Duplex Steel Research Articles

Characterization of the Isothermal and Thermomechanical Fatigue Behavior of a Duplex Steel Considering the Alloy Microstructure

Isothermal and thermomechanical fatigue behavior of duplex stainless steel (DSS) X2CrNiMoN22-5-3 was investigated. The aim of this work was to understand the fatigue behavior by correlation of the isothermal and thermomechanical fatigue behavior with microstructural observations. Fatigue tests at plastic-strain-amplitude of 0.2% were carried out at 20, 300 and 600 °C, while in-phase (IP) and out-of-phase (OP) thermomechanical fatigue (TMF) experiments were performed between 300 and 600 °C. During the 20 °C fatigue test, a continuous softening was observed. Transmission electron microscopy examinations reveal pronounced planar slip behavior in austenite. At 300 °C, deformation concentrates in the ferrite, where strong interactions between CrxN and dislocations were observed that explain the pronounced cyclic hardening. DSS studied exhibits softening throughout the whole isothermal fatigue test at 600 °C. In ferrite, during the 600 °C fatigue test, the G phase, γ′ austenite precipitated, and an unordered dislocation arrangement was observed. The stress responses of the TMF tests can be correlated to those of the isothermal fatigue tests. In IP mode, a positive mean stress resulted in premature failure. No γ′ austenite but the formation of subgrains in the ferrite phase was observed after TMF tests. The plastic deformation of the austenite at high temperatures results in an unordered dislocation arrangement.

Cavitation resistance of Stellite 21 coatings tungsten inert gas (TIG) deposited onto duplex stainless steel X2CrNiMoN22-5-3

AbstractCobalt-based alloys, called Stellite, have a microstructure consisting of complex carbides dispersed in a Co-based solid solution matrix. These alloys are resistant to corrosion, erosion through cavitation, abrasive, and sliding wear. To increase the erosion resistance through cavitation, hardfacing of the stainless steel duplex X2CrNiMoN22-5-3 with Stellite 21 alloy was performed using the pulsed tungsten inert gas (TIG) process. The positive effects of the hardfacing process are the low heat input, reduced distortions, controlled volume of the weld, and reduced susceptibility to hot cracking. The effect of dilution is essential for the quality of the deposited layers and, in this sense, the TIG pulsed current welding process was performed to reduce the excess linear energy and implicitly the substrate melting. Iron dilution levels were in the range between 5.9 and 6.1. The higher Fe content in the first layer does not significantly reduce its hardness or wear resistance through erosion cavitation. Compared with the substrate material, the cavity erosion resistance increases 7 to 11 times even in the first layer hardened by the TIG pulsed current welding process.

Tensile deformation behavior related with strain-induced martensitic transformation in a duplex Fe-Mn-Al-C low-density steel

The tensile deformation behavior of a duplex Fe-Mn-Al-C low-density steel with a structure of banded ferrite and austenite has been studied in the present work. The steel exhibits a good strength-ductility match and a typical three-stage deformation behavior, under the joint contributions of transformation-induced plasticity (TRIP) effect, twinning-induced plasticity (TWIP) effect and dislocation slipping. Even though the steel has a stacking fault energy of 53 mJ∙m −2 that is suitable for the TWIP effect, it just worked at the final deformation stage. The TRIP effect played an important role during the majority of deformation process except at an initial stage, and the austenite was dramatically consumed at the later stage. This is mainly determined by an unnormal stability of austenite. For estimating the austenite stability, the relationship between the critical size of austenite grain ( D crit ) and critical temperature for strain-induced transformation ( M s σ ) was established. The calculated D crit of 12 μm reflects that the strain-induced martensitic transformation dominates the TRIP effect in the duplex steel. • Joint effect of TRIP and TWIP effects contribute to the excellent ductility. • This duplex low-density steel shows a three-stage deformation behavior. • A quantitative estimation method of austenite stability is proposed.

