JPH0679421A - Horizontal continuous casting method for high alloy steel utilizing solidified analysis - Google Patents

Abstract

PURPOSE:To obtain a high alloy steel having high quality by executing highly precise solidification analysis in consideration of the solidified process of a cast billet draw out from a mold and stably casting the good cast billet having little generation of macro-segregation zone. CONSTITUTION:The molten steel 2 stored in a tundish 1 is drawn out as the cast billet by a drawing device through a mold 6 having a brake ring 4 and a water-cooled part 5 arranged in the opening at the lower part of the tundish 1. The molten steel temp., mold shape, tundish shape, brake ring shape and drawing speed are inputted as the conditions. By executing the highly precise solidification analysis in the consideration of the solidified process of the cast billet drawn from the mold, the surface shell forming process and the macro- segregation zone are estimated and the good cast billet having little development of the macro-segregation zone is stably cast. By this method, the optimum cast condition can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a horizontal continuous casting method, and in particular, an accurate solidification analysis is performed in consideration of the solidification process of a slab drawn out from a mold to stabilize a good slab with few macrosegregation zones. The present invention relates to a horizontal continuous casting method for high alloy steel utilizing solidification analysis for continuous casting.

[0002]

2. Description of the Related Art In recent years, in the field of continuous casting, instead of the conventional vertical or curved type continuous casting method, a molten metal (molten steel 2) is broken from a tundish (molten steel reservoir) 1 lower opening 3 shown in FIG. 4 is supplied to the mold 6 and cooled here to form a slab 8 which is solidified at least in the outer peripheral portion, and the slab 8 is continuously drawn by a drawing device 7 provided on the downstream side of the mold. It is becoming popular.

The mold 6 used in this horizontal continuous casting method is
The slab 8 is formed into a tubular body having the required cross-sectional shape and dimensions using a material having excellent thermal conductivity, and a cooling unit 5 is provided on the outer peripheral wall of the tubular body to cool the slab 8 in the hollow portion of the tubular body. Molten steel supplied 2
The amount of heat is taken by the cooling water to be cooled and solidified to form the slab 8.

This horizontal continuous casting method can reduce the size of the apparatus and can obtain a slab having a shape closer to that of a product, as compared with the vertical or curved continuous casting method, so that the processing cost after the casting step can be reduced. It is widely used for the production of considerable ferrous and non-ferrous alloys due to its high productivity such as low cost.

As a method of simulating horizontal continuous casting, Japanese Patent Laid-Open No. 62-282752 discloses a test piece mold having the same size according to the casting cross-sectional shape of cast iron, and after casting a cast iron container into the mold. The release time of the test mold that does not break out is determined, and under this condition, [Si (silicon) / C
(Carbon)] and the corner radius of the slab are changed, the mold is released, a model table is created from multiple test data, and the target component value in actual operation and the corner radius where chill does not occur based on the model table. There is a disclosure that estimates the value and obtains the optimum design value of cast iron.

[0006]

However, Japanese Patent Laid-Open No. 62-282752 discloses the optimum design value of cast iron by estimating the target component value of cast iron and the corner radius value where chill does not occur. It cannot be directly applied to high alloy steel.

In addition to this, there are many reports and disclosures about ordinary solidification analysis (for example, "Introduction to Computer Heat Transfer / Solidification Analysis (1985)" by Itsuo Ohnaka, and Japanese Patent Laid-Open No. 3-285737). However, in the horizontal continuous casting method, when the molten steel is drawn, the coordinate position of the molten steel portion moves in the drawing direction with time, and therefore the above general solidification analysis cannot be applied.

In a horizontal continuous casting method for high alloy steel, a massey solidification morphology is adopted due to a wide solid-liquid coexistence range during solidification, and when molten steel solidifies into a slab due to interdendritic flow of a concentrated liquid phase, A macrosegregation zone occurs on the surface of one piece. Then, a breakout easily occurs from this macrosegregation zone as a starting point, and stable operation is difficult. Further, in order to remove the macrosegregation zone after casting, the surface of the slab or the surface of the raw material after the slab has been rolled must be chamfered by a certain amount, which has been a cause of a decrease in yield.

