Method for producing quenched and tempered bar for high-temperature gas cooled reactor fastener by using rolling instead of forging

Abstract

The invention discloses a method for producing a quenched and tempered bar for a high-temperature gas cooled reactor fastener by using rolling instead of forging. The problem that the mechanical property requirement of a forged piece is difficult to meet in the prior art is solved. The method comprises the following steps: (1) optimally designing chemical components of steel, strictly controlling sulfur, phosphorus and oxygen, and adding a certain content of microalloy vanadium and niobium elements; deoxidation and denitrification are achieved through an LF furnace and VD degassing, and the purity of molten steel is improved; the structure segregation is reduced through the constant-melting-speed electroslag furnace; (2) the compactness and the uniformity of the core structure of the steel are improved through high-temperature and large-rolling-reduction controlled steel airing differential-temperature rolling; (3) through normalizing and tempering pretreatment, the uniformity and consistency of the hardening and tempering performance are ensured; and (4) the pre-straightening treatment before hardening and tempering is carried out, so that the straightening stress after hardening and tempering is effectively reduced. The method has the beneficial effects that the maximum production specification phi is 200mm, and the flaw detection quality is excellent; the purity of the steel is high, and the total amount of inclusions is within the 2.0 level; the mechanical property of the bar is ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear power steel, and specifically relates to a method for producing quenched and tempered bars for high-temperature gas-cooled reactor fasteners by rolling instead of forging, and relates to SA-540 Gr.B24 Cl.3 quenched and tempered bars. Background Art

[0002] SA-540 Gr.B24 Cl.3 quenched and tempered alloy bars are widely used in the manufacture of bolts, nuts, washers, support pins, etc. for fasteners of reactor pressure vessels of the fourth-generation nuclear power high-temperature gas-cooled reactor engineering. Due to the harsh service conditions of the parts, their processing accuracy is strict. The material is required to have sufficient strength and toughness (including room temperature tensile, 350℃ high tensile, and impact toughness). At the same time, there are strict requirements for size, shape, residual stress, surface quality, etc. Generally, forging production is used to ensure mechanical properties and internal quality, but the production efficiency is low and the cost is high. For this reason, rolling production has been tried, but compared with forging production, due to the limitation of rolling mill capacity, the reduction of a single rolling pass is limited, the extension deformation of the material is only on the surface, and the internal penetration deformation is insufficient. If the quenching cooling rate is not enough, it is difficult for the comprehensive mechanical properties to meet the technical requirements. Especially in the field of nuclear power, it is necessary to take samples at one-quarter of the bar diameter for performance experiments, which further increases the difficulty of production. Summary of the invention

[0003] The invention discloses a method for producing quenched and tempered bars for high temperature gas-cooled reactor fasteners by rolling instead of forging, and a method for producing SA-540 Gr.B24 Cl.3 quenched and tempered bars by rolling instead of forging, which solves the problem that the prior art is difficult to meet the mechanical property requirements of forgings.

[0004] The present invention adopts the following technical solutions:

[0005] ⑴ SA-540 Gr.B24 Cl.3 tempered bars for nuclear power high temperature reactor fasteners are produced by rolling instead of forging, with a maximum diameter of 200mm; the composition of the bars by mass percentage: carbon: 0.37%~0.44%, silicon: 0.15%~0.35%, manganese: 0.70%~0.90%, nickel: 1.65%~2.00%, chromium: 0.70%~0.95%, molybdenum: 0.30%~0.40%, phosphorus not more than 0.02%, sulfur not more than 0.015%, copper not more than 0.20%, and the balance is iron and unavoidable impurities.

[0006] (2) The production process of bars includes: smelting, electroslag remelting, electroslag ingot heating, rolling into bars, pretreatment (normalizing + tempering), quenching and tempering, straightening, stress relief annealing, performance testing, machining, finishing, and warehousing;

[0007] ① The smelting adopts EAF+LF+VD+ESR method.

[0008] Smelting process: The ingredients are high-quality scrap steel and alloys. The molten steel is first smelted in an electric furnace and then sent to the LF refining furnace for refining;

[0009] LF refining process: LF refining time is not less than 50min, aluminum wire is used for deoxidation, the refining white slag is kept for not less than 30min, and the molten steel temperature reaches 1620℃~1660℃ and is transferred to VD furnace for vacuum degassing treatment;

[0010] VD vacuum refining process: vacuuming time below 67pa is not less than 10min, and the oxygen content of molten steel is controlled to be no more than 0.0020% and the hydrogen content is no more than 0.00015%;

[0011] Mold casting process: using argon protection casting, casting electrode rod specification Φ470mm, casting temperature is 1550℃~1560℃, electrode rod mold is cooled to the bottom;

[0012] The electroslag remelting adopts a binary slag system of CaF2:Al2O3=70:30, the slag amount is 120kg / furnace, the remelting voltage of the constant melting rate electroslag furnace is controlled at 55V~65V, the remelting current is controlled at 10000A~12000A, the remelting melting rate is controlled at 6.5kg / min~7.5kg / min, the electroslag remelting ingot is φ610mm electroslag ingot, and the electroslag ingot is sent to the next step at a warm temperature;

[0013] ② For electroslag ingot heating, keep the furnace temperature below 850℃ without fire for 30 minutes, then heat it to 1270℃±10℃ in the insulation section at a heating rate of less than 100℃ / h, with a insulation time of 1.0h~1.5h and a total heating time of not less than 5h. Measure the temperature of the ingot body before tapping, and control the ingot temperature out of the furnace at 1200℃~1220℃.

