阅读说明：本技术 一种薄型精密紧固件微渗碳工艺 (Micro carburizing process for thin precision fastener ) 是由 蔡俊信 于 2020-07-27 设计创作，主要内容包括：本发明提供了一种薄型精密紧固件微渗碳工艺,属于金属处理技术领域。在渗碳处理过程中使用液化石油气分解气作为保护气,通过控制淬火炉内温度为875-885℃,碳浓度为0.65-0.75％,接触时间为18-22min,渗碳处理后的紧固件材料经油浴60～80℃条件冷却,得到渗碳紧固件材料,在实施过程中通过对温度、碳浓度以及时间进行合理控制,在保证机械性能较高的前提下保证薄型精密紧固件不会断裂,降低了成本,缩短了时间,本发明要求保护的微渗碳工艺主要针对0.5mm头厚以下薄型精密紧固件的渗碳处理,可以有效避免精密紧固件头部断裂现象的发生。(The invention provides a micro carburizing process for a thin precision fastener, and belongs to the technical field of metal treatment. In the carburizing treatment process, liquefied petroleum gas decomposition gas is used as protective gas, the temperature in a quenching furnace is controlled to be 875-plus 885 ℃, the carbon concentration is 0.65-0.75%, the contact time is 18-22min, the fastener material after the carburizing treatment is cooled by an oil bath at the temperature of 60-80 ℃ to obtain the carburizing fastener material, and the temperature, the carbon concentration and the time are reasonably controlled in the implementation process, so that the thin precision fastener is ensured not to be broken on the premise of ensuring higher mechanical performance, the cost is reduced, and the time is shortened.)

1. A thin precision fastener micro carburizing technology is characterized in that: the method comprises the following steps:

step 1): putting the fastener material into an aqueous solution containing a water-soluble degreasing agent for ultrasonic degreasing, then putting the degreased fastener material into cleaning equipment, adding water for cleaning to remove surface degreasing residues, carrying out net pulling frequency of 15 min/time, and washing again to obtain a cleaned fastener material;

step 2): placing the fastener material cleaned in the step 1) in a dehydrating machine for dehydrating to obtain a dry fastener material;

step 3): laying the fastener material cleaned in the step 2) on a mesh belt, wherein the laying thickness is 0.5-1cm, and obtaining the fastener material to be carburized;

step 4): introducing liquefied petroleum gas into the furnace, controlling the temperature to be 1040 ℃, decomposing the liquefied petroleum gas by coal contact, raising the temperature in the quenching furnace to 875-885 ℃, introducing the decomposed liquefied petroleum gas into the continuous quenching furnace, contacting the liquefied petroleum gas with the fastener material to be carburized obtained in the step 3), and cooling the fastener material subjected to carburization by an oil bath to obtain a quenched carburized fastener material;

step 5): putting the quenched fastener material obtained in the step 4) into an aqueous solution containing a water-soluble degreasing agent for ultrasonic degreasing, then putting the degreased fastener material into cleaning equipment, adding water for cleaning to remove surface degreasing residues, pulling the net for 20 minutes/time, and washing again to obtain a clean carburized fastener material;

step 6): putting the clean carburized fastener material obtained in the step 5) into a dehydrating machine, dehydrating and heating to obtain a dehydrated fastener;

step 7): and placing the dehydrated fastener into a baking tray for tempering treatment to obtain a carburized fastener finished product.

2. The micro carburizing process for the thin precision fastener according to claim 1, wherein: the temperature in the quenching furnace in the step 4) is 875 ℃ and 885 ℃.

3. The micro carburizing process for the thin precision fastener according to claim 2, wherein: the temperature in the quenching furnace in the step 4) is 880 ℃.

4. The micro carburizing process for the thin precision fastener according to claim 1, wherein: the carbon concentration in the carburizing process in the step 4) is 0.65-0.75%.

5. The micro carburizing process for the thin precision fastener according to claim 4, wherein: the carbon concentration in the carburizing process in the step 4) is 0.70%.

