Preparation process for low-temperature-resistant steel bar production

Abstract

The invention discloses a preparation process for low-temperature-resistant steel bar production, and relates to the technical field of steel bar production. The preparation process for low-temperature-resistant steel bar production comprises the following steps of S1, molten iron pretreatment, S2, converter control, S3, LF furnace control, S4VD furnace operation, S5, continuous casting control, S6, casting blank inspection, S7, rod first-line rolling (phi 12-32 mm), S8, finished product inspection, S9, warehousing, S10, slitting and S11, packaging and delivery, and residual Cr in steel is smaller than or equal to 0.55%, Mo is smaller than or equal to 0.55%, and Cu is smaller than or equal to 0.55%; wherein the residual As in the steel is less than or equal to 0.1%, the Sn is less than or equal to 0.1%, the Pb is less than or equal to 0.1%, the Bi is less than or equal to 0.1% Wherein the gas control target [N] is 40-85 ppm; according to the process, inclusions in steel and macrostructures of continuous casting billets are strictly controlled, a perfect deoxidation process is established, and the internal and surface quality of the billets is improved; and the surface quality is strictly controlled by a bar factory, so that the product quality meets user requirements.

Description

Technical Field

[0001] The invention relates to the technical field of steel bar production, and in particular to a preparation process for producing low-temperature resistant steel bars. Background Art

[0002] Natural gas is a high-quality energy source, the main component of which is methane. It has the characteristics of high combustion calorific value and low pollution. It is widely used in power generation, automobile fuel, residential life and industry. There are generally two ways to store and transport natural gas: compressed natural gas (CNG) and liquefied natural gas (LNG). The liquid formed by cooling gaseous natural gas under normal pressure to below -162°C is called liquefied natural gas. The storage pressure of liquefied natural gas is normal pressure, which is much lower than the storage pressure of compressed natural gas (20MPa). It avoids the potential danger caused by the use of high-pressure containers for CNG, and also greatly reduces the weight of the container itself. Compared with gaseous natural gas, the liquefied natural gas is only 1 / 625 of the original volume. Its storage and transportation have advantages that other transportation methods cannot match: first, it can reduce the risk of pipeline construction, making ocean natural gas trade possible, and is an effective way to solve the development and recovery of natural gas in oceans and desert areas; second, the storage and transportation costs are low, and the ground transportation cost per unit weight of liquefied natural gas is only one-third of the pipeline transportation cost.

[0003] In recent years, with the rapid development of the world's natural gas industry, LNG has become an important part of international natural gas trade. Compared with ten years ago, the world's LNG trade volume has doubled, showing a strong growth momentum. It is predicted that in 2012, the international market LNG trade volume will account for 36% of the total natural gas trade volume, and by 2020 it will reach 40% of the natural gas trade volume and 15% of the natural gas consumption.

[0004] However, large liquefied natural gas storage tanks are generally composed of a single-layer tank + an outer cement tank. The inner tank is generally welded from low-temperature steel plates (such as 9% Ni or austenitic stainless steel, etc.), and the outer cement tank is composed of multiple layers of reinforced concrete and thermal insulation layers such as perlite; the concrete near the inner layer of the low-temperature steel tank is mostly cast with low-temperature steel bars that can withstand minus 165°C, while the outer layer of concrete is cast with ordinary threaded steel bars HRB335, HRB400, and HRB500. The low-temperature steel bars used in the inner layer of reinforced concrete must not only meet the performance indicators of conventional hot-rolled steel bars, but also have good low-temperature performance. The existing preparation process for low-temperature steel bars is prone to problems such as inclusions in the steel and low-multiple structures in the continuous casting billet, which affects the quality of the finished product. Summary of the invention

[0005] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art and to provide a preparation process for producing low-temperature resistant steel bars, which can solve the problem of poor quality of traditional steel billets.

[0006] To achieve the above object, the present invention provides the following technical solution: A preparation process for the production of low temperature resistant steel bars, comprising the following steps: S1 molten iron pretreatment - S2 converter control - S3 LF furnace control - S4 VD furnace operation - S5 continuous casting control - S6 ingot inspection - S7 bar one-line rolling (φ12-32mm) - S8 finished product inspection - S9 warehousing - S10 cutting - S11 packaging and delivery;

[0007] Among them, the chemical composition (melting composition, wt%) is implemented according to the chemical composition specified in the following table:

[0008]

[0009] Note: Among them, residual Cr in steel ≤ 0.55%, Mo ≤ 0.55%, Cu ≤ 0.55%;

[0010] Among them, residual As in steel is ≤0.1%, Sn ≤0.1%, Pb ≤0.1%, Bi ≤0.1%, Sb ≤0.1%;

[0011] Among them, gas control target [N]: 40-85ppm; T[O]≤13ppm.

