Austenite Phase Research Articles

Effect of Retained Austenite on the Microstructure and Micro-Hardness of AISI 4330 Low Alloy Steel Using X-Ray Diffraction method

The mechanical properties of low alloy steel are significantly influenced by retained austenite (RA). Consequently, using the X-Ray diffraction (XRD) measurement method, the retained Austenite volume fractions in AISI4330 alloy steel have been assessed in this article. The specimens underwent heat treatment at various heating temperatures (800 ֯C, 900 1000 ֯C) and cooling rates (Water and Oil). The findings demonstrate that retained Austenite formation rises with rising heating (Austenitizing) temperatures for the same quenching media as well as with rising cooling rates. The specimens were heated to a temperature of 1000 °C and then quenched in water, yielding the highest amount of retained austenite (7.733 wt%), and the lowest amount (1.977 wt%), which was obtained when the specimens were heated to a temperature of 800 °C and quenched in oil. The Vickers method was employed to conduct micro-hardness testing, and the results demonstrate that hardness values are reduced as heating temperatures increase. Optical microscopy was used to investigate the effects of retained austenite on the microstructure. The results show that bainite and/or martensite phases with a small amount of retained austenite dominate the microstructure at low cooling rates, whereas martensite and retained austenite phases dominate the microstructure at higher heating and cooling rates.

Rate induced thermomechanical interactions in NiTi tensile tests on strips

The paper uses tensile experiments on NiTi strips at different displacement rates to establish and simulate the thermomechanical interactions caused by the latent heat of the reversible transformation between the austenitic and martensitic phases. The evolution of deformation in the specimen is synchronously monitored with digital image correlation, and the temperature field through infrared imaging, essential for structural modeling. Transformation leads to localized deformation that propagates through the specimen, while the latent heat released/absorbed at the propagating fronts locally heats/cools the specimen. The sensitivity of the transformation stress to temperature results in a complex interaction between the heat transfer conditions and the nucleation and evolution of transformation in the specimen. At low rates of loading, the alternate phase propagates nearly isothermally with a small number of fronts producing relatively flat stress plateaus. Higher rates lead to significant heating/cooling that results in progressive nucleation of multiple fronts and apparent "hardening" responses. The experiments are simulated in a three-dimensional static displacement transient temperature finite element analysis, using a new fully coupled thermomechanical constitutive model. Transformation strain and entropy are its internal variables whose evolution is governed by the motion in the stress-temperature space of a single transformation surface governing both transformations. The prevailing localization is captured by the introduction of softening over the unstable branches of the recorded isothermal material response. The results demonstrate how the important role of the thermal interaction between the specimen and the environment can be addressed. This, together with appropriate calibration of the constitutive and structural model, enable the analysis to reproduce the effect of rate on the recorded response, the evolution of localization patterns, and the associated thermal fields. The results can guide the development of constitutive and structural models of phase transforming materials with strong thermomechanical interactions.

Effect of Nb Content on the Microstructure and Impact Toughness of High-Strength Pipeline Steel

In this study, X80 pipeline steel is prepared with different Nb contents through the thermo-mechanically controlled rolling process. The effects of using two different Nb contents on the impact toughness and microstructure of the pipeline steel are examined using various experimental techniques. The results show that with the increase in Nb content, the transformation temperature Ar3 decreases, and the nucleation and growth of bainitic ferrite with lath features (LB) are promoted, while those of granular bainite (GB) are inhibited. In addition, the stability of the austenite phase increases with the increase in Nb content. Therefore, the volume fractions of LB and martensite–austenite (M/A) constituents increase, while the proportion of high-angle grain boundaries (HAGBs) decreases. The impact energy of pipeline steel at −45 °C is closely related to the Nb content. Specifically, the impact energy decreases from 217 J at 0.05 wt.% Nb to 88 J at 0.08 wt.% Nb. The cracks are preferentially formed near the M/A constituents, and the HAGBs significantly inhibit the crack propagation. The steel with 0.05 wt.% Nb has a lower content of M/A constituents and a higher proportion of HAGBs than the one with 0.08 wt.% Nb. In addition, as the Nb content increases, the crack initiation energy and the crack propagation energy decrease. Thus, the 0.05 wt.% Nb steel has a higher low-temperature impact energy.

