I. Basic Process

1. Electroslag casting: the electric current melts the metal electrode through the resistance generated by the liquid slag, and the molten metal flows into the molten pool through the slag layer, and then solidifies into the special-shaped casting in the special-shaped water-cooled mold.

2. Solidification process of casting: the casting is solidified from bottom to top, that is, the metal molten pool and slag pool continuously move upward. The rising slag pool first forms a layer of slag shell on the inner wall of the water cooling mold. This layer of slag shell not only makes the casting surface smooth, but also plays the role of heat preservation and slag isolation, and makes more heat transfer from the casting to the bottom cooling water, which will be more conducive to the casting crystallization process from bottom to top To carry out.



Two electrode melting

The melting characteristics of the electrode are related to the shape and size of the electrode, the smelting electric system and the depth of the slag pool. Whether the electrode melting process is normal or not is often reflected in the shape of the melting end of the electrode. When the descending speed of the electrode is from slow to accelerating, the shape of the melting end of the electrode and the depth buried in the slag pool have obvious changes.

The changes are as follows:

① When the falling speed of the electrode is too low, the end of the electrode presents a flat end face. At the edge of the end face of the electrode, there is a bulge of droplet collection. In the process of electrode melting, the metal droplet is on the end face of the electrode. When the droplet falls down, there is arc discharge. At this time, the current fluctuates greatly, so the electroslag process has been destroyed.

② When the electrode dropping speed is increased, i.e. the smelting current is increased, the end of the electrode will bulge. If the electrode dropping speed is increased gradually, the bulge in the center of the electrode end will become larger and larger, and gradually form a cone until a normal cone is formed. At this time, the fluctuation of current and voltage is smaller and smaller, and tends to be stable. This is a stable electroslag process. At this time, the electric system is the most suitable for smelting Good electricity system.

③ If the dropping speed of electrode continues to increase, the conical surface of electrode end protrudes, and the melting part of consumable electrode end is deeply buried in the slag pool. At this time, if the descending speed is maintained, the current gradually increases. If the electrode is further accelerated, the short circuit phenomenon between electrode and metal bath may be caused.

To sum up, the stable electroslag process range is between the arc discharge generated by the electrode end and slag surface, and the arc discharge generated by inserting the electrode end into the slag pool and the metal molten pool.

When the voltage, slag chemical composition, slag and electrode cross-section are the same, with the increase of electrode falling speed, the distance of discharge interval is equivalent to the decrease of slag pool resistance, which increases the smelting current intensity. Therefore, the relationship between smelting current and electrode falling speed is approximately linear.

When the electrode cross-section is increased, it is necessary to increase the current obviously in order to obtain a stable electroslag process. However, the current required to maintain a stable electroslag process is smaller than the increase rate of the electrode cross-section. Therefore, with the increase of the electrode cross-section, the current density required for the stabilization process decreases. With the increase of voltage, a large current density is needed to stabilize the electroslag process.

Formation and transition of three droplet

In the process of electroslag remelting, the metal consumable electrode enters into the metal bath through the slag layer through the formation of molten droplets. The droplets leaving the electrode are often dispersed and finely broken before they enter the molten pool. Their average size and distance through the slag layer all depend on the magnitude of electric pressure and current, the composition and quantity of slag, the cross section of electrode and the composition of remelted metal, The type and polarity of current and so on. The droplet gathered at the end of electrode is affected by gravity and electric force. These forces make the droplet separate from the electrode, and the interfacial tension between slag and molten surface prevents the droplet from falling off.

When the gravity and electric force exceed the interface tension, the droplets fall off. The droplets gathered at the end of the electrode reduce the distance of discharge interval in the increase of volume, and increase the conductivity, and the droplet shedding occurs when the current increases to the maximum value.

The results show that the frequency of droplet transfer increases with the increase of electrode supply speed and corresponding current, and the weight of droplet decreases with the increase of current. This is because the electric force increases with the increase of current, which promotes the drop off.

If the voltage of electroslag process is increased, the temperature of slag will increase, the interfacial tension of steel slag will decrease, the transfer frequency of droplet will increase, the size of droplet will decrease, and the weight of droplet will increase with the increase of electrode cross section, and the change of slag pool depth will have little effect on the droplet.



Four bath shape

In the process of electroslag casting, the shape and size of the metal bath directly affect the crystallization of the casting, thus affecting the quality of the ingot. The shape of the metal bath is closely related to the electrode melting and process parameters. The speed of electrode descent is accelerated and the depth of metal bath increases, which leads to the change of ingot crystallization characteristics, which makes the crystal growth direction close to radial shape, and the microstructure of this ingot is close to that of ordinary steel ingot. Therefore, it is necessary to select appropriate smelting current, i.e. appropriate electrode descending speed, to ensure the ideal axial crystallization of electroslag ingot.

With the increase of voltage, the bottom of molten pool develops to flat direction, the direction of crystal gradually approaches the axial direction, and the temperature of molten pool tends to be stable, which improves the surface quality of ingot. However, excessive increase of voltage can lead to slag pool boiling, destroy electroslag process and produce arc process.

When other parameters remain unchanged, the depth of metal bath decreases with the increase of slag content. This is because the increase of slag amount makes the slag pool deeper, and the heat consumed to maintain the slag in the melting and process state increases, so the heat to maintain the molten and superheated state of the metal bath is greatly reduced. Excessive increase of slag content will result in small volume of molten pool and low temperature, which will affect the quality of ingot. The depth of molten pool will decrease with the increase of thermal conductivity.