Solid State Phenomena Vol. 378

Abstract: This study aims to evaluate the cold cracking resistance of SKD 11 cold work tool steel during Metal Active Gas (MAG) welding. The experiments were conducted using implant testing in accordance with ISO 17642-3. The investigation focuses on critical factors, including tensile stress levels, lower critical stress (LCS), and time to failure (TTF). Additionally, the influence of tempered welds (Double weld passes) on fracture behavior was investigated. The experimental results revealed that the fracture surfaces of the specimens could be distinctly categorized into quasi-cleavage and final rupture region. These regions varied based on stress levels and the application of tempering heat treatment. Implant testing showed that fracture predominantly occurred in the coarse-grained heat-affected zone (CGHAZ). The time to failure of implant specimens increased as the stress level decreased. Tempered welds exhibited a lower TTF rate compared to single welds. Specifically, the LCS of single welds was approximately of 70 MPa, meanwhile tempered welds exhibited an LCS of approximately of 72 MPa. Hardness profiles were measured across the weld metal, heat-affected zone (HAZ), and base metal. The highest hardness values were observed in the CGHAZ, with an average peak of 770 HV10. However, in the case of tempered welds, the hardness value reduced to 650 HV10. Microstructural examination of the HAZ indicated a predominant martensitic matrix. The tempered weld-HAZ exhibited a finer structure with a mixed size distribution of alloy carbide particles within the martensitic matrix. These findings clearly demonstrate the high hardenability of SKD 11 cold work tool steel. The hardness value in the CGHAZ suggests its susceptibility to lower cold cracking resistance. Based on LCS experiments, tempering of the weld insignificantly enhances cold cracking resistance. This research provides valuable insights for designing suitable welding procedures to avoid cracking risks in future applications.

Abstract: This research investigates the cold cracking susceptibility of fully pearlitic rail steel during damage repair using the Flux-Cored Arc Welding (FCAW) process. Rail steel grade-R900A according to UIC 860V standard was used. The experiments were conducted using implant testing in accordance with ISO 17642-3, focusing on critical parameters such as tensile stress levels, lower critical stress (LCS), and time to failure (TTF). Furthermore, the effect of tempering welding techniques on fracture behavior was explored. The experimental results revealed that fracture surfaces could be distinctly categorized into quasi-cleavage and final rupture regions, with these regions varying according to the applied stress levels. Implant testing demonstrated that fractures predominantly occurred within the coarse-grained heat-affected zone (CGHAZ). A clear relationship was observed between stress levels and TTF, with lower stress levels resulting in longer times to failure. The LCS for single welds was approximately 290 MPa, whereas tempered welds showed higher LCS of about 792 MPa. Hardness profiles were measured across the weld metal, heat-affected zone (HAZ), and base metal. The highest hardness values for a single weld pass were provided in the CGHAZ, peaking at an average of 877 HV10. In contrast, tempered welds (double weld passes) significantly reduced peak hardness to 363 HV10. Metallurgical examination of the HAZ from single weld passes revealed a needle-like martensitic matrix, meanwhile tempering welds exhibited a finer structure with a tempered martensitic matrix. The average grain size within the HAZ was assessed, with the critical grain size of the CGHAZ at the fracture region measured at ASTM grain size No. of 10.63–10.75. Remarkably, under the given experimental conditions, specimens subjected to tempered welding exhibited no fractures. This indicates that appropriate welding procedures and controlled heat input can alleviate cold cracking susceptibility. The findings of this research provide deeply comprehension into the design of welding procedures to minimize cracking risks in fully pearlitic steels, contributing to safer and more reliable repair processes in future applications.

Abstract: This research focuses on studying weld cracking adjacent to a drilled hole edge in tool and die repair, as well as evaluating the inspection sensitivity of eddy current testing (ECT). The weld cracking near the drilled hole edge was simulated using the Tungsten Inert Gas (TIG) welding process on SKD11 steel machinery components. The weld characteristics were designed as spot welds using a U-bending type simulation, considering factors influencing cracking, such as residual stress levels of 154 MPa and 220 MPa, and welding durations of 3 and 6 seconds. Cracking was investigated using penetrant testing and eddy current testing methods. The results revealed that weld cracking occurred under all experimental conditions. Penetrant testing effectively identified the surface appearance of cracks, while eddy current testing was used to assess crack depth. The maximum weld crack depth, approximately 1.08 mm, was observed under a residual stress level of 220 MPa and a welding time of 6 seconds. The amplitude signals detected by eddy current testing closely matched those of a reference standard block of the welded part, demonstrating its accuracy in crack depth assessment. These important findings found the significance of residual stress and welding duration in weld cracking and the utility of eddy current testing for detecting and evaluating weld crack characteristics.

