JPH0399751A - Manufacture of cast complex steel material - Google Patents

Abstract

PURPOSE:To enable manufacture of a complex material while regulating by controlling and specifying distance from molten metal surface in a mold to melting position of iron-coated alloy so as to satisfy the inequalities. CONSTITUTION:The melting position L of iron-coated wire shown with the distance from the molten metal surface is made to more than the specified value in the left side of the inequality so that added alloy is not mixed into surface layer part of a cast slab and controlled to specify the value less than the specified value in the right side of the inequality so that the iron-coated wire under unmelting condition is not allowed to remain in the mold. Wherein, L : distance (m) of the melting position of iron-coated alloy wire from the molten metal surface in the mold, LN : distance (mm) of discharging hole in a submerged nozzle from the molten metal surface in the mold, H : long side width (mm) in the mold, B : short side thickness (mm) in the mold, VC : casting velocity (m/min), K : coefficient of solidification (mm/min<1/2>), C1 : factor 1 - 1.5, C2 : factor 0.5 - 0.6.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention involves adding an iron-coated alloy wire into the mold, so that the surface layer of the slab is made of the same composition as the molten steel in the tundish.
The present invention relates to a method of manufacturing a cast composite steel material in which alloy components are contained only in the slab core.

BACKGROUND OF THE INVENTION Composite steel materials whose surface layer and core portion have different characteristics are used as high value-added steel materials, and there have recently been reports on their production by continuous casting. For example, ``Continuous casting method for clad steel round billets'' in Tetsu to Hagane J 72 (198B), 5885, or ``Continuous casting method for stainless steel hollow round billets'' in ``Materials and Processes'' 1 (198B), 5288. These are related to methods for manufacturing composite steel materials using the casting method.

As another method for manufacturing composite steel materials, a core addition method in which alloying elements are added into a mold is known. For example, Japanese Patent Publication No. 55-14847 describes a method for manufacturing enameled steel sheets in which an iron-coated titanium-filled wire is added to the core, and JP-A-82-142053 describes a method for manufacturing enameled steel sheets by adding an iron-coated sulfur-filled wire to the core. A method for manufacturing sulfur free-cutting steel is disclosed.

[Problems to be Solved by the Invention] In manufacturing cast composite steel materials using the additive method, a surface layer with a predetermined thickness is secured that is made of the same components as the molten steel in the tundish, and the core portion is further increased in composition within a predetermined range by alloying. The aim is to obtain a composite steel material in which the surface layer portion and the core portion have different components.

The problem with the above method is that, as shown in Figure 1, it is necessary to separate and maintain the pool of molten steel components forming the surface layer and the pool of molten steel components containing additive alloys forming the core within the continuous slab. Therefore, controlling the melting position of iron-coated alloy wire filled with alloy becomes an important technology.

The flow of molten steel in the mold is generally caused by the influence of the discharge flow from the discharge hole of the iron-coated alloy wire, and the upper circulating flow area in the upper part of the mold (section A in the figure) and the upward circulation flow in the lower part (section B in the figure). It is broadly divided into areas that have been sedated.

In order to secure the two pools with different molten steel compositions mentioned above, it is necessary to insert the iron-coated alloy wire at a position where the required surface layer thickness can be secured in part B and complete the melting. - is required.

However, from the above point of view, if you use a wire that is difficult to melt in order to melt it at a lower part of the mold (section C in the figure), the molten steel in the mold will solidify and adhere to the outer periphery of the wire and will not melt inside the slab. There is a problem that even if the wire remains, or even if the wire is melted, the alloy is not uniformly mixed and diffused, and the alloy locally becomes concentrated.

In the present invention, in manufacturing composite steel materials by continuous casting,
In addition to optimizing the method for controlling the melting position of iron-coated wire, we have also made it possible to stably manufacture composite materials using the core addition method.

