Induction heating heat treatment 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] The present invention belongs to the technical field of heat treatment of metal materials, and specifically relates to an induction heating heat treatment method for austenitic stainless steel bars.

Background Art

[0002] 1Cr18Ni9Ti is one of the most commonly used austenitic stainless steels, having good heat resistance, corrosion resistance, welding, plasticity, strength and other properties, and is widely applied in the manufacture of aviation instruments and precision non-magnetic parts. 1Cr18Ni9Ti in the hot-rolled state has a high material hardness due to the precipitation of carbides at grain boundaries, and the properties such as plasticity and corrosion resistance are reduced. Therefore, after solution treatment, it is necessary to use it in subsequent processing. The currently commonly used solution treatment means is to heat to the austenite range using a trolley furnace / roll bottom furnace and then water-cool to remove rolling stress, rolling banding, carbides, etc. to obtain a complete austenite structure. For rolled bars, the bars are relatively long (usually more than 5 m), and each bar is also stacked, so the cold rate difference in each section of the water-cooling process is large, and the bending deformation of the bars is serious. On the one hand, the deformed bars increase the difficulty of straightening, and on the other hand, since the amount of deformation of the bars is large during the straightening process, martensitic transformation is caused, the material hardness rapidly increases, and the difficulty of subsequent processing is increased (Figure 1 is the metallographic structure diagram of austenitic stainless steel bars obtained after the hot-rolled bars are subjected to solution treatment and straightening treatment in a trolley furnace / roll bottom furnace. The metallographic structure has an obvious deformed structure, and the detected surface hardness reaches 297 HBW). Therefore, the solution bending problem of long bars is a major problem that troubles on-site production.

Summary of the Invention

Problems to be Solved by the Invention

[0003] In view of the deficiencies and defects existing in the prior art, the object of the present invention is to provide an induction heating and heat treatment method for austenitic stainless steel bars. Specifically, the induction heating and heat treatment is to perform a high-temperature solution treatment on the austenitic stainless steel bars after hot rolling using an induction heating device. The induction heating and heat treatment method in the present invention is an on-line continuous transmission production, which has the advantages of high automation degree, fast heating speed, and short heat preservation time after reaching the solution temperature. In the present invention, by adjusting the induction heating frequency, the heating depth of the austenitic stainless steel bars and the temperature uniformity in the radial direction can be realized. Furthermore, the heating uniformity of the entire cross-section of the austenitic stainless steel bars can be ensured, and complete austenitization can be realized.

Means for Solving the Problems

[0004] To achieve the above object, the present invention provides an induction heating and heat treatment method for austenitic stainless steel bars and adopts the following technical solutions.

[0005] An induction heating and heat treatment method for austenitic stainless steel bars, comprising placing the austenitic stainless steel bars after hot rolling on a conveying roller, and performing a high-temperature solution treatment and a rapid cooling treatment on the austenitic stainless steel bars after hot rolling using an induction heating device to obtain a completely austenitized stainless steel bar.

[0006] The main structure of the stainless steel bar after hot rolling in the present invention is austenite structure. However, due to a large amount of carbide precipitation at the grain boundary position (carbide is not austenite structure), the hardness is further increased, and the plasticity and corrosion resistance are reduced. The present invention can obtain a completely austenitized stainless steel bar by performing a high-temperature solution treatment and a rapid cooling treatment on the austenitic stainless steel bar after hot rolling by an induction heating device (including an induction coil and a medium-frequency power supply adapted thereto), and can deliver the product without performing a straightening treatment, thereby avoiding problems such as further increase in hardness due to straightening deformation.

