JP2009167511A - Method for producing ingot by electroslag remelting process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an ingot by an ESR (Electro-Slag Remelting) process by which an ingot having satisfactory surface properties can be obtained by regulating a melting current and a mold size in accordance with the melting point of a melting material. <P>SOLUTION: In the method for producing an ingot by an electroslag remelting process, when a steel or an Ni based alloy is subjected to electroslag remelting, provided that the melting point of a melting material is defined as TML(°C), melting current value is defined as i(kA) and the diameter of a mold is defined as D(cm), melting conditions are regulated so as to satisfy relations expressed in equations (1) and (2), and a remelting operation is performed; wherein, TML≤T-150≤1750 (1), and T=1130×(i/D)+1450 (2). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

   The present invention relates to a method for producing an ingot of steel or a Ni-based alloy by an electroslag remelting method, and in particular, by adjusting the mold size and the melting current value according to the melting point of the melting material, a good surface property can be obtained. The present invention relates to a method for producing an ingot by an electroslag remelting method capable of obtaining an ingot having the same.

  The electroslag remelting method (hereinafter also referred to as “ESR method”) is an agglomeration method that can be cast without causing problems of solidification defects such as a center cavity and macrosegregation. For this reason, the ESR method has long been used as a casting method for materials for manufacturing products that require high internal quality, such as large-diameter forged steel rolls, large die steels, and Ni-base superalloy seamless pipe materials. It is used. Furthermore, not only the quality of the ingot, but also the surface properties are very good compared to the ordinary ingot-making method, etc., so the man-hours for surface maintenance can be minimized, using high-grade materials, and It has many advantages as a melting method that can be expected to have a high yield.

The main feature of the ingot produced by the ESR method is that it has a sound internal quality and surface quality as described above. Furthermore, in the ingot produced by the ESR method, it is necessary depending on the use of the final material. It is required that active metal element components such as Al, Zr, and Ti that are assumed to be uniformly distributed in the steel to be melted. The molten slag mainly has a component composition in which Al ₂ O ₃ or CaO is added to CaF ₂ , but from the initial melted part of the ingot to the final melted part by the oxidation or reduction reaction between the active ingredient and the melted slag. There is a possibility that the composition of the ingredients may be non-uniform over a certain ingot top. In order to cope with the fluctuation of the component composition as described above, the component composition of the molten slag is often determined and adjusted in advance. For example, in order to suppress fluctuations in the Ti content, a treatment such as adding a TiO ₂ component in addition to the slag components such as CaF ₂ , Al ₂ O ₃ , and CaO is performed in advance.

In recent years, as seen in Patent Document 1, when an ingot containing a B component is produced by the ESR method, the relationship in which the composition of SiO ₂ and B ₂ O _{3 in} the slag is defined by a predetermined mathematical formula. An ingot B component control method is disclosed in which the B component in the ingot is controlled to a target value by adjusting the B ₂ O ₃ content in the slag so as to satisfy.

  On the other hand, in the ESR method, temperature control of the slag pool is important, and when melted at low power, the degree of superheat of the slag pool (ie, the value obtained by subtracting the liquidus temperature of the slag from the slag temperature) is sufficient. Since it is not large, the slag begins to solidify in the vicinity of the water-cooled copper mold. As a result, a thick slag skin is formed, and surface layer defects having irregularities called ripple skin are generated on the surface of the ingot. Therefore, in particular, it is necessary to consider the relationship between the melting point of the melting material (dissolving material) and the temperature of the slag pool. As described above, it is necessary to diversify the slag component composition from the need to control the fluctuations in the ingot component composition, the temperature change of the slag pool due to the change of the component composition, and the melting point and slag pool of various melting materials It is one of the important issues to understand the relationship with temperature change.

