JP2023530808A - Heat-resistant steel for steel pipes and castings - Google Patents

Abstract

The present invention provides an elemental composition of heat-resistant steel for steel pipes and castings, and uses thereof. The present invention further provides methods of manufacturing steel pipes and castings and uses thereof. The heat-resistant steel for steel pipes and castings provided by the present invention, the preferred elemental compositions, and the manufacturing steps thereof can produce heat-resistant steel pipes and castings with excellent performance. Steel pipes and castings made from such heat resistant steels have excellent creep rupture strength and can meet the requirements in the use of pressure vessels or power machinery parts at 650°C and below 650°C.

Description

The present invention belongs to the technical field of metallic materials, and relates to heat resistant steel for steel pipes and castings.

The boiler in the pressure vessel is an energy conversion device, the energy supplied to the boiler has chemical energy by fuel, electric energy, and the boiler takes out steam, hot water or organic heat medium with certain thermal energy. A steam turbine in a power machine, also called a steam turbine, is a rotary steam power device, in which high-temperature and high-pressure steam passes through a fixed nozzle to become an accelerated airflow, which is then injected into the blades to attach a row of blades. Work out as you rotate the rotor. Boilers and steam turbines are the main equipment of modern thermal power plants.

Improving the steam temperature parameter of coal-fired units in thermal power plants can improve unit efficiency, reduce fossil fuel consumption, and achieve energy savings and emission reductions. The operating temperatures of boilers and steam turbines are limited by the maximum operating temperatures of steel pipes, eg, boiler piping, and castings, eg, critical component materials such as cylinders and valves in steam turbines.

High temperature materials for components such as boiler piping, cylinders and valves in steam turbines have evolved from Cr-Mo steels to various 9%-12% Cr ferritic steels. Here, conventional steel pipes, e.g., boiler piping high-temperature materials, the currently available choices include T92/P92, etc., and conventional castings, e.g., cylinder and valve high-temperature materials in steam turbines, the current choice Possible ones include ZG13Cr9Mo2Co1NiVNbNB and the like. However, the maximum operating temperature of these steel grades is 630°C or less, and currently there is no heat resistant steel for steel pipes and castings with an operating temperature of 650°C.

In view of the shortcomings of the above prior art, an object of the present invention is to provide a heat resistant steel for steel pipes and castings, which can be used to manufacture boiler piping and steam turbine castings, and is capable of producing pressure vessels at 650°C and below 650°C Or it can meet the requirements in the use of power machinery parts.

To achieve the above and other related objects, a first aspect of the present invention provides a heat resistant steel for steel pipes and castings, comprising the following mass percent elements:

C (carbon): 0.08-0.14 wt%, Si (silicon): 0.20-0.40 wt%, Mn (manganese): 0.30-0.60 wt%, Cr (chromium): 9.00 ~10.00 wt%, Co (cobalt): 2.80 ~ 3.30 wt%, W (tungsten): 1.65 ~ 1.90 wt%, Mo (molybdenum): 0.55 ~ 0.80 wt%, V ( vanadium): 0.15 to 0.25 wt%, Nb (niobium): 0.03 to 0.08 wt%, N (nitrogen): 0.006 to 0.015 wt%, B (boron): 0.009 to 0 0.015 wt %, Ni (nickel): ≦0.20 wt %, the balance being Fe (iron) and unavoidable impurities.

Preferably, the impurities are P (phosphorus), S (sulfur), Al (aluminum), Ti (titanium), Zr (zirconium), Cu (copper), Sn (tin), As (arsenic), Sb (antimony) selected from one or more elements of Here, in the impurities, the mass percent content of the elements satisfies the following requirements. P: ≤0.020 wt%, S: ≤0.010 wt%, Al: ≤0.02 wt%, Ti: ≤0.02 wt%, Zr: ≤0.02 wt%, Cu: ≤0.15 wt%, Sn: ≤0.02 wt%, As: ≤0.02 wt%, Sb: ≤0.005 wt%.

Preferably, in the heat resistant steel for steel pipes and castings, the Cr (chromium) equivalent should be ≦8.5% based on Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N, and the B element and The mass ratio of the N element is 0.65-2.40:1.

Preferably, the heat-resistant steel for steel pipes and castings is composed of the following mass percent elements:

C: 0.08-0.13 wt%, Si: 0.20-0.30 wt%, Mn: 0.40-0.50 wt%, Cr: 9.00-9.60 wt%, Co: 2.90- 3.20 wt%, W: 1.70 to 1.85 wt%, Mo: 0.60 to 0.75 wt%, V: 0.18 to 0.25 wt%, Nb: 0.04 to 0.07 wt%, N : 0.007 to 0.014 wt%, B: 0.010 to 0.015 wt%, Ni: ≤ 0.10 wt%, the balance being Fe and unavoidable impurities.

More preferably, in said impurities, the mass percent content of elements satisfies the following requirements: P: ≤0.020 wt%, S: ≤0.005 wt%, Al: ≤0.01 wt%, Ti: ≤0.01 wt%, Zr: ≤0.01 wt%, Cu: ≤0.10 wt%, Sn: ≤0.01 wt%, As: ≤0.01 wt%, Sb: ≤0.003 wt%.

