JPH02235552A - Method for continuously casting cast compound steel material adding core - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention involves adding an iron-coated alloy wire into the mold, so that the surface layer of the slab has the same composition as the molten steel in the tundish, and only the core of the slab has the same composition as the molten steel in the tundish. The present invention relates to a method of manufacturing a cast composite steel material containing alloying 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 multi-layered 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 the slab is made of steel of a certain composition and the core part is made of steel of a different composition is as follows:
The core addition method of adding alloying elements into the mold is disclosed in, for example, Japanese Patent Publication No. 55-14847 or Japanese Patent Application Laid-Open No. 53-4:162.
Known by No. 5. Also, JP-A-62-1420
No. 5:l describes a method for producing sulfur free-cutting steel in which S is added to the core using an iron-coated S-filled wire.

[Problem to be solved by the invention: J problem] 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 component in the tundish to a predetermined range, and to Adding synthetic components and adjusting the concentration within 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 bare metal solidifies and adheres to the outer periphery of the wire that is fed into the mold due to the sensible heat of the wire. Easy to do. The deposited thickness of this base metal tends to be non-uniform in the longitudinal direction of the wire because there is some variation in the outer diameter and wall thickness due to the degree of manufacturing curvature of the wire. 'For this reason, 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 be sufficiently diffused and may be locally concentrated inside the slab. This is also an issue that needs to be resolved.

[! A Thousand Steps to Solve the Problem] The present invention solves the navigation problem by controlling the feed rate of iron-coated alloy wire. When the target solidification shell thickness is D (tnm), the wire melting position (+a) from the meniscus is calculated from the solidification formula (
1) It can be obtained using the formula.

L= (D/k)2-VC
-(1) where k is the coagulation coefficient (+++n/+in-
"'), Ve is the casting speed (III/ffiin). On the other hand, if the wire feeding speed is V, (m/min), the time T (+nin ) (hereinafter referred to as dissolution time) is (2
》It is given by the formula.

T=L/V, ...(2)
From <<1>> and equation (2), V, = (D/k)2・Vc/T −(3
) As described above, it is known that in order to adjust the solidified shell thickness D within a predetermined range, it is necessary to control the wire supply speed vw by the casting speed Vc and the wire melting time T.

According to the inventors' research, when the molten steel and the wire have similar melting points, the thicker the wire iron coating, the longer the melting time T of the iron coating wire in molten steel, and the thickness of the iron coating should be set appropriately. By doing so, the dissolution time T can be determined.

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

V, = a Vc+ b...
(4) Next, a method for adjusting the alloy component concentration in the core portion to a predetermined range will be described. The cross section of the unsolidified part of the solidified shell of the slab at the wire melting position is S (m')
, the density of the molten steel is ρ, the target concentration of alloy components added to the core is ΔC (t,), the inner diameter of the wire is R (m), the packing density of the alloy components in the wire is pc, the addition yield of the alloy components is η(
! k), the material balance of equation (5) holds true.

sxVcxp, xΔC == 7E R' X pcx
V, ×η − (5) Spindle size, alloy component addition! By setting the M concentration, wire conditions, etc. and substituting them into equation (5), the wire feeding speed for adjusting the core alloy component concentration within a predetermined range is the same as in the case of adjusting the surface layer thickness. It can be given by the formula. V= =aV e +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 becomes shorter, and the wire melting position falls within the circulation area of the discharge jet 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 the critical casting speed e, the wire feeding speed is controlled according to equations (6) and (7). That is, V,=cVc+d, however, f<VC≦e...(6) V,=O, itj, and 0≦ve
≦ f - (7) Here, c and d are constants satisfying the relationship 0≦c<a, bad, and e and f are casting speeds satisfying the relationship O<f<e. In this way, when the casting speed is less than the limit value e, by controlling the wire feeding speed to be greater than the speed determined by equation (4), it is possible to change the wire feeding speed to a deep position that avoids the circulation area of the discharge jet from the immersion nozzle. This makes it possible to manufacture the targeted covered steel material. 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 further decreases and becomes 0≦Vc≦f,
Do not supply wire. That is, when the casting speed is set below a certain limit value f in continuous casting of different steel types, etc., the purpose is to prevent interference with the work of inserting the iron plate for preventing molten metal from mixing into the mold. Vc is also set to 0 when casting is stopped or completed. Constants a, b, c, and d are determined using equations (1) to (5) above, depending on operating conditions such as 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 uniform distribution of the agglomerate components, the wire is heated by stirring the molten steel in the slab core with an electromagnetic stirring device installed in the secondary cooling zone. An effective method is to increase the coefficient of heat transfer from molten steel to the molten steel and to uniformly and disperse the added alloy components using electromagnetic stirring and flow.

