The present investigation finds the effect of electropulsing treatment on the mechanisms of refining and reprecipitation of ordered L20 structure (B2) and its impact on tensile properties of ...low-density duplex steel of Fe-18Mn-10.5Al-1 C-6Ni composition. The selected composition without manganese is melted at 1600°C by induction heating in a vacuum but Mn is added into the melt at 1560°C, in the argon atmosphere to reduce the loss. The melt is cast into a plate form in a copper mold. The cast steel is homogenized, hot rolled, and annealed (PD1-A sample) to get elongated bands, spheroids, and platelets of B2 phase with an austenitic matrix which results in a yield strength of 1015 MPa, and tensile strength of 1285 MPa with a plastic elongation of 16.3%. Electropulsing partially dissolves the B2 phase at a temperature much lower than the equilibrium solvus by reducing barrier energy because of electron wind. As a result, the sizes of bands and spheroids are reduced, and platelets are disintegrated. Electron wind force deforms coarse precipitates, and fragments as well as spheroidized it. Electropulsing of annealed steel (PD1-AE) mobilizes dislocations, and recovers it in B2, but induces localized recrystallization of austenite. At a later time of the signal, the temperature rapidly falls and the matrix becomes supersaturated but electropulsing accelerates low-temperature precipitation of the B2 phase. Therefore, electropulsing can be adopted as a fast manufacturing process to dissolve, deform, fragment, spheroidize and reprecipitate high temperature phase at much lower temperature by dominant athermal effect of electron wind energy over thermal effect. Electropulsing also induces recovery and recrystallization at a relatively low temperature and reduces defect density. Reduction in the overall size of B2 and its distribution towards better uniformity provided an increased yield strength of 1077 MPa, tensile strength of 1355 MPa, and a plastic elongation of 21.6%. The selected duplex low-density steel follows two-stage work hardening of Ludwigson model with an additional stage of dynamic recovery. Fractography analysis confirms that both samples show mixed modes of ductile and brittle fracture, with an increase in size and area percentage of dimples.
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•Major changes in microstructure are resulted from the electron wind energy.•Electropulsing (EP) dissolves ordered L20 (B2) phase at lower than solvus temperature.•EP deforms, fragments and refines existing B2 and accelerates precipitation of it.•EP partially recrystallizes austenite and recovers as well as spheroidizes B2.•Improvement in tensile properties by the refinement, and redistribution of phases.
The article presents the influence of heat treatment on the kinetics of transformations in lean duplex LDX2101 steel and a weld made of standard duplex 2209 material, which was welded by manual metal ...arc welding. Changes in the microstructure, hardness, and magnetic phase content were analyzed after heat treatment was conducted at a temperature of 800 °C for a period ranging from 15 to 1440 min. Light and scanning microscopy, Vickers hardness measurements, and magnetic phase content measurements using a ferritoscope were used for the research. In the LDX2101 steel, the presence of δ-ferrite and γ austenite was identified and additional Cr
N nitrides were observed in the heat-affected zone. After heat treatment, the decomposition of δ ferrite into γ
austenite and Cr
N nitrides was observed in both areas. In the case of weld made by the coated electrode in 2209 grade, a ferritic-austenitic microstructure with allotriomorphic austenite (γ
), Widmanstätten austenite (γ
), and idiomorphic austenite (γ
) and δ-ferrite area with "bee swarms" of fine precipitations of chromium nitrides Cr
N and non-metallic inclusions (NMIs) of slag, formed during the welding process, are observed in the as-welded state. After heat treatment, the presence of the χ phase (after 15 min of annealing) and the σ phase (after 120 min of annealing) was additionally identified. The kinetics of intermetallic phase evolution in welds made from 2209 material were presented. The obtained results of hardness measurements and metallographic tests were correlated, which allowed for a quick check of the precipitation processes on the used element.
