JPS6114909B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for manufacturing a steel ingot, and more particularly, in an electroslag melting method, an electrode to be melted is guided into a mold through a hole provided in a lid that closes the mold. In addition, a method for producing a clean steel ingot with low hydrogen and sulfur content by melting the electrode while supplying flush gas to the inside of the mold and the gap between the electrode and the hole in the lid. and regarding its equipment.

Traditionally, when producing steel ingots by electroslag melting, reagents such as _CaF2 are added to the slag and melt bath together with an inert gas (argon gas, helium gas, nitrogen gas, etc.) as a means of removing undesirable impurities. A blowing method is known (Austrian Patent No. 314107).

Furthermore, it is also known to introduce an inert gas into the mold through an annular box surrounding the electrode during the melting operation, and to curtain the inside of the mold with a jet of air introduced to the electrode ( (see German Published Patent No. 2308321).

However, conventional melting methods using these means cannot produce steel ingots with low hydrogen or sulfur content, and the bottom part of the steel ingot is more susceptible to undesirable impurities, especially It is also impossible to avoid the drawback of high hydrogen segregation. These drawbacks are explained as follows.
In other words, in the conventional operation method, melting starts immediately when pre-molten slag is introduced into the mold, but the slag takes in moisture from the surroundings when it is poured into the mold, which decomposes and hydrogen is released. Once generated and diffused into the steel, it remains in the steel without being removed. The hydrogen content at the bottom of the steel ingot substantially affects the time required for the subsequent processing of the steel ingot, regardless of the good or bad composition of the other parts of the steel ingot.
It determines the operation and cost, especially the annealing process time.

The purpose of the present invention is to eliminate the above-mentioned drawbacks and difficulties of conventional methods and to provide a new and improved electroslag melting method, which prevents contact with moisture from the atmosphere and facilitates desulfurization. By setting optimal conditions, it was possible to produce a steel ingot with low hydrogen and sulfur content and an extremely uniform composition from top to bottom.

Next, the present invention will be explained in detail.

According to the method of the present invention, (a) the amount of hydrogen in the slag is reduced prior to the start of melting, (b) dry air is introduced above the slag in the mold during melting, and (c) dry air is introduced above the slag in the mold. At the same time, a gas curtain of dry air is formed in the annular gap between the electrode passage hole of the mold closing lid and the electrode, and the curtain prevents air containing water vapor (moisture) from entering the mold. This makes it possible to produce a sound steel ingot with a uniform composition throughout.

According to the invention, it is advantageous to introduce dry air into the slag charged in the mold before starting the melting, so that the resulting drop in hydrogen partial pressure causes hydrogen to escape.

In this case, it is preferred to heat the slag with a graphite electrode and maintain the slag at a temperature slightly above its liquidus.

In addition, CaO is suitable for forming CaO-SiO ₂ complex.
Molten slag with content i.e. CaO approx.
40% (wt%, same below) and _SiO2 about 3-25
It is preferable to use %. According to the research conducted by the present inventors, it has been found that this also works preferably for reducing the hydrogen content.

By the combination of the measures according to the invention, the hydrogen content in the molten slag is very low, and the formation of a gas curtain of dry air prevents the intrusion of water vapor that would lead to the formation of hydrogen. Moreover, by feeding dry air into the mold, effects such as maintaining the excellent desulfurization effect of the slag can be obtained. Under the action of oxygen from the air, SO ₂
is formed and removed as a gas.

The invention also provides an apparatus for carrying out the electroslag melting process as described above. The device of the present invention has a mold for performing melting, and a lid that closes the mold during melting, and guides an electrode into the mold through a hole provided in the lid. Means are provided for supplying flush gas to the annular gap between the two.

The lid that closes the mold is composed of a plurality of divided lid parts, each of which is pivoted so that it can be opened and closed. As a result, multiple consumable electrodes are continuously melted down to form a single ingot, and a high degree of operational safety and accuracy is achieved to obtain the desired low hydrogen and low sulfur content steel. Secured.

Each hinged lid section is provided with an arcuate conduit section having a separate means for supplying dry air, and when the lid is closed, the sections complement each other to form an annular conduit section. Advantageously, a gas conduit is formed.

Further, it is preferable that two or more arcuate conduits each having an outlet are vertically arranged in multiple stages in each openable/closable lid portion.

Furthermore, during flushing of the slag, a water-cooled or graphitic blowing lance is immersed in the slag and a graphite electrode can be positioned above the slag.

Next, embodiments of the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a longitudinal sectional view of the apparatus in the slag flushing stage, and FIGS. 2 and 3 are a longitudinal sectional view and a plan view, respectively, in the melting stage.

