Free-cutting high-temperature low-expansion alloy for electronic vacuum device and manufacturing method of free-cutting high-temperature low-expansion alloy

Abstract

The invention discloses a free-cutting high-temperature low-expansion alloy for an electronic vacuum device and a manufacturing method. The high-temperature low-expansion alloy comprises the following chemical components in percentage by mass: less than or equal to 0.05% of C, less than or equal to 0.15% of Si, less than or equal to 0.25% of Mn, less than or equal to 0.02% of P, 32-35% of Ni, 6-9% of Co, 0.10-0.25% of S and the balance of Fe and inevitable impurities. According to the invention, improvement is carried out on the basis of the traditional invar alloy, and the Curie point is improved by reducing Ni and adding Co, so that the low-expansion performance of a high-temperature region is obtained, and meanwhile, martensite phase transformation does not occur in a low-temperature region; by adding S, the cutting performance of the alloy is improved, and finally the high-temperature low-expansion alloy easy to cut is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of manufacturing high-temperature low-expansion alloys for electronic vacuum devices, and particularly to an easily machinable high-temperature low-expansion alloy for electronic vacuum devices and a manufacturing method thereof. Background Art

[0002] An electronic vacuum device is a device that utilizes the emission, transmission, and control of electrons in a vacuum environment to achieve signal amplification, conversion, processing, and display. It mainly includes space charge control electron tubes, microwave electron tubes, cathode ray tubes, vacuum ion devices, vacuum phototubes, X-ray tubes, and fluorescent and glow displays, etc. Due to the advantages of high frequency, high power, high efficiency, high reliability, and long life, electronic vacuum devices are one of the indispensable basic components in national defense technology and various basic and emerging industries of the national economy.

[0003] The working environment of components in a certain electronic vacuum device is as follows: During use, starting from room temperature or low temperature (the lowest is -50°C), it is gradually heated (the highest is 300°C). During the heating process, the device undergoes dimensional changes due to expansion, resulting in unstable performance; if the expansion is too large, the device cannot be used.

[0004] Existing main low-expansion alloys, such as Invar, Super Invar, and Stainless Invar, etc., have relatively low Curie points. When the use temperature reaches 300°C, they lose their low-expansion characteristics. Through systematic research on Fe-Ni-Co ternary alloys, comparing the composition range with the corresponding Curie point diagram positions, an improved high-temperature low-expansion alloy based on 36% Ni-Fe Invar alloy was trial-produced, and its technical indicators are as follows: α 20-300℃ ≤2.0*10 -6 / °C, and no martensitic transformation occurs at -50°C; however, due to its high Ni content, it has high toughness, and the machinability is soft and sticky. There are problems such as large cutting force, high cutting temperature, and severe tool wear during the processing, ultimately resulting in excessive part deformation and low product qualification rate; therefore, it is urgent to solve the problems of tool sticking and poor product surface finish during the processing of this alloy.

[0005] After long-term development, the addition of Pb, S, etc. can enhance the machinability. Although Pb has stable chemical properties and a low melting point, during the cutting process, due to the action of cutting heat and stress, it can melt and precipitate to play a lubricating role on the contact surface, which is most beneficial to improving the cutting performance of steel. However, Pb will cause serious harm to the human body and the surrounding environment during smelting production and belongs to a product that must be phased out. The S series is the mainstream of current free-cutting steels, accounting for more than 90%; this series mainly plays a role in splitting the continuity of the steel matrix by forming MnS inclusions.

[0006] After a search of the prior art, no relevant technology regarding high-temperature low-expansion alloys and their easy machinability has been found; therefore, it is urgent to develop an easy-to-machine high-temperature low-expansion alloy. Summary of the Invention

[0007] Aiming at the defects existing in the prior art, the object of the present invention is to provide an easy-to-machine high-temperature low-expansion alloy for electronic vacuum devices and a manufacturing method thereof. Based on the traditional Invar alloy, the Curie point is increased by reducing Ni and adding Co, so as to obtain low-expansion performance in the high-temperature region, and no martensitic transformation occurs in the low-temperature region; the machinability of the alloy is improved by adding S, and finally an easy-to-machine high-temperature low-expansion alloy is obtained.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] The first aspect of the present invention provides an easy-to-machine high-temperature low-expansion alloy for electronic vacuum devices. The easy-to-machine high-temperature low-expansion alloy for electronic vacuum devices is characterized in that it comprises the following chemical components by mass percentage: C≤0.05%, Si≤0.15%, Mn≤0.25%, P≤0.02%, Ni: 32-35%, Co: 6-9%, S: 0.10-0.25%, and the balance is Fe and inevitable impurities.

