JP7608836B2 - Manufacturing method of stainless steel member and metal wire - Google Patents

Description

This disclosure relates to a method for manufacturing stainless steel members and metal wire rods.

A known method for manufacturing metal wire is the continuous casting and rolling method using a mold and a rolling mill (see Patent Document 1). In this method, molten metal (i.e., molten metal) stored in a tundish is sent into a mold, cooled into a rod shape, and then rolled by a rolling mill.

The amount of molten metal delivered from the tundish to the mold is adjusted by an adjustment pin located near the nozzle inside the tundish. The adjustment pin is generally made of stainless steel.

The adjustment pins are susceptible to melting due to contact with molten metal. Therefore, in order to prevent a decrease in product quality due to melting of the adjustment pins, stainless steel components with an oxide film on the surface of the base material have been developed (see Patent Document 2).

Patent No. 3552043 Japanese Unexamined Patent Publication No. 63-86826

In conventional stainless steel components, the oxide film formed on the surface of the base material can prevent the base material from dissolving, but there is a possibility that the oxide film may peel off. This can lead to a decrease in product quality due to the peeling of the oxide film and the resulting dissolution of the base material.

One aspect of the present disclosure aims to provide a stainless steel member that is highly resistant to melting damage.

One aspect of the present disclosure is a stainless steel member comprising a base material made of ferritic stainless steel containing, by mass%, Cr: 25% to 30%, Si: 0.25% to 2%, and the remainder being Fe and unavoidable impurities, a Si oxide film disposed on the surface of the base material, and a Cr oxide film disposed on the surface of the Si oxide film.

Another aspect of the present disclosure is a method for manufacturing metal wire comprising the steps of injecting molten metal into a tundish, delivering the molten metal from the tundish to a mold, cooling the molten metal injected into the mold to form a cast material, and rolling the cast material.

In the sending process, the amount of molten metal flowing out from the nozzle of the tundish is adjusted by an adjustment pin immersed in the molten metal in the tundish. The adjustment pin comprises a base material made of ferritic stainless steel containing, by mass%, Cr: 25% to 30%, Si: 0.25% to 2%, and the balance being Fe and unavoidable impurities, a Si oxide film disposed on the surface of the base material, and a Cr oxide film disposed on the surface of the Si oxide film.

FIG. 1 is a schematic diagram of a metal wire manufacturing apparatus according to an embodiment. FIG. 2 is a schematic diagram showing the configuration of the tundish of FIG. FIG. 3A is a schematic cross-sectional view of a stainless steel member constituting the adjustment pin of FIG. 2, and FIG. 3B is a photograph of the cross-section of the stainless steel member. FIG. 4 is a flow diagram of a method for manufacturing a metal wire rod according to an embodiment. FIG. 5 is a graph showing the relationship between immersion time and film thickness in the examples and comparative examples. FIG. 6 is a graph comparing the film thicknesses in the examples and the comparative examples. FIG. 7A is a schematic cross-sectional view of a stainless steel member in a comparative example, and FIG. 7B is a photograph of the cross-section of the stainless steel member.

Hereinafter, embodiments to which the present disclosure is applied will be described with reference to the drawings.
[1. First embodiment]
[1-1. Configuration]
The metal wire (i.e., wire rod) manufacturing apparatus 10 shown in FIG. 1 is a type of continuous casting and rolling machine (SCR).

The metal wire manufacturing apparatus 10 includes a melting furnace 20, a holding furnace 30, an addition section 40, a tundish 50, an adjustment pin 60 (see FIG. 2), a casting machine 70, a rolling machine 80, and a coiler 90.

<Melting furnace>
The melting furnace 20 heats and melts the metal that is the raw material of the metal wire. Examples of the metal that is the raw material of the metal wire include copper and aluminum.

The melting furnace 20 has a furnace body and a burner. The melting furnace 20 continuously produces molten metal (i.e., molten metal). The molten metal produced by the melting furnace 20 is transferred to the holding furnace 30 via the upper trough 25.

<Holding furnace>
The holding furnace 30 stores the molten metal produced by the melting furnace 20 at a predetermined temperature. A constant amount of the molten metal in the holding furnace 30 is transferred to the tundish 50 via a lower trough 35.

<Addition part>
The adding section 40 adds alloying components to the molten metal in the holding furnace 30. Examples of the alloying components include metal elements such as tin (Sn), titanium (Ti), magnesium (Mg), aluminum (Al), calcium (Ca), manganese (Mn), indium (In), and silver (Ag).

