Heat treatment method for the tie rod material 30CrNiMo8 steel of an ORC turbine unit

Abstract

The present invention discloses a heat treatment method for the tie rod material 30CrNiMo8 steel of an ORC turbine unit, including: 1) designing a tie rod heat treatment tooling; 2) assembling the tie rod and the heat treatment tooling; 3) performing high-temperature normalizing treatment at 850 - 880 °C for at least 2 h; 4) performing normalizing treatment on the critical region side at 800 - 830 °C for at least 2 h; 5) performing quenching treatment at 850 - 870 °C for at least 2 h; 6) performing tempering treatment up to 530 - 600 °C for at least 4 h. The heat treatment method of the present invention reduces the deformation amount of the tie rod during the heat treatment process by designing the tie rod heat treatment tooling; optimizes the heat treatment process and parameters of the tie rod, makes the material structure uniform, and effectively refines the grain size of the material, and the grain size can reach above grade 7, which can significantly improve the strength of the material 30CrNiMo8 steel.

Description

Technical Field

[0001] The present invention relates to the technical field of heat treatment, and particularly relates to a heat treatment method for 30CrNiMo8 steel, which is a tie rod material for an ORC turbine unit. Background Art

[0002] An ORC turbine unit is a device used to increase gas pressure and transport gas, and has been gradually widely used in industries such as petroleum, chemical industry, pharmaceutical, and sewage treatment. As the unit is used more and more widely, the requirements for materials and heat treatment are also getting higher and higher. The tie rod of the ORC turbine unit is a slender columnar structure. When traditional heat treatment is carried out with multiple tie rods lying horizontally on a heat treatment tray, bending, twisting and deformation are very likely to occur during the heat treatment process. Straightening and other cold deformation processes are required after heat treatment, and new internal stresses are generated during the cold deformation process. As an important component in the compressor rotor, the generation of internal stresses poses a hazard to the operation of the unit; in addition, as a rotating component of the compressor, the tie rod has high strength requirements. Due to the existence of mixed crystal structure in the original structure of 30CrNiMo8 steel raw materials, the corresponding structure is inherited during subsequent heat treatment, resulting in the heat treatment strength not meeting the requirements, and serious quality accidents will occur. Therefore, sometimes only relatively expensive materials can be selected for the tie rod material, which increases the production cost and reduces the production profit. Summary of the Invention

[0003] In order to solve the above problems, the present invention provides a heat treatment method for 30CrNiMo8 steel, which is a tie rod material for an ORC turbine unit.

[0004] A heat treatment method for 30CrNiMo8 steel, which is a tie rod material for an ORC turbine unit, includes:

[0005] 1) Design the heat treatment tooling for the tie rod

[0006] Rough machine the 30CrNiMo8 steel tie rod, and leave a boss at one end of the tie rod;

[0007] Design the heat treatment tooling for the tie rod according to the size of the tie rod. The heat treatment tooling includes a suspension plate and a suspension shaft. The suspension plate is provided with a suspension hole. The diameter of the tie rod is smaller than the diameter of the suspension hole, and the diameter of the boss is larger than the diameter of the suspension hole;

[0008] The suspension shaft is connected to the middle of the suspension plate, and the axes of the suspension shaft and the suspension plate coincide;

[0009] 2) Assemble the tie rod and the heat treatment tooling. The tie rod is hoisted on the suspension hole through the boss at the end, and the suspension plate is connected to the heat treatment equipment through the suspension shaft;

[0010] 3) High-temperature normalizing treatment, at 850 - 880 °C, with a holding time of ≥ 2 h;

[0011] 4) Normalizing treatment on the critical zone side, at 800 - 830°C, holding for ≥2 h;

[0012] 5) Quenching treatment, at 850 - 870°C, holding for ≥2 h;

[0013] 6) Tempering treatment, up to 530 - 600°C, holding for ≥4 h.