[0014] ③ The differential temperature rolling process is adopted, which is divided into two stages of rolling: the rolling temperature of stage I is 1030℃~1220℃, the single-pass reduction in this stage is 10mm~50mm, the cumulative reduction rate is 50%~65%, and then the steel is air-dried for 4min~6min; the rolling temperature of stage II is 850℃~980℃, and the cumulative reduction rate is 30%~50%.

[0015] ④ After rolling, the steel should be promptly cooled in a slow cooling pit. The pit temperature should not be lower than 400℃ and the pit cooling time should not be less than 60h.

[0016] ⑤ Pretreatment (normalizing and tempering), pre-normalizing temperature 920℃±10℃, holding time for at least 0.5h for every 25mm thickness, air cooling; pre-tempering temperature 670℃±10℃, holding time for at least 0.5h for every 25mm thickness, air cooling; after pretreatment, the steel is straightened, the straightness before straightening is not less than 8mm / m, and the straightness after straightening is not more than 3mm / m.

[0017] ⑥Quenching and tempering treatment, quenching heating temperature 860℃±10℃, holding time for at least 0.5h for every 25mm thickness, quenching medium water, water temperature 20℃~40℃; 0.5h~1.0h after quenching, the steel is put into the electric furnace for tempering, the tempering temperature is 610℃±10℃, the holding time is at least 1.0h for every 25mm thickness, and then air-cooled out of the furnace.

[0018] ⑦ Straighten after quenching and tempering to ensure that the straightness is not greater than 2mm / m.

[0019] ⑧After the steel is straightened, an electric heating furnace is used for stress relief annealing treatment. The heating temperature is 600℃±10℃ and the insulation time is 8h~10h.

[0020] ⑨ The steel is turned / peeled to meet the straightness of 0.3mm / m~1mm / m and surface roughness Ra not greater than 2.3μm.

[0021] Process analysis and invention points of the present invention:

[0022] ⑴Process analysis:

[0023] The purity of molten steel is improved through LF furnace white slag method, aluminum wire feeding, VD degassing and other steelmaking process measures. It is further purified by electroslag remelting, reducing inclusions and segregation, and the internal structure is more dense.

[0024] By controlling the temperature differential rolling method of the steel, a temperature gradient is formed from the surface to the inside of the bar, and a deformation resistance gradient is formed from the surface to the inside during the II stage rolling, so that the rolling deformation of the steel penetrates into the core and presses the looseness and shrinkage defects in the core;

[0025] The steel plate can be put into a slow cooling pit after rolling to prevent white spots or cracks; the normalizing + tempering pretreatment can refine the grains and make the structure uniform to ensure the uniformity of the quenching and tempering performance;

[0026] Through the pre-straightening treatment before quenching and tempering, only a small amount of deformation and a small degree of straightening are achieved after quenching, thereby achieving the purpose of reducing the straightening stress;

[0027] Through reasonable alloy element ratio and quenching + tempering + stress relief annealing heat treatment process, the steel can obtain tempered troostite + a small amount of ferrite structure, which can ensure the mechanical properties of the bar.

[0028] (2) Invention Point:

[0029] ① The chemical composition of steel is optimized. In addition to strictly controlling the sulfur, phosphorus and oxygen contents that affect the impact properties, a certain amount of micro-alloy vanadium (0.07%~0.10%) and niobium (0.02%~0.03%) elements are added to ensure the mechanical properties; the LF furnace uses the white slag method, aluminum wire feeding, and VD degassing process to achieve deoxidation and denitrification to improve the purity of the molten steel; through the constant melting rate electric slag furnace, controlling the voltage and current can stabilize the melting rate of the electrode billet and reduce organizational segregation.

[0030] ② Rolling process and parameter control: Improve the density and uniformity of the core structure of steel and improve the impact toughness of steel through high temperature, large reduction and controlled temperature differential rolling.

[0031] ③ By pre-treating the steel with normalizing + tempering, the grain size of the steel is refined, the distribution uniformity is improved, and the internal stress is reduced, thereby ensuring the uniformity and consistency of the quenching and tempering performance.

[0032] ④ By pre-straightening the steel before quenching and tempering, the degree of correction after quenching and tempering is effectively reduced, and the generation of straightening stress is reduced.

