JP2012157881A - Erosion-resistant cast, method for manufacturing the same and molten metal contacting member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an erosion-resistant cast which has an erosion resistance extremely more excellent than a conventional one and a molten metal contacting member composed of the cast, and further to provide a method for manufacturing the erosion-resistant cast capable of stably obtaining the erosion-resistant cast excellent in equipment cost or running cost and excellent in the erosion resistance.SOLUTION: The erosion-resistant cast includes a matrix metal layer having a predetermined composition and an oxide layer formed at the surface of the matrix metal layer. A part of the oxide layer is extended in the shape of cilia at the crystal grain boundary of the matrix metal.

Description

  The present invention relates to a melt resistant casting having an oxide layer having a melt resistant property on the surface of a cast product, a manufacturing method thereof, and a molten metal contact member made of the cast.

  In recent years, aluminum and aluminum alloys are lightweight and excellent in workability, corrosion resistance, and mechanical properties, and thus are widely used in household goods such as aircraft, railway vehicles, automobile parts, and sashes. Aluminum can be formed by various methods, and a casting method using molten aluminum is widely adopted.

Conventionally, the member in contact with the molten aluminum is made of cast iron. However, since the melting point of aluminum is as high as 660 ° C., the member is always exposed to a temperature of about 600 to 700 ° C., deteriorates quickly, reacts with aluminum and partially disappears, so-called melting damage. Had.
In order to solve such problems, structural members such as melting pots and the like that are required to have high resistance to melting are generally subjected to surface treatment for improving resistance to melting. Yes.
Common surface treatments for improving the resistance to melting of steel materials include nitriding treatment for forming a nitride layer and oxidation treatment for forming an oxide layer.

  In the nitriding treatment, a steel layer is heated to about 500 ° C. in an oven and ammonia gas is supplied to form a nitride layer on the surface. The surface layer of the nitride layer is so-called white that mainly contains iron nitride (Fe—N). It is called a layer and is not preferable because it is brittle and easily peeled off. It has also been proposed to form a nitrogen diffusion layer by supplying ammonia gas and hydrogen gas so as not to form iron nitride so that nitrogen element penetrates and dissolves in the steel material, and this nitrogen diffusion layer is brittle. However, although the improvement is recognized, the melt resistance is not satisfactory.

  Although it is one oxidation treatment, an oxide layer can be formed on the surface by heating the steel material in a furnace. There is a problem that it is easily peeled off from the metal.

  Therefore, Patent Document 1 discloses that a nitrogen diffusion layer is formed on the surface by supplying ammonia gas and hydrogen gas by heating general SKD61 (JIS standard) as a casting mold material to about 500 ° C. in a furnace. Subsequently, an oxygen layer containing only iron oxide is formed on the nitrogen diffusion layer by supplying oxygen gas and hydrogen gas into the furnace, thereby forming a composite layer structure on the surface of the cast product. A mold member is disclosed.

  According to the technique disclosed in Patent Document 1, the outermost oxide layer exhibits resistance to melting with respect to aluminum, and the nitrogen diffusion layer located in the lower layer suppresses deformation of the base metal due to thermal stress. This serves to prevent the oxide layer from peeling off.

  However, in the technique of Patent Document 1, it is necessary to provide a dedicated heat treatment furnace capable of supplying ammonia gas, hydrogen gas, and oxygen gas in order to stack an oxide layer made of only a nitrogen diffusion layer and iron oxide. Moreover, since it is necessary to continue supplying various gases during the heat treatment, the running cost increases.

  In addition, the bond between the nitrogen diffusion layer and the oxide layer composed only of iron oxide has a higher strength than the bond between the coating layer of the dissimilar material and the base metal by the PVD method, but the interface changes in physical characteristics. Since there is a possibility that iron nitride called a white layer may be formed at this interface, there is a problem that peeling may occur therefrom.

JP-A-2004-237301

  The present invention solves the above-mentioned problems of the prior art, and has a melt resistance that is extremely superior to that of the prior art, a method for producing a melt resistance casting that is superior in equipment cost and running cost, and further from the casting. An object of the present invention is to provide a molten metal contact member.

  The composition (wt%) of the melt-resistant casting of the present invention has a composition of 0.40 to 0.70% for C, 0.35 to 0.50% for Si, 0.50 to 0.70% for Mn, and P <0.00. 03%, S <0.02%, Cr 4.50 to 6.00%, Mo 0.50 to 0.75%, Co 0.70 to 0.90%, V 0.15 to 0.30%, W 0.50 to 0.70%, Nb <0.10%, Al <0.10%, the balance being formed on the base metal layer made of Fe and inevitable impurity elements, and on the surface of the base metal layer And a part of the oxide layer extends to the crystal grain boundary of the base metal.

