Microstructure Of Duplex Stainless Steel Research Articles

The effect of microstructure of an advanced duplex stainless steel on the pitting corrosion and chloride-induced stress corrosion cracking resistance

The effect of austenite morphology on the corrosion resistance of a newly-developed advanced duplex stainless steel (ADCS) was evaluated by electrochemical and chloride-induced stress corrosion cracking (CISCC) tests. By properly controlling heat treatment conditions, equiaxed (EQ) and elongated (EL) austenites were formed in ferrite matrix. ADCS-EQ exhibited higher pitting potential than ADCS-EL, primarily owing to less phase boundary. Meanwhile, ADCS-EL showed better CISCC resistance than ADCS-EQ, as the elongated austenite inhibited selective dissolution. Overall, the CISCC resistance of ADCS was more affected by austenite morphology and orientation, and would not be in accordance with pitting corrosion resistance.

Influence of arc energy on the microstructure and corrosion behavior of ER2209 duplex stainless steel deposited on Q345B low-alloy steel by GMAW

In order to eliminate the complex effects of thermal cycling and the thermal effects of the next pass on multi-layer multi-pass welding of low-alloy steel and duplex stainless steel, ER2209 welding wire was single-layer single-pass deposited on the surface of Q345B hot-rolled plate by gas metal arc welding (GMAW). The microstructure and corrosion resistance of welded joints were studied by different arc energies. The results showed that the arc energy had a significant impact on the “tongue-shaped” morphology and the width of heat affect zone in the welded joint, which in turn affected the corrosion performance of the welded joints. Due to the least distribution of “tongue-shaped” morphology and minimum width of heat affected zone in the welded joint with arc energy of 0.645kJ/mm, it owned the best corrosion resistance. The weld metals of the welded joints were composed of ferrite and austenite phases. The ferrite phases were distributed along grain boundaries and intergranular. As the heat input increases, the distribution of ferrite phase along grain boundaries gradually decreased. The corrosion products and corrosion morphology of the welded joint were also investigated and the corrosion mechanism was discussed in detail. The research results of this article provide a theoretical basis for improving the corrosion performance of multi-layer multi-pass welded joints of low-alloy and duplex stainless dissimilar steels.

Influence of Heat Treatment Temperature on Microstructure, Hardness and Sensitization of UNS S32205 Duplex Stainless Steel

Improper thermal cycles on duplex stainless steels can lead to the formation of detrimental phases or alter the proportion of ferrite and austenite phases, thus influencing the material’s mechanical properties and corrosion resistance. Therefore, this study aimed to evaluate the effect of aging (at 850 and 950 °C) and solubilization (at 1000 and 1150 °C) thermal treatments on microstructure, indentation hardness, elasticity modulus, and susceptibility to intergranular corrosion of UNS S32205 duplex stainless steel. The sigma phase (σ) formation in the aged samples, with hardness values between 8 and 10 GPa, was confirmed. Furthermore, the pieces treated from 1000 °C upwards showed that increased temperature favored the formation of more equiaxial grains and the ferrite fraction growth. The thermal treatments barely affected the elasticity modulus of austenite and ferrite grains, increasing the hardness of ferrite. The effect of sulfuric acid concentration in the intergranular corrosion was evaluated. Also, the deconvolution of the corrosion curves permits the determination of the influence of the different phases in the corrosion performance. These tests revealed sensitization only at the σ phase grain boundaries in the samples treated at 850 °C in electrolytes containing H2SO4 2.5 mol/L and HCl 1 mol/L. Although the treatment at 950 °C led to the σ phase formation, its higher corrosion resistance was ascribed to the lower volumetric fraction of this phase, its morphology, and its increased Cr mobility compared to the 850 °C treatment. Therefore, it was shown that the σ characteristics and the sulfuric acid concentrations are determining factors in the UNS S32205 intergranular corrosion resistance.

