Induction heating method for austenitic stainless steel bars

Abstract

The present invention provides a method for induction heating heat treatment of austenitic stainless steel bars, comprising placing a hot-rolled austenitic stainless steel bar on conveyor rollers and using an induction heating device to perform a high-temperature solution treatment by induction heating the hot-rolled austenitic stainless steel bar, followed by a rapid cooling treatment to obtain a fully austenitized stainless steel bar. The induction heating heat treatment method of the present invention is an online continuous transmission production method, and has the advantages of a high degree of automation, a fast heating rate, and a short temperature retention time after reaching the solution temperature. In the present invention, by adjusting the induction heating frequency, it is possible to achieve temperature uniformity in the heating depth and radial direction of the austenitic stainless steel bar, and further ensure uniform heating across the entire cross section of the austenitic stainless steel bar, thereby achieving full austenitization.

Description

[Technical Field]

[0001] This invention belongs to the field of heat treatment technology for metallic materials, and more specifically, to an induction heating method for austenitic stainless steel rods. [Background technology]

[0002] 1Cr18Ni9Ti is one of the most commonly used austenitic stainless steels, possessing excellent heat resistance, corrosion resistance, weldability, plasticity, and strength, and is widely applied in the manufacture of aircraft instruments and precision nonmagnetic components. In its hot-rolled state, 1Cr18Ni9Ti exhibits increased material hardness due to carbide precipitation at grain boundaries, resulting in reduced plasticity and corrosion resistance. Therefore, it requires solid solution treatment before subsequent processing. A commonly used solid solution treatment method currently involves heating the material to the austenite section using a trolley furnace / roll bottom furnace, followed by water cooling to remove rolling stress, rolled strips, and carbides, thereby obtaining a complete austenitic structure. For rolled bars, the bars are relatively long (usually 5m or more), and each bar is stacked, resulting in large differences in cooling rates in each section of the water cooling process, leading to serious bending deformation of the bars. On the one hand, the deformation of the bar material increases the difficulty of straightening it, and on the other hand, because the deformation is large during the straightening process, the bar material undergoes martensitic transformation, causing a rapid increase in material hardness and increasing the difficulty of subsequent processing (Figure 1 shows the metallurgical structure of an austenitic stainless steel bar material obtained after hot rolling, solid solution treatment in a trolley furnace / roll bottom furnace, and straightening treatment. The metallurgical structure clearly shows a deformation structure, and the detected surface hardness reaches 297 HBW). Therefore, the solid solution bending problem of long bars is a major challenge that poses difficulties to on-site production. [Overview of the Initiative] [Problems that the invention aims to solve]

[0003] To address the shortcomings and defects of the prior art, the object of the present invention is to provide an induction heating heat treatment method for austenitic stainless steel bars. Specifically, the induction heating heat treatment involves performing a high-temperature solid solution treatment on austenitic stainless steel bars after hot rolling using an induction heating device. The induction heating heat treatment method in the present invention is an online continuous transmission production method, has the advantages of a high degree of automation, a fast heating rate, and a short holding time after reaching the solid solution temperature. In the present invention, by adjusting the induction heating frequency, it is possible to achieve uniform heating depth and temperature in the radial direction of the austenitic stainless steel bars, and furthermore, to ensure uniform heating across the entire cross-section of the austenitic stainless steel bars, thereby achieving complete austenitization. [Means for solving the problem]

[0004] To achieve the above objective, the present invention provides an induction heating method for austenitic stainless steel bars, employing the following technical approach.

[0005] A method for induction heating heat treatment of austenitic stainless steel bars, comprising placing the hot-rolled austenitic stainless steel bar on a conveyor roller, performing a high-temperature solid solution treatment by induction heating the hot-rolled austenitic stainless steel bar using an induction heating device, and then performing a rapid cooling treatment to obtain a fully austenitized stainless steel bar.

[0006] In the present invention, the main structure of the hot-rolled stainless steel bar is austenitic, but because a large amount of carbides precipitate at the grain boundaries (carbides are not austenitic), the hardness increases further, and plasticity and corrosion resistance decrease. In the present invention, by performing high-temperature solid solution treatment and rapid cooling treatment on austenitic stainless steel bar after hot rolling using an induction heating device (including an induction coil and a compatible medium-frequency power supply), it is possible to obtain a fully austenitized stainless steel bar, which can be delivered without straightening treatment, thereby avoiding problems such as further increase in hardness due to straightening deformation.