More preferably, in the heat-resistant steel for steel pipes and castings, the Cr (chromium) equivalent should be ≦8.0% based on Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N, and the B element and the mass ratio of the N element is 0.75-2.10:1.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the C element ensures hardenability. During the tempering process, C is combined with other elements to form M23C6 carbides at the crystal boundaries and martensite lath boundaries, and form MX-type carbonitrides inside the martensite laths, which can improve high temperature strength. In addition to ensuring strength and toughness, C is also an essential element for suppressing the formation of harmful phases δ-ferrite and BN. However, when added excessively, it reduces the toughness and strength and impairs the long-term creep rupture strength. Therefore, the C content should be limited to 0.08-0.14%. Furthermore, the optimal content of the C element should be limited to 0.08-0.13%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, Si acts as a deoxidizing agent for molten steel and cooperates with Cr to further improve the oxidation resistance of the steel. However, if the amount of Si added is too large, the deoxidation product SiO2 will remain in the steel, degrading the purity and toughness of the molten steel. In addition, Si further promotes the precipitation of intermetallic compound Laves phases and reduces creep plasticity. Si improves temper brittleness when used at high temperatures. Therefore, the Si content should be limited to 0.20-0.40%. Furthermore, the optimum content of elemental Si should be limited to 0.20-0.30%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the Mn element removes oxygen and sulfur elements in the molten steel, improves the hardenability and strength of the steel, suppresses the formation of δ-ferrite and BN, It can promote the precipitation of carbides. However, increasing the content of the Mn element reduces the creep rupture strength. Therefore, the content of Mn element should be limited to 0.30-0.60%. Furthermore, the optimum content of Mn element should be limited to 0.40-0.50%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the Ni element can improve the hardenability of the steel, suppress the formation of δ-ferrite and BN, and improve room temperature strength and toughness. However, the addition of the Ni element is not beneficial to the high temperature creep properties of the steel and increases the temper brittleness of the steel. In order to ensure that the heat resistant steel of the present invention obtains the required high temperature creep strength, the amount of Ni element added should be as low as possible, preferably not more than 0.20%, and most preferably 0.10%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the Cr element can improve the oxidation resistance and corrosion resistance, and the M23C6 carbide precipitates to improve the high-temperature strength. In order to obtain the above effects, the content of Cr element in the heat resistant steel of the present invention is at least 9.00%. However, if it exceeds 10.00%, δ-ferrite tends to be formed, which lowers the high strength temperature and toughness. Therefore, the Cr element content should be limited to 9.00-10.00%. Furthermore, the optimal content of Cr element should be limited to 9.00-9.60%. At the same time, the Cr equivalent (Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N) of the heat-resistant steel of the present invention is limited to 8.5% or less, more preferably 8.0% or less, and δ-ferrite precipitation can be avoided.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the Mo element improves hardenability, suppresses temper embrittlement, promotes dispersed precipitation of M23C6 carbides, and improves the tensile strength and creep rupture strength of the steel. be able to. However, when the Mo element is excessive, it promotes precipitation of δ-ferrite and intermetallic compound Laves phase, and significantly reduces toughness. Therefore, the content of Mo element is limited to 0.55 to 0.80%. Furthermore, the optimum content of Mo element should be limited to 0.60-0.75%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the W element can effectively suppress the coarsening of M23C6 carbides, and its role exceeds that of the Mo element, and can significantly improve the creep rupture strength. W element is added to replace some Mo elements, and the Mo element equivalent (Mo+1/2W) is guaranteed to be around 1.5%, the strengthening effect is the most remarkable, and the intermetallic δ-ferrite There is no excessive formation of compound Laves phases. If the W element content exceeds 1.90%, plasticity, toughness and creep rupture strength are impaired, and segregation tends to occur in the steel. Therefore, the W element content should be limited to 1.65-1.90%. Furthermore, the optimum content of W element should be limited to 1.70-1.85%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the Co element enables solid-solution strengthening and suppresses the precipitation of δ-ferrite. The Co element remarkably improves the high temperature strength and improves the toughness of the steel under the interaction of the Mo element and the W element. At the same time, in order to keep costs down, too high a Co element content is not preferred. The Co element content should be limited to 2.80-3.30%. Furthermore, the optimal content of Co element should be limited to 2.90-3.20%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the V element can improve the tensile strength. In addition, by forming fine carbonitrides of the V element inside the martensite lath, the creep rupture strength is improved. A certain amount of V element can be added to refine grains and improve toughness. However, if the addition amount is too large, the toughness is lowered, and carbon is excessively fixed, which causes a decrease in the precipitation amount of M23C6 carbide. Therefore, its content is 0.15 to 0.25%. The expected value should be 0.18-0.25%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the Nb element can improve the tensile strength and creep rupture strength in the same manner as the V element. Nb element and C element can generate fine NbC, refine crystal grains, and improve toughness. In addition, MX carbonitrides formed by Nb element and V element play a role in improving high-temperature strength, and the lowest content should be 0.03%. However, when the content is 0.08% or more, similar to the V element, carbon is excessively fixed, thereby reducing the amount of precipitation of M23C6 carbides and lowering the high-temperature strength. Therefore, it should be limited to 0.03 to 0.08%. The expected value should be 0.04-0.07%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the N element and the V element can precipitate VN nitrides, and are combined with the Mo element and the W element in a solid solution state to improve the high temperature strength and contain The amount should be at least 0.005%. However, when adding more than 0.015%, the plasticity is impaired. In addition, when it coexists with elements, eutectic Fe2B and BN are likely to form, impairing the creep properties and toughness of the steel. Therefore, the N element content is limited to 0.006 to 0.015%. Furthermore, the optimal content of N element should be limited to 0.007-0.014%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the B element has the effect of strengthening the crystal boundaries, plays a role in suppressing the coarsening of M23C6 carbides, and improves the high-temperature strength. However, above 0.015%, it is not beneficial for forging and welding performance. Therefore, the content of element B is limited to 0.009 to 0.015%. Furthermore, the optimal content of the B element should be limited to 0.010-0.015%. In order to prevent the B and N elements from combining to form BN, the mass ratio of the B and N elements should be controlled to 0.65-2.40:1, more preferably It should be controlled between 0.75 and 2.10:1.

The unavoidable impurities mentioned above are inclusion elements unavoidably contaminated during the steel smelting process. The content of these elements should be as low as possible. Strict screening of raw materials for steelmaking causes the cost to rise. Therefore, the P content should be suppressed to 0.020% or less, the S content to 0.010% or less, and the Cu content to 0.15% or less. At the same time, other inclusion elements, such as Al, Ti, Zr, Sn, As, Sb, etc., have adverse effects on the mechanical performance of the heat-resistant steel, and their content should be reduced as much as possible.

A second aspect of the present invention provides a method for manufacturing a steel pipe, in which raw materials are taken from the heat-resistant steel according to the blending ratio of elements, mixed, and then smelted. Manufactured into a blank tube by any one of hot forging and then subjecting the tube to any one of hot rolling, hot drawing, thermal expansion, cold drawing, cold rolling or forging boring. A steel pipe is manufactured using the type, and the steel pipe is tempered after being normalized or quenched to obtain a product.

