A method for quenching and tempering a martensitic stainless steel bar and a quenching and tempering production line

Abstract

This invention provides a method and production line for quenching and tempering martensitic stainless steel bars. The method includes the following steps: Step 1, heating the martensitic stainless steel bars using electromagnetic induction heating; Step 2, quenching the heated martensitic stainless steel bars using water as the quenching medium; Step 3, performing low-temperature stress relief on the martensitic stainless steel bars using electromagnetic induction heating, with the stress relief heating temperature lower than the tempering temperature; Step 4, sending the stress-relieved martensitic stainless steel bars into a tempering furnace. Electromagnetic induction quenching ensures good bar straightness, while water quenching is environmentally friendly and prevents cracking. Gas-fired roller hearth tempering furnaces allow for prolonged carbide precipitation, resulting in uniform mechanical properties. To prevent cracking of the electromagnetically induction-quenched steel, low-temperature electromagnetic induction stress relief is performed first, which quickly eliminates stress.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel heat treatment technology, specifically relating to a tempering method and tempering production line for martensitic stainless steel bars. Background Technology

[0002] Stainless steel possesses superior corrosion resistance, heat resistance, wear resistance, and toughness, as well as good machinability and aesthetic appeal. It is widely used in aerospace, marine, chemical, military, and energy industries. Stainless steel is typically classified according to its microstructure into martensitic stainless steel, austenitic stainless steel, ferritic stainless steel, austenitic-ferritic duplex stainless steel, and precipitation-hardening stainless steel. Martensitic stainless steel has a martensitic matrix, and its mechanical properties can be adjusted through heat treatment. The heat treatment process typically involves heating martensitic stainless steel to a high temperature to transform it into austenite, followed by rapid cooling to transform the austenite back into martensite—this is known as quenching. Quenching increases strength and hardness, while tempering further refines hardness, strength, and toughness.

[0003] The heat treatment of martensitic stainless steel typically involves heating it in a bogie hearth or chamber furnace using electricity, natural gas, or coal gas, followed by quenching in quenching media such as oil and quenching liquid, and then tempering it in a bogie hearth or chamber furnace using electricity, natural gas, or coal gas.

[0004] The shortcomings and deficiencies of existing technologies:

[0005] 1. Martensitic stainless steel is prone to cracking during quenching. It is generally cooled by oil or quenching fluid. However, due to safety, environmental protection, and cost issues, many manufacturers do not have oil or quenching fluid as cooling media.

[0006] 2. Small-sized materials are heated in a bogie hearth furnace or chamber furnace. Due to their small size and long length, they bend severely during the heating process, making straightening difficult.

[0007] 3. Electromagnetic induction heating quenching and tempering methods, due to their short heating time, cannot achieve the expected mechanical properties for stainless steel materials with high alloy content.

[0008] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0009] The purpose of this invention is to provide a method for quenching and tempering martensitic stainless steel bars, namely a quenching and tempering production line, which solves the problems of difficulty in straightening caused by severe bending during the heating process of small-sized bars in bogie hearth furnaces or chamber furnaces due to their small size and long length.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] A method for quenching and tempering martensitic stainless steel bars, the method comprising the following steps:

[0012] Step 1: Heat the martensitic stainless steel bar using electromagnetic induction heating.

[0013] Step 2: Quench the heated martensitic stainless steel bar with water as the quenching medium.

[0014] Step 3: Low-temperature stress relief is performed on the martensitic stainless steel bar by heating it using electromagnetic induction. The stress relief heating temperature of the martensitic stainless steel bar is lower than the tempering temperature.

[0015] Step 4: The stress-relieved martensitic stainless steel bar is sent into the tempering furnace.

[0016] In the above-described quenching and tempering method, preferably, the diameter of the martensitic stainless steel bar is φ20mm-100mm, and the length of the martensitic stainless steel bar is 3000mm-8000mm.

[0017] The battery induction heating temperature range in step 1 is 950-1050℃.

[0018] In the tempering method described above, preferably, in step 3, the heating temperature range for low-temperature stress relief is controlled within 500-650℃.

[0019] In the tempering method described above, preferably, in step 4, a gas-fired roller hearth tempering furnace is used for tempering, and the tempering temperature of the martensitic stainless steel bar is controlled at 600-750℃.

[0020] The present invention also provides a tempering production line for martensitic stainless steel bars. The tempering production line includes a conveying channel, and a quenching induction heating device, a spray quenching device, a stress-relieving induction heating device, and a tempering heating device are sequentially arranged on the conveying channel along the conveying direction.

[0021] The quenching induction heating device is used to heat martensitic stainless steel bars before quenching.