Effect of nitrogen content on microstructure and mechanical properties of duplex stainless steels via wire arc additive manufacturing

Effect of nitrogen content on microstructure and mechanical properties of duplex stainless steels via wire arc additive manufacturing

On the correlation between fatigue behaviour and the multiphase microstructure of a super duplex stainless steel

This work investigates the relationship between the multiphase microstructure and the macroscale fatigue behaviour of a cast super duplex stainless steel (SDSS). The microstructure of a cast SDSS is typically composed of a FCC γ-phase and a BCC δ-phase. However, deleterious secondary phases (SP), such as sigma and chi, may precipitate when SDSS is exposed to high-temperature ranges, jeopardising its mechanical properties, namely fatigue performance. The purpose of this investigation was to quantify the correlation between SP amounts and fatigue life of a cast SDSS (CD3MWCuN, ASTM A890). Fatigue tests were conducted using miniature specimens taken from a cast C-Ring with different SP amounts. A numerical model was proposed to calibrate the fatigue test parameters. After the tests, SEM and EBSD techniques were used to quantify the SP and analyse the fatigue-crack propagation. The microstructural analysis was complemented with hardness and tensile tests. Regression models were developed to correlate the percentage of SP, the fatigue resistance and the number of cycles to failure, and to predict the microstructural stress concentration from the amount of SP. In addition, a methodology is proposed for predicting S-N curves as a function of the amount of SP, showing a high correspondence in the increase of the percentage of SP with the decrease in fatigue life. Furthermore, the fatigue strength, for a given number of cycles to failure, tends to decrease linearly with increasing the SP, while the microstructural stress concentration factor tends to increase with an increase in SP. These findings contribute to further knowledge on predicting the behaviour of cast SDSS under different cyclic conditions, which can be valuable for optimizing design and performance in various applications.

Influence of the direction of ferrite-austenite banding on hydrogen embrittlement of 2205 duplex stainless steel

In this study, the fracture behavior of 2205 duplex stainless steel (DSS) under in-situ hydrogen charging is evaluated. For this purpose, fracture toughness tests are performed on single-edge notched bending specimens, in which hydrogen is introduced electrochemically in-situ, using an acid and a saline electrolyte at different current densities. The hydrogen content of both electrochemically and gaseous pre-charged specimens is measured to assess the influence of the aggressiveness of the environment. Three environments are evaluated: realistic, severe and highly severe. As the microstructure of DSS is characterized by the presence of ferrite and austenite bands, the influence of directionality on fracture toughness is also studied. For this purpose, specimens are machined in two directions, being crack growth parallel to the bands in one case, while crack growth is perpendicular to the bands in the other case. Fracture toughness was found to decrease with increasing current density and in a more aggressive environment, and to increase when crack growth was perpendicular to the bands. The fracture surface was also evaluated, revealing splits in the direction of the bands in all in-situ tests. The origin and propagation of these splits were studied using electron backscatter diffraction scans, concluding that splits propagated through the ferrite-austenite interface.

Microstructure, Mechanical Properties, and Corrosion Resistance of ER2209 Duplex Stainless Steel Manufactured by Plasma Arc Welding

Microstructure, Mechanical Properties, and Corrosion Resistance of ER2209 Duplex Stainless Steel Manufactured by Plasma Arc Welding

The Effects of Heat Inputs on LDSS 2101 GTAW and SMAW Weld Microstructure and Mechanical Behavior

The welding has been utilized to stabilize the phase fractions in the microstructure of lean duplex stainless steel (LDSS) to build massive mechanical structures. The influence of heat input on the microstructure, mechanical properties, and corrosion behavior of LDSS 2101 during the gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) processes is investigated in the present work. Specifically, we compared the outcomes between low heat input (LHI) at 0.85 kJ/mm and high heat input (HHI) at 1.3 kJ/mm for both welding techniques. Throughout the welding process, ER2209 filler wire was utilized. To assess the microstructural changes in the weldments, we employed an optical microscope, a scanning electron microscope, and X-ray diffraction. The results revealed that the volume phase fraction of ferrite was significantly higher in the LHI sample of GTAW compared to HHI GTAW and all SMAW welds. LHI GTAW welds have 18.2% greater Charpy impact toughness than LHI SMAW, whereas HHI GTAW has 35.7% higher than HHI SMAW specimens. The microhardness of the LHI GTAW weldments increased (from 230 ± 3.2 to 252 ± 4.8 HV10), whereas the microhardness of the LHI SMAW weldments increased (from 227 ± 2.8 to 246 ± 5.2 HV10). GTAW exhibited a fine grain structure, showcasing favorable tensile properties and higher hardness compared to SMAW. Conversely, the SMAW welds and their heat-affected regions exhibited coarse grain structures. These findings highlight the superior performance of GTAW in terms of microstructural characteristics, and mechanical properties when working with LD SS 2101 in comparison to SMAW.