[0012] Preferably, the S1 molten iron pretreatment, molten iron: molten iron As≤0.004%, Sn≤0.004%, Sb≤0.002%, alloy: Ni plate, metal manganese, self-produced high-quality scrap steel, the laboratory uses ultra-low S standard sample;

[0013] S2 converter control, A. End point target: P ≤ 0.007%; use post-furnace slag removal or LF slag removal (fishing) to remove P;

[0014] B. Use self-produced scrap steel;

[0015] C. Stop slag from tapping, and slag is strictly prohibited;

[0016] D. Blow argon throughout the entire process behind the furnace.

[0017] Preferably, the S3LF furnace controls: A. the total time of molten steel in LF is ≥ 40 min;

[0018] B. During the refining process, Al particles can be used for diffusion deoxidation; rapid slag deoxidation, desulfurization, and rapid slag formation (slag formation within 25 minutes, target within 20 minutes);

[0019] C. Fine-tune the composition according to the target value to ensure that the outbound composition meets the internal control requirements, and the Al loss needs to be considered;

[0020] D. After refining, feed the calcium line for 150m for calcification treatment; fine-tuning of 20 to 50m can be performed according to actual conditions (such as converter overoxidation, abnormal continuous casting castability, etc.).

[0021] Preferably, the S4VD furnace is operated as follows: A. argon blowing and temperature measurement are started when molten steel enters the VD furnace;

[0022] B. The vacuum target is below 0.5tor and the holding time is not less than 15min;

[0023] C. Soft blowing of molten steel before leaving VD furnace should be no less than 15 minutes;

[0024] D. Feed 100m of calcium wire into the pouring furnace; it can be fine-tuned by 20-50m according to actual conditions;

[0025] E. The temperature of molten steel leaving the station shall be controlled according to the superheat temperature of the ladle of the pouring furnace ≤35℃ and that of the continuous pouring furnace ≤30℃.

[0026] Preferably, the S5 continuous casting control, A. adopts an integral water nozzle to protect the casting throughout the whole process;

[0027] B. Pulling speed 2.1~2.2m / min, typical pulling ladle superheat 20~30℃, ladle superheat of start pouring furnace ≤35℃, continuous pouring furnace ≤30℃.

[0028] Preferably, the S6 ingot inspection: A. Chemical composition: determined according to the internal control components specified in the following table;

[0029]

[0030] The size, weight, shape and surface quality of the square billet shall comply with the enterprise standard "Q / OHAB107-2022 Continuous Cast Steel Square Billet and Rectangular Billet".

[0031] Preferably, the S7 rolling (φ12~32mm), A. Heating: the temperature of the preheating section is controlled below 850℃, the temperature of the soaking section is controlled at 1050±20℃, and the temperature of the soaking section is internally controlled at 1050±10℃;

[0032] B. The temperature of the cooling bed after water penetration is 550-570℃; for specifications of φ20mm and below, pre-water penetration is not enabled;

[0033] C. Other operations shall be carried out in accordance with the technical operating procedures of the bar factory;

[0034] Steel bars shall be inspected and accepted in batches, and each batch shall consist of steel bars of the same brand, same furnace number, same specification and same process system; the weight of each batch shall not exceed 60t. For the part exceeding 60t, one room temperature tensile specimen, two low temperature tensile specimens and one bending test specimen shall be added for every additional 40t (or the remainder less than 40t);

[0035] Turning is not allowed for specimens of tensile, bending and reverse bending tests;

[0036] Reverse bending performance: the steel bar should be subjected to reverse bending performance test; the bending core diameter of the reverse bending test should be increased by one steel bar diameter compared with the bending test;

[0037] Reverse bending test: first bend forward 90° and then bend backward 20°; after the reverse bending test, no cracks shall occur on the surface of the steel bar where it is bent;

[0038] Mechanical properties at room temperature should meet the following requirements: Yield strength: 520MPa~630MPa. For steel without obvious yield strength, non-proportional elongation stress Rp0.2 is used;

[0039] Tensile strength: ≥1.10 times the yield strength, maximum tensile total elongation Agt: ≥5.0%;