Means for Solving the Problems The present invention solves the above-mentioned problems, and the means for controlling the melting position of the iron-coated wire will first be described below. When the target surface layer thickness of the composite material to be manufactured is Ls (m), the wire melting position L (+a) from the molten metal surface in the mold can be determined from the solidification equation using equation (1).

L= (Ls/K) 2・Vc −(1)
where -cK is the coagulation coefficient (m/l1in"), Vc
is the casting speed (m/min).

On the other hand, if the wire supply speed is Vw (m/min), the time T (win) for the wire supplied into the mold to reach the melting position (hereinafter referred to as melting time) is (
2) It is shown by the formula.

T=L/V
) From equations (1) and (2), equation (3) is obtained.

L-(Ls/K)" ・Vc=Vw ・T-
(3) In this way, if the target surface layer thickness Ls and casting speed VC are given, the position where the wire should be melted is determined, and this can be expressed by the wire feeding speed Vw and the wire melting time T. I can do it.

The inventors attempted to control the wire melting time by controlling the thickness t and diameter of a portion of the iron wire covering the alloy to be added. Of course, the wire is passing through the molten steel,
The molten steel goes through the processes of solidification, adhesion, and melting, and the melting time referred to here refers to the time when the iron coating finally melts and the alloying elements filled therein are discharged. In addition, here, we are focusing on the iron-coated part as the melting time because the alloy that is filled into the iron-coated wire is generally filled in the form of powder, so the presence of air spaces between the powders causes heat transfer resistance. This is largely due to the fact that heat transfer from molten steel is slower than in iron-coated parts.

As shown in Fig. 2, the inventor's investigation also found that the melting time was measured by keeping the molten steel temperature just above the melting point and by measuring the melting time when the molten steel and the iron coating of the wire had almost the same composition. The melting time is determined by the thickness t and diameter, and can be approximately expressed by the cross-sectional area of the iron coating as shown in FIG.

Based on the above, in order to clarify the factors that determine the melting time of iron-coated wire, and further clarify the relationship between these factors and the melting position in practical use, we conducted an actual composite material production.
We obtained the formula 4), which serves as an index for controlling the dissolution of iron-coated wire.

L=03・p5 *SIIVw −・・・・
・(4) Here, L is the melting position (■), ρs is the density of the wire coating part (kg/m2), Vw is the wire feeding speed (m#+in), and S is the cross-sectional area of the iron-covered wire (m
'), C3 is a coefficient of about 0.3 to 0.6.

S is the inner diameter D i (m) and outer diameter DO of the iron-coated wire
(m) can be found using the following formula.

S=π/4" (Do 2 D i2)"...
'・(5) (Equation 0 is an equation based on the idea that the melting position is controlled by the heat capacity of the wire that supplies it, and the coefficient varies somewhat depending on the molten steel temperature in the mold and the mold size, so it is within the above range. The wire feeding speed may be controlled by selecting the most appropriate coefficient among them.

Here, the cross-sectional shape of the iron-coated wire can be determined by treating the cross-sectional area S of the iron-coated wire in the same manner according to each shape, whether it is circular as described above, oval, square, or other shapes. ) may be applied.

The outline of the method for adjusting the melting position using iron-coated wire has been described above.

Next, a method for adjusting and supplying alloying elements to the core portion will be described.

The cross-sectional area of the molten steel in the solidified shell of the slab at the wire melting position is A (m2), and the density of the molten steel is pM (kg/m”
), the target concentration difference (increase) of alloy addition to the core part is △C(
%), the inner diameter of the wire is II (Peng), the packing density of the alloying element in the wire is pc (kg/rn”), the addition yield of the alloying element is η (%), the number of wires subjected to melting is N
If it is a tree, the material balance equation (6) can be found.

AxVcxpM×ΔC = π/4 ・D i2×pc XVw XηXN −
---・-(6) Here, the alloy addition amount Q supplied by the wire is Q= π/4* D i2×pc XVw
Since XN ・−・−(7), the operating factor of the iron-coated wire can be expressed as follows.