Preferably, the normalizing or quenching temperature is 1070-1160°C.

Preferably, said tempering comprises at least one time and said tempering temperature is between 740 and 790°C.

The above continuous casting, die casting, hot rolling, hot forging, hot drawing, thermal expansion, cold drawing, cold rolling or forging boring are all well-known technical processes in the steel manufacturing field.

The technical process of the above steel pipe meets the requirements of national standard GB5310.

A third aspect of the present invention provides a method for producing a casting, in which raw materials are taken from the heat-resistant steel according to the blending ratio of elements, mixed, smelted, and cast to obtain a casting, Further, the cast product is tempered after normalizing or quenching to obtain a product.

Preferably, the normalizing or quenching temperature is 1070-1160°C.

Preferably, said tempering comprises at least one time and said tempering temperature is 730-780°C.

The casting is a well-known technical process in the field of steel manufacturing.

A fourth aspect of the present invention provides the use of the above heat-resistant steel or steel pipe in a pressure vessel.

Preferably, said pressure vessel is a boiler line.

A fifth aspect of the present invention provides use of the above heat resistant steel or casting in a power machine.

Preferably, said power machine is a steam turbine.

In the steel pipe and/or casting manufacturing method, the smelting includes alloy smelting and refining steps. Both the alloy smelting and refining steps in the smelting and refining are well-known technical steps in the steel manufacturing field.

As described above, the heat-resistant steel for steel pipes and castings provided by the present invention, the preferred elemental compositions, and the manufacturing steps thereof can produce steel pipes and castings with excellent performance. Compared with the conventional boiler piping material T/P92, it adds Co element, adjusts the ratio of B and N, improves the content of Cr, Mo and B elements, and increases the content of Nb, N and Ni elements. , the content of Si and W elements is more strictly limited, the impurity elements Cu, Sn, As, and Sb are also limited, and the W element is added compared to the conventional casting material ZG13Cr9Mo2Co1NiVNbNB, Adjust the ratio of B and N, improve the content of Co and B elements, reduce the content of Mn, Mo, N and Ni elements, and reduce the impurity elements Ti, Zr, Cu, Sn, As, Sb limit even

The heat resistant steel for steel pipes and castings provided by the present invention improves the working temperature by improving the high temperature creep rupture strength and oxidation resistance, thus improving the thermal efficiency of the power plant, reducing coal consumption and reducing carbon dioxide emissions. reduce emissions of The material grade of the new heat-resistant steel is abbreviated as TB4 (small diameter pipe)/PB4 (large diameter pipe) when it is used as a steel pipe material, and is abbreviated as CB4 when it is used as a casting material.

The heat-resistant steel for steel pipes and castings provided by the present invention may be used to manufacture pressure vessels and power machinery, particularly boiler piping and steam turbine castings, and the boiler piping and steam turbine castings obtained by manufacturing. The product has good high temperature creep rupture strength and oxidation resistance in high temperature environments at 650°C and below 650°C, and can meet the requirements for use in boilers and steam turbines whose operating temperature is 650°C and below 650°C. can.

Hereinafter, the present invention will be described in detail according to specific examples, and it should be understood that these examples are only for the purpose of illustrating the present invention and limit the protection scope of the present invention. It is not for

Embodiments of the present invention will now be described through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed herein. The present invention may also be practiced or applied in accordance with different embodiments, each detail herein may be applied according to different viewpoints, and various modifications may be made without departing from the spirit of the invention. Or changes can be made.

Example 1
Each element component is taken according to the blending ratio, and as shown in Table 1, each component is composed of the following mass percent elements.

C: 0.10 wt%, Si: 0.30 wt%, Mn: 0.50 wt%, Cr: 9.30 wt%, Co: 3.00 wt%, W: 1.80 wt%, Mo: 0.65 wt%, V : 0.23 wt%, Nb: 0.05 wt%, N: 0.012 wt%, B: 0.012 wt%, Ni: 0.05 wt%, and the balance is Fe and unavoidable impurities.

As shown in Table 2, the mass percentage contents of the elements in the impurities are P: 0.008 wt%, S: 0.003 wt%, Al: 0.01 wt%, Ti: 0.003 wt%, Zr: 0.001 wt%. %, Cu: 0.05 wt%, Sn: 0.001 wt%, As: 0.001 wt%, Sb: 0.001 wt%.

Here, based on Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N, the Cr equivalent is 7.62%. The mass ratio of the B element to the N element is 1:1.

After taking and mixing the raw materials according to the blending ratio of each element, smelting is performed, that is, alloy smelting and refining are performed in order, die casting is performed to the mother pipe, and hot drawing is performed on the mother pipe. A steel pipe is obtained, and after the steel pipe is normalized, it is tempered to obtain a steel pipe sample 1#. Here, the normalizing temperature is 1100°C, the tempering is included once, and the tempering temperature is 780°C. Steel pipe sample 1# is boiler piping.

Example 2
Each element component is taken according to the blending ratio, and as shown in Table 1, each component is composed of the following mass percent elements.

C: 0.12 wt%, Si: 0.25 wt%, Mn: 0.45 wt%, Cr: 9.60 wt%, Co: 3.20 wt%, W: 1.75 wt%, Mo: 0.70 wt%, V : 0.20 wt%, Nb: 0.07 wt%, N: 0.009 wt%, B: 0.013 wt%, Ni: 0.10 wt%, and the balance is Fe (iron) and unavoidable impurities.

As shown in Table 2, the mass percentage contents of the elements in the impurities are P: 0.012 wt%, S: 0.005 wt%, Al: 0.01 wt%, Ti: 0.005 wt%, Zr: 0.001 wt%. %, Cu: 0.06 wt%, Sn: 0.001 wt%, As: 0.002 wt%, Sb: 0.0015 wt%.

