Method for achieving steel pipe normalizing annealing by reheating through hot rolling perforation waste heat

Abstract

The invention relates to the technical field of steel pipe machining, in particular to a method for achieving steel pipe normalizing annealing by reheating through hot rolling perforation waste heat. Performing hot rolling processing on the blank through a puncher to obtain a semi-finished steel pipe; and the semi-finished steel pipe is placed in equipment to be subjected to normalizing or annealing machining, and the steel pipe is obtained. According to the method, the waste heat after hot rolling of the steel pipe is adopted for normalizing and annealing processes, energy consumption needed in the subsequent heating process is remarkably reduced, cyclic utilization of energy is achieved, and therefore the production cost is greatly reduced, the heat energy is effectively utilized, the requirement for green production is met, remarkable economic benefits are also brought, and the method is suitable for large-scale popularization and application. Therefore, the problem that an existing steel pipe heat treatment method is high in production cost is solved.

Description

Technical Field

[0001] The invention relates to the technical field of steel pipe processing, and in particular to a method for achieving normalizing annealing of a steel pipe by reheating with residual heat from hot rolling piercing. Background Art

[0002] The known steel pipe is generally heated to 1160-1180°C and punched to produce hot rolled pipe; or rolled pipe is spheroidized annealed and then cold rolled and cold drawn to produce cold rolled and cold drawn pipes with smaller specifications and higher precision.

[0003] The heat treatment process of high-strength steel is carried out in an ordinary box furnace, and the surface is prone to oxidation and decarburization. If the grease on the surface cannot be completely cleaned, carbon deposition is likely to occur on the surface of the parts after heating, which will increase the amount of pickling before plating, and easily cause a large amount of hydrogen permeation in the substrate during the cleaning process, which is difficult to precipitate.

[0004] At present, when steel pipes are pierced by oblique rolling, the metal on the inner surface of the rough pipe is severely deformed, which is prone to defects such as cracks and internal folds. The use of forged billets and rolled billets can improve plasticity and eliminate defects on the inner surface during piercing, but this increases the production cost of steel pipes and is not convenient for widespread promotion. Summary of the invention

[0005] The purpose of the present invention is to provide a method for achieving normalizing annealing of a steel pipe by utilizing the residual heat of hot rolling piercing for reheating, aiming to solve the problem of high production cost of existing steel pipe heat treatment methods.

[0006] To achieve the above object, the present invention provides a method for normalizing and annealing a steel pipe by utilizing the residual heat of hot rolling and piercing for reheating, comprising the following steps:

[0007] Pre-treating the raw materials to obtain blanks;

[0008] Hot rolling the blank by a punching machine to obtain a semi-finished steel pipe;

[0009] Placing the semi-finished steel pipe in a normalizing device for normalizing processing;

[0010] The semi-finished steel pipe after normalizing is placed in an annealing device for annealing to obtain a steel pipe.

[0011] Among them, in “hot rolling the blank through a piercing machine to obtain a semi-finished steel pipe”, the following steps are included:

[0012] The blank is heated to 1150°C-1250°C

[0013] The heated blank is subjected to hot rolling and punching treatment by a punching machine to obtain a semi-finished steel pipe.

[0014] Among them, in “placing the semi-finished steel pipe in a device for normalizing or annealing to obtain a steel pipe”, the normalizing includes the following steps:

[0015] Transferring the semi-finished steel pipe to a placement rack and cooling it to a preset temperature;

[0016] The cooled semi-finished steel pipe is moved to a normalizing device for heating to obtain a steel pipe.

[0017] Among them, in “placing the semi-finished steel pipe in a device for normalizing or annealing to obtain a steel pipe”, the annealing includes the following steps:

[0018] The semi-finished steel pipe is placed in an annealing device and heated to 750°C-900°C;

[0019] The semi-finished steel pipe is kept warm for 10 to 40 minutes;

[0020] The heated semi-finished steel pipe is cooled to room temperature to obtain a steel pipe.

[0021] Among them, in “transferring the semi-finished steel pipe to a placement rack and cooling it to a preset temperature”, the preset temperature is below 700°C.