[0014] Furthermore, the diameter of the boss is not less than 10 mm larger than the diameter of the lifting hole, and the thickness of the boss is 20 - 25 mm.

[0015] Furthermore, a number of the lifting holes are provided on the hanging plate, and the minimum distance between the lifting holes is not less than 160 mm.

[0016] Furthermore, for the high-temperature normalizing treatment, the pull rod is first heated to 580 - 650°C, held for 1 - 3 h, and then heated to 850 - 880°C, holding for ≥2 h.

[0017] Furthermore, for the high-temperature normalizing treatment, the pull rod is heated according to the power when the temperature is ≤400°C, and after the temperature exceeds 400°C, it is heated to 580 - 650°C at a rate of ≤100°C / h, held for 1 - 3 h, then heated to 850 - 880°C at a rate of ≤80°C / h, held for ≥2 h, and then air-cooled.

[0018] Furthermore, for the normalizing treatment on the critical zone side, the pull rod after the high-temperature normalizing treatment is first heated to 560 - 620°C, held for 1 - 3 h, and then heated to 800 - 830°C, holding for ≥2 h.

[0019] Furthermore, for the normalizing treatment on the critical zone side, the pull rod after the high-temperature normalizing treatment is heated according to the power when the temperature is ≤400°C, and after the temperature exceeds 400°C, it is heated to 560 - 620°C at a rate of ≤100°C / h, held for 1 - 3 h, then heated to 800 - 830°C at a rate of ≤80°C / h, held for ≥2 h, and then air-cooled.

[0020] Furthermore, for the quenching treatment, the pull rod after the normalizing treatment on the critical zone side is heated according to the power when the temperature is ≤400°C, and after the temperature exceeds 400°C, it is heated to 580 - 650°C at a rate of ≤100°C / h, held for 1 - 3 h, then heated to 850 - 870°C at a rate of ≤80°C / h, held for ≥2 h, and then oil-cooled to ≤200°C before taking out the oil.

[0021] Furthermore, for the tempering treatment, the pull rod after the quenching treatment is heated according to the power when the temperature is ≤300°C, and after the temperature exceeds 300°C, it is heated to 530 - 600°C at a rate of ≤60°C / h, held for ≥4 h, and then air-cooled.

[0022] Further, after the high-temperature normalizing treatment, the tie rod is hung vertically. The tie rod is hot-loaded into the furnace at ≤400°C for the critical-region side normalizing treatment; after the critical-region side normalizing treatment, the tie rod is hung vertically. The tie rod is hot-loaded into the furnace at ≤400°C for the quenching treatment; after the quenching treatment, the tie rod is hung vertically. The tie rod is hot-loaded into the furnace at ≤300°C for the tempering treatment; after the tempering treatment, the tie rod is hung vertically.

[0023] The heat treatment method for the 30CrNiMo8 steel of the tie rod material of the ORC turbine unit provided by the present invention reduces the deformation amount of the tie rod during the heat treatment process by designing a heat treatment tooling for the tie rod. Moreover, there is no mutual contact between the tie rods, reducing the deformation caused by mutual extrusion between the tie rods and improving the heat treatment quality of the tie rod; the heat treatment process and parameters of the tie rod are optimized. The heat treatment methods of high-temperature normalizing treatment, critical-region side normalizing treatment, quenching treatment, and tempering treatment are adopted. The high-temperature and low-temperature fluctuation heat treatment method is used to break the heredity of the original structure of the material, making the material structure uniform, and effectively refining the grain size of the material. The grain size can reach above grade 7, which can significantly improve the strength of the 30CrNiMo8 steel material. Description of the Drawings

[0024] Figure 1 It is a schematic structural diagram of the heat treatment tooling provided by the embodiment of the present invention.

[0025] Figure 2 It is a front view of the hanging plate of the heat treatment tooling provided by the embodiment of the present invention.

[0026] Figure 3 It is an A-A sectional view of the hanging plate of the heat treatment tooling provided by the embodiment of the present invention.