According to the present invention, in the horizontal continuous casting method, the molten steel temperature, the mold shape, the tundish shape, the break ring shape and the drawing speed are input as conditions, and the solidification process of the slab drawn from the mold is taken into consideration with good accuracy. It is an object of the present invention to provide a horizontal continuous casting method for high alloy steel, in which a solidification analysis is performed to predict a skin formation process and a macrosegregation zone, and a good slab with less generation of the macrosegregation zone is stably cast.

[0010]

In order to solve the above-mentioned problems, a horizontal continuous casting method for high alloy steel utilizing solidification analysis of the present invention is a method for melting molten steel stored in a tundish to a lower opening of the tundish. (1) in a horizontal continuous casting method in which a mold having a break ring and a water-cooling part provided in
The molten steel, tundish, break ring, mold,
The water-cooled portion and the slab are expressed as a shape model divided into elements, (2) the physical property type of the element is input to the shape model, (3) the boundary condition of the shape model is input,
(4) With respect to the shape model, first the temperature field is calculated, then the solidification amount is calculated, and (5) the heat transfer and the mass transfer when the shape model is extracted are calculated, and (6) the break ring and the mold. The calculation of the movement of the alloying element into the void area is performed, and (7) the calculation is repeated from the above (4) to (6) until the temperature distribution of the shape model and the generation of the solidified layer reach a steady state, 8) The calculation is performed until the macrosegregation zone of the casting is minimized, and the molten steel temperature, the mold shape, the tundish shape, in which the macrosegregation zone is less generated,
It is characterized in that casting conditions such as break ring shape and drawing speed are obtained.

Further, the present invention will be described in detail with reference to FIGS. 1, 2, 3 and 4. FIG. 1 shows steps of a horizontal continuous casting method for high alloy steel utilizing solidification analysis of the present invention, FIG. 2 shows a flow chart of solute and heat transfer calculation for a bare region, and FIG. FIG. 4 is a schematic view of a horizontal continuous casting method, and FIG.
An enlarged view of the surroundings is shown.

In FIGS. 3 and 4, the molten steel 2 stored in the tundish 1 is passed through a mold 6 having a break ring 4 and a water cooling part 5 provided in a lower opening 3 of the tundish 1, and a drawing device 7 is provided. Each solidification analysis step will be described in detail based on horizontal continuous casting in which the slab 8 is pulled out by.

(1) Input of Shape Model First, the molten steel 2, the tundish 1, the break ring 4, the mold 6, the water cooling section 5 and the cast piece 8 are expressed as a shape model divided into elements.

(2) Input of physical property type of element Next, the physical property type of the element is input for the shape model.

(3) Input of Boundary Conditions Next, the boundary conditions of the elements of the shape model are input.

(4) Calculation of temperature field / solidification latent heat Next, the temperature field of the shape model is calculated.
Next, the latent heat of solidification is calculated.

(5) Calculation of Movement by Extraction Next, heat transfer and mass transfer when extracting the shape model will be calculated.

(6) Calculation of solute and heat transfer into the bare area In FIG. 4, a bare area 9 is generated between the break ring 4 and the bill 6 as the cast piece 8 is pulled out. Here, the solute and heat transfer calculation to this bare region 9 are performed. For the elements in the exposed area 9, the following equation 1 is used.
The liquid phase composition and the temperature are calculated according to Equation 3. And
Analyzing the solidification process of molten steel and predicting the formation of solidification layer and macrosegregation zone.

[0019]

F _l (i) = f _l (i) ^B + f ^l (m) where f ^l : liquid phase ratio f _l (i) ^B : previous liquid phase ratio of i element i: in calculation Element No m: Element having the largest liquid phase ratio among the surrounding elements The symbol in parentheses on the right side of the variable in Formula 1 represents the element No., for example, f _l (i) is the i element The value of f _l is shown.