INVESTIGATION ON EFFECT OF PULSED CURRENT MICRO PLASMA ARC WELD PARAMETERS ON UNS S32750 SUPER DUPLEX STAINLESS STEEL SHEETS

In this paper, a 0.33mm thick UNS S32750 super duplex stainless steel sheet is butt welded with welding with a micro-plasma arc. Peak current, base current, pulse width, and pulse rate are regarded welding input factors, whereas the tensile strength and hardness of the welded joint are known as output parameters. 31 distinct combinations of tests are carried out by integrating the response surface method (RSM) with central composite design (CCD) and taking into account four factors and five levels of weld process parameters. The main plots are used to visualize the variance in output responses as a function of weld input parameters. MINITAB software is used to establish mathematical models that take into account linear functions. At a 95% confidence level, ANOVA is used to compare two variables. The dominant parameter is identified using contour plots, and the optimum combination of welding parameters is determined using surface plots. Various welding parameters and their effect on stainless duplex steels have been comprehensively explored in this study.

Nano-mechanical properties and onset of plasticity in Fe–Mn–Al–Ni–C duplex lightweight steel processed by high temperature compression

In the present study, nano-indentation tests have been performed on the Fe–Mn–Al–Ni–C duplex lightweight steel following hot compression at 1223 K and 1423 K at a strain rate of 0.1 s−1. The nano-hardness values of various composite regions are determined and correlated with the complex deformed microstructural features, strain gradient, elemental partitioning, intergranular/intragranular precipitates and lattice distortion effect. The estimated elastic modulus value of FCC and BCC matrix regions in the studied steel is relatively higher than those reported for other conventional duplex steels, highlighting the contribution of intragranular B2 and к-carbide precipitates on the overall elastic modulus. Additionally, the deformation behavior of the matrix regions reveals that the onset of plasticity is governed by both homogeneous dislocation nucleation mechanism and multiplication of pre-existing dislocations under the indenter tip. The BCC + B2 region exhibits higher maximum shear stress (τmax) value as compared to the FCC + к-carbide region, indicating that the plastic deformation would first initiate in the latter region. This is related to the pre-existing high strain gradient in the soft FCC + к-carbide region that would facilitate the onset of plasticity more easily as compared to the BCC + B2 region during indentation. Moreover, it is observed that the elasto-plastic regime of the indentation loading curve exhibits random pop-in events associated with the resistance generated by the various intragranular precipitates in the FCC and BCC matrix regions, against the dislocation motion during nano-indentation test.

Spatially resolved EDS, XRF and LIBS measurements of the chemical composition of duplex stainless steel welds: A comparison of methods

Duplex steels (DSS) are used in all industries where corrosion problems play a major role. Examples include the chemical industry, the food industry and shipping industries. DSS have a balanced phase ratio of ferrite (α) and austenite (γ). Unlike single-phase stainless steels, DSS combine the advantages of these and can therefore fit many industry requirements, such as weight saving or high mechanical strength. When these steels are welded, alloying elements can burn off and condense as thin layers on cold surface regions. This loss of chemical elements can lead to changes in the microstructure. With the help of Laser-Induced Breakdown Spectroscopy (LIBS), chemical element distributions were visualized. The results were compared with those of conventional measurement methods, such as energy dispersive X-ray analysis (EDS) and X-ray fluorescence analysis (XRF), and the results from LIBS could be validated. LIBS is suitable as a fast, straightforward measurement method for producing line scans along the weld seam and provides spatially resolved information on accumulation phenomena of burned off alloying elements. LIBS is very well suited for the detection of sub-surface elements due to the exclusively superficial ablation of the material. In addition, the measurement method has been calibrated so that quantitative statements about element concentrations can also be made.

Comparison of Welding Deformation Characteristics by Circumferential Welding for Austenitic and Duplex Stainless Steel Pipe : Experimental Study

During welding of structure, non-uniform thermal distribution is occurred by local heating and conduction in copula. This process causes non-uniform thermal deformation and that occurs thermal stress. Especially, pipe is used in shipbuilding and laying pipe is essential. As well pipe material is applied with STS 316L (Stainless Steel) and STS Duplex(Stainless Steel Duplex) in LNG carrier ship. So welding property of that material is studied in order to predict welding deformation and thermal stress. First of all each material is made a experiment to know thermal distribution and shrinkage deformation. Through this experiment, it was possible to obtain differences in welding shrinkage due to the mechanical and thermal properties of the two materials. As a result, basic data on welding shrinkage for each material were obtained, and it will be used to develop a prediction equation through additional research in the future.