D + 2Vw = Q/(1)C・π/ 4・N)
-(8) From the above, the iron-covered wire condition that adds the desired amount of alloy Q to the core while satisfying the desired melting position L (surface layer Ls) satisfies equations (4) and (8). It can be obtained by combining the thickness, diameter, feeding speed, etc. of the iron-coated wire.

Using the above method, we have demonstrated the concept of a method for controlling the melting position of wire in the manufacture of composite materials using the core addition method.

The necessary melting position of the wire and the outline of the wire specifications can be determined by the method described above in manufacturing composite materials, but the melting position of the wire can be determined by taking into account the flow state of the molten steel in the mold, which is the problem mentioned above. The gist of the next invention is to define the conditions for determining sufficiency, and the details thereof will be described below.

When the wire is melted in part A in the mold shown in FIG. 1, mixing and diffusion of the additive alloy becomes a problem in manufacturing the composite material. Regarding this point, Fig. 4 shows the investigation results of the extra-mold circulation flow inside the mold through a water model test, and the larger the mold size, the deeper the mixing region inside the mold is.
Approximately the long side width of the mold based on the nozzle immersion depth (1~
2) Approximately 1 degree.

Therefore, in order to prevent mixing and diffusion of the additive alloy into the part A inside the mold, the melting position L(m) of the wire needs to be determined by the following formula.

L> (CIXH+LN)÷1000...
...(9) Here, H is the long side Ill of the mold size, 1(
11), LH is the immersion depth (am) of the nozzle, and C1 is a coefficient of about 1 to 1.5.

Furthermore, the inventors disclose a means for optimizing the flow in the mold by changing the discharge hole of the iron-coated alloy wire, that is, a means for relaxing the shallowest melting position constraint defined by equation (8).

(1) Swivel nozzle method By injecting the discharge hole of the iron-coated alloy wire at an angle to the inner wall surface of the mold as shown in Figure 5 (a), the kinetic energy of the discharge flow is prevented from reaching the lower part of the mold. This is a method of reducing the area A in FIG. 2 by suppressing the area. This method is particularly effective when the mold size is large.

(2) Straightening of iron-coated alloy wire 2 In addition to the conventional discharge hole facing the inner wall of the mold, Fig. 5(b)
By newly providing a discharge hole below the mold at the bottom of the iron-coated alloy wire, the former discharge hole supplies the amount of hot water needed to form the required surface layer thickness with as little kinetic energy as possible, and the latter discharge hole It is characterized by securing the amount of hot water for forming the core and the stirring energy for uniformly dispersing the added alloy. This method is particularly effective when the mold size is small.

The above describes the regulations regarding the required shallowest depth from the hot water surface for the melting position of iron-coated wire in the manufacture of composite materials, and methods for relaxing the constraints.

Next, we will discuss the maximum depth below the melting surface for the melting position of the iron-coated wire. The maximum depth limit is determined based on the problem of residual metal adhering to the iron-coated wire.
This is defined as the position at which the molten steel at the lower end of region B in FIG. 1 loses its heating degree ΔT (=molten steel temperature - melting point) and fluidity. This condition is approximately satisfied by the reduction in the temperature of the molten steel in the slab due to the heat removal due to the growth of the solidified shell relative to the heat capacity of the slab.

The second term on the left side of equation (10) is an equation that defines the solidification ratio within the slab, and the left side expresses the unsolidified ratio (%) within the slab. Based on real-temperature tests and other methods, we found that the conditions under which no metal remains attached to the iron-coated wire are found to be such that melting must be completed when the unsolidified rate of the slab at the molten steel position of the wire is 40 to 50% or more. be.

......(10) Here, K is the coagulation coefficient (m/min), L is the melting position of the iron-coated wire (m), and Vc is the casting speed (m/min).
, H is the long side width of the mold (mm), B is the short side thickness of the mold (m
m).

From the equation (10), the maximum depth L from the melting surface for the melting position is determined by the following equation.

