High-pressure heat-resistant round steel and preparation method thereof

Abstract

The present invention discloses a high-pressure, heat-resistant round steel and a preparation method thereof, belonging to the fields of materials and metallurgy. The steel comprises the following components by mass percentage: C: 0.13% to 0.17%, Si: 0.17% to 0.35%, Mn: 0.45% to 0.65%, P < 0.010%, S ≤ 0.008%, Cr: 0.92% to 0.98%, and Mo: 0.42% to 0.46%, wherein 0.47 < (Si + Mn + P) / (Cr + Mo) < 0.66, with the remainder being iron and unavoidable impurities. The present invention utilizes clean steel smelting technology, a continuous casting process combining increased mold volume with ultra-multi-strand casting, and rational composition design to achieve a low segregation index and excellent surface quality. The high-pressure, heat-resistant round steel exhibits a segregation index of less than 1.0, an oxidation resistance of 0.1 mm / a to 0.3 mm / a, and a high-temperature service strength of ≥ 500 MPa, offering excellent economic efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of materials and metallurgy, and more particularly to high-pressure and heat-resistant round steel and a preparation method thereof. Background Art

[0002] High-pressure, heat-resistant round steel is a product currently in high market demand. Its primary application is as a carrier for transmission steel in the power and energy industries. The thermal strength and oxidation resistance of this product at high temperatures determine the service life and effectiveness of energy equipment. To achieve these properties, some domestic steel manufacturers and research institutions, based on their own tooling conditions, add various alloying elements to the composition design of these products, ensuring performance through the coordination of these elements. However, the increased complexity of alloying elements leads to a significant problem: the widespread internal segregation and surface cracking of this type of round steel. In recent years, several technical solutions have been published to address this issue.

[0003] Chinese patent publication number CN115519083A discloses a method for controlling the surface quality of 15CrMoG continuous casting billets. Specifically, the method involves ensuring the superheat of the molten steel at approximately 20°C, ensuring a 100% water ratio in the primary and secondary cooling roll sections, implementing end-stage electromagnetic stirring, and utilizing a casting speed of 1.10 m / min. Low-alkalinity, high-viscosity mold slag is used to increase the taper of the copper tube, resulting in a surface depression depth of less than 1 mm on the round steel, thereby improving the steel's performance stability. However, the invention's design fails to address the issue of internal segregation in the round steel, resulting in limited resistance to high pressure and high temperatures.

[0004] Chinese patent publication number CN119016699A discloses a method for continuous casting large-sized round billets for power station boiler tubes. By optimizing the continuous casting machine's start-up and casting process parameters, optimizing the mold taper, and changing the mold powder type, the method addresses issues such as steel leaks during start-up and longitudinal cracks on the surface of the ingot. However, the invention discloses that the steel is P92 steel. Based on production standards, its disadvantages include high levels of W, Cr, and N, resulting in high manufacturing costs, difficulty in control, and difficulty in organizing production. Both manufacturing and delivery cycles are long, negatively impacting the product's market competitiveness.

[0005] Chinese patent publication number CN113399461A discloses a method for processing niobium-containing austenitic heat-resistant stainless steel round tube billets, which specifically comprises: heating and heat preservation in a soaking furnace; initial rolling to open the billet; heating and heat preservation of the initial billet; and rolling into a round tube billet. The main components of the alloy are C: 0.04~0.10%, Si≤1.00%, Mn<2.00%, P≤0.0300%, S≤0.015%, Cr: 24.0~26.0%, Ni: 19.0~22.0%, N: 0.20~0.35%, Nb: 0.20~0.60%, Mo: 0.10~0.40%, Co: 0.10~0.40%, B: 0.003~0.005%, Al≤0.04%. However, the invention still contains a large amount of elements such as Cr, Ni, and N, and the manufacturing cost is also high, making it difficult to implement industrially. The manufacturing cycle and delivery cycle are both long, which is not conducive to the market competitiveness of the product.