The addition unit 40 is, for example, configured with a device that throws a wire made of the alloy component to be added to the molten metal into the molten metal. The addition unit 40 may also add the alloy component to the molten metal in the lower trough 35.

<Tundish>
The tundish 50 is a storage tank for continuously supplying molten metal to the casting machine 70. As shown in Fig. 2, a nozzle 51 for delivering the molten metal M stored inside the tundish 50 to the casting machine 70 is provided on the bottom surface of the tundish 50.

<Adjustment pin>
As shown in FIG. 2 , the adjustment pin 60 is at least partially disposed within the tundish 50 and is immersed in the molten metal within the tundish 50 .

The adjustment pin 60 adjusts the amount of molten metal M flowing out of the nozzle 51 of the tundish 50 by moving in the axial direction. Specifically, the tip of the adjustment pin 60 arranged near the inlet 52 to the nozzle 51 changes the effective opening area of the inlet 52, thereby adjusting the amount of molten metal M flowing into the nozzle 51. The material of the adjustment pin 60 will be described later.

<Casting machine>
The casting machine 70 has a mold for casting molten metal and continuously forms rod-shaped casting material C.

The casting machine 70 in this embodiment is a known belt-wheel type casting machine having a wheel 71 and a belt 72. Note that a twin-belt type casting machine may also be used as the casting machine 70.

The wheel 71 has a groove on its outer circumferential surface. The belt 72 moves in a circular motion so as to contact a portion of the outer circumferential surface of the wheel 71. The wheel 71 and the belt 72 are each cooled, for example, by cold water.

The molten metal in the tundish 50 is injected from the nozzle 51 into the casting space between the groove of the wheel 71 and the belt 72. The molten metal injected into the casting space is cooled by the wheel 71 and the belt 72 and solidifies into a rod shape.

<Rolling mill>
The rolling machine 80 rolls the casting material C cast by the casting machine 70. A surface cleaning process such as removal of an oxide film is performed between the rolling machine 80 and the coiler 90, and a metal wire W having a predetermined outer diameter (e.g., 6 mm or more) is continuously formed.

<Koira>
The coiler 90 continuously winds the metal wire W.

<Adjustment pin material>
The adjustment pin 60 is composed of the stainless steel member 1 shown in Figures 3A and 3B. The stainless steel member 1 includes a base material 2, a Si oxide film 3, and a Cr oxide film 4. Note that Figures 3A and 3B show a cross section of the stainless steel member 1 (i.e., the adjustment pin 60) placed in molten metal M (e.g., molten copper).

(Base material)
The base material 2 is made of ferritic stainless steel containing, by mass%, Cr: 25% to 30%, Si: 0.25% to 2%, and the remainder being Fe and unavoidable impurities.

If the Cr content of the base material 2 is less than the lower limit, the growth of the Cr oxide film 4 may be insufficient. On the other hand, if the Cr content of the base material 2 is greater than the upper limit, the hardness of the base material 2 may be too high, resulting in insufficient impact resistance.

If the Si content of the base material 2 is less than the lower limit, the growth of the Cr oxide film 4 may be excessive. On the other hand, if the Si content of the base material 2 is greater than the upper limit, Si oxide may be easily generated inside the base material 2.

The entire surface of the base material 2, at least the portion that is immersed in the molten metal M, is covered with a protective oxide film including a Si oxide film 3 and a Cr oxide film 4, which will be described later.

(Protective oxide film)
The protective oxide film protects the base material 2 from the molten metal M and suppresses the base material 2 from being damaged by the molten metal M. The protective oxide film has a two-layer structure of a Si oxide film 3 and a Cr oxide film 4.

The Si oxide film 3 is a film whose main component is an oxide of silicon (Si) (e.g., SiO, _SiO2 (cristobalite, etc.)), with the remainder being unavoidable impurities. The "main component" refers to a component contained in the film in an amount of, for example, 85 mass% or more.

The "unavoidable impurities" contained in the Si oxide film 3 are, for example, chromium (Cr), manganese (Mn), iron (Fe), aluminum (Al), copper (Cu), etc. The content of silicon oxide contained in the Si oxide film 3 is, for example, 85 mass% or more.

The Si oxide film 3 is disposed on the surface of the base material 2. The Si oxide film 3 has the function of increasing the adhesion strength of the Cr oxide film 4 to the base material 2. The Si oxide film 3 also has the function of suppressing excessive growth of the Cr oxide film 4.