[0027] Figure 4 It is a front view of the hanging shaft of the heat treatment tooling provided by the embodiment of the present invention.

[0028] Among them, the reference numerals are: 1, tie rod; 2, hanging plate; 3, hanging shaft. Detailed Embodiments

[0029] In order to better understand the above technical solutions, the technical solutions of the embodiments of the present application will be described in detail below with reference to the drawings and specific embodiments.

[0030] A heat treatment method for the 30CrNiMo8 steel of the tie rod material of the ORC turbine unit includes:

[0031] 1) Design a heat treatment tooling for the tie rod

[0032] Rough-machine the 30CrNiMo8 steel tie rod, and leave a boss at one end of the tie rod;

[0033] Design a heat treatment tooling for the tie rod according to the size of the tie rod. The heat treatment tooling includes a hanging plate and a hanging shaft. The hanging plate is provided with a hanging hole. The diameter of the tie rod is smaller than the diameter of the hanging hole, and the diameter of the boss is larger than the diameter of the hanging hole.

[0034] The hanging shaft is connected to the middle of the hanging plate, and the axes of the hanging shaft and the hanging plate coincide.

[0035] 2) Assemble the tie rod and the heat treatment tooling. The tie rod is hoisted on the hanging hole through the boss at the end, and the hanging plate is connected to the heat treatment equipment through the hanging shaft.

[0036] 3) High-temperature normalizing treatment, 850 - 880 °C, holding time ≥ 2 h.

[0037] 4) Sub-critical zone side normalizing treatment, 800 - 830 °C, holding time ≥ 2 h.

[0038] 5) Quenching treatment, 850 - 870 °C, holding time ≥ 2 h.

[0039] 6) Tempering treatment, up to 530 - 600 °C, holding time ≥ 4 h.

[0040] A heat treatment method for the 30CrNiMo8 steel of the tie rod material of the ORC turbine unit provided by the embodiment of the present invention reduces the deformation amount of the tie rod during the heat treatment process by designing the heat treatment tooling for the tie rod, and there is no mutual contact between the tie rods, reducing the deformation caused by mutual extrusion between the tie rods and improving the heat treatment quality of the tie rod; the heat treatment process and parameters of the tie rod are optimized, and the heat treatment methods of high-temperature normalizing treatment, sub-critical zone side normalizing treatment, quenching treatment and tempering treatment are adopted. The high-temperature and low-temperature fluctuation heat treatment method is used to break the heredity of the original structure of the material, make the material structure uniform, and effectively refine the grain size of the material. The grain size can reach above grade 7, which can significantly improve the strength of the 30CrNiMo8 steel material.

[0041] In some embodiments, the diameter of the boss is not less than 10 mm larger than the diameter of the hanging hole, and the thickness of the boss is 20 - 25 mm.

[0042] Specifically, in order to ensure that the tie rod is stably hung on the hanging plate, the diameter of the boss is designed to be not less than 10 mm larger than the diameter of the hanging hole, and the thickness of the boss is 20 - 25 mm.

[0043] In some embodiments, the hanging plate is provided with a plurality of the hanging holes, and the minimum distance between the hanging holes is not less than 160 mm.

[0044] Specifically, in order to ensure that the hanging plate can lift the tie rod, the minimum distance between the hanging holes is controlled to be not less than 160 mm.

[0045] In some embodiments, for the high-temperature normalizing treatment, the pull rod is first heated to 580 - 650 °C and held for 1 - 3 h, then heated to 850 - 880 °C and held for ≥2 h. Further, for the high-temperature normalizing treatment, the pull rod is heated according to power when the temperature is ≤400 °C, and after the temperature exceeds 400 °C, it is heated to 580 - 650 °C at a rate of ≤100 °C / h, held for 1 - 3 h, then heated to 850 - 880 °C at a rate of ≤80 °C / h, held for ≥2 h, and then air-cooled.