[0022] The present invention discloses a method for normalizing and annealing a steel pipe by utilizing the residual heat of hot rolling and perforation and reheating, comprising the following steps: heating the raw material to obtain a blank; hot rolling the blank by a perforator to obtain a semi-finished steel pipe; placing the semi-finished steel pipe in a device for normalizing or annealing to obtain a steel pipe. The present invention reduces the demand for independent heating equipment and reduces the initial equipment investment cost. Since the frequent startup and operation time of the equipment are reduced, the maintenance cost and failure rate of the equipment are also reduced accordingly, and the service life of the equipment is extended. The residual heat after hot rolling of the steel pipe is used for normalizing and annealing processes, which significantly reduces the energy consumption required in the subsequent heating process, realizes the recycling of energy, and thus greatly reduces the production cost. The effective utilization of this heat energy not only meets the requirements of green production, but also brings significant economic benefits, thereby solving the problem of high production cost of the existing steel pipe heat treatment method. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1The present invention provides a flow chart of a method for achieving normalizing annealing of a steel pipe by reheating with residual heat from hot rolling and piercing.

[0025] Figure 2 The flow chart is that the blank is hot-rolled by a piercing machine to obtain a semi-finished steel pipe.

[0026] Figure 3 The semi-finished steel pipe is placed in the equipment for normalizing or annealing to obtain the steel pipe, and the flow chart of the normalizing process.

[0027] Figure 4 The semi-finished steel pipe is placed in the equipment for normalizing or annealing to obtain the steel pipe, and the flow chart of the annealing process is shown in FIG. DETAILED DESCRIPTION

[0028] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0029] See also Figures 1 to 4 The present invention provides a method for achieving normalizing annealing of a steel pipe by utilizing the residual heat of hot rolling piercing for reheating, comprising the following steps:

[0030] S1 pre-treats the raw materials to obtain blanks;

[0031] Specifically, impurities in the raw materials are removed and the quality of molten steel is improved. The prepared raw materials are loaded into the blast furnace and heated by blowing hot air through the hot blast furnace. Under high temperature, the iron oxides in the raw materials are reduced to molten iron, and the molten iron smelted in the blast furnace is then sent to the converter for further refining. In the converter, molten iron is added together with scrap steel, ferroalloys, etc., and an oxidation reaction is carried out by blowing in oxygen. The refined molten steel is sent to the ladle and transported to the pouring position of the continuous casting machine through equipment such as the ladle turntable. The molten steel is injected into the tundish from above the tundish. The temperature of the molten steel is kept stable by adding insulation and other measures, and the molten steel flowing out of the tundish is injected into the crystallizer through the nozzle. The ingot with liquid core comes out of the crystallizer and enters the secondary cooling section. After cooling in the secondary cooling section, the ingot is continuously pulled out and sent to the straightening machine for straightening. The straightened ingot is cut into a certain length of billet according to the order requirements and transported to the subsequent process for further processing through the roller.

[0032] S2 hot-rolls the blank through a piercing machine to obtain a semi-finished steel pipe;

[0033] S21: heating the blank to 1150°C-1250°C

[0034] Specifically, the prepared blank is sent to the heating furnace. The heating furnace is equipped with an advanced temperature control system that can accurately adjust the temperature in the furnace to the target range, that is, between 1150℃ and 1350℃. This temperature range is carefully selected based on the chemical composition, physical properties and subsequent processing requirements of the steel, in order to ensure that the blank can be evenly heated and reach an ideal softening state, which is convenient for subsequent perforation processing. The blank needs to be left standing in the heating furnace for a period of time to ensure that its internal temperature is uniform. The standing time is determined comprehensively based on factors such as the size, shape, material of the blank and the heating efficiency of the heating furnace, and is generally between 1 hour and 2 hours. During the standing process, the hot air circulation system in the heating furnace will continuously blow the surface of the blank to promote uniform heat transfer, reduce temperature gradients, and avoid cracks or deformation of the blank due to uneven heating.

[0035] S22: hot rolling and punching the heated blank through a punching machine to obtain a semi-finished steel pipe.

[0036] Specifically, after the blank is heated to the specified temperature and left to stand for a sufficient time, it is taken out of the heating furnace and quickly sent to the piercing machine for hot rolling piercing. The piercing machine squeezes and stretches the heated blank through rotating rollers, causing it to gradually deform and form a hollow channel. After the hot rolling piercing process of the piercing machine, the solid blank is processed into a semi-finished steel pipe.

