Materials Science Forum Vol. 1139

Abstract: This article presents the optimal method of melting the 35XGCL (analog is JIS G 5111) low alloy steel alloy in DSP-2.0 2000 kg electric arc furnace. All the main stages of melting in an electric arc furnace are considered. In addition, analytical data on the study of the slag mode during the fluidization of the alloy are presented. The results of the evaluation of oxygen activity in metal depending on the chemical composition of slag oxidation and reduction cycles in the furnace are presented. Graphs of oxygen activity in the alloy depending on the total amount of iron, silicon, and manganese oxides in the slag are presented. Moreover, the effect of constant and additional deoxidizing aluminum content in the alloy on the impact strength of low alloy steel alloy is presented. The impact strength is improved when the constant aluminum content is in the range of 0.05-0.07%.

Abstract: In this article, the effect of TiC nanopowder particles on the wear resistance of low-alloy steel 35XGCL (analog is JIS G 5111) is mathematically modeled. First of all, the composition for liquefaction in an electric arc furnace was calculated. 5 and 10% TiC nanopowder particles were added to the alloy as a modifier before pouring liquid metal into the ladle. This process was performed before pouring the liquid metal from the furnace into the ladle. 15% of TiC was added in the furnace as a modifier. Lagrangian interpolation polynomial construction was used in this modeling. The amount of wear resistance was calculated by polynomial expression of the function with determination of unknown coefficients. The results obtained on the basis of the developed model were compared with case studies. The results of the analysis are shown by graphs.

Abstract: This paper studies the effect of the direct energy deposition (DED) process parameters varying within 20% on the geometric accuracy and formation of residual stresses in the products. In the course of the study, an experiment was carried out according to Taguchi's L9 plan to fabricate samples by varying the laser travel speed, effective focusing distance, feed rate of metal powder composition, and process pause, which were then compared with the rates of geometry change and crystal lattice distortion. The obtained results were subjected to statistical analysis using correlation, regression and factor analysis to determine the influence and significance of factors. As a result, correlations between the process parameters and sample characteristics were identified. As correlation and factor analysis showed, a change in process factors within 20% does not significantly affect most of the quality parameters, except for the level of residual stresses. Geometric and strain parameters are weakly correlated with each other, but no statistically significant correlations were found between them. The analysis of variance showed that the fusion rate and powder flow rate have the greatest influence on the geometric accuracy parameters. These factors have the most significant statistical influence on the response, indicating the importance of controlling these parameters to achieve high geometry accuracy. Regression analysis allowed to obtain adequate models of residual stress level. It was found that the model for residual stress level by planes (200) is more reliable than the model for residual stress level by crystallographic plane (111). The obtained data allow to optimize the DED process in order to achieve a given geometric accuracy and reduce residual stresses in the manufactured products.

Abstract: Despite its remarkable structural strength, austenitic stainless steels such as SS304 are susceptible to stress corrosion cracking (SCC) under thermal insulation due to the synergism of cyclic loading and chloride-containing environments. This study aims to detect SCC for insulated SS304 samples using the acoustic emission technique (AET) as monitoring tool to characterize the various stages of SCC damage mechanism. As-received (AR) and sensitized (SEN) SS304 samples were prepared as per ASTM G30 and experimented with soluble chloride drip test under calcium silicate thermal insulation following ASTM C692. Both AR and SEN samples revealed SCC behavior correlated with measured acoustic signals. AR samples exhibited a single crack with low energetic signals, whereas SEN showed multiple cracks with higher energetic signal events. The difference can be attributed to microstructure change by heat sensitization and the enhancement of the corrosion environment under calcium silicate insulation when wetted by salt solution. The acoustic emission (AE) parameters were characterized and correlated with different stages of SCC phenomena, showing that AET is useful for predicting SCC to avoid catastrophic failures in industries.