[0046] Specifically, through the high-temperature normalizing treatment, excessive internal stress in the workpiece can be eliminated, the structure can be made uniform, and controlling the heating rate is mainly to ensure the uniformity of the part and the furnace temperature and prevent part deformation.

[0047] In some embodiments, for the normalizing treatment on the critical region side, the pull rod after the high-temperature normalizing treatment is first heated to 560 - 620 °C and held for 1 - 3 h, then heated to 800 - 830 °C and held for ≥2 h. Further, for the normalizing treatment on the critical region side, the pull rod after the high-temperature normalizing treatment is heated according to power when the temperature is ≤400 °C, and after the temperature exceeds 400 °C, it is heated to 560 - 620 °C at a rate of ≤100 °C / h, held for 1 - 3 h, then heated to 800 - 830 °C at a rate of ≤80 °C / h, held for ≥2 h, and then air-cooled.

[0048] Specifically, the normalizing treatment on the critical region side and the high-temperature normalizing treatment form a heating method with high and low temperature fluctuations, breaking the structure heredity of the raw material, refining the grains, and controlling the heating rate is mainly to ensure the uniformity of the part and the furnace temperature and prevent part deformation.

[0049] In some embodiments, for the quenching treatment, the pull rod after the normalizing treatment on the critical region side is heated according to power when the temperature is ≤400 °C, and after the temperature exceeds 400 °C, it is heated to 580 - 650 °C at a rate of ≤100 °C / h, held for 1 - 3 h, then heated to 850 - 870 °C at a rate of ≤80 °C / h, held for ≥2 h, and then oil-cooled to ≤200 °C and taken out of the oil.

[0050] Specifically, by controlling the heating rate, the uniformity of the pull rod and the furnace temperature is ensured; after the quenching treatment, more martensite or lower bainite structures are obtained.

[0051] In some embodiments, for the tempering treatment, the pull rod after the quenching treatment is heated according to power when the temperature is ≤300 °C, and after the temperature exceeds 300 °C, it is heated to 530 - 600 °C at a rate of ≤60 °C / h, held for ≥4 h, and then air-cooled.

[0052] Specifically, by controlling the heating rate, the uniformity of the pull rod and the furnace temperature is ensured; after the tempering treatment, mechanical properties meeting the design requirements are obtained.

[0053] In some embodiments, after the high-temperature normalizing treatment, the tie rod is hung vertically. The tie rod is hot-loaded into the furnace at a temperature ≤400°C for the critical-region side normalizing treatment; after the critical-region side normalizing treatment, the tie rod is hung vertically. The tie rod is hot-loaded into the furnace at a temperature ≤400°C for the quenching treatment; after the quenching treatment, the tie rod is hung vertically. The tie rod is hot-loaded into the furnace at a temperature ≤300°C for the tempering treatment; after the tempering treatment, the tie rod is hung vertically.

[0054] Specifically, hanging the tie rod vertically after taking it out of the furnace can avoid contact between the tie rods and reduce deformation caused by the mutual force between the tie rods. Hot-loading the tie rod into the furnace at a temperature ≤400°C for the critical-region side normalizing treatment, hot-loading the tie rod into the furnace at a temperature ≤400°C for the quenching treatment, and hot-loading the tie rod into the furnace at a temperature ≤300°C for the tempering treatment can save time and energy costs while ensuring the heat treatment performance.

