Enhancement and underlying fatigue mechanisms of laser powder bed fusion additive-manufactured 316L stainless steel

In this study, the enhancement of additively manufactured (AM) 316L, by annealing, to the fully reversed tension-compression fatigue performance, in terms of fatigue life and fatigue damage, were investigated under two conditions: as-built (AB) and heat-treated (HT) at 900 °C. The underlying fatigue mechanisms were comprehensively characterised through intensive microstructural observations of cyclic-strained microstructures and fracture surfaces using laser confocal scanning microscopy (LCSM) and secondary electron imaging using scanning electron microscopy (SEM). The experimental results showed that the fatigue resistance of HT 316L was significantly enhanced by 100% as the fatigue limit was increased from 75 to 150 MPa for AB and HT 316L, respectively. The fatigue cracking mechanism in AB 316L is mainly related to two imperfections of the AM-induced microstructural components: residual stresses, which cause highly localised deformation, and dendritic cellular structures, which possess a weak link in their grain boundaries against crack propagation. Upon heat treatment at 900 °C, the residual stresses and dendritic structure were effectively reduced. Consequently, the fatigue life of AM 316L was significantly enhanced by promoting the formation of high-angle boundaries. More precisely, the cyclic deformation processes in fatigued HT 316L involve persistent slip bands and strain hardening.publishedVersionPeer reviewe

Assessment of Emissions from Cement Plants Using AERMOD Modeling

Coal combustion generates many gases and emissions which are harmful to public health and the environment. So, it is necessary to assess the health risks for the people living in the nearby cement plants that use coal as a fuel. In this article, a health risk assessment HRA was carried out concerning the air emissions from a cement plant in the heavy industry area located at Beni Suef governorate - Egypt. The article handles the assessment of the health risks for pollutants classified as non-carcinogenic i.e. sulfur dioxide - mercury and the health risks for pollutants classified as carcinogenic i.e. arsenic – chromium VI. An Air dispersion modeling program AERMOD is used to measure and evaluate long and short terms health impacts to expect the concentration of pollutants at the ground level within 30 km radius of the studied cement plant. The emissions measurements findings are used as input to the model in addition to some factors such as meteorology and surrounding terrain. Consequently, the program can implement simulations for the emissions concentration level of the mentioned pollutants and their effects on the population at Jazirat Abu Salih village, which is 10 km far from the studied cement plant. The results for mentioned pollutants concentrations levels matched with acceptance and safe levels of ambient air quality standards. In addition, the increment lifetime cancer risk ILCR by inhalation was calculated for arsenic and chromium and all results conformed with the safe and accepted limits

Constitutive modeling and hot deformation processing map of a new biomaterial Ti–14Cr alloy

A new biomaterial Ti–14Cr alloy was designed for biomedical applications. The manufacturing process of Ti alloys through hot deformation is crucial for controlling the grain structure and the mechanical performance of the alloy. In the present study, several compression tests at elevated temperatures (1123–1273 K) and strain rate ranges of 0.01–10 s−1 were conducted using a Gleeble-3800 thermomechanical simulator. A processing map of the studied alloy was constructed using the principles of the dynamic material model to evaluate the hot workability and deformation mechanisms at different ranges of temperature and strain rate. The resulting grain structure was correlated with the processing map. The processing map showed that adiabatic shear bands are expected to form at low temperatures (1123–1223 K) and moderate to high strain rates (1–10 s−1), whereas the nucleation of wedge cracks is likely to develop at the grain boundary at high temperatures and low strain rates (1248–1273/0.01 s−1). Consequently, a deterministic domain in the temperature and strain rate ranges of 1148–1273 K and 0.01–0.1 s−1, respectively, was identified as the domain of dynamic recrystallization with a peak efficiency of the order of ∼70% at 1173 K/0.01 s−1, and these were considered to be the optimum parameters for hot deformation. The constitutive flow behavior was modeled based on the hyperbolic–sinusoidal Arrhenius-type equations, and a mathematical relation was used to elucidate the influence of true strain on material constants.publishedVersionPeer reviewe

