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.

Effect of electromagnetic stirring on metallurgical quality of GCr15 electroslag ingot

To further improve the metallurgical quality of electroslag remelting,remove the large inclusions in electroslag ingot and refine the solidification structure of electroslag ingot,an electroslag remelting furnace with electromagnetic stirring was designed,and the influence of different magnetic induction intensities on metallurgical quality of GCr15 electroslag ingot was studied.Inclusions with different sizes and types were analyzed by an ASPEX scanning electron microscope,and the morphology and composition of inclusions were further observed by a JSM-6510LV scanning electron microscope.The distribution of alloying elements on the cross section of electroslag ingot was analyzed by original position analysis(OPA).The results show that whether or not electromagnetic stirring is used,the inclusions in electroslag ingot are mainly composed of Al_(2)O_(3),MnS,MnS-oxide and other oxides,among which Al_(2)O_(3) is the most.Compared with an electroslag ingot without electromagnetic stirring,the number of inclusions decreases considerably,and the proportion of small inclusions increases while the proportion of large inclusions decreases when the electromagnetic stirring with remelting current of 1.1 kA and magnetic induction intensity of 62 Gs is applied.However,excessive electromagnetic force will cause the number and diameter of inclusions to increase again.Electromagnetic stirring has different effects on the segregation of different elements.Under the experimental conditions,the weak electromagnetic force with 1.1 kA and magnetic induction intensity of 108 Gs has little effect on the segregation of C,but decreases the segregation of P,and the excessive electromagnetic force aggravates the segregation of alloy elements.

Effect of mold rotation on the bifilar electroslag remelting process

A novel electroslag furnace with a rotating mold was fabricated, and the effects of mold rotational speed on the electroslag remelting process were investigated. The results showed that the chemical element distribution in ingots became uniform and that their compact density increased when the mold rotational speed was increased from 0 to 28 r/min. These results were attributed to a reasonable mold speed, which resulted in a uniform temperature in the slag pool and scattered the metal droplets randomly in the metal pool. However, an excessive rotational speed caused deterioration of the solidification structure. When the mold rotational speeds was increased from 0 to 28 r/min, the size of Al2O3 inclusions in the electroslag ingot decreased from 4.4 to 1.9 μm. But the excessive mold rotational speed would decrease the ability of the electroslag remelting to remove the inclusions. The remelting speed gradually increased, which resulted in reduced power consumption with increasing mold rotational speed. This effect was attributed to accelerated heat exchange between the consumable electrode and the molten slag, which resulted from mold rotation. Nevertheless, when the rotational speed reached 28 r/min, the remelting speed did not change because of limitations of metal heat conduction. Mold rotation also improved the surface quality of the ingots by promoting a uniform temperature distribution in the slag pool.

Effect of ultrasonic power introduced by a mold copper plate on the solidification process

An electroslag furnace with ultrasonic vibration introduced by a mold copper plate was designed. The effects of ultrasonic power on the element distribution and compactness in electroslag remelting （ESR） ingots were studied, and the mechanism of ultrasonic assistance was analyzed in cold experiments. In the results, silicon, manganese and chromium are uniformly distributed at an ultrasonic power of 300-750 W. The absence of ultrasonic or higher ultrasonic power is not conducive to the uniformity of alloying elements. Carbon demon- strates a highly uneven distribution at 300 W, gradually reaches the uniform distribution as the ultrasonic power further increases, and shows the poor distribution at 1000 W. The compactness of ESR ingots gradually increases with increasing ultrasonic power and reaches the uni- form distribution at 500 W. A further increase in ultrasonic power does not improve the compactness. Introducing ultrasonic vibrations by a mold copper plate can improve the solidification quality; however, an appropriate ultrasonic power level should be determined.

Solidification structure refinement of ferritic stainless steel based on heterogeneous nucleation technology

The ridging defect on the surface of stainless steel products is related to the solidification structure of ferritic stainless steel.Refining the solidification structure and increasing the proport io n of equiaxed grains are necessary to lesse n the ridging defect.Therefore,a new idea of using a heterogeneous nucieating agent which was composed of the composite core containing Ti was proposed,that is,a large amount of dispersed fine particles were initially formed on the solidification front,and a great amount ofδiron was then nucleated using these fine particles as the heterogeneous cores.Through analyzing the crystallographic relationship between different crystals and inducing the calculation formulas of disregistry,the disregistry between the different oxides and TiNδiron was explored and the type of nucleation core was determined.The key parameters of forming the composite core containing Ti were obtained through a thermodynamic calculatio n.The experimental results further con firm the correctness of the theoretical analysis.

Effect of electropulsing on austenite to ferrite transformation in low-carbon steel

We explore the application of electropulsing for the control of phase transformation in a low-carbon steel.The effect of electropulsing on the transformation from austenite to ferrite in continuous casting low-carbon steel slab has been studied through experimental and thermodynamic investigations.The results reveal that electropulsing promotes the precipitation of ferrite within austenite grain in the low-carbon steel.When the electropulsing intensity increases,the precipitation of ferrite increases within austenite grains,and ferrite omentum precipitates become thinner along the austenite grain boundary.The results provide a basis for controlling the austenite to ferrite transformation in low-carbon steel.

Effect of Noncontact Ultrasonic Technology on Solidification Quality of Electroslag Steel

A new electroslag furnace with ultrasonic vibration introduced through water-cooled base plate was de- signed and the effects of ultrasonic power on the distribution of elements, compactness and carbides in the electroslag remelting （ESR） ingots was investigated. The results showed that the distribution of elements on the entire excita- tion section changed with the change of ultrasonic power under experimental conditions. The statistical segregation of elements was minimum when the ultrasonic power was 500 W, whereas excessively high or excessively low power was not conducive to the uniform distribution of elements. Meanwhile, the compactness of ESR ingots gradually in- creased with the increase in ultrasonic power and distribution of compactness was the most uniform when ultrasonic power reached 500 W. Further increase in the ultrasonic power was not conducive to the improvement of compactness. The distribution characteristic of carbides was similar to the distribution of elements and compactness. The re- sults indicated that the ultrasonic vibration introduced through water-cooled base plate was advantageous in impro- ving solidification quality. However, this method needed reasonable ultrasonic power. Moreover, the effects of ultra- sonic power varied for different elements.

Effect of magnetic field on elements segregation in electroslag ingot

In order to improve the production efficiency of electroslag remelting process and the solidification quality of electroslag ingot,a novel electroslag furnace with electromagnetic stirring was designed and the effects of external magnetic field and different electrical parameters on electroslag remelting process were studied.The distribution of carbon,chromium,phosphorus and compactness in electroslag ingot was analyzed through original position analysis apparatus.Results show that the external magnetic field accelerates the remelting of consumable electrode.Under the condition of remelting voltage of 34 V and current of 1500 A,the remelting rate of metal consumable electrode increases from 20 to 27 mm min−1 when the magnetic induction intensity of 62×10^(−4) and 108×10^(−4) T is applied.However,the remelting current decreases from 1500 to 1100 A under the condition of constant remelting rate and remelting voltage,thereby reducing the energy consumption.The effect of external magnetic field on the segregation of different elements in electroslag ingot is different.Under the experimental conditions,the carbon segregation is unremarkable,but the phosphorus segregation is improved when the electromagnetic force generated by the interaction between the external magnetic field and the remelting current is small.However,the excessive electromagnetic force aggravates the segregation of carbon and phosphorus.With the increase in electromagnetic force,the chromium segregation gradually increases.

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.