4 To summarize the above, by specifying the shallowest depth from the hot water surface of the melting position of the iron-coated wire using equation (9), and specifying the critical maximum depth L using equation (11), it is possible to The melting position of the coated wire is C1 from 1 to 1.5 and C2 from 0.5 to
0.6 and is defined by equation (12).

(12) Function The present invention describes the control of the melting position of an iron-coated wire filled with an additional alloying element. The control range for the melting position has been clarified, and the second effect is to control the melting position within the above control range by using the dimensions and feeding speed of the iron-coated wire as control factors, and to adjust the melting position to the core as necessary. The goal is to clarify a method for supplying alloying elements.

Melting position control of iron-coated wire according to the present invention 5 O-R allows for the production of good composite materials.

Examples Examples of continuous casting of sulfur free-cutting steel having a high core sulfur concentration will be described below.

0.06%C10, 02%Si, 0.50%Mn in converter
, 0.025%P, 0.012%S, 0.015%M molten steel was melted using a curved continuous casting machine with a radius of curvature of 12m, and the cross-sectional size was 182mmX 1B2mm Nobi L/
−/to, using a 5-hole iron-coated alloy wire (having 4 horizontal holes and 1 vertical discharge hole), and casting speed ■e = 1
．． 8-2. It was cast in Om1 set.

A wire feed guide was installed above the mold, and casting was performed using a wire feeder to continuously feed the iron-coated wire filled with powdered sulfur into the mold from between the mold and the iron-coated alloy wire.

Two types of sulfur-filled wires were prepared to manufacture steel type A with a core sulfur concentration of 0.150 to 0.250%S and steel type B with a core sulfur concentration of 0.050 to o, too%S. 6
．． 5+u+φ, iron coating thickness 0.9m, external diameter 4.5+imφ for B#4 type, iron coating thickness 1. ompeng.

6. The target thickness of the surface layer of the slab without adding sulfur was 10 to 25 m for all steel types.

Table 1 shows the manufacturing conditions for the sulfur free-cutting steel mentioned above, the measurement results of the surface layer thickness in a cross-sectional sample taken from the obtained billet slab, the analysis results of the sulfur concentration in the core, and the residual metal content in the core. Observation results regarding the presence or absence of sulfur and the presence or absence of local concentration of sulfur are shown.

FIG. 6 shows the melting position of the wire calculated from the surface layer thickness after solidification with respect to the feeding speed of the iron-coated wire.

Here, a concrete application method of the present invention will be described in detail in correspondence with the two-legged embodiment. Here, as a basic condition, V C = 1.8 m for the slab size.
/min and solidification coefficient K = 24m5+/sin'h to ensure a surface layer thickness of 15 to 20mm, (1)
From the formula, the wire melting position is 0.7 to 1 from the mold surface.
．． It needs to be 25m deep.

On the other hand, in Equation (12), which defines the conditions for separating the two molten steel pools in the mold and the conditions for complete melting of the wire in order to produce a good composite material, the left side of Equation (12) specifies the nozzle immersion depth by 0.2. If it is Rin (0.3B~0.44)
m, and the right side is in the range of (1,28 to 1.80) m, and it is expected that the desired composite material will be obtained by controlling the melting position of the wire to the depth of 0.7 to 1.25 m described above. stand.

Next, the wire dimensions and wire supply speed that can supply the target concentration to the core portion while controlling the melting position as described above are determined. Now, if we try to increase the core part from 0.050%S to 0.200%S, the required sulfur is 0.42kg/mi.
By combining equation (8) for the mass balance with the density of sulfur as 2000 kg/rn' and equations (4) and (5) for controlling the melting position of the iron-coated wire, the outer diameter of the wire can be determined by the law of nature. = 8.5mmφ, iron coating thickness 0.9m1
1. Wire supply speed Vw = 10.7m/min
, the feeding rate of the iron coating part is 2.8 kg/in.