[0007] In the above induction heating heat treatment method for austenitic stainless steel bars, in a preferred embodiment, in the high-temperature solid solution treatment, the induction heating is divided into a heating stage and a heat retention stage, and preferably, the induction heating is divided into heating stage I, heating stage II, and heating stage III, with heating stage I and heating stage II being heating stages and heating stage III being a heat retention stage.

[0008] In the induction heating heat treatment method for austenitic stainless steel rods described above, in a preferred embodiment, in the high-temperature solid solution treatment, the holding temperature (solid solution temperature) of the heating stage III is 1040 to 1060°C (for example, 1042°C, 1045°C, 1050°C, 1053°C, 1055°C, 1058°C), and the holding time is 30 to 60 s (for example, 32 s, 35 s, 40 s, 45 s, 50 s, 55 s).

[0009] In the high-temperature solid solution treatment of the present invention, it is advantageous to set the heating stages to two stages, heating I and heating II, by employing a relatively high heating rate in the heating stage so that the surface temperature of the rod reaches the solid solution temperature when the rod enters the heat retention stage, and by adjusting the heating rate of the rod according to the specifications of the rod. If the solid solution temperature, which is the heat retention temperature in heating stage III, is lower than 1040°C, solid solution will be insufficient, and a complete austenite structure cannot be obtained. If the solid solution temperature, which is the heat retention temperature in heating stage III, is higher than 1060°C, the grain growth tendency will be pronounced, and the grain size will likely be poor.

[0010] In the above-described induction heating heat treatment method for austenitic stainless steel bars, in a preferred embodiment, in the high-temperature solid solution treatment, the induction heating apparatus includes a plurality of induction coils and a suitable medium-frequency power supply, the induction coils surround the hot-rolled austenitic stainless steel bars in a spring-like manner, and the medium-frequency power supply controls the induction coils by output voltage, output current and induction heating frequency to induce heating the hot-rolled austenitic stainless steel bars.

[0011] In the above induction heating heat treatment method for austenitic stainless steel bars, in a preferred embodiment, in the high-temperature solid solution treatment, in the heating stage I, the output voltage of the medium-frequency power supply is 500~700V (e.g., 550V, 600V, 620V, 650V), the output current is 80~300A (e.g., 100A, 150A, 200A, 250A), and the induction heating frequency is 2000~4000Hz (e.g., 2500Hz, 2700Hz, 3000Hz, 3500Hz), and in the heating stage II, the output voltage of the medium-frequency power supply is 500~700V (e.g., 550V, 600V, The output voltage is 620V, 650V), the output current is 80-300A (e.g., 100A, 150A, 200A, 250A), and the induction heating frequency is 2000-4000Hz (e.g., 2500Hz, 2700Hz, 3000Hz, 3500Hz). In the heating stage III, the output voltage of the medium frequency power supply is 400-600V (e.g., 450V, 480V, 520V, 550V), the output current is 30-150A (e.g., 50A, 80A, 100A, 120A), and the induction heating frequency is 2000-4000Hz (e.g., 2500Hz, 2700Hz, 3000Hz, 3500Hz). It is more preferable that the induction heating frequencies in heating stage I, heating stage II, and heating stage III are the same.

[0012] In this invention, the heating power of the induction coil (i.e., P=UI) is further controlled by controlling the output voltage and output current of the medium-frequency power supply. The higher the heating power, the faster the heating rate. The induction heating frequency generates an alternating magnetic field in the induction heating coil, and further generates eddy currents in the hot-rolled stainless steel bar to achieve heating. The induction heating frequency affects the heating depth and radial temperature uniformity of the bar. In this invention, by limiting the induction heating frequency to the range of 2000 to 4000 Hz, temperature uniformity in the heating depth and radial direction of the austenitic stainless steel bar can be achieved, and further heating uniformity across the entire cross-section of the austenitic stainless steel bar can be ensured, thereby achieving complete austenitization.

