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As important strategic metals, titanium and vanadium have some common problems such as low efficiency, high energy consumption and high cost in traditional fire or wet extraction and purification processes. Molten salt electrolysis technology provides a new idea for the extraction and purification of titanium and vanadium with its advantages of short process, high product purity and green environmental protection. In this paper, the latest research progress in the extraction and purification of titanium and vanadium by molten salt electrolysis was reviewed. The advantages and disadvantages and application potential of halides molten salts electrolysis, FFC method and USTB method were analyzed. The electrochemical behavior of titanium and vanadium in molten salt systems and the optimization strategy of process parameters were discussed. In the future, in terms of corrosion resistance of equipment materials, current efficiency improvement, and industrial scale application, the molten salt electrolysis technology of titanium and vanadium still needs to be further explored.

Non-metallic element O dissolves in the V lattice to form a V-O solid solution. The oxygen removal limit of the solid solution depends on the oxygen activity and temperature, but currently, there are few studies on the thermodynamic properties of the V-O solid solution. In this paper, based on the Sieverts’ law as the calculation criterion, the thermodynamic data of the V-O system was collected, and the oxygen potential of the solid solution VO_y with different oxygen contents was calculated. At the same time, the thermodynamic model was imported into Factsage and a custom database was established to assist in calculating the phase transition and equilibrium composition of vanadium prepared by the metal thermal reduction method, and to clarify the limit deoxidation ability of reducing agents such as Ca, Mg, and Al. The results show that by reasonably controlling the addition amount of Al and the reaction temperature, the oxygen content in the prepared metallic vanadium can theoretically be reduced to approximately 0.1 wt%-0.5 wt%. When Mg is used as the reducing agent, the metallic vanadium product with an oxygen content of 0.01 wt%-0.1 wt% can be theoretically prepared. The reduction ability of Ca is more excellent, and the oxygen content in the prepared metallic vanadium product is < 0.01 wt%. Increasing the addition amount of C, increasing the reaction temperature, and reducing P_CO can theoretically prepare metallic vanadium products with an oxygen content lower than 0.1 wt%.

In order to recover the valuable metals vanadium and chromium from vanadium precipitation wastewater, this study adopted ethylenediaminetetraacetic acid (EDTA) complexation and membrane separation to treat vanadium precipitation wastewater. The effects of complexation effect, membrane type, water flux, pressure difference and other parameters on the recovery of vanadium and chromium were investigated. The results showed that when the molar ratio of EDTA was 1.5, the wastewater was filtered by NF5 nanofiltration membrane at 0.8 MPa for 3 times. The retention rates of vanadium and chromium were 99.88% and 99.97%, respectively, and the concentrations of vanadium and chromium in the concentrate were 24.97 g/L and 2.499 g/L, respectively, which realized the effective recovery of vanadium and chromium in vanadium precipitation wastewater. The contents of vanadium and chromium in the permeate were 0.573 mg/L and 0.015 mg/L, respectively, meeting the industrial wastewater discharge standard. The results of DLS, SEM and AFM showed that the vanadium and chromium in the solution could be effectively recovered by using EDTA complexation and membrane separation technology.

Due to the similar physical and chemical properties of iron and manganese in ferromanganese ore, it is difficult to achieve efficient separation of iron and manganese components by using existing methods. In this paper, V₂O₅ was introduced as an additive for mixed roasting with iron-manganese ore, and the phase evolution of the mixed roasting process, the migration and separation of manganese, iron and vanadium elements in the acid leaching process and the recycling mechanism were systematically studied. The results show that the manganese-containing phase in the iron-manganese ore is converted into acid-soluble manganese pyrovanadate after roasting, while iron and silicon still exist in the form of Fe₂O₃ and SiO₂. The leaching rates of Mn, Fe and V reach 81.25%, 0.0074% and 5.77%, respectively, after acid leaching at pH 2.0 and 1.8, respectively, which realizes the effective separation of manganese and iron components. MnSO₄ is obtained by vacuum drying of manganese-containing leaching solution, which can be used as an intermediate product in manganese metallurgy and manganese chemical industry. The separation of iron and vanadium is realized after alkali leaching, and the Fe₂O₃ content in the iron-rich tailings reaches 83.02%, which can be used as a raw material for blast furnace ironmaking. The V₂O₅ obtained from alkali leaching solution can be returned to the roasting system after hydrolysis precipitation and roasting, and its recycling rate is more than 90%, and the wastewater generated in the process can also be returned to the leaching system for reuse. This study provides a new method for the clean and efficient utilization of co-associated iron-manganese resources.