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10 years; 78.2% included were male with a median age of 37 years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

Manufacturing, mechanical properties and corrosion behaviour of high-Mn TWIP steels

Abstract Austenitic high-Mn (15–30 wt.%) based twinning-induced plasticity (TWIP) steels provide great potential in applications for structural components in the automotive industry, owing to their excellent tensile strength-ductility property combination. In certain cases, these steels might also substitute austenitic Cr-Ni stainless steels. The aim of this present work is to investigate the high-temperature flow resistance, recrystallisation and the evolution of microstructure of high-Mn steels by compression testing on a Gleeble simulator. The influence of Al alloying (0–8 wt.%) in the hot rolling temperature range (800°C–1100°C) is studied in particular, but also some observations are made regarding the influence of Cr alloying. Microstructures are examined in optical and electron microscopes. The results are compared with corresponding properties of carbon and austenitic stainless steels. In addition, the mechanical properties are studied briefly, using tension tests over the temperature range from -80°C to 200°C. Finally, a preliminary study is conducted on the corrosion behaviour of TWIP steels in two media, using the potentiodynamic polarization technique. The results show that the flow stress level of high-Mn TWIP steels is considerably higher than that of low-carbon steels and depends on the Al concentration up to 6 wt.%, while the structure is fully austenitic at hot rolling temperatures. At higher Al contents, the flow stress level is reduced, due to the presence of ferrite. The static recrystallisation kinetics is slower compared to that of carbon steels, but it is faster than is typical of Nb-microalloyed or austenitic stainless steels. The high Mn content is one reason for high flow stress as well as for slow softening. Al plays a minor role only; but in the case of austenitic-ferritic structure, the softening of the ferrite phase occurs very rapidly, contributing to overall faster softening. The high Mn content also retards considerably the onset of dynamic recrystallisation, but the influence of Al is minor. Similarly, the contribution of Cr to the hot deformation resistance and static and dynamic recrystallisation, is insignificant. The grain size effectively becomes refined by the dynamic and static recrystallisation processes. The tensile testing of TWIP steels revealed that the Al alloying and temperature have drastic effects on the yield strength, tensile strength and elongation. The higher Al raises the yield strength because of the solid solution strengthening. However, Al tends to increase the stacking fault energy that affects strongly the deformation mechanism. In small concentrations, Al suppresses martensite formation and enhances deformation twinning, leading to high tensile strength and good ductility. However, with an increasing temperature, SFE increases, and consequently, the density of deformation twins decreases and mechanical properties are impaired. Corrosion testing indicated that Al alloying improves the corrosion resistance of high-Mn TWIP steels. The addition of Cr is a further benefit for the passivation of these steels. The passive film that formed on 8wt.% Al-6wt.%Cr steel was found to be even more stable than that on Type 304 steel in 5–50% HNO3 solutions. A prolonged pre-treatment of the steel in the anodic passive regime created a thick, protective and stable passive film that enhanced the corrosion resistance also in 3.5% NaCl solution

Investigation of microstructure and mechanical properties of laser welded complex phase steel lap joints

Abstract In this study the microstructure and mechanical properties of laser welded complex phase steel lap joints were evaluated. Three different welding parameters were used in the experiments. The weld geometry and microstructure of the weld were studied. The joints were evaluated by hardness measurements, shear strength and fatigue strength tests. The geometry of the lap joints was affected by the welding parameters, and the width of the joint increased the lower the welding speed was. The weld metal (WM) microstructure with highest welding speed exhibits a fine columnar grain structure. As welding speed increased, the dendritic grain structure was coarser. With lowest welding speed, the microstructure changed to an equiaxed grain structure due to slower cooling. The WM with highest welding speed had the highest hardness with an average value 413 HV. The shear strengths of the joints were markedly influenced by the welding speed. With the lowest welding speed, the shear strength of the single weld was 222% higher than that of the highest welding speed. A joint with multiple welds achieved shear strength corresponding to the strength of the base material (1000 MPa). Fatigue limit of the lap joint with lowest welding speed was low < 20 MPa