A fine-grained duplex steel with a composition of Fe–5Mn–2Al-0.6C (wt.%) was fabricated using a powder metallurgy (PM) technology of thermomechanical consolidation by hot extrusion of powder compact. ...The microstructure consisted of α′-martensite, residual austenite (RA), and a small amount of Al2O3 particles. Subsequent heat treatment was performed to adjust the microstructure and mechanical properties. This study focuses on the pre-and post-heat treatment microstructure of the material, elucidates the reasons for its formation, and explains how microstructural changes influence tensile deformation behavior. The results show that the heat treatment caused the precipitation of nanoscale carbide within the martensite, which significantly increased the yield strength from 792 MPa to 1078 MPa. While heat treatment altered the size and distribution of RA regions in the microstructure, the amount of RA transformed during deformation remained proportional to the flow stress in both materials, indicating that the flow stress dictates the amount of phase transformation of ultrafine grained RA. Therefore, in the heat-treated material with a higher yield strength, a larger amount of RA transformed during the initial stage of plastic deformation, leaving less RA to sustain a work-hardening rate in subsequent deformation, resulting in a decrease in ductility from 5.5 % to 3.6 % and fracture stress from 1674 to 1453 MPa. In addition, the in-situ formed Al2O3 particles facilitated grain refinement of the extruded rod, but had less effect on the microstructure and properties of the heat-treated sample. This study serves as a valuable reference for comprehending the influence of microstructural changes in PM manganese steel on tensile deformation behavior.
Electrochemical hydrogen absorption in duplex steels is not fully understood. In this work, an in-situ synchrotron cross-sectional X-ray micro-diffraction analysis is performed on steel with ...comparable phase fractions of ferrite and austenite, coupled with electrolytic hydrogen charging. The results reveal that charging with a constant current density of 10 mA/cm² for 5 h leads to expanding the austenitic lattice to a depth of approximately 250 µm, up to ≥0.15 %. In contrast, the lattice parameter of the ferrite phase remains unchanged during this process. As the austenite expansion progresses, it generates different amounts of equivalent in-plane compressive stresses, which amount to approximately -150 and -450MPa in the austenite and ferrite phases at the sample surface, respectively. Using a finite element model of grain interaction, this difference is qualitatively interpreted by mutual mechanical constraints between ferrite and austenite, as well as between the hydrogen-charged surface layer and the underlying material.
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The present work aims to investigate the microstructure and mechanical behavior of the dissimilar welded joint (DWJ) of martensitic A 335-grade P91 steel and high alloy ferritic austenitic A 182 F69 ...steel produced by the gas tungsten arc welding (GTAW) process. The microstructural studies showed the variety of the microstructure across the DWJ, which formed mainly due to the solidification and solid-state phase transformation as a result of the weld thermal cycle. The microstructural studies were performed in as-welded as well as post-weld heat treatment (PWHT) conditions. PWHT has been conducted to improve the mechanical properties of the P91 heat-affected zone (HAZ) at 760 °C (PW 1) and 810 °C (PW 2) for 2 h. For the mechanical properties of the DWJ, tensile tests, and microhardness tests were conducted. The fractured tensile specimen has been characterized using the scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS). The centre region of the weld metal showed the equiaxed dendrites while the interface near the boat fusion line, on both the P91 and F69 sides, showed the cellular and columnar dendrites. PWHT has observed a negligible effect on the microstructure and hardness of WFZ and F69 HAZ, while a significant change was observed for P91 HAZ. The tensile strength of the DWJ was measured maximum (735 MPa) for as-welded condition and reduced after the PWHT and for PW 2, it was measured lower than that of P91 and F69 base metal. The failure of the tensile specimen was also noticed in the soft inter-critical HAZ (ICHAZ) region for PW 2 condition.
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•Study on mechanical properties of dissimilar welded joint of P91 and F69 steel.•Study on the role of filler and heat treatment on the mechanical performance of the DWJ.•Detail characterization of the weld metal and HAZ interface for the different conditions of the DWJ.
•Machining of 2205 Duplex Stainless Steel under dry and different positions of MQL nozzles conditions was performed.•Influence of different nozzle spray mode i.e., rake face and flank face was ...studied.•The tribological and machining characteristics were analysed.•The mixed nozzle position i.e., on rake and flank face significantly improves the machining as well as tribological characteristics.
