In order to eliminate the common carbide networks in Fe-Cr-C tool steel, a low-cost Fe-Cr-C steel with high hardness and high toughness was designed. Correspondingly, a multistage heat treatment process is also designed. Multistage heat treatment includes homogenization, spheroidizing annealing, quenching and low temperature tempering. Compared to AISI D2 steel (58–62HRC, 24.3–27.9 J/cm2), the designed steel maintains high hardness (60.5HRC) and higher unnotched impact toughness (46.2 J/cm2). The hardening and toughening mechanisms of the designed Fe-Cr-C steel were studied by mechanical properties testing, multi-scale characterization and thermodynamic calculation. Experimental results show that the complete austenite phase region of Fe-Cr-C steel is the key factor to eliminate carbide networks by homogenization treatment. The gradient scale M7C3 produced by the spheroidizing annealing and quenching enhances the hardening effect through refining prior austenite grains size, promoting martensite nucleation, and limiting martensite growth. During the low temperature tempering, volume fraction reduction of retained austenite weakens the transformation induced plasticity (TRIP) effect and softens martensite, which is beneficial to improve the toughness. Finally, the decomposition of twinning martensite caused by nanoscale θ-Fe3C precipitation and the precipitation hardening of nanoscale θ-Fe3C play important role in maintaining hardness and improving toughness.

Ambient PM2.5 samples were collected in Laiwu, a small industrial city in China known for steel production, to measure and evaluate the mass concentrations of PM2.5 and the inorganic water-soluble ions (IWS ions). The highest PM2.5 value recorded was 251.28 μg/m3, which occurred during winter and was lower than other major Chinese cities. The spatial distribution showed that the center of the city, which is connected to the downtown area, was heavily polluted (170 μg/m3 higher) compared to the suburbs. With the exception of winter, the weight of PM2.5 was dominated by IWS ions, with three secondary ions (NO3 -, SO4 2-, and NH4 +) accounting for more than 70% of the total ions in mass. This percentage is higher than that of big cities. An increase in sulfur oxidation ratios (SOR), nitrogen oxidation rate (NOR), and anion equivalent/cation equivalent (AE/CE) indicated that the atmosphere in Laiwu was more oxidized than other big cities. The ion analysis revealed that PM2.5 was highly correlated with NO3 -, SO4 2-, and NH4 +. The principal component analysis indicated that district heating during winter and industrial output and secondary transformation during summer were the major sources of the water-soluble ions. The backward trajectory study identified the north of Shandong Province as the likely source-area that affected air quality in Laiwu.

Titanium alloys have been increasingly used for downhole tubular and components for corrosive oil wells due to their combination of strength, density, and corrosion resistance. The present study investigated the effect of annealing temperature on microstructures and mechanical properties of a Ti-6Al-4V-0.5Ni-0.5Nb alloy developed for oil well application. The α/β- and β-rolled Ti-6Al-4V-0.5Ni-0.5Nb alloy plates were subjected to annealing at different temperatures ranging from 750 to 900 °C and held for 1 h, and the microstructure and mechanical properties were evaluated. The experimental results show that the developed alloy exhibited both high strength and ductility than that of the conventional Ti-6Al-4V alloy. The α/β- and β-rolled alloy after annealing exhibited bimodal structures and provided well-balanced strength, ductility, and impact toughness, high strength of 950−1000 MPa, elongation of 17%−18%, and impact toughness of 90−120 J cm−2. From a mechanical viewpoint, the new alloy after appropriate annealing is suitable for oil well applications.

ABSTRACT At present, most of the energy analysis of the engineering system is only from the energy point of view. In this paper, the theory of exergoeconomics is combined with the operation optimization of the gathering and transportation system. In terms of exergy flow distribution and the construction of each equipment, the exergy value of total 17 exergy flows and the non-energy cost of 6 main equipment in the process are calculated. An exergoeconomic model in technological process of gathering and transportation system is established. Combined with the exergoeconomic cost valuation strategy, 11 auxiliary equations are used to get the economic cost of each flow unit in the process. Taking the minimum operation exergy cost as the objective function, a mathematical model of operation optimization in exergoeconomics is established, and each decision variable is constrained on the basis of the actual site conditions. The objective function within the range of process requirements is solved by iterative method. The optimal water mixing temperature is 47.1°C, and the optimal water mixing volume is 840.7 m3/d under the actual working condition of the site in light of the calculation results.