[0020]

## EQU2 ## C _l (i) = {C _l (i) ^B × f _l (i) ^B + C _l (m) × f _l (m)} / f _l (i) where C _l : alloy composition f _l (i) ^B : previous liquid phase ratio of i element C _l (i) ^B : previous alloy composition of i element

[0021]

T _l (i) = {T _l (i) × f _l (i) ^B + T _l (m) × f _l (m)} / f _l (i) where C _l : alloy composition f _l (i) ^B : previous temperature of i element

As shown in the flow chart of solute and heat transfer calculation for the bare region in FIG. 2, the calculation is repeated until the liquid phase ratio of the element becomes 1.

Next, the movement calculation of the alloy element into the exposed region 9 between the break ring 4 and the mold 6 is performed.

(7) Calculation of Steady State Next, the above calculations (4) to (6) are repeated until the temperature distribution of the shape model and the generation of the solidified layer reach the steady state.

(8) Calculation until the macro segregation zone of the casting is minimized The above calculation is repeated until the macro segregation zone of the casting is minimized, and the molten steel temperature, mold shape, and tundish in which the macro segregation zone is less likely to occur Obtain casting conditions of shape, break ring shape and drawing speed.

By the steps (1) to (8) above,
The optimum conditions are determined by predicting the skin formation process and macrosegregation by performing solidification analysis by changing the molten steel temperature, mold shape, tundish shape, break ring shape, and drawing speed.

[0027]

EXAMPLES A horizontal continuous casting method for high alloy steel utilizing the solidification analysis of the present invention will be described below. In the horizontal continuous casting method shown in FIG. 1, the break ring 4 having three types of shapes (a), (b) and (c) shown in FIG. 5 was used. The high alloy steel used in the experiment is an alloy corresponding to SKH3, and its chemical composition is shown in Table 1.

[0028]

[Table 1] Chemical composition (% by weight) C Si Mn P S Cr Co W V Fe 0.82 0.30 0.30 0.01 0.01 4.0 5.0 18.2 1.05 Remainder

Next, with respect to the elements used in the analysis, Table 2 shows the thermophysical property types of the materials.

TABLE 2 Thermal Properties type thermal conductivity of the elements of the material specific heat density element material (W / m · K) ( J / kg · K) (g / cm 3) of molten steel and the cast slab SKH3 42 590 7.7 template copper mold 340 420 8.5 Break Link Boron Nitride 20 840 1.7 Tundish Refractory 3 840 2.8

Table 3 shows the heat transfer coefficient between the materials used in the analysis.

TABLE 3 Element between materials heat transfer coefficient that is heat transfer (W / m ² · K) slab-mold SKH3~ copper mold 20000 molten steel-break link Bu SKH3~ break links Bu 20000 molten steel-Thante Bu Isshu SKH3~ refractories 20000 Water cooling part ~ Mold water ~ Copper mold 40,000 Tundish ~ Atmosphere Refractory ~ Atmosphere 10

Table 4 shows other calculation conditions used in the analysis.

[Table 4] Calculation items Calculation conditions Drawing speed 3 m / min Size and shape of slab 100 mm diameter, cylinder Temperature of molten steel in tundish 1500 ° C Liquidus temperature 1450 ° C Solidus temperature 1300 ° C Latent heat of solidification 272000J / kg

5 to 7 show formation of a solidified layer when the break ring 4 is cast with three different shapes. Figure 5
In the case of the break ring 4a, the thickness of the solidified layer 9 is large, and the thickness of the solidified layer 9 decreases in the order of using the break ring 4b in FIG. 6 and the break ring 4c in FIG.

8 to 10 show the state of formation of the macrosegregation zone 10 when the three types of break rings 4 of FIGS. 5 to 7 are used. The macrosegregation zone 10 is represented as a region in which the C (carbon) concentration is increased by 50% or more from the initial composition (C: 0.82% in Table 1). In the case of the break ring 4a of FIG. 8, the length of the macro segregation zone 10 is large, and the macro segregation zone decreases in the order of using the break ring of 4b of FIG. 9 and 4c of FIG.