6. The micro carburizing process for the thin precision fastener according to claim 1, wherein: the carburizing time in the step 4) is 18-22 min.

7. The micro carburizing process for the thin precision fastener according to claim 1, wherein: the carburizing time in the step 4) is 21 min.

8. The micro carburizing process for the thin precision fastener according to claim 1, wherein: the tempering temperature in the step 7) is 390 ℃ and 395 ℃ for 60 min.

9. The micro carburizing process for the thin precision fastener according to claim 1, wherein: the catalyst in the step 4) is a nickel catalyst.

10. The micro carburizing process for the thin precision fastener according to claim 9, wherein: the nickel catalyst is a two-stage conversion catalyst which takes nickel as an active component and alumina as a main carrier.

Technical Field

The invention belongs to the technical field of metal treatment, and particularly relates to a micro carburizing process for a thin precision fastener.

Background

With the rapid development of the fastener industry and the increasingly fierce market competition, and the continuous improvement of the requirements of customers on the fastener product quality such as light weight, environmental protection, long service life and the like, the treatment process needs to be continuously adapted to the market requirements and continuously develops. Carburization, a case hardening process, has a long history and is the most widely used heat treatment process in machine manufacturing, aircraft engine or bearing gear industries.

The aim of carburizing is to obtain a carburized layer with high hardness and wear resistance on the surface of a low-carbon steel or low-carbon alloy steel part, and then the carburized layer is subjected to a series of processes such as quenching, tempering and the like, and the core of the part has high toughness. The carburizing process features that the low carbon steel or low carbon alloy steel part is heated and maintained in medium containing active carbon atoms for permeating into the surface of the part and under the action of carbon concentration gradient, the carbon atoms are diffused from surface to inside to form the diffusion layer and carburized layer of required thickness and carbon concentration. General carburizing processes are classified into gas carburizing, liquid carburizing, and solid carburizing according to the state of a carburizing medium.

The carburization can only improve the carbon content of the surface of the part, so that the part has high hardness and wear resistance, and the part with high strength and toughness in the center part of the part needs to be quenched and tempered at low temperature after carburization, so that the surface layer of the part is a high-carbon tempered martensite structure, and the center part is a low-carbon tempered martensite structure, thereby achieving the purpose of strengthening the part by carburization. A series of heat treatments such as carburizing, quenching, and low-temperature tempering must be properly completed. Most carburized parts are important parts, require high mechanical property and reliability and are commonly used for gears or pistons, so the carburized steel has high requirements on the metallurgical quality, chemical components and the like of steel, and most carburized steel belongs to high-quality steel and high-grade high-quality steel.

Carburizing and other chemical heat treatments also comprise 3 basic processes of decomposition, adsorption and diffusion, and the decomposition of a carburizing medium generates activated carbon atoms; after being absorbed by the surface of the steel part, the activated carbon atoms are dissolved in surface austenite, so that the carbon content in the austenite is increased; the increase of the carbon content on the surface and the carbon content in the core are concentration difference, the carbon on the surface is diffused inwards, the diffusion speed of the carbon in the steel is mainly dependent on the temperature, and the difference of the internal and external concentrations of the infiltrated element in the workpiece is related to the content of the alloy element in the steel.

In order to improve the mechanical property and hardenability of steel and other heat treatment properties, various alloy elements are usually added into the steel, such as chromium, manganese, nickel, molybdenum and boron, so as to improve the hardenability, the quenching strength after carburization is realized by utilizing parts, namely, the surface layer and the core of the quenched and carburized parts can obtain martensite structures, and the parts have good mechanical properties, namely, the surfaces have high hardness, wear resistance and contact fatigue strength, and the cores have high obdurability.

The carburizing process dates back to 2000 in china, and in order to produce sharp and stronger weapons, craftsmen in the age of cold weapons have generally used a solid carburizing process for optimizing the weapons produced. Liquid and gas carburization occurred in the 20 th century and was widely used, with vacuum carburization and ion carburization occurring by the 70 s.