Using V₂O₃ and Al powder as raw materials, AlV55 alloy was prepared by vacuum aluminothermic reduction method. The process of preparing vanadium-aluminum alloy by aluminothermic method was analyzed using thermodynamic software and differential thermal analysis method. The results showed that the thermodynamic calculation of aluminothermic reduction reaction at room temperature can reduce V₂O₃ to V in one step. The actual reduction process is carried out in stages, with a starting temperature of 749 ℃, belonging to the category of liquid-solid reactions. The unit thermal effect is

J/g, and the adiabatic combustion temperature is

℃. The effects of insulation temperature and the amount of slag forming agent calcium oxide added during vacuum heating on vanadium yield were studied. When the insulation temperature exceeded

℃, the vanadium yield of vanadium-aluminum alloy could reach about 95%. The vanadium-aluminum alloy ingot had no cracks or oxide film, and the yield of vanadium-aluminum alloy was significantly improved. In addition, the influence of CaO/Al₂O₃ ratio on slag viscosity was also determined. When the amount of slag forming agent exceeded 22.5%, the separation effect of slag and metal was significantly improved.

In this study, TC4 alloy ingots were prepared using surplus titanium plate, titanium chip, surplus titanium billet and high-purity raw material. The suitability of centrifugal casting technology to different scrap titanium was systematically analyzed in terms of composition, microstructure and hardness. The results show that the contents of N, O and H elements in the four ingots satisfy the requirements of GB/T6614-2014. However, due to the physical and chemical reactions that occur in scrap titanium materials during different hot forming processes, they can have an important influence on the solidification process of TC4 alloys, resulting in some differences in microstructural and mechanical properties of ingots. In addition, the hardness of the four ingots meets the requirements of GB/T6614-2014, which further confirms that the centrifugal casting technology can be applied to the recovery of scrap titanium. After heat treatment, the microstructure homogenization of 4^# alloy was significantly improved, and the abnormal areas disappeared. The maximum hardness value of 32.5 HRC was obtained for the samples treated by vacuum argon quenching process I.

The study investigated the influence of Aspergillus niger on the corrosion behavior of industrial pure titanium TA2. Surface analysis techniques, including laser confocal microscopy and scanning electron microscopy, were employed alongside electrochemical analysis methods such as electrochemical impedance spectroscopy and potentiodynamic polarization curves to examine the corrosion resistance of TA2 in the presence of Aspergillus niger biofilms. The findings revealed that the adherence and growth of Aspergillus niger on the TA2 surface modified the electrochemical properties of the titanium, with its corrosion resistance initially improving and then declining over time. The biofilm enhanced corrosion resistance within a specific timeframe, and a thicker biofilm correlated with better resistance. However, after 21 days of immersion in the Aspergillus niger solution, minor pitting was observed on the titanium surface, indicating the initiation of microbial-induced corrosion.

Based on the three-period minimal surface (TPMS) porous structure of TC4 titanium alloy and the horizontal differences of laser power P, scanning speed v and scanning distance h, a three-factor and three-level orthogonal experiment was designed. On the one hand, the influences of laser selective melting manufacturing (SLM) process parameters on the dimensional accuracy, mass and mechanical strength of TC4 titanium alloy porous structure were studied through range and variance analysis. On the other hand, the porous structure of titanium alloy was treated by HF pickling, the influences of pickling process on the parameters and mechanical properties of porous structure was studied. The results show that the physical size and mass of TPMS porous structure are positively correlated with the energy density E of SLM process. The mechanical strength of TPMS porous structure is less affected by SLM process parameters, and the optimization of SLM process parameters should be based on the accuracy control of size and mass parameters of 3D printed porous structure. Pickling treatment can improve the surface roughness of TPMS porous structure, enhance the size and mass accuracy of TPMS porous structure. In addition, pickling treatment makes the elastic modulus of TPMS porous structure closer to the mechanical properties of natural cancellous bone.