Microstructure evolution and lath martensite precipitation behavior of Co@GNPs/CoCrMo composites fabricated by selective laser melting

Spherical cobalt nanoparticles were reduced and deposited in situ on the graphene (GNP) surface using a novel hydrothermal method, and the prepared Co@GNPs reinforced powder were uniformly dispersed in the alloy matrix. The Co@GNPs/CoCrMo composite fabricated using selective laser melting (SLM) was densely organized with reduced hole defects, and fine equiaxed grains, elongated columnar grains, and duplex ε + γ were observed in the composite organization. Meanwhile, a high density of dislocations and nanoscale stacked layer dislocations were observed at the equiaxed grain boundaries. Further, the GNPs acted as heterogeneous nucleation sites, which promoted the transformation of the γ-Co (FCC) austenite phase to the ε-Co (HCP) martensite phase by means of slip. A unique characteristic structure of nanoscale parallel-arranged lath martensite is formed on the surface of GNPs. Therefore, a co-lattice structure between ε-co and γ-co shows the specific orientation relationship between the crystallographic plane (1 1 1)γ-co//(0 0 0 2)ε-co and the crystallographic zone axis [1 1 0]γ-co//[1 1 2‾ 0]ε-co.

Theoretical investigation of structural instabilities of newly predicted superconducting Heusler alloys Rh2NbZ (Z = Al, Ga, Sn): Ab initio approach

We systematically investigate the structural and elastic properties of Rh2NbZ (Z = Al, Ga, Sn) through ab initio calculations. We determine the equilibrium lattice parameters in the cubic austenitic phase of Rh2NbZ and observe martensitic structural transitions in all compositions. These transitions are attributed to the lone pair effect of s electrons on the Z element, leading to a paramagnetic ground state for all alloys. In addition, we discover superconducting behavior of Rh2NbZ, as evident from the total density of states plots. Furthermore, we calculate various elastic parameters in cubic phase to understand the structural stability.

Study on Fatigue Performance of Pulsed Tungsten Inert Gas Welding Joint of Duplex Stainless Steel Thin Tube.

To solve the shortage of austenite phase precipitation caused by nitrogen loss in the welding process of UNS S2205 duplex stainless steel (DSS), shielding gas nitriding was investigated by adding different N2 contents in Ar shielding gas during the welding process. A good thin-walled pipe butt joint was formed using the pulsed tungsten inert gas (P-TIG) welding method with Ar-N2 shielding gas. High cycle fatigue tests of the weld joints were conducted to study the effect of shielding gas nitriding on the fatigue properties. Fatigue tests at three stress levels of 225 MPa, 270 MPa, and 360 MPa were carried out on the weld joints with different N2 contents, and the fatigue samples were all fractured in the high temperature heat-affected zone (H-HAZ). Within the current process parameters, the fatigue life of the 4 vol.% N2 welded joints was optimal. Fatigue striations appeared in the fatigue crack propagation zone, and the transient fracture zone was similar to the tensile fracture. Under the low-stress level, the area of the crack propagation zone under 4 vol.% N2 was the highest, the tear ridges all expanded around the crack source area, and the fatigue crack propagation zone presented a radial distribution. The proliferation and expansion of dislocations were mainly carried out in the austenite grains, and the dislocation density of the fatigue specimens under 4 vol.% N2 was smaller than that of the Ar specimens. Shielding gas nitriding effectively improved the balance of the two-phase ratio and the hardness of austenite phase, optimized the internal slip system, inhibited the proliferation of dislocations in the austenite phase, and improved the fatigue life of weld joints.