[0033] The benefits of the present invention are:

[0034] The SA-540 Gr.B24 Cl.3 quenched and tempered bar produced by the rolling-forging process has a maximum specification of Φ200mm and has excellent flaw detection quality, which can fully meet the flaw detection requirements of standard ASME BPVCⅢDⅠNB-2585 and meet the use requirements of customers; the steel has high purity, and the total amount of inclusions A+B+C+D is controlled within 2.0 levels; the mechanical properties are that the impact energy at -12℃ at 1 / 4 diameter is more than 60J, and the impact energy at 13℃ is more than 80J; the room tension Rm value is 1115MPa~1170MPa, and the 350℃ high tension Rm value is 951MPa~1050MPa; after quenching and tempering, the residual stress of the bar tested according to ASTM E837 does not exceed 50MPa (absolute value), which meets the use requirements of customers. DETAILED DESCRIPTION

[0035] The following is a detailed description in conjunction with three preferred embodiments.

[0036] Example 1

[0037] Production of finished round steel Ф120mm.

[0038] (1) The EAF+LF+VD+ESR method is used for smelting. High-quality scrap steel and alloy are selected as the raw materials. The molten steel is first smelted in an electric furnace and then sent to the LF refining furnace for refining. The LF refining time is 60 minutes and the white slag time is 40 minutes. When the molten steel temperature reaches 1650℃, it is transferred to the VD furnace for vacuum degassing. The VD vacuum degree is not greater than 0.67mbar and is maintained for 10 minutes. After opening the tank, the molten steel is set to [H]1.2×10 -6 ; Argon protection is used to cast φ470mm round electrode rods, the pouring temperature is 1555℃, and the electrode rod mold is cooled to the bottom; the electroslag remelting adopts a binary slag system CaF2:Al2O3=70:30, the slag amount is 120kg / furnace, the constant melting rate electroslag furnace remelting voltage is controlled at 55V~65V, the remelting current is controlled at 10000A~12000A, the remelting melting rate is controlled at 7kg / min, the electroslag remelting ingot is φ610mm electroslag ingot, and the electroslag ingot is sent to the next step at temperature; the chemical composition analysis of the electroslag ingot is as follows: carbon: 0.41%, silicon: 0.28%, manganese: 0.84%, nickel: 1.87%, chromium: 0.92%, molybdenum: 0.36%, phosphorus: 0.006%, sulfur: 0.001%, copper: 0.11%, vanadium: 0.08%, niobium: 0.023%, and the remainder is iron and unavoidable impurities.

[0039] (2) Heating of electroslag ingots: electroslag steel ingots are loaded into the furnace at a furnace temperature of 640℃. After being kept without fire for 30 minutes, the temperature is increased at a rate of 80℃ / h to 1260℃ and the holding time is started. The holding and equalizing temperature fluctuates within the range of 1260℃ to 1275℃. The holding (averaging) time is 1.5h and the total heating time is 9.5h. The temperature of the ingot out of the furnace is controlled at 1200℃ to 1220℃.

[0040] ⑶ Rolling adopts differential temperature rolling process, that is, it is divided into two stages: the rolling temperature of stage I is 980℃~1200℃, of which the starting rolling temperature is 1100℃ and the final rolling temperature is 980℃. The single pass reduction in this stage is 10mm~50mm, and the cumulative reduction rate is 65%. Then the steel is air-dried for 5 minutes, and the steel size is 190mm×190mm. The starting rolling temperature of stage II is 910℃, the final rolling temperature is 850℃, and the cumulative reduction rate is 39%.

[0041] (4) Cooling: After rolling, the steel enters a slow cooling pit with a pit temperature of 500°C and a pit cooling time of 60h.

[0042] ⑸ Pretreatment (normalizing and tempering): pre-normalizing temperature 920℃, heating rate 70℃ / h, holding time 2.5h, air cooling; pre-tempering temperature 660℃, heating rate 50℃ / h, holding time 4h, air cooling; use ten-roll straightening equipment for pre-straightening, the straightness after straightening is 3mm / m.

[0043] (6) Quenching and tempering treatment: quenching heating temperature 860℃, holding time 3h, quenching medium water, water temperature 20℃~40℃; 0.5h~1.0h after quenching, the steel is put into the electric furnace for tempering, the tempering temperature is 620℃, the holding time is 8h, and it is air-cooled after being taken out of the furnace.

[0044] ⑺After quenching and tempering, local point straightening is carried out, and the straightness is 1.5mm / m~2mm / m.

[0045] ⑻ Stress relief annealing: The stress relief annealing heating temperature is 600℃ and the holding time is 10h.

[0046] ⑼ The steel surface is polished, with a straightness of 0.5mm / m~0.7mm / m and a surface roughness of Ra0.5μm~1μm.

[0047] ⑽The finished product meets the flaw detection requirements of ASME BPVCⅢDⅠNB-2585; Steel gas [H] 1.0×10 -6 The total amount of inclusions A+B+C+D is level 1.5. The mechanical properties are impact energy at -12℃ at 1 / 4 diameter 80 / 85 / 88J, and impact energy at 13℃ 95.5 / 100.7 / 99.0J. The average room tensile Rm is 1140MPa, and the average 350℃ high tensile Rm is 1020MPa. The residual stress of the bar tested according to ASTM E837 does not exceed 50MPa (absolute value), which meets customer requirements.

[0048] Example 2

[0049] Production of finished round steel Ф150mm.