[0022] The spray quenching device is used to spray water to quench martensitic stainless steel bars.

[0023] The stress-relieving induction heating device is used to heat and relieve stress on quenched martensitic stainless steel bars.

[0024] The tempering heating device is used to temper and heat the stress-relieved martensitic stainless steel bars.

[0025] In the conditioning production line described above, preferably, the conveying channel is a conveying chain, and the conveying chain is provided with a plurality of bar fixing bars, the extension direction of which is perpendicular to the conveying direction;

[0026] The bar fixing bars are arranged in pairs, and each pair of bar fixing bars is fixed to both ends of the martensitic stainless steel bar. The martensitic bar fixed on the conveyor chain extends in a direction parallel to the conveying direction.

[0027] In the tempering production line described above, preferably, a plurality of fixing grooves are arranged side by side along the extension direction on the bar fixing strip. The fixing grooves are used to press and fix one end of the martensitic bar onto the chain. A fixing through hole is provided at the far end of the bar fixing strip.

[0028] In the conditioning production line described above, preferably, multiple fixing holes are provided on both sides of the conveyor chain. The fixing holes are threaded holes or pin holes. Bolts or pins pass through the fixing through holes at both ends of the bar fixing strip and are respectively connected to the fixing holes on both sides of the conveyor chain to fix the bar fixing strip on the conveyor chain.

[0029] In the tempering production line described above, preferably, the quenching induction heating device and the stress-relieving induction heating device are induction heating furnaces, and the conveyor chain passes through the induction heating furnace;

[0030] The tempering heating device is a gas-fired roller hearth tempering furnace, and the conveyor chain passes through the gas-fired roller hearth tempering furnace.

[0031] In the quenching and tempering production line described above, preferably, a first air curtain machine is provided at the inlet of the gas-fired roller hearth tempering furnace. The first air curtain machine is an electrically heated air curtain machine used to blow out hot air. A second air curtain machine is provided at the outlet of the gas-fired roller hearth tempering furnace. The second air curtain machine is a natural air curtain machine used to blow out natural air.

[0032] The air blowing direction of both the first and second air curtain machines is perpendicular to the conveying direction.

[0033] Beneficial effects: Electromagnetic induction hardening ensures good straightness of the bars; water quenching is environmentally friendly and prevents cracking; gas-fired roller hearth tempering furnaces allow for prolonged carbide precipitation, resulting in uniform mechanical properties. To prevent cracking of electromagnetically induction hardened steel, low-temperature electromagnetic induction stress relief is first performed, which quickly eliminates stress. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the conditioning production line in an embodiment of the present invention;

[0035] Figure 2 This is a cross-sectional view of the rod fixing strip in an embodiment of the present invention.

[0036] In the figure: 1. Quenching induction heating device; 2. Spray quenching device; 3. Stress relief induction heating device; 4. Tempering heating device; 5. Conveyor chain; 6. First air curtain machine; 7. Second air curtain machine; 8. Bar fixing bar; 81. Fixing groove; 82. Fixing hole. Detailed Implementation

[0037] 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, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0038] In the description of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. The terms "connected" and "linked" used in this invention should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through intermediate components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0039] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0040] According to specific embodiments of the present invention, such as Figure 1-2 As shown, the present invention provides a method for quenching and tempering martensitic stainless steel bars. The martensitic stainless steel bars with diameters ranging from φ20mm to 100mm and lengths ranging from 3000mm to 8000mm are suitable for this method.

[0041] The conditioning method includes the following steps:

[0042] Step 1: Heat the martensitic stainless steel bar using electromagnetic induction heating; the electromagnetic induction heating temperature range is 950-1050℃.

[0043] In existing technologies, trolley furnaces are often used for heating. Due to the small size of the bars, severe bending deformation occurs during the heating and quenching process due to gravity and uneven cooling, resulting in twisted or sickle-shaped bends that are difficult to straighten with a straightening machine. Electromagnetic induction heating and quenching ensures uniform heating and cooling of the bars, and the tempering method used in this application guarantees that the bars will not bend.

[0044] Step 2 involves quenching the heated martensitic stainless steel bar with water as the quenching medium. Using water as the medium makes the raw material easier to obtain and is more environmentally friendly.

[0045] In this step, water is a low-cost and environmentally friendly quenching medium, but it can make martensitic stainless steel bars prone to cracking during quenching. Therefore, timely low-temperature stress relief is necessary to prevent the bars from cracking during quenching.

[0046] Step 3: Low-temperature stress relief is performed on the martensitic stainless steel bar using electromagnetic induction heating. The stress relief heating temperature of the martensitic stainless steel bar is lower than the tempering temperature. The low-temperature stress relief heating temperature range is controlled between 500-650℃.