[0006] Chinese patent publication number CN109023122A discloses a method and ingot mold for manufacturing alloy steel ingots for forging supercritical boiler tubes. The ingot mold comprises the following chemical ingredients: C: 0.05-0.2%, Si: 0.1-0.6%, Mn: 0.1-0.7%, Cr: 7.0-12.0%, Ni: 0.01-0.05%, Nb: 0.01-0.15%, V: 0.1-0.3%, Mo: 0.8-1.2%, S: 0.0005-0.3%, N: 0.04-0.08%, RE: 0.001-0.005%, with the remainder being Fe and unavoidable impurities. Two-plate casting is used, and the ingot mold comprises a mold body and lugs, with a taper of 1.0-5.0%. The invention primarily addresses the quality issue of tubes failing flaw detection inspections. However, the composition design of this invention involves many types of alloy elements, the interactions between the elements are complex and difficult to control, and the product quality and performance stability are poor.

[0007] Chinese patent publication number CN114606428A discloses a method for refining and reducing low-silicon, low-aluminum, high-pressure boiler tube billets (P91), comprising the following steps: Step 1: Before LF treatment, tapping from an electric converter; Step 2: Adding 700-1000 kg of lime, 300-600 kg of synthetic slag, and 100-200 kg of aluminum shot to the electric furnace along with the steel stream for slagging and pre-deoxidation; Step 3: Slagging and diffusion deoxidation during LF feeding; Step 4: Slagging and diffusion deoxidation; Step 5: After all components are adjusted and fed into the line, tapping. This invention reduces the oxygen content in the molten steel of low-silicon, low-aluminum, high-pressure boiler tube billets (P91) to below 25 ppm, avoiding the risk of interruption during continuous casting due to Al2O3 nodules at the nozzle. However, the composition design of this invention contains a large number of alloying elements, and the interactions between the elements are complex and difficult to control, resulting in poor product quality and performance stability.

[0008] In summary, the above existing technologies all have shortcomings such as insufficient component design, high manufacturing process cost, poor product quality and performance stability, and low production efficiency. Summary of the Invention

[0009] The purpose of the present invention is to overcome the above-mentioned defects in the prior art and provide a high-pressure heat-resistant round steel and a preparation method thereof.

[0010] To achieve the above object, the technical solution of the present invention is as follows:

[0011] A high-pressure and heat-resistant round steel comprises the following components in percentage by mass: C: 0.13%-0.17%, Si: 0.17%-0.35%, Mn: 0.45%-0.65%, P < 0.010%, S ≤ 0.008%, Cr: 0.92%-0.98%, Mo: 0.42%-0.46%, wherein 0.47 < (Si+Mn+P) / (Cr+Mo) < 0.66, and the balance is iron and unavoidable impurities.

[0012] The present invention also discloses a method for preparing the high-pressure heat-resistant round steel, which comprises the following steps: a smelting process and a casting process; in the casting process, a 50m 3 The crystallizer and 8 to 10 ingot streams have a casting section of 200mm×240mm; the temperature of the tundish for molten steel casting is ≥1150℃, and the nozzle baking temperature is ≥700℃; the protective gas flow rate for protective casting is 14Nm / h~16Nm / h, and the gas pressure is 0.16MPa~0.19MPa; the immersion depth of the crystallizer nozzle is 120mm~140mm; the casting superheat is controlled to be ≤28℃.

[0013] The implementation of the present invention will have the following beneficial effects:

[0014] The present invention provides a high-pressure heat-resistant round steel and a preparation method thereof. The clean steel smelting technology is adopted to produce a cast steel billet with high-pressure heat-resistant performance through a continuous casting process of increasing the crystallizer volume + ultra-multi-stream casting combined with reasonable component design. The internal structure of the billet is uniform and has a high quality rate. The internal structure of the billet is further made fine and uniform, so that the segregation index of the round steel is low and the surface quality is excellent. The segregation index of the high-pressure heat-resistant round steel is less than 1.0, the oxidation resistance is 0.1mm / a~0.3mm / a, and the high-temperature service strength is ≥500MPa. It meets the use requirements of steel in the electric power energy industry, solves the problem of low production efficiency in traditional processes, and has good economic efficiency.