[0013] Induction heating using an induction coil mainly follows the basic principles of electromagnetic induction, the skin effect, and heat conduction. During the heating process, there are two types of heating methods for the material: transmission heating and conduction heating. However, the high-temperature solution treatment of the present invention is an on-line continuous transmission production. Since the holding time after reaching the solution temperature is short, in order to ensure the uniformity of the solution, the current penetration depth needs to be greater than the radius of the bar. Since the current penetration depth is inversely proportional to the induction heating frequency, the higher the induction heating frequency, the smaller the current penetration depth. When the induction heating frequency is lower than 2000 Hz, the heating efficiency is low. When the induction heating frequency is higher than 4000 Hz, due to the small current penetration depth, the internal and external temperatures of the bar during heating become non-uniform, and furthermore, the austenite structure of the bar becomes non-uniform.

[0014] In the induction heating and heat treatment method of the austenitic stainless steel bar, as a preferred embodiment, the roller speed of the conveying roller is 1 to 2 m / min (for example, 1.2 m / min, 1.4 m / min, 1.5 m / min, 1.8 m / min, 1.9 m / min).

[0015] In the induction heating and heat treatment method of the austenitic stainless steel bar, as a preferred embodiment, water cooling treatment is used for the rapid cooling treatment. Preferably, specifically in the water cooling treatment, after the high-temperature solution treatment is completed, the bar is made to enter the shower ring under the conveyance of the conveying roller and water is sprayed, and the shower direction of the shower ring is perpendicular to the transmission direction of the conveying roller.

[0016] In the induction heating and heat treatment method of the austenitic stainless steel bar, as a preferred embodiment, in the water cooling treatment, the water spray flow rate is 30 to 80 m 3 / h (for example, 40 m 3 / h, 45 m 3 / h, 50 m 3 / h, 55 m 3 / h, 60 m 3 / h, 65 m 3 / h, 70 m 3 / h, 75 m 3(h), and the duration of water spraying at the same position of the bar is 15 - 30 s (for example, 18 s, 20 s, 22 s, 25 s, 27 s, 29 s).

[0017] In the water cooling treatment of the present invention, if the water spraying flow rate is less than 30 m 3 / h, the cooling of the bar is insufficient, and further the hardness of the bar increases, and a fully austenitized stainless steel bar cannot be obtained. If the water spraying flow rate is greater than 80 m 3 / h, the cooling rate becomes too fast, and the bar is likely to bend.

[0018] In the induction heating and heat treatment method of the above austenitic stainless steel bar, as a preferred embodiment, the part number of the austenitic stainless steel bar after hot rolling is 1Cr18Ni9Ti, and the chemical composition is C≤0.12%, Si≤0.80%, Mn≤2.00%, P≤0.035%, S≤0.020%, Cr 17.0 - 19.0% (for example, 17.3%, 17.5%, 18.0%, 18.2%, 18.5%), Ni 8.0 - 11.0% (for example, 8.2%, 8.5%, 9.0%, 9.5%, 10.0%), Ti 5×(C - 0.02) - 0.80% (where C is the carbon content in the steel), and the balance is iron and inevitable impurity elements, in mass percentage.

[0019] In the induction heating and heat treatment method of the above austenitic stainless steel bar, as a preferred embodiment, the diameter of the austenitic stainless steel bar after hot rolling is 20 - 50 mm (for example, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 48 mm), and the length is 5 m - 9 m (for example, 5.5 m, 6 m, 6.5 m, 7 m, 8 m, 8.5 m).

[0020] In the induction heating and heat treatment method of the above austenitic stainless steel bar, as a preferred embodiment, the hardness of the fully austenitized stainless steel bar is ≤187 HBW, the straightness is ≤4 mm / m, and the crystal grain size is ≥5 grades.

[0021] The present invention has the following advantages compared with the prior art.

[0022] (1) The induction heating heat treatment method in the present invention has the advantages of high degree of automation, high heating rate, and short heat preservation time after reaching the solution temperature.

[0023] (2) The hardness of the fully austenitized stainless steel bar obtained by the induction heating heat treatment method of the present invention is ≦187 HBW, the straightness is ≦4 mm / m, and the crystal grain size is ≧5 grades.

[0024] (3) Since the fully austenitized stainless steel bar obtained by the induction heating heat treatment method of the present invention has a short heating time, there are no surface burns or heating defects, and the surface quality is good. Since the thermal deformation of the bar is small, there is no need to perform straightening processing, and it can meet the negotiation requirements. Moreover, the surface hardening problem caused by straightening processing can be avoided.

