JP2006316326A - Ultrahigh-strength anti-weathering steel and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrahigh-strength anti-weathering steel which is excellent in all of strength, toughness, ductility, corrosion resistance and weathering resistance in comparison with conventional ultrahigh-strength steel, and can be cast in the air without needing a vacuum melting facility or a vacuum casting facility. <P>SOLUTION: The ultrahigh-strength stainless steel is cast in the air after having blent C, Si, Cr, Cu, Mo, Ni, Co and Fe; and has a yield strength of 1,585 MPa (230,000 psi) or higher, a tensile strength of 1,723 MPa (250,000 psi) or higher and an elongation of 6% or higher. The steel desirably further includes at least one component selected from the group consisting of V, W, N and a mixture of them. The steel preferably includes 0.16-0.23 wt.% C, 0.2-1.5 wt.% Si, 2-5 wt.% Cr, 0.2-2 wt.% Cu, 0.8-3 wt.% Mo, 7-12 wt.% Ni, 13-17 wt.% Co and the balance Fe. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultra-high strength steel, and more particularly to an ultra-high strength steel that can be cast in the air and is superior in strength, ductility, toughness, and corrosion resistance compared to conventional ultra-high strength steel.

  Conventional ultra-high strength steel has various drawbacks. For example, most martensitic and marage steels lack atmospheric corrosion resistance, particularly during casting. Conventional maraging steel is melted in a vacuum using high-purity raw materials in order to strictly limit intruding elements and impurity elements.

  Ultra high strength precipitation hardened steel such as maraging steel prevents melting and casting in a vacuum so as to prevent exposure to the environment so that essential components with high reactivity such as titanium and aluminum are not exposed to the atmosphere. In order to prevent oxidation of reactive elements, contact with the atmosphere is avoided as much as possible during melting and casting. It is known that when reactive elements are present as oxides, the mechanical properties of steel deteriorate significantly.

  However, vacuum melting and vacuum casting are expensive. Further, the conventional ultra-high strength steel has to be subjected to vacuum melting and vacuum casting many times in order to achieve the required high purity. The steel obtained by melting and casting needs to be sufficiently hot worked to obtain the predetermined mechanical properties. Since hot working is required, various dies are required to achieve the predetermined shape and mechanical properties, which increases manufacturing costs and manufacturing time. Furthermore, many of the conventional ultra-high strength steels have to be plated with chromium or cadmium in most applications in order to impart corrosion resistance.

  Table 1 shows typical alloy components (wt%) of conventional ultra-high strength maraging steel.

  Titanium and aluminum are essential components for increasing the strength and hardness of maraging steel. However, steel using titanium and aluminum cannot easily be dissolved in the atmosphere as described above because a compound that causes embrittlement is easily generated. Therefore, ultra high strength steel using titanium and aluminum must be vacuum melted and vacuum cast.

  Also, existing ultra-high strength steels such as AISI 4340, H11, and 300M have a toughness level to have practicality in many high-strength steel applications that need to have both desired toughness and some degree of corrosion resistance such as outdoor use. Insufficient and low atmospheric corrosion resistance. Moreover, due to the alloy components used in the production of these steels, the weldability of the steel is degraded and the mechanical properties of the cast product are inferior to those of the hot-worked product.

  On the other hand, it is known that ultra-high strength maraging steel has excellent toughness and weldability. However, as already mentioned, maraging steels are vulnerable to atmospheric corrosion and associatedly stress corrosion cracking. Moreover, maraging steel is very expensive.

  As already mentioned briefly, the most common process for producing ultra-high strength maraging steel is a double or triple melting process with at least one melting and refining cycle in vacuum. After this melting and refining cycle, forging and rolling are generally performed to obtain a sheet material or a bar material. Maraging steel has the best properties when manufactured by hot working. It is known that maraging steel can provide good strength even with a cast material, but in the case of net shape casting, the ductility is inferior as shown in Table 2 below (compared with the one machined after hot working).