[0015] The present invention omits the use of added W, N, and Ni elements and simultaneously reduces the amount of Cr added, thereby reducing the types of alloy elements and precisely controlling the interaction between the elements, thereby reducing the manufacturing cost and the complexity of the production organization. DETAILED DESCRIPTION

[0016] The present invention will be further described below with reference to specific examples, but the present invention is not limited thereto in any way.

[0017] The invention discloses a high-pressure heat-resistant round steel, comprising the following components in percentage by mass: C: 0.13%-0.17%, Si: 0.17%-0.35%, Mn: 0.45%-0.65%, P < 0.010%, S ≤ 0.008%, Cr: 0.92%-0.98%, Mo: 0.42%-0.46%, wherein 0.47 < (Si+Mn+P) / (Cr+Mo) < 0.66, and the balance is iron and unavoidable impurities.

[0018] Specifically, the present invention sets 0.47<(Si+Mn+P) / (Cr+Mo)<0.66. The setting of this empirical range is a key parameter for balancing the material's room temperature processing performance, room temperature mechanical strength and high temperature service performance; if it is less than 0.47, the product's oxidation resistance and corrosion resistance are poor, and corrosion oxidation defects are prone to occur; if it is greater than 0.66, the product's processing performance will be reduced, resulting in processing defects.

[0019] In a specific embodiment, the segregation index of the high-pressure heat-resistant round steel is less than 1.0, which reduces the occurrence of surface cracks and uneven performance in the subsequent production process of the high-pressure heat-resistant round steel. The oxidation resistance rate is 0.1mm / a~0.3mm / a, and the high-temperature service strength is ≥500MPa, which improves the service life and service effect of the high-pressure heat-resistant round steel in energy equipment under high temperature.

[0020] The present invention also discloses a method for preparing the high-pressure heat-resistant round steel, which comprises a smelting process and a casting process, specifically comprising the following steps:

[0021] S1. In the smelting process, clean scrap steel and auxiliary materials are used as furnace charges, with the amount of clean scrap steel added being ≤5t / furnace; the amount of auxiliary materials added being ≤1t / furnace; 0.55t / furnace to 0.75t / furnace of active lime is added, the final slag basicity R value is ≥0.35, the tapping temperature is 1630℃~1650℃, and the one-time carbon extraction rate is increased to 100%; the amount of slag discharged during tapping is ≤3t / furnace, and 16t / furnace to 23t / furnace of slag-forming agent is added to the ladle.

[0022] Specifically, under the premise of ensuring the charging capacity, use less or no or use clean scrap steel, reduce the addition of non-essential auxiliary materials such as temperature raising agents and sludge balls, and improve the purity of molten steel; increase the amount of lime input appropriately, increase the final slag alkalinity and steel tapping temperature, increase the one-time carbon pulling rate, and avoid deep blowing; strengthen the control of slag discharge during the steel tapping process, and add lime and fluorite slagging agents to the ladle for subsequent desulfurization to improve the cleanliness of molten steel.

[0023] S2, in the casting process, a volume of 50m 3 The crystallizer and 8 to 10 ingot streams have a casting section of 200mm×240mm; the temperature of the tundish for molten steel casting is ≥1150℃, and the nozzle baking temperature is ≥700℃ to improve the cleanliness of the molten steel; the protective gas flow rate for protective casting is 14Nm / h~16Nm / h, and the gas pressure is 0.16MPa~0.19MPa, which reduces the pollution of the external environment to the molten steel and promotes the removal of impurities inside the molten steel; the immersion depth of the crystallizer nozzle is 120mm~140mm, which not only improves the fluidity of the molten steel and promotes the continuity of casting, but also suppresses the large fluctuation of the crystallizer liquid level and improves the surface quality of the billet; the casting superheat is controlled to be ≤28℃ to reduce the occurrence of cracks on the billet surface.