Brief Description of the Drawings

[0025] [Figure 1] It is a metallographic structure diagram of an austenitic stainless steel bar obtained after solution treatment and straightening treatment in the prior art. [Figure 2] It is a structural schematic diagram of the induction heating heat treatment method of the present invention. [Figure 3] It is a metallographic structure diagram of the surface of the fully austenitized stainless steel bar obtained in Example 4 of the present invention. [Figure 4] It is a metallographic structure diagram of the core part of the fully austenitized stainless steel bar obtained in Example 4 of the present invention.

Modes for Carrying Out the Invention

[0026] The technical solutions in the embodiments of the present invention are clearly and completely described below. As is clear, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art belong to the protection scope of the present invention.

[0027] The raw materials described in the following examples can all be obtained through the disclosed commercial channels. The product code of the hot-rolled austenitic stainless steel bar used in the following examples is 1Cr18Ni9Ti, and the mass percentages of each element are shown in Table 1.

[0028] [Table 1]

[0029] A specific embodiment of the present invention provides an induction heating heat treatment method for austenitic stainless steel bars, the schematic diagram of which is shown in Figure 2. The method comprises a conveyor roller 1 that moves a hot-rolled austenitic stainless steel bar 4 along its longitudinal direction, an induction heating device 2 sequentially arranged along the transmission direction of the hot-rolled austenitic stainless steel bar 4, and a shower ring 3 whose shower direction is perpendicular to the transmission direction of the conveyor roller 1. The induction heating device 2 includes a plurality of induction coils that surround the stainless steel bar in a spring-like manner and a medium-frequency power supply that matches the induction coils. In the embodiment of the present invention, austenitic stainless steel bar material 4 after hot rolling is induction heated using three induction coils (induction heating can also be performed using multiple induction coils), which are denoted as the first induction coil 21, the second induction coil 22, and the third induction coil 23, respectively. The corresponding medium-frequency power supplies are denoted as the first medium-frequency power supply 24, the second medium-frequency power supply 25, and the third medium-frequency power supply 26. Here, the first induction coil 21 corresponds to the first heating stage during induction heating, the second induction coil 22 corresponds to the second heating stage during induction heating, and the third induction coil 23 corresponds to the third heating stage (solid solution temperature) during induction heating.

[0030] The induction heating treatment described above specifically includes the following steps:

[0031] (1) Hot-rolled austenitic stainless steel bars 4 (20-50 mm in diameter, 5-9 m in length) were placed on a conveyor roller 1, and the roller speed of the conveyor roller 1 was set to 1-2 m / min.

[0032] (2) The austenitic stainless steel bar stock 4 after hot rolling is subjected to high-temperature solid solution treatment in an induction heating device 2. The induction heating is divided into heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are heating and temperature increase stages, and heating stage III is a temperature holding stage. Of these, the temperature (solid solution temperature) in heating stage III is 1040 to 1060°C, and the temperature holding time is 30 to 60 seconds. In heating stage I, the output voltage of the first medium-frequency power supply 24 is 500-700V, the output current is 80-300A, and the induction heating frequency is 2000-4000Hz. In heating stage II, the output voltage of the second medium-frequency power supply 25 is 500-700V, the output current is 80-300A, and the induction heating frequency is 2000-4000Hz. In heating stage III, the output voltage of the third medium-frequency power supply 26 is 400-600V, the output current is 30-150A, and the induction heating frequency is 2000-4000Hz. To ensure uniform heating, it is preferable to set the induction heating frequencies of each medium-frequency power supply to match.

[0033] (3) After the high-temperature solid solution treatment is completed, the rods are placed under the conveyor roller 1 and placed in the shower ring 3 for water cooling. The shower direction of the shower ring 3 is perpendicular to the transmission direction of the conveyor roller 1, and the flow rate of the water jet is 30-80 m³. 3 The water pressure was / h, and the duration of the fountain at the same position on the bar was 15-30s. After water cooling, fully austenitized stainless steel bars were obtained.

[0034] Example 1: An induction heating method for treating an austenitic stainless steel bar, comprising the following steps.