Here, based on Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N, the Cr equivalent is 6.7%. The mass ratio of the B element to the N element is 1.4:1. After taking and mixing the raw materials according to the blending ratio of each element, smelting is performed, that is, alloy smelting and refining are performed in order, and the material is cast into a casting, and after the casting is normalized. It is tempered to obtain Casting Sample 1*. Here, the normalizing temperature is 1140°C, the tempering includes 2 times, and the tempering temperature is 755°C. Casting sample 1* is a steam turbine valve housing casting.

Comparative example 1
The conventional steel pipe material T92/P92 and the casting material ZG13Cr9Mo2Co1NiVNbNB were selected.

Test example 1
According to standard ASTM A213/A335 and JB/T 11018, the mechanical performance index of conventional steel pipe material T92/P92 and casting material ZG13Cr9Mo2Co1NiVNbNB are listed, and the specific data are shown in Table 4. In Table 4, Rp0.2 is the yield strength, Rm is the tensile strength, A is the elongation ratio, Z is the cross-sectional shrinkage ratio, and KV2 is the impact absorption energy. At the same time, the steel pipe sample 1# obtained in Example 1 and the casting sample 1* obtained in Example 2 were subjected to a tensile test at room temperature according to the national standard GB/T228.1. /T229, the impact test was performed at room temperature and the results of the test are shown in Table 4.

As shown in Table 4, by comparing the steel pipe sample 1# obtained in Example 1 with the conventional steel pipe material T92/P92, the room temperature mechanical performance obtained for the steel pipe sample 1# is an index of T92/P92. meet the demands.

As shown in Table 4, by comparing the conventional casting material ZG13Cr9Mo2Co1NiVNbNB with the casting sample 1* obtained in Example 2, the room temperature mechanical performance obtained with the casting sample 1* is higher than the index requirement of ZG13Cr9Mo2Co1NiVNbNB. meet.

Test example 2
The steel pipe sample 1# obtained in Example 1 and the casting sample 1* obtained in Example 2 were subjected to a creep rupture strength test according to the national standard GB/T 2039 standard, and then the national standard GB The creep rupture strength limit Ru _{100,000h/650°C was derived under the condition of 650°C} /100,000 hours according to the extrapolation method specified in /T 2039, and 650°C/100,000 hours for T92/P92 and ZG13Cr9Mo2Co1NiVNbNB, respectively. The results are shown in Table 4 in comparison with the creep rupture strength under the conditions.

As can be seen from Table 4, the extrapolated value of the creep rupture strength of the steel pipe sample 1# obtained in Example 1 is improved by 50% or more compared to the conventional steel pipe material T92/P92, and the strengthening effect is remarkable. It can meet the requirements in the use of boiler piping under 650°C.

As can be seen from Table 4, the creep rupture strength extrapolated value of the casting sample 1* obtained in Example 2 is improved by 40% or more compared to the conventional casting material ZG13Cr9Mo2Co1NiVNbNB, and the strengthening effect is remarkable. It can meet the requirements in the use of steam turbine castings under 650°C.

Test example 3
Oxidation under 620° C. and 650° C. for steel pipe sample 1# obtained in Example 1 and casting sample 1* obtained in Example 2, and conventional steel pipe material T92/P92 and casting material ZG13Cr9Mo2Co1NiVNbNB Each increase test is performed. The sample is placed in a steam environment of 620°C/650°C and 27MPa flow, the time is 2000 hours at the longest, and the change in weight gain of each sample is tested within this time period. explain that the

According to the test results, under the same temperature, the oxidation resistance of steel pipe sample 1# is significantly better than T92/P92, and the oxidation resistance of casting sample 1* is significantly better than ZG13Cr9Mo2Co1NiVNbNB.

At different temperatures, for example, under 650°C, the oxidation weight gain of steel pipe sample 1# is similar to that of T92/P926620°C, and that of casting sample 1* is similar to that of ZG13Cr9Mo2Co1NiVNbNB620°C. The steel pipes and castings produced from the heat-resistant steel of the present invention basically meet the needs of long-term use under 650° C. operating conditions on the premise that the surface protective coating layer does not provide oxidation resistance. can.

Therefore, the present invention effectively solves various drawbacks in the prior art and has high industrial application value.

The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the scope of the present invention. Those skilled in the art can make modifications or changes to the above-described embodiments without departing from the spirit and scope of the invention. Therefore, any equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical ideas disclosed by the present invention should still be included in the scope of the claims of the present invention.

The present invention belongs to the technical field of metallic materials, and relates to heat resistant steel for steel pipes and castings.

The boiler in the pressure vessel is an energy conversion device, the energy supplied to the boiler has chemical energy by fuel, electric energy, and the boiler takes out steam, hot water or organic heat medium with certain thermal energy. A steam turbine in a power machine, also called a steam turbine, is a rotary steam power device, in which high-temperature and high-pressure steam passes through a fixed nozzle to become an accelerated airflow, which is then injected into the blades to attach a row of blades. Work out as you rotate the rotor. Boilers and steam turbines are the main equipment of modern thermal power plants.

Improving the steam temperature parameter of coal-fired units in thermal power plants can improve unit efficiency, reduce fossil fuel consumption, and achieve energy savings and emission reductions. The operating temperatures of boilers and steam turbines are limited by the maximum operating temperatures of steel pipes, eg, boiler piping, and castings, eg, critical component materials such as cylinders and valves in steam turbines.

High temperature materials for components such as boiler piping, cylinders and valves in steam turbines have evolved from Cr-Mo steels to various 9%-12% Cr ferritic steels. Here, conventional steel pipes, e.g., boiler piping high-temperature materials, the currently available choices include T92/P92, etc., and conventional castings, e.g., cylinder and valve high-temperature materials in steam turbines, the current choice Possible ones include ZG13Cr9Mo2Co1NiVNbNB and the like. However, the maximum operating temperature of these steel grades is 630°C or less, and currently there is no heat resistant steel for steel pipes and castings with an operating temperature of 650°C.

In view of the shortcomings of the above prior art, an object of the present invention is to provide a heat resistant steel for steel pipes and castings, which can be used to manufacture boiler piping and steam turbine castings, and is capable of producing pressure vessels at 650°C and below 650°C Or it can meet the requirements in the use of power machinery parts.