This study employs numerical simulation methods to construct a simulation model of the hot spinning and pressure forming of TC4 titanium alloy gas cylinders, and the reliability of the model is verified through experimental validation. In thermal simulation experiments conducted at three strain rates of 0.1, 1 s^?1 and 10 s^?1, the rheological stress distribution of TC4 material at temperatures ranging from 700 ℃ to

℃ is extensively investigated. Through comprehensive numerical simulation analysis, the study delves into the influence of key process parameters such as forming temperature, spindle speed, and feed rate on the shaping of TC4 titanium alloy. Ultimately, a thermal spinning and pressure forming process for gas cylinders is formulated. The feasibility of the proposed process is further validated through multiple iterations of TC4 titanium alloy hot spinning and pressure forming experiments. This research provides a scientifically sound and viable technological pathway for the manufacturing of TC4 titanium alloy gas cylinders.

The high-temperature thermal deformation test was carried out by thermal simulation testing machine, and the stress-strain curves of wrought TC21 titanium alloy at temperature 850-1100℃ and strain rate 0.001-10 s^?1 were obtained. The effects of deformation temperature and strain rate on the flow stress in the compressive stress state were analyzed, and the intrinsic relationship was established based on the Arrhenius hyperbolic sinusoidal function. The thermal processing diagrams under different true strains from 0.1 to 0.6 were plotted, so that the range of parameters suitable for thermal deformation of wrought alloys was summarized. The results indicate that the flow stress of wrought TC21 alloy is greatly affected by deformation parameters, which decreases with the increase of deformation temperature and increases with the increase of strain rate. The activation energy of TC21 alloy in the α+β two-phase region and β single-phase region is 770.86 kJ/mol and 261.00 kJ/mol, respectively. As true strain increases the destabilization zone becomes larger in the thermal processing map and the suitable hot working region is deformation temperature of 900-1100℃, and strain rate of 0.005-0.153 s^?1. The test results can provide theoretical support for the formulation of TC21 alloy hot working parameters.

A series of Na₃V₂(PO₄)₃/C anode materials were synthesized by sol-gel method, using the intermediate products ammonium polyvanadate (APV, NH₄V₃O₈) prepared by different vanadium extraction processes and high-purity vanadium pentoxide as vanadium sources, and Na₂CO₃, NH₄H₂PO₄, and citric acid as sodium, phosphorus, and carbon sources, respectively. The effects of different vanadium sources on Na₃V₂(PO₄)₃/C anode materials were investigated in detail through XRD, SEM, battery testing system and electrochemical workstation. The results show that the Na₃V₂(PO₄)₃/C (NaH-NVP) cathode materials prepared by ammonium polyvanadate from sodium method for vanadium extraction as the vanadium source present superior high-rate performance, i.e., reversible capacities of 98 mAh/g and 64 mAh/g at 5C and 10C, respectively. The research has expanded the selection of vanadium sources for synthesizing sodium vanadium phosphate materials, which has a positive significance in reducing the preparation cost of sodium vanadium phosphate.

The high-speed stirring process of sub-millimeter fine-grained artificial rutile was studied in this paper. Through testing and comparison, the optimal granulation conditions were determined as follows: NA as an additive, 1.5% NA addition, 20% moisture content, a mixing speed of 300 r/min and 600 r/min for 3 and 5 minutes, respectively, and a cutting knife speed of 600 r/min. The resulting granulated products had particle sizes ranging from 0.097 mm to 0.45 mm, with particles smaller than 0.097 mm comprising less than 15% of the total. The strength of the granulated products was assessed, revealing wear indices of 8.54% after drying and 4.40% after heat treatment at

°C, indicating a significant improvement in granule strength after heat treatment. The pelletized product maintained its structural integrity in a fluidized chlorination environment. After 30 min of chlorination, the residual TiO₂ content was only 12.64%, demonstrating effective chlorination performance.