[0035] (1) A hot-rolled austenitic stainless steel bar 4 (20 mm in diameter, 9 m in length) was placed on a conveyor roller, and the roller speed of the conveyor roller was set to 1.8 m / min.

[0036] (2) Hot-rolled austenitic stainless steel bars are subjected to high-temperature solid solution treatment using an induction heating device. The induction heating is divided into three stages: heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are heating and temperature increase stages, while heating stage III is a temperature retention stage. In heating stage III, the temperature (solid solution temperature) is 1050°C, and the temperature retention time is 33 seconds. The output voltage of the first medium-frequency power supply is 600V, the output current is 100A, and the induction heating frequency is 3000Hz. The output voltage of the second medium-frequency power supply is 620V, the output current is 110A, and the induction heating frequency is 3000Hz. The output voltage of the third medium-frequency power supply is 450V, the output current is 50A, and the induction heating frequency is 3000Hz.

[0037] (3) After the high-temperature solid solution treatment is completed, the rods are immediately placed under the conveyor rollers to be showered, and the water flow rate of the shower is 40 m³. 3 The value was / h, and the duration of the fountain at the same position on the bar was 17s, resulting in a fully austenitized stainless steel bar.

[0038] Example 2: An induction heating method for austenitic stainless steel bar stock, comprising the following steps.

[0039] (1) A hot-rolled austenitic stainless steel bar 4 (25 mm in diameter, 8 m in length) was placed on a conveyor roller, and the roller speed of the conveyor roller was set to 1.7 m / min.

[0040] (2) Hot-rolled austenitic stainless steel bars are subjected to high-temperature solid solution treatment using an induction heating device. The induction heating is divided into three stages: heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are heating and temperature increase stages, while heating stage III is a temperature retention stage. In heating stage III, the temperature (solid solution temperature) is 1045°C, and the temperature retention time is 35 s. The output voltage of the first medium-frequency power supply is 610V, the output current is 110A, and the induction heating frequency is 2800Hz. The output voltage of the second medium-frequency power supply is 630V, the output current is 120A, and the induction heating frequency is 2800Hz. The output voltage of the third medium-frequency power supply is 460V, the output current is 60A, and the induction heating frequency is 2800Hz.

[0041] (3) After the high-temperature solid solution treatment is completed, the rods are immediately placed under the conveyor rollers to be showered, and the water flow rate of the shower is 45 m³. 3 The value was / h, and the duration of the fountain at the same position on the bar was 18s, resulting in a fully austenitized stainless steel bar.

[0042] Example 3: An induction heating method for austenitic stainless steel rod, comprising the following steps.

[0043] (1) A hot-rolled austenitic stainless steel bar 4 (30 mm in diameter, 7.5 m in length) was placed on a conveyor roller, and the roller speed of the conveyor roller was set to 1.6 m / min.

[0044] (2) Hot-rolled austenitic stainless steel bars are subjected to high-temperature solid solution treatment using an induction heating device. The induction heating is divided into three stages: heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are heating and temperature increase stages, while heating stage III is a temperature retention stage. In heating stage III, the temperature (solid solution temperature) is 1048°C, and the temperature retention time is 38 s. The output voltage of the first medium-frequency power supply is 625V, the output current is 125A, and the induction heating frequency is 2600Hz. The output voltage of the second medium-frequency power supply is 650V, the output current is 135A, and the induction heating frequency is 2600Hz. The output voltage of the third medium-frequency power supply is 475V, the output current is 65A, and the induction heating frequency is 2600Hz.

[0045] (3) After the high-temperature solid solution treatment is completed, the rods are immediately placed under the conveyor rollers to be sprayed with water, and the water flow rate is 50 m³. 3 The value was / h, and the duration of the fountain at the same position on the bar was 19s, resulting in a fully austenitized stainless steel bar.

[0046] Example 4: An induction heating method for treating an austenitic stainless steel bar, comprising the following steps.

[0047] (1) A hot-rolled austenitic stainless steel bar 4 (35 mm in diameter, 7 m in length) was placed on a conveyor roller, and the roller speed of the conveyor roller was set to 1.5 m / min.