Study on the Composition Design, Microstructure, Wear and Corrosion Resistant of Duplex Stainless Steels Based on Machine Learning

Study on the Composition Design, Microstructure, Wear and Corrosion Resistant of Duplex Stainless Steels Based on Machine Learning

Effect of annealing process on microstructure, residual stress, and fatigue behaviour of AISI 2205 duplex stainless steel

ABSTRACT This study investigated the microstructure, residual stress, and fatigue behavior of duplex stainless steels that have been annealed with different annealing processes. A cold-rolled AISI 2205 Duplex Stainless Steel (DSS) sample was annealed in three ways for this purpose. In modes 1 and 2, samples were annealed at 500°C for 6 and 8 hours, respectively. The sample was annealed for 6 hours at 950°C for mode 3.The Optical Microscopy (OM) technique was used to determine the crystallographic texture and microstructural characteristics. An X-ray Diffraction (XRD) analysis was used to determine the residual stresses in austenite and ferrite phases on pre- and post-heat-treated samples. The Scanning Electron Microscope (SEM) technique was utilized to assess fatigue cracks. The results showed that the texture microstructure of the specimens using mode 1 and 2 were remained; the grain had a smaller fragmentation. The elongation grains of the specimen after mode 3 were smaller, relatively spheroidal, and more homogeneous. There was a reduction in residual stress after mode 3 annealing process. The fatigue strength of the specimens that under applied this process was 11.1% higher than that of specimens in the as-received state.

Advancing Duplex Stainless Steel Microstructure: Synergistic Ferrite Grain Refinement and Austenite Formation Through Permanent Magnet Stirring

Advancing Duplex Stainless Steel Microstructure: Synergistic Ferrite Grain Refinement and Austenite Formation Through Permanent Magnet Stirring

Corrosion Study on Duplex Stainless Steel UNS S31803 Subjected to Solutions Containing Chloride Ions.

In the present work, the influence of a corrosive environment and temperature on the corrosion resistance properties of duplex stainless steel S31803 was evaluated. The corrosive process was carried out using solutions of 1.5% HCl (m/m) and 6% FeCl3 (m/m), at temperatures of 25 and 50 °C. The microstructure of UNS S31803 duplex stainless steel is composed of two phases, ferrite and austenite, oriented in the rolling direction, containing a ferrite percentage of 46.2% in the rolling direction and 56.1% in the normal direction. Samples, when subjected to corrosive media and temperature, tend to decrease their mechanical property values. It was observed, in both corrosive media, that with increasing test temperature, there is an increase in the corrosion rate, both uniform and pitting. The sample in HCl solution obtained a uniform corrosion rate of 0.85% at 25 °C and 0.92% at 50 °C and pitting rates of 0.77% and 1.47% at the same temperatures, respectively. When tested in FeCl3 solution, it obtained uniform corrosion of 0.0006% and 0.93% and pitting of 0.53% and 18.5%, at the same temperatures. A reduction in dissolution potentials is also noted, thus characterizing greater corrosion in the samples with increasing temperature.