The mineral characteristics and laboratory discarding tailings and iron separation of a high chromium vanadium-titanium magnetite from Panxi were studied by using Zeiss Sigma 500 scanning electron microscope, Bruker energy spectrometer, AMICS automatic mineral analysis system, sieving, grinding and magnetic separation. The main minerals in the ore are titanomagnetite, diopside, olivine, ilmenite and hornblende. The embedding relationship between gangue, ilmenite and titanomagnetite is complex. The ilmenite is closely coexisting with titanomagnetite, and V, Cr are occurrenced in titanomagnetite. There are micrometer sized guest crystal minerals within titanomagnetite, which limites the increase of TFe grade and the decrease of TiO₂ content in iron concentrates. The wet high-intensity magnetic separation used for the ore sample has a good effect on discarding tailings, and discarding tailings concentrate can only achieve significant dissociation and separation of ilmentite and titanomagnetite at a finer particle size. During iron separation process, V and Cr were mainly distributed in the iron concentrate. Using a wet high-intensity magnetic discarding tailings and three-stage stage grinding and stage iron selection process under the conditions of grinding fineness of ?38 μm accounting for 97.58% obtained a vanadium chromium iron concentrate containing 57.06% TFe, 11.07% TiO₂ , 0.591% V₂O₅ and 1.10% Cr. Relative to the original ore, the recovery rate of TFe, TiO₂, V₂O₅, and Cr were respectively 67.51%, 38.66%, 90.95% and 87.55%.

Compared with traditional silicate cement, alkali-activated cementitious materials have advantages such as simple production processes, low investment, low energy consumption, low carbon dioxide emissions, and high slag utilization rates. This study develops alkali-activated high-titanium heavy slag cementitious materials by designing different water-to-cement ratios, alkali activators, and their dosages, and analyzes their mechanical properties to obtain the optimal material composition ratio. At the same time, through XRD and SEM analysis, the phase composition and microstructure are examined, revealing the hydration products and hydration mechanisms of alkali-activated high-titanium heavy slag cementitious materials. The main conclusions are as follows:Sodium silicate demonstrates significantly better activation effectiveness than sodium hydroxide. The alkali-activated high-titanium heavy slag cementitious material achieves optimal mechanical properties when prepared with a water-to-cement ratio of 0.32, 6% liquid sodium silicate content, and a modulus of 1. with a compressive strength of up to 13.5 MPa after 28 days. Phase and microstructure analyses indicate that the primary hydrated product of the cementitious material is calcium silicate hydrate, while a small amount of calcium aluminum silicate crystals is also generated.

The sources of hydrogen and hydrogen-rich reducing gases are the key factors restricting the application of hydrogen energy in the iron and steel industry. However, chemical looping gasification technology can produce high quality hydrogen-rich reducing gases, and this process is mature with low cost. Oxygen carriers play a crucial role in the chemical looping gasification technology. Based on the capabilities and categories of the oxygen carrier, this paper reviews the application of iron-based oxygen carriers in the chemical looping gasification technology. The preparation and utilization of oxygen carriers from metallurgical solid waste are described in detail. The feasibility of generating hydrogen-rich reducing gases by coupling metallurgical solid waste oxygen carriers with chemical looping gasification technology is discussed further. Finally, the research trends and future development directions of solid waste oxygen carriers by using chemical looping gasification technology to produce hydrogen-rich reducing gas are prospected.

Vanadium titano-magnetite is a special iron ore resource rich in multiple elements such as iron, vanadium, titanium. The blast furnace process for vanadium titano-magnetite is very mature, but it requires the addition of ordinary iron concentrate, resulting low TiO₂ content in the slag, making it difficult to recover TiO₂ from slag. To achieve comprehensive utilization of vanadium titano-magnetite, the process of direct reduction in gas-based shaft furnace and smelting in electric arc furnace is currently considered as the most effective technology to recover iron, vanadium and titanium. This technology can smelt vanadium titano-magnetite entirely without the need for flux, producing slag with high TiO₂ content. During the electric arc furnace melting of vanadium titano-magnetite metalized pellets, reducing agents need be added to deeply reduce vanadium into the molten iron, and vanadium and titanium in the slag will compete for reduction. In this paper, the thermodynamics of reduction reaction of V₂O₅ and TiO₂ with carbon in slag was calculated. The reaction process of TiO₂ with C to form TiC, and the inhibition relationship of V₂O₅ on the TiC formation were analyzed. The results show that TiC is inevitable when the melting temperature is above