  Accordingly, an object of the present invention is to newly develop an ultra-high strength steel that simultaneously has improved strength, toughness, ductility, corrosion resistance, or weather resistance as compared with the conventional ultra-high strength steel. It is another object of the present invention to allow such steel to be cast in the atmosphere without requiring expensive and time-consuming vacuum melting / vacuum casting.

  According to the first invention, it is an ultra-high strength weather-resistant steel that is cast in the air containing C, Si, Cr, Cu, Mo, Ni, Co, and Fe, and has a yield strength of 1585 MPa (230,000 psi) or more. There is provided a weather resistant steel characterized by a tensile strength of 1723 MPa (250,000 psi) or more and an elongation of 6% or more.

  In a desirable embodiment, it further comprises at least one component selected from the group consisting of V, W, N and mixtures thereof. In another desirable embodiment, C: 0.16-0.23 wt%, Si: 0.2-1.5 wt%, Cr: 2-5 wt%, Cu: 0.2-2 wt%, Mo: 0.2%. 8 to 3 wt%, Ni: 7 to 12 wt%, Co: 13 to 17 wt%, and the balance: Fe.

  According to the second invention, C: 0.16-0.23 wt%, Si: 0.2-1.5 wt%, Cr: 2-5 wt%, Cu: 0.2-2 wt%, Mo: 0.8 There is provided an ultra high strength weathering steel consisting essentially of ~ 3 wt%, Ni: 7-12 wt%, Co: 13-17 wt%, and the balance: Fe. In a preferred embodiment, it further contains at least one component selected from the group consisting of V, W, N and mixtures thereof.

  According to the third invention, C: 0.16-0.23 wt%, Si: 0.2-1.5 wt%, Cr: 2-5 wt%, Cu: 0.2-2 wt%, Mo: 0.8 A weathering steel comprising -3 wt%, Ni: 7-12 wt%, Co: 13-17 wt%, V: 2 wt% or less, W: 2 wt% or less, N: 0.4 wt% or less, and the balance: Fe Provided. In a preferred embodiment, the yield strength is 1585 MPa (230,000 psi) or more, the tensile strength is 1723 MPa (250,000 psi) or more, and the elongation is 6% or more.

  According to the fourth invention, a step of applying hot isostatic pressing for 3 to 5 hours at a temperature of 1038 ° C. (1900 ° F.) or higher and a pressure of 96 MPa (14,000 psi) or higher to a cast member made of weathering steel; A step of homogenizing the cast member at a temperature of 1093 ° C. (2,000 ° F.) or more for 1 to 6 hours; the cast member at a temperature of 871-1149 ° C. (1,600-2,100 ° F.) A solution heat treatment of holding for 1 to 4 hours and then cooling to room temperature; a step of subjecting the cast member to a subzero treatment of holding at a temperature of −46 ° C. (−50 ° F.) or lower for 1 to 8 hours; and a temperature of 427 A weather-resistant steel casting produced by a process of aging treatment at ˜538 ° C. (800 to 1000 ° F.) for 4 to 5 hours is provided. In a desirable embodiment, C: 0.16-0.23 wt%, Si: 0.2-1.5 wt%, Cr: 2-5 wt%, Cu: 0.2-2 wt%, Mo: 0.8- 3 wt%, Ni: 7 to 12 wt%, Co: 13 to 17 wt%, and the balance: a step of blending Fe; a step of melting the blended components to create a weatherable steel melt; and The cast member is formed by a process of casting the molten metal to form the cast member.

According to the fifth aspect of the present invention, there is provided a method for producing a weathering steel cast member, wherein C: 0.16-0.23 wt%, Si: 0.2-1.5 wt%, Cr: 2-5 wt%, Cu: 0.2-2 wt%, Mo: 0.8-3 wt%, Ni: 7-12 wt%, Co: 13-17 wt%, and the balance: Fe is blended; A method is provided comprising the steps of: creating a molten steel; and casting the molten weatherable steel to form the cast member.