[0050] (1) The EAF+LF+VD+ESR method is used for smelting. High-quality scrap steel and alloy are selected as the raw materials. The molten steel is first smelted in an electric furnace and then sent to the LF refining furnace for refining. The LF refining time is 60 minutes and the white slag time is 45 minutes. When the molten steel temperature reaches 1660℃, it is transferred to the VD furnace for vacuum degassing. The VD vacuum degree is not greater than 0.67mbar and is maintained for 10 minutes. After opening the tank, the molten steel is set to [H]1.0×10 -6; Argon protection is used to cast φ470mm round electrode rods, the pouring temperature is 1550℃, and the electrode rod mold is cooled to the bottom; the electroslag remelting adopts a binary slag system CaF2:Al2O3=70:30, the slag amount is 120kg / furnace, the remelting voltage of the constant melting rate electroslag furnace is controlled at 55V~65V, the remelting current is controlled at 10000A~12000A, the remelting melting rate is controlled at 7kg / min, the electroslag remelting ingot is φ610mm electroslag ingot, and the electroslag ingot is sent to the next step at temperature; the chemical composition analysis of the electroslag ingot is as follows: carbon: 0.415%, silicon: 0.24%, manganese: 0.82%, nickel: 1.84%, chromium: 0.88%, molybdenum: 0.36%, phosphorus: 0.005%, sulfur: 0.001%, copper: 0.07%, vanadium: 0.08%, niobium: 0.025%, and the remainder is iron and unavoidable impurities.

[0051] (2) Heating of electroslag ingots: electroslag ingots are loaded into the furnace at a furnace temperature of 600℃. After being kept without fire for 30 minutes, the temperature is increased at a rate of 80℃ / h to 1260℃ and the timing of insulation is started. The insulation and uniform heating temperature fluctuates within the range of 1260℃ to 1275℃. The insulation (uniform heating) time is 1.5h, and the total heating time is 9.8h. The temperature of the ingot out of the furnace is controlled at 1200℃ to 1220℃.

[0052] ⑶ Rolling adopts differential temperature rolling process, that is, it is divided into two stages: the rolling temperature of stage I is 1100℃~1220℃, of which the starting rolling temperature is 1180℃ and the final rolling temperature is 1100℃. The single pass reduction in this stage is 10mm~50mm, and the cumulative reduction rate is 50%. Then the steel is air-dried for 6 minutes, and the steel size is 270mm×250mm. The starting rolling temperature of stage II is 920℃, the final rolling temperature is 880℃, and the cumulative reduction rate is 43%.

[0053] (4) Cooling: After rolling, the steel enters a slow cooling pit with a pit temperature of 550°C and a pit cooling time of 60 hours.

[0054] ⑸ Pretreatment (normalizing and tempering): pre-normalizing temperature 920℃, heating rate 78℃ / h, holding time 4h, air cooling; pre-tempering temperature 650℃, heating rate 60℃ / h, holding time 6h, air cooling; use ten-roll straightening equipment for pre-straightening, the straightness after straightening is 3mm / m.

[0055] (6) Quenching and tempering treatment: quenching heating temperature 860℃, holding time 3.5h, quenching medium water, water temperature 20℃~40℃; 0.5h~1.0h after quenching, the steel is put into the electric furnace for tempering, the tempering temperature is 615℃, the holding time is 10h, and it is air-cooled after being taken out of the furnace.

[0056] ⑺After quenching and tempering, local point straightening is carried out, and the straightness is 1.5mm / m~2mm / m.

[0057] ⑻ Stress relief annealing: The stress relief annealing heating temperature is 600℃ and the holding time is 10h.

[0058] ⑼ The steel surface is polished, with a straightness of 0.5mm / m~0.7mm / m and a surface roughness of Ra0.5μm~1μm.

[0059] ⑽The finished product meets the flaw detection requirements of ASME BPVCⅢDⅠNB-2585; Steel gas [H] 1.0×10 -6 The total amount of inclusions A+B+C+D is level 1.5. The mechanical properties are 75 / 78 / 80J impact energy at -12℃ at 1 / 4 diameter, and 85 / 90 / 92J impact energy at 13℃. The average room tensile Rm is 1120MPa, and the average 350℃ high tensile Rm is 975MPa. The residual stress of the bar tested according to ASTM E837 does not exceed 50MPa (absolute value), which meets customer requirements.

[0060] Example 3

[0061] Production of finished round steel Ф200mm.