℃ and the reducing agent of carbon is sufficient. It is difficult for V₂O₅ to inhibit the formation of TiC because of the high TiO₂ activity and low V₂O₅ activity in slag. The problem of slag thickening and difficult slag discharge in electric arc furnace is still existed in smelting of vanadium-titanium magnetite metallized pellets.

The study explored the effects of aggregate quantity and reduction temperature on the gas-based reduction metallization rate and compressive strength of vanadium-titanium magnetite through a synergistic reduction method using vanadium-titanium magnetite concentrate powder internally mixed with semi-coke aggregate and hydrogen. X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray computed tomography (XCT) were employed to analyze the phase composition, micro-morphology, and pore structure changes of the reduced products. The results indicated that the reduction effect of vanadium-titanium magnetite was significantly enhanced when reduced with internally mixed semi-coke in hydrogen atmosphere. In contrast, no reduction of vanadium-titanium magnetite was observed with semi-coke in a nitrogen atmosphere. After the reduction of vanadium-titanium magnetite mixed with semi-coke, the XRD diffraction peaks of metallic iron were intensified, while the semi-coke diffraction peaks were decreased. On the surface of the samples after reduction with semi-coke, the semi-coke particles remained relatively intact, with numerous pores in their vicinity. The embedded semi-coke increased the number of pores within the samples and enlarged the pore diameters, facilitating the penetration of reducing gases into the samples for reduction, thus enhancing the reduction effect of vanadium-titanium magnetite.

The CaO-Al₂O₃-TiO₂-based protective slag effectively solves the problem of serious slag interface reaction in the production of ER70-Ti steel, but it is still unknown whether a liquid/solid slag film with reasonable structure can be formed. In this study, the finite element software was used to establish a heat transfer model and a slag film heat transfer model for ER70-Ti steel, to analyse the changes of liquid/solid slag film in the crystallizer and to explore the influence of process parameters on the distribution of liquid slag film. The results show that the temperature of the slag film on the billet side ranges from 777.87 to

℃ at the exit of the mould; the temperature of the slag film on the mould side is lower, ranging from 89.92 to 450.54 ℃. Along the direction of billet drawing, the thickness of liquid slag film decreases gradually, while the solid slag film thickens gradually, and the maximum thickness is up to 1.168 mm. The increase of drawing speed is conducive to the increase of the thickness of liquid slag film, and every increase of the drawing speed by 0.2 m/min, the liquid lubrication zone can be lengthened by an average of 40 mm. When the pouring temperature is increased from

to

℃, the thickness of the liquid slag film at the centre of the surface increases from 0.252 to 0.272 mm, and the liquid slag film thickness at the outlet of the crystalliser increased from 0 to 0.036 mm.

The effect of Al₂O₃ content on the microstructure and properties of low basicity refining slag system CaO-MgO-Al₂O₃-SiO₂ was investigated. The effect of different Al₂O₃ contents on the microstructure and properties of the low basicity refining slag system was systematically analyzed using molecular dynamics simulation. The results showed that the increase of Al₂O₃ content had no significant effect on the radial distribution function, coordination number and bond angle of the system, but significantly reduced the FO and NBO contents of the system and strengthened the network structure of the system. In addition, the increase of Al₂O₃ content decreased the diffusion ability of elements in the slag system, and the order of diffusion ability was Mg²⁺>Ca²⁺>Al³⁺>O^2?>Si⁴⁺. The viscosity of the slag system gradually increased with the increase of Al₂O₃ mass fraction, which was opposite to the trend of the diffusion coefficient. The results establish a link between the structure and performance of low basicity slag systems, and provide theoretical support for the use of suitable low basicity slags for non-aluminum deoxidation processes.