Chinese patent application 201510274624.7 discloses a screw carburizing and quenching process, which comprises the following steps: 1) putting the screws into a heat treatment furnace, heating to 875 ℃ and keeping the carbon potential at 0.1 percent for 30 minutes; 2) raising the carbon potential in the heat treatment furnace to 1.05%, introducing ammonia gas with the flow rate of 1.2-2L/min, keeping the temperature of the furnace at 875 ℃, and keeping the temperature for 350 minutes; 3) reducing the carbon potential in the heat treatment furnace to 0.7%, controlling the flow of ammonia gas to be 1.0-1.5L/min, keeping the furnace temperature at 875 ℃, controlling the furnace temperature fluctuation range within +/-0.2 ℃, and keeping the temperature for 200 minutes; 4) and quenching and cooling the screw after the step 3). The invention can ensure that the surface hardness HV0.3 of the screw made of 20CrMo is less than or equal to 430, the core hardness HV0.3 is more than or equal to 342, the depth of the carbonitriding layer of the screw is 0.7-1.0mm, and the carbide in the metallographic structure is 1-3 grade; meanwhile, the process continuously performs carburization and quenching, so that the process flow is shortened, the costs of transportation, heat treatment and the like are reduced, the production efficiency is higher, but the carbon concentration in the heat treatment furnace is higher, the heat preservation time is longer, and ammonia gas is introduced in the carburization process, so that the head fracture of the precision fastener with the thin head thickness of less than 0.5mm is easily caused due to carbonitriding.

For another example, the Chinese patent application 201510125673.4 discloses a heat treatment carburizing process for carburizing steel, which sequentially adopts pre-carburizing (at 800-. The invention adds a special pre-carburizing process and cooperates with the circulating carburization to form a large amount of fine carbide particles in the surface carburized layer, effectively refines the grain size from 7 to 9, and greatly improves the wear resistance of the surface on the basis of meeting the performance of a core part.

Therefore, it is highly desirable to develop a micro carburizing technology capable of protecting a precision fastener with a thin head thickness of 0.5mm or less and preventing head breakage of a precision fastener with a thin head thickness of 0.5mm or less.

Disclosure of Invention

In order to overcome the defects and shortcomings of the prior art, the invention aims to provide the micro carburizing process for the thin precision fastener.

In order to achieve the purpose, the invention provides the following technical scheme: a thin precision fastener micro carburizing process comprises the following steps:

step 1): putting the fastener material into an aqueous solution containing a water-soluble degreasing agent for ultrasonic degreasing, then putting the degreased fastener material into cleaning equipment, adding water for cleaning to remove surface degreasing residues, carrying out net pulling frequency of 15 min/time, and washing again to obtain a cleaned fastener material;

step 2): placing the fastener material cleaned in the step 1) in a dehydrating machine for dehydrating to obtain a dry fastener material;

step 3): laying the fastener material cleaned in the step 2) on a mesh belt, wherein the laying thickness is 0.5-1cm, and obtaining the fastener material to be carburized;

step 4): introducing liquefied petroleum gas into the furnace, controlling the temperature to be 1040 ℃, decomposing the liquefied petroleum gas by coal contact, raising the temperature in the quenching furnace to 875-885 ℃, introducing the decomposed liquefied petroleum gas into the continuous quenching furnace, contacting the liquefied petroleum gas with the fastener material to be carburized obtained in the step 3), and cooling the fastener material subjected to carburization by an oil bath to obtain a quenched carburized fastener material;

step 5): putting the quenched fastener material obtained in the step 4) into an aqueous solution containing a water-soluble degreasing agent for ultrasonic degreasing, then putting the degreased fastener material into cleaning equipment, adding water for cleaning to remove surface degreasing residues, pulling the net for 20 minutes/time, and washing again to obtain a clean carburized fastener material;

step 6): putting the clean carburized fastener material obtained in the step 5) into a dehydrating machine, dehydrating and heating to obtain a dehydrated fastener;

step 7): and placing the dehydrated fastener into a baking tray for tempering treatment to obtain a carburized fastener finished product.