  In Patent Document 2, by setting the value of (input current) / (inner diameter of mold) to 15 A / mm or more, the heat capacity of the molten steel pool or slag pool is increased, and the maximum length of the nonmetallic inclusion is 20 μm or less. A method for producing highly clean maraging steel is disclosed. However, this document makes no mention of the temperature of the molten steel pool or slag pool, the melting point of the molten material, and the surface properties of the ingot, and therefore the ESR method for obtaining an ingot with good surface properties. It is not a reference for the study and development of the ingot manufacturing method.

  As described above, in order to establish an ESR method capable of producing an ingot having excellent surface quality by adjusting the mold size and the melting current value according to the melting point of the melting material, there is a problem that must be solved. It was left.

JP 2001-11546 A (claims, paragraphs [0006] and [0007]) JP 2003-183765 A (claims, paragraphs [0006] and [0011])

  The present invention has been made in view of the above-mentioned problems, and the problem is that by adjusting the melting current and the mold size according to the melting point of the melting material and controlling the temperature of the slag pool, a good surface property is achieved. It is to provide an ingot manufacturing method by an ESR method capable of obtaining an ingot.

  The inventors of the present invention provide an ingot manufacturing method based on the ESR method in which an ingot having a good surface property can be obtained by adjusting the melting current and the mold size according to the melting point of the melting material to control the temperature of the slag pool. Research was repeated and the following knowledge (a) to (c) was obtained from both theoretical and experimental aspects to complete the present invention.

  (A) The average temperature of the molten slag in the slag pool formed by melting by the ESR method (hereinafter also referred to as “slag bulk temperature”) is not dependent on the type of slag, and uses melting conditions such as mold diameter and melting current. Can be formulated.

  Here, in the slag pool, strong stirring is generated by electromagnetic force, and the temperature in the slag pool is made uniform. Strictly speaking, a temperature boundary layer is formed near the mold, and a large temperature gradient exists, so the slag temperature near the mold is lower than the slag temperature in other regions, but the slag pool occupies the entire slag pool. Since the ratio of the regions is very small, the temperature of the slag pool in the region near the electrode can be set as the average temperature of the slag.

  (B) The temperature of the slag bulk formulated according to the above (a) is not less than the minimum temperature considering the melting point of the dissolved material, and the surface properties of the ingot are deteriorated due to the non-formation of the slag skin in the ingot surface layer portion. An ingot having a good surface quality can be produced by adjusting the temperature so that it does not become an extremely high temperature that causes seizure with the mold.

(C) The slag bulk temperature T (° C.) described in (a) above is formulated as shown in the following equation (2) using the dissolution current value i (kA) and the mold diameter D (cm). In addition, the appropriate range of the slag bulk temperature T (° C.) described in the above (b) can be expressed by the following equation (1). TML represents the melting point (° C.) of the dissolved material.
TML ≦ T−150 ≦ 1750 (1)
T = 1130 × (i / D) +1450 (2)

  Therefore, an ingot having good surface quality can be produced by adjusting the melting conditions so as to satisfy the relationship represented by the following formulas (1) and (2).

  The present invention has been completed based on the above findings, and the gist of the present invention resides in a method for producing an ingot by the following electroslag remelting method.

“When remelting steel or Ni-based alloy with electroslag, the melting point of the melting material is TML (° C.), the melting current value is i (kA), and the mold diameter is D (cm). (2) A method for producing an ingot by an electroslag remelting method, wherein the remelting operation is performed by adjusting the melting conditions so as to satisfy the relationship represented by the equation (2).
TML ≦ T−150 ≦ 1750 (1)
T = 1130 × (i / D) +1450 (2) ”

  In the present invention, “steel” means carbon steel and stainless steel, and “melting point of melting material” means the liquidus temperature of the melting material.

  “Mold diameter” means the inner diameter of the mold. When the shape of the cross section of the mold is rectangular, it means the equivalent diameter obtained by dividing the inner peripheral length of the mold cross section by π.

  The “melting condition” means the melting point of the melting material, the mold diameter, and the melting current value. When the type of the melting material is determined and the melting point of the melting material is determined, the melting current value and the casting mold are determined. Means diameter.

