Hot Deformation Behavior of Non-Alloyed Carbon Steels

The hot deformation behavior of selected non-alloyed carbon steels was investigated by isothermal continuous uniaxial compression tests. Based on the analysis of experimentally determined flow stress curves, material constants suitable for predicting peak flow stress σp, peak strain εp and critical strain εcrDRX necessary to induce dynamic recrystallization and the corresponding critical flow stresses σcrDRX were determined. The validity of the predicted critical strains εcrDRX was then experimentally verified. Fine dynamically recrystallized grains, which formed at the boundaries of the original austenitic grains, were detected in the microstructure of additionally deformed specimens from low-carbon investigated steels. Furthermore, equations describing with perfect accuracy a simple linear dependence of the critical strain εcrDRX on peak strain εp were derived for all investigated steels. The determined hot deformation activation energy Q decreased with increasing carbon content (also with increasing carbon equivalent value) in all investigated steels. A logarithmic equation described this dependency with reasonable accuracy. Individual flow stress curves of the investigated steels were mathematically described using the Cingara and McQueen model, while the predicted flow stresses showed excellent accuracy, especially in the strains ranging from 0 to εp.

The Improvement of the Operational Characteristics of the Ventilated Front Brake Discs

Wear and crack resistance are important operational characteristics of brake discs. The paper presents the most optimal concentration of sulfur in cast iron, which ensures its least wear, and discusses the implementation of the front brake discs manufacture from Gh190 cast iron having 0.11 ... 0.13% sulfur content at contrast to the 0.01 ... 0.03% sulfur content, and proves the change leads to a significant increase in wear and frictional properties of the discs. In the course of research, it is found that the increase in the crack resistance of brake discs is possible due to the improvement of the thermophysical properties of cast iron with the increase in the carbon content (up to 3.55 ... 3.60%) and the decrease in the silicon content (up to 1.45 ... 1.50%), while the carbon equivalent is constant.

Agricultural Greenhouse Gas Fluxes Under Different Cover Crop Systems

Cultivated lands that support high productivity have the potential to produce a large amount of GHG emissions, including carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). Intensive land management practices can stimulate CO2, N2O, and CH4 emissions from the soil. Cover crop establishment is considered as one of the sustainable land management strategies under warm and humid environmental conditions. To better understand how the incorporation of cover crops affect three major GHGs, we compared trace gas fluxes in a no-till maize field over the whole growing season in 2018 in a no cover crop (Tr) system and three cover crop systems: crimson clover (CC), cereal rye (CR), and living mulch (LM) using white clover. In 2019, we further explored potential differences in the three GHGs between in-row (IR) and between-row (BWR) of maize for LM and Tr systems during the early growing season. Measurements were taken using a cavity ring-down spectroscopy gas analyzer in Watkinsville, GA. In 2018, the highest CO2 flux (7.00 μmol m−2 s−1) was observed from BWR of maize for LM. The maximum N2O flux observed in LM on June 20th in 2018 was when soil N increase rate was the largest. Soils served as sinks for CH4 and Tr system served as the smallest CH4 sink compared to the other three cover crop systems. For N2O, the highest fluxes were observed from the TrIR plot (4.13 μmol m−2 hr−1) in 2019 with the greatest N inputs. In 2019, we observed a smaller CH4 sink in TrIR (−0.13 μmol m−2 hr−1) compared to TrBWR (−0.67 μmol m−2 hr−1) due potentially to greater NH4+ inhibition effects on CH4 consumption from greater N fertilizer inputs. The net carbon equivalent (CE) from May 23rd to Aug 16th in 2018, taking into account the three GHG fluxes, soil carbon content, and fertilizer, irrigation, and herbicide application, were 32–97, 35–101, 63–139, and 40–106 kg ha−1 yr−1 for CC, CR, LM, and Tr, respectively. LM had the lowest net CE after removing white clover respiration (−16–60 kg ha−1 yr−1). Our results show that implementing different types of cover crop systems and especially the LM system have some potential to mitigate climate change.