To clarify the role of borax as a fluoride substitute in fluoride-free and titanium-bearing mold fluxes, the test samples were prepared using industrial raw materials such as titanium-bearing blast furnace slag, limestone, quartz, soda ash, witherite, and borax. Molecular dynamics simulation and Raman spectroscopy were used to study structural characteristics of the samples, including radial distribution function, average coordination number, bond angle distribution, and structural unit Qⁿ distribution. The intrinsic factors of the viscosity changing with borax content were analyzed from the perspective of slag structure. The results show that with the increase of borax content (from 4% to 12%), the stability of the Ca-O structure deteriorates, a large amount of low polymerization degree B-O structure forms, the order degree of Si-O-Si bond angle decreases, and the structural units Q⁰ gradually depolymerize into Q¹ and Q², making the slag structure more complex and the overall polymerization degree smaller. That is, the viscosity performance decreases macroscopically. Moreover, when the borax content increases to more than 8%, the fluoride-free and titanium-bearing mold fluxes reaches a low and steady viscosity level.

Dynamic recrystallization usually occurs on nickel-based superalloys during hot deformation, which can refine the initial coarse solidification columnar grains and be served as the theoretical base for controlling the quality of superalloys. Hot deformation tests were conducted on a nickel-based C276 superalloy in this work. The flow curve characterization and microstructural evolution were investigated. Then a 3D cellular automaton model was developed to simulate the dynamic recrystallization of nickel-based superalloys. The results indicate the dynamic recrystallization of nickel-based superalloys is sensitive to the deformation temperature, deformation degree and strain rate. The developed 3D cellular automaton model can simulate the topological evolution of recrystallization nucleation and grain growth in 3D space. And it can also capture the stress response caused by work hardening and dynamic recrystallization softening. The topological microstructure analysis in 3D shows it is more superior as compared to 2D section. The developed model is supposed to be beneficial for understanding the dynamic recrystallization of nickel-based superalloys and supervising the microstructure control during hot working process.

MoNbTaW powder prepared by spray granulation was used as raw material to prepare spherical refractory high entropy MoNbTaW alloy powder by RF plasma spheroidization. The effects of spheroidizing power, carrier gas flow and sheath gas composition on the spheroidization rate of powder were studied. The morphology, phase, particle size, fluidity and microhardness of the powder before and after spheroidization were measured and analyzed by scanning electron microscope, X-ray diffractometer, laser particle size analyzer, Hall velocity meter and nanoindentation test system. The results show that the powder is not alloyed after ball milling, and the powder is completely transformed into body-centered cubic phase after spheroidization. When the plasma power was increased from 32 kW to 40 kW, the nodulization rate increased and the nodulization rate was close to 100%. When the carrier gas flow rate was increased from 1 L/min to 4 L/min, the surface nanoparticles of the nodulization powder decreased and became smoother, and the nodulization rate was close to 100%. After the carrier gas flow rate was further increase to 7 L/min, the powder appeared unmelted particles. Adding hydrogen in the sheath gas was helpful to improve the spheroidization rate. After spheroidization, the particle size distribution narrowed. As a result, the vibration density was increased from 2.00 g/cm³ to 8.33 g/cm³, the loose density increased from 1.43 g/cm³ to 7.24 g/cm³, and the Hall flow rate increased from 50.8 s/50 g to 8.5 s/50 g. The resulted microhardness reached up to 8.57 GPa.

In this paper the specialized powder and supporting technology for laser additive manufacturing and repair on the surface of 921 steel had been investigated. By adjusting the alloy composition reasonably a spherical atomized powder with uniform size can be obtained through atomization process. A laser coaxial powder feeding equipment had been used for additive manufacturing on 921 steel substrate. As a result a well matched mechanical performance and macroscopic defect free cladding layer can be obtained, achieving the purpose of additive and repair on 921 steel substrate. Testing result indicates the mechanical properties of the repaired layer meet the relevant repair index requirements, the chemical composition remains consistent with the setting, and there are no defects such as cracking and layering. It has good machining performance, which helps to achieve autonomous repair of large marine structures and improve service reliability.