[0062] (1) The EAF+LF+VD+ESR method is used for smelting. High-quality scrap steel and alloy are selected as the raw materials. The molten steel is first smelted in an electric furnace and then sent to the LF refining furnace for refining. The LF refining time is 60 minutes and the white slag time is 40 minutes. When the molten steel temperature reaches 1656℃, it is transferred to the VD furnace for vacuum degassing. The VD vacuum degree is not greater than 0.67mbar and is maintained for 10 minutes. After opening the tank, the molten steel is set to [H]1.2×10 -6 ; Argon protection is used to cast φ470mm round electrode rods, the pouring temperature is 1550℃, and the electrode rod mold is cooled to the bottom; the electroslag remelting adopts a binary slag system CaF2:Al2O3=70:30, the slag amount is 120kg / furnace, the constant melting rate electroslag furnace remelting voltage is controlled at 55V~65V, the remelting current is controlled at 10000A~12000A, the remelting melting rate is controlled at 7kg / min, the electroslag remelting ingot is φ610mm electroslag ingot, and the electroslag ingot is sent to the next step at temperature; the chemical composition analysis of the electroslag ingot is as follows: carbon: 0.42%, silicon: 0.28%, manganese: 0.86%, nickel: 1.90%, chromium: 0.90%, molybdenum: 0.37%, phosphorus: 0.007%, sulfur: 0.001%, copper: 0.10%, vanadium: 0.09%, niobium: 0.025%, and the balance is iron and unavoidable impurities.

[0063] (2) Heating of electroslag ingots: electroslag steel ingots are loaded into the furnace at a furnace temperature of 660℃. After being kept without fire for 30 minutes, the temperature is increased at a rate of 80℃ / h to 1260℃ and the timing of insulation is started. The insulation and uniform heating temperature fluctuates within the range of 1260℃ to 1280℃. The insulation (uniform heating) time is 1.5h, and the total heating time is 9.5h. The temperature of the ingot out of the furnace is controlled at 1200℃ to 1220℃.

[0064] ⑶ Rolling adopts differential temperature rolling process, that is, it is divided into two stages: the rolling temperature of stage I is 1100℃~1220℃, of which the starting rolling temperature is 1180℃ and the final rolling temperature is 1105℃. The single pass reduction in this stage is 10mm~50mm, and the cumulative reduction rate is 50%. Then the steel is air-dried for 6min, and the steel size is 270mm×250mm. The starting rolling temperature of stage II is 930℃, the final rolling temperature is 900℃, and the cumulative reduction rate is 32%.

[0065] (4) Cooling: After rolling, the steel enters a slow cooling pit with a pit temperature of 600°C and a pit cooling time of 60h.

[0066] ⑸ Pretreatment (normalizing and tempering): pre-normalizing temperature 920℃, heating rate 65℃ / h, holding time 6h, air cooling; pre-tempering temperature 660℃, heating rate 60℃ / h, holding time 7h, air cooling; use ten-roll straightening equipment for pre-straightening, the straightness after straightening is 3mm / m.

[0067] (6) Quenching and tempering treatment: quenching heating temperature 860℃, holding time 4.5h, quenching medium water, water temperature 20℃~40℃; 0.5h~1.0h after quenching, the steel is put into the electric furnace for tempering, the tempering temperature is 610℃, the holding time is 10h, and it is air-cooled after being taken out of the furnace.

[0068] ⑺After quenching and tempering, local point straightening is carried out, and the straightness is 1.5mm / m~2mm / m.

[0069] ⑻ Stress relief annealing: The stress relief annealing heating temperature is 600℃ and the holding time is 10h.

[0070] ⑼ The steel surface is polished, with a straightness of 0.5mm / m~0.7mm / m and a surface roughness of Ra0.5μm~1μm.

[0071] ⑽The finished product meets the flaw detection requirements of ASME BPVCⅢDⅠNB-2585; Steel gas [H] 1.0×10 -6 The total amount of inclusions A+B+C+D is level 1.5. The mechanical properties are 67 / 68 / 65J impact energy at -12℃ at 1 / 4 diameter, and 75 / 70 / 72J impact energy at 13℃. The average room tensile Rm is 1122MPa, and the average 350℃ high tensile Rm is 962MPa. The residual stress of the bar tested according to ASTM E837 does not exceed 50MPa (absolute value), which meets customer requirements.