[0040] Low temperature mechanical properties should meet the following requirements: HRB500DW-1 should be tested at -105℃; HRB500DW-2 should be tested at -165℃;

[0041] Total elongation of unnotched steel bars at maximum force Agt: ≥3.0%;

[0042] Total elongation of notched steel bar under maximum force Agt: ≥1.0%;

[0043] Yield strength of unnotched steel bars: ≥575MPa;

[0044] Notch sensitivity (NSR) = tensile strength of notched steel bar / lower limit of yield strength of unnotched steel bar ≥ 1.0, or (NSR) = tensile strength of notched steel bar / strength of unnotched steel bar when residual strain is 0.2% ≥ 1.0.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The preparation process for the production of low-temperature resistant steel bars strictly controls the inclusions in the steel and the low-magnification structure of the continuous casting billet, establishes a complete deoxidation process, and improves the internal and surface quality of the billet; the bar factory strictly controls the surface quality to ensure that the product quality meets user requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present invention is further described below in conjunction with the accompanying drawings and embodiments:

[0048] Figure 1 It is a schematic diagram of a steel bar without a notch according to the present invention;

[0049] Figure 2 It is a schematic diagram of a notched steel bar of the present invention;

[0050] Figure 3 It is a schematic diagram of the V-shaped notch of the present invention. DETAILED DESCRIPTION

[0051] This section will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it cannot be understood as a limitation on the scope of protection of the present invention.

[0052] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0053] In the description of the present invention, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0054] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0055] See also Figure 1-3 , the present invention provides a technical solution: a preparation process for the production of low temperature resistant steel bars, comprising the following steps, S1 molten iron pretreatment - S2 converter control - S3 LF furnace control - S4 VD furnace operation - S5 continuous casting control - S6 ingot inspection - S7 bar one-line rolling (φ12-32mm) - S8 finished product inspection - S9 warehousing - S10 cutting - S11 packaging and delivery;

[0056] Among them, the chemical composition (melting composition, wt%) is implemented according to the chemical composition specified in the following table:

[0057]

[0058] Note: Among them, residual Cr in steel ≤ 0.55%, Mo ≤ 0.55%, Cu ≤ 0.55%;

[0059] Among them, residual As in steel is ≤0.1%, Sn ≤0.1%, Pb ≤0.1%, Bi ≤0.1%, Sb ≤0.1%;

[0060] Among them, gas control target [N]: 40-85ppm; T[O]≤13ppm.

[0061] Among them, the S1 molten iron pretreatment, molten iron: molten iron As≤0.004%, Sn≤0.004%, Sb≤0.002%, alloy: Ni plate, metal manganese, self-produced high-quality scrap steel, the laboratory uses ultra-low S standard sample;

[0062] S2 converter control, A. End point target: P ≤ 0.007%; use post-furnace slag removal or LF slag removal (fishing) to remove P;

[0063] B. Use self-produced scrap steel;

[0064] C. Stop slag from tapping, and slag is strictly prohibited;

[0065] D. Blow argon throughout the entire process behind the furnace.

[0066] Wherein, the S3LF furnace is controlled as follows: A. the total time of molten steel in LF is ≥ 40 min;

[0067] B. During the refining process, Al particles can be used for diffusion deoxidation; rapid slag deoxidation, desulfurization, and rapid slag formation (slag formation within 25 minutes, target within 20 minutes);

[0068] C. Fine-tune the composition according to the target value to ensure that the outbound composition meets the internal control requirements, and the Al loss needs to be considered;

[0069] D. After refining, feed the calcium line for 150m for calcification treatment; fine-tuning of 20 to 50m can be performed according to actual conditions (such as converter overoxidation, abnormal continuous casting castability, etc.).

[0070] Among them, the operation of the S4VD furnace is as follows: A. When the molten steel enters the VD furnace, argon blowing and temperature measurement are started throughout the process;

[0071] B. The vacuum target is below 0.5tor and the holding time is not less than 15min;

[0072] C. Soft blowing of molten steel before leaving VD furnace should be no less than 15 minutes;

[0073] D. Feed 100m of calcium wire into the pouring furnace; it can be fine-tuned by 20-50m according to actual conditions;

[0074] E. The temperature of molten steel leaving the station shall be controlled according to the superheat temperature of the ladle of the pouring furnace ≤35℃ and that of the continuous pouring furnace ≤30℃.