  The ciliated oxide that constitutes the oxide layer extends to the crystal grain boundary of the base metal layer, so to speak, it appears to be rooted in the earth, so the oxide layer and the base metal The bond with the layer is very strong. Therefore, the melt-resistant casting of the present invention has a drastic resistance to melt damage because the oxide layer having a very high resistance to melt is held very firmly on the base metal layer by the cilia-like oxide. Will be improved.

Moreover, the manufacturing method of the erosion resistant casting of the present invention has a composition (% by weight) of C 0.40 to 0.70%, Si 0.35 to 0.50%, Mn 0.50 to 0.70%. , P <0.03%, S <0.02%, Cr 4.50 to 6.00%, Mo 0.50 to 0.75%, Co 0.70 to 0.90%, V 0.15 0.30%, W 0.50 to 0.70%, Nb <0.10%, Al <0.10%, the balance being Fe and unavoidable impurity elements, 780-980 ° C. in the furnace Heating and maintaining the temperature,
Slowly cooling the heated metal member in a furnace at a rate of temperature decrease of 30 ± 10 ° C./hour;
including.

  By this method, an oxide layer extending in a cilia shape can be stably formed at the crystal grain boundary of the base metal layer.

  Moreover, the molten metal contact member of the present invention is made of the above-mentioned melt resistant casting. The melt resistant casting of the present invention is extremely excellent in melt resistance compared to conventional castings, and therefore can be suitably used as a molten metal contact member that contacts a molten metal of aluminum or magnesium.

  According to the present invention, it is possible to provide a melt-resistant casting having extremely excellent melt resistance, and it is possible to provide a molten metal contact member made of the cast. In addition, according to the method for producing a melt-resistant casting according to the present invention, it is excellent in equipment cost and running cost, and includes an oxide layer partially including ciliary oxide extending to the crystal grain boundary of the base metal layer. It is possible to stably obtain a melt-resistant casting having excellent melt resistance.

It is a partial cross-sectional microscope picture of the melt-resistant casting of this invention. (A) is 100 times magnification, (b) is 200 times magnification, and (c) is 500 times magnification. It is temperature conditions in the process of forming the melt resistant coating layer formed on the surface of the base metal of the melt resistant cast of the present invention. It is the cross-sectional microscope picture (magnification 1500 times) which expanded the part of the cilia-like oxide among the corrosion-resistant oxide layers formed in the surface of the base metal layer of the melt-resistant casting of this invention. It is a photograph which shows the result of the erosion test in the fusion-resistant casting (Example 1) of this invention, and the conventional mold steel (comparative example 1). (A) is before immersion, and (b) is after immersion. 4 is a partial cross-sectional photomicrograph of an immersion test piece of Comparative Example 1. (A) is 100 times magnification, (b) is 200 times magnification, and (c) is 400 times magnification. 3 is a partial cross-sectional photomicrograph (magnification 100 times) of a test piece for immersion in Comparative Example 2. 6 is a partial cross-sectional photomicrograph (magnification 100 times) of a test piece for immersion in Comparative Example 3. 6 is a partial cross-sectional photomicrograph (magnification 100 times) of a test piece for immersion in Comparative Example 4. 6 is a partial cross-sectional photomicrograph (magnification 100 times) of a test piece for immersion in Comparative Example 5. 6 is a partial cross-sectional photomicrograph (magnification 100 times) of a test piece for immersion in Comparative Example 6. 10 is a partial cross-sectional photomicrograph (magnification 100 times) of a test piece for immersion in Comparative Example 7. 10 is a partial cross-sectional photomicrograph (magnification 100 times) of a test piece for immersion in Comparative Example 8.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

  A cross-sectional photomicrograph of the melt resistant casting of the present embodiment is shown in FIG. FIG. 1 (a) shows a partial cross-sectional photomicrograph of a melt resistant casting (magnification 100 times), and FIG. 1 (b) is a partially enlarged photograph of a portion surrounded by a circle in FIG. 1 (a). One region 22 is shown enlarged (200 × magnification). FIG. 1C is a partially enlarged photograph of a portion surrounded by a circle in FIG. 1B, and further enlarges the first region 22 (magnification 500 times).