The Cr oxide film 4 is _a film mainly composed of chromium (Cr) oxide (e.g. _{, Cr2O3} , _CrO3 , _CrO2 , CrO, _{Cr3O4 , Cr5O12} , _Cr6O15 , etc.), with the remainder being unavoidable impurities. The content of chromium oxide contained in the Cr oxide film 4 is, for example, ₉₈ mass % or more.

The "unavoidable impurities" contained in the Cr oxide film 4 are, for example, manganese (Mn), iron (Fe), aluminum (Al), silicon (Si), copper (Cu), etc. The Cr oxide film 4 is disposed on the surface of the Si oxide film 3. When molten copper is used as the molten metal M, the stable presence of the Cr oxide film 4 in the molten copper adequately suppresses the melting damage of the base material 2.

Therefore, the adjustment pin 60 having the Cr oxide film 4 can be suitably used in the manufacture of copper wire. In the manufacturing process of copper wire, the temperature of the molten copper in the tundish 50 is, for example, 1083°C or higher and 1200°C or lower, and the oxygen concentration is, for example, 100 ppm or higher and 450 ppm or lower.

The Si oxide film 3 and the Cr oxide film 4 are formed by heat treating the base material 2. The heat treatment temperature is, for example, 700°C or higher and 1500°C or lower, and the heat treatment time is, for example, 0.5 hours (30 minutes) or higher and 10 hours or lower. By the heat treatment, the Si contained in the base material 2 reacts with external oxygen to form the Si oxide film 3, and the Cr contained in the base material 2 reacts with external oxygen to form the Cr oxide film 4. By performing the heat treatment for the above-mentioned heat treatment time, the formed Si oxide film 3 does not become too thin, and the Si oxide film 3 is less likely to peel off from the surface of the base material 2.

The thickness of the protective oxide film is, for example, 0.5 μm to 1 μm before the stainless steel member 1 is used (i.e., before the adjustment pin 60 is immersed in the molten metal M). The protective oxide film thickens as the stainless steel member 1 is used due to the growth of the Si oxide film 3 and the Cr oxide film 4 in the molten metal M. The Si oxide film 3 and the Cr oxide film 4 grow due to the reaction of the Si and Cr contained in the base material 2 with the oxygen in the molten metal.

<Metal Wire Manufacturing Method>
4 shows a flow of a metal wire manufacturing method using the metal wire manufacturing apparatus 10. The metal wire manufacturing method of the present embodiment includes a melting step S10, a pouring step S20, a sending step S30, a casting step S40, and a rolling step S50.

(Dissolving process)
In this process, metal as a raw material for the metal wire is melted in a melting furnace 20 to continuously produce molten metal.

(Injection process)
In this process, molten metal produced in the melting furnace 20 is continuously poured into the tundish 50 .

(Sending process)
In this process, molten metal is continuously delivered from the tundish 50 to a mold of a casting machine 70. In this process, the amount of molten metal flowing out from a nozzle 51 of the tundish 50 is adjusted by an adjustment pin 60 immersed in the molten metal in the tundish 50.

(Casting process)
In this process, the molten metal poured into the mold of the casting machine 70 is cooled to continuously form the casting material C.

(Rolling process)
In this process, the cast material C is rolled by a rolling mill 80. A surface cleaning process such as removal of an oxide film is performed between the rolling mill 80 and a coiler 90, so that a metal wire W having a predetermined outer diameter (for example, 6 mm or more) is continuously formed.

[1-2. Effects]
According to the embodiment described above in detail, the following effects can be obtained.
(1a) The base material 2 is protected by the Si oxide film 3 and the Cr oxide film 4, both of which have high melting points, and thus the base material 2 is prevented from being eroded. Furthermore, these oxide films grow due to the Si and Cr contained in the base material 2, and thus the resistance to erosion is maintained.

In addition, the Si oxide film 3 suppresses excessive growth of the Cr oxide film 4, which suppresses peeling of the Cr oxide film 4. As a result, a stainless steel member 1 (i.e., adjustment pin 60) with high resistance to melting damage caused by molten metal is obtained.

(1b) By using an adjustment pin 60 that is highly resistant to melting damage, it is possible to prevent components derived from the adjustment pin 60 (e.g., Fe-Cr oxides) from being mixed into the metal wire. This improves the quality of the metal wire.