[0075] Among them, the S5 continuous casting control, A. adopts an integral water nozzle to protect the casting throughout the whole process;

[0076] B. Pulling speed 2.1~2.2m / min, typical pulling ladle superheat 20~30℃, ladle superheat of start pouring furnace ≤35℃, continuous pouring furnace ≤30℃.

[0077] Among them, the S6 ingot inspection, A. Chemical composition: determined according to the internal control components specified in the following table;

[0078]

[0079] The size, weight, shape and surface quality of the square billet shall comply with the enterprise standard "Q / OHAB107-2022 Continuous Cast Steel Square Billet and Rectangular Billet".

[0080] Among them, the S7 rolling (φ12~32mm), A. Heating: the temperature of the preheating section is controlled below 850℃, the temperature of the soaking section is controlled at 1050±20℃, and the temperature of the soaking section is internally controlled at 1050±10℃;

[0081] B. The temperature of the cooling bed after water penetration is 550-570℃; for specifications of φ20mm and below, pre-water penetration is not enabled;

[0082] C. Other operations shall be carried out in accordance with the technical operating procedures of the bar factory;

[0083] Steel bars shall be inspected and accepted in batches, and each batch shall consist of steel bars of the same brand, same furnace number, same specification and same process system; the weight of each batch shall not exceed 60t. For the part exceeding 60t, one room temperature tensile specimen, two low temperature tensile specimens and one bending test specimen shall be added for every additional 40t (or the remainder less than 40t);

[0084] Turning is not allowed for specimens of tensile, bending and reverse bending tests;

[0085] Reverse bending performance: the steel bar should be subjected to reverse bending performance test; the bending core diameter of the reverse bending test should be increased by one steel bar diameter compared with the bending test;

[0086] Reverse bending test: first bend forward 90° and then bend backward 20°; after the reverse bending test, no cracks shall occur on the surface of the steel bar where it is bent;

[0087] Mechanical properties at room temperature should meet the following requirements: Yield strength: 520MPa~630MPa. For steel without obvious yield strength, non-proportional elongation stress Rp0.2 is used;

[0088] Tensile strength: ≥1.10 times the yield strength, maximum tensile total elongation Agt: ≥5.0%;

[0089] Low temperature mechanical properties should meet the following requirements: HRB500DW-1 should be tested at -105℃; HRB500DW-2 should be tested at -165℃;

[0090] Total elongation of unnotched steel bars at maximum force Agt: ≥3.0%;

[0091] Total elongation of notched steel bar under maximum force Agt: ≥1.0%;

[0092] Yield strength of unnotched steel bars: ≥575MPa;

[0093] Notch sensitivity (NSR) = tensile strength of notched steel bar / lower limit of yield strength of unnotched steel bar ≥ 1.0, or (NSR) = tensile strength of notched steel bar / strength of unnotched steel bar when residual strain is 0.2% ≥ 1.0.

[0094] Furthermore, the process strictly controls the inclusions in the steel and the low-magnification structure of the continuous casting billet, establishes a complete deoxidation process, and improves the internal and surface quality of the billet; the bar factory strictly controls the surface quality to ensure that the product quality meets user requirements.

[0095] The embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present invention.

Claims

1. A preparation process for producing low temperature resistant steel bars, characterized in that: It includes the following steps: S1 hot metal pretreatment - S2 converter control - S3 LF furnace control - S4 VD furnace operation - S5 continuous casting control - S6 ingot inspection - S7 bar first-line rolling (φ12~32mm) - S8 finished product inspection - S9 warehousing - S10 cutting - S11 packaging and delivery; Among them, the chemical composition (melting composition, wt%) is implemented according to the chemical composition specified in the following table: Note: Residual Cr in steel ≤ 0.55%, Mo ≤ 0.55%, Cu ≤ 0.55%; Among them, residual As in steel is ≤0.1%, Sn ≤0.1%, Pb ≤0.1%, Bi ≤0.1%, Sb ≤0.1%; Among them, gas control target [N]: 40-85ppm; T[O]≤13ppm.

2. The preparation process for producing low temperature resistant steel bars according to claim 1, characterized in that: The S1 molten iron pretreatment, molten iron: molten iron As≤0.001%, Sn≤0.01%, Sb≤0.01%, alloy: Ni plate, metal manganese, self-produced high-quality scrap steel, the laboratory uses ultra-low S standard sample; S2 converter control, A. End point target: P ≤ 0.01%; use post-furnace slag removal or LF slag removal (fishing) to remove P; B. Use self-produced scrap steel; C. Stop slag from tapping, and slag discharge is strictly prohibited; D. Blow argon throughout the entire process behind the furnace.