Claims

1. A method for producing quenched and tempered bars for high temperature gas-cooled reactor fasteners by rolling instead of forging, characterized in that: ⑴ The chemical composition of the steel is optimized. In addition to strictly controlling the sulfur, phosphorus and oxygen content that affect the impact performance, vanadium: 0.07%~0.10% and niobium: 0.02%~0.03% are added; ⑵Smelting process: The ingredients are high-quality scrap steel and alloys. The molten steel is first smelted in an electric furnace and then sent to the LF refining furnace for refining; (3) LF refining process: LF refining time is not less than 50min, aluminum wire is used for deoxidation, and the refining white slag is kept for not less than 30min. When the molten steel temperature reaches 1620℃~1660℃, it is transferred to VD furnace for vacuum degassing treatment; (4) VD vacuum refining process: vacuuming time below 67Pa is not less than 10min, and the oxygen content of molten steel is controlled to be no more than 0.0020% and the hydrogen content is no more than 0.00015%; ⑸Mold casting process: Use argon protection casting, casting electrode rod specification Φ470mm, casting temperature is 1550℃~1560℃, and the electrode rod mold is cooled to the bottom; (6) The electroslag remelting adopts a binary slag system of CaF2:Al2O3=70:30, the slag amount is 120kg / furnace, the remelting voltage of the constant melting rate electroslag furnace is controlled at 55V~65V, the remelting current is controlled at 10000A~12000A, the remelting melting rate is controlled at 6.5kg / min~7.5kg / min, the electroslag remelting ingot is φ610mm electroslag ingot, and the electroslag ingot is sent to the next step at a warm temperature; ⑺ Heating of electroslag ingot: after keeping the furnace temperature below 850℃ without fire for 30min, the temperature is raised to 1270℃±10℃ in the insulation stage at a heating rate of less than 100℃ / h, the insulation time is 1.0h~1.5h, and the total heating time is not less than 5h. The temperature of the ingot body is measured before tapping, and the ingot temperature out of the furnace is controlled at 1200℃~1220℃; ⑻ The differential temperature rolling process is adopted, which is divided into two stages of rolling: the rolling temperature of the first stage is 1030℃~1220℃, the single pass reduction in this stage is 10mm~50mm, the cumulative reduction rate is 50%~65%, and then the steel is air-dried for 4min~6min; the rolling temperature of the second stage is 850℃~980℃, and the cumulative reduction rate is 30%~50%; ⑼ After rolling, the steel should be promptly cooled in a slow cooling pit, the pit temperature should not be lower than 400℃, and the pit cooling time should not be less than 60h; ⑽ Pretreatment, normalizing and tempering, pre-normalizing temperature 920℃±10℃, holding time for at least 0.5h per 25mm thickness, air cooling; pre-tempering temperature 670℃±10℃, holding time for at least 0.5h per 25mm thickness, air cooling; after pretreatment, the steel is straightened, the straightness before straightening is not less than 8mm / m, and the straightness after straightening is not more than 3mm / m; ⑾Quenching and tempering treatment, quenching heating temperature 860℃±10℃, holding time for at least 0.5h for every 25mm thickness, quenching medium water, water temperature 20℃~40℃; 0.5h~1.0h after quenching, the steel is put into the electric furnace for tempering, the tempering temperature is 610℃±10℃, the holding time is at least 1.0h for every 25mm thickness, and air cooling is carried out after leaving the furnace ⑿ Straighten after quenching and tempering to ensure that the straightness is no more than 2mm / m; ⒀After the steel is straightened, an electric heating furnace is used for stress relief annealing treatment, the heating temperature is 600℃±10℃, and the holding time is 8h~10h; ⒁ The steel is turned / peeled to meet the straightness of 0.3mm / m~1mm / m and surface roughness Ra not greater than 2.3μm.

2. The method for producing quenched and tempered bars for high temperature gas-cooled reactor fasteners by rolling instead of forging according to claim 1, characterized in that: Production of finished round steel Ф120mm; (1) The EAF+LF+VD+ESR method is used for smelting. High-quality scrap steel and alloy are selected as the raw materials. The molten steel is first smelted in an electric furnace and then sent to the LF refining furnace for refining. The LF refining time is 60 minutes and the white slag time is 40 minutes. When the molten steel temperature reaches 1650℃, it is transferred to the VD furnace for vacuum degassing. The VD vacuum degree is not greater than 0.67mbar and is maintained for 10 minutes. After opening the tank, the molten steel is set to [H]1.2×10 -6 ; Argon protection is used to cast φ470mm round electrode rods, the casting temperature is 1555℃, and the electrode rod mold is cooled to the bottom; the electroslag remelting adopts a binary slag system CaF2:Al2O3=70:30, the slag amount is 120kg / furnace, the remelting voltage of the constant melting rate electroslag furnace is controlled at 55V~65V, the remelting current is controlled at 10000A~12000A, the remelting melting rate is controlled at 7kg / min, the electroslag remelting ingot is φ610mm electroslag ingot, and the electroslag ingot is sent to the next step at temperature; the chemical composition analysis of the electroslag ingot is as follows: carbon: 0.41%, silicon: 0.28%, manganese: 0.84%, nickel: 1.87%, chromium: 0.92%, molybdenum: 0.36%, phosphorus: 0.006%, sulfur: 0.001%, copper: 0.11%, vanadium: 0.08%, niobium: 0.023%, and the balance is iron and unavoidable impurities; (2) Heating of electroslag ingot: electroslag ingot is loaded into the furnace at a furnace temperature of 640℃, and kept without fire for 30 minutes. Then the temperature is increased at a rate of 80℃ / h to 1260℃ and the timer is kept warm. The warming temperature fluctuates within the range of 1260℃~1275℃. The warming time is 1.5h, the total heating time is 9.5h, and the temperature of the ingot out of the furnace is controlled at 1200℃~1220℃; ⑶ Rolling adopts differential temperature rolling process, that is, it is divided into two stages: the rolling temperature of stage I is 980℃~1200℃, of which the starting rolling temperature is 1100℃ and the final rolling temperature is 980℃. The single pass reduction in this stage is 10mm~50mm, and the cumulative reduction rate is 65%. Then the steel is air-dried for 5 minutes, and the steel size is 190mm×190mm. The starting rolling temperature of stage II is 910℃, the final rolling temperature is 850℃, and the cumulative reduction rate is 39%; (4) Cooling: After rolling, the steel enters a slow cooling pit with a pit temperature of 500°C and a pit cooling time of 60h; ⑸ Pretreatment, normalizing and tempering: pre-normalizing temperature 920℃, heating rate 70℃ / h, holding time 2.5h, air cooling; pre-tempering temperature 660℃, heating rate 50℃ / h, holding time 4h, air cooling; pre-straightening with ten-roll straightening equipment, straightness after straightening 3mm / m; (6) Quenching and tempering treatment: quenching heating temperature 860℃, holding time 3h, quenching medium water, water temperature 20℃~40℃; 0.5h~1.0h after quenching, the steel is put into the electric furnace for tempering, the tempering temperature is 620℃, the holding time is 8h, and it is air-cooled after leaving the furnace; ⑺ After quenching and tempering, local point straightening and straightening, straightness 1.5mm / m~2mm / m; ⑻ Stress relief annealing: Stress relief annealing heating temperature is 600℃, and the holding time is 10h; ⑼ The steel surface is polished, with a straightness of 0.5mm / m~0.7mm / m and a surface roughness of Ra0.5μm~1μm; ⑽The finished product meets the flaw detection requirements of ASME BPVCⅢDⅠNB-2585; Steel gas [H] 1.0×10 -6 The total amount of inclusions A+B+C+D is level 1.