Enhancing the single-track deposition quality of AISI 308L wire arc additive manufacturing via process optimization and cold forging treatment

Wire arc additive manufacturing (WAAM) has been established as a promising additive manufacturing technique for fabricating and repairing medium-to-large scale metallic engineering parts. However, achieving an excellent geometrical accuracy and high mechanical properties close to the parent metal require an optimal setting of parameters for every material system and, sometimes, post-processing treatment. In this work, WAAM of 308L stainless steel was performed, using gas metal arc welding as the heat source, at varying values of wire feed rate (WFR) and traverse speed (TS) to investigate its effects on the geometry, microstructure and mechanical properties of the deposited track. Thereafter, post-cold forging treatment was performed on the track deposited at the optimum parametric setting. The track width and height decreased with increasing TS due to reduction in the wire deposition volume per unit length of track. The track height increased as the WFR increased from 61.67 to 95 mm/s, after which the process became unstable, leading to a decline in height. The microstructure of the deposited track mainly comprised δ-ferrite and austenite phases while the hardness of the track deposits (ranging between 124–172 HV) was largely influenced by the presence of carbide precipitates and equiaxed grains size which reduced as the TS and WFR increased. The post-cold forging treatment resulted in strain hardening, which resulted in significant improvement in the track hardness (up to 219 HV) but a fall in its impact strength due to loss of ductility.

Investigation on the Attainment of High-Density 316L Stainless Steel with Selective Laser Sintering.

Due to the low density of the green part produced by selective laser sintering (SLS), previous reports mainly improve the sample's density through the infiltration of low-melting metals or using isostatic pressing technology. In this study, the feasibility of preparing high-density 316L stainless steel using 316L and epoxy resin E-12 as raw materials for SLS combined with debinding and sintering was investigated. The results indicated that in an argon atmosphere, high carbon and oxygen contents, along with the uneven distribution of oxygen, led to the formation of impurity phases such as metal oxides, including Cr2O3 and FeO, preventing the effective densification of the sintered samples. Hydrogen-sintered samples can achieve a high relative density exceeding 98% without losing their original design shape. This can be attributed to hydrogen's strong reducibility (effectively reducing the carbon and oxygen contents in the samples, improving their distribution uniformity, and eliminating impurity phases) and hydrogen's higher thermal conductivity (about 10 times that of argon, reducing temperature gradients in the sintered samples and promoting better sintering). The microstructure of the hydrogen-sintered samples consisted of equiaxed austenite and ferrite phases. The samples exhibited the highest values of tensile strength, yield strength, and elongation at 1440 °C, reaching 513.5 MPa, 187.4 MPa, and 76.1%, respectively.

Effect of martensitic transformation on ratchetting in medium-manganese steel: Experiment and homogenized constitutive model

Transformation-induced plasticity (TRIP) behavior and related cyclic plasticity model of medium-manganese steel subjected to uniaxial cyclic loading were studied. Cyclic loading tests were conducted at different mean stresses and stress amplitudes. The results show that medium-manganese steel exhibits two different ratchetting evolution characteristics. Moreover, microscopic characterizations reveal that martensitic transformation occurs in medium-manganese steel during asymmetrical cyclic stressing, and the higher the applied stress amplitude, the greater the ratchetting strain and the more likely the martensitic transformation will occur. The interaction between TRIP and ratchetting leads to accelerated accumulation of plastic strain. Based on the existing meso-mechanics cyclic elastoplastic constitutive model, a kinetic equation for the strain-induced martensitic transformation and a modified nonlinear kinematic hardening equation are introduced. Subsequently, the two-leveled homogenization method was used to construct a homogenized cyclic plasticity model containing a three-phase microstructure of austenite, martensite, and ferrite. By comparing the predicted results with the experimental results, the proposed model can reasonably describe the evolutionary features of each phase and the effect of the phase transformation on the ratchetting of medium-manganese steel. Finally, ratchetting is further predicted and discussed for different austenite contents and phase transformation rates using the proposed model.