[0010] Preferably, in the easy-to-machine high-temperature low-expansion alloy for electronic vacuum devices, C≤0.02%, Si≤0.10%, Ni: 32.5-34.5%, Co: 7-8%, S: 0.15-0.18%.

[0011] Preferably, the expansion coefficient α of the easy-to-machine high-temperature low-expansion alloy for electronic vacuum devices 200-300℃ ≤2.0*10 -6 / °C, and there is no martensitic transformation at -50°C.

[0012] The second aspect of the present invention provides a manufacturing method of an easy-to-machine high-temperature low-expansion alloy for electronic vacuum devices as described in the first aspect of the present invention, comprising the following steps:

[0013] S1, vacuum induction melting. After raw materials are proportioned according to the composition of the easy-to-machine high-temperature low-expansion alloy for electronic vacuum devices and added into the furnace, the vacuum is pumped to a vacuum degree ≤2.0 Pa, and then the raw materials are melted. After complete melting, the power is reduced for holding and refining, and an ingot is obtained after pouring out the steel.

[0014] S2, hot working. The ingot is forged and bloomed, and then hot rolled to obtain a rolled bar.

[0015] S3, Annealing heat treatment, heating the rolled bar to 830°C - 850°C, quenching in water after heat preservation, and then continuing to hold at 300°C - 320°C, and obtaining a free-cutting high-temperature low-expansion alloy for electronic vacuum devices after furnace cooling.

[0016] Preferably, in the step S1, the power during the melting of the raw materials is 200 - 250 kw, and after the raw materials are completely melted, the power is reduced to 120 - 150 kw for heat preservation refining for 20 - 30 minutes.

[0017] Preferably, in the step S1, the tapping temperature is 1560 ± 10°C; the ingot mold is demolded and air-cooled after the cold time is greater than 60 minutes.

[0018] Preferably, in the step S2, during the forging and cogging process, the ingot is heated to 1150 - 1200°C and then forged, and the final forging temperature ≥ 850°C.

[0019] Preferably, in the step S2, during the hot rolling process, the forged billet obtained after forging is heated to 1150 - 1200°C in a continuous furnace and then rolled, and the final rolling temperature ≥ 800°C.

[0020] Preferably, in the step S3, during the annealing heat treatment process, the heat preservation time for heating and continuous heating is 1h - 1.5h.

[0021] The principles of the composition design of the free-cutting high-temperature low-expansion alloy for electronic vacuum devices of the present invention are as follows:

[0022] C: Exists in the alloy solid solution in the form of interstitial atoms and carbides, which will have an adverse effect on the expansion performance; however, during the production process of the alloy, C is an inevitable impurity, and during smelting in a vacuum atmosphere, C can play a role in deoxidizing O. Therefore, C is controlled ≤ 0.05%, preferably, the C content ≤ 0.02%.

[0023] Si: Adding to the alloy plays a good deoxidizing role, but at the same time will increase the expansion coefficient of the material. Under the condition of ensuring good deoxidation of the molten steel, the Si content in the alloy is reduced as much as possible. Therefore, Si is controlled ≤ 0.15%, preferably, the Si content ≤ 0.10%.

[0024] Mn: The addition of Mn is mainly to improve the hot working performance of the alloy, form MnS in combination with S to improve the cutting performance of the alloy, and can also play a role in deoxidizing O; however, when its content is too high, the expansion coefficient of the alloy will increase. Therefore, it is desired that the Mn content be controlled below 0.25%.

[0025] P: It is a harmful element and is preferably as low as possible, but controlling it too low will lead to an increase in manufacturing cost. Therefore, the control range of P is: not greater than 0.02%.

[0026] Ni: It is an essential element to ensure that the alloy has a single austenite and a low coefficient of expansion. Too high or too low Ni content will increase the coefficient of expansion. Therefore, the Ni content in the alloy is controlled at 32-35%, preferably 32.5-34.5%.

[0027] Co: Co has a greater Invar anomaly effect than Ni. Appropriate addition of Co can achieve high strength and low expansion of the alloy. However, the cost of Co is high and it is not suitable to add too much. Therefore, the Co content in the alloy is 6-9%, preferably controlled at 7-8%.