Tehokkaat rakenteet:laserhitsattujen liitosten ominaisuudet

Tiivistelmä Tehokkaat rakenteet (TeRa) -hankkeessa pyrittiin edistämään yhteiskunnan vähähiilisyyden vaatimuksia rakenteiden materiaali-, energia- ja päästötehokkuuden kautta. Tehokkaiden rakenteiden suunnittelun ja valmistuksen kehittäminen johtaa kustannustehokkaampiin tuotteisiin, mikä mahdollistaa kilpailukykyiset valmistuskustannukset vähäisellä hiilijalanjäljellä. Hankkeessa kehitettiin teknisesti ja taloudellisesti tehokkaiden rakenteiden suunnittelu- ja valmistusmenetelmiä. Tehokkaat rakenteet hankkeen lähtökohtana oli Pohjois-Pohjanmaan älykkään erikoitumisen strategia ja hankkeen tukirankana oli vankka erikoisteräs-osaaminen sekä teräs- ja suunnitteluosaaminen uusien materiaalien hyödyntämisessä ja rakenteiden keventämisessä. Laserhitsausta hyödyntäen ultralujista teräksistä voidaan valmistaa entistä keveämpiä ja kestävämpiä rakenteita. Menetelmän etuna on pieni, tarkkaan kohdistettu lämmöntuonti sekä hitsausnopeus. Hankkeessa kehitettiin teknisesti ja taloudellisesti tehokkaiden rakenteiden suunnittelu- ja valmistusmenetelmiä. Ultralujille koemateriaaleille löydettiin entistä kustannustehokkaammat ja kestävyyden kannalta paremmat laserhitsauksen liitostavat. Laserhitsiliitosten, vähentyneen materiaalin tarpeen ja lujemman akenteen avulla ympäristövaikutukset pienenevät tuotteen koko elinkaaren aikana. Lopputuloksena hankkeessa valmistettiin teknisesti erinomaisia ja kustannustehokkaita rakenteita. Ultralujista teräksistä valmistettujen kennorakenteiden lujuusominaisuuksia tutkittiin erilaisten kokeiden avulla. Hankkeen tuloksena saatiin myös huomattavan paljon uutta tietoa ultralujien terästen laserhitsausliitoksista. Hankkeessa tehtiin merkittävä määrä laserhitsattujen limiliitosten ominaisuuksien tutkimiseen liittyviä kokeita. Hitsiliitoksia tutkittiin pääasiassa veto- ja väsytyskokeilla sekä liitosten mikrorakenne tutkimuksilla. Hankkeessa tehdyn kirjallisuustutkimuksen mukaan hankkeessa tutkitun AR600 ultralujan kulutusteräksen laserhitsausliitoksista ei löytynyt lainkaan aikaisemmin tutkittua tietoa, joten hankkeessa tehtyä tutkimusta voidaan pitää merkittävänä avauksena kyseisen materiaalin tutkimuksessa. Raportti perustuu Tehokkaat rakenteet (TeRa) -hankkeessa tehtyyn tutkimukseen. Tässä raportissa keskitytään pääasiassa laserhitsausliitosten koetulosten esittelyyn. TeRa-hanke on Euroopan aluekehitysrahaston EAKR-hanke ja sen on myöntänyt Pohjois- Pohjanmaan liitto. Hankkeen kuntarahoittajina ovat toimineet Nivala-Haapajärven seutukunta NIHAK r.y., Nivalan Teollisuuskylä Oy ja Nivalan kaupunki. Hankkeen yksityisrahoittajina ovat olleet Wärtsilä Finland Oy, SSAB Europe Oy, HT Laser Oy, Randax Oy, Konestar Oy ja Miilux Oy.Abstract The Efficient Structures (TeRa) project promoted society’s low-carbon requirements through the material, energy and emission efficiency of structures. Developing the design methods and manufacture of the structures will lead to more cost-effective products, enabling competitive manufacturing costs with a low carbon footprint. Methods for designing were developed in the project and manufacturing technically and economically efficient structures. The Efficient Structures project was based on Oulu Region’s smart specialization strategy. The project was also supported by special steel expertise as well as steel and design expertise in utilizing new materials and lightening structures. Based on the research carried out in the project, it became clear that by utilizing laser welding and ultra-high-strength steels even lighter and more durable structures can be manufactured. The advantage of the laser welding is the small heat input and the high welding speed. For ultra-high-strength steel test materials, more cost-effective and robust laser welded joints were developed. Laser welded joints, reduced need of material and a stronger structure reduce the environmental impact throughout the product’s life cycle. As a result, technically excellent and cost-effective structures were produced in the project. New types of structures were developed in the project. Benefits of different sandwich structures were demonstrated in the project. The strength properties of sandwich structures made of ultra-high-strength steels were studied by various experiments. The project carried out a significant number of experiments related to the study of the properties of laser welded lap joints. Laser welded joints were mainly studied by tensile and fatigue tests and by microstructure studies of joints. According to a literature review made in the project, no previously published papers were found on the laser welded joints of AR600 ultra-high-strength abrasion resistant steel studied in the project, so the research conducted in the project can be considered a significant opening in the study of that material. The project produced a significant number of peer-reviewed publications, demonstrating the internationally significant quality of the research carried out in the project. This report is based on research conducted in the Efficient Structures (TeRa) project. The report presents only some of the results of the project and this report focuses mainly on the test results of laser welded joints. The TeRa project is a European Regional Development Fund (ERDF) project and has been funded by the Council of Oulu Region. The Nivala-Haapajärvi region, NIHAK r.y., Nivalan Teollisuuskylä Oy and the city of Nivala have acted as municipal funders for the project. The private funders of the project have been Wärtsilä Finland Oy, SSAB Europe Oy, HT Laser Oy, Randax Oy, Konestar Oy and Miilux Oy