Lattice dynamics of Mg-Sc lightweight shape memory alloys

Lattice vibrations play a significant role in the martensitic phase transformation of MgSc alloys, thus in the shape memory effects as well. In this article, the phonon spectra and thermodynamic properties of MgSc alloys with different structures were systemically studied by first-principles methods. The phonon spectra of Mg-18.75 at%Sc and Mg-20.83 at%Sc in austenite phase are fundamentally different, and the experimental martensitic transition behavior of MgSc alloys with different compositions can be well explained by the lattice dynamics. The occurred Fermi surface nesting at specific compositions leads to the appearance of phonon imaginary frequency, thus resulting in the lattice instability. The entropy change and latent heat obtained from harmonic phonon calculations suggests that the MgSc alloys are promising for the application in low-temperature elastocaloric cooling, and that the entropy changes are comparable to the well known cooling materials such as BaTiO3 and NiTi.

Measurement of G-phase volume fraction and number density in duplex stainless steels using transmission electron microscopy

Duplex stainless steels (DSS) have a high toughness and strength due the presence of both austenitic and ferritic phases. These alloys have had limited use in power production applications due to thermal embrittlement caused by spinodal decomposition and development of G-phase precipitates in the ferrite. Lean grade DSS alloys (e.g., 2101, 2003) may offer improved thermal stability due to the reduction of Cr- and Ni-equivalent elements when compared to standard grade compositions (e.g., 2205, 2209). The abundance of the G-phase was measured in five duplex stainless steels, three wrought alloys (2101, 2003, 2205) and their matching filler metals (2101-w, 2209-w), after aging at 427 °C for 1000 h and 10,000 h. The G-phase volume fraction, number density, size, and precipitate spacing were found using quantitative analysis of transmission electron microscopy dark field images and the composition of G-phase precipitates on other clusters were characterized with atom probe tomography (APT). In the welded alloys, the G-phase was found to develop rapidly, relative to the wrought material. A positive correlation was found between the nickel equivalent composition of the alloy and the G-phase volume fraction. The alloys 2205, 2209, and 2101-w, which are higher in Cr and Ni, all showed significant G-phase precipitation, further strengthening the hypothesis that lean grade DSS alloys are more thermally stable against precipitation in the ferrite. Electron diffraction showed a secondary phase present in the 2101 wrought alloy at 10,000 h, but it was not crystallographically consistent with the G-phase; APT showed the presence of nanoclusters rich in both nickel and copper for this alloy. No secondary phases or clusters were found in 2003 after 10,000 h of aging, so it may be a candidate alloy for applications that require long-life times at high operating temperatures.

Dual nanoprecipitation and nanoscale chemical heterogeneity in a secondary hardening steel for ultrahigh strength and large uniform elongation

Nanoprecipitates and nanoscale retained austenite (RA) with suitable stability play crucial roles in determining the yield strength (YS) and ductility of ultrahigh strength steels (UHSSs). However, owing to the kinetics incompatibility between nanoprecipitation and austenite reversion, it is highly challenging to simultaneously introduce high-density nanoprecipitates and optimized RA in UHSSs. In this work, through the combination of austenite reversion treatment (ART) and subsequent flash austenitizing (FA), nanoscale chemical heterogeneity was successfully introduced into a low-cost UHSS prior to the aging process. This chemical heterogeneity involved the enrichment of Mn and Ni in the austenite phase. The resulting UHSS exhibited dual-nanoprecipitation of Ni(Al,Mn) and (Mo,Cr)2C and nanoscale austenite stabilized via Mn and Ni enrichment. The hard martensitic matrix strengthened by high-density dual-nanoprecipitates constrains the plastic deformation of soft RA with a relatively low fraction of ∼15 %, and the presence of relatively stable nanoscale RA with adequate Mn and Ni enrichment leads to a marginal loss in YS but keeps a persistent transformation-induced plasticity (TRIP) effect. As a result, the newly-developed UHSS exhibits an ultrahigh YS of ∼ 1.7 GPa, an ultimate tensile strength (UTS) of ∼1.8 GPa, a large uniform elongation (UE) of ∼8.5 %, and a total elongation (TE) of ∼13 %. The strategy of presetting chemical heterogeneity to introduce proper metastable phases before aging can be extended to other UHSSs and precipitation-hardened alloys.

