A heat treatment method for thick forgings

Abstract

The present invention relates to the field of metal heat treatment technology, specifically to a heat treatment method for thick forgings. It is used to accurately control the temperature of thick forgings entering the aging and heat preservation stage. It includes the following steps, S1: opening a countersink on the surface of the forging, and installing a first thermocouple in the countersink, and installing a second thermocouple on the surface of the forging; S2: heating the heat treatment furnace to a first temperature, and then placing the forging into the heat treatment furnace; S3: heating the forging to the first temperature and keeping it warm for a first time; S4: closing the heat treatment furnace, opening the exhaust system, until the surface temperature of the forging drops to the aging temperature; S5: opening the heating furnace, keeping the temperature in the furnace at the aging temperature, gradually reducing the exhaust power of the exhaust system, so that the temperature of the core of the forging is gradually reduced, and the surface temperature of the forging is kept in the range of the aging temperature to the aging temperature-5°C, until the value of the first thermocouple drops to the aging temperature, and closing the exhaust system; S6: keeping the forging at the aging temperature for a second time.

Description

Technical Field

[0001] The invention relates to the technical field of metal heat treatment, in particular to a heat treatment method for thick forgings. Background Art

[0002] At present, heat treatment furnaces can be divided into "front zone", "middle zone", "rear zone" or "front zone", "middle zone", "middle zone", "rear zone" according to the size of the furnace. Each area has a thermocouple and a temperature control system. The thermocouple is used to detect the furnace temperature, and the temperature control system controls the equipment power in real time through the detected temperature of the thermocouple to ensure the accuracy of the temperature.

[0003] During the heat treatment process of thick forgings in the heat treatment furnace, when the thermocouple detects that the furnace has cooled to the aging temperature, the system will automatically enter the aging and heat preservation stage, while the actual temperature of the forging is still higher than the aging temperature. The reason for this phenomenon is that the thermocouple can only detect the furnace temperature and cannot accurately reflect the temperature of the forging. For thick forgings (forgings with a thickness greater than 100mm), the furnace temperature can drop quickly. When the furnace temperature drops to the aging temperature, the surface temperature of the forging reaches the aging temperature, but the temperature of the core of the forging will be higher than the aging temperature. At this time, the heat from the core of the forging will be transferred to the surface of the forging, causing the surface temperature of the forging to rise. This phenomenon will cause the temperature of the forging during the aging and heat preservation stage to be higher than the preset aging temperature, thereby affecting the uniformity of the overall organizational properties of the forging. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a heat treatment method for thick forgings, which can accurately control the temperature of the thick forgings entering the aging and heat preservation stage.

[0005] The technical solution adopted by the present invention to solve the technical problem is a heat treatment method for thick forgings, comprising the following steps:

[0006] S1: at least one countersunk hole is opened on the surface of the forging, and the maximum hole depth of the countersunk hole is 1 / 2 of the effective value of the thickness of the forging; and a first thermocouple is installed in the countersunk hole, and at least one second thermocouple is arranged on the surface of the forging;

[0007] S2: The heat treatment furnace is heated to a set first temperature, and then the forging is placed in the heat treatment furnace;

[0008] S3: heating the forging to a first temperature, bringing the core of the forging to a temperature, and keeping the temperature for a first time;

[0009] S4: closing the heat treatment furnace, opening the exhaust system, and cooling the forging until the second thermocouple detects that the surface temperature of the forging drops to the aging temperature;

[0010] S5: Turn on the heating furnace to keep the temperature in the furnace at the aging temperature, use the first thermocouple to detect the temperature of the core of the forging, gradually reduce the exhaust power of the exhaust system to gradually reduce the temperature of the core of the forging, and keep the surface temperature of the forging within the range of the aging temperature to the aging temperature -5°C, until the value of the first thermocouple drops to the aging temperature, and then turn off the exhaust system;

[0011] S6: keeping the forging at the aging temperature for a second time;

[0012] S7: Turn off the heat treatment furnace and allow the forging to air cool to room temperature.

[0013] Furthermore, the forging material is Ti-55531 alloy, the first temperature is 890°C±5°C, the first time is 1 hour, the aging temperature is 560°C±5°C, and the second time is 8 hours.

[0014] Further, in step S4, the surface temperature of the forging is reduced from the first temperature to the aging temperature in three temperature ranges, namely, high-temperature slow cooling from the first temperature to 700°C, medium-temperature fast cooling from 700°C to 600°C, and low-temperature slow cooling from 600°C to the aging temperature. The cooling rate of high-temperature slow cooling is 2°C / min, the cooling rate of medium-temperature fast cooling is 5°C / min, and the cooling rate of low-temperature slow cooling is 2°C / min.

[0015] Furthermore, the thermocouple is an armored thermocouple, and the armored thermocouple is installed in the countersunk hole by welding, and the thermocouple is sealed in the hole after installation.