[0024] Specifically, the volume of the crystallizer for molten steel casting is increased from 30m3 in conventional process to 3 Expanded to 50m 3 The number of ingot streams is increased from 4 in the conventional process to 8~10, and the casting section is set to 200mm×240mm, which greatly improves the homogeneity and fluidity of the molten steel.

[0025] In a specific embodiment, the casting process further includes: using special protective slag for the round steel product to ensure the black liquid level operation in the crystallizer and improve the surface quality of the steel billet.

[0026] In a specific embodiment, the auxiliary materials include a temperature raising agent and / or sludge balls.

[0027] In a specific embodiment, the selection of the temperature raising agent and the sludge balls is relatively flexible and can be freely selected according to actual needs without much restriction.

[0028] In one embodiment, the slag former includes lime or fluorite.

[0029] The following are specific embodiments

[0030] Example 1

[0031] The high-pressure heat-resistant round steel of this embodiment includes the following components in mass percentage: C: 0.13%, Si: 0.17%, Mn: 0.45%, P: 0.009%, S: 0.008%, Cr: 0.92%, Mo: 0.42%, wherein (Si+Mn+P) / (Cr+Mo)=0.47, and the balance is iron and unavoidable impurities.

[0032] The method for preparing high-pressure heat-resistant round steel of this embodiment comprises the following steps:

[0033] S1. In the smelting process, clean scrap steel and auxiliary materials are used as furnace charges, with 5t of clean scrap steel added per furnace; 1t of auxiliary materials are added per furnace, including temperature raising agent and sludge balls; 0.55t of active lime is added per furnace, the final slag alkalinity R value is 0.35, the tapping temperature is 1630℃, and the one-time carbon extraction rate is increased to 100%; the amount of slag discharged during tapping is 2.8t per furnace, and 16t of slag-forming agent is added to the ladle per furnace.

[0034] S2, in the casting process, a volume of 50m 3 The crystallizer and 8 ingot streams have a casting section of 200mm×240mm; the temperature of the molten steel casting intermediate tank is 1150℃, and the nozzle baking temperature is 700℃; the protective gas flow rate for protective casting is 14Nm / h, and the gas pressure is 0.16MPa; the crystallizer nozzle immersion depth is 120mm; and the casting superheat is controlled at 28℃.

[0035] The product of this embodiment has a segregation index of 0.9 and a surface quality qualification rate of 99.8%.

[0036] Example 2

[0037] The high-pressure heat-resistant round steel of this embodiment includes the following components in mass percentage: C: 0.14%, Si: 0.20%, Mn: 0.50%, P: 0.008%, S: 0.0075%, Cr: 0.93%, Mo: 0.43%, wherein (Si+Mn+P) / (Cr+Mo)=0.52, and the balance is iron and unavoidable impurities.

[0038] The method for preparing high-pressure heat-resistant round steel of this embodiment comprises the following steps:

[0039] S1. In the smelting process, clean scrap steel and auxiliary materials are used as furnace charges, with 4.8t of clean scrap steel added per furnace; 0.95t of auxiliary materials are added per furnace, including temperature raising agent and sludge balls; 0.57t of active lime is added per furnace, the final slag alkalinity R value is 0.37, the tapping temperature is 1634℃, and the one-time carbon extraction rate is increased to 100%; the amount of slag discharged during tapping is 3t per furnace, and 23t of slag-forming agent is added to the ladle per furnace.

[0040] S2, in the casting process, a volume of 50m 3 The crystallizer and 9 ingot streams have a casting section of 200mm×240mm; the temperature of the tundish for molten steel casting is 1155℃, and the nozzle baking temperature is 705℃; the protective gas flow rate for protective casting is 14.8Nm / h, and the gas pressure is 0.17MPa; the crystallizer nozzle immersion depth is 124mm; and the casting superheat is controlled at 27.5℃.

[0041] The product of this embodiment has a segregation index of 0.8 and a surface quality qualification rate of 99.85%.