To achieve the above and other related objects, a first aspect of the present invention provides a heat resistant steel for steel pipes and castings, comprising the following mass percent elements:

C (carbon): 0.08 to 0.14 wt%, Si (silicon): 0.20 to 0.40 wt%, Mn (manganese): 0.30 to 0.60 wt%, P (phosphorus): ≤0. 020 wt%, S (sulfur): ≤ 0.010 wt%, Cr (chromium): 9.00 to 10.00 wt%, Co (cobalt): 2.80 to 3.30 wt%, W (tungsten): 1.65 ~1.90 wt%, Mo (molybdenum): 0.55 ~ 0.80 wt%, V (vanadium): 0.15 ~ 0.25 wt%, Nb (niobium): 0.03 ~ 0.08 wt%, N ( Nitrogen): 0.006 to 0.015 wt%, B (boron): 0.009 to 0.015 wt%, Ni (nickel): ≤ 0.20 wt%, Al (aluminum): ≤ 0.02 wt%, Ti ( titanium): ≤0.02 wt%, Zr (zirconium): ≤0.02 wt%, Cu (copper): ≤0.15 wt%, Sn (tin): ≤0.02 wt%, As (arsenic): ≤0. 02 wt %, Sb (antimony): ≦0.005 wt %, and the balance is Fe (iron) .

Preferably , in said heat resistant steel for steel pipes and castings, the Cr (chromium) equivalent should be ≦8.5% based on Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N, and said B The mass ratio of the element to the N element is 0.65-2.40:1.

Preferably, the heat-resistant steel for steel pipes and castings is composed of the following mass percent elements:

C: 0.08 to 0.13 wt%, Si: 0.20 to 0.30 wt%, Mn: 0.40 to 0.50 wt%, P (phosphorus): ≤0.020 wt%, S (sulfur): ≤ 0.005 wt%, Cr: 9.00-9.60 wt%, Co: 2.90-3.20 wt%, W: 1.70-1.85 wt%, Mo: 0.60-0.75 wt%, V : 0.18 to 0.25 wt%, Nb: 0.04 to 0.07 wt%, N: 0.007 to 0.014 wt%, B: 0.010 to 0.015 wt%, Ni: ≤ 0.10 wt% , Al (aluminum): ≤ 0.01 wt%, Ti: (titanium) ≤ 0.01 wt%, Zr (zirconium): ≤ 0.01 wt%, Cu (copper): ≤ 0.10 wt%, Sn (tin): ≤0.01 wt%, As: (arsenic) ≤0.01 wt%, Sb (antimony): ≤0.003 wt%, and the balance is Fe .

More preferably, in the heat resistant steel for steel pipes and castings, the Cr (chromium) equivalent should be ≦8.0% based on Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N, and the B The mass ratio of the element to the N element is 0.75-2.10:1.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the C element ensures hardenability. During the tempering process, C is combined with other elements to form M23C6 carbides at the crystal boundaries and martensite lath boundaries, and form MX-type carbonitrides inside the martensite laths, which can improve high temperature strength. In addition to ensuring strength and toughness, C is also an essential element for suppressing the formation of harmful phases δ-ferrite and BN. However, when added excessively, it reduces the toughness and strength and impairs the long-term creep rupture strength. Therefore, the C content should be limited to 0.08-0.14%. Furthermore, the optimal content of the C element should be limited to 0.08-0.13%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, Si acts as a deoxidizing agent for molten steel and cooperates with Cr to further improve the oxidation resistance of the steel. However, if the amount of Si added is too large, the deoxidation product SiO2 will remain in the steel, degrading the purity and toughness of the molten steel. In addition, Si further promotes the precipitation of intermetallic compound Laves phases and reduces creep plasticity. Si improves temper brittleness when used at high temperatures. Therefore, the Si content should be limited to 0.20-0.40%. Furthermore, the optimum content of elemental Si should be limited to 0.20-0.30%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the Mn element removes oxygen and sulfur elements in the molten steel, improves the hardenability and strength of the steel, suppresses the formation of δ-ferrite and BN, It can promote the precipitation of carbides. However, increasing the content of the Mn element reduces the creep rupture strength. Therefore, the content of Mn element should be limited to 0.30-0.60%. Furthermore, the optimum content of Mn element should be limited to 0.40-0.50%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the Ni element can improve the hardenability of the steel, suppress the formation of δ-ferrite and BN, and improve room temperature strength and toughness. However, the addition of the Ni element is not beneficial to the high temperature creep properties of the steel and increases the temper brittleness of the steel. In order to ensure that the heat resistant steel of the present invention obtains the required high temperature creep strength, the amount of Ni element added should be as low as possible, preferably not more than 0.20%, and most preferably 0.10%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the Cr element can improve the oxidation resistance and corrosion resistance, and the M23C6 carbide precipitates to improve the high-temperature strength. In order to obtain the above effects, the content of Cr element in the heat resistant steel of the present invention is at least 9.00%. However, if it exceeds 10.00%, δ-ferrite tends to be formed, which lowers the high strength temperature and toughness. Therefore, the Cr element content should be limited to 9.00-10.00%. Furthermore, the optimal content of Cr element should be limited to 9.00-9.60%. At the same time, the Cr equivalent (Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N) of the heat-resistant steel of the present invention is limited to 8.5% or less, more preferably 8.0% or less, and δ-ferrite precipitation can be avoided.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the Mo element improves hardenability, suppresses temper embrittlement, promotes dispersed precipitation of M23C6 carbides, and improves the tensile strength and creep rupture strength of the steel. be able to. However, when the Mo element is excessive, it promotes precipitation of δ-ferrite and intermetallic compound Laves phase, and significantly reduces toughness. Therefore, the content of Mo element is limited to 0.55 to 0.80%. Furthermore, the optimum content of Mo element should be limited to 0.60-0.75%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the W element can effectively suppress the coarsening of M23C6 carbides, and its role exceeds that of the Mo element, and can significantly improve the creep rupture strength. W element is added to replace some Mo elements, and the Mo element equivalent (Mo+1/2W) is guaranteed to be around 1.5%, the strengthening effect is the most remarkable, and the intermetallic δ-ferrite There is no excessive formation of compound Laves phases. If the W element content exceeds 1.90%, plasticity, toughness and creep rupture strength are impaired, and segregation tends to occur in the steel. Therefore, the W element content should be limited to 1.65-1.90%. Furthermore, the optimum content of W element should be limited to 1.70-1.85%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the Co element enables solid-solution strengthening and suppresses the precipitation of δ-ferrite. The Co element remarkably improves the high temperature strength and improves the toughness of the steel under the interaction of the Mo element and the W element. At the same time, in order to keep costs down, too high a Co element content is not preferred. The Co element content should be limited to 2.80-3.30%. Furthermore, the optimal content of Co element should be limited to 2.90-3.20%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the V element can improve the tensile strength. In addition, by forming fine carbonitrides of the V element inside the martensite lath, the creep rupture strength is improved. A certain amount of V element can be added to refine grains and improve toughness. However, if the addition amount is too large, the toughness is lowered, and carbon is excessively fixed, which causes a decrease in the precipitation amount of M23C6 carbide. Therefore, its content is 0.15 to 0.25%. The expected value should be 0.18-0.25%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the Nb element can improve the tensile strength and creep rupture strength in the same manner as the V element. Nb element and C element can generate fine NbC, refine crystal grains, and improve toughness. In addition, MX carbonitrides formed by Nb element and V element play a role in improving high-temperature strength, and the lowest content should be 0.03%. However, when the content is 0.08% or more, similar to the V element, carbon is excessively fixed, thereby reducing the amount of precipitation of M23C6 carbides and lowering the high-temperature strength. Therefore, it should be limited to 0.03 to 0.08%. The expected value should be 0.04-0.07%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the N element and the V element can precipitate VN nitrides, and are combined with the Mo element and the W element in a solid solution state to improve the high temperature strength and contain The amount should be at least 0.005%. However, when adding more than 0.015%, the plasticity is impaired. In addition, when it coexists with elements, eutectic Fe2B and BN are likely to form, impairing the creep properties and toughness of the steel. Therefore, the N element content is limited to 0.006 to 0.015%. Furthermore, the optimal content of N element should be limited to 0.007-0.014%.

