Hot forging method for super duplex stainless steel

Abstract

The present invention relates to a hot forging method for super duplex stainless steel, comprising: an initial heating step of heating a material; a saddening step of crushing a surface structure of the material; a reheating step of reheating the material; and a forging step of pressing the material. The present invention enables improvement in formability while maintaining the quality of super duplex stainless steel, by initially heating an unprocessed material, processing the surface of the material via a saddening process, and then reheating the material to perform a forging process.

Description

Hot forging method of super duplex stainless steel

[0001] The present invention relates to a hot forging method for super duplex stainless steel, and more particularly, to a hot forging method for super duplex stainless steel capable of optimizing the forging process by alleviating thermal shock and re-dissolving harmful precipitates generated during hot mass transfer.

[0002] In general, super duplex stainless steels are used in chemical plants, chemical tanks, desalination plants, and seawater pumps due to their excellent mechanical properties and corrosion resistance. In particular, high yield strength and high corrosion resistance are required for components that come into primary contact with seawater.

[0003] These super duplex stainless steels have a structure composed of equal proportions of ferrite and austenite, and have the advantages of higher strength than austenitic stainless steels and excellent resistance to pitting corrosion and stress corrosion cracking due to chloride ions.

[0004] Typically, for super duplex stainless steels, controlling the balance between the austenite and ferrite phases to ensure excellent corrosion resistance and improve hot workability to suppress defects that may occur during sheet manufacturing is also an important task.

[0005] Conventional super duplex stainless steels are manufactured through a four-step process: casting, forging, drawing, and solution annealing. However, the austenitic structure of conventional super duplex stainless steels begins to form non-uniformly after the casting process, becomes even more non-uniform during the forging and drawing processes, and persists even after the solution annealing process. Therefore, there is a need for improvement.

[0006] The background technology of the present invention is published in Korean Patent Publication No. 2019-0094717 (published on August 14, 2019, title of the invention: Super duplex stainless steel with improved corrosion resistance and manufacturing method thereof).

[0007] The present invention has been devised to improve the above-mentioned problems, and its purpose is to provide a hot forging method for super duplex stainless steel that can alleviate thermal shock and optimize the forging process by re-dissolving harmful precipitates generated during hot mass transfer.

[0008] A hot forging method of super duplex stainless steel according to the present invention comprises: an initial heating step of heating a material; a shad-ening step of crushing a surface structure of the material; a reheating step of reheating the material; and a forging step of pressurizing the material.

[0009] The above initial heating step may include a first initial heating step of heating the material at a first temperature for a first time; a second initial heating step of heating the furnace to a second temperature; and a third initial heating step of heating the material at the second temperature for a second time.

[0010] The above-mentioned shad-forming step may include a preheating step of preheating the shad-forming part to a set temperature; a moving step of moving the material between the shad-forming parts by the gripping part; and a pressing step of pressing the material while the shad-forming part rotates the material.

[0011] The above-mentioned shad-ing step may further include a shad-ing temperature measurement step for measuring the surface temperature of the material in real time; and a shad-ing protection step for putting the material into a heating furnace when the surface temperature of the material drops below the shad-ing set temperature.

[0012] The forging step may include an upsetting step for upsetting the material; a holder forming step for forming a holder in the material; and a cogging step for performing cogging on the material.

[0013] The above holder forming step may include a first holder forming step of holding one end of the material; a second holder forming step of pressing the other end of the material to form a holder portion; and a third holder forming step of holding the holder portion.

[0014] The forging step may further include a forging temperature measurement step for measuring the surface temperature of the material in real time; and a forging protection step for putting the material into a heating furnace when the surface temperature of the material drops below an upsetting set temperature.

[0015] The hot forging method of super duplex stainless steel according to the present invention can improve formability while maintaining the quality of super duplex stainless steel by initially heating an unprocessed material, processing the surface of the material through a shad-ning process, and then reheating the material to perform a forging process.

[0016] FIG. 1 is a flow chart schematically illustrating a hot forging method of super duplex stainless steel according to one embodiment of the present invention.

[0017] Figure 2 is a drawing schematically showing an initial heating step according to one embodiment of the present invention.