[0028] S: In steel, it forms MnS inclusions with Mn. MnS is relatively soft and easy to deform and fracture. MnS inclusions disrupt the continuity of the steel matrix, and stress concentration during cutting is likely to cause material cracking. Under the action of a certain cutting heat and force, it can play a lubricating role between the tool, chip and machined surface. In addition, MnS can also wrap harmful hard particles, reducing tool wear, which is very beneficial to improving the cutting performance of steel. Therefore, the S content is controlled at 0.10-0.25%, preferably controlled at 0.15%-0.18%.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. The free-cutting high-temperature low-expansion alloy for electronic vacuum devices and its manufacturing method of the present invention reduce the high-temperature expansion performance of the alloy by controlling Ni and Co, and improve the cutting performance of the alloy by adding S. The high-temperature low-expansion alloy produced by this technology has the comprehensive characteristics of high-temperature low-expansion, no martensitic transformation at low temperature, excellent cutting performance and environmental protection, and is particularly suitable for making components for electronic vacuum.

[0031] 2. The performance indexes of the free-cutting high-temperature low-expansion alloy for electronic vacuum devices prepared by the present invention are as follows: α 200-300℃ ≤2.0*10 -6 / ℃, there is no martensitic transformation at -50℃, and the cutting performance is improved by more than 1.5 times compared with similar alloys (the cutting performance is detected by the time required to drill a 10mm deep hole). Specific Embodiments

[0032] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form.

[0033] Invar alloy originated in 1896. Guillaume in France discovered that the α 20-100℃ =0.877*10 -6 / °C, this alloy has an extremely low expansion coefficient, which completely does not conform to the normal thermal expansion law, being an abnormal thermal expansion phenomenon, called Invar alloy; subsequently, other alloys with low expansion coefficients have been developed successively. Representative ones are Fe-Ni-Co series super Invar alloy and Fe-Co-Cr series stainless Invar alloy. These alloys are low-expansion alloys with both high strength and high hardness. The present invention is an improvement based on the traditional Invar alloy. By reducing Ni and adding Co, the Curie point is increased, thereby obtaining low-expansion performance in the high-temperature region, and no martensitic transformation occurs in the low-temperature region; in addition, the cutting performance is improved by adding S.

[0034] The free-cutting high-temperature low-expansion alloy for electronic vacuum devices provided by the present invention comprises the following chemical components by mass percentage: C≤0.05%, Si≤0.15%, Mn≤0.25%, P≤0.02%, Ni: 32-35%, Co: 6-9%, S: 0.10-0.25%, and the balance is Fe and unavoidable impurities.

[0035] In a preferred embodiment, the contents of C, Si, Ni, Co and S in the free-cutting high-temperature low-expansion alloy for electronic vacuum devices are further limited, C≤0.02%, Si≤0.10%, Ni: 32.5-34.5%, Co: 7-8%, S: 0.10-0.20%.

[0036] The expansion coefficient α of the above-mentioned free-cutting high-temperature low-expansion alloy for electronic vacuum devices 200-300℃ ≤2.0×10 -6 / °C, there is no martensitic transformation at -50°C, and it has good machinability (its cutting performance is more than 1.5 times higher than that of similar alloys).

[0037] The manufacturing method of the above-mentioned free-cutting high-temperature low-expansion alloy for electronic vacuum devices adopts vacuum induction melting → hot working (forging and hot rolling) → annealing heat treatment, and specifically comprises the following steps:

[0038] S1, vacuum induction melting, after proportioning the raw materials according to the composition of the free-cutting high-temperature low-expansion alloy for electronic vacuum devices and adding them into the furnace, evacuating to a vacuum degree ≤2.0 Pa and then melting the raw materials, reducing the power for heat preservation and refining after full melting, and obtaining an ingot after casting and tapping.

[0039] Specifically, the alloy is smelted by vacuum induction melting. First, according to the ingredient ratio of the free-cutting high-temperature low-expansion alloy for electronic vacuum devices, all raw materials are rust-removed and baked. Then, the prepared raw materials are added to the furnace, and the vacuum is pumped to a vacuum degree ≤ 2 Pa, and then melted at a high power (200 - 250 kw). After all the raw materials are completely melted, the power is reduced to 120 - 150 kw, and heat preservation refining is carried out for 20 - 30 minutes to remove harmful impurities, gases and non-metallic inclusions to the greatest extent. Then, the steel is poured out to obtain an ingot, where the tapping temperature is 1560 ± 10 °C, and the ingot mold is cooled for more than 60 minutes and then demolded and air-cooled.