[0048] (2) Hot-rolled austenitic stainless steel bars are subjected to high-temperature solid solution treatment using an induction heating device. The induction heating is divided into three stages: heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are heating and temperature increase stages, while heating stage III is a temperature retention stage. In heating stage III, the temperature (solid solution temperature) is 1052°C, and the temperature retention time is 40 s. The output voltage of the first medium-frequency power supply is 640V, the output current is 140A, and the induction heating frequency is 2400Hz. The output voltage of the second medium-frequency power supply is 660V, the output current is 155A, and the induction heating frequency is 2400Hz. The output voltage of the third medium-frequency power supply is 480V, the output current is 70A, and the induction heating frequency is 2400Hz.

[0049] (3) After the high-temperature solid solution treatment is completed, the rods are immediately placed under the conveyor rollers to be showered, and the water flow rate of the shower is 55 m³. 3 The water pressure was / h, and the duration of the fountain at the same position on the bar was 20s, resulting in a fully austenitized stainless steel bar. The metallurgical diagrams of the surface and core are shown in Figures 3 and 4, respectively.

[0050] Example 5: An induction heating method for treating an austenitic stainless steel bar, comprising the following steps.

[0051] (1) A hot-rolled austenitic stainless steel bar 4 (40 mm in diameter, 6.5 m in length) was placed on a conveyor roller, and the roller speed of the conveyor roller was set to 1.4 m / min.

[0052] (2) Hot-rolled austenitic stainless steel bars are subjected to high-temperature solid solution treatment using an induction heating device. The induction heating is divided into three stages: heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are heating and temperature increase stages, while heating stage III is a temperature retention stage. In heating stage III, the temperature (solid solution temperature) is 1055°C, and the temperature retention time is 43 s. The output voltage of the first medium-frequency power supply is 650V, the output current is 145A, and the induction heating frequency is 2300Hz. The output voltage of the second medium-frequency power supply is 670V, the output current is 160A, and the induction heating frequency is 2300Hz. The output voltage of the third medium-frequency power supply is 485V, the output current is 75A, and the induction heating frequency is 2300Hz.

[0053] (3) After the high-temperature solid solution treatment is completed, the rods are immediately placed under the conveyor rollers to be showered, and the water flow rate of the shower is 58 m³. 3 The value was / h, and the duration of the fountain at the same position on the bar was 21s, resulting in a fully austenitized stainless steel bar.

[0054] Example 6: An induction heating method for treating an austenitic stainless steel bar, comprising the following steps.

[0055] (1) A hot-rolled austenitic stainless steel bar 4 (45 mm in diameter, 6 m in length) was placed on a conveyor roller, and the roller speed of the conveyor roller was set to 1.3 m / min.

[0056] (2) Hot-rolled austenitic stainless steel bars are subjected to high-temperature solid solution treatment using an induction heating device. The induction heating is divided into three stages: heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are heating and temperature increase stages, while heating stage III is a temperature retention stage. In heating stage III, the temperature (solid solution temperature) is 1055°C, and the temperature retention time is 46 s. The output voltage of the first medium-frequency power supply is 665V, the output current is 170A, and the induction heating frequency is 2200Hz. The output voltage of the second medium-frequency power supply is 680V, ​​the output current is 185A, and the induction heating frequency is 2200Hz. The output voltage of the third medium-frequency power supply is 490V, the output current is 78A, and the induction heating frequency is 2200Hz.

[0057] (3) After the high-temperature solid solution treatment is completed, the rods are immediately placed under the conveyor rollers to be showered, and the water flow rate of the shower is 65 m³. 3 The value was / h, and the duration of the fountain at the same position on the bar was 23s, resulting in a fully austenitized stainless steel bar.

[0058] Example 7: An induction heating method for treating an austenitic stainless steel bar, comprising the following steps.

[0059] (1) A hot-rolled austenitic stainless steel bar 4 (50 mm in diameter, 5 m in length) was placed on a conveyor roller, and the roller speed of the conveyor roller was set to 1.2 m / min.

[0060] (2) Hot-rolled austenitic stainless steel bars are subjected to high-temperature solid solution treatment using an induction heating device. The induction heating is divided into three stages: heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are heating and temperature increase stages, while heating stage III is a temperature retention stage. The temperature (solid solution temperature) of heating stage III is 1058°C, and the temperature retention time is 50 s. The output voltage of the first medium-frequency power supply is 675V, the output current is 185A, and the induction heating frequency is 2000Hz. The output voltage of the second medium-frequency power supply is 690V, the output current is 190A, and the induction heating frequency is 2000Hz. The output voltage of the third medium-frequency power supply is 495V, the output current is 85A, and the induction heating frequency is 2000Hz.