In the figure, 1 is a cooled bottom plate, and 2 is a mold that can be raised and lowered. Slag 3, which has been melted in advance outside the apparatus, is charged into a mold, and an arc 5 is generated between graphite electrode 4 and the slag surface to heat the slag. A water-cooled blowing lance 6 connected to a source of dry air via a gas inlet pipe 7 is immersed in the slag and air is introduced until the desired cleaning effect is achieved.

FIG. 2 is a diagram showing the melting stage, in which the mold 2 is covered with a lid 8, a hole is provided in the center of the lid to guide an electrode 9, and a gap 10 is created around the electrode to melt the mold. The electrodes are fed smoothly into the mold. The lid 8 has a segmented configuration, with each lid portion 8' and 8'' being mounted on a pivot 11 and 11', respectively, about which it is pivotable into a closed position. Highly fire-resistant insulation material 1 between the openings
2. Insulation, preferably consisting of fiber mat, is installed. A refrigerant passage pipe 13 is provided in each lid portion. The annular gap 10 of each lid part is provided with at least one arcuate conduit section 16 for conveying dry air, each section having a source tube 15 for conveying gas. When each lid portion pivots to the closed position, each arcuate conduit 16 complements each other to form an annular conduit 14. Each arcuate or annular conduit is provided with a respective gas outlet 17 pointing towards the jacket of the electrode 9. If these outlets are formed in the form of slits and arranged in two or more layers above and below, the dry air flow flowing out from these slit-shaped openings prevents the intrusion of water vapor-containing air into the annular gap. A kind of labyrinth sealing can be formed that can be reliably prevented. The main pipe 15 is provided with a branch pipe 18 that passes through the lid and communicates with the inside of the mold.

By introducing dry air under pressure into the mold interior, favorable conditions are provided for desulfurization and furthermore the sealing effect of the dry air curtain formed in the annular gap is improved. According to the method of the present invention, an atmosphere free from water vapor can be reliably maintained even when using a slightly conical electrode or when replacing the electrode.

Next, the present invention will be specifically described with reference to Examples.

Example Using an electrode (diameter 500 mmφ) of 28NiCrMoV85 steel (DIN standard) that has been quenched and tempered, an electroslag melted steel ingot (diameter 1000 mmφ, length
4m) was manufactured.

The amount of hydrogen in the consumable electrode used for degassing was 2.1ppm.
The amount of sulfur was 200 ppm. The air humidity in the dissolution apparatus was 12 g (water vapor)/Nm ³ . In addition, the slag melted in advance in the slag melting furnace is SiO ₂ 20
%, CaO 20%, CaF ₂ 30% and A ₂ O ₃ 30%, and the amount of hydrogen was 32 ppm. This slag was poured into the mold by opening the lid, and a graphite electrode was placed on top of the slag as shown in FIG. After igniting the arc, the slag should be heated to about 50 ~ below its liquidus line.
The temperature is maintained at 100°C higher, approximately 1500°C, and dry air is pumped 1/2 way below the slag surface using a water cooling lance.
The hydrogen content in the slag was reduced to 13 ppm. The graphite electrode and the blowing lance are then removed, the mold is closed by pivoting the lid part together with the arcuate conduit for supplying insulation and drying air, the electrode to be melted is introduced inside the mold and the original Through tube 15, approx.
Pressurized dry air at 1.5 atmospheres was blown into the mold at a rate of 1/min to form an air curtain in the annular gap between the electrode and the lid to initiate melting.

According to a sample taken from the bottom area of the steel ingot in the steel bath one hour after the start of melting, the amount of hydrogen was
It was 2.2ppm. Thus, no noticeable increase in the amount of hydrogen was observed compared to the initial amount of hydrogen in the dissolving electrode. After another 2 hours and after completion of dissolution,
When several samples were taken, the amount of hydrogen in each was
They were 2.1ppm and 2.2ppm. The latter amount of hydrogen corresponds to the amount of hydrogen in the cropped region of the obtained steel ingot. The sulfur content of the steel ingot was 60 ppm, which was uniform over the entire length of the steel ingot. Annealing treatment for reducing the hydrogen content of the produced steel ingot was unnecessary.

Next, a comparative example will be given and explained.

Comparative Example Melting was carried out using the same consumable electrode as in the above example without flashing the slag or supplying dry air into the mold or annular gap. One hour after the start of melting, the bottom of the steel ingot The amount of hydrogen is
5.8ppm, the amount of hydrogen in the middle and upper part of the steel ingot is
It was 3.5ppm. If the hydrogen content is high and uneven between the bottom and top of the ingot, the produced ingot must be annealed for more than 100 hours to reduce the hydrogen content to an acceptable value. Processing is required.