  As shown in the cross-sectional view (cross-sectional micrograph) of FIG. 1A, the melt-resistant casting 1 in this embodiment includes a base metal layer 10 and an oxide layer 20 formed on the surface of the base metal layer 10. And comprising. The base metal layer 10 includes a ferrite region 12 whose crystal structure is a ferrite structure on the surface layer side, and a pearlite region 14 whose crystal structure is a pearlite structure below (inside) the ferrite region 12.

  The base metal layer 10 is made of an alloy in which tungsten and cobalt are added based on SKD61, which is a general alloy tool steel as a material for a hot mold. The composition is as shown in Table 1.

  According to said composition, it is suitable not only for formation of the oxide layer 20 provided with the cilia-like oxide 22a which bears melt-resistance, but also has the mechanical strength inherent to SKD61. If the base metal is an alloy obtained by adding tungsten and cobalt to SKD61, the second region and the first region can be formed stably.

  The oxide layer 20 has a ciliary oxide 22a as a part thereof, as shown in the partial enlarged cross-sectional views shown in FIGS. 1B and 1C. It extends ciliately at the grain boundaries 16). FIG. 3 is a cross-sectional photomicrograph (magnification 1500 times) of the ciliary oxide 22a formed in another location. According to this, the ciliary oxide 22a is in the ferrite crystal grain boundary 16 like a plant root. You can check the state of intrusion.

  Since the cilia-like oxide 22a extends to the ferrite crystal grain boundary 16 in this way, the oxide layer 20 having excellent resistance to melting damage is firmly bonded to the base metal layer 10 and peeling is suppressed. Accordingly, the melt resistance is dramatically improved and the deterioration of the characteristics is suppressed.

  According to FIG. 1, the oxide layer 20 is composed of a first region 22, a second region 24, and a third region 26. Due to the difference in composition, the oxide layer 20 is conveniently divided into three regions, but these three regions are mainly composed of oxides, and between these three regions, in particular, the first region 22 and the second region. 24, it can be said that there is no physical interface in the optical micrograph. Therefore, there is no separation between these regions, and in particular, the second region 24 does not separate from the first region 22. When a qualitative analysis is performed using an electron beam microanalyzer (EPMA) or the like, the presence of an interface due to a difference in composition can be confirmed. In FIG. 1A, the interface is displayed for convenience based on the analysis result of EPMA. The first region 22 has a ciliary oxide 22a, which extends to the ferrite crystal grain boundary 16 of the base metal 10, and exhibits an anchor effect. Therefore, the oxide layer 20 and the base metal layer 10 are bonded very firmly, and the melt resistant casting of the present embodiment is excellent in melt resistance.

The melt-resistant casting 1 according to this embodiment can be manufactured as follows.
First, a base metal having the above composition is cast into a predetermined shape to obtain a metal member, and then the oxide layer 20 is formed.

  The step of forming the oxide layer 20 includes a first step of heating and holding a metal member composed of a base metal to a predetermined temperature in a furnace in a normal atmosphere, and a step in the furnace while controlling the temperature drop rate. It consists of a second step of gradual cooling, and the temperature rise-hold-temperature drop conditions are as shown in FIG. The heat treatment furnace used is a general annealing furnace and does not require any special atmosphere control.

  The metal member is heated to 780 to 980 ° C. over 2 hours and held at that temperature for a predetermined time. The temperature range maintained after the temperature rise is 780 to 980 ° C., but more preferably 900 ± 30 ° C. The holding time is adjusted according to the thickness of the metal member made of the base metal. For example, the holding time can be defined as 1 hour with respect to the thickness of the member being 25 mm.

This temperature rise / holding corresponds to the first step of the present embodiment, and an oxide layer is formed and grown on the surface layer portion of the base metal layer 10 and a decarburized layer (ferrite trim) is formed, and free carbon elements are formed. Is considered to react with the constituent elements of the base metal layer 10 to form the double carbide 28. A large amount of double carbide is distributed in the first region 22 on the base metal layer 10 side, and a third region 26 in which the double carbide 28 hardly exists is formed on the second region 24. Therefore, the third region 26 is more excellent in resistance to melting damage.
Subsequently, the base metal is cooled at a predetermined temperature decrease rate, and the temperature decrease rate maintains a range of 30 ± 10 ° C. per hour.