In the heat-resistant steel for steel pipes and castings provided by the present invention, the B element has the effect of strengthening the crystal boundaries, plays a role in suppressing the coarsening of M23C6 carbides, and improves the high-temperature strength. However, above 0.015%, it is not beneficial for forging and welding performance. Therefore, the content of element B is limited to 0.009 to 0.015%. Furthermore, the optimal content of the B element should be limited to 0.010-0.015%. In order to prevent the B and N elements from combining to form BN, the mass ratio of the B and N elements should be controlled to 0.65-2.40:1, more preferably It should be controlled between 0.75 and 2.10:1.

The unavoidable impurities mentioned above are inclusion elements unavoidably contaminated during the steel smelting process. The content of these elements should be as low as possible. Strict screening of raw materials for steelmaking causes the cost to rise. Therefore, the P content should be suppressed to 0.020% or less, the S content to 0.010% or less, and the Cu content to 0.15% or less. At the same time, other inclusion elements, such as Al, Ti, Zr, Sn, As, Sb, etc., have adverse effects on the mechanical performance of the heat-resistant steel, and their content should be reduced as much as possible.

A second aspect of the present invention provides a method for manufacturing a steel pipe, in which raw materials are taken from the heat-resistant steel according to the blending ratio of elements, mixed, and then smelted. Manufactured into a blank tube by any one of hot forging and then subjecting the tube to any one of hot rolling, hot drawing, thermal expansion, cold drawing, cold rolling or forging boring. A steel pipe is manufactured using the type, and the steel pipe is tempered after being normalized or quenched to obtain a product.

Preferably, the normalizing or quenching temperature is 1070-1160°C.

Preferably, said tempering comprises at least one time and said tempering temperature is between 740 and 790°C.

The above continuous casting, die casting, hot rolling, hot forging, hot drawing, thermal expansion, cold drawing, cold rolling or forging boring are all well-known technical processes in the steel manufacturing field.

The technical process of the above steel pipe meets the requirements of national standard GB5310.

A third aspect of the present invention provides a method for producing a casting, in which raw materials are taken from the heat-resistant steel according to the blending ratio of elements, mixed, smelted, and cast to obtain a casting, Further, the cast product is tempered after normalizing or quenching to obtain a product.

Preferably, the normalizing or quenching temperature is 1070-1160°C.

Preferably, said tempering comprises at least one time and said tempering temperature is 730-780°C.

The casting is a well-known technical process in the field of steel manufacturing.

A fourth aspect of the present invention provides the use of the above heat-resistant steel or steel pipe in a pressure vessel.

Preferably, said pressure vessel is a boiler line.

A fifth aspect of the present invention provides use of the above heat resistant steel or casting in a power machine.

Preferably, said power machine is a steam turbine.

In the steel pipe and/or casting manufacturing method, the smelting includes alloy smelting and refining steps. Both the alloy smelting and refining steps in the smelting and refining are well-known technical steps in the steel manufacturing field.

As described above, the heat-resistant steel for steel pipes and castings provided by the present invention, the preferred elemental compositions, and the manufacturing steps thereof can produce steel pipes and castings with excellent performance. Compared with the conventional boiler piping material T/P92, it adds Co element, adjusts the ratio of B and N, improves the content of Cr, Mo and B elements, and increases the content of Nb, N and Ni elements. , the content of Si and W elements is more strictly limited, the impurity elements Cu, Sn, As, and Sb are also limited, and the W element is added compared to the conventional casting material ZG13Cr9Mo2Co1NiVNbNB, Adjust the ratio of B and N, improve the content of Co and B elements, reduce the content of Mn, Mo, N and Ni elements, and reduce the impurity elements Ti, Zr, Cu, Sn, As, Sb limit even

The heat resistant steel for steel pipes and castings provided by the present invention improves the working temperature by improving the high temperature creep rupture strength and oxidation resistance, thus improving the thermal efficiency of the power plant, reducing coal consumption and reducing carbon dioxide emissions. reduce emissions of The material grade of the new heat-resistant steel is abbreviated as TB4 (small diameter pipe)/PB4 (large diameter pipe) when it is used as a steel pipe material, and is abbreviated as CB4 when it is used as a casting material.