Investigation of the mechanical properties and corrosion behaviour of hybrid L 80 Type 1 and duplex steel joints produced by magnetically impelled arc butt welding

In the field of deep geothermal energy, the mono-tube design will be increasingly used in the future, as significant cost savings can be expected in the production of boreholes up to depths of 6000 m. The previously used bolting of the pipe lengths by means of sleeves contributes significantly to the construction costs. In addition, there is an increased risk of failure for the sleeve bolting, especially if different materials have to be used in different layers for the purpose of increasing the corrosion resistance. Magnetically Impelled Arc Butt Welding (MIAB) was used for direct welding of pipe segments with complete elimination of socket bolting. In the process, the casing material (L80 Type 1), which is a cost-effective standard material, and a corrosion-resistant duplex steel (1.4462) were hybrid welded. The results show excellent properties both in terms of mechanical properties and corrosion resistance. It is shown that the advantages of the MIAB process in joining these different materials can successfully overcome the metallurgical challenges. This new approach for the production of borehole liners can contribute significantly to cost reduction in the construction of geothermal boreholes.

Magnetic and Thermoelectric Detection of Sigma Phase in 2507 Duplex Stainless Steel

Duplex stainless steel has significantly broadened the range of applications of stainless steel. They have a dual-phase microstructure containing ferrite and austenite at approximately a 50–50% phase ratio. Their corrosion resistance is much better compared to the traditional austenitic stainless steel, especially in surroundings containing chloride ion. Moreover, the large stress yield of duplex steels offers significant advantages in structural applications. The ferrite phase in some duplex stainless steels is metastable due to its composition. Consequently, the ferrite can decompose to a secondary austenite and sigma phase due to heat input. The sigma phase is a hard and brittle intermetallic compound phase that significantly deteriorates the mechanical and corrosion-resistant properties of duplex stainless steel. The embrittlement can cause a safety risk in industrial applications. This paper is a preliminary study to investigate what physical properties can be used to obtain information on sigma-phase-induced embrittlement. In this work, the effect of plastic deformation and heat treatment was studied in the appearance of the sigma phase in 2507 duplex stainless steel. Magnetic saturation polarization and thermoelectric power measurements were used to monitor the microstructural changes due to cold rolling and heat treatment. It was found that the magnetic saturation polarization and thermoelectric power measurements can be effective tools for monitoring the sigma-phase formation in duplex stainless steels due to heat input. Their application helps to prevent the embrittlement problems caused by the sigma-phase formation in duplex stainless steel structures.

H2O Innovation's Piedmont secures international orders for housings and couplings

H2O Innovation Inc's independent subsidiary Piedmont recently secured 13 orders for fibreglass reinforced (FRP) cartridge filter housings, stainless steel duplex couplings and PiPerLinkTM permeate connectors.

Hybrid welding of duplex steels for chemical vessels

Hybrid welding of duplex steels for chemical vessels

Effects of FeNiN phases on the corrosion behavior in 2205 duplex steels

Corrosion resistance is of practical importance for the application of 2205 duplex steels in chemical industries. For taking an insight into pitting corrosion behavior, electrolysis was employed to distinguish the 2205 duplex steel samples. In the following, X-ray diffraction, scanning electron microscopy and electron backscattering diffraction are used to characterize the regions with superior and inferior corrosion performance, thus constructing the relationship between the microstructure and their corrosion behavior.