[0055] In summary, the heat treatment method for the tie rod material 30CrNiMo8 steel of an ORC turbine unit provided by the present invention first adjusts the traditional horizontal placement method of the 30CrNiMo8 steel tie rod during heat treatment. By designing a heat treatment lifting tooling, the tie rod is always in a vertical manner during the heat treatment process, and the tie rod is also placed in a vertically hanging manner after being taken out of the furnace, reducing the deformation amount of the tie rod during the heat treatment process. Moreover, there is no mutual contact between the tie rods, reducing the deformation caused by mutual extrusion between the tie rods and improving the heat treatment quality of the tie rod. Secondly, the heat treatment process and parameters of the tie rod are optimized. The high-temperature normalizing treatment and the critical-region side normalizing treatment are added to the traditional process, that is, a heat treatment method of high-temperature normalizing treatment, critical-region side normalizing treatment, quenching treatment, and tempering treatment is adopted. By using the combination of high-temperature normalizing treatment and critical-region side normalizing treatment, the hereditary property of the original structure of the material is broken by using the high-temperature and low-temperature fluctuation heat treatment method, making the material structure uniform, and effectively refining the grain size of the material. The grain size can reach above grade 7. And with the tempering treatment temperature controlled within the range of 530 - 600°C, the strength of the material 30CrNiMo8 steel can be significantly improved, enabling 30CrNiMo8 steel to be applied to high-strength tie rods. Thus, 30CrNiMo8 steel can be used to replace relatively expensive materials, effectively saving production costs and improving economic benefits.

[0056] Example 1 A high-strength heat treatment method for the tie rod material 30CrNiMo8 steel of an ORC turbine unit

[0057] Tie rods with a diameter of Φ90mm before heat treatment are produced. The tie rod heat treatment process includes rough machining before tie rod heat treatment, installation of lifting tooling, high-temperature normalizing treatment, critical-region side normalizing treatment, quenching treatment, and tempering treatment:

[0058] (1) Rough machine the 30CrNiMo8 steel tie rod. The rough machining size of the tie rod is 100 mm. The thickness of the boss at one end of the tie rod is 20 mm, and the diameter of the boss is 160 mm.

[0059] (2) Select a suspension plate with an inner hole diameter of 150 mm.

[0060] (3) Assemble the heat treatment tooling for the tie rod, which consists of a suspension shaft and a suspension plate. The suspension shaft passes through the central inner hole of the suspension plate and coincides with the axis of the suspension plate.

[0061] (4) Insert 6 tie rods into the inner hole of the suspension plate, and the bosses of the tie rods rest on the surface of the suspension plate.

[0062] (5) Hang the hook of the heat treatment equipment on the square hole of the suspension shaft of the heat treatment hoisting tool.

[0063] (6) High-temperature normalizing treatment: The tie rods are loaded into the furnace at 223 °C, heated to 400 °C according to the power, then heated to 600 °C at a rate of 80 °C / h, held for 1 h, then heated to 860 °C at a rate of 60 °C / h, held for 2 h, and then air-cooled. After being taken out of the furnace, they are hung on the normalizing rack and placed vertically.

[0064] (7) Sub-critical region side normalizing treatment: The tie rods after high-temperature normalizing treatment are loaded into the furnace at 180 °C, heated to 400 °C according to the power, then heated to 610 °C at a rate of 90 °C / h, held for 1 h, then heated to 810 °C at a rate of 60 °C / h, held for 2 h, and then air-cooled. After being taken out of the furnace, they are hung on the normalizing rack and placed vertically.

[0065] (8) Quenching treatment: The tie rods after sub-critical region side normalizing treatment are loaded into the furnace at 200 °C, heated to 400 °C according to the power, then heated to 600 °C at a rate of 70 °C / h, held for 1 h, then heated to 850 °C at a rate of 50 °C / h, held for 2 h, and then oil-cooled. After being taken out of the oil, they are hung and placed vertically to drain the oil.

[0066] (9) Tempering treatment: The tie rods after quenching treatment are loaded into the furnace at 180 °C, heated to 300 °C according to the power, then heated to 560 °C at a rate of 30 °C / h, held for 4 h, and then air-cooled. After being taken out of the furnace, they are hung on the normalizing rack and placed vertically.

[0067] Mechanical properties after heat treatment: Rm: 1250 Mpa; Rp0.2: 1084 Mpa; A: 20%; Z: 70%; HBW: 370.

