JP4299719B2 - Manufacturing method and processed product of steel material with partially different components - Google Patents

Description

  The present invention relates to a method for producing a steel material having partially different components from a continuous cast slab of steel, and a processed product obtained using the method.

By producing two kinds of metals having different properties at the slab stage, a composite material having a combined function can be manufactured in a normal processing process. As a continuous casting method of a slab in which the slab surface layer and the inner layer have different components, for example, in continuous casting, a method of simultaneously casting two types of molten steel (Patent Document 1), and in a lubricant (Patent Document 2) discloses a method of mixing elements in Furthermore, in order to improve these conventional methods, the present inventors melted the surface layer of the slab by one or both of induction heating and plasma heating, and in the surface layer portion of the molten steel slab, A melt reforming method of adding an additive element or an alloy thereof is proposed in (Patent Document 3).
JP 63-108947 A Japanese Patent Application Laid-Open No. 07-26109 Japanese Patent Application No. 2002-367196

  However, in the method of simultaneously casting two types of molten steel as disclosed in (Patent Document 1), it is possible to obtain a multi-layer slab of various combinations. It is necessary to prepare a ladle for putting the molten steel, and two types of tundish and nozzles necessary for pouring the molten steel into the mold. . On the other hand, the method of mixing an element in a lubricant as disclosed in (Patent Document 2) solves the above-mentioned problem and can reduce the cost. There are problems such that the additional range is not stable and the amount is limited due to a lack of heat source.

Furthermore, the method of (Patent Document 3) surely solves the problems of the above (Patent Documents 1 and 2), but the techniques disclosed in these documents are all on one surface side of the material. Is intended to obtain a composite steel material of different components in the cross-sectional thickness direction, and does not provide a steel material that integrally includes metals with partially different properties, which are the object of the present invention. In the present invention, the “steel material having a partially different component” refers to a steel material that is not the entire surface of the steel material, but has a central part or an end part that is different from other parts and has a different material such as mechanical properties. . For example, a product in which the central portion of the steel material is high-tensile steel or the end portion is high-nitrogen ferritic stainless steel can be considered.
The present invention relates to a manufacturing method and a processed product thereof that can obtain a composite steel material having partially different components at low cost by selectively subjecting an arbitrary part of the surface layer of a continuous cast slab of steel to a melt reforming treatment. The purpose is to provide.

In order to solve the above-described problems, the present invention provides a method for producing a partially different steel material in which a part of a continuous cast slab of steel is melted using plasma heating, or both induction heating and plasma heating , A pure metal or an alloy is added to the molten part. Moreover, depending on the case, nitrogen gas can also be added to a fusion | melting part. Furthermore, the metal components in the pure metal or alloy to be added are carbon, silicon, manganese, phosphorus, sulfur, nickel, chromium, molybdenum, copper, gold, silver, boron, aluminum, magnesium, titanium, niobium, rare earth metal (REM) ), The non-metallic component in the alloy is preferably selected from any one or a combination of at least nitrogen. In the plasma heating, it is preferable that a pure metal or alloy is previously heated and melted and added in the plasma.
In addition, a processed product having partially different components according to the present invention is a product obtained by processing a steel material obtained by the method described above, and the surface layer or any part thereof is at least one of a pure metal , an alloy, and nitrogen. and wherein the or a component containing a.

  As described above, by using the manufacturing method of the present invention, it is possible to manufacture steel materials with different materials such as mechanical properties at low cost, and to utilize for various applications such as special automobile parts and machine parts. Can do.

In the present invention, as a method for welding an additive element or an alloy thereof to a part of a steel slab surface layer, the steel slab surface layer is melted using plasma heating, or both induction heating and plasma heating , and added thereto. It has been found that by adding an element or an alloy thereof, it is possible to reliably and inexpensively manufacture a composite steel material having partially different components. Details will be described below.