[0047] In this step, the stress-relief heating temperature should be 100°C lower than the tempering heating temperature to avoid the electromagnetic induction stress-relief temperature being too high, which would prevent the bar from meeting the mechanical property requirements.

[0048] Step 4: The stress-relieved martensitic bars are fed into a gas-fired roller hearth tempering furnace; the tempering temperature of the martensitic stainless steel bars is controlled at 600-750℃.

[0049] A gas-fired roller hearth tempering furnace is used to ensure uniform mechanical properties by utilizing its furnace temperature uniformity of ±8℃ and its ability to maintain temperature for a long time to control carbide precipitation.

[0050] The present invention also provides a tempering production line for martensitic stainless steel bars. The tempering production line includes a conveying channel, and a quenching induction heating device, a spray quenching device, a stress-relieving induction heating device, and a tempering heating device are sequentially arranged along the conveying direction on the conveying channel.

[0051] In this embodiment, the conveying channel is a conveyor roller, and the bar can be placed directly on the conveyor roller. In other embodiments, the conveying channel is a conveyor chain, and the conveyor chain is provided with multiple bar fixing bars, the extension direction of the bar fixing bars being perpendicular to the conveying direction; the bar fixing bars are arranged in pairs, and a pair of bar fixing bars are respectively fixed to both ends of the martensitic stainless steel bar, and the extension direction of the martensitic bar fixed on the conveyor chain is parallel to the conveying direction.

[0052] Multiple fixing grooves are arranged side by side along the extension direction on the bar fixing strip. The fixing grooves are used to press and fix one end of the martensitic stainless steel bar onto the chain. A fixing through hole is provided at the very end of the bar fixing strip.

[0053] Multiple fixing holes are provided on both sides of the conveyor chain. The fixing holes are threaded holes or pin holes. Bolts or pins pass through the fixing through holes at both ends of the bar fixing strip and are connected to the fixing holes on both sides of the conveyor chain to fix the bar fixing strip to the conveyor chain.

[0054] The bar fixing strips span the conveyor chain, meaning their extension direction is perpendicular to the conveying direction. When the fixing holes on the conveyor chain are threaded holes, two bolts are passed through the fixing through holes at both ends of the bar fixing strips, and then the two bolts are respectively connected to the fixing holes on both sides of the conveyor chain. This causes the fixing grooves in a pair of bar fixing strips to press against both ends of a martensitic bar, thus firmly fixing a martensitic bar to the conveyor chain. Because the bar fixing strips have multiple fixing grooves, a pair of bar fixing strips can fix multiple martensitic bars. The extension direction of the multiple martensitic bars is parallel to the conveying direction, and the multiple martensitic bars are arranged side by side on the conveyor chain.

[0055] The bar fixing strip of this application can not only fix the martensitic bar, but also restrict the deformation of the martensitic bar, which is beneficial to improving the quenching and tempering qualification rate of the martensitic bar.

[0056] The quenching induction heating device and the stress-relieving induction heating device are both induction heating furnaces, and the conveyor chain passes through the induction heating furnace; the tempering heating device is a gas-fired roller hearth tempering furnace, and the conveyor chain passes through the gas-fired roller hearth tempering furnace.

[0057] A first air curtain machine is installed at the inlet of the gas-fired roller hearth tempering furnace. The first air curtain machine is an electrically heated air curtain machine used to blow out hot air. A second air curtain machine is installed at the outlet of the gas-fired roller hearth tempering furnace. The second air curtain machine is a natural air curtain machine used to blow out natural air. The blowing direction of the first air curtain machine and the second air curtain machine is perpendicular to the conveying direction.

[0058] Air curtains are installed at the inlet and outlet of the gas-fired roller hearth tempering furnace. The airflow from the air curtains isolates the furnace from the external environment. This results in better heat preservation, allowing the martensitic bars to be fully insulated. Consequently, the microstructure of the martensitic bars can fully develop within the furnace, ensuring better tempering and ultimately leading to superior overall mechanical properties.

[0059] In operation, this tempering production line first arranges multiple martensitic bars side-by-side on a conveyor chain using solid bar strips, with the extension direction of the martensitic bars parallel to the conveyor chain's conveying direction. The conveyor chain is then started, feeding the martensitic bars into a quenching induction heating device, where the bars are heated to 950-1050℃ (the heating temperature is selected based on the bar material). Induction heating is highly efficient and results in minimal deformation of the martensitic bars. Next, the conveyor chain is rotated to feed the martensitic bars into a spray quenching device, where cooling water is sprayed to quench the martensitic bars. During the quenching process, bar fixing strips fix and limit the martensitic bars, thus preventing significant deformation. After quenching, the conveyor chain rotates to transport the martensitic bar to the stress-relieving induction heating device, which heats the martensitic bar to relieve stress, thereby preventing the martensitic bar from undergoing large deformation. Finally, the martensitic bar is transferred to the tempering heating device to complete the tempering process, thus completing the entire quenching and tempering treatment of the martensitic bar.