  The present invention relates to ultra-high strength weathering steel (hereinafter “weathering steel”) and a method for producing the same. The weather resistant steel of the present invention contains cobalt, nickel, chromium, copper, molybdenum, silicon, and carbon as basic alloy components. By using these alloy components in a specific configuration and using a specific heat treatment, the steel of the present invention has improved strength, ductility, toughness and atmospheric corrosion resistance compared to conventional ultra-high strength steel and can be cast in the air. was gotten. If the weather resistant steel of the present invention is melted in vacuum and directly cast into a mold (investment casting), or if it is forged as an ingot, the toughness and fatigue characteristics are further enhanced.

  A major feature of the weathering steel of the present invention is that excellent properties can be achieved while intentionally avoiding the use of reactive elements such as titanium and / or aluminum. In producing typical maraging steel, these elements are generally used to ensure hardness. Therefore, the fact that a high hardness level can be achieved while intentionally avoiding the use of these elements is a surprising phenomenon that cannot be expected from the prior art.

  By intentionally excluding these reactive elements, the weathering steel of the present invention can be dissolved in the atmosphere. The desired mechanical properties could be achieved by rigorously selecting other alloying elements and adjusting the overall component balance. By using other elements instead of reactive elements in this way, it is no longer necessary to repeat the melting and casting cycle in a non-reactive environment, so that weatherproof steel can be manufactured in a low cost and in a short time. became.

  The weathering steel can be composed of the following elements: Fe, Ni, Mo, Co, Cr, C, Si and Cu. As described above, a major feature of distinguishing the steel of the present invention from conventional ultra-high strength steel such as maraging steel is that the use of reactive elements titanium and aluminum is intentionally excluded.

  Table 3 shows the contents of the alloy components of the weather resistant steel of the present invention. Both values are approximate numbers.

  The balance is essentially normal impurities contained in iron, optional additive elements, and commercial maraging steel. For example, the weather resistant steel of the present invention may contain S: 0.01 wt% or less, P: 0.01 wt% or less, and N: 0.04 wt% or less as a trace component.

  C is added to improve strength and improve hardenability during heat treatment. The C content is 0.16 to 0.23 wt%. Si is added to improve castability and fluidity during production. The Si content is 0.2 to 1.5 wt%. Cr is added to enhance corrosion resistance, strength, and hardenability. The Cr content is 2 to 5 wt%.

  Cu is added to enhance corrosion resistance and weather resistance, and enhances corrosion resistance in the presence of Cr, Ni, and Mo. Cu content is 0.2 to 2 wt%. Mo is added to improve hardenability. Mo content is 0.8-3 wt%. Ni is added to increase the strength and toughness. The Ni content is 7 to 12 wt%. Co is added to increase the strength. Co content is 13-17 wt%.

  Alloy elements V, W, and N are optional components. The addition of V improves the hardness and improves the toughness at the same hardness level. V addition amount is 2 wt% or less. Addition of W improves strength and hardness. The amount of W added is 2 wt% or less. The addition of N stabilizes the austenite phase and adds strength. N addition amount is 0.04 wt% or less.

  The weather-resistant steel of the present invention is obtained by using an element having a small adverse effect instead of a highly reactive element such as aluminum and / or titanium used in precipitation hardening type ultra-high strength steel such as conventional maraging steel. Increased resistance to atmospheric corrosion. By deliberately replacing highly reactive elements with less reactive elements and at the same time optimizing the levels of C and Si, the weathering steel of the present invention is stable and cast even when dissolved and cast in the atmosphere. The property (fluidity) is extremely excellent.

  In a preferred embodiment, the weathering steel of the present invention is cast into the desired shape by investment casting. Desirably, the weathering steel of the present invention is manufactured in a single melting and casting cycle that does not need to be performed in a non-reactive environment, unlike conventional maraging steels. The weathering steel of the present invention can be easily cast into a complex shape in the atmosphere.