Abstract: Corrosion fatigue is a phenomenon in which corrosion damage is superimposed on fatigue damage and can result in a significant decrease in fatigue strength. Because corrosion fatigue cracks initiate from the bottom of corrosion pits, corrosion fatigue strength evaluation methods based on the corrosion pit shape have been proposed and put into practical use. However, corrosion fatigue strength evaluation methods have not been fully investigated for cases in which only corrosion damage precedes. Therefore, the state of the corroded surface due to corrosion damage was evaluated using the arithmetic mean waviness Wa. The arithmetic mean waviness Wa is an appropriate parameter for evaluating the degree of corrosion damage in structural steel immersed in synthetic sea water for long period.

Abstract: One candidate material for boiler components in supercritical water gasification (SCWG) processes is oxide dispersion-strengthened steels (ODS), which can resist aggressive humidified atmospheres under high pressures and temperatures. The high-temperature oxidation resistance of ODS steel can be improved by adding nanooxide particles such as Al₂O₃. In this study, the corrosion resistance of Fe-18Cr ferritic ODS steel reinforced with different nanoAl₂O₃ between 0.5-3.0 wt% in a humidified atmosphere containing 80% H₂O at 800 °C was investigated. The lump phase of chromium and nanoAl₂O₃ particles were dispersed on iron matrixes after sintering. Several pores occurred in the Fe-18Cr ODS matrix due to air entrainment during forming processes, but they decreased after reinforcing with the nanoAl₂O₃. Adding 0.5 wt% nanoAl₂O₃ decreased the porosity of the ODS steel by around 1.8 times. After the oxidation test for 10 hours, the mass gain of the ferritic ODS steel decreased by about 9 % when the nanooxide was added. Fe-Al-rich oxides were found with hematite and Fe-Cr spinel oxide layers, which increased the oxidation resistance of the ODS steel.

Abstract: This work examines the phase stability during hot corrosion and the compressive strength of the AlCrFeNiCu-Nb high entropy alloy (HEA) produced using laser additive manufacturing, emphasizing its prospective uses in energy materials. The alloy's distinctive composition was chosen for its capacity to endure severe environments, including elevated temperatures and corrosive conditions, essential for energy-related applications. Phase stability was evaluated by X-ray diffraction, demonstrating remarkable preservation of critical phases despite high-temperature oxidation exposure. Compressive strength tests revealed the alloy's exceptional mechanical capabilities, underscoring its significant resistance to deformation. The AlCrFeNiCu-Nb HEA demonstrates significant promise for application in rigorous energy sectors, encompassing components for advanced power generation systems, high-temperature reactors, and corrosive conditions inside energy infrastructure.

Abstract: High-entropy alloys (HEAs) have garnered significant attention due to their exceptional properties, such as high strength, hardness, corrosion resistance, and excellent formability, which present promising opportunities for energy-related applications. This study successfully synthesized a Ti-doped AlCrFeNiCu high-entropy alloy (HEA) using the laser additive manufacturing (LAM) technique, with potential applications in energy materials. The effects of Ti doping (1 at% and 3 at%) on the mechanical properties and microstructural development of the AlCrFeNiCu HEA were systematically examined. Microstructural analysis using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) identified a dual-phase structure comprising BCC and FCC solid solutions. An Instron universal testing machine and Vickers microhardness (HVN) testing were utilized to evaluate mechanical properties. The findings indicated that although compressive strength diminished with elevated Ti content, Ti enhanced the microhardness of the alloy. The findings indicate the potential applications of Ti-doped AlCrFeNi Cu HEAs in energy sectors, such as components for concentrated solar power systems, nuclear reactors, and advanced gas turbines, which require materials capable of withstanding elevated temperatures, mechanical stress, and corrosive environments. The tailored mechanical and microstructural properties of this HEA position it as a viable candidate for enhancing the longevity and efficiency of energy systems operating under challenging conditions.

Abstract: Twin Wire Arc spraying (TWAS) is a well-established method to deposit metallic coatings to protect mechanical components from wear and corrosion. In this work were used coatings that can be divided into two groups: FeCr-based ones and NiCr-based ones. The microstructure, and mechanical properties such as hardness, adhesion, abrasion and erosion resistance were evaluated on these coatings. The wear behavior of the coatings was investigated by Solid Particle Erosion resistance test and by Dry sand/Rubber wheel abrasion test. The aim of this work is to study the wear mechanism by SEM observation of worn tracks.

Abstract: This study examines the properties of laser coatings applied to structural steel using 316L stainless steel to enhance corrosion resistance. It compares conventional laser cladding with the Extreme High Speed Laser Cladding (EHSLC) method. Six samples were produced, with Sample 1 using conventional cladding and Samples 2 through 6 using EHSLC with varying parameters. The hardness of the layers varied significantly, with conventional cladding showing the lowest hardness (below 200 HV 0.1) and EHSLC samples reaching up to 600 HV 0.1. These differences are attributed to microstructural variations: austenitic structures had lower hardness and good corrosion resistance is assumed, while martensitic structures exhibited lower chromium and nickel content, leading to different mechanical properties and probably reduced corrosion resistance. The results highlight the importance of parameter selection in EHSLC for optimizing the performance of treated parts.