  According to the method for producing an ingot by the electroslag remelting method of the present invention, the melting conditions are adjusted so as to satisfy the relationship represented by the above formulas (1) and (2) according to the melting point of the melted material. In addition, since the remelting operation is performed while controlling the average temperature of the molten slag in the slag pool within an appropriate temperature range, an ingot of steel or Ni-based alloy having good surface properties can be produced.

1. Basic Mode for Carrying Out the Invention The present invention provides a method for melting a slag pool by adjusting a melting current value and a melting condition according to a melting point of a melting material when remelting steel or a Ni-based alloy. This is a steel or Ni-based alloy ingot manufacturing method by the ESR method in which remelting operation is performed while controlling the average temperature of slag within an appropriate temperature range. Hereinafter, the contents of the present invention will be described in more detail.

  FIG. 1 is a diagram schematically showing an example of an apparatus configuration used for carrying out the method for producing an ingot by the electroslag remelting method of the present invention.

  Electricity is supplied from the power supply device 8 through the electric wiring 9 between the consumable electrode 1 made of a predetermined type of metal that is a melting material and the water-cooled surface plate 10 cooled by the cooling water 7. When the molten slag 3 in the water-cooled mold 2 generates Joule heat, the consumable electrode 1 is melted, and the melted metal droplets are refined in the process of descending the slag pool (molten slag) 3, and non-metallic inclusions, etc. Are separated and removed to form a metal pool 4 made of clean molten metal. The metal pool 4 formed in this way solidifies sequentially from the bottom in the water-cooled mold 2 to form a clean solidified phase (metal ingot) 6. Here, a solid-liquid coexistence phase 5 is formed between the metal pool 4 and the solidified phase 6.

2. Derivation of slag bulk temperature by heat balance Based on the steady state heat balance in the electroslag remelting method, the average temperature of molten slag is obtained. FIG. 2 is a diagram showing a heat balance in the molten slag in the ingot manufacturing method by the ESR method.

If the heat balance about the molten slag in a slag pool is taken, the following (1) Formula and (2) Formula will be materialized.
^{_{πDL × q m + (πD 2}} /4) × (q r + q i) = eW ···· (1)
q _m = h × (T−T ₀ ) (2)

Where T is the temperature of the slag bulk (average temperature of the molten slag), q _m is the heat flux from the slag pool to the mold, q _r is the radiant heat flux from the free surface of the slag pool to the outside, and q _i is The heat flux from the slag pool to the ingot, h is the heat transfer coefficient between the slag and the mold, T ₀ is the temperature of the cooling water, D is the mold diameter, and L is the depth (height of the slag pool ), W represents input power, and e represents energy equivalent.

Substituting the above equation (2) into equation (1), the radiant heat flux q _r from the slag pool surface to the outside and the heat flux q _i from the slag pool to the ingot are the heat flux q _m from the slag pool to the mold. When it is solved for the temperature T of the slag bulk, the following equation (3) is obtained.
T = (e / h) × (W / (πDL)) + T ₀ (3)

Here, since the depth of the slag pool and the voltage V are in a proportional relationship, L = k × V (where k is a proportional constant) and W = i × V (where i is a dissolved current value). Is substituted, the following equation (4) is obtained.
T = (e / (πkh)) × (i / D) + T ₀ (4)

  From the relationship of the above equation (4), it can be seen that the temperature T of the slag bulk and the value of (dissolution current value i / template diameter D) have a linear relationship.

2. Formulation of slag bulk temperature In order to formulate the slag bulk temperature by experiment, it is shown in Table 1 using a mold for ESR having a square shape of 48.5 cm square and a circular shape of 77.5 cm in diameter. Dissolution experiments were conducted under the conditions.

