C for χ-phase, respectively. The precipitation sequence involves a partial transformation of χ into σ, as previously evidenced in 2205 and 2507 grades. Furthermore, the experimental data were compared to the results of Thermo-Calc calculations. Understanding and ability to predict phase stability in 2510 duplex stainless steel is a key factor to design optimal welding processes that avoid any secondary phase precipitation in the weld bead as well as in the heat-affe...
Metallurgical Research & Technology
The present paper investigates the microstructural features and associated hardening state of three different martensitic stainless steels (CX13, XD15 and MLX17 produced by Aubert&Duval), subjected to three different thermomechanical treatments, aimed at producing hard materials for tribological applications. It is thus shown that all treatments (cementation, HF quenching or Age Hardening) are efficient to produce hard surfaces. The bulk martensitic state is also studied. Although the three martensites look somewhat different, it is shown that the transformation always obeys the KS orientation relationship with some variant selection, which produces a significant amount of twin boundaries. These results are quite different from those found in low C steels. Based on a quantitative analysis of the EBSD microstructures, a quantification of the various relative hardening contributions (phase transformation, grain size, dislocation density, solid solution effect or precipitation) is then...
Influence of severe plastic deformation in phase transformation of superduplex stainless steels
Journal of Materials Science
Duplex and superduplex stainless steels are characterised by high corrosion resistance and high mechanical strength. However, these steels can suffer formation of secondary brittle phases when they reach temperatures between 600°C 600 and 950°C950 °C, which can lead to the catastrophic service failure of components. In order to understand the influence of the mechanical history of the steel part, equal-channel angular pressing was applied followed by different thermal treatments. Microstructural characterisation was carried out on the ECAPed samples before and after thermal treatment. The analysis of the hardness evolution of the same samples was also evaluated.
2018
Super Duplex Stainless Steels (SDSSs) are composed of α-ferrite and γ-austenite grains, the simultaneous presence of which forms an optimal microstructure to achieve the best combination of mechanical and corrosion resistance properties. Moreover, international quality standards are strict about the phase fraction ratio. The purpose of this work is the achievement of a better description of the phase ratio evolution taking place during annealing at 1080°C in the super duplex stainless steels F53–S32750 and F55–S32760. The experimental results show a damped sinusoidal trend in the α/γ phase ratio evolution with the increase of the soaking time of thermal treatment. This can be described by coupling both the competitive coarsening growth regime and the concept of the local equilibrium phase transformations, pointing out a good correspondence with the experimental data. Further, recrystallization phenomena also play a major role. Finally, the additivity character of the observed processes has been proven
Mechanical and Thermal Induced Phase Transformations in Superduplex Stainless Steel
The aim of this work is to study the microstructural changes in SAF 2507 type superduplex stainless steel due to heat treatments and mechanical fatigue process. Specimens were heat treated in the 400-1360 °C temperature range for 1 and 5 hours respectively. An other series of specimens were periodically loaded by using a fatigue testing machine. The microstuctural changes were investigated by using a complex micromagnetic measuring system which includes a Barkhausen noise measuring and a magnetic harmonic analysing system. The RMS value of the Barkhausen noise, the distortion factor (k), and magnetic coercivity values were measured. The microstuctural changes were investigated by metallography using scanning electron microscope.
Materials Characterization, 2008
Three austenitic steels (18Cr-8Ni, 18Cr-10Ni, 21Cr-30Ni), used for long-term applications at temperatures between 600 and 800°C were investigated. In the investigation, metallography, transmission electron microscopy, selected area electron diffraction, energy dispersive X-ray spectroscopy, and scanning electron microscopy were used. In additional to the experimental measurements, thermodynamic predictions were done using the ThermoCalc software and the non-commercial database STEEL16F. Various combinations of M 23 C 6 , sigma, and MC phases were identified in the austenite matrix of these steels. It was confirmed experimentally that extra large particles (up to 10 μm) observed in the 21Cr-30Ni steel are M 23 C 6 , even though this carbide was not predicted as the equilibrium carbide at service temperature (800°C). The analytical-experimental approach, combining thermodynamic predictions and experimental measurements, was found to be reliable for the characterization of austenitic steels.