  Although it is desirable to use air dissolution, a protective atmosphere may be used. For example, if Ar is supplied in a liquid or gas state to the surface of the molten metal being melted, the castability can be improved. Moreover, if the cooling shell is covered with a can and the air around the cooling shell is shut off during the period from the start of solidification to about 10 minutes during casting, the quality of the casting surface is improved. However, it is not necessary to limit to this.

  The weather resistant steel of the present invention generally has mechanical properties such as (i) yield strength of 1585 MPa (230,000 psi) or more, preferably 1757-2067 MPa (255,000-300,000 psi), (ii) tensile strength 1723 MPa ( 250,000 psi) or more, preferably 1757-2205 MPa (255,000-320,000 psi), (iii) elongation of 6% or more, preferably 10-14%. In addition to these mechanical properties, the weathering steel of the present invention is excellent in castability, fluidity, weldability, and atmospheric corrosion resistance.

  The weather resistant steel of the present invention can adjust each level of strength, toughness, elongation and corrosion resistance in accordance with a specific application within the above range. By selecting the type and / or content of the alloy element, the characteristic level can be varied.

  As described above, the weathering steel of the present invention can be melted and cast in an atmospheric environment. That is, it can be melted and poured in the atmosphere and cast into a desired shape. Typical treatment processes after casting are (a) high temperature / high pressure consolidation, (b) homogeneous heat treatment, (c) solution heat treatment, (d) cooling, and (e) aging.

  The high temperature / high pressure consolidation step is preferably performed by hot isostatic pressing (HIP). In the HIP process, the investment cast member is placed in a special pressure vessel and heated to a predetermined temperature under an inert gas pressure of 96 MPa (14,000 psi) or more. Internal defects such as voids, bubbles, and shrinkage cavities in cast members are crushed by high temperature and pressure. This reduces the internal defects of the cast member and improves the mechanical properties.

  Desirable HIP conditions for the cast member are a pressure of 103 MPa (15,000 psi), a temperature of 1038 ° C. (1,900 ° F.) or more, more preferably 1038 ° C. to 1232 ° C. (1,900 ° F. to 2,250 ° F.). And in a chamber filled with an inert gas such as argon gas. After filling the pressure chamber with argon gas to a predetermined pressure, the chamber is heated. When the temperature in the chamber is increased to a desired temperature, the pressure in the chamber is increased to a desired level. After maintaining the desired temperature for about 3 to 5 hours, the cast member is cooled to room temperature. After HIP processing, check for defect closure by appropriate means.

  The homogenization heat treatment is performed in a neutral atmosphere at a temperature range of 1093 ° C. to 1218 ° C. (2,000 ° F. to 2,225 ° F.) and a holding time of 1 to 6 hours. The homogenized heat treatment process recovers the microstructural changes that occur during the HIP cycle and minimizes component segregation.

  The solution heat treatment step is carried out in a neutral atmosphere at a temperature range of 871 ° C. to 1149 ° C. (1,600 ° F. to 2,100 ° F.) for 1 to 4 hours and then rapidly cooled to room temperature by cooling with a fan using a gas. To do. In the solution heat treatment step, the microstructure is made into an austenite state by holding at the above temperature, and then transformed into martensite by rapid cooling.

  In the cooling step, the cast member at room temperature is brought to −46 ° C. (−50 ° F.) or less, preferably −68 ° C. to −73 ° C. (−90 ° F. to −100 ° F.) within 24 hours from the completion of solution treatment. The transformation from austenite to martensite is performed completely by sub-zero treatment for 1 to 4 hours. In the aging treatment step, the above-mentioned mechanical properties are brought into a desired combination state by holding for 1 to 6 hours in a temperature range of 427 ° C. to 538 ° C. (800 ° F. to 1,000 ° F.).

  Table 4 below shows desirable conditions, more desirable conditions, and most desirable conditions as treatment conditions for producing the weathering steel of the present invention. Each value in the table is an approximate number.