The temperature of the aqueous solution in the step 1) is 55-65 ℃, and the ultrasonic cleaning time is 3-5 min.

The water is added for cleaning for 1-3min in the step 1);

the dehydration time in the step 2) is 3-5 min;

the temperature in the quenching furnace in the step 4) is 875-885 ℃; preferably 876-884 ℃; and then 877-882 ℃ is selected, and still more 878-881 ℃ is selected; still more preferably 880 ℃.

The carbon concentration in the carburizing process in the step 4) is 0.65-0.75%; preferably 0.66-0.74%; more preferably 0.67-0.73%; further preferably 0.68 to 0.72%; still more preferably 0.69 to 0.71%; still more preferably 0.70%.

The carburizing time in the step 4) is 18-22 min; preferably 19-21 min; preferably 20-21 min; more preferably 21 min.

The oil bath temperature in the step 4) is 60-80 ℃.

The temperature of the aqueous solution in the step 5) is 55-65 ℃, and the ultrasonic cleaning time is 5-8 min; the washing time by adding water is 2-5 min.

The dehydration temperature in the step 6) is 60-80 ℃, and the time is 5-10 min;

the tempering temperature in the step 7) is 390 ℃ and 395 ℃ for 60 min.

The material of the fastener is 1018 or 1022 low carbon steel.

The catalyst in the step 4) is a nickel catalyst, and is a two-stage conversion catalyst taking nickel as an active component and alumina as a main carrier;

the net pulling frequency is the number of times that the fastener material is turned in the net.

The invention discloses a thin precision fastener micro carburizing process, which specifically comprises the following steps:

step 1): putting the fastener material into an aqueous solution containing a water-soluble degreasing agent at 55-65 ℃ for ultrasonic degreasing for 3-5min, then putting the degreased fastener material into cleaning equipment, adding water for cleaning for 1-3min to remove surface degreasing residues, carrying out net pulling at a frequency of 15 min/time, and washing again to obtain a cleaned fastener material;

step 2): placing the fastener material cleaned in the step 1) in a dehydrating machine for dehydrating for 3-5min to obtain a dry fastener material;

step 3): laying the fastener material cleaned in the step 2) on a mesh belt, wherein the laying thickness is 0.5-1cm, and obtaining the fastener material to be carburized;

step 4): introducing liquefied petroleum gas into the furnace, controlling the temperature to be 1040 ℃, decomposing the liquefied petroleum gas by coal contact, raising the temperature in the quenching furnace to 875-885 ℃, introducing the decomposed liquefied petroleum gas into the continuous quenching furnace, contacting the liquefied petroleum gas with the fastener material to be carburized obtained in the step 3), wherein the carbon concentration is 0.65-0.75%, the contact time is 18-25min, and cooling the fastener material after carburization at the temperature of 60-80 ℃ by using an oil bath to obtain the carburized fastener material after quenching;

step 5): putting the quenched fastener material obtained in the step 4) into an aqueous solution containing a water-soluble degreasing agent at 55-65 ℃ for ultrasonic degreasing for 5-8min, then putting the degreased fastener material into cleaning equipment, adding water for cleaning for 2-5min to remove surface degreasing residues, carrying out net pulling frequency for 20 min/time, and washing again to obtain a clean carburized fastener material;

step 6): putting the clean carburized fastener material obtained in the step 5) into a dehydrating machine, dehydrating for 5-10min, and heating to 60-80 ℃ to obtain a dehydrated fastener;

step 7): and (3) placing the dehydrated fastener into a baking tray for tempering treatment at 390-.