In the present invention, the slab surface layer portion to be partially modified is an arbitrary position of the slab, for example, a certain range of edge from the end of the slab, or a certain range of the center of the slab. For example, as shown in FIG. 1, it is selected according to the processed product to be finally used. In the slab 5 shown in FIG. 1 (a), the constant width and thickness portions on both sides of the slab central part are used as the addition part 9 of pure metal or alloy element. In the slab 5 shown in FIG. The fixed range and the thickness portion of the four corners of the slab are the pure metal or alloy element addition portion 9.
The thickness of the portion to be modified of the steel slab targeted in the present invention is not particularly specified, but is usually about 0.5 to 20 mm. This is because the surface is oxidized and lost in a normal heating / rolling process if it is less than 0.5 mm, and in the case of more than 20 mm, there is no particular requirement in the production of the intended composite steel material. The reason is that the melt processing cost increases in the melt processing by this process. In many cases, the slab is manufactured by continuous casting.

The present invention manufactures a composite steel material by welding an additive element or an alloy thereof to a part of the surface layer of the slab. The additive element or the alloy thereof will be described later. A method for melting a part will be described.
As a method of melting a part of the slab surface layer of the steel, it may be either flop plasma heating alone, the induction heating and plasma heating the combination.

In addition, when plasma heating alone is performed, an additive element or an alloy thereof is supplied into the plasma and supplied to a melted portion of the steel, so that it can be added to a partially melted portion of the slab surface layer. Since the plasma is generally axisymmetric, in order to continuously treat the surface of the slab, the plasma torch is scanned in the width direction of the slab, or the plasma disclosed in Japanese Patent Application Laid-Open No. 54-1421545 is used. A flat reciprocating method using electromagnetic force in the slab width direction can be used. In some cases, a plurality of plasma torches may be arranged over the entire width of the slab, and only the torch corresponding to the predetermined melting target portion of the slab may be operated.
The slab obtained by the continuous casting machine is transported to a melting treatment site after cutting, and the additive element or its alloy is supplied to the plasma to partially melt the slab surface layer with plasma, while the additive element or The alloy is supplied and welded by supplying it to the molten part of the steel. Then it is cooled again and solidifies.

In this method, the melting temperature of a part of the slab is set to the liquidus temperature (iron contains other components, so the melting state is not determined at one temperature such as the melting point, and the temperature at which solidification starts is set to the solid phase temperature. The temperature at which all the liquids become liquid is called the liquidus temperature (the same applies hereinafter), and the solidification structure can be made smaller by rapidly cooling and solidifying after the addition, thereby reducing the size of the crystal grains. By doing so, there is an advantage that the uniformity of the additive element in the melt-processed portion is increased, and defects such as cracks are less likely to occur during rolling.
In addition, when an additive element or an alloy thereof is added and welded to the molten part of the slab, it is preferable to prevent oxidation of the slab, so that the gas atmosphere in the chamber is an inert gas atmosphere 4 (for example, argon, nitrogen, etc.). Etc.), and in order to prevent the oxidation more reliably, it is preferable to melt and reform the inert gas atmosphere containing about 2% by mass of hydrogen .

Further, a case where induction heating and plasma heating are performed in combination will be described.
The slab that has been continuously cast by the continuous casting machine is cut and then transported to a melting processing place, and is arranged so as to selectively heat and melt a part of the slab 5 as a melting target portion as shown in FIG. Further, the additive element or its alloy 10 is supplied to the plasma 2 from the plasma torch 1 by being heated by the induction coil 3, and the additive element or its alloy is added and welded to the slab part melting portion. In addition to supplying the additive element or its alloy 10 to the plasma 2, it may be added by a normal supply method , that is, added to the partially melted portion of the slab in the form of a wire or a sheet . In the above case, an electromagnetic force acts on the melted portion due to the interaction between the magnetic field generated by the induction coil and the current induced in the slab, which is a conductor. This electromagnetic force has an action of compressing the melted portion called pinch force, and contributes to stabilization of the surface of the melted portion. Accordingly, the induction coil 3 creates a stable molten portion surface by pressing the molten portion toward the inner surface by electromagnetic force in the slab portion melting portion 7 by electromagnetic force, and then cooled and solidified again, and a stable element addition portion 9 is obtained. Form. For this reason, even if a fusion object part is a location including the edge part of a slab, a stable fusion part is obtained. The melting part 7 is gradually solidified by the movement 11 of the slab 5 to form a stable element addition part 9.