  According to the method of the present invention, a weathering steel sample was produced as an example of the present invention. These are indicated in Table 5 below as RNR-2, RNR-3, RNR-4, RNR-5, RNR-6 and RNR-2L. The alloy components were blended as shown in Table 5, and melted, poured and cast in the atmosphere to obtain a cast member.

  The obtained cast member was subjected to HIP treatment for 3 hours at a temperature of 1163 ° C. (2,125 ° F.) and a pressure of 103 MPa (15,000 psi). After the HIP treatment, a homogenization heat treatment is performed for 4 hours at a temperature within the range of 1163 ° C. to 1204 ° C. (2,125 ° F. to 2,200 ° F.), and then at a temperature of 1038 ° C. (1,900 ° F.). Solution heat treatment was performed for a holding time of 1.5 hours. After the solution heat treatment, it was rapidly cooled to room temperature by cooling with a fan using a gas, and then subzero treatment was performed at a temperature of −73 ° C. (−100 ° F.) for 1 to 3 hours to transform residual austenite into martensite. Next, an aging treatment was performed at a temperature of 510 ° C. (950 ° F.) for 4 to 6 hours to obtain desired mechanical properties.

  Table 5 shows the mechanical properties of the samples of the present invention obtained as described above.

  As described above, the weathering steel sample of the present invention has yield strength and tensile strength equivalent to those of a conventional ultra-high strength stainless steel vacuum-melting / hot-working material. However, the weathering steel sample of the present invention is an investment casting material produced by atmospheric melting and atmospheric casting.

  Table 6 below shows the physical / mechanical property data of the above weather resistant steel samples of the present invention compared to conventional steel.

  According to the above characteristic data, the weathering steel of the present invention is superior in yield strength and tensile strength to the conventional steel, and at the same time, the elongation and corrosion resistance are equivalent to the conventional steel.

  Therefore, the weather-resistant steel of the present invention can be cast in the atmosphere, and has solved the disadvantages of the conventional ultra-high strength steel described above. The weather resistant steel of the present invention is more resistant to atmospheric corrosion than conventional martensitic and maraging steels, has a better balance of mechanical properties and yield strength than most hot work hardened and age hardened stainless steels. 1585 MPa (230,000 psi), tensile strength 1723 MPa (250,000 psi), elongation 10% or more, aperture 35% or more.

  Since the weather resistant steel of the present invention is excellent in fluidity and castability, it is possible to cast a thin material having a complicated shape. The weather-resistant steel of the present invention is less reactive than other maraging steels, so it can be melted in the atmosphere and cast in air, and has well-balanced mechanical properties without the need for multiple times of vacuum melting and hot working. can get. Since the reactivity is low, there is little reaction with the template and generation of porosity. Also, near net shape casting can be performed directly by investment casting. It is much cheaper and easier to obtain than conventional maraging steel. Desired mechanical properties are obtained without the need for high purity raw materials. Recycling is easy, reducing costs and reducing environmental impact. It has better weldability than low alloy martensitic steel (4140, 300M). Because most applications do not require chrome plating or cadmium plating, they have less environmental impact than conventional ultra-high strength steel.

  Since the weathering steel of the present invention requires only one melting step, the manufacturing cost is greatly reduced. Since it is possible to manufacture complex shaped products that can be melted and cast by air, there is no need for capital investment for vacuum casting furnaces. Since it can be cast in the air, productivity (manufactured amount per hour) is greatly improved compared to vacuum melting. Short delivery time, fast production cycle time, and low production cost. Since the manufacturing process is simple and the manufacturing throughput and cycle time (preparation time and operation time) are high, inventory can be reduced. Since good properties are obtained without the need for hot working, a series of dies for obtaining a predetermined shape and mechanical properties is not required. If even better properties are required depending on the application, hot processing and vacuum melting can be performed at a high cost.