[0042] Example 3

[0043] The high-pressure heat-resistant round steel of this embodiment includes the following components in mass percentage: C: 0.15%, Si: 0.23%, Mn: 0.55%, P: 0.007%, S: 0.007%, Cr: 0.94%, Mo: 0.44%, wherein (Si+Mn+P) / (Cr+Mo)=0.57, and the balance is iron and unavoidable impurities.

[0044] The method for preparing high-pressure heat-resistant round steel of this embodiment comprises the following steps:

[0045] S1. In the smelting process, clean scrap steel and auxiliary materials are used as furnace charges, with 4.3t of clean scrap steel added per furnace; 0.98t of auxiliary materials are added per furnace, including temperature raising agent and sludge balls; 0.55t of active lime is added per furnace, the final slag alkalinity R value is 0.39, the tapping temperature is 1637℃, and the one-time carbon extraction rate is increased to 100%; the amount of slag discharged during tapping is 2.7t per furnace, and 19t of slag-forming agent is added to the ladle per furnace.

[0046] S2, in the casting process, a volume of 50m 3 The crystallizer and 10 ingot streams have a casting section of 200mm×240mm; the temperature of the molten steel casting intermediate tank is 1157℃, and the nozzle baking temperature is 707℃; the protective gas flow rate for protective casting is 15.10Nm / h, and the gas pressure is 0.165MPa; the crystallizer nozzle immersion depth is 127mm; and the casting superheat is controlled at 27℃.

[0047] The product of this embodiment has a segregation index of 0.5 and a surface quality qualification rate of 99.9%.

[0048] Example 4

[0049] The high-pressure heat-resistant round steel of this embodiment includes the following components in mass percentage: C: 0.16%, Si: 0.25%, Mn: 0.60%, P: 0.006%, S: 0.005%, Cr: 0.95%, Mo: 0.45%, wherein (Si+Mn+P) / (Cr+Mo)=0.61, and the balance is iron and unavoidable impurities.

[0050] The method for preparing high-pressure heat-resistant round steel of this embodiment comprises the following steps:

[0051] S1. In the smelting process, clean scrap steel and auxiliary materials are used as furnace charges, with 4.5t of clean scrap steel added per furnace; 0.93t of auxiliary materials are added per furnace, including temperature raising agent and sludge balls; 0.55t of active lime is added per furnace, the final slag alkalinity R value is 0.41, the tapping temperature is 1639℃, and the one-time carbon extraction rate is increased to 100%; the amount of slag discharged during tapping is 2.5t per furnace, and 17t of slag-forming agent is added to the ladle per furnace.

[0052] S2, in the casting process, a volume of 50m 3 The crystallizer and 8 ingot streams have a casting section of 200mm×240mm; the temperature of the molten steel casting intermediate tank is 1159℃, and the nozzle baking temperature is 710℃; the protective gas flow rate for protective casting is 15.30Nm / h, and the gas pressure is 0.18MPa; the crystallizer nozzle immersion depth is 129mm; and the casting superheat is controlled at 26.5℃.

[0053] The product of this embodiment has a segregation index of 0.7 and a surface quality qualification rate of 99.95%.

[0054] Example 5

[0055] The high-pressure heat-resistant round steel of this embodiment includes the following components in mass percentage: C: 0.17%, Si: 0.28%, Mn: 0.65%, P: 0.009%, S: 0.004%, Cr: 0.97%, Mo: 0.46%, wherein (Si+Mn+P) / (Cr+Mo)=0.66, and the balance is iron and unavoidable impurities.

[0056] The method for preparing high-pressure heat-resistant round steel of this embodiment comprises the following steps:

[0057] S1. In the smelting process, clean scrap steel and auxiliary materials are used as furnace charges, with 4.1t of clean scrap steel added per furnace; 0.89t of auxiliary materials are added per furnace, including temperature raising agent and sludge balls; 0.59t of active lime is added per furnace, the final slag alkalinity R value is 0.43, the tapping temperature is 1641°C, and the one-time carbon extraction rate is increased to 100%; the amount of slag discharged during tapping is 2.6t per furnace, and 21t of slag-forming agent is added to the ladle per furnace.

