Search

This study conducts a comparative electrochemical evaluation of three types of pearlitic steels used in flexible pipelines for oil transport in marine environments. The steels have been manufactured with chemical composition and geometry variations to optimize operation performance under adverse conditions. Electrochemical tests were conducted using solutions simulating marine environments with NaCl and CO2, and at high temperatures. The results indicated that spheroidized (SC) steel demonstrated the best corrosion resistance under these specific conditions. Additionally, the Raman spectroscopy characterization technique was used to analyze the layers of corrosion products formed during the tests, identifying the presence of FeCO3 (siderite) and other corrosive oxides. These discoveries are valuable for selecting and improving materials in flexible pipelines used in oil production in marine waters. The study highlights the importance of the cementite morphology present in pearlite as a relevant factor in the corrosive behavior of steels, contributing to the development of more efficient and durable solutions for the offshore oil and gas industry. [ABSTRACT FROM AUTHOR]

Among the most studied semiconducting transition metal dichalcogenides (TMDCs), WS 2 showed several advantages in comparison to their counterparts, such as a higher quantum yield, which is an important feature for quantum emission and lasing purposes. We studied transferred monolayers of WS 2 on a drilled Si 3 N 4 substrate in order to have insights about on how such heterostructure behaves from the Raman and photoluminescence (PL) measurements point of view. Our experimental findings showed that the Si 3 N 4 substrate influences the optical properties of single-layer WS 2 . Beyond that, seeking to shed light on the causes of the PL quenching observed experimentally, we developed density functional theory (DFT) based calculations to study the thermodynamic stability of the heterojunction through quantum molecular dynamics (QMD) simulations as well as the electronic alignment of the energy levels in both materials. Our analysis showed that along with strain, a charge transfer mechanism plays an important role for the PL decrease. [ABSTRACT FROM AUTHOR]

Flexible pipelines connect offshore platforms to subsea production systems due to their high flexibility, applicability, and recycling. Flexible armor layers in flexible pipelines are constructed using the parallel helical wrapping of several rectangular wires. The complex stress modes to which pipelines are subjected provide complex failure modes that are mostly unpredictable, requiring expensive pipeline integrity verification methods. This work investigates texture and microstructure evolution in pearlite-drawn wires due to different heat treatments. The material was subjected to annealing and isothermal heat treatments to obtain changes in its microstructure and texture. The changes were characterized using SEM, XRD, and EBSD techniques. Samples were subjected to tensile testing to evaluate their mechanical properties. This work revealed that annealing and isothermal treatments mainly modify the material microstructure, whereas annealing provides a material with grains with ease of deformation. In contrast, isothermal treatment provides grain growth with high internal energy and more deformation resistance. Annealing increases the intensity of all texture components, while isothermal treatment reduces intensity. These findings provide insights into the relationship between material properties and heat treatments, which can be used to optimize the design and performance of flexible pipelines, thereby reducing the need for expensive integrity verification methods. [ABSTRACT FROM AUTHOR]

Physical simulation is a useful tool for examining the events that occur during the multiple stages of thermomechanical processing, since it requires no industrial equipment. Instead, it involves hot deformation testing in the laboratory, similar to industrial-scale processes, such as controlled hot rolling and forging, but under different conditions of friction and heat transfer. Our purpose in this work was to develop an artificial neural network (ANN) to optimize the thermomechanical behavior of stainless-steel biomaterial in a double-pass hot compression test, adapted to the Arrhenius–Avrami constitutive model. The method consists of calculating the static softening fraction (Xs) and mean recrystallized grain size (ds), implementing an ANN based on data obtained from hot compression tests, using a vacuum chamber in a DIL 805A/D quenching dilatometer at temperatures of 1000, 1050, 1100 and 1200 °C, in passes (ε1 = ε2) of 0.15 and 0.30, a strain rate of 1.0 s−1 and time between passes (tp) of 1, 10, 100, 400, 800 and 1000 s. The constitutive analysis and the experimental and ANN-simulated results were in good agreement, indicating that ASTM F-1586 austenitic stainless steel used as a biomaterial undergoes up to Xs = 40% of softening due solely to static recovery (SRV) in less than 1.0 s interval between passes (tp), followed by metadynamic recrystallization (MDRX) at strains greater than 0.30. At T > 1050 °C, the behavior of the softening curves Xs vs. tp showed the formation of plateaus for long times between passes (tp), delaying the softening kinetics and modifying the profile of the curves produced by the moderate stacking fault energy, γsfe = 69 mJ/m2 and the strain-induced interaction between recrystallization and precipitation (Z-phase). Thus, the use of this ANN allows one to optimize the ideal thermomechanical parameters for distribution and refinement of grains with better mechanical properties. [ABSTRACT FROM AUTHOR]

When austenite is deformed within the austenite phase field, that is, above the equilibrium transformation temperature Ae3, it partially transforms dynamically into ferrite. Here, rough rolling simulations are conducted at 1100 °C on an X70 steel to study the influence of grain size and residual strain on this type of transformation. Three simulated roughing passes are applied with pass strains of 0.4 at a strain rate of 1.0 s−1. The resulting stress–strain curves are recorded and analyzed. The volume fractions of ferrite and martensite (prior austenite) are determined on quenched samples by means of metallographic techniques. It is observed that dynamic transformation took place during the first roughing pass and that the volume fraction of transformed ferrite increases with the cumulative strain. Both the critical strain to the onset of dynamic transformation as well as the grain size decrease with pass number. [ABSTRACT FROM AUTHOR]