Analytical modeling of work hardening of duplex steel alloys in the milling process

Severe plastic deformation in cutting operations such as milling might change mechanical properties (especially the strength and hardness) of the machined surface and its underlying layers. This phenomenon called work hardening and reduces machinability. This study presents an analytical solution to calculate the work hardening of the upper layers of the workpiece in the milling process of 2205 duplex stainless steel. In this regard, the stresses in the cutting regions are calculated to find the stress and temperature fields in the workpiece. Then the strain and strain rate values are calculated for each point of the surface and subsurface layers using the determined stress field. Finally, the Johnson-Cook material model is used to calculate flow stress and work hardening. Experimental results of the different machining conditions have been used to validate the proposed model. However, comparisons of subsurface microhardness and resultant cutting force obtained by an analytical model with experimental tests showed that the model properly predicts the amount of work hardening.

Numeric simulation of the α/γ-phase ratio of ferritic-austenitic duplex steels

Abstract In the past, the necessity to predict the α/γ-phase ratio in duplex steels gave rise to a number of empirical equations and diagrams, which, however, do not guarantee a reliable prediction. Due to the insufficient agreement between experiment and empirical calculation, the new and further development of duplex steels is still carried out by means of very time-consuming and costly experiments. The CALPHAD method (CALculation of PHAse Diagrams) [1], whose calculational realization is effected by the software program Thermo-Calc [2] in connection with the optimized thermodynamic database TCFE2 (Thermo-Calc FErrum Database, Version 2), can now be used to establish a reliable (parameter optimization), thermodynamic database for duplex steels and to estimate the phase ratio.

Characterization of the fcc/bcc orientation relationship by EBSD using pole figures and variants

Abstract The orientation relationship (OR) between fcc and bcc lattices are described by crystallographic fundamentals using the example of Kurdjumov–Sachs (K–S) and Nishiyama–Wassermann (N–W). Complete pole figures containing all variants will be used to distinguish even between slightly different ORs. EBSD on iron meteorites and duplex steel has been used to analyse a large number of crystal orientations with regard to a high statistical significance and a high probability to capture all variants in a single measurement. It is shown that the use of fixed OR models like K–S, N–W, Bain, Pitsch, or Greninger–Troiano does not satisfacturally reflect the observed experimental pole distributions. It is not convenient to use high-indexed lattice planes and directions to describe the small deviations from the given models. The Euler subspace representation offers a readily comprehensible tool to get an idea about the characteristic of the experimentally detected OR.

Study on as-cast microstructure of Fe-15Mn-10Al-5Ni-0.8C low density duplex steel

The microstructure of Fe-15Mn-10Al-5Ni-0.8C low density duplex steel ingots was studied by laser confocal scanning calorimetry , metallographic microscopy and scanning electron microscopy. The results indicated that: the microstructure of Fe-15Mn-10Al-5Ni-0.8C low density steel was mainly composed of coarse austenite dendrites and δ-ferrite phase in dendrite. The δ-ferrite could be completely eliminated by solution treatment. A dynamic model of austenite grain growth was established. Through analysis, it was concluded that the critical temperature for rapid austenite growth was 1250 °C. The activation energy for austenite grain growth was 365 KJ/mol as calculated by Sellars’ model.

Processing and properties of yttria and lanthana dispersed ODS duplex stainless steels

In the present study, yttria (alloy B) and lanthana (alloy C) based oxide dispersion strengthened (ODS) duplex stainless steels (Fe–21Cr–8Ni–1Ti) have been synthesized using mechanical alloying followed by spark plasma sintering (SPS). For comparison, duplex steel without dispersion (alloy A) has also been synthesized. The variation of sintering temperature (900, 1000 and 1050 °C) on the density, microstructure, and mechanical properties of the steels have been reported. The austenite phase fraction increased with the sintering temperature as well as by the addition of oxides. TEM analysis confirmed the presence of nano-clusters (size in the range of 2–8 nm) of Y–Ti–Cr–O and La–Ti–Cr–O in the alloy B and alloy C, respectively. Alloy C, sintered at 1000 °C, exhibited the highest micro-hardness and compressive strength of 739 ± 9.1 HV and 2835 ± 87 MPa, respectively. At all sintering temperatures, the lower hardness values of the alloy B as compared to alloy A were ascribed to the significantly higher austenite phase fraction in the former, which resulted in overcoming the dispersion strengthening effect. Overall, La2O3-based ODS duplex stainless steels exhibited the better room temperature mechanical properties than Y2O3-based ODS steels.