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

0.0 with 280T converter. IO%; C - 0.02% S
i-0.3596Mn-0.030%P-0
．． 015t, S - 0.0124Ii Molten steel with A-cross composition system was melted and cast in a curved continuous casting machine with a curvature radius of 12ml.
A billet with a cross-sectional size of 162 am x 162 mm was cast at a casting speed of Vc≦2.5 m. Mold F
A wire feed guide is installed in the section, and a wire feeder is used to feed powdered sulfur-filled powder into the mold from between the mold and the immersion nozzle, with an outer diameter of 6.5 φ and an iron coating thickness of f. 2mm soft
Jl4 wire was continuously supplied, and at the same time, an electromagnetic stirrer installed at a position 460° from the meniscus was used to cast the unstruck solid solution steel in the slab while applying a horizontal rotation stirring flow of about 20 cm/sec.

In the example, the target value of the thickness of the surface layer of the slab without adding sulfur was set to 10 to 30 ffim, the target value of the sulfur addition concentration in the core part was set to 0.1 to 0.5 t, and the sulfur supply rate was set to the second value. Sulfur free-cutting steel with a high core sulfur concentration was produced by controlled casting using the method shown in the figure. The limit value e is I. On
+/min, f is 0.5m/min, constant a is 1
1.0, b was O, c was 3.7, and d was 7.3.

V. =11.0Vc, however, 1.0<VC -...(
8) V, = 3.7 V, +7J, however, 0.5<VC≦+. o −(!l)V
,=O, however, 0≦Vc≦0.5 -...(10
) That is, the casting speed is I. If it exceeds Om/min, the wire feeding speed V, (n/min) is controlled by equation (8),
Casting speed is 1.0m/oIin or less 0.5m/rBin
In the case of super high speed, in order to adjust the wire melting position so that it does not enter the discharge jet circulation area (700 mm from the meniscus) from the thinning nozzle, the wire feeding speed equation is changed to equation (9), and on the other hand, the wire feeding speed equation is changed to equation (9) Casting speed 0.5m/II
Below Iin, the 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. Due to the flow of the present invention, no residual metal attached to the wire or local concentration of sulfur was observed, and a uniform core structure and component distribution were obtained. In addition, the surface layer thickness was the target of 10 to 301 mm at any casting speed, except for the part where the casting speed was lowered due to continuous casting of different steel types.
The core sulfur concentration was also adjusted to within 0.1.
It was adjusted to the target range of ~0.5t, which is fully satisfied as a 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 in the initial stage, final stage, continuous casting fiber mesh area, and unsteady parts where the casting speed decreases due to other factors.

[Brief Description of the Drawings] Figure 1 is a diagram showing the method of the present invention, i21J is a diagram showing an example, and Figure 3 is a diagram showing the measured values of the surface layer thickness and the core sulfur concentration of the billet in the example. It is a figure showing an analysis value.

Claims (1)

[Claims] 1. In a method of producing a cast composite steel material by continuously supplying and melting an iron-coated alloy wire into unsolidified molten steel in a slab from above a mold, the wire supply speed V_w (m/min )
A continuous casting method for core-added cast composite steel material, characterized in that control is performed based on the following speed classifications in relation to the casting speed V_c (m/min) of the slab to be cast. If e<V_c, V_w=aV_c+bf<V_
If c≦e, V_w=cV_c+d0≦V_c≦
If f, V_w=0 However, e: Limit casting speed (m/min) where the wire melting position falls within the discharge jet circulation area from the immersion nozzle f: Limit casting speed (m/min) that is lower than e , 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 stirrer 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.