The heat-resistant steel for steel pipes and castings provided by the present invention may be used to manufacture pressure vessels and power machinery, particularly boiler piping and steam turbine castings, and the boiler piping and steam turbine castings obtained by manufacturing. The product has good high temperature creep rupture strength and oxidation resistance in high temperature environments at 650°C and below 650°C, and can meet the requirements for use in boilers and steam turbines whose operating temperature is 650°C and below 650°C. can.

Hereinafter, the present invention will be described in detail according to specific examples, and it should be understood that these examples are only for the purpose of illustrating the present invention and limit the protection scope of the present invention. It is not for

Embodiments of the present invention will now be described through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed herein. The present invention may also be practiced or applied in accordance with different embodiments, each detail herein may be applied according to different viewpoints, and various modifications may be made without departing from the spirit of the invention. Or changes can be made.

Example 1
Each element component is taken according to the blending ratio, and as shown in Table 1, each component is composed of the following mass percent elements.

C: 0.10 wt%, Si: 0.30 wt%, Mn: 0.50 wt%, P: 0.008 wt%, S: 0.003 wt%, Cr: 9.30 wt% , Co: 3.00 wt%, W : 1.80 wt%, Mo: 0.65 wt%, V: 0.23 wt%, Nb: 0.05 wt%, N: 0.012 wt%, B: 0.012 wt%, Ni: 0.05 wt%, Al: 0.01 wt%, Ti: 0.003 wt%, Zr: 0.001 wt%, Cu: 0.05 wt%, Sn: 0.001 wt%, As: 0.001 wt%, Sb: 0.001 wt%, the balance being F is e .

Here , based on Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N, the Cr equivalent is 7.62%. The mass ratio of the B element to the N element is 1:1.

After taking and mixing the raw materials according to the blending ratio of each element, smelting is performed, that is, alloy smelting and refining are performed in order, die casting is performed to the mother pipe, and hot drawing is performed on the mother pipe. A steel pipe is obtained, and after the steel pipe is normalized, it is tempered to obtain a steel pipe sample 1#. Here, the normalizing temperature is 1100°C, the tempering is included once, and the tempering temperature is 780°C. Steel pipe sample 1# is boiler piping.

Example 2
Each element component is taken according to the blending ratio, and as shown in Table 1, each component is composed of the following mass percent elements.

C: 0.12 wt%, Si: 0.25 wt%, Mn: 0.45 wt%, P: 0.012 wt%, S: 0.005 wt%, Cr: 9.60 wt%, Co: 3.20 wt%, W : 1.75 wt%, Mo: 0.70 wt%, V: 0.20 wt%, Nb: 0.07 wt%, N: 0.009 wt%, B: 0.013 wt%, Ni: 0.10 wt%, Al: 0.01 wt%, Ti: 0.005 wt%, Zr: 0.001 wt%, Cu: 0.06 wt%, Sn: 0.001 wt%, As: 0.002 wt%, Sb: 0.0015 wt%, the balance being Fe (iron ) .

Here , based on Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N, the Cr equivalent is 6.7%. The mass ratio of the B element to the N element is 1.4:1. After taking and mixing the raw materials according to the blending ratio of each element, smelting is performed, that is, alloy smelting and refining are performed in order, and the material is cast into a casting, and after the casting is normalized. It is tempered to obtain Casting Sample 1*. Here, the normalizing temperature is 1140°C, the tempering includes 2 times, and the tempering temperature is 755°C. Casting sample 1* is a steam turbine valve housing casting.

Comparative example 1
The conventional steel pipe material T92/P92 and the casting material ZG13Cr9Mo2Co1NiVNbNB were selected.

Test example 1
According to standard ASTM A213/A335 and JB/T 11018, the mechanical performance index of conventional steel pipe material T92/P92 and casting material ZG13Cr9Mo2Co1NiVNbNB are listed, and the specific data are shown in Table 3 . In Table 3 , Rp0.2 is yield strength, Rm is tensile strength, A is elongation, Z is cross-sectional shrinkage, and KV2 is impact absorption energy. At the same time, the steel pipe sample 1# obtained in Example 1 and the casting sample 1* obtained in Example 2 were subjected to a tensile test at room temperature according to the national standard GB/T228.1. /T229, the impact test was performed at room temperature and the results of the test are shown in Table 3 .

As shown in Table 3 , by comparing the steel pipe sample 1# obtained in Example 1 with the conventional steel pipe material T92/P92, the room temperature mechanical performance obtained for the steel pipe sample 1# is an index of T92/P92. meet the demands.

As shown in Table 3 , by comparing the conventional casting material ZG13Cr9Mo2Co1NiVNbNB with the casting sample 1* obtained in Example 2, the room temperature mechanical performance obtained with the casting sample 1* is higher than the index requirement of ZG13Cr9Mo2Co1NiVNbNB. meet.

Test example 2
The steel pipe sample 1# obtained in Example 1 and the casting sample 1* obtained in Example 2 were subjected to a creep rupture strength test according to the national standard GB/T 2039 standard, and then the national standard GB The creep rupture strength limit Ru _{100,000h/650°C was derived under the condition of 650°C} /100,000 hours according to the extrapolation method specified in /T 2039, and 650°C/100,000 hours for T92/P92 and ZG13Cr9Mo2Co1NiVNbNB, respectively. The results are shown in Table 4 in comparison with the creep rupture strength under the conditions.

As can be seen from Table 3 , the extrapolated value of the creep rupture strength of the steel pipe sample 1# obtained in Example 1 is improved by 50% or more compared to the conventional steel pipe material T92/P92, and the strengthening effect is remarkable. It can meet the requirements in the use of boiler piping under 650°C.

As can be seen from Table 3 , the creep rupture strength extrapolated value of the casting sample 1* obtained in Example 2 was improved by 40% or more compared to the conventional casting material ZG13Cr9Mo2Co1NiVNbNB, and the strengthening effect was remarkable. It can meet the requirements in the use of steam turbine castings under 650°C.