The dynamic transformation (DT) of austenite to ferrite and the retransformation of the dynamically transformed ferrite back into the more stable austenite were studied at temperatures above the Ae3. For this purpose, compression tests were carried out on a C-Mn and a Nb microalloyed steel over the temperature range 870-960 °C. The samples were deformed to a strain of 0.75 at a strain rate of 1 s−1 and held isothermally for times of 1-1000 s to permit retransformation. The samples were water quenched after testing and the volume fractions of retransformed ferrite were measured to allow for the construction of TTRT (time-temperature-reverse transformation) curves. The present type of diagram can be combined with strain-temperature-transformation (STT) curves to model the occurrence of dynamic transformation and retransformation during thermomechanical processing. [ABSTRACT FROM AUTHOR]

The dynamic transformation (DT) of austenite to ferrite and the retransformation of the dynamically transformed ferrite back into the more stable austenite were studied at temperatures above the Ae3. For this purpose, compression tests were carried out on a C-Mn and a Nb microalloyed steel over the temperature range 870-960 °C. The samples were deformed to a strain of 0.75 at a strain rate of 1 s−1 and held isothermally for times of 1-1000 s to permit retransformation. The samples were water quenched after testing and the volume fractions of retransformed ferrite were measured to allow for the construction of TTRT (time-temperature-reverse transformation) curves. The present type of diagram can be combined with strain-temperature-transformation (STT) curves to model the occurrence of dynamic transformation and retransformation during thermomechanical processing. [ABSTRACT FROM AUTHOR]

A five-pass rolling schedule is simulated by means of torsion testing. The first and last pass temperatures are 920 and 860 °C with 15° of cooling between passes. All of the rolling is carried out above the Ae3 temperature of 845 °C that applies to this steel. Interpass times of 10, 20, and 30 s are employed, which correspond to cooling rates of 1.5, 0.75, and 0.5 °C s−1, respectively. Samples were quenched before and after the first, third, and fifth passes in order to determine the amount of dynamic ferrite produced in a given pass. The data also allow for estimation of the amounts of ferrite that retransform to austenite during the time between passes. The volume fractions of ferrite and martensite (prior austenite) were determined by optical metallography. The amount of dynamic ferrite formed and retained increased with pass number. The volume fraction of ferrite that retransformed increased with pass number, averaging about 4, 6, and 9% for the 10, 20, and 30 s interpass times, respectively. The simulations indicate that ferrite is unavoidably produced during plate rolling and that the microstructure present at the initiation of accelerated cooling does not consist solely of austenite. [ABSTRACT FROM AUTHOR]

The occurrence of dynamic transformation is investigated during the simulated hot rolling of an API‐X80 steel. Torsion tests are carried out under continuous cooling conditions, with all deformation passes applied above the equilibrium transformation temperature. Three different interpass times are investigated: 1, 8, and 20 s. Samples are water‐quenched before and after the odd‐numbered passes, and the volume fraction of ferrite is evaluated metallographically. Dynamic transformation took place under all conditions and the volume fraction of retained ferrite increased with the retained strain. The increase in flow stress during simulated rolling is less than expected under all conditions, which is evidence for the dynamic formation of ferrite. The driving forces and energies barriers are evaluated, indicating that dynamic transformation is mechanically activated. [ABSTRACT FROM AUTHOR]

It has been previously demonstrated that austenite may undergo partial dynamic transformation (DT) during the plate rolling process. Austenite dynamically transforms into unstable ferrite during hot deformation even at very high temperatures. In this work, the plate rolling simulations, with emphasis on Steckel mill operations, through torsion testing under isothermal conditions were performed on an X70 steel. Four different roughing schedules were tested followed by five finishing passes with pass strains of 0.3 applied at 900 °C. The roughing schedules had zero, one, two and three roughing passes at a temperature of 1100 °C, strain of 0.4 and strain rate of 1 s−1. The stress–strain curves as well as the mean flow stress (MFS) behaviors indicated that both dynamic transformation (DT) and dynamic recrystallization (DRX) occurred during straining. The critical strains for the onset of DT and DRX were determined by means of the double differentiation method and the critical strain values decreased with the number of roughing and finishing strains from the first going to the last pass. It was observed that the volume fraction of the dynamically formed ferrite increased sharply during the finishing stage as the number of previous roughing passes increased, which can be attributed to higher strain accumulation. The results presented here indicate that improved models are needed to control the microstructure of the material during subsequent cooling. [ABSTRACT FROM AUTHOR]

A five-pass torsion simulation of the roughing passes applied during hot plate rolling was performed in the single-phase austenite region of a Nb-microalloyed steel under continuous cooling conditions. The deformation temperatures were approximately half-way between the Ae3 and the delta ferrite formation temperature (i.e., 250 °C above the Ae3) in which the free energy difference of austenite and ferrite is at maximum. The microstructures in-between passes were analyzed to characterize and quantify the occurrence of deformation-induced dynamic phase transformation. It was observed that about 7% of austenite transforms into ferrite right after the final pass. The results are consistent with the calculated critical strains and driving forces which indicate that dynamic transformation (DT) can take place at any temperature above the Ae3. This mechanism occurs even with the presence of high Nb in the material, which is known to retard and hinder the occurrence of DT by means of pinning and solute drag effects. The calculated cooling rate during quenching and the time–temperature–transformation curves of the present material further verified the existence of dynamically transformed ferrite. [ABSTRACT FROM AUTHOR]