Theoretical investigations on pressure-driven large-volume-change martensitic phase transition in ductile all-d-metal Heusler compound Ni2MnTa

The creation of innovative functional materials with outstanding overall performance is the main challenge encountered in practical application. This study investigated the pressure-dependent martensitic phase transition in ductile compound Ni2MnTa and also revealed its physical mechanism. Theoretically, when pressure was applied, the martensitic phase transition in Ni2MnTa was accompanied by a significant volume change of −4 %. The results indicate that the inherent volume contraction leads to enhanced interatomic d–d orbital hybridization during the tetragonal deformation, a process in which thermodynamic driving force increases significantly and deformation ability is subsequently enhanced. Their synergistic interaction induced the large-volume-change martensitic transformation in ductile all-d-metal Heusler compound Ni2MnTa. A metamagnetic martensitic phase transition could occur due to the magnetic moment difference between the austenite and marensite phases. Practically and importantly, Ni2MnTa shows better ductile properties. The combination of excellent ductility and potential large-volume-change martensitic transformation in Ni2MnTa makes it an interesting candiade material. This study can provide significant research guidance for exploring and developing novel materials for future industrial application.

Cold metal transfer welding of 316L/430 dissimilar stainless-steel welds

Purpose This paper aims to examine dissimilar joints for various applications in chemical, petrochemical, oil, gas, shipbuilding, defense, rail and nuclear industry. Design/methodology/approach This study examined the effects of cold metal transfer welding on stainless steel welds for 316L austenitic and 430 ferritic dissimilar welds with ER316L, ER309L and without (autogenous) fillers. The microstructural observation was done with an optical microscope. The mechanical test was done to reveal the strength, hardness and toughness of the joint. The electrochemical polarization tests were done to reveal intergranular and pitting corrosion in the dissimilar joints. Findings This microstructural study shows the presence of austenitic and ferritic phases with vermicular ferrite for ER309L filler weld, and for ER316L filler weld specimen shows predominately martensitic phase in the weld region, whereas the autogenous weld shows lathy ferrite mixed with martensitic phase. Mechanical test results indicated that filler welded specimen (ER316L and ER309L) has relatively higher strength and hardness than the autogenous weld, whereas ER316L filler weld exhibited the highest impact toughness than ER309L filler weld and lowest in autogenous weld. The electrochemical corrosion results displayed the highest degree of sensitization (DOS) in without filler welded specimen (45.62%) and lower in case of filler welded specimen ER309L (4.95%) and least in case of ER316L filler welded specimen (3.51%). The high DOS in non-filler welded specimen is correlated with the chromium carbide formation. The non-filler welded specimen shows the highest pitting corrosion attack as compared to the ER316L filler weld specimen and relatively better in ER309L filler welded specimen. The highest pitting corrosion resistance is related with the high chromium content in ER309L composition. Originality/value This experimental study is original and conducted with 316L and 430 stainless steel with ER316L, ER309 and without fillers, which will help the oil, shipbuilding and chemical industries.

Effect of thermal ageing on the deformation behaviour of ferrite and austenite in a duplex stainless steel: Micropillar characterisation and dislocation density modelling

The deformation behaviour of the austenitic and ferritic phases in an aged duplex stainless steel is investigated experimentally and numerically. The effect of the ferritic phase’s spinoidal decomposition during thermal ageing on the mechanical behaviour of the alloy is studied through micropillar compression tests on the individual single crystal phases before and after ageing, and APT and TEM investigations of the decomposed ferrite and corresponding dislocation structures. Dislocation density-based crystal plasticity models are formulated for the austenitic and ferritic phases, and calibrated from the measured micropillars responses.A considerably higher and more homogeneously distributed initial dislocation density is observed in the austenite, resulting in a more homogeneous deformation of the austenitic micropillars than the ferritic ones. The spinoidal decomposition of the ferrite leads to a considerable increase of its initial flow stress. The strengthening effect of thermal ageing and the resulting localised deformation response of the aged ferritic micropillars are correctly described by the crystal plasticity results, which required a higher initial obstacle (dislocations + inter-phases of the newly formed α′ domains) density to dislocation motion. Moreover, a strong size effect was observed on the behaviour of the as-received and aged austenitic and as-received ferritic micropillars, but not in the aged ferritic ones. Such contrasting behaviour originates from the fact that, for the size sensitive cases, the dislocation mean free path is controlled by the mean micropillar diameter, whereas in the aged ferrite micropillars, it is by the ∼ 5 nm wide Cr-rich domains within the spinoidal decomposed ferrite.