Quantitative Analysis of Hydrogen‐Assisted Microcracking in Duplex Stainless Steel through X‐Ray Refraction 3D Imaging

While the problem of the identification of mechanisms of hydrogen‐assisted damage has and is being thoroughly studied, the quantitative analysis of such damage still lacks suitable tools. In fact, while, for instance, electron microscopy yields excellent characterization, the quantitative analysis of damage requires at the same time large field‐of‐views and high spatial resolution. Synchrotron X‐ray refraction techniques do possess both features. Herein, it is shown how synchrotron X‐ray refraction computed tomography (SXRCT) can quantify damage induced by hydrogen embrittlement in a lean duplex steel, yielding results that overperform even those achievable by synchrotron X‐ray absorption computed tomography. As already reported in the literature, but this time using a nondestructive technique, it is shown that the hydrogen charge does not penetrate to the center of tensile specimens. By the comparison between virgin and hydrogen‐charged specimens, it is deduced that cracks in the specimen bulk are due to the rolling process rather than hydrogen‐assisted. It is shown that (micro)cracks propagate from the surface of tensile specimens to the interior with increasing applied strain, and it is deduced that a significant crack propagation can only be observed short before rupture.

Determination of retained austenite in multiphase steels by magnetic force microscopy

Abstract The use of atomic force microscopy (AFM) in the magnetic force mode (MFM) for the determination of austenite (nonmagnetic phase) in duplex and TRIP (transformation-induced plasticity) steels is described. The influence of the sample preparation for the MFM measurements is investigated, showing that a final electropolishing stage is necessary in the case of TRIP-steels. The results of the determination of austenite in the range of 6 – 15% with AFM were compared with those obtained with electron backscattered diffraction (EBSD) and light optical microscopy. For TRIP-steels an identification of retained austenite with MFM was found to show a better resolution than classical light optical microscopy.

Synthesis and Characterization of Zn-Organic Frameworks Containing Chitosan as a Low-Cost Inhibitor for Sulfuric-Acid-Induced Steel Corrosion: Practical and Computational Exploration.

In this work, a Zn–benzenetricarboxylic acid (Zn@H3BTC) organic framework coated with a dispersed layer of chitosan (CH/Zn@H3BTC) was synthesized using a solvothermal approach. The synthesized CH/Zn@H3BTC was characterized by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), thermal gravimetric analysis (TGA), and Brunauer, Emmett, and Teller (BET) surface area. The microscopic observation and the analysis of the BET surface area of CH/Zn@H3BTC nanocomposites indicated that chitosan plays an important role in controlling the surface morphology and surface properties of the Zn@H3BTC. The obtained findings showed that the surface area and particle size diameter were in the range of 80 m2 g−1 and 800 nm, respectively. The corrosion protection characteristics of the CH/Zn@H3BTC composite in comparison to pristine chitosan on duplex steel in 2.0 M H2SO4 medium determined by electrochemical (E vs. time, PDP, and EIS) approaches exhibited that the entire charge transfer resistance of the chitosan- and CH/Zn@H3BTC-composite-protected films on the duplex steel substrate was comparatively large, at 252.4 and 364.8 Ω cm2 with protection capacities of 94.1% and 97.8%, respectively, in comparison to the unprotected metal surface (Rp = 20.6 Ω cm2), indicating the films efficiently protected the metal from corrosion. After dipping the uninhabited and protected systems, the surface topographies of the duplex steel were inspected by FESEM. We found the adsorption of the CH/Zn@H3BTC composite on the metal interface obeys the model of the Langmuir isotherm. The CH/Zn@H3BTC composite revealed outstanding adsorption on the metal interface as established by MD simulations and DFT calculations. Consequently, we found that the designed CH/Zn@H3BTC composite shows potential as an applicant inhibitor for steel protection.