This temperature drop corresponds to the second step of the present invention, and the crystal structure of the surface layer side of the base metal layer 10 changes from pearlite to ferrite. Then, the oxide that continues to grow from the previous step extends into the ferrite crystal grain boundary 16 in a cilia-like manner. The ciliary oxide 22a that is a part of the first region 22 bonds the oxide layer 20 and the base metal layer 10 very firmly.
The first region 22 which is the greatest feature of the present invention is formed for the first time by maintaining the temperature drop rate within the above-mentioned range, and therefore it is necessary to strictly control the temperature drop.
Through such steps, the oxide layer 20 having excellent resistance to melting damage is formed on the surface of the base metal layer 10.

According to the manufacturing method of the erosion resistant casting of the present embodiment, the process can be performed in the same furnace, and it is not necessary to provide a dedicated heat treatment furnace capable of supplying various gases, thereby reducing the equipment cost. be able to. Furthermore, it is not necessary to continue supplying various gases during the heat treatment, and the running cost in manufacturing can be reduced.
Although the details of the formation mechanism of the second region 24 and the first region 22 in the method for producing the melt resistant casting of the present embodiment are unknown, it can be assumed that the following is true.

  In the first step, an oxide layer is formed and grown on the surface layer of the base metal layer 10 and a decarburized layer (ferrite trim) is formed, and the liberated carbon element reacts with the constituent elements of the base metal to form a composite. The second region 24 including the carbide 28 is formed. A large amount of the double carbide 28 is distributed in the first region 22 on the base metal layer 10 side, and a third region 26 where no double carbide exists is formed on the surface side of the second region 24.

  In the second step, the surface layer side of the base metal changes the crystal structure from pearlite to ferrite, and the oxide that continues to grow from the previous step extends into the ferrite crystal grain boundary in a cilia-like manner.

As described above, the method for producing a erosion-resistant casting according to the present invention does not supply a reaction gas in the heat treatment step as in the conventional surface treatment, but only controls the temperature rising temperature, the holding time, and the temperature lowering rate. Yes, it is possible to use a general annealing furnace.
The melt-resistant casting of the present embodiment is a member (metal melt contact member) that comes into contact with a metal melt such as aluminum or magnesium in a die casting machine, a molten metal processing apparatus, a metal melting furnace, a mold used in a mold casting method, or the like. ).
Examples of the die casting machine include a hot chamber type die casting machine and a cold chamber type die casting machine. The melt resistant casting of the present embodiment can be used as a molten metal contact member such as gooseneck, pot, nozzle, sleeve, plunger in a hot chamber die casting machine. The melt-resistant casting of the present embodiment can be used as a molten metal contact member such as a ladle, an ingot case, a stalk stirring blade, a thermocouple protection tube, and a skim door in a cold chamber die casting machine.

Examples of the molten metal treatment apparatus include a molten metal sealed container, a molten metal pump, a molten metal pouring machine, a molten metal degassing apparatus, a flux dispersion apparatus for molten metal, etc. In these apparatuses, it can be suitably used for a member that contacts the molten metal.
The melt-resistant casting of the present embodiment is extremely excellent in melt resistance, and by using the casting as a member that comes into contact with a molten metal such as aluminum or magnesium, the product reliability of various apparatuses including the member is improved. .
Further, since the molten metal contact member of the present embodiment is composed of a melt-resistant casting having extremely excellent melt resistance, there is no need to use an expensive ceramic member (or a member in which ceramic is cast). Equipment costs and manufacturing costs can be reduced.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited at all by these examples.

[Example 1]
(Immersion test)
The composition (wt%) is C 0.50, Si 0.45, Mn 0.70, P 0.02, S 0.01, Cr 5.50, Mo 0.65, Co 0.85, V 0. 20, Base metal composed of W 0.60, Nb 0.05, Al 0.05, balance Fe and unavoidable impurity elements is cast to φ20.1 × 100.5 mm to obtain a steel material.
The steel material was heated to 900 ° C. in an annealing furnace over 2 hours, held at that temperature for 1 hour, cooled to 200 ° C. at a cooling rate of 30 ° C./hour, taken out from the furnace, and a test piece for dipping was removed. obtain.

In the immersion test piece, as shown in FIG. 1, an oxide layer 20 including a first region 22, a second region 24, and a third region 26 is formed on the surface of the base metal layer 10. The weight of the test piece was 240 g.
The test piece for immersion was immersed in aluminum melted at 700 ° C. for 102 hours. When the weight of the test piece for immersion pulled up from aluminum was measured, it was 240 g, and the residual ratio (weight after immersion ÷ weight before immersion × 100) was 100%. The state of the surface was not particularly changed compared to before immersion. Fig.4 (a) shows the test piece for immersion before immersion, FIG.4 (b) shows the test piece for immersion after immersion.

