Papers by Keyword: Impact Toughness

Abstract: To meet the engineering applications, mechanical and physical properties of materials especially steels and their alloys are improved through thermal treatments. This research aimed to augment the impact toughness of EN-31 steel by picking the combinations of different levels of Charpy impact test control variables and thermal treatments built in three-level (L9) Orthogonal Arrays (OAs). For this reason, the experimental runs were conducted to examine the influence of varying V-notch angles (30°, 45° and 60°), heights of the hammer (1370 mm, 1570 mm, and 1755 mm), temperatures (-196°C, -50°C, and 28°C), and heat treatments (hardening followed by cryogenic treatment and low-temperature tempering - HCTLTT, hardening followed by cryogenic treatment and medium-temperature tempering - HCTMTT, and hardening followed by cryogenic treatment and high-temperature tempering - HCTHTT) on the impact toughness of EN-31 Steel specimens. Several patterns of thermal treatment sequences were executed with an aim to modify the material properties. Cryogenic treatment (CT) was conducted through a cryocan at 77K. The hardness of specimens were measured by employing a Brinell hardness tester. The results reported that height of the hammer and thermal treatments enhanced the toughness and hardness of the specimens most significantly.

Abstract: This study investigates the mechanical properties and microstructure of 316L stainless steel fabricated using laser powder bed fusion (PBF-LB) additive manufacturing with different layer thick nesses and orientations. Impact toughness is evaluated under various conditions as well as bending fatigue performance to understand the influence of layer thickness and surface quality on fatigue lim its. Microstructural analysis using scanning electron microscopy (SEM) provides insights into grain structure. Key findings include the superior impact toughness of the vertical orientation, particularly notable in specimens with a layer thickness of 40 µm. Bending fatigue tests revealed distinctive behav ior influenced by layer thickness and surface quality, with the 80 µm thickness and vertical orientation demonstrating lower fatigue limits. These insights contribute to optimizing manufacturing processes and enhancing material suitability for diverse applications.

Abstract: Titanium alloys are highly valued in various industries due to their exceptional qualities. This study examines how the build orientation affects the mechanical and fatigue properties of Laser Powder Bed Fusion (PBF-LB) produced Ti6Al4V, without heat treatment. The research shows mechanical properties vary based on build orientation with vertically oriented specimens exhibiting the highest yield and tensile strengths, while vertical orientation excels in ductility, measured through elongation at break. Impact toughness sees variations with horizontal orientation performing the best. However, build orientation has minimal influence on flexural bending fatigue performance. Both diagonal and vertical orientations show similar fatigue limits at around 40 MPa. Dry electropolishing proves to be an effective technique, significantly enhancing fatigue performance with limits stabilizing at about 150 MPa. This study underscores the importance of considering build orientation in PBF-LB manufacturing for specific mechanical and impact properties and the potential of dry electropolishing in improving the fatigue performance of Ti6Al4V components. These findings offer valuable insights for the additive manufacturing industry, aiding in the optimization of Ti6Al4V component production.

Abstract: Wire-arc additive manufacturing is a method of 3D printing metal using welding techniques. However, due to heat, the mechanical properties of the deposited material may be affected. Various methods have been proposed to mechanically improve the properties. In this study, cold deformation was introduced to enhance the properties. The effects of a few parameters, including welding speed, wire feed rate, heat input, thickness ratio, and types of material, were studied. Based on the result, the hardness, tensile, and wear properties of the manufactured part improved, while other properties, like impact toughness, had a lower value. Based on the preliminary result, cold deformation shows potential alternatives for part repair or reconstruction of worn or broken parts.

Abstract: Steel hydrogen embrittlement (HE), a complex and multifaceted issue, can lead to sudden and catastrophic failure, without significant plastic deformation, making it a critical concern in the industrial sector. The present investigation focuses on the evaluation of HE effects regarding microstructure, mechanical properties degradation and type of fracture of AISI 1010 low-carbon steel, after accelerated hydrogen cathodic charging. Hydrogen was diffused electrolytically in 0.2 Μ H₂SO₄ solution, containing 3g/L of NH₄SCN, using a cathodic current density of 10 and 20 mA/cm², for 6 and 18 h. Mechanical properties were investigated through slow-rate tensile tests, as well as Charpy V-notch (CVN) impact tests, to determine the value of fracture toughness, both in uncharged and electrochemically pre-charged specimens. Vickers microhardness tests were conducted on the cross-sections of the hydrogen charged samples to evaluate embrittlement susceptibility, due to the presence of dissolved hydrogen. The microstructure modification was carried out through light optical (LOM) and scanning electron microscopy (SEM), in conjunction with an energy-dispersive X-ray detector (EDS). Slow scan X-ray diffraction (SSXRD) was also conducted for crystal structure analysis. The microstructure analysis showed the presence of large amounts of secondary cracks and cavities into the steel matrix, due to hydrogen diffusion and its accumulation at various sites. Hydrogen charging caused a significant gradual elongation decrease of the parent material, from 25% to 6.73%, in case of embrittlement at 20 mA/cm² for 18h. Accordingly, after 18 h of exposure, the impact energy decrement was determined at 31.5%, at a current density of 10 mA/cm², whereas the corresponding reduction at 20 mA/cm² reached 68%.