[0068] The bending deformation of the tie rod after heat treatment is 1.2 mm, and no torsional deformation occurs.

[0069] Example 2 A high-strength heat treatment method for the tie rod material 30CrNiMo8 steel of an ORC turbine unit

[0070] Produce a pull rod with a diameter of Φ120mm before heat treatment. The heat treatment process of the pull rod includes normalizing treatment at high temperature, normalizing treatment on the critical zone side, quenching treatment and tempering treatment:

[0071] (1) Rough machine the 30CrNiMo8 steel pull rod. The rough machining size of the pull rod is 130mm, the thickness of the boss at one end of the pull rod is 20mm, and the diameter of the boss is 160mm;

[0072] (2) Select a hanging disc with an inner hole diameter of 150mm;

[0073] (3) Assemble the heat treatment tooling for the pull rod, which consists of a hanging shaft and a hanging disc. The hanging shaft passes through the central inner hole of the hanging disc and coincides with the axis of the hanging disc;

[0074] (4) Insert 4 pull rods into the inner hole of the hanging disc, and the bosses of the pull rods rest on the surface of the hanging disc;

[0075] (5) Hang the hook of the heat treatment equipment on the square hole of the hanging shaft of the heat treatment hoisting tool;

[0076] (6) Normalizing treatment at high temperature: The pull rod is loaded into the furnace at 210°C, heated to 400°C according to the power, then heated to 610°C at a rate of 60°C / h, held for 2h, then heated to 850°C at a rate of 50°C / h, held for 3h and then air-cooled. After taking out of the furnace, it is hung and placed on the normalizing rack, vertically placed;

[0077] (7) Normalizing treatment on the critical zone side: The pull rod after high-temperature normalizing treatment is loaded into the furnace at 240°C, heated to 400°C according to the power, then heated to 600°C at a rate of 70°C / h, held for 1h, then heated to 800°C at a rate of 70°C / h, held for 3h and then air-cooled. After taking out of the furnace, it is hung and placed on the normalizing rack, vertically placed;

[0078] (8) Quenching treatment: The pull rod after normalizing treatment on the critical zone side is loaded into the furnace at 180°C, heated to 400°C according to the power, then heated to 605°C at a rate of 75°C / h, held for 1h, then heated to 850°C at a rate of 60°C / h, held for 3h and then oil-cooled. After taking out of the oil, it is hung and vertically placed to drain the oil;

[0079] (9) Tempering treatment: The pull rod after quenching treatment is loaded into the furnace at 160°C, heated to 300°C according to the power, then heated to 550°C at a rate of 40°C / h, held for 5h and then air-cooled. After taking out of the furnace, it is hung and placed on the normalizing rack, vertically placed.

[0080] Mechanical properties after heat treatment: Rm: 1274Mpa; Rp0.2: 1120Mpa; A: 18%; Z: 62%; HBW: 383.

[0081] The bending deformation of the pull rod after heat treatment is 2.5mm, and no torsional deformation occurs.

[0082] Comparative Example 1

[0083] The drawbar lies horizontally on the heat treatment tray and then undergoes normalizing treatment at high temperature, normalizing treatment on the critical region side, quenching treatment, and tempering treatment.

[0084] (1) Normalizing treatment at high temperature: The drawbar is loaded into the furnace at 223°C, heated to 400°C according to the power, then heated to 600°C at a rate of 80°C / h, held for 1 h, then heated to 860°C at a rate of 60°C / h, held for 2 h, and then air-cooled. After being taken out of the furnace, it lies horizontally on the tray;

[0085] (2) Normalizing treatment on the critical region side: The drawbar after high-temperature normalizing treatment is loaded into the furnace at 180°C, heated to 400°C according to the power, then heated to 610°C at a rate of 90°C / h, held for 1 h, then heated to 810°C at a rate of 60°C / h, held for 2 h, and then air-cooled. After being taken out of the furnace, it lies horizontally on the tray;

