JPH0573503B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] 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 dungeon, and the alloy is applied only to the core of the slab. The present invention relates to a method of manufacturing a cast composite steel material containing added components.

[Prior art] Composite steel materials, in which the surface layer and core portion of the steel material have different characteristics, are used as high value-added steel materials. There is a method of obtaining a coated steel ingot by placing a lump and injecting different molten steel around it and solidifying it.

Another method for obtaining a composite steel material in which the surface layer of a cast slab is made of steel with a certain composition and the core part is made of steel with a different composition is the core addition method in which alloying elements are added into the mold, for example, It is known from No. 14847 or Japanese Patent Application Laid-Open No. 53-43625. Further, JP-A-62-142053 discloses a method for producing sulfur free-cutting steel in which S is added to the core using an iron-coated S-filled wire.

[Problems to be solved by the invention] In the production of cast composite steel materials by the core addition method, it is necessary to adjust the thickness of the surface layer consisting of the same components as the molten steel components in the tundish to a predetermined range, and to add synthetic components to the core. Adding and adjusting the concentration to a predetermined range is extremely important in terms of steel properties.

In order to adjust the surface layer thickness and the core synthetic component concentration to predetermined ranges, in addition to the feeding speed of the iron-coated alloy wire that is continuously fed from above the mold into the unsolidified molten steel in the slab, the casting speed are closely related. In particular, since the casting speed fluctuates during casting depending on operating conditions such as casting temperature and continuous casting operation, it is necessary to control the wire feeding speed against fluctuations in the casting speed.

In addition, the wire that is continuously fed into the slab from above the mold melts due to heat transfer from the molten steel, but the outer periphery of the wire that is fed into the mold is melted by the bare metal due to the sensible heat of the wire. tends to coagulate and adhere. The thickness of this base metal adhered to the wire tends to be non-uniform in the longitudinal direction because there is some variation in the outer diameter and wall thickness due to the precision in manufacturing the wire. Therefore, during the melting process, the wire may be cut short in the longitudinal direction, settle in a crater, and be trapped inside the slab, and the alloy components may not diffuse sufficiently and become locally concentrated inside the slab. This is also an issue that needs to be resolved.

[Means for Solving the Problems] The present invention solves the above problems by controlling the feed rate of the iron-coated alloy wire. When the target solidified shell thickness is D (mm), the wire melting position L (m) from the meniscus
can be obtained from the solidification equation using equation (1).

L=(D/K) ² ·V _C ...(1) Here, k is the solidification coefficient (mm/min _-1/2 ), and V _C is the casting speed (m/min). On the other hand, if the wire feeding speed is V _W (m/min), the time T (min) for the wire fed into the mold to reach the melting position L is
(hereinafter referred to as dissolution time) is given by equation (2).

T=L/V _W ...(2) From equations (1) and (2), V _W = (D/K) ²・V _C /T...(3) In this way, the solidified shell thickness D is set to a predetermined value. It is known that in order to adjust the wire supply speed V _W to the range of , it is necessary to control the wire supply speed V W by the casting speed V _C and the wire melting time T.

According to the inventors' research, the melting time T of the iron-coated wire in molten steel is longer as the wire iron-coating becomes thicker when the melting point is similar to that of the molten steel, and it is necessary to set the iron-coating thickness appropriately. According to
The dissolution time T can be determined.

By substituting the melting time, solidification shell thickness, and solidification coefficient into equation (3), the wire feeding speed V _W for adjusting the surface layer thickness within a predetermined range is determined as shown in equation (4). Here, a and b are constants.

V _W =aV _C +b (4) Next, a method for adjusting the alloy component concentration in the core portion to a predetermined range will be described. The cross-sectional view of the unsolidified part in the solidified shell of the slab at the wire melting position is S (m ² ), the density of the molten steel is ρ _S , the target concentration of alloying components added to the core is ΔC (%), and the inner diameter of the wire R(m),
If the packing density of the alloy component in the wire is ρ _C and the addition yield of the alloy component is η (%), then the material balance of equation (5) holds true.

S + V _C ×ρ _S ×ΔC=πR ² ×ρ _C ×V _W ×η ...(5) By setting the slab size, alloying component addition target concentration, wire conditions, etc., and substituting them into equation (5), the core The wire feeding speed for adjusting the alloy component ratio within a predetermined range can be given by equation (4) as in the case of adjusting the surface layer thickness.

V _W =aV _C +b (4) Next, the reason why the wire feeding speed is changed when the casting speed is below a certain limit value e in the present invention will be explained below. As the casting speed decreases, the distance from the meniscus at which a given solidified shell is obtained decreases, and the wire melting location falls within the discharge jet circulation region from the submerged nozzle. In this region, since the molten steel flows in the meniscus direction, the alloy components added to the molten steel by melting the wire are also added to the surface layer of the slab, making it impossible to obtain the target composite steel material.

Therefore, in the present invention, as shown in FIG. 1, when the casting speed is less than this critical casting speed e, equations (6) and (7)
The wire feeding speed is controlled according to the formula. That is, V _W =cV _C +d, where f<V _C ≦e...(6) V _W =0, where 0≦V _C ≦f...(7) Here, c and d are constants and are 0. It is assumed that the relationships of ≦c<a and b<d are satisfied, and e and f are casting speeds and satisfy the relationship of 0<f<e. In this way, when the casting speed is below the limit value e, by controlling the wire feeding speed to be greater than the speed determined by equation (4),
The discharge jet from the immersion nozzle can be moved to a deeper position avoiding the circulation area, making it possible to manufacture the target composite steel structure. In this case, it is necessary to appropriately select the constants c and d so that the thickness of the surface layer and the concentration of alloy components in the core are adjusted within predetermined ranges.

