Effect of electrical parameters and slag system on macrostructure of electroslag ingot

To investigate the influence of electric parameters and slag system on the solidification quality of electroslag ingot during electroslag remelting,different power supply modes,current strengths and remelting slag systems were used to conduct electroslag remelting experiments on 304L austenitic stainless steel,and the macrostructure of electroslag ingots was analyzed.The results indicate that the depth of the metal pool decreases with the reduction of remelting frequency in the low frequency power supply mode.The effects of different power supply modes,such as low-frequency,direct current straight polarity(DCSP),and direct current reverse polarity(DCRP),on reducing the depth of the metal pool increase in that order.By reducing the remelting current strength in the same power supply mode,the depth of metal pool is reduced.When compared to the binary slag system of 70%CaF2+30%Al2O3,the ternary slag system of 60%CaF2+20%Al2O3+20%CaO is more effective in reducing the depth of the metal pool during remelting.Utilizing the 60%CaF2+20%Al2O3+20%CaO ternary slag system results in a shallower and flatter metal pool,with columnar crystal growth occurring closer to the axial crystal.This effect is observed for both low frequency and direct current(DC)power supply modes.

Microstructure and mechanical properties of Fe/NbC composite layer prepared by in-situ reaction

NbC ceramic surface-reinforced steel matrix composites were prepared by an in-situ reaction method at different temperatures(1,050℃,1,100℃and 1,150℃)for different times(1 h,2 h and 3 h).The phase constitution,microstructure and fracture morphology of NbC ceramic surface-reinforced steel matrix composites were analyzed by XRD,SEM and EDS,and the effects of the in-situ reaction temperature and time on the mechanical properties were systematically studied.The results indicate that the NbC reinforcement layer is formed through the reaction between Nb atoms and carbon atoms diffused from the steel matrix to the Nb plate.The thickness of this reinforcement layer increases as the reaction time prolongs.Additionally,an increase in reaction temperature results in a thicker reinforcement layer,although the rate of increase gradually decreases.The relationship among the thickness of the Nb C reinforcement layer,the reaction time and temperature was established by data fitting.The optimal tensile performance is achieved at 1,100℃for 1 h,with a tensile strength of 228 MPa.It is also found that the defects between the reinforcement layer and the steel matrix are related to reaction temperature.At 1,100℃,these defects are minimal.Fracture mostly occurs in the NbC reinforced layer of the composites,and the fracture mode is characterized by typical intergranular brittle fracture.

Improving Internationally Core Competences Based on the Capabilities of Precise and Accurate Project Management

Modern international project management has entered the phase of precise and accurate project management after the global financial crisis broke out at the beginning of the 21 stcentury. However, its development has faced new challenges since there has been lack of explicitly unanimous definition for the capability dimensions of precise and accurate project management, as well as the models and their process control parameters. The required core capabilities based on the precise and accurate project management for various rings are involved in the project life cycle, namely, the required internationally core competences and their components for the phases of project strategic planning and decision making in the early project phase, as well as the value engineering, and the project supervision and controls during the execution phase.Through studying the effects of the internationally core competences based on precise and accurate project management capabilities for the success and excellence of projects and configuring such models, the goal is to help the main contractors continuously obtain project success and excellence, thus improve its internationally core competences with continuous project success and excellence.

Effect of slag composition and current density on ingot cleanliness during low-frequency/DC electroslag process

For in-depth investigation of the effect of low-frequency and DC remelting on the cleanliness of electroslag ingot,laboratory experiments were performed with different current densities and slag compositions to analyze the variation of oxygen content and inclusions in electroslag ingots.When 70%CaF_(2)+30% Al_(2)O_(3) binary slag is used for remelting,the current density has different effects on the cleanliness of electroslag ingots with different power supply modes.At the power frequency of 2 Hz,the oxygen content and the number of inclusions in the electroslag ingot increase significantly with the increase in remelting current density.By contrast,when consumable electrode connected to cathode(DCSP)or consumable electrode connected to anode(DCRP)is employed,the current density has little influence on ingot cleanliness.At the same current density,DCSP remelting has a more adverse effect on ingot cleanliness compared with DCRP remelting.Compared with the use of 70%CaF_(2)+30% Al_(2)O_(3) binary slag,using 60%CaF_(2)+20% Al_(2)O_(3) +20%CaO ternary slag significantly reduces the oxygen content and the number of inclusions in electroslag ingots,regardless of whether low-frequency or DC electroslag remelting occurs.The increase in oxygen and inclusions in electroslag ingot is caused by the electrolysis of Al_(2)O_(3) in the slag pool.The increased inclusions mainly involve Al_(2)O_(3) or Al-containing oxides with small size.As regards the power supply mode,low frequency,DCRP,and DCSP promote the electrolysis of Al_(2)O_(3) in the slag pool.From the perspective of remelting slag composition,the slag with lower Al2O3 content can reduce the pollution of electrolysis on electroslag ingot.