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

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

[0009] In the high-temperature solution treatment of the present invention, a relatively high heating rate is adopted in the temperature-raising stage so that the surface temperature of the bar reaches the solution temperature when the bar enters the heat-holding stage, and setting the temperature-raising stages into Heating Stage I and Heating Stage II is advantageous in adjusting the heating rate of the bar to meet the bar specifications. If the heat-holding temperature in Heating Stage III, i.e., the solution temperature, is lower than 1040°C, the solid solution will be insufficient and a complete austenite structure will not be obtained. If the heat-holding temperature in Heating Stage III, i.e., the solution temperature, is higher than 1060°C, the tendency for grain growth will be pronounced, making the grain size prone to be poor.

[0010] In the above-mentioned induction heating heat treatment method for austenitic stainless steel bars, as a preferred embodiment, in the high-temperature solid solution treatment, the induction heating device 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 means of an output voltage, an output current, and an induction heating frequency to induction heat the hot-rolled austenitic stainless steel bar.

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

[0012] In the present invention, by controlling the output voltage and output current of the medium-frequency power supply, the heating power of the induction coil (that is, P = UI) is further controlled. 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 stainless steel bar after hot rolling to realize heating. The induction heating frequency affects the heating depth and the temperature uniformity in the radial direction of the bar. In the present invention, by limiting the induction heating frequency to the range of 2000 - 4000Hz, the heating depth and the temperature uniformity in the radial direction of the austenitic stainless steel bar are realized, and further, the heating uniformity of the entire cross-section of the austenitic stainless steel bar is ensured, and complete austenitization can be realized.

[0013] Induction heating using an induction coil mainly follows the basic principles of electromagnetic induction, 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, the current penetration depth is small, resulting in non-uniform internal and external temperatures of the bar during heating, and further non-uniform austenite structure of the bar.

[0014] In the induction heating and heat treatment method for the austenitic stainless steel bar described above, as a preferred embodiment, the roller speed of the conveying roller is 1 - 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 for the austenitic stainless steel bar described above, 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 advanced into the shower ring under the conveyance of the conveying roller and water is sprayed. 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 for the austenitic stainless steel bar described above, as a preferred embodiment, in the water cooling treatment, the water spraying flow rate is 30 - 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, by 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 ≤ 187 HBW, the straightness ≤ 4 mm / m, and the crystal grain size ≥ grade 5.

[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 speed, and short holding time after reaching the solution temperature.

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

[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 burn marks or heating defects, and the surface quality is good. Since the thermal deformation of the bar is small, there is no need for 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

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. 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 from the disclosed commercial channels. The product number of the austenitic stainless steel bar after hot rolling used in the following examples is 1Cr18Ni9Ti, and the mass % of each elemental component is 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. As shown in the structural schematic diagram in Figure 2, a conveying roller 1 for moving the austenitic stainless steel bar 4 after hot rolling along its longitudinal direction, an induction heating device 2 arranged sequentially along the transmission direction of the austenitic stainless steel bar 4 after hot rolling, and a shower ring 3 whose shower direction is perpendicular to the transmission direction of the conveying roller 1 are provided. The induction heating device 2 is provided with a plurality of induction coils surrounding the stainless steel bar in a spring shape and an intermediate frequency power source adapted to the induction coils. In the embodiment of the present invention, three induction coils are used to inductively heat the austenitic stainless steel bar 4 after hot rolling (it is also possible to use a plurality of induction coils for induction heating), which are respectively denoted as the first induction coil 21, the second induction coil 22, and the third induction coil 23, and the intermediate frequency power sources adapted thereto are denoted as the first intermediate frequency power source 24, the second intermediate frequency power source 25, and the third intermediate frequency power source 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 (solution temperature) during induction heating.

[0030] Specifically, the induction heating heat treatment includes the following steps.

[0031] (1) Place the austenitic stainless steel bar 4 (diameter 20 - 50 mm, length 5 - 9 m) after hot rolling on the conveying roller 1, and set the roller speed of the conveying roller 1 to 1 - 2 m / min.