  As shown in the table, in addition to the mold size, the melting voltage, current, slag type, and melting material (melting material) were changed to perform a melting experiment, and a thermocouple was inserted and immersed in the slag pool from above the mold. Then, the average temperature (slag bulk temperature) in the slag pool when the steady state was reached was measured. The measurement results of the slag bulk temperature obtained as described above are also shown in Table 1. For the 48.5 cm square mold listed in the column of mold diameter in the same table, the equivalent diameter is calculated by the equivalent diameter of the mold = (inner peripheral length of the mold cross section / π), and this is calculated as the mold diameter. did.

  Furthermore, the data obtained in the same table was arranged as a relationship between the value of (i / D), which is the ratio between the dissolution current value and the mold diameter, and the temperature T of the slag bulk, based on the above equation (4). . FIG. 3 is a diagram showing the relationship between the (melting current value / mold diameter) value and the slag bulk temperature in the ingot manufacturing method of the present invention.

From the results shown in the figure, it was found that the slag bulk temperature T (° C.) can be expressed by the regression equation represented by the following equation (2) using the value of (i / D) (kA / cm).
T = 1130 × (i / D) +1450 (2)

  As shown in the above equation (2), it can be seen that the temperature of the slag bulk in the steady state is almost determined by the dissolution current and the mold diameter, regardless of the type of slag and the type of dissolved material.

  However, the relationship of the above formula (4) is that the radiant heat flux from the free surface of the slag pool to the outside and the heat flux from the slag pool to the ingot are extremely small compared to the heat flux from the slag pool to the mold. It is assumed that the heat transfer coefficient is constant. However, when the mold diameter is small, the influence of the slag type on the heat transfer coefficient between the slag and the mold cannot be ignored. Therefore, the data can be organized as shown in FIG. 3 only when the mold diameter is 30 cm or more.

  On the other hand, as the mold diameter increases, the effect of heat dissipation due to radiant heat transfer from the free surface of the slag pool becomes so large that it cannot be ignored compared to cooling by heat transfer from the slag pool to the mold. Therefore, the data can be organized as shown in FIG. 3 within a range where the mold diameter is 150 cm or less.

  For the above reason, the relationship of the formula (2) can be applied only to the ingot manufacturing method by the ESR method in which the mold diameter is in the range of 30 to 150 cm.

3. ESR proper dissolution conditions Furthermore, as a result of changing the dissolution conditions of ESR in various ways using the formula (2) and conducting a dissolution test as described in the examples described later, the melting point of the dissolved material is TML (° C. When the temperature of the slag bulk is T (° C.), it is found that an ingot having a good surface property can be obtained by operating so as to satisfy the relationship of the following formula (1A).
TML ≦ T-150 (1A)

  The reason is as follows. That is, in the vicinity of the mold, the temperature of the molten slag is low, and a thin solidified shell peculiar to ESR melting, so-called slag skin, is formed so as to surround the slab surface. Compared to the fact that the molten metal itself is in direct contact with the low-temperature mold, the slag skin is sandwiched between the mold and the slag skin so that it can be cooled slowly. Rather, it is a characteristic that should be considered an advantage of the ESR method.

  However, if the amount of heat supplied becomes insufficient due to insufficient power input, the slag pool begins to solidify first in the vicinity of the mold, forming a thick solidified shell, and a metal pool is formed along the solidified shell. The Due to fluctuations in current and voltage, that is, fluctuations in heat input, the thickness of the solidified shell of the slag varies greatly in the longitudinal direction of the mold, and as a result, the surface of the ingot solidified along the solidified shell generates significant irregularities. Will be. In order to keep the surface of the ingot in good condition, the thinner the slag skin is, the more advantageous it is. For this purpose, a sufficient amount of heat is required to dissolve the melting material and the superheat of the slag bulk is as high as possible. is important.