Abstract: Stainless steels are the material that has chromium as a main component. The chromium content reacts with oxygen in air, subsequently, forms thin chromium oxide film on the surface of stainless steels. Thus, when these steels are exposed to high temperature for a long period of time in many applications, chromium carbide could precipitate along the grain boundary and reduce the corrosion resistance. This project is conducted to study annealing time effect on stainless steels when exposed to high temperature at various exposure time periods. Three different kind of stainless steels, namely, AISI 304, AISI 304D and AISI 2205 were used in this study. Stainless steels were heated at 600°C for 0, 6, 24, 48 and 96 hours, then cool down in air. Consequently, the investigations were performed by using double-loop Electrochemical Potentiokinetic Reactivation (DL-EPR) and Cyclic Potentiodynamic Polarization (CPP) to study degree of sensitization and film properties. In addition, chromic acid and oxalic acid were used as reagent of acid etching to observe microstructures. Finally, Vickers hardness test were also conducted. Percentage degree of sensitization increased from 2.93% to 62.20% in AISI 304, increased from 5.26% to 55.54% in AISI 304D and from 12.19% to 69.35% in AISI 2205. The pitting potential decreased from 0.47 mV to 0.23 mV for AISI 304 but remained relatively constant for AISI 304D and AISI 2205. The results indicated that after the specimens were exposed to high temperature for a long period of time, all specimens had more chromium depleted areas, more carbide along the grain boundaries, worse film quality and small changes in hardness value.

Abstract: Electrochemical analysis of corrosion in molten nitrate salt of stainless steel grade SS 430, SS 2205, SS 2507 and SS 304 is directly performed to evaluate corrosion resistance. Stainless steels are exposed to molten nitrate salt at 600 °C for two hours. This is done in a furnace equipped with a working electrode terminal, reference and counter electrodes. According to this, electrochemical impedance spectroscopy and potentiodynamic polarization techniques are applied in situ to measure corrosion rates and corrosion resistance. Microstructures of stainless steel reveal the ferrite phase for SS 430, the austenite phase for SS 304 and the duplex phase for SS 2205 and SS 2507. In this study, the existence of an austenite phase promotes corrosion resistance in molten nitrate salt.

Abstract: The development of multiphase bainitic/martensitic steel aims to enhance the mechanical properties and corrosion resistance compared to traditional pearlitic steel. However, the impact of elevated temperatures on the corrosion resistance behavior of these materials cannot be overlooked. This study investigates the corrosion resistance behavior of multiphase bainitic/martensitic steel and pearlitic steel at varying temperatures. Electrochemical tests using Electrochemical Impedance Spectroscopy (EIS) and Linear Polarization (LP) in a 3.5 wt.% NaCl solution demonstrate a consistent trend: acicular bainitic steel exhibits superior corrosion resistance compared to granular bainitic steel and pearlitic steel at both room temperature and elevated temperatures. Further characterization using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) reveals that the formation of oxide layers significantly contributes to the enhanced corrosion resistance observed in these materials.

Abstract: Internal pipeline corrosion is a well-recognized issue in the oil and gas industry, especially in multiphase flow systems, such as wet gas transportation pipelines that contain mixed phases. Internal corrosion typically manifests as either top-of-the-line corrosion (TLC) or bottom-of-the-line corrosion (BLC). While corrosion mechanisms in sweet environments (dominated by CO₂) are relatively well-understood, those in sour environments (dominated by H₂S) remain less thoroughly examined. In sour environments, the primary corrosion product is iron sulfide (FeS), while in sweet environments, iron carbonate (FeCO₃) tends to form. In marginally sour conditions, FeS layers are often non-uniform, promoting localized corrosion and pitting because low concentration of H₂S. It is hypothesizes that higher concentrations of H₂S reduce both the pitting rate and depth.The objective of this research is to investigate the corrosion rate, surface profile, and morphology in a marginal sour environment, using profilometry analysis (ASTM G46) to assess pitting. The experiments were conducted in a glass cell setup simulating pipeline conditions with 3 wt% brine solution and 1000 ppm acetic acid. Corrosion behavior was assessed at H₂S concentrations of 0 ppm, 30 ppm, and 80 ppm using weight loss analysis, surface morphology, and profilometry measurements. Results indicate that increasing H₂S concentration decreases the pitting rate, supporting the study’s hypothesis.

Abstract: A styrene-butadiene rubber having a gradient crosslink density in the thickness direction was simply prepared by vulcanizing under a temperature gradient to study its mechanical properties and swelling behavior. The graded rubber exhibited considerable strain recovery after stress removal despite having a low crosslinked part. Notably, the graded rubber also manifested greater hysteresis loss during cyclic test compared to a homogeneously crosslinked rubber, even though they had similar initial moduli. Furthermore, anomalous swelling behavior was observed in the graded rubber. The graded rubber exhibited shape transformation upon swelling. The mechanism was thoroughly explained using gel swelling theory under constraints. This must be a common phenomenon in graded rubbers with a crosslink gradient in the thickness direction. This comprehensive research provides a novel approach for material design with tailored properties and promising applications for this potential material.