5. The mechanical properties are impact energy at -12℃ at 1 / 4 diameter 80 / 85 / 88J, and impact energy at 13℃ 95.5 / 100.7 / 99.0J. The average room tensile Rm is 1140MPa, and the average 350℃ high tensile Rm is 1020MPa. The residual stress of the bar tested according to ASTM E837 does not exceed 50MPa, which is an absolute value.

3. The method for producing quenched and tempered bars for high temperature gas-cooled reactor fasteners by rolling instead of forging according to claim 1, characterized in that: Production of finished round steel Ф150mm; (1) The EAF+LF+VD+ESR method is used for smelting. High-quality scrap steel and alloy are selected as the raw materials. The molten steel is first smelted in an electric furnace and then sent to the LF refining furnace for refining. The LF refining time is 60 minutes and the white slag time is 45 minutes. When the molten steel temperature reaches 1660℃, it is transferred to the VD furnace for vacuum degassing. The VD vacuum degree is not greater than 0.67mbar and is maintained for 10 minutes. After opening the tank, the molten steel is set to [H]1.0×10 -6 ; Argon protection is used to cast φ470mm round electrode rods, the casting temperature is 1555℃, and the electrode rod mold is cooled to the bottom; the electroslag remelting adopts a binary slag system CaF2:Al2O3=70:30, the slag amount is 120kg / furnace, the remelting voltage of the constant melting rate electroslag furnace is controlled at 55V~65V, the remelting current is controlled at 10000A~12000A, the remelting melting rate is controlled at 7kg / min, the electroslag remelting ingot is φ610mm electroslag ingot, and the electroslag ingot is sent to the next step at temperature; the chemical composition analysis of the electroslag ingot is as follows: carbon: 0.415%, silicon: 0.24%, manganese: 0.82%, nickel: 1.84%, chromium: 0.88%, molybdenum: 0.36%, phosphorus: 0.005%, sulfur: 0.001%, copper: 0.07%, vanadium: 0.08%, niobium: 0.025%, and the balance is iron and unavoidable impurities; (2) Heating of electroslag ingot: electroslag ingot is loaded into the furnace at a furnace temperature of 600℃, and kept without fire for 30 minutes, and then the temperature is increased at a rate of 80℃ / h to 1260℃ and the timer is kept warm. The warming temperature fluctuates within the range of 1260℃~1275℃, and the warming time is 1.5h. The total heating time is 9.8h, and the temperature of the ingot out of the furnace is controlled at 1200℃~1220℃; ⑶ Rolling adopts differential temperature rolling process, that is, it is divided into two stages: the rolling temperature of stage I is 1100℃~1220℃, of which the starting rolling temperature is 1180℃ and the final rolling temperature is 1100℃. The single pass reduction in this stage is 10mm~50mm, and the cumulative reduction rate is 50%. Then the steel is air-dried for 6 minutes, and the steel size is 270mm×250mm. The starting rolling temperature of stage II is 920℃, the final rolling temperature is 880℃, and the cumulative reduction rate is 43%; ⑷ Cooling: After rolling, the steel enters the slow cooling pit with a pit temperature of 550°C and a pit cooling time of 60h; ⑸ Pretreatment, normalizing and tempering: pre-normalizing temperature 920℃, heating rate 78℃ / h, holding time 4h, air cooling; pre-tempering temperature 650℃, heating rate 60℃ / h, holding time 6h, air cooling; pre-straightening with ten-roll straightening equipment, straightness after straightening 3mm / m; (6) Quenching and tempering treatment: quenching heating temperature 860℃, holding time 3.5h, quenching medium water, water temperature 20℃~40℃; 0.5h~1.0h after quenching, the steel is put into the electric furnace for tempering, the tempering temperature is 615℃, the holding time is 10h, and the furnace is air-cooled; ⑺ After quenching and tempering, local point straightening and straightening, straightness 1.5mm / m~2mm / m; ⑻ Stress relief annealing: Stress relief annealing heating temperature is 600℃, and the holding time is 10h; ⑼ The steel surface is polished, with a straightness of 0.5mm / m~0.7mm / m and a surface roughness of Ra0.5μm~1μm; ⑽The finished product meets the flaw detection requirements of ASME BPVCⅢDⅠNB-2585; Steel gas [H] 1.0×10 -6 The total amount of inclusions A+B+C+D is level 1.