Compared with the prior art, the invention has the beneficial effects that:

1) in the implementation process, the temperature, the carbon concentration and the time are reasonably controlled, so that the thin precision fastener is prevented from being broken on the premise of ensuring the mechanical properties (the hardness of carburizing steel and the breaking torque), the cost is reduced, and the time is shortened;

2) the micro carburizing process claimed by the invention mainly aims at the carburizing treatment of the thin precision fastener with the head thickness of less than 0.5mm, and controls the surface hardness of the fastener to be between 390 and 420HV, while the presently disclosed more carburizing technologies require that the surface hardness of the fastener is more than or equal to 450HV, and the hardness easily causes the breakage of the thin precision fastener with the head thickness of less than 0.5mm, thereby influencing the use;

3) the micro-carburizing process disclosed in the prior art usually adopts nitrogen as a protective gas, while the carburizing process claimed in the invention adopts liquefied petroleum gas decomposition gas as the protective gas.

Detailed Description

The present invention will be further described with reference to the following examples.

Example 1 micro carburizing process for thin precision fastener

The method specifically comprises the following steps:

step 1): putting the fastener material into an aqueous solution containing a water-soluble degreasing agent at 55 ℃ for ultrasonic degreasing for 5min, then putting the degreased fastener material into cleaning equipment, adding water for cleaning for 3min to remove surface degreasing residues, carrying out net pulling at a frequency of 15 min/time, and washing again to obtain a cleaned fastener material;

step 2): placing the fastener material cleaned in the step 1) in a dehydrating machine for dehydrating for 5min to obtain a dry fastener material;

step 3): laying the fastener material cleaned in the step 2) on a mesh belt, wherein the laying thickness is 0.5cm, and obtaining the fastener material to be carburized;

step 4): introducing liquefied petroleum gas into the furnace, controlling the temperature to be 1040 ℃, decomposing the liquefied petroleum gas by coal contact, raising the temperature in the quenching furnace to 875 ℃, introducing the decomposed liquefied petroleum gas into the continuous quenching furnace, contacting the liquefied petroleum gas with the fastener material to be carburized obtained in the step 3), wherein the carbon concentration is 0.65%, the contact time is 22min, and cooling the fastener material after carburization at the temperature of 60 ℃ in an oil bath to obtain a carburized fastener material;

step 5): putting the quenched fastener material obtained in the step 4) into an aqueous solution containing a water-soluble degreasing agent at 55 ℃ for ultrasonic degreasing for 8min, then putting the degreased fastener material into a cleaning device, adding water for cleaning for 5min to remove surface degreasing residues, carrying out net pulling frequency for 20 min/time, and washing again to obtain a clean carburized fastener material;

step 6): putting the clean carburized fastener material obtained in the step 5) into a dehydrating machine, dehydrating for 5min, and heating to 80 ℃ to obtain a dehydrated fastener;

step 7): and (3) placing the dehydrated fastener into a baking tray for tempering treatment at 390 ℃ for 60min to obtain a finished carburized fastener.

The catalyst in the step 4) is a two-stage conversion catalyst which takes nickel as an active component and alumina as a main carrier.

Example 2 micro carburizing process for thin precision fastener

The method specifically comprises the following steps:

step 1): putting the fastener material into a 65 ℃ water solution containing a water-soluble degreasing agent for ultrasonic degreasing for 3min, then putting the degreased fastener material into cleaning equipment, adding water for cleaning for 1min to remove surface degreasing residues, carrying out net pulling frequency of 15 min/time, and carrying out water cleaning again to obtain a cleaned fastener material;

step 2): placing the fastener material cleaned in the step 1) in a dehydrating machine for dehydrating for 5min to obtain a dry fastener material;

step 3): laying the fastener material cleaned in the step 2) on a mesh belt, wherein the laying thickness is 0.5-1cm, and obtaining the fastener material to be carburized;