[0037] S3 placing the semi-finished steel pipe in equipment for normalizing or annealing to obtain a steel pipe;

[0038] S301: transferring the semi-finished steel pipe to a storage rack and cooling it to a preset temperature;

[0039] The preset temperature is below 700°C

[0040] Specifically, the semi-finished steel pipe after hot rolling and piercing is taken out from the piercing machine outlet and immediately transferred to the preset placement rack. The placement rack is placed in a well-ventilated area to help the steel pipe quickly dissipate heat by natural convection or forced ventilation. In order to accurately control the cooling process, a temperature sensor is installed on the placement rack or an infrared thermometer is used to monitor the surface or internal temperature of the steel pipe in real time.

[0041] S302: The cooled semi-finished steel pipe is moved to a normalizing device for heating.

[0042] Specifically, the semi-finished steel pipe cooled below the preset temperature is moved to the normalizing equipment to start the heating system of the normalizing equipment, gradually raising the temperature in the furnace to the range of 30-50°C above the Ac3 line. After the steel pipe is heated to the target temperature, the temperature is maintained for a period of insulation treatment.

[0043] S311 placing the semi-finished steel pipe into an annealing device and heating it to 750° C.-900° C.;

[0044] Specifically, the semi-finished steel pipe is transferred to the annealing equipment, the heating system of the annealing equipment is started, and the temperature in the furnace is gradually increased to a range of 750°C to 900°C.

[0045] S312: keeping the heated semi-finished steel pipe warm for 10 to 40 minutes;

[0046] Specifically, after the steel pipe is heated to the target temperature, it needs to maintain the temperature for a period of time, between 1 hour and 3 hours. The purpose of insulation is to make the temperature distribution inside the steel pipe more uniform, promote further adjustment and stabilization of the internal structure, and also help eliminate or reduce the internal stress generated during the processing.

[0047] S313 cools the heated semi-finished steel pipe to room temperature to obtain a steel pipe.

[0048] Specifically, after the annealing treatment is completed, the steel pipe needs to be taken out of the annealing equipment and cooled. Natural cooling or air cooling is usually used to avoid thermal stress and uneven structure caused by too fast cooling. The steel pipe is placed in a well-ventilated area to help it dissipate heat and cool to room temperature through natural convection or forced ventilation. When the steel pipe is cooled to room temperature, it is subjected to final inspection. The inspection content includes but is not limited to size inspection, appearance quality inspection, mechanical property test, etc. The qualified steel pipes are stored in the warehouse.

[0049] Embodiment 1

[0050] Smelting and continuous casting: The raw materials are smelted by conventional smelting processes, and continuous billets are obtained through continuous casting machines. Surface cleaning: Use a sandblaster or wire brush to thoroughly clean the outer surface of the billet to remove impurities such as scale, oil stains, and set aside. Heating and standing: The billet is sent to the heating furnace, heated to 1200℃, and stood for 1.5 hours to ensure that the temperature inside and outside the billet is uniform. Hot rolling and piercing: The heated billet is hot-rolled and pierced by a piercing machine to form a semi-finished steel pipe. Cooling: The semi-finished steel pipe is transferred to the placement rack and naturally cooled to 650℃. Normalizing treatment: The cooled semi-finished steel pipe is sent to the normalizing equipment, heated to Ac3+40℃, and kept warm for 45 minutes. Annealing treatment: The steel pipe is then placed in the annealing equipment, heated to 850℃, and kept warm for 2 hours. Final cooling: After annealing, it is naturally cooled to room temperature to obtain a finished steel pipe.

[0051] Embodiment 2

[0052] Smelting and continuous casting: Vacuum smelting technology is used to reduce impurities, and high-quality billets are obtained through continuous casting. Surface cleaning: High-pressure water jet cleaning technology is used to deeply clean the surface of the billet. Heating and standing: Under a nitrogen protective atmosphere, the billet is heated to 1300℃ and stood for 2 hours. Hot rolling and piercing: Use a high-precision piercing machine for hot rolling and piercing to ensure uniform wall thickness of the steel pipe. Cooling: The semi-finished steel pipe is quickly cooled to 500℃ by forced air cooling. Normalizing treatment: In the normalizing equipment, the temperature is accurately controlled to Ac3+30℃ and kept warm for 1 hour. Annealing treatment: The annealing temperature is set to 880℃ and the holding time is 1.5 hours. Final cooling: A combination of air cooling and slow cooling is used to ensure stable performance of the steel pipe.