In the above examples, the shape of the break ring was changed to predict the formation of the solidified layer of the slab and the macrosegregation zone. Similarly, the shape of the break ring is not limited, and other elements are changed. Then, it is also possible to predict the solidification layer and macrosegregation zone of the slab.

[0035]

As described above, in the horizontal continuous casting method for high alloy steel, (1) the molten steel, the tundish,
The break ring, the mold, the water-cooled portion and the slab are expressed as a shape model divided into elements, (2) the physical property type of the element is input to the shape model, (3) the boundary condition of the shape model is input, and 4) For the shape model, first calculate the temperature field, then calculate the solidification amount,
(5) Calculation of heat transfer and mass transfer at the time of drawing out the shape model, (6) Calculation of transfer of alloying elements into the exposed region between the break ring and the mold, (7) Temperature of the shape model Repeat the above calculation from (4) to (6) until the distribution and the generation of solidified layer reach a steady state.
(8) Calculation is performed until the macrosegregation zone of the casting is minimized, and optimum casting conditions such as molten steel temperature, mold shape, tundish shape, break ring shape, and drawing speed with less generation of macrosegregation zone can be obtained. Because you can
It is possible to analyze the solidification process of slabs that could not be done conventionally, predict the skin formation process and macro segregation zone, and stably cast good slabs with few macro segregation zones, so high quality High alloy steel can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing steps of a horizontal continuous casting method for high alloy steel utilizing solidification analysis of the present invention.

FIG. 2 is a diagram showing a flow chart of solute and heat transfer calculation for an exposed region.

FIG. 3 is a sectional view of a main part of a horizontal continuous casting method.

FIG. 4 is a diagram showing an enlarged view around a mold.

FIG. 5 is a diagram showing a formation state of a solidified layer of a slab cast in the shape of a break ring 4a.

FIG. 6 is a diagram showing a formation state of a solidified layer of a slab cast in the shape of a break ring 4b.

FIG. 7 is a diagram showing a formation state of a solidified layer of a slab cast in the shape of a break ring 4c.

FIG. 8 is a diagram showing a formation state of a solidified layer of a macro segregation zone cast in the shape of a break ring 4a.

FIG. 9 is a view showing a formation state of a solidified layer of a macro segregation zone cast in the shape of a break ring 4b.

FIG. 10 is a view showing a formation state of a solidified layer of a macro segregation zone cast in the shape of a break ring 4c.

[Explanation of symbols]

1: Tundish, 2: Molten steel, 3: Opening,
4: Break ring, 5: Water cooling part, 6: Mold, 7:
Drawing device, 8: slab, 9: solidified layer, 10: macrosegregation zone

Claims (1)

[Claims] 1. A horizontal continuous casting method in which molten steel stored in a tundish is passed through a mold having a break ring and a water cooling part provided in a lower opening of the tundish, and a slab is drawn out by a drawing device. (1) The molten steel, the tundish, the break ring,
The mold, the water-cooled portion, and the slab are expressed as a shape model divided into elements, (2) the physical property type of the element is input to the shape model, (3) the boundary condition of the shape model is input, (4) the For the shape model, first calculate the temperature field, then calculate the solidification amount, (5) calculate the heat transfer and mass transfer when the shape model is pulled out, and (6) pull out between the break ring and the mold. The calculation of the movement of alloying elements into the region is performed. (7) The calculation is repeated from the above (4) to (6) until the temperature distribution of the shape model and the generation of the solidified layer are in a steady state. (8) Cast part The calculation is performed until the macro segregation zone is minimized, and the casting conditions such as molten steel temperature, mold shape, tundish shape, break ring shape, and drawing speed with less generation of macro segregation zone are obtained. Horizontal continuous casting method of high alloy steel by using coagulation analysis.