2. Other embodiments
Although the embodiments of the present disclosure have been described above, it goes without saying that the present disclosure is not limited to the above-described embodiments and can take various forms.

(2a) The stainless steel member of the above embodiment can be used for parts other than adjustment pins used in metal wire manufacturing equipment. In addition, the stainless steel member of the above embodiment can be used in manufacturing equipment for metal products other than metal wire.

(2b) The function of one component in the above embodiments may be distributed among multiple components, or the functions of multiple components may be integrated into one component. In addition, part of the configuration of the above embodiments may be omitted. In addition, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments. All aspects included in the technical idea identified from the wording of the claims are embodiments of the present disclosure.

3. Examples
The following describes the content of the tests conducted to confirm the effects of the present disclosure and their evaluation.

Example 1
A base material composed of ferritic stainless steel containing 25% Cr and 1% Si, with the remainder being Fe and unavoidable impurities, was heat-treated at 900°C for 4 hours to form a Si oxide film (a film containing 85% _SiO2 by mass, with the remainder being unavoidable impurities (Al, Fe, Cr, Mn)) and a Cr oxide film (a _film containing 98% _Cr2O3 by mass, with the remainder being unavoidable impurities (Al, Fe, Si, Mn)).

Example 2
A base material composed of ferritic stainless steel containing 25% Cr and 2% Si, with the remainder being Fe and unavoidable impurities, was heat-treated at 900°C for 4 hours to form a Si oxide film (a film containing 85% _SiO2 by mass, with the remainder being unavoidable impurities (Al, Fe, Cr, Mn)) and a Cr oxide film (a _film containing 98% _Cr2O3 by mass, with the remainder being unavoidable impurities (Al, Fe, Si, Mn)).

Example 3
A base material composed of ferritic stainless steel containing 30% Cr and 1% Si, with the remainder being Fe and unavoidable impurities, was heat-treated at 900°C for 4 hours to form a Si oxide film (a film containing 85% _SiO2 by mass, with the remainder being unavoidable impurities (Al, Fe, Cr, Mn)) and a Cr oxide film (a _film containing 98% _Cr2O3 by mass, with the remainder being unavoidable impurities (Al, Fe, Si, Mn)).

Example 4
A base material composed of ferritic stainless steel containing 28% Cr and 2% Si, with the remainder being Fe and unavoidable impurities, was heat-treated at 900°C for 4 hours to form a Si oxide film (a film containing 85% _SiO2 by mass, with the remainder being unavoidable impurities (Al, Fe, Cr, Mn)) and a Cr oxide film (a _film containing 98% _Cr2O3 by mass, with the remainder being unavoidable impurities (Al, Fe, Si, Mn)).

Comparative Example
A base material made of ferritic stainless steel containing 25% Cr with the remainder being Fe and unavoidable impurities was heat treated at 900°C for 4 hours to form a Si oxide film (a film containing 85% _SiO2 by mass with the remainder being unavoidable impurities (Al, Fe, Cr, Mn)) and a Cr oxide film (a _film containing 98% _Cr2O3 by mass with the remainder being unavoidable impurities (Al, Fe, Si, Mn)). This base material contains Si as an unavoidable impurity resulting from the Fe-Cr alloy that is the material from which the base material is formed, but the content is less than 0.25%.

<Evaluation of oxide film growth>
The stainless steel members of Examples 1 to 3 and Comparative Example were each immersed in molten copper with an oxygen concentration of 300 ppm and at 1150°C, and the thickness of the protective oxide film was measured. The results are shown in Figures 5 and 6. Figure 5 is a graph showing the change in thickness of the protective oxide film over time, with the horizontal axis representing the square root of the immersion time T. The thickness of the protective oxide film when the immersion time T is 0 (zero) is the thickness of the stainless steel member before use (i.e., before the stainless steel member is immersed in molten copper). Figure 6 also shows the thickness of the protective oxide film after immersion for 30 minutes.

Figure 5 confirms that a protective oxide film grows in molten copper. Also, Figures 5 and 6 show that the comparative example, in which the Si content is less than 1%, has a greater increase in film thickness due to the growth of the Cr oxide film than Example 1-3. In contrast, in Example 1-3, the excessive growth of the Cr oxide film is suppressed by Si.

When the cross section of the stainless steel member 1 of Example 2 after immersion in molten copper for 180 minutes was observed, a layered Si oxide film 3 was formed on the surface of the base material 2, as shown in Figures 3A and 3B. On the other hand, when the cross section of the stainless steel member 101 of the comparative example after immersion in molten copper for 180 minutes was observed, a granular Si oxide film 103 was formed on the surface of the base material 102, as shown in Figures 7A and 7B.