Characterization and Microstructure of Recycled Eroded Particles from Die-Sink Electro Discharge Machining of H11 Alloy for Applicability in Additive Manufacturing

Different waste streams from electro discharge machining (EDM) were investigated for an upcycled usage in processes for additive manufacturing (AM). These erosion sludges accumulate in filter cartridges and at the bottom of machining basins. The enclosed particles were extracted, sieved and investigated via laser diffraction, dynamic image analysis, scanning electron microscopy, optical emission spectroscopy, elemental analysis and flowability measurements. Additionally, thermal, crystallographic and metallographic investigations as well as X-ray micro-computed tomography (µ-CT) were utilized for the characterization of particle and material properties. In general, eroded powders fulfill the requirements for AM regarding particle size and shape very well, which is confirmed in morphological investigations and powder flow characteristics showing similar properties as the H11 AM reference material. The chemical composition of the powders is equal to the machined H11 alloy, except for the high carbon content. Carbon is entrapped in the iron lattice originating from pyrolysis of the present dielectric fluid and the graphite electrode during rapid solidification, which leads to a transition from martensite to cementite structures. This change is observed in the microstructure of powders, in which acicular primary cementite and austenite are present. After remelting with slow heating and cooling rates the microstructure changed to ledeburite II with retained austenite and martensitic phases. The pore size and shape distributions obtained by µ-CT measurements showed a pore formation in the compact sample. These results provide a fundament of major properties as well as handling and recycling suggestions for eroded particles enclosed in waste sludges.Graphical

Magnetization and exchange-bias effect in powders of the Heusler Ni2MnSn-based alloys

Experimentalinvestigation of properties of powders of the Heusler Ni2MnSn-based alloys revealed the extreme suppression of both, the magnetization and the exchange-bias and exchange spring effects in powders of the alloys. Furthermore, the structural transformation between austenite and martensite phases of the alloys is hindered in the powders, hysteresis curves do not exhibit saturation and observed cluster-glass behavior of the powders at low temperature is almost independent on magnetic field and on composition of the alloys. A complex conjunction of exchange-bias effect and frozen magnetization contribution has been revealed in the case of the powders. All the mentioned phenomena are strongly dependent on the size and the shape of particles of the powders prepared either in an agate mortar or in a ball mill. Temperature treatment of the powders and the compressed pellets at temperature 1173 K under argon led to a recovery of the applicable properties that are characteristic for the bulk alloys. Results of the earlier quantum mechanical calculations of effects of different arrangement of Mn and Sn atoms in crystal structure of the alloys have been used to discuss the observed properties of the powders and to assess a formation of clusters in magneto-crystalline structure of the alloys.