  As mentioned above, although the specific sample was shown and demonstrated, this invention does not need to be limited to this, A chemical composition can be adjusted variously according to each product use. Further, the disclosed temperature, time, pressure, and the like are merely examples, and various modifications can be made within the scope of the present invention.

Claims (29)

  C, Si, Cr, Cu, Mo, Ni, Co, Fe is an ultra-high-strength weathering steel cast in air with a yield strength of 1585 MPa or more, tensile strength of 1723 MPa or more, and elongation of 6% or more Weather-resistant steel characterized by being.   The weathering steel according to claim 1, which has a yield strength of 1757 to 2067 MPa, a tensile strength of 1757 to 2205 MPa, and an elongation of 10 to 14%.   The weathering steel according to claim 1, further comprising at least one component selected from the group consisting of V, W, N and mixtures thereof. In claim 1,
C: 0.16-0.23 wt%,
Si: 0.2 to 1.5 wt%,
Cr: 2 to 5 wt%
Cu: 0.2-2 wt%
Mo: 0.8-3 wt%
Ni: 7-12 wt%,
Co: 13-17 wt%, and the balance: Fe
A weather-resistant steel characterized by   The weathering steel according to claim 1, which is substantially free of Al and Ti. In claim 1,
C: 0.17 to 0.22 wt%,
Si: 0.3-1.2 wt%
Cr: 2.5-4 wt%
Cu: 0.5 to 1.5 wt%,
Mo: 1 to 2 wt%,
Ni: 8 to 10.5 wt%,
Co: 14-16 wt%
A weather-resistant steel characterized by   The weatherproof steel according to claim 6, further comprising at least one component selected from the group consisting of V, W, N, and a mixture thereof. In claim 1,
C: 0.18 to 0.21 wt%
Si: 0.5 to 0.9 wt%,
Cr: 3 to 4 wt%
Cu: 0.7 to 1.5 wt%,
Mo: 1.3 to 1.7 wt%,
Ni: 9 to 10.5 wt%,
Co: 14 to 15.5 wt%
A weather-resistant steel characterized by   The weatherproof steel according to claim 8, further comprising at least one component selected from the group consisting of V, W, N, and a mixture thereof. The following ingredients:
C: 0.16-0.23 wt%
Si: 0.2 to 1.5 wt%,
Cr: 2 to 5 wt%
Cu: 0.2-2 wt%
Mo: 0.8-3 wt%
Ni: 7-12 wt%,
Co: 13-17 wt%, and the balance: Fe
An ultra-high strength weatherproof steel consisting essentially of.   The weatherproof steel according to claim 10, further comprising at least one component selected from the group consisting of V, W, N, and a mixture thereof.   The weather-resistant steel according to claim 10, which has a yield strength of 1585 MPa or more, a tensile strength of 1723 MPa or more, and an elongation of 6% or more. The following ingredients:
C: 0.16-0.23 wt%
Si: 0.2 to 1.5 wt%,
Cr: 2 to 5 wt%
Cu: 0.2-2 wt%
Mo: 0.8-3 wt%
Ni: 7-12 wt%,
Co: 13-17 wt%,
V: 2 wt% or less,
W: 2 wt% or less,
N: 0.4 wt%, and the balance: Fe
Weatherproof steel comprising.   The weathering steel according to claim 13, wherein the weathering steel has a yield strength of 1585 MPa or more, a tensile strength of 1723 MPa or more, and an elongation of 6% or more. The following steps:
A step of applying hot isostatic pressing for 3 to 5 hours at a temperature of 1038 ° C. or higher and a pressure of 96 MPa or higher to a weathering steel cast member;
A step of homogenizing the cast member at a temperature of 1093 ° C. or more for 1 to 6 hours;
A step of subjecting the cast member to a solution heat treatment that is held at a temperature of 871-1149 ° C. for 1-4 hours and then cooled to room temperature;
A weather-resistant steel casting produced by subjecting the cast member to a sub-zero treatment for holding at a temperature of −46 ° C. or lower for 1 to 8 hours, and an aging treatment at a temperature of 427 to 538 ° C. for 4 to 5 hours. In claim 15, prior to the hot isostatic pressing step, the following steps:
C: 0.16-0.23 wt%
Si: 0.2 to 1.5 wt%,
Cr: 2 to 5 wt%
Cu: 0.2-2 wt%
Mo: 0.8-3 wt%
Ni: 7-12 wt%,