Additive friction stir deposition of super duplex stainless steel: Microstructure and mechanical properties

Additive Friction Stir Deposition (AFSD) is an emerging solid-state metal additive manufacturing (AM) process that offers several key benefits, including high deposition rates and wrought-equivalent mechanical properties even in the as-deposited condition. The work presented is the first study to report on the development of microstructure and mechanical properties of AFSD-processed duplex stainless steel (DSS2507). The banded microstructure of the starting material was remarkably affected by AFSD processing; the austenite grains exhibited a refined and equiaxed morphology, while the ferrite grains appeared slightly larger and elongated. Microstructural observations revealed that the potential mechanism of microstructure evolution in austenite was discontinuous dynamic recrystallization (DDRX), while in ferrite, it was continuous dynamic recrystallization (CDRX). The occurrence of multiple thermal cycles during the AFSD process resulted in σ phase precipitation, which in turn led to considerable variation in mechanical properties with respect to the build direction. The top region of the as-built part with an insignificant σ phase fraction showed improved tensile strength and ductility combination compared to the as-received DSS2507 as well as other AM-processed DSS2507 alloys.

Evaluation of hydrogen interactions with defects induced by deformation in the duplex stainless steel microstructure: An internal friction study

Despite their good corrosion resistance and optimal mechanical properties, duplex stainless steels are affected by hydrogen embrittlement. Therefore, understanding the hydrogen-defect interactions in these steels is crucial. This study uses internal friction to evaluate the interactions of hydrogen with microstructural defects. Analysis of the internal friction spectra of the steels subjected to straining and hydrogen charging, together with thorough microstructural characterization, gives new insights in hydrogen interactions with defects present in the different phases, i.e. ferrite (body centered cubic) and austenite (face centered cubic).While no significant effect of tensile deformation can be observed by thermal desorption spectroscopy, the internal friction spectra show a clear influence of the presence of defects. Detailed analysis of these spectra reveals the interactions in the austenite as dominant, while no indications for hydrogen-dislocation interactions in ferrite are observed. This can be related to limited trapping in ferrite due to the austenite sink action or to limited dislocation formation in ferrite. Indications for hydrogen interactions with dislocations in the austenite are found, possibly suggesting enhanced dislocation mobility when surrounded by hydrogen. Moreover, a pronounced influence of hydrogen charging on the vacancy cluster related peaks is observed, indicating strong interactions between hydrogen and vacancy clusters in austenite. This can be put in contrast to behavior of pure ferritic steels, where dislocations provided the strongest hydrogen interactions. As these specific defects are of primary interest in the hydrogen embrittlement mechanisms, internal friction is concluded to provide important unique insights in hydrogen-defect interactions, even for complicated multiphase microstructures.

Influence of Shielding Gas on the Microstructure and Mechanical Properties of Duplex Stainless Steel in Wire Arc Additive Manufacturing

Influence of Shielding Gas on the Microstructure and Mechanical Properties of Duplex Stainless Steel in Wire Arc Additive Manufacturing

Effect of build orientation and heat treatment on the microstructure, mechanical and corrosion performance of super duplex stainless steels fabricated via laser powder bed fusion

Correction for ‘Effect of build orientation and heat treatment on the microstructure, mechanical and corrosion performance of super duplex stainless steels fabricated via laser powder bed fusion’ by Karl Peter Davidson et al., Mater. Adv., 2024, 5, 8177–8198, https://doi.org/10.1039/D4MA00448E.

Impact of process parameters and gas atmospheres on density and microstructure of super duplex stainless steel produced by Laser Powder Bed Fusion

Super duplex stainless steel (2507 SDSS) is an alloy renowned for its excellent corrosion resistance and mechanical properties. This unique combination arises from a duplex microstructure characterized by austenite and ferrite. However, when processed using the laser powder bed fusion (LPBF) process, this steel contains only the ferritic phase due to the rapid cooling rates inherent in LPBF, which suppresses the formation of the austenitic phase. This study explores a parameter process optimization for this steel in two different atmospheres, Ar and N, with the latter being an austenite-stabilizing element intended to enhance the formation of the austenitic phase. A comparison of the optimal process windows between the two atmospheres is conducted, and the amount of austenitic content is evaluated as a function of the process parameters and the shielding gas employed. Findings demonstrate that utilizing a nitrogen atmosphere, in conjunction with process parameters that reduce normalized enthalpy and material evaporation, increases austenite content post-manufacture. Additionally, nitrogen as the processing gas effectively minimizes and stabilizes nitrogen content within the samples.