Abstract: Additive manufacturing (AM) has transformed the production of complex geometries and customized components.Powder Bed Fusion with Laser Beam (PBF-LB) is a popular AM technique known for its ability to produce parts with excellent mechanical properties. This study focuses on the characterization of AlSi10Mg, an aluminum alloy widely used in aerospace and automotive industries, manufactured through PBF-LB. The influence of printing orientation on the mechanical properties of the material is investigated. Previous research has shown that PBF-LB manufactured AlSi10Mg can exhibit superior mechanical properties compared to traditional material, but the anisotropic nature of parts produced by PBF-LB can significantly affect their properties. Tensile, impact, and fatigue testing are conducted to assess the mechanical behavior of the printed AlSi10Mg specimens under different loading conditions. Microstructural analysis is performed using Field-Emission Scanning Electron Microscopy (FESEM) equipped with Electron Backscatter Diffraction (EBSD) to examine the microstructural features introduced during the PBF-LB process. The results provide insights into the mechanical behavior of AlSi10Mg produced through PBF-LB and contribute to the design and utilization of components manufactured using this AM technique.

Abstract: The influence of small contents of nitrogen present as an impurity in 0.3C Al-bearing steels, which were processed through thermomechanical rolling followed by direct quenching and partitioning (TMR-DQP), was examined in respect of room temperature tensile ductility and impact toughness. Two similar chemical compositions (in wt.%): Fe-0.3C-0.6Si-1.1Al (High-Al) with different N contents of 10 and 30 ppm were selected for this study. In addition, two other DQP steels with compositions: Fe-0.3C-1.0Si (High-Si) and Fe-0.3C-0.5Si-0.5Al (Al-Si), both containing about 30 ppm nitrogen, were also included in the study to compare the properties. Detailed metallographic studies using FESEM-EDS, TEM, EPMA and XRD combined with tensile testing and fractographic analysis indicated that already 30 ppm of nitrogen could impair tensile ductility of TMR-DQP processed High-Al steel in comparison to that with 10 ppm nitrogen. Similarly, the effect was adverse also in Al-Si steel (30 ppm N) despite its reduced Al content (0.5 wt.%), but High-Si steel (Al < 0.002 wt.%, N 30 ppm) did not show any such detrimental effect on tensile ductility. Extensive material characterization verified that even 30 ppm of nitrogen could impair ductility of Al-bearing steels, essentially due to the presence of AlN inclusions, despite that TMR-DQP processing enabled stabilization of 6–10% retained austenite (RA) in the steels. The capacity of RA in promoting improved ductility and strain hardening capacity was impaired by the presence of these inclusions. In contrast, impact toughness transition temperature T_28J was not clearly affected with Al-Si when compared to low-N High-Al steel, although excessive splitting in Al-Si caused pronounced scatter in the results and increase in upper shelf impact toughness.

Abstract: Gleeble 3800-thermomechanical simulator was used to simulate the heat affected zone of quenched and tempered 0.16 wt.% C steels with variation of molybdenum-and niobium contents. The purpose of the study was to evaluate the effect of alloying content on the properties of the coarse-grained zone of HAZ region (CGHAZ) and partially re-austenitised inter-critical zone (ICHAZ) with two different t_8/5 times (5 s and 15 s). Results showed that Mo and Nb decreased the amount of softening in the HAZ-region, especially with longer t_8/5 -time (15 s). 0Mo steel had mixed microstructure of bainite and martensite in the CGHAZ region with t_8/5 time of 15 s, which led to higher degree of softening compared to other steels. Shorter t_8/5 time of 5 s produced martensitic microstructure in CGHAZ region in all cases leading to higher hardness values. Impact energy values at-40 °C were at least 34 J/cm² in all cases. Highest hardness values in the ICHAZ-region were achieved in the case of 0.5Mo steel. Also, at-40 °C impact energy values of ICHAZ were at least 34 J/cm² in all cases, however Mo-free steel achieved clearly higher impact energies in ICHAZ region, which is result from softer microstructure with relatively low hardness compared to other steels. Overall, it can be concluded that longer t_8/5 time can be used, which corresponds to higher heat input in welding, if Mo and/or Nb alloying is used.

Abstract: The article deals with the problems of withstanding harsh temperatures by steel and iron. The authors of the work discuss iron denser high-temperature of γ modification and maximums and minimums of impact. In addition, the article analyses the transformations of iron and anomalies of properties: peak of heat capacity, acceleration of diffusion, etc. The authors take into account the consensus on the causes of polymorphism and the theoretical model of ferromagnetism. Besides, there is a consideration of "transformation" in interaction between Fe atoms that produce anomalies of steel properties. It is necessary to note the transformation detected by anomalies of any properties including mechanical. In the presented work the authors have made an attempt to prove transformations in iron at ~650 °C on the basis of extreme values of hardness and microhardness, metallographic structure, parameters of fine structure, precipitation resistance force depending on temperature. Therefore, the analysis of literature sources on physical and mechanical properties of iron and its derivatives has been made.

Abstract: The quantitative microstructure - impact toughness relationships in two batches of the same steel grade subjected to quenching and tempering (Q&T) have been established via characterization using EBSD technique and FIB visualization. The EBSD-based criterion for separation of structural constituents in microstructure of Q&T low carbon low alloy steels is proposed. Impact toughness differences between two steel batches subjected to nominally identical Q&T are caused by the changes in the volume fraction of structural constituents caused by various cooling conditions at quenching stage. High volume fraction of bainite containing more distorted bainitic ferrite and the highest amount of brittle cementite precipitates leads to the increase in strength and to the decrease in impact toughness.