[0016] The beneficial effect of the present invention is that: by connecting a thermocouple outside the forging body, when the surface temperature of the forging reaches the aging temperature but the core temperature of the forging does not reach the aging temperature, the exhaust volume of the exhaust system is reduced to reduce the core temperature of the forging and ensure that the surface temperature of the forging is in a dynamic equilibrium state. After the core temperature of the forging reaches the aging temperature, the aging insulation stage is entered to ensure the performance of the forging after aging insulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0018] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0019] like Figure 1 As shown, a heat treatment method for thick forgings of the present invention comprises the following steps:

[0020] S1: at least one countersunk hole is opened on the surface of the forging, and the maximum hole depth of the countersunk hole is 1 / 2 of the effective value of the thickness of the forging; and a first thermocouple is installed in the countersunk hole, and at least one second thermocouple is arranged on the surface of the forging; when there is one countersunk hole, it is located at the center of the upper surface of the forging; when there are at least two countersunk holes, the countersunk holes can be arranged at intervals along the length direction of the forging and / or along the width direction of the forging, and the first thermocouple and the second thermocouple are armored thermocouples, the first thermocouple is welded in the countersunk hole, and the first thermocouple is sealed in the hole after installation, and the second thermocouple is welded to the surface of the forging.

[0021] S2: The heat treatment furnace is heated to a set first temperature, and then the forging is placed in the heat treatment furnace.

[0022] S3: The forging is heated to a first temperature, and the core of the forging is heated to a first temperature, and then kept warm for a first time; different materials use different heat treatment temperatures and holding times. For example, TC4 uses a heat treatment temperature of 910-940°C and a holding time of 0.5-2 hours; 7050 aluminum alloy uses a heat treatment temperature of 475°C and a holding time of 2 hours.

[0023] S4: Turn off the heat treatment furnace, open the exhaust system, and cool the forging until the second thermocouple detects that the surface temperature of the forging drops to the aging temperature; it should be noted that the second thermocouple reflects the surface temperature of the forging. The aging temperature is related to the material. For example, TC4 uses a temperature of 520-550°C for aging treatment, and the insulation time is 2-4 hours. 7050 aluminum alloy uses a temperature of 120°C for aging treatment, and the insulation time is 6 hours.

[0024] S5: Turn on the heating furnace to keep the temperature in the furnace at the aging temperature, use the first thermocouple to detect the temperature of the core of the forging, gradually reduce the exhaust power of the exhaust system, so that the temperature of the core of the forging is gradually reduced, and the surface temperature of the forging is maintained in the range of the aging temperature to the aging temperature-5°C, until the value of the first thermocouple is reduced to the aging temperature, and then turn off the exhaust system; it should be noted that since the exhaust system will take away the heat from the surface of the forging, and the core of the forging will also have heat transferred to the surface of the forging, the heat on the surface of the forging taken away by the exhaust system and the heat transferred to the surface of the forging from the core of the forging reach a dynamic balance, so that the surface temperature of the forging is maintained in the range of the aging temperature to the aging temperature-5°C, for example, when the aging temperature is 560°C, the surface temperature of the forging is maintained in the range of 555°C-560°C; since the heat of the core of the forging will gradually be transferred to the surface of the forging, the temperature of the core of the forging will gradually decrease, and the heat transferred from the core of the forging to the surface of the forging per unit time will also decrease, so it is necessary to gradually reduce the exhaust power of the exhaust system.

[0025] S6: Keep the forging at the aging temperature for a second time.

[0026] S7: Turn off the heat treatment furnace and allow the forging to air cool to room temperature.

[0027] Since the temperature in the heat treatment furnace may fluctuate, the first temperature and the aging temperature are both within a numerical range. Furthermore, the forging material is Ti-55531 alloy, the first temperature is 890°C±5°C, the first time is 1h, the aging temperature is 560°C±5°C, and the second time is 8h.

[0028] In order to avoid the influence of extremely rapid cooling on the performance of forgings, further, in step S4, the temperature range of the forgings from the first temperature to the aging temperature is divided into three temperature ranges, namely, high-temperature slow cooling from the first temperature to 700°C, medium-temperature rapid cooling from 700°C to 600°C, and low-temperature slow cooling from 600°C to the aging temperature. The cooling rate of high-temperature slow cooling is 2°C / min, the cooling rate of medium-temperature rapid cooling is 5°C / min, and the cooling rate of low-temperature slow cooling is 2°C / min.

[0029] Example 1

[0030] A countersink is opened at the center of a Ti-55531 alloy forging with a length of 1000mm, a width of 500mm, and a thickness of 200mm. The depth of the countersink is 50mm. A first thermocouple is installed in the countersink, and a second thermocouple is installed on the surface of the forging. The heat treatment furnace is heated to 890°C and the Ti-55531 alloy forging is placed in the heat treatment furnace. After the core of the Ti-55531 alloy forging is heated to temperature, it is kept warm for 1 hour.