[0086] (3) Quenching treatment: The drawbar after normalizing treatment on the critical region side is loaded into the furnace at 200°C, heated to 400°C according to the power, then heated to 600°C at a rate of 70°C / h, held for 1 h, then heated to 850°C at a rate of 50°C / h, held for 2 h, and then oil-cooled. After being taken out of the oil, it lies horizontally on the tray;

[0087] (4) Tempering treatment: The drawbar after quenching treatment is loaded into the furnace at 180°C, heated to 300°C according to the power, then heated to 560°C at a rate of 30°C / h, held for 4 h, and then air-cooled. After being taken out of the furnace, it lies horizontally on the tray.

[0088] The difference from Example 1 is that during heat treatment, the drawbar lies horizontally on the heat treatment tray and lies horizontally on the tray after being taken out of the furnace.

[0089] Mechanical properties after heat treatment:

[0090] Mechanical properties after heat treatment: Rm: 1231 Mpa; Rp0.2: 1079 Mpa; A: 21%; Z: 68%; HBW: 377.

[0091] The bending deformation of the drawbar after heat treatment is 6 mm, and local torsional deformation occurs.

[0092] Comparative Example 2

[0093] Produce a drawbar with a diameter of Φ90 mm before heat treatment. The heat treatment process of the drawbar includes rough machining before drawbar heat treatment, installation of a lifting tooling fixture, quenching treatment, and tempering treatment:

[0094] (1) Rough machine the 30CrNiMo8 steel drawbar. The rough machining dimensions of the drawbar are 100 mm, the thickness of the boss at one end of the drawbar is 20 mm, and the diameter of the boss is 160 mm;

[0095] (2) Select a suspension plate with an inner hole diameter of 150 mm;

[0096] (3) Assemble the heat treatment tooling for the tie rod, which consists of two parts: a suspension shaft and a suspension plate. The suspension shaft passes through the central inner hole of the suspension plate and coincides with the axis of the suspension plate;

[0097] (4) Insert 6 tie rods into the inner hole of the suspension plate, and the boss of the tie rod rests on the surface of the suspension plate;

[0098] (5) Hang the hook of the heat treatment equipment on the square hole of the suspension shaft of the heat treatment hoisting tool;

[0099] (6) Quenching treatment: Load the tie rod into the furnace, heat it up to 400 °C according to the power, then heat it up to 600 °C at a rate of 70 °C / h, hold for 1 h, then heat it up to 850 °C at a rate of 50 °C / h, hold for 2 h and then cool it in oil. After taking out of the oil, hang it and place it vertically to drain the oil;

[0100] (7) Tempering treatment: The tie rod after quenching treatment is loaded into the furnace at 180 °C, heated up to 300 °C according to the power, then heated up to 560 °C at a rate of 30 °C / h, held for 4 h and then air-cooled. After taking out of the furnace, hang it and place it on the normalizing rack, vertically.

[0101] The difference from Example 1 is that it does not undergo high-temperature normalizing and critical zone side normalizing treatments.

[0102] Mechanical properties after heat treatment:

[0103] Mechanical properties after heat treatment: Rm: 1080 Mpa; Rp0.2: 1010 Mpa; A: 17%; Z: 52%; HBW: 366.

[0104] The bending deformation of the tie rod after heat treatment is 1.5 mm, and no torsional deformation occurs.

[0105] It is easy for those skilled in the art to understand that, on the premise of no conflict, the above advantageous methods can be freely combined and superimposed. The above is only the preferred embodiment of the present application, and is not used to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above is only the preferred implementation manner of the present application. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present application, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present application.