In this work, the sustainable machining approach is promoted by implementing the dry and minimum quantity lubrication (MQL) cooling conditions in the turning of duplex stainless steel. Initially, the turning experiments were performed under dry as well as MQL conditions and then, the influence of different positions of MQL nozzles on tribological and machining performance of 2205 duplex steel was investigated. The cutting parameters were kept fixed and the performance is evaluated in terms of surface roughness, micro-hardness, energy consumption, tool wear, machined surface microstructure and chips morphology. The results demonstrated that the highest average surface roughness values were obtained under dry conditions, with a value of 2.20 µm while MQL (flank + rake directions) produces the lowest surface roughness value of 1.55 µm with an improvement of 30%. Moreover, dual-jet MQL gives the lowest energy consumption (229 kJ) and tool wear (0.15 mm) with 23.67% and 52.38% enhancement, respectively.
Versatility of powder metallurgy was used to design new duplex and compositionally graded steels. Rapid consolidation by Spark Plasma Sintering (SPS) and longer consolidation by Hot Isostatic ...Pressing (HIP) were applied on two austenitic 316L and martensitic Fe-9Cr powders, either homogeneously blended or uniaxially graded before sintering.
The microstructural investigations by micro-hardness, SEM, EDX and EBSD showed a continuous crystallographic structure at the austenite–martensite interface and a similar grain size in SPS and HIP samples, whereas a larger interdiffusion length of Cr and Ni was observed in the HIP sample, as confirmed by diffusion calculations. The tensile behaviour of materials could not be described by a simple law of mixtures. To better understand this phenomenon, the obtained materials were described as a composite and iso-strain and iso-stress models were used and discussed. The microstructural characterizations show that during the consolidation, diffusion of the chemical species modifies the nature and the respective fractions of phases, which explains the discrepancy between the models and the experimental mechanical behaviour of the duplex alloys.
This paper discusses the use of the Barkhausen noise technique to monitor duplex steel components after turning. The surface of duplex steel 1.4470 after face turning is investigated as a function of ...increasing tool flank wear (VB, width of the flank wear) as the major factor affecting severe plastic deformation of the machined surface at elevated temperatures. The Barkhausen noise emission and its extracted features are correlated with residual stresses as well as microstructure. It was found that the subsurface layers are preferentially strained in the cutting direction due to severe plastic deformation during the cutting. For this reason, the machined surface exhibits remarkable stress and magnetic anisotropy and the preferential orientation of the duplex steel matrix plays a major role with respect to the increasing Barkhausen noise emission with increasing flank wear VB. On the other hand, the contribution of increasing dislocation density is only minor.
•Barkhausen noise is sensitive to the surface state after turning duplex steel.•Increasing texture of ferrite increases Barkhausen noise emission.•Surface after turning exhibits strong magnetic and stress anisotropy.
The precipitation kinetics and formation mechanisms of σ phase during isothermal holding of a hyper duplex stainless steel in the temperature range from 750 °C to 1025 °C were studied by means of ...in-situ high energy X-ray diffraction experiments. Rietveld analysis of the data determined the nose temperature as 900 °C where a σ phase fraction of 1 wt% is attained after 15 s. The measurements revealed a distinct change from initial interface controlled nucleation of σ phase to a later stage of diffusion controlled growth during holding at 1000 °C after the σ phase fraction reaches half its final value. At lower holding temperatures the change from interface control to diffusion control happens more gradual and at later stages of the transformation. At these lower temperatures σ phase precipitation is accompanied by the formation of secondary austenite. Changes in σ phase formation mechanisms and kinetics were correlated with variations in the morphology of the precipitates through SEM analysis of quenched samples. Isothermal holding at 1000∘C and 1025 °C as well as above the solvus temperature of σ phase at 1120 °C leads to local fluctuations of austenite and ferrite phase fractions and the concomitant movement of austenite/ferrite phase boundaries even when no overall change in the phase fractions occurs.
•Kinetics of σ phase formation were measured by in-situ high energy X-ray diffraction.•At the nose temperature of 900 °C σ phase reaches 1 wt% within 10 s.•At holding temperatures below 1000 °C secondary austenite forms alongside σ phase.•Formation mechanisms of σ phase change with temperature and during isothermal holding.•At T > 1000 °C austenite and ferrite fractions oscillate locally.