[0018] Figure 3 is a drawing schematically showing a shaded step according to one embodiment of the present invention.

[0019] Figure 4 is a graph schematically showing a reheating temperature according to one embodiment of the present invention.

[0020] Figure 5 is a flowchart schematically showing a forging step according to one embodiment of the present invention.

[0021] Figure 6 is a drawing schematically showing a holder forming step according to one embodiment of the present invention.

[0022] Hereinafter, an embodiment of B having A according to the present invention will be described with reference to the attached drawings. In this process, the thickness of lines and the sizes of components depicted in the drawings may be exaggerated for clarity and convenience. Furthermore, the terms described below are defined based on their functions in the present invention and may vary depending on the intent or custom of the user or operator. Therefore, the definitions of these terms should be based on the contents throughout this specification.

[0023] Figure 1 is a flow chart schematically illustrating a hot forging method of super duplex stainless steel according to one embodiment of the present invention. Referring to Figure 1, the hot forging method of super duplex stainless steel according to one embodiment of the present invention includes an initial heating step (S10), a shaded step (S20), a reheating step (S30), and a forging step (S40).

[0024] The initial heating step (S10) can heat the material (10) illustrated in FIG. 3. For example, the material (10) can be an ingot formed using a mold. After being formed from the mold, the material (10) can be transported through a heat transfer device to suppress temperature reduction. If the temperature reduction of the material (10) is suppressed, energy can be saved during the initial heating and the precipitation phase can be easily reused. When the material (10) is transported through a heat transfer means, the initial heating time of the material (10) can be optimized through temperature gradient analysis. The initial heating of the material (10) can be performed in a direction to alleviate thermal shock and reduce internal and external temperature differences.

[0025] The shad-ing step (S20) can fracture the surface structure of the material (10). For example, the shad-ing step (S20) can fracture the coarse cast structure of the surface by lightly forging the surface of the material (10). The shad-ing step (S20) can be performed to uniformly deform the material (10) in a subsequent upsetting process.

[0026] The reheating step (S30) can reheat the material (10). For example, in the shaded step (S20), the material (10) may be cooled while the surface of the material (10) is lightly forged. The reheating step (S30) can reheat the material (10) that has been cooled through the shaded process.

[0027] The forging step (S40) can deform the material (10) into a set shape by applying pressure. For example, the material (10) can be deformed into a bar shape through the forging process.

[0028] Fig. 2 is a drawing schematically illustrating an initial heating step according to one embodiment of the present invention. Referring to Fig. 2, an initial heating step (S10) according to one embodiment of the present invention may include a first initial heating step (S11), a second initial heating step (S12), and a third initial heating step (S13).

[0029] The first initial heating step (S11) can heat the material (10) at a first temperature for a first hour. At this time, the first temperature can be 500 degrees Celsius to 600 degrees Celsius, and the first hour can be 1 hour to 2 hours. Since the material (10) is heated at the first temperature for a first hour after being placed in the heating furnace, thermal shock to the material (10) caused by rapid heating can be alleviated.

[0030] The second initial heating step (S12) heats the furnace to a second temperature. For example, the furnace may be heated to a second temperature of 1200 to 1300 degrees Celsius. At this time, the heater may be driven so that the interior of the furnace rises by a maximum of 100 degrees Celsius per hour.

[0031] The third initial heating step (S13) can heat the material (10) at a second temperature for a second time. For example, the third initial heating step (S13) can heat the material (10) at a second temperature for 10 to 12 hours.

[0032] Meanwhile, in order to sufficiently re-dissolve the harmful precipitated phase generated during transport of the material (10), the material (10) may be heated at the first temperature or the second temperature for 30 minutes per 25 mm of length.

[0033] Figure 3 is a schematic diagram illustrating a shad-off step according to one embodiment of the present invention. Referring to Figure 3, the shad-off step (S20) according to one embodiment of the present invention may include a preheating step (S21), a moving step (S22), and a pressing step (S23).