[0053] Embodiment 3

[0054] Smelting and continuous casting: Electric furnace smelting combined with off-furnace refining technology is used to improve the purity of molten steel, and the blank is obtained by continuous casting. Surface cleaning: Combine mechanical cleaning and chemical cleaning to thoroughly remove impurities on the surface of the blank. Heating and standing: In the heating furnace, the blank is heated to 1180℃ and stood for 1.2 hours. Hot rolling and piercing: Advanced multi-roll piercing machines are used to improve piercing efficiency and steel pipe quality. Cooling: Use natural convection and weak air cooling to cool the semi-finished steel pipe to 680℃. Normalizing treatment: Accurately control the normalizing temperature to Ac3+45℃, and the holding time is 30 minutes. Annealing treatment: The annealing temperature is set to 820℃, and the holding time is 2.5 hours. Final cooling: Naturally cool to room temperature, and perform necessary surface treatment and testing.

[0055] Beneficial effects:

[0056] 1. Improve product quality: By adopting advanced technologies such as vacuum smelting and high-pressure water jet cleaning, impurities in raw materials are effectively reduced, the purity of molten steel and the overall quality of steel pipes are improved. Precise control of temperature and time during heating, normalizing and annealing optimizes the organizational structure of the steel pipe and improves its mechanical properties and corrosion resistance.

[0057] 2. Improve production efficiency: The use of high-precision piercing machines and multi-roller piercing technology improves the efficiency and accuracy of hot rolling piercing and shortens the production cycle. The optimized cooling and heating process reduces unnecessary waiting time and improves overall production efficiency.

[0058] 3. Reduce production costs: By reducing scrap rates and increasing finished product rates, direct material costs are reduced. Efficient production processes reduce energy consumption and labor costs, further reducing overall production costs.

[0059] 4. Enhanced process stability: The use of nitrogen protective atmosphere heating, precise temperature control system and other technical means has improved the stability and controllability of the production process. Standardized operating procedures and strict quality control system ensure the stability and consistency of product quality.

[0060] The above disclosure is only a preferred embodiment of the method of utilizing the residual heat of hot rolling piercing to achieve normalizing annealing of steel pipes. Of course, this cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for normalizing and annealing a steel pipe by reheating the residual heat of hot rolling and piercing, characterized in that: The following steps are involved: Heating the raw materials to obtain blanks; Hot rolling the blank by a punching machine to obtain a semi-finished steel pipe; The semi-finished steel pipe is placed in equipment for normalizing or annealing to obtain a steel pipe.

2. The method for normalizing and annealing a steel pipe by reheating with residual heat from hot rolling and piercing as claimed in claim 1, characterized in that: In “hot rolling the blank by a piercing machine to obtain a semi-finished steel pipe”, the following steps are included: The blank is heated to 1150° C.-1250° C.; The heated blank is subjected to hot rolling and punching treatment by a punching machine to obtain a semi-finished steel pipe.

3. The method for normalizing and annealing a steel pipe by reheating with residual heat from hot rolling and piercing as claimed in claim 1, characterized in that: In “placing the semi-finished steel pipe in a device for normalizing or annealing to obtain a steel pipe”, the normalizing includes the following steps: Transferring the semi-finished steel pipe to a placement rack and cooling it to a preset temperature; The cooled semi-finished steel pipe is moved to a normalizing device for heating to obtain a steel pipe.

4. The method for normalizing and annealing a steel pipe by reheating with residual heat from hot rolling and piercing as claimed in claim 1, characterized in that: In “placing the semi-finished steel pipe in a device for normalizing or annealing to obtain a steel pipe”, the annealing includes the following steps: The semi-finished steel pipe is placed in an annealing device and heated to 750°C-900°C; The semi-finished steel pipe is kept warm for 10 to 40 minutes; The heated semi-finished steel pipe is cooled to room temperature to obtain a steel pipe.

5. The method for normalizing and annealing a steel pipe by reheating with residual heat from hot rolling and piercing as claimed in claim 4, characterized in that: In "transferring the semi-finished steel pipe to a placement rack and cooling it to a preset temperature", the preset temperature is below 700°C.

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