Thus, even when the above method is used in combination, the heat load on the slab melting target part can be made smaller than in the prior art, so the temperature of the melted part of the resulting partially modified slab is lower than the liquidus temperature. The solidification structure can be made smaller by keeping it at a slightly high temperature and rapidly cooling and solidifying after addition, and by reducing the size of the crystal grains, the uniformity of the additive element in the melt-treated part is increased, and also during rolling. There is an advantage that defects such as cracks are less likely to occur.
Further, when the additive element or its alloy 10 is added and welded to the slab surface layer melting portion, it is preferable to prevent the slab from being oxidized, so the gas atmosphere in the atmosphere gas container 6 is an inert gas as described above. The atmosphere 4 is preferable. Furthermore, the electromagnetic force due to the induction coil acts as described above.

In addition, as a component of the additive element, carbon, silicon, manganese, phosphorus, sulfur, nickel, chromium, molybdenum, copper, gold, silver, boron, aluminum, magnesium, as used to change the characteristics of steel Examples include titanium, niobium, and rare earth metal (REM). Further, the alloy of the additive element includes a compound of the additive element component and nitrogen or oxygen in addition to the alloy of a plurality of additive elements.
Also, in the present invention, nitrogen gas is blown into the molten part, which is a part of the slab at the time of melting and heating, so that the nitrogen component in that part is made higher than the other part, and a partially heterogeneous slab can be obtained. it can.

The additive elements will be described below.
Carbon: It works to increase the strength of steel. For example, by adding carbon only to the surface layer of an ultra-low carbon steel, it is possible to produce a steel sheet that is excellent in both strength by maintaining the workability with the internal steel and increasing the strength at the surface layer.
Nickel, chromium: has the effect of improving the corrosion resistance of steel. For example, the surface layer can be made of stainless steel by adding nickel and chromium to the surface layer of the low carbon steel.
Molybdenum: Adding molybdenum in addition to the above nickel and chromium has the effect of further improving the corrosion resistance.
Silicon, manganese: It has the effect | action which improves a strength especially with respect to an iron-type alloy.
Phosphorus: Adds to ultra-low carbon steel to increase strength.
Sulfur: Has the effect of enhancing the machinability of steel.
Copper: Workability and strength can be increased at the same time by adding nickel together with ultra-low carbon steel.
Gold: Can increase antibacterial properties.
Silver: Can improve antibacterial properties.
Boron: The hardenability of steel can be improved.
Aluminum: Corrosion resistance can be increased by adding to ordinary steel.
Magnesium, titanium, niobium, rare earth metal: When combined with oxygen and sulfur in the steel, producing fine oxides and sulfides to reduce the structure of the steel, and when used for welded materials such as steel pipes, In the heat-affected zone of welding, the structure becomes rough and the strength decreases, but this can be suppressed by a fine compound.

The alloy of the additive element is not particularly limited as long as it is a multi-component alloy of the additive element, but ferromanganese, ferronickel, ferroline, and other iron alloys are usually used.
Furthermore, with regard to the compound of the additive element component and nitrogen, for example, in ferritic stainless steel, there is a problem that the structure of the slab end is rough and the surface properties are poor, but these structures can be obtained by adding nitrogen, which is an austenite forming element. Can be reduced. That is, adding nitrogen such as iron nitride in the form of an alloy has the effect of reducing crystal grains, so that the surface roughness during rolling can be kept uniform and the surface shape of steel can be improved. In addition, the compound of the additive element component and oxygen has the effect of refining the structure by adding oxygen, such as magnesium oxide, in the form of an alloy. Reduction can be prevented.

In addition, as another form when both induction heating and plasma heating are used in combination, preheating the additive element or its alloy added to the slab surface layer part in the form of a wire or sheet in combination with the slab surface layer by induction heating, Thereafter, a method of melting the added pure metal or alloy by plasma heating may be used.
In this method, induction heating is simply used as a preheating function, and the additive element or its alloy is melted and alloyed by subsequent plasma heating. In general, the shape of the additive element or its alloy is powdery for heating and melting with plasma. However, this method is advantageous in that it can be carried out regardless of the shape of the additive element or its alloy.