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

[0033] (3) After the high-temperature solid solution treatment is completed, the rod is transported by the transport roller 1 and enters the shower ring 3 for water cooling treatment. The shower direction of the shower ring 3 is perpendicular to the transmission direction of the transport roller 1, and the water flow rate is 30 to 80 m 3 / h, and the duration of the water spray at the same position on the bar was 15 to 30 s. After water cooling, a fully austenitized stainless steel bar was obtained.

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

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

[0036] (2) After hot rolling, the austenitic stainless steel bar was subjected to high-temperature solution treatment in an induction heating system. The induction heating was divided into heating stages I, II, and III. Stages I and II were heating stages, and Stage III was a holding stage. The temperature (solution temperature) in Stage III was 1050°C, and the holding time was 33 seconds. The first medium-frequency power supply had an output voltage of 600V, an output current of 100A, and an induction heating frequency of 3000Hz. The second medium-frequency power supply had an output voltage of 620V, an output current of 110A, and an induction heating frequency of 3000Hz. The third medium-frequency power supply had an output voltage of 450V, an output current of 50A, and an induction heating frequency of 3000Hz.

[0037] (3) After the high-temperature solid solution treatment is completed, the rod material is immediately transported by the conveying rollers into the shower ring, where the water is sprayed. The water flow rate is 40m 3 / h, and the duration of the fountain at the same position on the bar was 17 s, resulting in a fully austenitic stainless steel bar.

[0038] Example 2 An induction heat treatment method for an austenitic stainless steel bar, comprising the following steps:

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

[0040] (2) After hot rolling, the austenitic stainless steel bar was subjected to high-temperature solution treatment in an induction heating system. The induction heating was divided into heating stages I, II, and III. Stages I and II were heating stages, and Stage III was a holding stage. The temperature (solution temperature) in Stage III was 1045°C and the holding time was 35 seconds. The first medium-frequency power supply had an output voltage of 610V, an output current of 110A, and an induction heating frequency of 2800Hz. The second medium-frequency power supply had an output voltage of 630V, an output current of 120A, and an induction heating frequency of 2800Hz. The third medium-frequency power supply had an output voltage of 460V, an output current of 60A, and an induction heating frequency of 2800Hz.

[0041] (3) After the high-temperature solution treatment is completed, the bar immediately enters the shower ring under the conveyance of the conveyance roller for water spraying. The water spraying flow rate is 45 m 3 / h, and the duration of water spraying at the same position of the bar is 18 s, obtaining a fully austenitized stainless steel bar.

[0042] Example 3 An induction heating and heat treatment method for austenitic stainless steel bars, comprising the following steps.

[0043] (1) Place the austenitic stainless steel bar 4 (diameter 30 mm, length 7.5 m) after hot rolling on the conveyance roller, and set the roller speed of the conveyance roller to 1.6 m / min.

[0044] (2) Heat the austenitic stainless steel bar after hot rolling by induction heating in a high-temperature solution treatment. 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-rising stages, and heating stage III is a heat preservation stage. Among them, the temperature (solution temperature) of heating stage III is 1048 °C, and the heat preservation time is 38 s. The output voltage of the first intermediate frequency power supply is 625 V, the output current is 125 A, the induction heating frequency is 2600 Hz, the output voltage of the second intermediate frequency power supply is 650 V, the output current is 135 A, the induction heating frequency is 2600 Hz, and the output voltage of the third intermediate frequency power supply is 475 V, the output current is 65 A, and the induction heating frequency is 2600 Hz.

[0045] (3) After the high-temperature solution treatment is completed, the bar immediately enters the shower ring under the conveyance of the conveyance roller for water spraying. The water spraying flow rate is 50 m 3 / h, and the duration of water spraying at the same position of the bar is 19 s, obtaining a fully austenitized stainless steel bar.

[0046] Example 4 An induction heating and heat treatment method for austenitic stainless steel bars, comprising the following steps.

[0047] (1) Place the austenitic stainless steel bar 4 (diameter 35 mm, length 7 m) after hot rolling on the conveying roller, and set the roller speed of the conveying roller to 1.5 m / min.