[0031] Close the heat treatment furnace, open the exhaust system, and cool down at 2°C / min from 890°C to 700°C, 5°C / min from 700°C to 600°C, and 2°C / min from 600°C to 560°C. When the second thermocouple detects that the surface temperature of the forging is about to reach 560°C, the first thermocouple detects that the core temperature of the Ti-55531 alloy forging is 600°C, and gradually reduces the exhaust power of the exhaust system to gradually reduce the core temperature of the Ti-55531 alloy forging. The surface temperature of the Ti-55531 alloy forging is within the range of 555°C to 560°C, until the first thermocouple detects that the core temperature of the Ti-55531 alloy forging is 560°C, and then closes the exhaust system.

[0032] The heat treatment furnace maintained the temperature at 560°C and kept the Ti-55531 alloy forgings warm for 8 hours. The heat treatment furnace was then closed to allow the Ti-55531 alloy forgings to be air-cooled to room temperature.

[0033] Comparative Example 1

[0034] The length of the Ti-55531 alloy forging is 1000mm, the width is 500mm, and the thickness is 200mm. The heat treatment furnace is heated to 890°C and the Ti-55531 alloy forging is placed in the heat treatment furnace. After the core of the Ti-55531 alloy forging is heated to temperature, it is kept warm for 1 hour.

[0035] Close the heat treatment furnace, open the exhaust system, and cool at 2°C / min from 890°C to 700°C, 5°C / min from 700°C to 600°C, and 2°C / min from 600°C to 560°C. When the surface temperature of the forging reaches 560°C, close the exhaust system.

[0036] The heat treatment furnace maintained the temperature at 560°C and kept the Ti-55531 alloy forgings warm for 8 hours. The heat treatment furnace was then closed to allow the Ti-55531 alloy forgings to be air-cooled to room temperature.

[0037] The mechanical properties of the forgings formed in Example 1 and Comparative Example 1 were tested, as shown in the following table.

[0038] serial number tensile strength Yield Strength Elongation Sectional shrinkage Impact toughness Example 1 1196 1100 12.5 28 32 Comparative Example 1 1107 1004 14 32 39

[0039] The results of mechanical properties test show that if the influence of reverse heating is ignored, that is, when the surface temperature of the forging is reduced to 560℃ and then aging and heat preservation treatment is carried out, the strength performance of the forging is significantly lower than that of the forging after the internal and external temperatures of the forging are reduced to 560℃ and then aging and heat preservation treatment is carried out.

[0040] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A heat treatment method for thick forgings, characterized in that: The following steps are included: S1: at least one countersunk hole is opened on the surface of the forging, and the maximum hole depth of the countersunk hole is 1 / 2 of the effective value of the thickness of the forging; a first thermocouple is installed in the countersunk hole, and at least one second thermocouple is arranged on the surface of the forging; the forging material is Ti-55531 alloy; S2: The heat treatment furnace is heated to a set first temperature, and then the forging is placed in the heat treatment furnace; S3: heating the forging to a first temperature, so that the core of the forging reaches the temperature, and keeping the temperature for a first time; the first temperature is 890°C ± 5°C, and the first time is 1h; S4: close the heat treatment furnace, open the exhaust system, and cool the forging until the second thermocouple detects that the surface temperature of the forging is reduced to the aging temperature; in step S4, the surface temperature of the forging is reduced from the first temperature to the aging temperature in three temperature ranges, namely, high-temperature slow cooling from the first temperature to 700°C, medium-temperature fast cooling from 700°C to 600°C, and low-temperature slow cooling from 600°C to the aging temperature, the cooling rate of high-temperature slow cooling is 2°C / min, the cooling rate of medium-temperature fast cooling is 5°C / min, and the cooling rate of low-temperature slow cooling is 2°C / min; S5: Turn on the heating furnace to keep the temperature in the furnace at the aging temperature, use the first thermocouple to detect the temperature of the core of the forging, gradually reduce the exhaust power of the exhaust system to gradually reduce the temperature of the core of the forging, and keep the surface temperature of the forging within the range of the aging temperature to the aging temperature -5°C, until the value of the first thermocouple drops to the aging temperature, and then turn off the exhaust system; S6: keeping the forging at the aging temperature for a second time; the aging temperature is 560°C ± 5°C, and the second time is 8h; S7: Turn off the heat treatment furnace and allow the forging to air cool to room temperature.

2. A heat treatment method for thick forgings according to claim 1, characterized in that: The first thermocouple and the second thermocouple are armored thermocouples. The first thermocouple is welded in the countersunk hole. After installation, the first thermocouple is sealed in the hole, and the second thermocouple is welded to the surface of the forging.

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