A dynamic recrystallization kinetics model of vanadium microalloyed steel at different deformation temperatures and strain rates was established using the DIL805A/D dilatometers for experiments. The variation of ferrite structure in vanadium microalloyed steel with dynamic recrystallization grain size was studied through microstructure analysis and model comparison. The results indicate that the dynamic recrystallization grain size of austenite in vanadium microalloyed steel has a certain impact on the transformation of intragranular ferrite, and there is a parabolic relationship between the two issues. Both large and small grain sizes can cause excessive growth of grain boundary structures, which is not conducive to the nucleation of intragranular ferrite structures. When the austenite grain size is 40-50 μm, the nucleation ability of intragranular ferrite is the strongest, and the refinement effect of intragranular structure is significant.

The CCT curve of DP600 steel was measured and the steel was industrially produced under different laminar flow cooling processes. The effects of cooling rate, air cooling temperature, and coiling temperature on the microstructures and mechanical properties of the steel were studied. The results show that when the cooling rate is less than 10 °C/s, pearlite transformation occurs in DP600 steel. Bainite transformation occurs in DP600 steel when the cooling rate is ≥ 10 °C/s. And martensite transition occurs in DP600 steel when the cooling rate is higher than 20 ℃/s. As the air cooling temperature decreased from 700 ℃ to 620℃ and 500 ℃, the microstructures of the tested steel were ferrite/martensite, pearlite and bainite respectively, and the tensile strength decreased first and then increased. When the coiling temperature reduced from 500 ℃ to below 200 ℃, the microstructures changed from ferrite/pearlite to ferrite/martensite. When the coiling temperature was below 100 ℃, the morphology of martensite changed from diffusing distribution to banded segregation distribution, which in turn leads to the unqualified elongation and cold bending properties. When the air cooling temperature was 700 ℃ and coiling temperature was 200 ℃, the mechanical properties of DP600 steel met the requirements, with the microstructure of 75% ferrite and 25% martensite in volume fraction, the average grain size of (8.5±0.3) μm, the yield strength of (397±9) MPa, the tensile strength of (659±13) MPa, and the elongation rate of 27%±1.1%.

Fatigue is one of the common failure modes of high strength steels in service. Once it occurs, it will cause catastrophic accidents. In this study, the microstructures and high cycle fatigue life of A100 high strength steel in the atmosphere were studied. The results show that the microstructures of A100 high strength steel are mainly composed of martensite bundles, the reversed austenite films with a thickness of 8 nm and rod-like M₂C carbides with 2～4 nm in diameter and 9～14 nm in length. In the fatigue tests, the number of subgrain boundaries in the microstructures increases with a significant decrease of the number of lath boundaries as the stress decreases, and the martensite structure is elongated. In the meanwhile, the relationship between the fatigue life and stress level was obtained by fitting the S-N fatigue life curves: lgN = 7.54?1.29lg (S_max-953.06 ).

Seawater desalination is considered one of the most viable and technically feasible strategies for the mitigation of water scarcity in the coastal areas, water quality degradation in the inland regions, and the promotion of green transitions in industrial structure. It is beneficial to the integrated water resources, water ecology and water environment development. Modern seawater reverse osmosis (SWRO) desalination technology has attracted more attention because of flexible design, less investment and energy-consuming in water production. However, SWRO desalination plants pose a high level of corrosion risk as they handle and process aggressive seawater under severe operating conditions. And the rising salinity and temperature of seawater, or even trace amount of free chlorine, are important challenges that further exacerbate the pitting and crevice corrosion phenomena of austenitic stainless steels. According to the investigation of domestic and international research findings and engineering experience, the most practical material for use in SWRO desalination plants under different operating environments is summarized. The corrosion mechanism and protective measures of high-pressure piping system in some extreme environments have been discussed. Furthermore, after long-term application, it has been proved that the high-pressure piping system with titanium alloy is effective to resist pitting and crevice corrosion under the extremely aggressive environment. Titanium alloy is suitably used in SWRO desalination plants located in the South China Sea, as well as in the Middle East, North Africa, and South Asia.