[0034] The preheating step (S21) can preheat the shad molding part (20) to a set temperature. For example, in the preheating step (S21), a second shad molding part (22) can be arranged on a first shad molding part (21), and a third shad molding part (23) can be arranged above the second shad molding part (22). The first shad molding part (21) can rotate on its own. The second shad molding part (22) and the third shad molding part (23) can have their own heaters built in so that they can be preheated to a set temperature. This set temperature can be 400 degrees Celsius to 500 degrees Celsius. The third saddle forming part (23) can be raised and lowered by the fourth saddle forming part (24), and the pressing force can be transmitted by the fourth saddle forming part (24).

[0035] The moving step (S22) can cause the gripping part (30) to grip the material (10) and move it between the shading forming parts (20). For example, the gripping part (30) can grip the top and the injection port of the ingot, which is the material (10), and rotate it to perform shading several times.

[0036] In the pressing step (S23), the gripper (30) can rotate the material (10) and the saddle forming part (20) can press the material (10). For example, the second saddle forming part (22) and the third saddle forming part (23) can lightly press the surface of the material (10) by the up and down movement of the fourth saddle forming part (24).

[0037] The sadding process can be performed to forge the surface of the material (10) to break up the coarse cast structure on the surface, and to ensure uniform deformation of the material (10) in the subsequent upsetting process. Once the setting of the sadding forming section (20) is completed, the heating furnace is opened within 10 minutes to introduce the material (10), thereby suppressing supercooling of the material (10) due to a decrease in the temperature of the sadding forming section (20). The pressing force of the sadding forming section (20) can be a maximum of 30 mm to 50 mm. This pressing force can increase or decrease depending on the surface condition of the material (10).

[0038] The method may further include a step of measuring the surface temperature of the material (10) in real time while the shadowing process is being performed, and a step of protecting the material (10) by putting the material (10) into a heating furnace when the surface temperature of the material (10) drops below the shadowing set temperature. For example, a temperature sensor may measure the surface temperature of the material (10) while the material (10) is pressed by the shadowing forming part (20). When the surface temperature of the material (10) drops below the shadowing set temperature, the material (10) may be put into a heating furnace to prevent excessive cooling of the material (10). For example, the shadowing set temperature may be 900 degrees Celsius to 1000 degrees Celsius. Meanwhile, when the surface temperature of the material (10) drops below the shadowing set temperature, a surface bursting phenomenon may occur. Typically, the material (10) withdrawn from the furnace can be reloaded into the furnace within 5 to 10 minutes.

[0039] Fig. 4 is a graph schematically illustrating the reheating temperature according to one embodiment of the present invention. Since the difference between the surface temperature and the core temperature of the material (10) increases after the shaded process, the difference between the surface temperature and the core temperature of the material (10) can be reduced through the reheating process. Referring to Fig. 4, at least 1.5 hours of reheating may be required to ensure that the difference between the surface temperature and the core temperature of the material (10) is within 10 degrees Celsius after 51 minutes of reheating.

[0040] Fig. 5 is a flowchart schematically illustrating a forging step according to one embodiment of the present invention. Referring to Fig. 5, a forging step (S40) according to one embodiment of the present invention may include an upsetting step (S41), a holder forming step (S42), and a cogging step (S43). The forging process may open the heating furnace within 10 minutes after the die and setting are completed. At this time, the opening of the heating furnace and the movement of the material (10) may be within 2 minutes. In the upsetting process, in order to manage the forging temperature to be 900 to 100 degrees Celsius based on the surface of the material (10), the time for forging requires re-loading within 5 to 10 minutes after ejection from the heating furnace.

[0041] The upsetting step (S41) can upset the material (10). For example, the upsetting process can be performed by putting the material (10) into a die preheated to 400 to 500 degrees Celsius, and the die can pressurize the material (10). The initial pressing amount is performed at 90 mm to 110 mm, and from the second pass, the pressing amount is reduced to 50 mm, so that upsetting of at least 1.2 U or more can be achieved. Meanwhile, the surface temperature drop to 950 degrees Celsius is expected to take about 7 minutes based on a room temperature of 20 degrees Celsius, but in reality, it is difficult to make an accurate calculation due to the deviation of the room temperature and the deformation heat generated when the material (10) is deformed. Therefore, if the surface temperature drops below 950 degrees Celsius through real-time temperature measurement, the material can be immediately put into the heating furnace.