Effect of build orientation and heat treatment on the microstructure, mechanical and corrosion performance of super duplex stainless steels fabricated via laser powder bed fusion

Build orientation in PBF-L manipulates microstructures, thus tuning the mechanical and corrosion properties of duplex stainless steel before and after heat treatment.

Microstructure and corrosion resistance of 23Cr9Ni4Mo2Mn filler duplex stainless steel 2205 fabricated by wire arc additive manufacturing with subsequent severe shot peening and Ni58Cr20Fe5Mo10 plasma spray coating

In the current study, 23Cr9Ni4Mo2Mn (FeAs) filler and duplex stainless steel 2205 materials were used in multi-layer deposition processes for wire arc additive manufacturing (WAAM) process. The WAAM samples were prepared with WAAM coated (WAAM-C) and Post-shot peening coated WAAM (PSPC-WAAM) in order to improve the microstructure and surface properties. The severe shot peening process and Ni58Cr20Fe5Mo10 plasma spray coating was increase the corrosion resistance and outer layer strength, whereas different types of structure were observed in the WAAM-DSS plates: Solid phase martensite (SPM), acicular austenite phase (AAS), FeCr2O4, martensite-austensite phase (MAP) and multi-phase ferrite structure. The severe shot peening procedure and Ni58Cr20Fe5Mo10 plasma spray coating samples were clearly visible in the Electron Backscatter Diffraction (EBSD) analyses, which also showed that the outer and inner surface layers of the samples contained CrFe2O4, NiFe2O4 cubic ferromagnetic oxide, and BiFeO3 phase. Direct mixing of the 23Cr9Ni4Mo2Mn filler with the base materials produced a homogenous structure with a high bonding strength. Bi1<001>, Bi2<111>, and Bi3<110> of the BiFeO3 crystal structure were discovered in the inner surface layer according to the PSPC-WAAM sample of angle 0–1800 texture results, whereas the WAAM-C sample of the outer layer revealed that As1<001>, As2 < 100>, and As3 < 111> of the α-martensite structure were exposed at the outer surface layer. PSPC-WAAM had a 6 % increase in hardness over WAAM-C in both the inner and outer surface regions. Hardness value of PSPC-WAAM was 286 HV on NiCr bulk structure demanded, whereas ferrite secondary phase of WAAM-C have increased the hardness value at 224 HV compared to the base materials. Both the PSPC-WAAM and WAAM-C samples achieved improved corrosion resistance and strong surface bonding. The WAAM, WAAM-C, and PSPC-WAAM samples were the subject of potential dynamic experiments, AFM and wear properties.

Sigma phase kinetics in DSS filler metals: A comparison of sigma phase formation in the as-welded microstructure of super duplex stainless steel and hyper duplex stainless steel

This study investigates and compares the kinetics of sigma phase formation in established Super Duplex Stainless Steel (SDSS) and recently developed Hyper Duplex Stainless Steel (HDSS) filler metal wires. Experimental sigma phase time-temperature-transformation (TTT) maps were developed, revealing nearly equivalent interface area/volume, resulting in similar sigma phase kinetics for 1% volume despite the higher Cr and Mo content in HDSS. However, the growth rate to 5% and 10% sigma phase volumes was slightly higher in HDSS. The sigma phase kinetics in both SDSS and HDSS were analyzed using the exponential Johnson-Mehl-Avrami-Kolmogorov (JMAK) approach based on experimental TTT data. Linearized plots from the JMAK calculations showed a transition in kinetics mechanism from eutectoid decomposition and interface-controlled growth to a diffusion-controlled growth stage in both materials. The higher volumes and morphologies of the sigma phase were found to be diffusion-dependent, mainly occurring during the second kinetics stage. The influence of HDSS's higher Cr and Mo content on the growth rate was observed for these higher volumes. For applications within the 1% sigma phase limit, both wires exhibited equivalent susceptibility to sigma phase formation, regardless of the higher alloying in HDSS.