  In the present invention, various dissolution tests were conducted, and as a result of investigation and analysis using the equation (2), it was found that it was necessary to ensure 150 ° C. or higher as the degree of superheat of the slag bulk. Of course, the temperature of the molten slag bulk needs to be higher than the melting point of the slag. Since the melting point of ordinary slag in the ESR method is in the range of 1200 to 1400 ° C., the temperature T of the slag bulk determined by the above (2) satisfies the condition that it is equal to or higher than the melting point of slag.

As described above, the thinner the slag skin, the more advantageous, but when the surface slag skin becomes extremely thin or no slag skin is formed at all, the surface properties of the ingot deteriorate, or This causes a trouble that the ingot cannot be removed from the mold. In order to avoid such a situation, the temperature T (° C.) of the slag bulk needs to satisfy the relationship of the following formula (1B).
T-150 ≦ 1750 (1B)

  For the reason described above, in order to produce an ingot having a good surface quality by the ESR method, the temperature T (° C.) of the slag bulk satisfies the relationship of the above formulas (1A) and (1B) at the same time. It is necessary to satisfy the relationship of equation (1).

  4). Preferred range of dissolution conditions, etc.

  In the ingot manufacturing method according to the ESR method of the present invention, the melting voltage is preferably in the range of 40 to 80V.

  If the melting voltage is less than 40V, the melting current drifts and only the center of the slag pool is easily heated. On the other hand, the slag in the vicinity of the mold is easily solidified, which causes deterioration of the cast skin property of the ingot. It is. On the other hand, when the melting voltage becomes higher than 80V, the depth of the slag pool becomes extremely deep, and in this case also, a short path to the mold wall that is a current drift occurs, and the input power is sufficient to heat the slag. There is a risk that it will no longer be used. As a result, even if the dissolution current value is the same, the slag pool temperature is likely to be extremely lowered.

  In the above description and the examples to be described later, ESR melting of carbon steel and stainless steel has been described as an object. However, the present invention uses a Ni-based alloy (Ni content: 40 to 90% by mass) as a melting material. The same effect as in the case of carbon steel and stainless steel can be obtained. The melting point of the Ni-based alloy is in the range of 1500 to 1250 ° C. depending on the type of alloy and is slightly lower than that of steel, but there is no significant difference from steel, and the same actions and effects as in the case of steel are exhibited. It is.

1. Test method
In order to confirm the effect of the ingot manufacturing method according to the ESR method of the present invention, the following tests were conducted and the results were evaluated.

  Using the ESR apparatus shown in FIG. 1 above, using a mold having a square cross section of 48.5 cm square (equivalent diameter: 61.7 cm) and a mold having a circular cross section having a mold diameter of 77.5 cm, A dissolution test was performed. Table 2 shows the melting voltage, the melting current, the mold diameter, the temperature of the slag bulk calculated by the formula (2), the melting material constituting the consumable electrode, the melting point of the melting material, the type of slag used, the formula (1) and ( 2) Satisfaction of the formula, and the degree of surface care as a scale for evaluating the surface properties of the obtained ingot were shown.

  As shown in the table, all the slag used had a melting point of less than 1400 ° C. In the table of satisfaction of the formulas (1) and (2) in the table, “◯” indicates that the relationship between the above formulas (1) and (2) is satisfied, and “×” indicates the same relationship. This means that you are not satisfied. Moreover, in the column of the surface maintenance degree, “A” indicates that the surface was not maintained, and “B” indicates that the surface cutting amount at the stage before rolling or forging of the ingot after casting was less than 2 mm. "C" represents that the same surface cutting amount was 2 mm or more.

2. Ingot manufacturing test results Test Nos. 1 to 9 are tests for the present invention examples that satisfy the conditions specified in the present invention, and Test Nos. 10 to 16 are comparative examples that do not satisfy the conditions specified in the present invention. This is a test.