Claims

1. A heat treatment method for the tie rod material 30CrNiMo8 steel of an ORC turbine unit, characterized in that, Including: 1) Design the heat treatment tooling for the pull rod Rough machine the pull rod made of 30CrNiMo8 steel, and leave a boss at one end of the pull rod; Design the heat treatment tooling for the pull rod according to the dimensions of the pull rod. The heat treatment tooling includes a hanging plate and a hanging shaft. The hanging plate is provided with a hanging hole. The diameter of the pull rod is smaller than the diameter of the hanging hole, and the diameter of the boss is larger than the diameter of the hanging hole; The hanging shaft is connected to the middle of the hanging plate, and the axes of the hanging shaft and the hanging plate coincide; 2) Assemble the pull rod and the heat treatment tooling. The pull rod is hoisted on the hanging hole through the boss at the end, and the hanging plate is connected to the heat treatment equipment through the hanging shaft; 3) High-temperature normalizing treatment, at 850 - 880 °C, with a holding time of ≥ 2 h; 4) Sub-critical zone side normalizing treatment, at 800 - 830 °C, with a holding time of ≥ 2 h; 5) Quenching treatment, at 850 - 870 °C, with a holding time of ≥ 2 h; 6) Tempering treatment, up to 530 - 600 °C, with a holding time of ≥ 4 h; Among them, the diameter of the boss is more than 10 mm larger than the diameter of the hanging hole, and the thickness of the boss is 20 - 25 mm; For the high-temperature normalizing treatment, when the temperature of the pull rod is ≤ 400 °C, it is heated at a rated power. After the temperature is > 400 °C, it is heated to 580 - 650 °C at a rate of ≤ 100 °C / h. After holding for 1 - 3 h, it is heated to 850 - 880 °C at a rate of ≤ 80 °C / h. After holding for ≥ 2 h, it is air-cooled; For the sub-critical zone side normalizing treatment, after the high-temperature normalizing treatment, when the temperature of the pull rod is ≤ 400 °C, it is heated at a rated power. After the temperature is > 400 °C, it is heated to 560 - 620 °C at a rate of ≤ 100 °C / h. After holding for 1 - 3 h, it is heated to 800 - 830 °C at a rate of ≤ 80 °C / h. After holding for ≥ 2 h, it is air-cooled; For the quenching treatment, after the sub-critical zone side normalizing treatment, when the temperature of the pull rod is ≤ 400 °C, it is heated at a rated power. After the temperature is > 400 °C, it is heated to 580 - 650 °C at a rate of ≤ 100 °C / h. After holding for 1 - 3 h, it is heated to 850 - 870 °C at a rate of ≤ 80 °C / h. After holding for ≥ 2 h, it is oil-cooled to ≤ 200 °C and then taken out of the oil; 2. The heat treatment method of the tie rod material 30CrNiMo8 steel for the ORC turbine unit as described in claim 1, characterized in that, The hanging plate is provided with a number of the hanging holes, and the minimum distance between the hanging holes is not less than 160 mm.

3. The heat treatment method of the 30CrNiMo8 steel for the tie rod of the ORC turbine unit as described in claim 1, characterized in that, For the tempering treatment, after the quenching treatment, when the temperature of the pull rod is ≤ 300 °C, it is heated at a rated power. After the temperature is > 300 °C, it is heated to 530 - 600 °C at a rate of ≤ 60 °C / h. After holding for ≥ 4 h, it is air-cooled.

4. The heat treatment method of the 30CrNiMo8 steel for the tie rod of the ORC turbine unit as described in claim 1, characterized in that, After the high-temperature normalizing treatment, hang the pull rod vertically. When the temperature of the pull rod is ≤ 400 °C, it is hot-loaded into the furnace for the sub-critical zone side normalizing treatment; after the sub-critical zone side normalizing treatment, hang the pull rod vertically. When the temperature of the pull rod is ≤ 400 °C, it is hot-loaded into the furnace for the quenching treatment; after the quenching treatment, hang the pull rod vertically. When the temperature of the pull rod is ≤ 300 °C, it is hot-loaded into the furnace for the tempering treatment; after the tempering treatment, hang the pull rod vertically.

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