[0048] (2) Subject the austenitic stainless steel bar after hot rolling to solution heat treatment at high temperature with 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-rising stages, and heating stage III is the heat preservation stage. Among them, the temperature (solution temperature) in heating stage III is 1052 °C, and the heat preservation time is 40 s. The output voltage of the first intermediate frequency power supply is 640 V, the output current is 140 A, and the induction heating frequency is 2400 Hz. The output voltage of the second intermediate frequency power supply is 660 V, the output current is 155 A, and the induction heating frequency is 2400 Hz. The output voltage of the third intermediate frequency power supply is 480 V, the output current is 70 A, and the induction heating frequency is 2400 Hz.

[0049] (3) After the solution heat treatment at high temperature is completed, the bar immediately enters the shower ring under the conveyance of the conveying roller for water spraying. The flow rate of the water spraying is 55 m 3 / h, and the duration of the water spraying at the same position of the bar is 20 s, obtaining a fully austenitized stainless steel bar. The metallographic structure diagrams of its surface and core parts are shown in Figure 3 and Figure 4 respectively.

[0050] Example 5 A method for induction heating and heat treatment of an austenitic stainless steel bar, comprising the following steps.

[0051] (1) Place the austenitic stainless steel bar 4 (diameter 40 mm, length 6.5 m) after hot rolling on the conveying roller, and set the roller speed of the conveying roller to 1.4 m / min.

[0052] (2) The austenitic stainless steel bar after hot rolling is subjected to a high-temperature solution treatment in 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-rising stages, and heating stage III is a heat preservation stage. Among them, the temperature of heating stage III (solution temperature) is 1055 °C, and the heat preservation time is 43 s. The output voltage of the first intermediate frequency power supply is 650 V, the output current is 145 A, and the induction heating frequency is 2300 Hz. The output voltage of the second intermediate frequency power supply is 670 V, the output current is 160 A, and the induction heating frequency is 2300 Hz. The output voltage of the third intermediate frequency power supply is 485 V, the output current is 75 A, and the induction heating frequency is 2300 Hz.

[0053] (3) After the high-temperature solution treatment is completed, the bar immediately enters the showering for water spraying under the conveyance of the conveying roller. The flow rate of the water spraying is 58 m 3 / h, and the duration of the water spraying at the same position of the bar is 21 s, obtaining a fully austenitized stainless steel bar.

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

[0055] (1) The austenitic stainless steel bar 4 (diameter 45 mm, length 6 m) after hot rolling is placed on the conveying roller, and the roller speed of the conveying roller is set to 1.3 m / min.

[0056] (2) The austenitic stainless steel bar after hot rolling is subjected to a high-temperature solution treatment in 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-rising stages, and heating stage III is a heat preservation stage. Among them, the temperature of heating stage III (solution temperature) is 1055 °C, and the heat preservation time is 46 s. The output voltage of the first intermediate frequency power supply is 665 V, the output current is 170 A, and the induction heating frequency is 2200 Hz. The output voltage of the second intermediate frequency power supply is 680 V, the output current is 185 A, and the induction heating frequency is 2200 Hz. The output voltage of the third intermediate frequency power supply is 490 V, the output current is 78 A, and the induction heating frequency is 2200 Hz.

[0057] (3) After the high-temperature solution treatment is completed, the bar immediately enters the shower ring under the conveyance of the conveyance roller for water spraying. The water spraying flow rate is 65 m 3 / h, and the duration of water spraying at the same position of the bar is 23 s, obtaining a fully austenitized stainless steel bar.

[0058] Example 7 An induction heating heat treatment method for austenitic stainless steel bars, comprising the following steps.

[0059] (1) Place the austenitic stainless steel bar 4 (diameter 50 mm, length 5 m) after hot rolling on the conveyance roller, and set the roller speed of the conveyance roller to 1.2 m / min.