[0058] S2, in the casting process, a volume of 50m 3 The crystallizer and 9 ingot streams have a casting section of 200mm×240mm; the temperature of the molten steel casting intermediate tank is 1160℃, and the nozzle baking temperature is 711℃; the protective gas flow rate for protective casting is 15.50Nm / h, and the gas pressure is 0.178MPa; the crystallizer nozzle immersion depth is 131mm; and the casting superheat is controlled at 26℃.

[0059] The product of this embodiment has a segregation index of 0.6 and a surface quality qualification rate of 99.93%.

[0060] Example 6

[0061] The high-pressure heat-resistant round steel of this embodiment includes the following components in mass percentage: C: 0.135%, Si: 0.30%, Mn: 0.48%, P: 0.008%, S: 0.003%, Cr: 0.98%, Mo: 0.43%, wherein (Si+Mn+P) / (Cr+Mo)=0.56, and the balance is iron and unavoidable impurities.

[0062] The method for preparing high-pressure heat-resistant round steel of this embodiment comprises the following steps:

[0063] S1. In the smelting process, clean scrap steel and auxiliary materials are used as furnace charges, with 4.4t of clean scrap steel added per furnace; 0.88t of auxiliary materials are added per furnace, including temperature raising agent and sludge balls; 0.61t of active lime is added per furnace, the final slag alkalinity R value is 0.44, the tapping temperature is 1643°C, and the one-time carbon extraction rate is increased to 100%; the amount of slag discharged during tapping is 2.7t per furnace, and 20t of slag-forming agent is added to the ladle per furnace.

[0064] S2, in the casting process, a volume of 50m 3 The crystallizer and 10 ingot streams have a casting section of 200mm×240mm; the temperature of the tundish for molten steel casting is 1161℃, and the nozzle baking temperature is 712℃; the protective gas flow rate for protective casting is 15.70Nm / h, and the gas pressure is 0.176MPa; the immersion depth of the crystallizer nozzle is 133mm; and the casting superheat is controlled at 25℃.

[0065] The product of this embodiment has a segregation index of 0.5 and a surface quality qualification rate of 100%.

[0066] Example 7

[0067] The high-pressure heat-resistant round steel of this embodiment includes the following components in mass percentage: C: 0.145%, Si: 0.32%, Mn: 0.52%, P: 0.007%, S: 0.005%, Cr: 0.93%, Mo: 0.44%, wherein (Si+Mn+P) / (Cr+Mo)=0.62, and the balance is iron and unavoidable impurities.

[0068] The method for preparing high-pressure heat-resistant round steel of this embodiment comprises the following steps:

[0069] S1. In the smelting process, clean scrap steel and auxiliary materials are used as furnace charges, with 4.7t of clean scrap steel added per furnace; 0.90t of auxiliary materials are added per furnace, including temperature raising agent and sludge balls; 0.62t of active lime is added per furnace, the final slag alkalinity R value is 0.46, the tapping temperature is 1645℃, and the one-time carbon extraction rate is increased to 100%; the amount of slag discharged during tapping is 2.3t per furnace, and 21.5t of slag-forming agent is added to the ladle per furnace.

[0070] S2, in the casting process, a volume of 50m 3 The crystallizer and 8 ingot streams have a casting section of 200mm×240mm; the temperature of the molten steel casting intermediate tank is 1162℃, and the nozzle baking temperature is 714℃; the protective gas flow rate for protective casting is 16Nm / h, and the gas pressure is 0.185MPa; the crystallizer nozzle immersion depth is 136mm; and the casting superheat is controlled at 27℃.

[0071] The product of this embodiment has a segregation index of 0.6 and a surface quality qualification rate of 99.96%.