step 4): introducing liquefied petroleum gas into the furnace, controlling the temperature to be 1040 ℃, decomposing the liquefied petroleum gas by coal contact, raising the temperature in the quenching furnace to 885 ℃, introducing the decomposed liquefied petroleum gas into the continuous quenching furnace, contacting the liquefied petroleum gas with the fastener material to be carburized obtained in the step 3), wherein the carbon concentration is 0.75%, the contact time is 18min, and cooling the fastener material after carburization at the temperature of 80 ℃ in an oil bath to obtain a carburized fastener material;

step 5): putting the quenched fastener material obtained in the step 4) into a 65 ℃ water solution containing a water-soluble degreasing agent for ultrasonic degreasing for 5min, then putting the degreased fastener material into a cleaning device, adding water for cleaning for 2min to remove surface degreasing residues, carrying out net pulling frequency for 20 min/time, and washing again to obtain a clean carburized fastener material;

step 6): putting the clean carburized fastener material obtained in the step 5) into a dehydrating machine, dehydrating for 10min, and heating to 80 ℃ to obtain a dehydrated fastener;

step 7): and (3) placing the dehydrated fastener into a baking tray for tempering treatment at 395 ℃ for 60min to obtain a carburized fastener finished product.

The catalyst in the step 4) is a two-stage conversion catalyst which takes nickel as an active component and alumina as a main carrier.

Example 3 micro carburizing process for thin precision fastener

The method specifically comprises the following steps:

step 1): putting the fastener material into an aqueous solution containing a water-soluble degreasing agent at 60 ℃ for ultrasonic degreasing for 4min, then putting the degreased fastener material into cleaning equipment, adding water for cleaning for 2min to remove surface degreasing residues, carrying out net pulling at a frequency of 15 min/time, and carrying out water cleaning again to obtain a cleaned fastener material;

step 2): placing the fastener material cleaned in the step 1) in a dehydrating machine for dehydrating for 4min to obtain a dry fastener material;

step 3): laying the fastener material cleaned in the step 2) on a mesh belt, wherein the laying thickness is 0.8cm, and obtaining the fastener material to be carburized;

step 4): introducing liquefied petroleum gas into a furnace, changing the temperature into 1040 ℃, decomposing the liquefied petroleum gas by contacting with coal, raising the temperature in a quenching furnace to 880 ℃, introducing the decomposed liquefied petroleum gas into continuous quenching and contacting with the fastener material to be carburized obtained in the step 3), wherein the carbon concentration is 0.70%, the contact time is 21min, and cooling the fastener material after carburization at 70 ℃ in an oil bath to obtain a carburized fastener material;

step 5): putting the quenched fastener material obtained in the step 4) into an aqueous solution containing a water-soluble degreasing agent at 60 ℃ for ultrasonic degreasing for 6min, then putting the degreased fastener material into a cleaning device, adding water for cleaning for 4min to remove surface degreasing residues, carrying out net pulling frequency for 20 min/time, and washing again to obtain a clean carburized fastener material;

step 6): putting the clean carburized fastener material obtained in the step 5) into a dehydrating machine, dehydrating for 8min, and heating to 70 ℃ to obtain a dehydrated fastener;

step 7): and (3) placing the dehydrated fastener into a baking tray for tempering treatment at 392 ℃ for 60min to obtain a finished carburized fastener.

The catalyst in the step 4) is a two-stage conversion catalyst which takes nickel as an active component and alumina as a main carrier.

Comparative example

Finished carburized fasteners were prepared using methods conventional in the art and then tested for performance

The specific operation method comprises the following steps:

step 1): putting the fastener material into a 65 ℃ water solution containing a water-soluble degreasing agent for ultrasonic degreasing for 3min, then putting the degreased fastener material into cleaning equipment, adding water for cleaning for 1min to remove surface degreasing residues, carrying out net pulling frequency of 15 min/time, and carrying out water cleaning again to obtain a cleaned fastener material;

step 2): placing the fastener material cleaned in the step 1) in a dehydrating machine for dehydrating for 5min to obtain a dry fastener material;

step 3): laying the fastener material cleaned in the step 2) on a mesh belt, wherein the laying thickness is 2cm, and obtaining the fastener material to be carburized;