[0060] (2) Heat the austenitic stainless steel bar after hot rolling by an induction heating device for high-temperature solution treatment. 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-rising stages, and heating stage III is a heat preservation stage. Among them, the temperature (solution temperature) of heating stage III is 1058 °C, and the heat preservation time is 50 s. The output voltage of the first intermediate frequency power supply is 675 V, the output current is 185 A, the induction heating frequency is 2000 Hz, the output voltage of the second intermediate frequency power supply is 690 V, the output current is 190 A, the induction heating frequency is 2000 Hz, the output voltage of the third intermediate frequency power supply is 495 V, the output current is 85 A, and the induction heating frequency is 2000 Hz.

[0061] (3) After the high-temperature solution treatment is completed, the bar immediately enters the shower ring under the conveyance of the conveyance roller for water spraying. The water spraying flow rate is 75 m 3 / h, and the duration of water spraying at the same position of the bar is 25 s, obtaining a fully austenitized stainless steel bar.

[0062] Comparative Example 1 An induction heating heat treatment method for austenitic stainless steel bars, comprising the following steps.

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

[0064] (2) Austenitic stainless steel bars after hot rolling are subjected to solution heat treatment at high temperature 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-rising stages, and heating stage III is a heat preservation stage. Among them, the temperature (solution temperature) in heating stage III is 1020 °C, and the heat preservation time is 33 s. The output voltage of the first intermediate frequency power supply is 500 V, the output current is 95 A, and the induction heating frequency is 3000 Hz. The output voltage of the second intermediate frequency power supply is 580 V, the output current is 100 A, and the induction heating frequency is 3000 Hz. The output voltage of the third intermediate frequency power supply is 400 V, the output current is 40 A, and the induction heating frequency is 3000 Hz.

[0065] Comparative Example 2 An induction heating heat treatment method for austenitic stainless steel bars, comprising the following steps.

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

[0067] (2) Austenitic stainless steel bars after hot rolling are subjected to solution heat treatment at high temperature 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-rising stages, and heating stage III is a heat preservation stage. Among them, the temperature (solution temperature) in heating stage III is 1070 °C, and the heat preservation time is 33 s. The output voltage of the first intermediate frequency power supply is 650 V, the output current is 110 A, and the induction heating frequency is 3000 Hz. The output voltage of the second intermediate frequency power supply is 650 V, the output current is 120 A, and the induction heating frequency is 3000 Hz. The output voltage of the third intermediate frequency power supply is 480 V, the output current is 60 A, and the induction heating frequency is 3000 Hz.

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

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

[0070] (2) Austenitic stainless steel bars after hot rolling are subjected to high-temperature solution treatment with 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-rising stages, and heating stage III is a heat preservation stage. Among them, the temperature (solution temperature) in heating stage III is 1050 °C, and the heat preservation time is 33 s. The output voltage of the first intermediate frequency power supply is 650 V, the output current is 180 A, and the induction heating frequency is 1800 Hz. The output voltage of the second intermediate frequency power supply is 650 V, the output current is 170 A, and the induction heating frequency is 1800 Hz. The output voltage of the third intermediate frequency power supply is 500 V, the output current is 90 A, and the induction heating frequency is 1800 Hz.

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

[0072] In Comparative Example 4, it is the same as Example 1 except for the differences from step (2) in Example 1.

[0073] (2) Austenitic stainless steel bars after hot rolling are subjected to high-temperature solution treatment with 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-rising stages, and heating stage III is a heat preservation stage. Among them, the temperature (solution temperature) in heating stage III is 1050 °C, and the heat preservation time is 33 s. The output voltage of the first intermediate frequency power supply is 580 V, the output current is 90 A, and the induction heating frequency is 5000 Hz. The output voltage of the second intermediate frequency power supply is 590 V, the output current is 100 A, and the induction heating frequency is 5000 Hz. The output voltage of the third intermediate frequency power supply is 400 V, the output current is 50 A, and the induction heating frequency is 5000 Hz.