(Strength test)
The above-mentioned base metal was cast into a JIS-14A test piece (mark distance: 50 mm), subjected to the same heat treatment, and then cut to obtain a test piece for mechanical strength.
When the tensile test was carried out by putting three test pieces for mechanical strength on a tensile tester, the average tensile strength was 250 N / mm ² , and it was confirmed that the test piece had substantially the same tensile strength as standard SDK61. .

(Thermal shock test)
The aforementioned base metal was cast to 100 × 150 × 12 mm and subjected to the same heat treatment to obtain a thermal shock test piece.
When the test piece for thermal shock was heated to 850 to 1050 ° C. → water cooling was repeated three times, some distortion was observed, but the surface state was not changed. From this, it was speculated that even when the erosion-resistant casting of Example 1 was used as a contact member of a molten metal such as aluminum, deterioration such as cracks and cracks did not occur.

[Comparative Example 1]
A steel material having a size of φ18.7 × 101 mm, which is a rolled drawn material of commercially available SKD61 (that is, a base metal having a composition in which tungsten and cobalt are not added in the composition of Example 1), was prepared as a test piece for immersion.
Since this immersion test piece is rolled under heating conditions, a third region 26 is formed on the surface of the base metal layer 10 as shown in FIG. The area was not recognized. The weight of the test piece was 220 g.
The test piece for immersion was immersed in aluminum melted at 700 ° C. for 102 hours. The test piece for immersion pulled up from aluminum was significantly melted and measured for its weight. As a result, it was 140 g and the residual rate was 63.6%. Fig.4 (a) shows the test piece for immersion before immersion, FIG.4 (b) shows the test piece for immersion after immersion.

[Comparative Example 2]
A base metal having the same composition as in Example 1 was cast to 20 × 300 mm. The base metal was heated in an annealing furnace to 900 ° C. over 2 hours, held at that temperature for 1 hour, then cooled to 200 ° C. at a cooling rate of 10 ° C./hour, taken out from the furnace, and tested for immersion. I got a piece.
As shown in FIG. 6, no ciliated oxide was observed in this immersion test piece. From this, it was guessed that the immersion test piece was melted in the immersion test.

[Comparative Example 3]
A base metal having the same composition as in Example 1 was cast to 20 × 300 mm. The base metal was heated to 760 ° C. in an annealing furnace over 2 hours, held at that temperature for 1 hour, cooled to 200 ° C. at a temperature drop rate of 30 ° C./hour, taken out from the furnace, and tested for immersion. I got a piece.

  In this immersion test piece, as shown in FIG. 7, only the third region 26 was formed on the surface of the base metal layer 10, and ciliated oxide was not observed. From this, it was guessed that the immersion test piece was melted in the immersion test.

[Comparative Example 4]
A base metal having the same composition as in Example 1 was cast to 20 × 300 mm. The base metal is heated up to 1000 ° C. in an annealing furnace over 2 hours, held at that temperature for 1 hour, cooled to 200 ° C. at a cooling rate of 30 ° C./hour, taken out of the furnace and tested for immersion. I got a piece.

  As shown in FIG. 8, no ciliated oxide was observed in this immersion test piece. This is probably because the ferrite grains in the ferrite region 12 were coarsened, so that the ciliary oxide was not formed because the ferrite region 12 could not extend from the first region 22 to the crystal grain boundary. From this, it was guessed that the immersion test piece was melted in the immersion test. Moreover, the 3rd area | region 26 of the outermost surface peeled easily.

[Comparative Example 5]
A base metal having a composition in which 0.80 wt% of tungsten and 0.85 wt% of cobalt are added to the composition of Comparative Example 1 is cast to 20 × 300 mm.
This base metal was heat-treated under the same conditions as in Example 1 to obtain a test piece for immersion.
As shown in FIG. 9, the immersion test piece has the second region 24 formed on the surface of the base metal layer 10 and the third region 26 formed on the outermost surface. The 1st area | region which has a ciliary oxide between the 2nd area | regions 24 was not recognized. From this, it was guessed that the immersion test piece was melted in the immersion test.