[0072] Example 8

[0073] The high-pressure heat-resistant round steel of this embodiment includes the following components in mass percentage: C: 0.155%, Si: 0.35%, Mn: 0.57%, P: 0.008%, S: 0.006%, Cr: 0.97%, Mo: 0.46%, wherein (Si+Mn+P) / (Cr+Mo)=0.65, and the balance is iron and unavoidable impurities.

[0074] The method for preparing high-pressure heat-resistant round steel of this embodiment comprises the following steps:

[0075] S1. In the smelting process, clean scrap steel and auxiliary materials are used as furnace charges, with 4.5t of clean scrap steel added per furnace; 0.97t of auxiliary materials are added per furnace, including temperature raising agent and sludge balls; 0.63t of active lime is added per furnace, the final slag alkalinity R value is 0.48, the tapping temperature is 1646℃, and the one-time carbon extraction rate is increased to 100%; the amount of slag discharged during tapping is 2.1t per furnace, and 17.5t of slag-forming agent is added to the ladle per furnace.

[0076] S2, in the casting process, a volume of 50m 3 The crystallizer and 9 ingot streams have a casting section of 200mm×240mm; the temperature of the tundish for molten steel casting is 1163℃, and the nozzle baking temperature is 716℃; the protective gas flow rate for protective casting is 15.5Nm / h, and the gas pressure is 0.19MPa; the crystallizer nozzle immersion depth is 140mm; and the casting superheat is controlled at 28℃.

[0077] The product of this embodiment has a segregation index of 0.3 and a surface quality qualification rate of 99.97%.

[0078] The round steel produced by this invention adopts a brand-new composition design and process design, which ensures that the composition, structural uniformity, surface quality and other performance are all at a good level. The product segregation index is less than 1.0, and the surface quality pass rate is ≥99.8%. It has high quality and performance stability. In contrast, the round steel products produced by conventional processes have a segregation index greater than 1.0 and a surface quality pass rate of ≤95%. Specific production data are shown in the table below:

[0079] Table 1 Comparison of properties of round steel produced by the process of the present invention and conventional process

[0080]

[0081] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A high-pressure heat-resistant round steel, characterized in that: The following components are included in mass percentage: C: 0.135%~0.155%, Si: 0.23%~0.35%, Mn: 0.48%~0.57%, P<0.010%, S≤0.008%, Cr: 0.93%~0.98%, Mo: 0.43%~0.46%, of which 0.56≤(Si+Mn+P) / (Cr+Mo)≤0.57 or 0.62≤(Si+Mn+P) / (Cr+Mo)≤0.65, and the balance is iron and unavoidable impurities; The segregation index of the high-pressure heat-resistant round steel is less than 1.0, and the oxidation resistance is 0.1 mm / a to 0.3 mm / a; The method for preparing high-pressure heat-resistant round steel comprises the following steps: a smelting process and a casting process; In the casting process, a volume of 50m 3 The crystallizer and 8 to 10 ingot streams have a casting cross-section of 200mm×240mm; the temperature of the tundish for molten steel casting is ≥1150℃, and the nozzle baking temperature is ≥700℃; the protective gas flow rate for protective casting is 14Nm / h~16Nm / h, and the gas pressure is 0.16MPa~0.19MPa; the crystallizer nozzle immersion depth is 120mm~140mm; the casting superheat is controlled to be ≤28℃; In the smelting process, clean scrap steel and auxiliary materials are used as furnace charges, wherein the amount of clean scrap steel added is ≤5t / furnace; the amount of auxiliary materials added is ≤1t / furnace; 0.55t / furnace to 0.75t / furnace of active lime is added, the final slag basicity R value is ≥0.35, the tapping temperature is 1630°C to 1650°C, and the one-time carbon extraction rate is increased to 100%; the amount of slag discharged during tapping is ≤3t / furnace, and 16t / furnace to 23t / furnace of slag-forming agent is added to the ladle.

2. The high-pressure heat-resistant round steel according to claim 1, characterized in that: The auxiliary materials include a temperature raising agent and / or sludge balls.

3. The high-pressure heat-resistant round steel according to claim 1, characterized in that: The slagging agent includes lime or fluorite.

Images