step 4): introducing liquefied petroleum gas into the furnace, controlling the temperature to be 1000 ℃, decomposing the liquefied petroleum gas by coal contact, raising the temperature in the quenching furnace to 900 ℃, introducing the decomposed liquefied petroleum gas into the quenching continuous heating furnace, contacting the liquefied petroleum gas with the fastener material to be subjected to heat treatment obtained in the step 4), wherein the carbon concentration is 0.5%, the contact time is 35min, and cooling the fastener material subjected to heat treatment by an oil bath at the temperature of 80 ℃ to obtain the quenched fastener material;

step 5): putting the quenched fastener material obtained in the step 4) into a 65 ℃ water solution containing a water-soluble degreasing agent for ultrasonic degreasing for 5min, then putting the degreased fastener material into a cleaning device, adding water for cleaning for 2min to remove surface degreasing residues, carrying out net pulling frequency for 20 min/time, and washing again to obtain a clean carburized fastener material;

step 6): putting the clean fastener material obtained in the step 5) into a dehydrating machine, dehydrating for 10min, and heating to 80 ℃ to obtain a dehydrated fastener;

step 7): and (4) placing the dehydrated fastener into a baking tray for tempering treatment at the temperature of 410 ℃ for 90min to obtain a finished fastener product.

The catalyst in the step 4) is a two-stage conversion catalyst which takes nickel as an active component and alumina as a main carrier.

Effect test

200 finished carburized fasteners were prepared according to the methods disclosed in examples 1 to 4 and comparative examples, and 50 finished carburized fasteners were randomly selected for hardness and breaking torque tests, and averaged to obtain the test results shown in tables 1 and 2 below.

1. Hardness test

The detection method comprises the following steps: the test was carried out according to the method disclosed in ISO Standard 898-1:2009, the test results are given in Table 1 below.

TABLE 1 hardness test results for fasteners made in accordance with examples 1-3 and comparative examples

According to the detection data in the table 1, it can be seen that when the micro carburizing process disclosed in the present invention is used for preparing a carburized fastener finished product, the surface hardness of the thin precision fastener with the outer diameter of M1.2 and the head thickness of less than 0.5mm can be controlled between 390-420HV, and the core hardness can be controlled between 335-355HV, so that the use requirement can be met, and the situation that the head of the precision fastener is broken can not be caused, while in the comparative example, the surface hardness of the thin precision fastener obtained by changing the process parameters out of the protection range required by the present invention can only reach 327HV, the core hardness is 315HV, which is significantly lower than the present invention, and the difference between the surface hardness and the core hardness is not large, so that the obtained product can not meet the industry requirement.

2. Destructive torsion test

The detection method comprises the following steps: the measurements were carried out according to the method disclosed in ISO Standard 898-1:1992 and are shown in Table 2 below.

TABLE 2 destructive torque results for fasteners made with 1-3 and comparative examples

Examples of the invention	Breaking torsion
		Example 1	1.47kgf.cm
Example 2	1.49kgf.cm
		Example 3	1.52kgf.cm
Comparative example	1.18kgf.cm

According to the detection data in the table 2, the micro carburizing process provided by the invention can be used for preparing carburized fastener finished products, the breaking torsion of the thin precision fastener with the outer diameter of M1.2 and the head thickness of less than 0.5mm can be improved to 1.47kgf.cm, the head fracture phenomenon cannot occur, the use requirement is completely met, the breaking torsion of the thin precision fastener obtained by changing the process parameters in the comparative example out of the protection range required by the invention can only reach 1.18kgf.cm, and is obviously lower than that of the invention, and the obtained product cannot meet the industry requirement.

However, the above description is only a preferred embodiment of the present invention, and should not be taken as limiting the scope of the invention, which is intended to cover all the modifications and equivalents of the claims and the specification. In addition, the abstract and the title are provided to assist the patent document searching and are not intended to limit the scope of the invention.