[0060] In summary, the technical solution of the martensitic bar adjustment method provided by this invention uses electromagnetic induction quenching to ensure good bar straightness, and water quenching is environmentally friendly and prevents cracking; the gas-fired roller hearth tempering furnace allows for long-term carbide precipitation, resulting in uniform mechanical properties. To prevent cracking of the electromagnetically induction quenched steel, low-temperature electromagnetic induction stress relief is first performed, which can quickly eliminate stress.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for quenching and tempering martensitic stainless steel bars, characterized in that, The conditioning method includes the following steps: Step 1: Heating the martensitic stainless steel bar using electromagnetic induction heating; the electromagnetic induction heating temperature range in Step 1 is 950-1050℃. Step 2: Quench the heated martensitic stainless steel bar with water as the quenching medium. Step 3: Low-temperature stress relief is performed on the martensitic stainless steel bar by heating it using electromagnetic induction. The stress relief heating temperature of the martensitic stainless steel bar is lower than the tempering temperature. Step 4: Send the stress-relieved martensitic stainless steel bar into the tempering furnace. The diameter specifications of the martensitic stainless steel bars are as follows: The length specifications for martensitic stainless steel bars are 3000mm-8000mm, ranging from 20mm to 100mm. In step 3, the low-temperature stress relief heating temperature range is controlled between 500-650℃, and the stress relief heating temperature is 100℃ lower than the tempering heating temperature. In step 4, a gas-fired roller hearth tempering furnace is used for tempering.

2. The conditioning method according to claim 1, characterized in that, In step 4, the tempering temperature of the martensitic stainless steel bar is controlled at 600-750℃.

3. A quenching and tempering production line for martensitic stainless steel bars, characterized in that, The quenching and tempering method for martensitic stainless steel bars as described in claim 1 is adopted; The tempering production line includes a conveying channel, on which a quenching induction heating device, a spray quenching device, a stress-relieving induction heating device, and a tempering heating device are sequentially arranged along the conveying direction. The quenching induction heating device is used to heat martensitic stainless steel bars before quenching. The spray quenching device is used to spray water to quench martensitic stainless steel bars. The stress-relieving induction heating device is used to heat and relieve stress on quenched martensitic stainless steel bars. The tempering heating device is used to temper and heat the stress-relieved martensitic stainless steel bars. The conveying channel is a conveying chain, and the conveying chain is provided with multiple rod fixing bars, the extension direction of which is perpendicular to the conveying direction; The bar fixing bars are arranged in pairs, and each pair of bar fixing bars is fixed to both ends of the martensitic stainless steel bar. The martensitic bar fixed on the conveyor chain extends in a direction parallel to the conveying direction.

4. The conditioning and tempering production line according to claim 3, characterized in that, The bar fixing strip has multiple fixing grooves arranged in parallel along the extension direction. The fixing grooves are used to press one end of the martensitic bar and fix it on the conveyor chain. A fixing through hole is provided at the far end of the bar fixing strip.

5. The conditioning and tempering production line according to claim 4, characterized in that, Multiple fixing holes are provided on both sides of the conveyor chain. The fixing holes are threaded holes or pin holes. Bolts or pins pass through the fixing through holes at both ends of the bar fixing strip and are respectively connected to the fixing holes on both sides of the conveyor chain to fix the bar fixing strip on the conveyor chain.

6. The conditioning and tempering production line according to claim 3, characterized in that, The quenching induction heating device and the stress-relieving induction heating device are induction heating furnaces, and the conveyor chain passes through the induction heating furnace; The tempering heating device is a gas-fired roller hearth tempering furnace, and the conveyor chain passes through the gas-fired roller hearth tempering furnace.

7. The conditioning and tempering production line according to claim 6, characterized in that, A first air curtain machine is installed at the inlet of the gas-fired roller hearth tempering furnace. The first air curtain machine is an electrically heated air curtain machine used to blow out hot air. A second air curtain machine is installed at the outlet of the gas-fired roller hearth tempering furnace. The second air curtain machine is a natural air curtain machine used to blow out natural air. The air blowing direction of both the first and second air curtain machines is perpendicular to the conveying direction.

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