The slab obtained by the above method has an advantage that it is a low-cost steel material, part of which has the characteristics of steel having different properties.
Therefore, the low-cost product which has the characteristic of the steel partially different in property about the processed product obtained by processing said partially modified composite steel material slab is obtained. Processed products include steel plates such as thin plates and thick plates, shaped steels, steel pipes, etc., but all steel products obtained by processing slabs in a normal steel process are targeted. Also included are semi-finished products such as hot rolled coils.

0.001% C-0.11% Mn-0.01Si having a width of 1500 mm, a thickness of 250 mm, and a length of 10 m using a method of melting and reforming by induction heating after cutting a slab that has been continuously cast. -0.007% P-0.009% S-0.045% Al-0.049% Ti (unit: mass%) The width 20mm of the continuous cast slab excluding both ends 50mm is melt-treated, carbon Carbon alloy addition was performed using a wire, and only the carbon component of the surface layer was 0.03% by mass.
The obtained slab was subjected to a cross-sectional analysis. As a result, the variation in the depth direction was plus or minus 1 mm, and the variation of the element components was within 3%. By processing this slab, a steel sheet for a thin plate having excellent workability as a whole, including an end portion having excellent fatigue strength only at the central portion and at the same time having poor workability, as shown in FIG. I was able to get it.

0.07% C-0.6% Mn-0.6Si having a width of 1200 mm, a thickness of 250 mm, and a length of 10 m using a method of melting and reforming by induction heating after cutting a slab that has been continuously cast. -0.03% P-0.005% S-16.5% Cr (unit: mass%) of the continuous casting slab of the width of both ends 50mm and the surface layer 10mm are melt-treated, the plasma gas is argon However, nitrogen was added instead of nitrogen, and only the nitrogen component of the surface layer was 0.07% by mass.
The obtained slab was subjected to cross-sectional analysis. As a result, the variation in the depth direction was plus or minus 1 mm, and the variation of the element components was within 5%. By processing this slab, a stainless steel plate for a thin plate having a good surface property at the end as shown in FIG. 1B could be obtained.

The perspective view which shows the example of the steel materials from which a component differs partially. The cross-sectional schematic diagram for demonstrating the method to manufacture the steel materials from which a component differs partially by electromagnetic induction heating. The cross-sectional schematic diagram for demonstrating the method to manufacture the steel materials from which a component differs partially by electromagnetic induction and plasma heating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Plasma torch 2 Plasma 3 Electromagnetic induction coil 4 Inert gas atmosphere 5 Cast piece 6 Atmosphere gas container 7 Melting part 8 Heating part 9 Element addition part 10 Element addition by alloys etc. 11 Movement 12 Magnetic flux

Claims (5)

A part of a continuous cast slab of steel is melted using plasma heating, or both induction heating and plasma heating , and a pure metal or an alloy is added to the melted part. Different steel manufacturing methods.   The metal component in the pure metal or alloy to be added is carbon, silicon, manganese, phosphorus, sulfur, nickel, chromium, molybdenum, copper, gold, silver, boron, aluminum, magnesium, titanium, niobium, rare earth metal (REM), The method for producing a steel material with partially different components according to claim 1, wherein the nonmetallic component in the alloy is at least one of nitrogen or a combination thereof. A part of a continuously cast slab of steel is melted using plasma heating or both induction heating and plasma heating , and nitrogen gas is added to the melted part, and the steel material is partially different in composition. Manufacturing method.   The method for producing a steel material having partially different components according to any one of claims 1 to 3, wherein a pure metal or an alloy is previously heated and melted and added in the plasma during plasma heating. A product obtained by processing the steel material obtained by the method according to claim 1, wherein an arbitrary part of the surface layer is a component containing at least one of a pure metal , an alloy, and nitrogen. Characterized processed product with partially different ingredients.

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