Co: 13-17 wt%, and the balance: Fe
A step of blending,
Casting characterized in that the cast member is formed by a step of melting the blended components to create a melt of weathering steel, and a step of casting the melt of the weathering steel to form the cast member Goods.   The cast product according to claim 16, wherein at least one component selected from the group consisting of V, W, N, and a mixture thereof is further added in the blending step.   The cast product according to claim 16, wherein the melting step and the casting step are performed in an atmospheric environment.   16. The cast product according to claim 15, wherein the cast member after the aging treatment step has a yield strength of 1585 MPa or more, a tensile strength of 1723 MPa or more, and an elongation of 6% or more.   The hot isostatic pressing is performed at 1093 to 1227 ° C, the homogenization heat treatment is performed at 1177 to 1216 ° C, the solution heat treatment is performed at 982 to 1066 ° C, and the sub-zero treatment is performed. Is performed at -79 to -59 ° C, and the aging treatment is performed at 482 to 538 ° C. In claim 15, prior to the hot isostatic pressing step, the following steps:
C: 0.17 to 0.22 wt%,
Si: 0.3-1.2 wt%
Cr: 2.5-4 wt%
Cu: 0.5 to 1.5 wt%,
Mo: 1 to 2 wt%,
Ni: 8 to 10.5 wt%,
Co: 14 to 16 wt%, and balance: Fe
A step of blending,
Casting characterized in that the cast member is formed by a step of melting the blended components to create a melt of weathering steel, and a step of casting the melt of the weathering steel to form the cast member Goods.   The cast product according to claim 21, wherein at least one component selected from the group consisting of V, W, N and a mixture thereof is further added in the blending step.   The cast product according to claim 21, wherein the melting step and the casting step are performed in an atmospheric environment.   24. The cast product according to claim 23, wherein the cast member after the aging treatment step has a yield strength of 1585 MPa or more, a tensile strength of 1723 MPa or more, and an elongation of 6% or more. A method for producing a cast member of weathering steel comprising the following steps:
C: 0.16-0.23 wt%
Si: 0.2 to 1.5 wt%,
Cr: 2 to 5 wt%
Cu: 0.2-2 wt%
Mo: 0.8-3 wt%
Ni: 7-12 wt%,
Co: 13-17 wt%, and the balance: Fe
A step of blending,
A method comprising the steps of: melting the blended components to create a weatherable steel melt; and casting the weatherable steel melt to form the cast member.   26. The method according to claim 25, wherein at least one component selected from the group consisting of V, W, N and a mixture thereof is further added in the blending step.   26. The method according to claim 25, wherein the melting step and the casting step are performed in an atmospheric environment. 26. The process of claim 25, further comprising:
A step of applying hot isostatic pressing for 3 to 5 hours at a temperature of 1038 ° C. or higher and a pressure of 96 MPa or higher to the cast member;
A step of homogenizing the cast member for 1 to 6 hours at a temperature of 1149 ° C. or higher;
A step of subjecting the cast member to a solution heat treatment that is held at a temperature of 871-1149 ° C. for 1-4 hours and then cooled to room temperature;
A method comprising: subjecting the cast member to a sub-zero treatment for holding at a temperature of −46 ° C. or lower for 1 to 4 hours; and subjecting the cast member to an aging treatment at a temperature of 427 to 538 ° C. for 4 to 5 hours.   The method according to claim 28, wherein the cast member after the aging treatment step has a yield strength of 1585 MPa or more, a tensile strength of 1723 MPa or more, and an elongation of 6% or more.