[Comparative Example 6]
A base metal having a composition in which 0.40 wt% of tungsten and 0.85 wt% of cobalt are added to the composition of Comparative Example 1 is cast to 20 × 300 mm.
This base metal was heat-treated under the same conditions as in Example 1 to obtain a test piece for immersion.
As shown in FIG. 10, the immersion test piece has the second region 24 formed on the surface of the base metal layer 10 and the third region 26 formed on the outermost surface. The 1st area | region which has a ciliary oxide between the 2nd area | regions 24 was not recognized. From this, it was guessed that the immersion test piece was melted in the immersion test.

[Comparative Example 7]
A base metal having a composition in which 0.60 wt% of tungsten and 1.00 wt% of cobalt are added to the composition of Comparative Example 1 is cast to 20 × 300 mm.
This base metal was heat-treated under the same conditions as in Example 1 to obtain a test piece for immersion.
As shown in FIG. 11, the immersion test piece has the second region 24 formed on the surface of the base metal layer 10 and the third region 26 formed on the outermost surface. A first region containing ciliated oxide was not observed between the second regions 24. From this, it was guessed that the immersion test piece was melted in the immersion test.

[Comparative Example 8]
A base metal having a composition in which 0.60 wt% of tungsten and 0.60 wt% of cobalt are added to the composition of Comparative Example 1 is cast to □ 20 × 300 mm.
This base metal was heat-treated under the same conditions as in Example 1 to obtain a test piece for immersion.
As shown in FIG. 12, the immersion test piece has the second region 24 formed on the surface of the base metal layer 10 and the third region 26 formed on the outermost surface. The 1st area | region which has a ciliary oxide between the 2nd area | regions 24 was not recognized. From this, it was guessed that the immersion test piece was melted in the immersion test.

  From the above results, the erosion-resistant casting of the present invention obtained by heat-treating a metal member made of a base metal having a predetermined composition under a predetermined temperature condition is formed on the ferrite crystal grain boundary 16 of the base metal layer 10. Since the ciliary oxide 22a is extended and exhibits an anchor effect, the oxide layer 20 and the base metal layer 10 are compared with the melt-resistant casting (comparative example) that does not have ciliary oxide. Can be bonded very firmly, and it is considered that the resistance to melting is improved.

As described above, the melt-resistant casting of the present invention is extremely excellent in melt resistance, and the tensile strength is substantially the same as that of the standard SDK 61, and has excellent characteristics in the thermal shock test. It became clear. Therefore, it was speculated that various apparatuses provided with a molten metal contact member made of the fusible casting of the present invention are excellent in melt resistance and the like, and the product reliability is improved.
Furthermore, according to the manufacturing method of the melt resistant casting of the present invention, it is excellent in equipment cost and running cost, and stably provides a melt resistant cast comprising a ciliary oxide extending to the crystal grain boundary of the base metal layer. It was confirmed that it was obtained.

1 Casting resistant cast 10 Base metal layer 12 Ferrite region (decarburized layer; ferrite trim)
14 Pearlite region 16 Ferrite grain boundary 20 Oxide layer 22 First region 22a Ciliated oxide 24 Second region 26 Third region 28 Double carbide

Claims (3)

Composition (% by weight): C 0.40 to 0.70%, Si 0.35 to 0.50%, Mn 0.50 to 0.70%, P <0.03%, S <0.02% , Cr 4.50 to 6.00%, Mo 0.50 to 0.75%, Co 0.70 to 0.90%, V 0.15 to 0.30%, W 0.50 to 0.70% Nb <0.10%, Al <0.10%, the balance being a base metal layer made of Fe and inevitable impurity elements, and an oxide layer formed on the surface of the base metal layer,
A part of the oxide layer extends to a crystal grain boundary of the base metal layer. Composition (% by weight): C 0.40 to 0.70%, Si 0.35 to 0.50%, Mn 0.50 to 0.70%, P <0.03%, S <0.02% , Cr 4.50 to 6.00%, Mo 0.50 to 0.75%, Co 0.70 to 0.90%, V 0.15 to 0.30%, W 0.50 to 0.70% , Nb <0.10%, Al <0.10%, the remainder of the metal member composed of the base metal composed of Fe and inevitable impurity elements is heated in a furnace to 780 to 980 ° C. Holding, and
Slowly cooling the heated metal member in a furnace at a rate of temperature decrease of 30 ± 10 ° C./hour;
A method for producing a melt-resistant casting, characterized by comprising:   A molten metal contact member comprising the melt-resistant casting according to claim 1.