Review on the Solid-State Welding of Steels: Diffusion Bonding and Friction Stir Welding Processes

Solid-state welding (SSW) is a relatively new technique, and ongoing research is being performed to fulfill new design demands, deal with contemporary material advancements, and overcome welding defects associated with traditional welding techniques. This work provides an in-depth examination of the advancements in the solid-state welding of steels through diffusion bonding (DB) and friction stir welding (FSW). Considerable attention was given to DB of steel, which overcame the difficulties of segregation, cracking, and distortion stresses that are usually formed in liquid-phase welding techniques. The defects that affected DB included two types: two-dimensional defects of a metallic lattice, i.e., phases and grain boundaries, and three-dimensional defects, i.e., precipitation. FSW, on the other hand, was distinguishable by the use of relatively low heat input when compared to fusion welding processes such as tungsten inert gas (TIG), resulting in the formation of a limited heat-affected zone. Moreover, fine grain structures were formed in the FSW interface because of the stirring tool’s severe plastic deformation, which positively affected the strength, ductility, and toughness of the FSW joints. For instance, higher strength and ductility were reported in joints produced by FSW than in those produced by TIG. Nevertheless, the HAZ width of the specimens welded by FSW was approximately half the value of the HAZ width of the specimens welded by TIG. Some defects associated with FSW related to the diffusion of elements, such as C/Cr atoms, through the weld zone, which affected the local chemical composition due to the formation of rich/depleted regions of the diffused atoms. Moreover, the lack-of-fill defect may exist when inappropriate welding conditions are implemented. On the other hand, the stirring tool was subjected to extensive wear because of the high hardness values, which negatively affected the economical usage of the FSW process. A summary of the results is presented, along with recommendations for future studies aimed at addressing existing difficulties and advancing the solid-state technology for steel