From these results, it is inferred that in the comparative stainless steel member 101, the Cr oxide film 104 grew excessively as the Cr contained in the base material 102 passed through the granular Si oxide film 103.

On the other hand, in the stainless steel member 1 of Example 2, it is presumed that the layered Si oxide film 3 suppresses the diffusion of Cr contained in the base material 2, thereby suppressing the excessive growth of the Cr oxide film 4.

<Evaluation of Adhesion of Oxide Film>
The stainless steel member of Example 2 was immersed for 30 minutes in molten copper having an oxygen concentration of 300 ppm and at 1150° C. Thereafter, the stainless steel member was inserted and removed from the molten copper 100 times, and then the state of the protective oxide film was confirmed.

As a result, the Cr oxide film peeled off, but the Si oxide film remained on the surface of the base material. It is presumed that the Cr oxide film peeled off due to the contraction of the Si oxide film, which has a large thermal expansion coefficient, after the evaluation test. Therefore, it is presumed that both the Si oxide film and the Cr oxide film were in close contact with the base material during the evaluation test.

<Evaluation of resistance to corrosion>
The stainless steel member of Example 2 was immersed in molten copper at 1150° C. and an oxygen concentration of 300 ppm for 30 minutes. The stainless steel member was then inserted and removed from the molten copper 100 times, and rotated at 300 rpm in the molten copper for 30 minutes. The stainless steel member was then checked for melting damage. No melting damage was observed in the stainless steel member.

<Crack evaluation>
The stainless steel members of Example 4 and Comparative Example were each rotated at 200 rpm for 10 minutes in molten copper with an oxygen concentration of 300 ppm and at 1,150° C., and then the surfaces of the base materials were observed.

As a result, in the comparative example, multiple cracks occurred on the surface of the base material, and oxides were formed inside the cracks. These oxides were mainly silicon oxides, and chromium oxides were also formed in larger cracks.

The mechanism of Cr oxide formation in these cracks is presumed to be as follows: First, internal oxidation occurs in the base material, which generates Si oxide on the surface of the base material. As this Si oxide grows, a crack originating from the surface of the base material occurs. As this cracked area is further oxidized, Cr oxide is formed inside the crack.

On the other hand, no cracks were found in the base material of Example 4. It is presumed that in Example 4, the silicon oxide film suppresses the diffusion of oxygen in the base material, thereby suppressing the occurrence of cracks.

1...stainless steel member, 2...base material, 3...Si oxide film, 4...Cr oxide film,
10... Metal wire manufacturing apparatus, 20... Melting furnace, 25... Upper trough, 30... Holding furnace, 35... Lower trough,
40: Addition portion, 50: Tundish, 51: Nozzle, 52: Inlet port,
60: adjustment pin, 70: casting machine, 71: wheel, 72: belt, 80: rolling machine,
90...This guy.

Claims (3)

A base material made of ferritic stainless steel containing, by mass%, Cr: 25% to 30%, Si: 0.25% to 2%, and the balance being Fe and unavoidable impurities;
A silicon oxide film disposed on the surface of the base material;
a Cr oxide film disposed on a surface of the Si oxide film;
A stainless steel member , wherein the thickness of a protective oxide film containing the Si oxide film and the Cr oxide film is 0.5 μm or more and 1 μm or less . The stainless steel member according to claim 1,
A stainless steel member which is an adjustment pin that is immersed in the molten metal in a tundish and adjusts the amount of the molten metal flowing out of a nozzle of the tundish. pouring molten metal into the tundish;
discharging the molten metal from the tundish into a mold;
cooling the molten metal poured into the mold to form a casting;
rolling the cast material;
Equipped with
In the step of sending out, an amount of the molten metal flowing out from a nozzle of the tundish is adjusted by an adjustment pin immersed in the molten metal in the tundish;
The adjustment pin is
A base material made of ferritic stainless steel containing, by mass%, Cr: 25% to 30%, Si: 0.25% to 2%, and the balance being Fe and unavoidable impurities;
A silicon oxide film disposed on the surface of the base material;
a Cr oxide film disposed on a surface of the Si oxide film;
The method for producing a metal wire, wherein a thickness of the protective oxide film including the Si oxide film and the Cr oxide film is 0.5 μm or more and 1 μm or less .