[0040] S2, hot working: The ingot is forged and bloomed, and then hot-rolled to obtain a rolled bar.

[0041] Specifically, the hot working of the alloy is divided into forging and hot rolling.

[0042] Forging: The ingot is bloomed by forging. The ingot is heated to 1150 - 1200 °C and then forged, and the final forging temperature ≥ 850 °C. After forging, the ingot obtains a forged blank. The forged blank can be a square blank (such as a square blank with a size of 120 mm). Then, the above forged blank is ground and peeled to remove surface defects.

[0043] Hot rolling: The forged blank obtained by forging is heated to 1150 - 1200 °C in a continuous furnace and then rolled to obtain a rolled bar (such as a round bar with a diameter of 30 mm), where the final rolling temperature ≥ 800 °C.

[0044] S3, annealing heat treatment: The rolled bar is heated to 830 °C - 850 °C, heat-preserved for 1 h - 1.5 h, and water-quenched; then continue to heat-preserve at a heat-preservation temperature of 300 °C - 320 °C for 1 h - 1.5 h, and the free-cutting high-temperature low-expansion alloy for electronic vacuum devices is obtained after furnace cooling. The heat-preservation temperature should not be too high. If the heat-preservation temperature is too high, the alloy grains will be too coarse, affecting the machining performance.

[0045] For the free-cutting high-temperature low-expansion alloy for electronic vacuum devices obtained through the above process, its various performance indicators are as follows: α 200-300℃ ≤ 2.0 * 10 -6 / °C, there is no martensite phase transformation at -50 °C, and the cutting performance is about 2 times higher than that of similar alloys.

[0046] The following further illustrates the free-cutting high-temperature low-expansion alloy for electronic vacuum devices and its manufacturing method of the present invention with specific examples;

[0047] Example

[0048] Five furnaces of free-cutting high-temperature low-expansion alloy for electronic vacuum devices are prepared by using the manufacturing method of the present invention, and its composition is shown in Table 1. The specific manufacturing process is as follows:

[0049] (1) Vacuum induction melting: According to the ingredient ratio of raw materials shown in Table 1, all raw materials are rust-removed and baked, and then the prepared raw materials are added to the furnace. After evacuating to a vacuum degree ≤ 2 Pa, it is melted at high power (200 - 250 kw). After all the raw materials are completely melted, the power is reduced to 120 - 150 kw, and it is held for refining for 20 - 30 minutes to remove harmful impurities, gases and non-metallic inclusions to the maximum extent. Then, the molten steel is poured to obtain an ingot. The tapping temperature is 1560 ± 10 °C, and the ingot mold is cooled for more than 60 minutes before demolding and air-cooling.

[0050] (2) Hot working is divided into forging and hot rolling. The heating temperature of the ingot is 1150 - 1200 °C, and the final forging temperature: ≥ 850 °C. It is forged into a square billet of 120 mm, and the above square billet is ground and peeled to remove surface defects. The square billet obtained by forging is heated to 1150 - 1200 °C in a continuous furnace, and then rolled into a round bar with a diameter of 30 mm. The final rolling temperature ≥ 800 °C.

[0051] (3) Annealing heat treatment. The heat treatment process is: heating temperature 830 °C - 850 °C, holding time 1 h - 1.5 h, water quenching. Then continue to hold for 1 h at a heating temperature of 300 °C - 320 °C and cool with the furnace to obtain an easy-cutting high-temperature low-expansion alloy for electronic vacuum devices.

[0052] Comparative example

[0053] For Comparative Example 1 and Comparative Example 2, the ingredients shown in Table 1 are adopted, the S content is controlled below 0.01 wt%, and the remaining ingredients are the same as those required in the examples. Then, the high-temperature low-expansion alloy hot-rolled bars are manufactured according to the method in the examples of the present invention.

[0054] Table 1 Chemical composition of the alloy (wt%)

[0055]

[0056] Table 2 Properties of the alloy

[0057]

[0058] The physical properties and processing properties of the alloys in the examples and comparative examples are detected. When detecting the cutting performance, a Ф5 mm drill bit is used, the thrust is 40 kg, the rotation speed is 1000 rpm, and the time required to drill a 10 mm hole depth is detected to judge the cutting performance of the alloy. The specific results are shown in Table 2.