[0042] The forging process may further include a forging temperature measurement step for measuring the surface temperature of the material (10) in real time while the upsetting process is being performed, and a forging protection step for putting the material (10) into a heating furnace when the surface temperature of the material (10) drops below the upsetting set temperature. At this time, the upsetting set temperature may be 900 degrees Celsius to 1000 degrees Celsius.

[0043] The holder forming step (S42) may form a holder portion (50) in the material (10). The cogging step (S43) may perform cogging on the material (10). For example, the holder process may form the holder portion (50) by forging one end of the material (10). The cogging process may form the material (10) excluding the holder portion (50) into a forged material (10) in the shape of a bar. The forging process may further include a forging temperature measuring step for measuring the surface temperature of the material (10) in real time while the holder process and the cogging process are in progress, and a forging protection step for putting the material (10) into a heating furnace when the surface temperature of the material (10) drops below a set temperature. At this time, the set temperature may be 900 degrees Celsius to 1000 degrees Celsius.

[0044] Fig. 6 is a drawing schematically illustrating a holder forming step according to one embodiment of the present invention. Referring to Fig. 6, the holder forming step (S42) according to one embodiment of the present invention may include a first holder forming step (S421), a second holder forming step (S422), and a third holder forming step (S423).

[0045] In the first holder forming step (S421), the gripping part (30) can grip one end of the material (10). For example, a pair of gripping parts (30) arranged vertically can move vertically to grip and fix the material (10) to be processed.

[0046] In the second holder forming step (S422), the holder forming part (40) can press the other end of the material (10) to form the holder part (50). For example, the holder forming part (40) can press the other end of the material (10) to form it into a grippable shape.

[0047] In the third holder forming step (S423), the gripping part (30) can grip the holder part (50). If the gripping part (30) stably grips the holder part (50), one end of the material (10) that does not include the holder part (50) can become a processing target, and a cogging process can be performed on this area to produce a product.

[0048] A hot forging method of super duplex stainless steel according to one embodiment of the present invention can improve formability while maintaining the quality of super duplex stainless steel by initially heating an unprocessed material (10), processing the surface of the material (10) through a shad-ing process, and then reheating the material (10) to perform a forging process.

[0049] While the present invention has been described with reference to the embodiments illustrated in the drawings, these are merely exemplary, and those skilled in the art will understand that various modifications and equivalent embodiments are possible. Accordingly, the true technical protection scope of the present invention should be defined by the following claims.

Claims

1. Initial heating stage for heating the material; A shaving step for destroying the surface structure of the above material; A reheating step for reheating the above material; and A hot forging method for super duplex stainless steel, characterized by including a forging step of pressurizing the above material.

2. In paragraph 1, the initial heating step A first initial heating step of heating the above material at a first temperature for a first hour; A second initial heating step for heating the furnace to a second temperature; and A method for hot forging super duplex stainless steel, characterized by including a third initial heating step of heating the material at the second temperature for a second time.

3. In paragraph 1, the shade step A preheating step for preheating the shad-forming part to a set temperature; and A moving step in which the phage section phages the material and moves it between the shad-forming sections; and A hot forging method for super duplex stainless steel, characterized in that it includes a pressing step in which the saddle forming part presses the material while the above-mentioned pressing part rotates the material.

4. In the third paragraph, the shade step A step for measuring the surface temperature of the above material in real time; and A hot forging method for super duplex stainless steel, characterized in that it further includes a shad-protection step of putting the material into a heating furnace when the surface temperature of the material drops below the shad-setting temperature.

5. In paragraph 1, the forging step An upsetting step for upsetting the above material; A holder forming step for forming a holder on the above material; and A hot forging method for super duplex stainless steel, characterized by including a cogging step of performing cogging on the above material.

6. In the fifth paragraph, the holder forming step A first holder forming step of breaking one end of the above material; A second holder forming step of forming a holder part by pressing the other end of the above material; and A hot forging method for super duplex stainless steel, characterized by including a third holder forming step of holding the holder portion.

7. In paragraph 5, the forging step A forging temperature measurement step for measuring the surface temperature of the above material in real time; and A hot forging method for super duplex stainless steel, characterized in that it further includes a forging protection step of putting the material into a heating furnace when the surface temperature of the material drops below the upsetting set temperature.

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