Economic Analysis of Developing a Sustainable Aviation Fuel Supply Chain Incorporating With Carbon Credits: A Case Study of the Memphis International Airport

Sustainable aviation fuel (SAF) has been considered as a potential means to mitigate greenhouse gas (GHG) emissions from the aviation sector, which is projected to continuously expand. This study examines the impact of developing a SAF sector along with carbon credits on carbon equivalent emissions from aviation using a Stackelberg leader-follower model that accounts for economic interaction between SAF processor and feedstock producers. The modeling framework is applied to an ex-ante optimization of commercial scale SAF production for the Memphis International Airport from the switchgrass-based alcohol-to-jet pathway. Results suggest that supplying 136 million gallons of SAF to the Memphis International Airport annually could reduce 62.5% of GHG emissions compared to conventional jet fuel (CJF). Incorporating with carbon credits, SAF could lower GHG emissions by about 65% in total from displacing CJF and generate additional welfare gains ranging between $12 and $51 million annually compared to the case without carbon credits. In addition, sensitivity analysis suggests advancing SAF conversion rate from biomass could lower the SAF break-even considerably and enhance the competitiveness of SAF over CJF.

Comprehensive Analysis of Cold-Cracking Ratio for Flux-Cored Arc Steel Welds Using Y- and y-Grooves

This study investigates various factors that influence the cold-cracking ratio (CCR) of flux-cored arc welds through Y- and y-groove tests. Factors affecting the CCR include the alloy component, diffusible hydrogen content, microstructure, hardness, and groove shape. In weld metals (WMs; WM375-R and WM375-B) of a low-strength grade, the diffusible hydrogen content has a more significant effect on the CCR than the carbon equivalent (Ceq) and microstructure. However, the combined effects of the microstructure and diffusible hydrogen content on the CCR are important in high-strength-grade WM. The CCR of the WM increased upon increasing Ceq and the strength grade because hard martensite and bainite microstructures were formed. Moreover, y-groove testing of the 500 MPa grade WM revealed a more significant CCR than that of the 375 MPa grade WM. Therefore, in high-strength-grade WMs, it is necessary to select the groove shape based on the morphology in the real welds.

Floristic Inventory and Evaluation of Carbon Sequestration Potential of the Misomuni Forest Massif, Kikwit City (Democratic Republic of the Congo)

The aim of this study was to inventory plant biodiversity and to evaluate the carbon sequestration potential of the Misomuni forest massif. An inventory of all trees with diameter at breast height (dbh) ≥ 10 cm measured at 1.30 m height was performed. The aerial biomass (AGB) was used for estimating the stored CO2 and its carbon equivalent. 88 plant species belonging to 71 genera and 32 families were inventoried. Fabaceae family displayed the highest number of species and genera. The highest basal area values were displayed by Scorodophloeus zenkeri (7.34 ± 2.45 m2 /ha), Brachystegia laurentii (5.82 ± 1.94 m2 /ha), Entandrophragma utile (5.28 ± 1.94 m2 /ha), Pentadesma butyracea (4.53 ± 1.51 m2 /ha). The highest values of stored carbon and their carbon equivalent were observed in Pentadesma butyracea (15.13 ± 5.00 and 50.55 ± 16.85 t/ha), Picralima nitida (7.02 ± 2.34 and 23.66 ± 7.88 t/ha), Strombosia tetandra (6.56 ± 2.18 and 22.10 ± 7.36 t/ha). The Misomuni forest massif is thus much floristically diversified and plays a significant role in the sequestration of CO2. The total AGB of the inventoried trees is 183.78 ± 61.26 t/ha corresponding to stored carbon and carbon equivalent of 96.63 ± 32.21 t/ha and 289.92 ± 96.64 t/ha respectively. The protection of this ecosystem is highly needed for combatting climatic changes at local, national and regional scales and for the conservation biodiversity habitat.

Technological, Microstructural and Strength Aspects of Welding and Post-Weld Heat Treatment of Martensitic, Wear-Resistant Hardox 600 Steel

The study presents technological and structural aspects of production and heat treatment of welded joints of high-strength, abrasion-resistant Hardox 600 steel. As a result of the conducted research, it was found that the use of welding processes for joining this steel leads to the formation of a wide heat-affected zone, characterized by various structures favoring the reduction of abrasion resistance and deterioration of plastic properties, while increasing the susceptibility to brittle fracture. On the basis of the structural and strength characteristics, an effective welding technology for Hardox 600 steel was proposed, as well as the conditions and parameters of post-welding heat treatment, leading to obtaining structures close to a base material in the entire area of the welded joint. Despite the limited high-carbon equivalent CEV of the metallurgical weldability of the tested steel, the tests carried out in laboratory conditions allowed researchers to obtain welded joints characterized by very high strength indexes, corresponding to the base material, while maintaining satisfactory plastic and impact properties.