Test example 3
Oxidation under 620° C. and 650° C. for steel pipe sample 1# obtained in Example 1 and casting sample 1* obtained in Example 2, and conventional steel pipe material T92/P92 and casting material ZG13Cr9Mo2Co1NiVNbNB Each increase test is performed. The sample is placed in a steam environment of 620°C/650°C and 27MPa flow, the time is 2000 hours at the longest, and the change in weight gain of each sample is tested within this time period. explain that the

According to the test results, under the same temperature, the oxidation resistance of steel pipe sample 1# is significantly better than T92/P92, and the oxidation resistance of casting sample 1* is significantly better than ZG13Cr9Mo2Co1NiVNbNB.

At different temperatures, for example, under 650°C, the oxidation weight gain of steel pipe sample 1# is similar to that of T92/P926620°C, and that of casting sample 1* is similar to that of ZG13Cr9Mo2Co1NiVNbNB620°C. The steel pipes and castings produced from the heat-resistant steel of the present invention basically meet the needs of long-term use under 650° C. operating conditions on the premise that the surface protective coating layer does not provide oxidation resistance. can.

Therefore, the present invention effectively solves various drawbacks in the prior art and has high industrial application value.

The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the scope of the present invention. Those skilled in the art can make modifications or changes to the above-described embodiments without departing from the spirit and scope of the invention. Therefore, any equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical ideas disclosed by the present invention should still be included in the scope of the claims of the present invention.

Test example 1
According to standard ASTM A213/A335 and JB/T 14047 , the mechanical performance index of conventional steel pipe material T92/P92 and casting material ZG13Cr9Mo2Co1NiVNbNB are listed, and the specific data are shown in Table 3. In Table 3, Rp0.2 is yield strength, Rm is tensile strength, A is elongation, Z is cross-sectional shrinkage, and KV2 is impact absorption energy. At the same time, the steel pipe sample 1# obtained in Example 1 and the casting sample 1* obtained in Example 2 were subjected to a tensile test at room temperature according to the national standard GB/T228.1. /T229, the impact test was performed at room temperature and the results of the test are shown in Table 3.

Claims (12)

A heat-resistant steel composed of the following mass percent elements:
C: 0.08-0.14 wt%, Si: 0.20-0.40 wt%, Mn: 0.30-0.60 wt%, Cr: 9.00-10.00 wt%, Co: 2.80- 3.30 wt%, W: 1.65-1.90 wt%, Mo: 0.55-0.80 wt%, V: 0.15-0.25 wt%, Nb: 0.03-0.08 wt%, N : 0.006-0.015 wt%, B: 0.009-0.015 wt%, Ni: ≤ 0.20 wt%, and the balance being Fe and inevitable impurities. The impurities are selected from one or more elements of P, S, Al, Ti, Zr, Cu, Sn, As, and Sb, and the mass percentage content of the elements in the impurities is P: ≤0. 020 wt%, S: ≤0.010 wt%, Al: ≤0.02 wt%, Ti: ≤0.02 wt%, Zr: ≤0.02 wt%, Cu: ≤0.15 wt%, Sn: ≤0.02 wt% , As: ≤0.02 wt%, Sb: ≤0.005 wt%. In said heat-resistant steel, the Cr equivalent should be ≦8.5% based on Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N, and the mass ratio of said B element and N element should be 0.65- 2. The heat resistant steel of claim 1, characterized in that it is 40:1. The heat-resistant steel is composed of the following mass percent elements,
C: 0.08-0.13 wt%, Si: 0.20-0.30 wt%, Mn: 0.40-0.50 wt%, Cr: 9.00-9.60 wt%, Co: 2.90- 3.20 wt%, W: 1.70 to 1.85 wt%, Mo: 0.60 to 0.75 wt%, V: 0.18 to 0.25 wt%, Nb: 0.04 to 0.07 wt%, N : 0.007 to 0.014 wt%, B: 0.010 to 0.015 wt%, Ni: ≤ 0.10 wt%, and the balance being Fe and inevitable impurities. heat resistant steel. In the impurities, the mass percentage content of the elements is P: ≤0.020 wt%, S: ≤0.005 wt%, Al: ≤0.01 wt%, Ti: ≤0.01 wt%, Zr: ≤0.01 wt% %, Cu: ≤0.10 wt%, Sn: ≤0.01 wt%, As: ≤0.01 wt%, Sb: ≤0.003 wt%. heat resistant steel. In said heat-resistant steel, the Cr equivalent should be ≦8.0% based on Cr+6Si+4Mo+1.5W+11V+5Nb-40C-2Mn-4Ni-2Co-30N, and the mass ratio of said B element and N element should be 0.75- 2. Heat resistant steel according to claim 4, characterized in that it is 10:1. A method for manufacturing a steel pipe, wherein the heat-resistant steel according to any one of claims 1 to 6 is mixed with raw materials according to the blending ratio of elements, and then smelted. Manufactured into a tube by any one of hot rolling or hot forging, after which the tube is subjected to hot rolling, hot drawing, thermal expansion, cold drawing, cold rolling or forging boring. A method of manufacturing a steel pipe, comprising the steps of manufacturing a steel pipe using any one of them, and then tempering the steel pipe after normalizing or quenching the steel pipe to obtain a product. 8. The method according to claim 7, wherein the normalizing or quenching temperature is 1070-1160°C, the tempering includes at least one tempering, and the tempering temperature is 740-790°C. A method of manufacturing steel pipes. A method for producing a cast product, wherein the heat-resistant steel according to any one of claims 1 to 6 is mixed with raw materials according to the element mixing ratio, smelted and cast, and then the cast product is produced. A method for producing a cast product, characterized in that the cast product is obtained by normalizing or quenching the cast product, and then tempering the cast product. 10. The method according to claim 9, wherein the normalizing or quenching temperature is 1070-1160°C, the tempering includes at least one tempering, and the tempering temperature is 730-780°C. Method of manufacturing castings. Use of the heat-resistant steel according to any one of claims 1 to 6 or the steel pipe according to any one of claims 7 to 8 in a pressure vessel. Use of the heat resistant steel according to any one of claims 1 to 6 or the casting according to any one of claims 9 to 10 in power machinery.