This feeding rate allows control to the melting position shown in FIG. 6, where the composite material can be stably produced.

A similar method can be applied to cases where casting conditions are different.

8 19 Effects of the Invention As explained in 2, according to the present invention, by adding iron-coated alloy wire into the mold, continuous casting of composite steel materials becomes possible, and composite steel materials conventionally cast by the ingot method can be cast. The effects on reducing manufacturing costs and stabilizing quality are extremely large.

[Brief explanation of drawings]

Figure 1 is a longitudinal cross-sectional view, Figure 2 is a diagram showing the relationship between iron coating thickness and wire melting time, Figure 3 is a diagram showing the relationship between iron coating cross-sectional area and wire melting time, and Figure 4 is a diagram showing the relationship between iron coating thickness and wire melting time. A diagram showing the investigation results of upward circulation flow, Figures 5(a) and (b) are explanatory diagrams of means for optimizing the flow in the mold, and Figure 6 is a diagram showing the wire feeding speed and melting position. . lφΦ, nozzle, 2...discharge port, 3, wire,
4... Surface layer part, 5... Core layer.

Claims (1)

[Claims] (1) In continuous casting of steel, molten steel supplied from a tundish forms the surface layer (rim layer) of the mother molten steel components, and further, by adding alloy to the unsolidified portion, In a cast composite steel manufacturing method that forms an interior (core layer) of different components from molten steel, the melting position L of the iron-coated wire expressed as the distance from the molten metal surface is determined by the following formula to prevent the additive alloy from mixing with the surface layer of the slab. A method for manufacturing a cast composite steel material, characterized by controlling the value to be equal to or higher than the specification on the left side of the equation, and below the specification on the right side of the equation below, such that the iron-coated wire is not unmelted and remains in the slab. (L_N+C1×H/1000)<L<Vc・(C2・
(H×B)/K・2(H×B))^2 where, L: Distance from the mold surface of the melting position of the iron-coated alloy wire (m) L_N: Molten surface of the discharge hole of the immersion nozzle Distance from (m)
m) H: Width of the long side of the mold (mm), B: Thickness of the short side of the mold (
mm) Vc: Casting speed (m/min), K: Solidification coefficient (
mm/min^1^/^2) C1: Coefficient (1 to 1.5)
, C2: Coefficient (0.5 to 0.6) (2) As a means for controlling the melting position of the iron-coated alloy wire within the range of claim (1), the melting position L is as shown in the following formula at the wire coating part. A method for manufacturing a cast composite steel material, characterized by an approximate control method in which the speed is proportional to the input weight speed. L=C3・ρs・S・Vw where, ρs: Density of wire coating part (kg/m^3), S: Cross-sectional area of wire coating part (m^2) =π/4・(Do^2- Di^2) Do: Outer diameter of coated wire (m), Di: Inner diameter of coated wire (m) Vw: Feeding speed of iron coated wire (m/min), C3
: Coefficient (0.3 to 0.6) (3) The following equation as a material balance equation to satisfy claims (1) and (2) and obtain the required alloy addition amount is one of the control conditions. A method for manufacturing a cast composite steel material, which is characterized by finally determining wire conditions and feeding conditions and arbitrarily selecting a desired core component. Di＾2Vw=(Q/N・π/4・ρc) Here, Di: Inner diameter of iron-coated wire (m) N: Number of wires Vw: Feeding speed of iron-coated wire (m/min) Q: Alloy addition Quantity (kg/min) ρc: Alloy packing density (kg/m^3) (4) Suppressing the upward circulation flow of molten steel in the mold and promoting uniform dispersion of the added alloy, and/or In order to obtain a composite steel material with a thin rim layer, the discharge hole of the immersion nozzle is inclined with respect to the inner wall surface of the mold (rotary flow utilization), or the discharge hole is provided at the bottom of the immersion nozzle and the discharge is directed downward (downward flow). Claims (1)-(
3) The method for manufacturing the cast composite steel material described above.