[0061] (3) After the high-temperature solid solution treatment is completed, the rods are immediately placed under the conveyor rollers to be showered, and the water flow rate of the shower is 75 m³. 3 The value was / h, and the duration of the fountain at the same position on the bar was 25s, resulting in a fully austenitized stainless steel bar.

[0062] Comparative Example 1: An induction heating method for austenitic stainless steel bar stock, comprising the following steps.

[0063] Comparative Example 1 is the same as Example 1, except that step (2) is different from that of Example 1.

[0064] (2) Hot-rolled austenitic stainless steel bars are subjected to high-temperature solid solution treatment using an induction heating device. The induction heating is divided into three stages: heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are heating and temperature increase stages, while heating stage III is a temperature retention stage. In heating stage III, the temperature (solid solution temperature) is 1020°C, and the temperature retention time is 33 seconds. The output voltage of the first medium-frequency power supply is 500V, the output current is 95A, and the induction heating frequency is 3000Hz. The output voltage of the second medium-frequency power supply is 580V, the output current is 100A, and the induction heating frequency is 3000Hz. The output voltage of the third medium-frequency power supply is 400V, the output current is 40A, and the induction heating frequency is 3000Hz.

[0065] Comparative Example 2: An induction heating method for austenitic stainless steel bar stock, comprising the following steps.

[0066] Comparative Example 2 is the same as Example 1, except that step (2) is different from that of Example 1.

[0067] (2) Hot-rolled austenitic stainless steel bars are subjected to high-temperature solid solution treatment using an induction heating device. The induction heating is divided into heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are heating and temperature increase stages, and heating stage III is a temperature retention stage. In heating stage III, the temperature (solid solution temperature) is 1070°C and the temperature retention time is 33 s. The output voltage of the first medium-frequency power supply is 650V, the output current is 110A, and the induction heating frequency is 3000Hz. The output voltage of the second medium-frequency power supply is 650V, the output current is 120A, and the induction heating frequency is 3000Hz. The output voltage of the third medium-frequency power supply is 480V, the output current is 60A, and the induction heating frequency is 3000Hz.

[0068] Comparative Example 3: An induction heating method for austenitic stainless steel rod, comprising the following steps.

[0069] Comparative Example 3 is the same as Example 1, except that step (2) is different from that of Example 1.

[0070] (2) Hot-rolled austenitic stainless steel bars are subjected to high-temperature solid solution treatment using an induction heating device. The induction heating is divided into three stages: heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are heating and temperature increase stages, while heating stage III is a temperature retention stage. In heating stage III, the temperature (solid solution temperature) is 1050°C, and the temperature retention time is 33 seconds. The output voltage of the first medium-frequency power supply is 650V, the output current is 180A, and the induction heating frequency is 1800Hz. The output voltage of the second medium-frequency power supply is 650V, the output current is 170A, and the induction heating frequency is 1800Hz. The output voltage of the third medium-frequency power supply is 500V, the output current is 90A, and the induction heating frequency is 1800Hz.

[0071] Comparative Example 4: An induction heating method for austenitic stainless steel rod, comprising the following steps.

[0072] Comparative Example 4 is the same as Example 1, except that step (2) and Example 1 are different.

[0073] (2) Hot-rolled austenitic stainless steel bars are subjected to high-temperature solid solution treatment using an induction heating device. The induction heating is divided into three stages: heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are heating and temperature increase stages, while heating stage III is a temperature retention stage. In heating stage III, the temperature (solid solution temperature) is 1050°C, and the temperature retention time is 33 seconds. The output voltage of the first medium-frequency power supply is 580V, the output current is 90A, and the induction heating frequency is 5000Hz. The output voltage of the second medium-frequency power supply is 590V, the output current is 100A, and the induction heating frequency is 5000Hz. The output voltage of the third medium-frequency power supply is 400V, the output current is 50A, and the induction heating frequency is 5000Hz.

[0074] Performance measurement The rod materials obtained in Examples 1 to 7 and Comparative Examples 1 to 4 of the present invention were subjected to hardness measurements (performed in reference to GBT231.1-2018) and straightness measurements (performed in reference to T / SSEA 0069-2020), and microstructural tests were performed using a metallurgical microscope. The measurement results are shown in Table 2.