Phase-field description of fracture in NiTi single crystals

A phase-field model for thermomechanically-induced fracture in NiTi at the single crystal level, i.e., fracture under loading paths that may take advantage of either of the functional properties of NiTi–superelasticity or shape memory effect–, is presented, formulated within the kinematically linear regime. The model accounts for reversible phase transformation from austenite to martensite habit plane variants and plastic deformation in the austenite phase. Transformation-induced plastic deformation is viewed as a mechanism for accommodation of the local deformation incompatibility at the austenite–martensite interfaces and is accounted for by introducing an interaction term in the free energy derived based on the Mori–Tanaka and Kröner micromechanical assumptions and the hypothesis of martensite instantaneous growth within austenite. Based on experimental observations suggesting that NiTi fractures in a stress-controlled manner, damage is assumed to be driven by the elastic energy, i.e., phase transformation and plastic deformation are assumed to contribute in crack formation and growth indirectly through stress redistribution. The model is restricted to quasistatic mechanical loading (no latent heat effects), thermal loading sufficiently slow with respect to the time rate of heat transfer by conduction (no thermal gradients), and a temperature range below Md, which is the temperature above which the austenite phase is stable, i.e., stress-induced martensitic transformation is suppressed. The numerical implementation of the model is based on an efficient scheme of viscous regularization in both phase transformation and plastic deformation, an explicit numerical integration via a tangent modulus method, and a staggered scheme for the coupling of the unknown fields. The model is shown able to capture transformation-induced toughening, i.e., stable crack advance attributed to the shielding effect of inelastic deformation left in the wake of the growing crack under nominal isothermal loading, actuation-induced fracture under a constant bias load, and crystallographic dependence on crack pattern.

Structure characterization and failure mechanisms of high chromium cast iron grate bar

Grate bars represent the main failure components within sintering machine trolleys. The quality of grate bars significantly impacts the production efficiency of the sintering process, and understanding the failure mechanisms of grate bars guides research in grate material development. In this study, we analyze the failure mechanisms of grate bars by comparing the structure of the grate matrix before and after failure and by examining the structural morphology of the failed zones. Our findings reveal that the austenite phase of the grate bars transforms into granular pearlite. The carbide type changes from M7C3 to M7C3 and eventually to M23C6 after extended service. P and S accumulate at the grain boundaries, resulting in the formation of the brittle phase Mx(S,P)y. Additionally, Cr diffuses to the surface, forming an oxide layer at high temperatures. The structural transformation from austenite to pearlite and the diffusion of Cr in the matrix phase increase electrode potential differences, which promote electrochemical corrosion between the matrix phase and the carbide at the grain boundary and within the inner grain. Cl being present in the service environment played an important role in the failure of grate bars by promoting high-temperature oxidation and being involved in crevice corrosion. Grate bar failure primarily results from high-temperature oxidation, electrochemical corrosion, brittle fractures, and compound actions. Finally, we propose recommendations to enhance the performance of grate bars through alloying treatments.

Parametric Study and Optimization the Effect of TIG Welding Process Parameters on the Corrosion Resistance of 2205 DSS Weldment using Potentiodynamic Polarization Technique

The aim of this research is to analyze and optimize, using response surface methodology RSM, the effect of tungsten inert gas TIG welding parameters, namely welding current WC, welding speed WS, and N2 addition with Ar as shielding gas, on the corrosion resistance of duplex stainless steel DSS weldments. Due to the combination of alloying elements and the nearly equal amounts of austenite and ferrite phases, DSS has great mechanical characteristics and good corrosion resistance. However, most DSS applications require welding processes to join parts together; these processes affect the microstructure of DSS and lead to the formation of precipitations, resulting in poor mechanical properties and corrosion resistance. Therefore, it is necessary to investigate the effect of TIG welding process parameters on the corrosion resistance of DSS weldments. In this study, the corrosion penetration rate of all DSS weldments was determined using the potentiodynamic polarization technique. The response surface methodology was applied in order to achieve the mathematical model that describes the relationship between above mentioned welding variables and corrosion penetration rate of DSS weldment. Results showed that WC and N2 are the most important parameters that affected the corrosion penetration rate. Meanwhile, the results clarified that when increasing WC with decreasing WS, which corresponds to the highest heat input, the corrosion penetration rate increased due to the appearance of the precipitations. The same results were obtained for decreasing welding current while increasing welding speed, which corresponds to the lowest heat input due to the increase in ferrite content. On the other hand, the results also found that the addition of a small amount of N2 with Ar as shielding gas leads to a decrease in the corrosion penetration rate. However, the increase in the amount of N2 leads to an increase in the corrosion penetration rate due to the reappearance of the precipitations.