When the slag is used as it is made in the melting furnace without being flashed, the amount of hydrogen in the steel bath 1 hour after the start of melting is reduced by the gas curtain created by dry air (air blowing rate: 1.8/min) in the annular gap. reached 4.7ppm, and then gradually
Reduced to 2.8ppm. In such cases, steel ingots
Contains 120ppm sulfur.

If a slag with equal proportions of alumina, lime and fluorspar is used and the other conditions are the same as in the previous example, the amount of hydrogen in the bottom region of the steel ingot will be 2.6 ppm and the amount of hydrogen in the top region will be 2.4 ppm. becomes.

In addition, if a basic slag without flushing is used and a curtain of inert gas such as nitrogen or argon gas is formed in the annular gap between the hole in the lid and the electrode, one hour after the start of melting, the steel The amount of hydrogen in the steel melt corresponding to the lump bottom region reaches 4.5 ppm, and then decreases to 3.0 ppm. The sulfur content in the bottom region of the obtained steel ingot is 120 ppm, and that in the upper region is 200 ppm. This means that the slag has some sulfur dissolving ability at the beginning of dissolution, and this dissolving ability disappears as the dissolution progresses as saturation is reached.

Furthermore, if a neutral slag is used and otherwise the conditions are the same as in the previous example, the hydrogen and sulfur contents will be unsatisfactory, with hydrogen contents of about 4.0 to
Although slightly lower at 3.0ppm, the sulfur content is as high as 150ppm at the bottom of the steel ingot and 200ppm at the top.

As can be seen from the above comparison, according to the invention, the means of flushing the slag, the gas curtain of the annular gap, the introduction of dry air into the interior of the mold and the composition of the slag are controlled under suitable conditions and under their interaction. , a steel ingot with a low hydrogen and sulfur content and a uniform composition over its entire length is obtained.
Therefore, the steel ingot obtained by the present invention does not require annealing treatment, and even if necessary, a very short treatment is sufficient.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the device showing the slag flushing situation, FIG. 2 is a sectional view of the device showing the situation during melting, and FIG. 3 is an overhead view of the device during melting. 2... Mold, 3... Slag, 4... Graphite electrode, 6... Water-cooled lance for flushing gas injection, 7... Gas introduction pipe, 8 (8', 8'')... Lid, 9... Melting electrode, 10
...Annular gap, 11, 11'... Pivot of lid, 12... Insulating material, 13... Cooling medium delivery tube, 14... Annular gas conduit, 15... Gas supply source pipe, 16, 17... Arc-shaped conduit portion, 18 ...Branch tube.

Claims (1)

[Claims] 1 Electrolysis carried out by guiding a melting electrode into the mold through a hole in a lid that closes the mold, and introducing flash gas into the annular gap inside the mold and between the hole in the lid and the electrode. A method for producing a steel ingot with low hydrogen and sulfur content by a slag melting method, the method comprising: (a) prior to starting melting of the electrode, slag charged in a mold is introduced into the mold by introducing dry air; (b) introducing dry air above the slag in the mold during melting of the electrode, and (c) simultaneously flushing the slag with the holes in the mold lid. A method for producing a steel ingot, characterized in that a gas curtain of dry air is formed in an annular gap between the electrode and the gas curtain prevents air containing moisture or steam from entering the mold. . 2. During flushing of the slag with dry air, the slag is heated with a graphite electrode to maintain the slag temperature slightly above its liquidus line.
Section method. 3 Flushing the slag with dry air,
The method according to item 2 above, wherein a water-cooled lance or a graphite lance for blowing flash gas is immersed in the slag, and at the same time, a graphite electrode for heating the slag is placed on top of the slag to heat the slag. 4 Contains CaO3~40%, _SiO2 3~25%, CaO-
The method according to item 1 above, characterized in that a slag suitable for forming a SiO ₂ complex is used. 5 An apparatus for producing steel ingots with lower hydrogen and sulfur content than by electroslag melting method, which comprises a mold and a lid that closes inside the mold, and a melting electrode is inserted into the mold through a hole provided in the lid. and means for supplying flash gas into the interior of the mold and into the annular gap between the hole in the lid and the electrode therethrough, the lid being divided into sections; A steel ingot manufacturing device characterized in that each part is pivotally connected so that it can be opened and closed. 6. The means for supplying flush gas consists of a gas conduit section having a separate dry air feed tube provided in the lid section, the gas conduit section being configured to form an annular shape when the lid is closed. Apparatus according to paragraph 5. 7. The device according to item 6 above, wherein the gas conduit portion is arranged in two or more stages in the vertical direction on the lid portion.