[0075] [Table 2]

[0076] Here, A represents austenite and F represents ferrite.

[0077] Comparative Example 2 passes the test, but its grain size is close to the lower limit of the requirement, posing a risk of defects during mass production.

[0078] The above description is merely a preferred embodiment of the present invention and does not limit the invention. Any modifications, equivalent substitutions, improvements, etc., made in the spirit and principles of the invention are included within the scope of protection of the claims to which the invention is granted. [Explanation of Symbols]

[0079] 1 Conveyor roller 2 Induction heating device 21. First induction coil 22. Second induction coil 23. Third induction coil 24. First Medium Frequency Power Supply 25. Second Medium Frequency Power Supply 26 Third Medium Frequency Power Supply 3. Showering 4. Hot-rolled austenitic stainless steel bars

Claims

1. A method for induction heating and heat treatment of austenitic stainless steel bars, The process includes placing a hot-rolled austenitic stainless steel bar on a conveyor roller, performing a high-temperature solid solution treatment by induction heating the hot-rolled austenitic stainless steel bar using an induction heating device, and then performing a rapid cooling treatment to obtain a fully austenitized stainless steel bar. In the aforementioned high-temperature solid solution treatment, the induction heating is divided into a heating stage and a heat retention stage. The induction heating is divided into heating stage I, heating stage II, and heating stage III, with heating stage I and heating stage II being heating stages, and heating stage III being a heat retention stage. The heat retention temperature of the heating stage III is 1040 to 1060°C, and the heat retention time is 30 to 60 seconds. In the high-temperature solid solution treatment, in the first heating stage, the output voltage of the medium-frequency power supply is 500 to 700 V, the output current is 80 to 300 A, and the induction heating frequency is 2000 to 4000 Hz; in the second heating stage, the output voltage of the medium-frequency power supply is 500 to 700 V, the output current is 80 to 300 A, and the induction heating frequency is 2000 to 4000 Hz; and in the third heating stage, the output voltage of the medium-frequency power supply is 400 to 600 V, the output current is 30 to 150 A, and the induction heating frequency is 2000 to 4000 Hz. The induction heating frequencies in the heating stage I, heating stage II, and heating stage III are the same. Water cooling is used in the aforementioned rapid cooling process. In the aforementioned water cooling treatment, the flow rate of the fountain is 30 to 80 m ３ The duration of the spray at the same position on the austenitic stainless steel bar after hot rolling is 15 to 30 seconds. The product code for the hot-rolled austenitic stainless steel bar is 1Cr18Ni9Ti, and its chemical composition in mass percent is as follows: C is 0.12% or less, Si is 0.80% or less, Mn is 2.00% or less, P is 0.035% or less, S is 0.020% or less, Cr is 17.0-19.0%, Ni is 8.0-11.0%, Ti is 5×(C-0.02)-0.80%, and the remainder is iron and unavoidable impurity elements. An induction heating method for an austenitic stainless steel bar, characterized in that the diameter of the hot-rolled austenitic stainless steel bar is 20 to 50 mm and the length is 5 to 9 m.

2. The heat treatment method according to claim 1, characterized in that, in the high-temperature solid solution treatment, the induction heating apparatus includes a plurality of induction coils and a medium-frequency power supply compatible therewith, the induction coils surround the hot-rolled austenitic stainless steel bar in a spring-like manner, and the medium-frequency power supply controls the induction coils by output voltage, output current and induction heating frequency to induce heating the hot-rolled austenitic stainless steel bar.

3. The heat treatment method according to claim 1, characterized in that the roller speed of the conveying roller is 1 to 2 m / min.

4. The heat treatment method according to claim 1, characterized in that, after the high-temperature solid solution treatment is completed, the hot-rolled austenitic stainless steel bar is introduced into a shower ring under the conveyance of the conveyor roller and water is sprayed, and the direction of the shower in the shower ring is perpendicular to the transmission direction of the conveyor roller.

5. The heat treatment method according to claim 1, characterized in that the fully austenitized stainless steel rod has a hardness of 187 HBW or less, a straightness of 4 mm / m or less, and a grain size of grade 5 or higher.

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