3. The preparation process for producing low temperature resistant steel bars according to claim 1, characterized in that: The S3LF furnace control: A. The total time of molten steel in LF is ≥ 40 min; B. During the refining process, Al particles can be used for diffusion deoxidation; rapid slag deoxidation, desulfurization, and rapid slag formation (slag formation within 25 minutes, target within 20 minutes); C. Fine-tune the composition according to the target value to ensure that the outbound composition meets the internal control requirements, and the Al loss needs to be considered; D. After refining, feed the calcium line for 150m for calcification treatment; fine-tuning of 20 to 50m can be performed according to actual conditions (such as converter overoxidation, abnormal continuous casting castability, etc.).

4. The preparation process for producing low temperature resistant steel bars according to claim 1, characterized in that: The operation of the S4VD furnace is as follows: A. When the molten steel enters the VD furnace, argon blowing and temperature measurement are started throughout the process; B. The vacuum target is below 0.5tor and the holding time is not less than 15min; C. Soft blowing of molten steel before leaving VD furnace should be no less than 15 minutes; D. Feed 100m of calcium wire into the pouring furnace; it can be fine-tuned by 20-50m according to actual conditions; E. The temperature of molten steel leaving the station shall be controlled according to the superheat temperature of the ladle of the pouring furnace ≤35℃ and that of the continuous pouring furnace ≤30℃.

5. The preparation process for producing low temperature resistant steel bars according to claim 1, characterized in that: The S5 continuous casting control, A. adopts an integral nozzle to protect the casting throughout the whole process; B. Pulling speed 2.1~2.2m / min, typical pulling ladle superheat 20~30℃, ladle superheat of start pouring furnace ≤35℃, continuous pouring furnace ≤30℃.

6. The preparation process for producing low temperature resistant steel bars according to claim 1, characterized in that: The S6 ingot inspection: A. Chemical composition: determined by the internal control components specified in the following table; B. The size, weight, shape and surface quality of the billet shall comply with the enterprise standard "Q / OHAB107-2022 Continuously Cast Steel Square Billet and Rectangular Billet".

7. The preparation process for producing low temperature resistant steel bars according to claim 1, characterized in that: The S7 rolling (φ12~32mm), A. Heating: the temperature of the preheating section is controlled below 850℃, the temperature of the soaking section is controlled at 1050±20℃, and the temperature of the soaking section is internally controlled at 1050±10℃; B. The temperature of the cooling bed after water penetration is 550-570℃; for specifications of φ20mm and below, pre-water penetration is not enabled; C. Other operations shall be carried out in accordance with the technical operating procedures of the bar factory; Steel bars shall be inspected and accepted in batches, and each batch shall consist of steel bars of the same brand, same furnace number, same specification and same process system; the weight of each batch shall not exceed 60t. For the part exceeding 60t, one room temperature tensile specimen, two low temperature tensile specimens and one bending test specimen shall be added for every additional 40t (or the remainder less than 40t); Turning is not allowed for specimens of tensile, bending and reverse bending tests; Reverse bending performance: the steel bar should be subjected to reverse bending performance test; the bending core diameter of the reverse bending test should be increased by one steel bar diameter compared with the bending test; Reverse bending test: first bend forward 90° and then bend backward 20°; after the reverse bending test, no cracks shall occur on the surface of the steel bar where it is bent; Mechanical properties at room temperature should meet the following requirements: Yield strength: 520MPa~630MPa. For steel without obvious yield strength, non-proportional elongation stress Rp0.2 is used; Tensile strength: ≥1.10 times the yield strength, maximum tensile total elongation Agt: ≥5.0%; Low temperature mechanical properties should meet the following requirements: HRB500DW-1 should be tested at -105℃; HRB500DW-2 should be tested at -165℃; Total elongation of unnotched steel bars at maximum force Agt: ≥3.0%; Total elongation of notched steel bar under maximum force Agt: ≥1.0%; Yield strength of unnotched steel bars: ≥575MPa; Notch sensitivity (NSR) = tensile strength of notched steel bar / lower limit of yield strength of unnotched steel bar ≥ 1.0, or (NSR) = tensile strength of notched steel bar / strength of unnotched steel bar when residual strain is 0.2% ≥ 1.0.

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