[0059] Combined with Table 1 and Table 2, it can be seen that the expansion coefficients (including high temperature and low temperature), Curie temperature T of the alloys in the examples and comparative examples cThe differences are not significant; in addition, they are all γ-phase structures even after being placed at -50°C for half an hour, and no martensitic transformation occurs. However, there are obvious differences in the cutting performance between the examples and the comparative examples. The time required to drill a 10-mm deep hole in the free-cutting high-temperature low-expansion alloy manufactured in the examples is 6 - 10 s, while the time required to drill a 10-mm deep hole in the alloy in the comparative examples is 15 - 17 s, which is more than 1.5 times that of the examples. Thus, it can be seen that by adding S, the cutting performance of the alloy in the examples of the present invention is improved, and the cutting performance is more than 1.5 times higher than that of the alloy of the same kind without adding S.

[0060] In summary, the free-cutting high-temperature low-expansion alloy for electronic vacuum devices produced according to the alloy composition and manufacturing process specified in the present invention is easy to cut. At the same time, its high-temperature low-expansion performance is also excellent, and there is no martensitic transformation at low temperatures (-50°C).

[0061] It should be noted that the above examples are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. An easily machinable high-temperature low-expansion alloy for electronic vacuum devices, characterized in that, It includes the following chemical components by mass percentage: C ≤ 0.05%, Si ≤ 0.15%, Mn ≤ 0.25%, P ≤ 0.02%, Ni: 32 - 35%, Co: 6 - 9%, S: 0.10 - 0.25%, and the balance is Fe and inevitable impurities.

2. The easily machinable high-temperature low-expansion alloy for electronic vacuum devices according to claim 1, characterized in that, In the free-cutting high-temperature low-expansion alloy for electron vacuum devices, C ≤ 0.02%, Si ≤ 0.10%, Ni: 32.5 - 34.5%, Co: 7 - 8%, S: 0.10 - 0.20%.

3. The easily machinable high-temperature low-expansion alloy for electronic vacuum devices according to claim 1, characterized in that, The coefficient of thermal expansion α of the free-cutting high-temperature low-expansion alloy for electronic vacuum devices 200-300℃ ≤2.0×10 -6 / °C, and there is no martensitic transformation at -50°C.

4. A manufacturing method of the easily machinable high-temperature low-expansion alloy for electronic vacuum devices according to any one of claims 1 to 3, characterized in that, It includes the following steps: S1, Vacuum induction melting. After proportioning the raw materials according to the composition of the free-cutting high-temperature low-expansion alloy for electron vacuum devices, add them into the furnace. Evacuate to a vacuum degree ≤ 2.0 Pa and then melt the raw materials. After complete melting, reduce the power for holding and refining, and obtain an ingot after pouring and tapping. S2, Hot working. Forge and bloom the ingot, and then perform hot rolling to obtain a rolled bar. S3, Annealing heat treatment. Heat the rolled bar to 830 °C - 850 °C, hold for a certain time and then water quench. Then continue to hold at 300 °C - 320 °C, and obtain the free-cutting high-temperature low-expansion alloy for electron vacuum devices after furnace cooling.

5. The manufacturing method of the easily machinable high-temperature low-expansion alloy for electronic vacuum devices according to claim 4, characterized in that, In the step S1, the power during raw material melting is 200 - 250 kw, and after complete melting of the raw materials, the power is reduced to 120 - 150 kw for holding and refining for 20 - 30 minutes.

6. The manufacturing method of the easily machinable high-temperature low-expansion alloy for electronic vacuum devices according to claim 4, characterized in that, In the step S1, the tapping temperature is 1560 ± 10 °C; the ingot mold is cooled for more than 60 minutes and then demolded for air cooling.

7. The manufacturing method of the easily machinable high-temperature low-expansion alloy for electronic vacuum devices according to claim 4, characterized in that, In the step S2, during the forging and blooming process, heat the ingot to 1150 - 1200 °C and then forge, and the final forging temperature ≥ 850 °C.

8. The manufacturing method of the easily machinable high-temperature low-expansion alloy for electronic vacuum devices according to claim 4, characterized in that, In the step S2, during the hot rolling process, heat the forged billet to 1150 - 1200 °C in a continuous furnace and then roll, and the final rolling temperature ≥ 800 °C.

9. The manufacturing method of the easily machinable high-temperature low-expansion alloy for electronic vacuum devices according to claim 4, characterized in that, In the step S3, during the annealing heat treatment process, the holding time for heating and continuous heating is 1 h - 1.5 h.

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