If the casting speed decreases further and becomes 0≦V _C ≦f, no wire is supplied. That is, when the casting speed is lower than a certain limit value f in continuous casting of different steel types, etc.
This is to prevent any hindrance to the work of inserting the iron plate for preventing hot water from mixing into the mold. V _C =0 is also set when casting is stopped or completed. The constants a, b, c, and d are determined using the above equations (1) to (5) depending on operating conditions such as the machine type or steel type.

In addition, in order to promote the melting of the base metal that solidifies and adheres to the outer circumference of the wire and to ensure a uniform distribution of alloy components, the molten steel in the core of the slab is stirred by an electromagnetic stirring device installed in the secondary cooling zone. An effective method is to increase the heat transfer coefficient from the molten steel and to uniformly disperse the added alloy components using electromagnetic stirring flow.

[Example] Examples regarding continuous casting of sulfur free-cutting steel with a high core sulfur concentration will be described below.

0.10%C-0.02%Si-0.35%Mn- in 280T converter
Molten steel with a composition system of 0.030%P-0.015%S-0.012%Al is melted, and a billet with a cross-sectional size of 162mm x 162mm is cast using a curved continuous casting machine with a curvature radius of 12mR at a casting speed of V _C ≦2.5mm. It was cast in the range of . Install a wire supply guide above the mold, and use a wire feeder to continuously feed a difficult steel wire filled with powdered sulfur with an outer diameter of 6.5 mmφ and an iron coating thickness of 1.2 mm from between the mold and the immersion nozzle into the mold. At the same time, an electromagnetic stirring device installed 4.0 m from the meniscus
The unsolidified molten steel in the slab was cast while applying a horizontal rotation stirring flow of approximately 20 cm/sec.

In the example, the target thickness of the surface layer of the slab without sulfur added was set to 10 to 30 mm, the target value of the sulfur addition concentration in the core part was set to 0.1 to 0.5%, and the wire feeding speed was controlled by the method shown in Fig. 2. A sulfur free-cutting steel with a high sulfur concentration in the core was produced by casting. limit value
e1.0m/min, f is 0.5m/min, constant a is
11.0, b was 0, c was 3.7, and d was 7.3.

V _W =11.0V _C , however, 1.0＜V _C ……(8) V _W =3.7V _C +7.3, however, 0.5＜V _C ≦1.0 …(9) V _W =0, however, 0≦ V _C ≦0.5 ... (10) That is, when the casting speed is over 1.0 m/min, the wire supply speed V _W (m/min) is controlled by equation (8), and the casting speed is 1.0 m/min or less. If the speed exceeds m/min,
In order to adjust the wire melting position so that it does not enter the jet flow circulation area from the immersion nozzle (700 mm from the meniscus), the wire feeding speed equation was changed to equation (9), and the steel manufacturing speed for continuous casting of different steel types was changed. 0.5m/
Below min, wire supply was stopped.

FIG. 3 shows the measurement results of the surface layer thickness and the analysis results of the core sulfur concentration in a cross-sectional sample taken from the obtained free-cutting steel billet. By applying the present invention, a uniform core structure and component distribution were obtained without any remaining wire-adhered metal or localized concentration of sulfur. In addition, the surface layer thickness was adjusted to within the target 10 to 30 mm at all casting speeds, except for the part where the casting speed was lowered due to continuous casting of different steel types, and the core sulfur concentration was also adjusted.
It has been adjusted to a target range of 0.1 to 0.5%, which is fully satisfactory for sulfur free-cutting steel.

[Effects of the Invention] As explained above, according to the present invention, even if the casting speed varies, the thickness of the surface layer of the slab and the concentration of the alloy component in the core can be adjusted within a predetermined range. As a result, stable continuous casting of a composite steel material is possible even at the initial stage, end stage, continuous casting joint, and unsteady parts where the casting speed decreases due to other factors.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the method according to the present invention, Fig. 2 is a diagram showing an example, and Fig. 3 is a diagram showing measured values of the surface layer thickness and analysis values of the core sulfur concentration in the billet in the example. It is.

Claims (1)

[Claims] 1. In a method of manufacturing a cast composite steel material by continuously supplying an iron-coated alloy wire from above a mold into unsolidified molten steel in a slab and melting the wire, the wire feeding speed is
Casting speed V _C of the slab being cast V _W (m/min)
(m/min), the continuous casting method for core-added cast composite steel material is controlled based on the following speed classifications. When e<V _C , V _W =aV _C +b When f<V _C ≦e, V _W = cV _C +d When 0≦V _C ≦f, VW0 However, e: The wire melting position is immersed The critical casting speed (m/
min) f: limit casting speed (m/
min) a, b, c, and d are constants that satisfy the relationships 0≦c<a, b<d. 2. Stirring the molten steel in the slab core with an electromagnetic stirring device installed in the secondary cooling zone promotes the melting of the base metal that solidifies and adheres to the outer periphery of the wire, and also aims at uniform distribution of alloy components. The method according to claim 1.