[0074] Performance measurement The hardness of the bars obtained in Examples 1 to 7 and Comparative Examples 1 to 4 of the present invention was measured (performed with reference to GBT231.1―2018), the straightness was measured (performed with reference to T / SSEA 0069―2020), and a microstructure test was performed using a metallurgical microscope. The measurement results are shown in Table 2.

[0075]

Table 2

[0076] Here, A refers to austenite and F refers to ferrite.

[0077] Comparative Example 2 is qualified, but the crystal grain size is close to the required lower limit, and there is 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 present invention. Any changes, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the claims to which the present invention is to be approved.

Description of Reference Numerals

[0079] 1 Conveyor roller 2 Induction heating device 21 First induction coil 22 Second induction coil 23 Third induction coil 24 First intermediate frequency power supply 25 Second intermediate frequency power supply 26 Third intermediate frequency power supply 3 Shower ring 4 Austenitic stainless steel bar after hot rolling

Claims

1. An induction heating and heat treatment method for austenitic stainless steel bars, which includes placing the austenitic stainless steel bars after hot rolling on a conveying roller, and performing a high-temperature solution treatment and a rapid cooling treatment to inductively heat the austenitic stainless steel bars after hot rolling using an induction heating device to obtain a fully austenitized stainless steel bar, In the high-temperature solution treatment, the induction heating is divided into a temperature rising stage and a heat preservation stage, The induction heating is divided into heating stage I, heating stage II, and heating stage III. Heating stage I and heating stage II are temperature rising stages, and heating stage III is a heat preservation stage, The heat preservation temperature in heating stage III is 1040 - 1060 °C, and the heat preservation time is 30 - 60 s, In the high-temperature solution treatment, in heating stage I, the output voltage of the medium-frequency power supply is 500 - 700 V, the output current is 80 - 300 A, and the induction heating frequency is 2000 - 4000 Hz. In heating stage II, the output voltage of the medium-frequency power supply is 500 - 700 V, the output current is 80 - 300 A, and the induction heating frequency is 2000 - 4000 Hz. In heating stage III, the output voltage of the medium-frequency power supply is 400 - 600 V, the output current is 30 - 150 A, and the induction heating frequency is 2000 - 4000 Hz, The induction heating frequencies in heating stage I, heating stage II, and heating stage III are the same, Water cooling treatment is used for the rapid cooling treatment, In the water cooling treatment, the flow rate of the water spray is 30 to 80 m ３ / h, and the duration of the water spray at the same position of the austenitic stainless steel bar after the hot rolling is 15 to 30 s, The part number of the austenitic stainless steel bars after hot rolling is 1Cr18Ni9Ti, and the chemical composition is as follows in mass percentage: 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 balance is iron and inevitable impurity elements, The diameter of the austenitic stainless steel bars after hot rolling is 20 - 50 mm, and the length is 5 m - 9 m. A method for induction heating and heat treatment of austenitic stainless steel bars, characterized by the above.

2. In the high-temperature solution treatment, the induction heating device includes a plurality of induction coils and a medium-frequency power source adapted thereto. The induction coil surrounds the austenitic stainless steel bar after hot rolling in a spring shape, and the medium-frequency power source controls the induction coil by an output voltage, an output current, and an induction heating frequency to induction-heat the austenitic stainless steel bar after hot rolling. The heat treatment method according to claim 1, characterized in that.

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 water cooling treatment is characterized in that, after the high-temperature solution treatment is completed, the austenitic stainless steel bar after hot rolling is made to enter a 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. The heat treatment method according to claim 1.

5. The heat treatment method according to claim 1, characterized in that the hardness of the fully austenitized stainless steel bar is 187 HBW or less, the straightness is 4 mm / m or less, and the crystal grain size is 5 or more.

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