5. The mechanical properties are impact energy of -12℃ at 1 / 4 diameter 75 / 78 / 80J, and impact energy of 13℃ 85 / 90 / 92J. The average value of room tensile Rm is 1120MPa, and the average value of high tensile Rm at 350℃ is 975MPa. The residual stress of the bar tested according to ASTM E837 does not exceed 50MPa, which is an absolute value.

4. The method for producing quenched and tempered bars for high temperature gas-cooled reactor fasteners by rolling instead of forging according to claim 1, characterized in that: Production of finished round steel Ф200mm; (1) The EAF+LF+VD+ESR method is used for smelting. High-quality scrap steel and alloy are selected as the raw materials. The molten steel is first smelted in an electric furnace and then sent to the LF refining furnace for refining. The LF refining time is 60 minutes and the white slag time is 40 minutes. When the molten steel temperature reaches 1656℃, it is transferred to the VD furnace for vacuum degassing. The VD vacuum degree is not greater than 0.67mbar and is maintained for 10 minutes. After opening the tank, the molten steel is set to [H]1.2×10 -6 ; Argon protection is used to cast φ470mm round electrode rods, the casting temperature is 1550℃, and the electrode rod mold is cooled to the bottom; the electroslag remelting adopts a binary slag system CaF2:Al2O3=70:30, the slag amount is 120kg / furnace, the remelting voltage of the constant melting rate electroslag furnace is controlled at 55V~65V, the remelting current is controlled at 10000A~12000A, the remelting melting rate is controlled at 7kg / min, the electroslag remelting ingot is φ610mm electroslag ingot, and the electroslag ingot is sent to the next step at temperature; the chemical composition analysis of the electroslag ingot is as follows: carbon: 0.42%, silicon: 0.28%, manganese: 0.86%, nickel: 1.90%, chromium: 0.90%, molybdenum: 0.37%, phosphorus: 0.007%, sulfur: 0.001%, copper: 0.10%, vanadium: 0.09%, niobium: 0.025%, and the balance is iron and unavoidable impurities; (2) Heating of electroslag ingot: electroslag ingot is loaded into the furnace at a furnace temperature of 660℃, and kept without fire for 30 minutes. Then the temperature is increased at a rate of 80℃ / h to 1260℃ and the timing of heat preservation is started. The heat preservation temperature fluctuates within the range of 1260℃~1280℃, and the heat preservation time is 1.5h. The total heating time is 9.5h, and the temperature of the ingot out of the furnace is controlled at 1200℃~1220℃; ⑶ Rolling adopts differential temperature rolling process, that is, it is divided into two stages: the rolling temperature of stage I is 1100℃~1220℃, of which the starting rolling temperature is 1180℃ and the final rolling temperature is 1105℃. The single pass reduction in this stage is 10mm~50mm, and the cumulative reduction rate is 50%. Then the steel is air-dried for 6 minutes, and the steel size is 270mm×250mm. The starting rolling temperature of stage II is 930℃, the final rolling temperature is 900℃, and the cumulative reduction rate is 32%; (4) Cooling: After rolling, the steel enters a slow cooling pit with a pit temperature of 600°C and a pit cooling time of 60h; ⑸ Pretreatment, normalizing and tempering: pre-normalizing temperature 920℃, heating rate 65℃ / h, holding time 6h, air cooling; pre-tempering temperature 660℃, heating rate 60℃ / h, holding time 7h, air cooling; pre-straightening with ten-roll straightening equipment, straightness after straightening 3mm / m; (6) Quenching and tempering treatment: quenching heating temperature 860℃, holding time 4.5h, quenching medium water, water temperature 20℃~40℃; 0.5h~1.0h after quenching, the steel is put into the electric furnace for tempering, the tempering temperature is 610℃, the holding time is 10h, and the furnace is air-cooled; ⑺ After quenching and tempering, local point straightening and straightening, straightness 1.5mm / m~2mm / m; ⑻ Stress relief annealing: Stress relief annealing heating temperature is 600℃, and the holding time is 10h; ⑼ The steel surface is polished, with a straightness of 0.5mm / m~0.7mm / m and a surface roughness of Ra0.5μm~1μm; ⑽The finished product meets the flaw detection requirements of ASME BPVCⅢDⅠNB-2585; Steel gas [H] 1.0×10 -6 The total amount of inclusions A+B+C+D is level 1.

5. The mechanical properties are 67 / 68 / 65J impact energy at -12℃ at 1 / 4 diameter, and 75 / 70 / 72J impact energy at 13℃. The average room tensile Rm is 1122MPa, and the average 350℃ high tensile Rm is 962MPa. The residual stress of the bar tested according to ASTM E837 does not exceed 50MPa, which is an absolute value.