  Test Nos. 1 to 5 are tests on examples of the present invention in which SUS304 steel was used as a melting material and melted with a square square mold having a cross-sectional shape of 48.5 cm square. Under these conditions, the temperature (T) of the slag bulk obtained by the above formula (2) is 150 ° C. or more higher than 1450 ° C. which is the melting point (liquidus temperature) of the dissolved material and 1900 ° C. or less, 1) The relationship of the formula is satisfied. As a result, the surface of the ingot was extremely smooth and could be supplied to the lower process without care.

  Test Nos. 6 to 9 are tests on examples of the present invention in which 1.3% C-10% Cr steel was used as a melting material and melted by a mold having a circular cross section having a mold diameter of 77.5 cm. The temperature (T) of the slag bulk calculated under these conditions is 150 ° C. or more higher than 1418 ° C., which is the melting point of the dissolved material, and 1900 ° C. or less, which satisfies the relationship of formula (1). Also in these tests, the surface of the ingot was extremely smooth and could be supplied to the lower process without requiring maintenance.

  On the other hand, test numbers 10 to 12 are tests on comparative examples in which SUS304 steel was melted by a square mold having a cross-sectional shape of 48.5 cm square, and compared with test numbers 1 to 3 and the like. This is a test in which As a result, although the temperature (T) of the slag bulk obtained by the equation (2) is higher than the melting point of the melting material, 1450 ° C., the difference is less than 150 ° C. and does not satisfy the relationship of the equation (1). . As a result, the surface of the ingot lost smoothness, and the surface properties deteriorated as the current value decreased. In particular, in Test No. 12 having a low current value, the surface cutting amount needs to be maintained at 2 mm or more.

  Test Nos. 13 to 16 are tests for comparative examples in which 1.3% C-10% Cr steel was used as a melting material and melted by a mold having a circular cross section having a mold diameter of 77.5 cm. This is a test in which the dissolution current value is lowered as compared with the above. As a result, the difference between the temperature (T) of the slag bulk and the melting point of the dissolved material is less than 150 ° C., which does not satisfy the relationship of the expression (1). The surface property of the ingot was inferior to that of the above-described example of the present invention, and deteriorated as the current value decreased. In particular, in Test Nos. 15 and 16 having a low current value, the surface cutting amount needs to be maintained at 2 mm or more.

  From the above examples, the excellent effect of the ingot manufacturing method by the electroslag remelting method according to the present invention was confirmed.

  According to the method for producing an ingot by the ESR method according to the present invention, according to the melting point of the melting material, the melting conditions are adjusted so as to satisfy the relationship represented by the above formulas (1) and (2), Since the remelting operation is performed while controlling the average temperature of the molten slag in the slag pool within an appropriate temperature range, a steel or Ni-based alloy ingot having good surface properties can be produced. Therefore, the method of the present invention is a method for producing an ingot having high practical value that can be widely used as a remelting and solidifying method that can easily produce a metal ingot having excellent surface properties for high-grade steel.

It is a figure which shows typically an example of the apparatus structure used in order to implement the manufacturing method of the ingot by the electroslag remelting method of this invention. It is a figure which shows the heat balance in the molten slag in the manufacturing method of the ingot by an electroslag remelting method. It is a figure which shows the relationship between the value of (melting electric current value / mold diameter) and the average temperature of the molten slag in a slag pool in the manufacturing method of the ingot of this invention.

Explanation of symbols

1: consumable electrode (melting material metal), 2: water-cooled mold, 3: slag pool (molten slag),
4: Metal pool, 5: Solid-liquid coexisting phase, 6: Solidified phase (metal ingot), 7: Cooling water,
8: Power supply device, 9: Electrical wiring, 10: Water-cooled surface plate

Claims (1)

When remelting steel or Ni-based alloy with electroslag, the melting point of the melting material is TML (° C.), the melting current value is i (kA), and the mold diameter is D (cm). 2) A method for producing an ingot by an electroslag remelting method, wherein the remelting operation is performed by adjusting the melting conditions so as to satisfy the relationship represented by the formula.
TML ≦ T−150 ≦ 1750 (1)
T = 1130 × (i / D) +1450 (2)

Images