A long rod bolt heat treatment process

Abstract

The application discloses a long rod bolt heat treatment process and relates to the technical field of metal heat treatment. The long rod bolt heat treatment process steps of the application successively comprise ultrasonic cleaning, primary salt quenching, secondary salt quenching and tempering. The molten salt solution for the primary salt quenching is magnesium borate, magnesium oxide grains are formed in the long rod bolt after the primary salt quenching, so that the grain boundaries of austenite are pinned, the growth of austenite grains is suppressed, and the formation of acicular ferrite is promoted. The molten salt solution for the secondary salt quenching is aluminum silicate. When the secondary salt quenching is performed, the aluminum silicate and the borate on the surface of the long rod bolt after the primary salt quenching are combined to form a dense ceramic layer. The long rod bolt prepared by the application has high toughness and good corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of metal heat treatment technology, specifically a heat treatment process for long bolts. Background Technology

[0002] Bolts are mechanical parts, cylindrical threaded fasteners that are fitted with nuts. They consist of a head and a shank (a cylinder with external threads), and require a nut to fasten two parts with through holes. Long shank bolts are a type of bolt frequently used in mining, metallurgy, highway, railway, water conservancy, and chemical industries, where crushers or grinding mills are commonly employed. These machines typically use long shank bolts, which have a relatively long and thin shank, while the head has a relatively short axial length. The bolt head is hexagonal or square-headed, requiring a hex wrench or square-head wrench to tighten the bolt to the nut.

[0003] However, it has the following disadvantages when used: because the environments of mining, metallurgy, highways, railways, water conservancy and chemical industries are often high temperature, high humidity and highly corrosive, long bolts are easily corroded in the environment, which greatly shortens the service life of long bolts and increases the cost of long bolts. Moreover, since the heads of commonly used bolts are hexagonal or square, a shoulder is formed at the connection between the bolt head and the threaded part. The stress is most concentrated at this shoulder. Under strong impact, the connection between the threaded part and the head of the bolt will fracture, further shortening the service life of the bolt.

[0004] Therefore, it is urgent to improve the heat treatment process for long bolts to make them more tough and have better corrosion resistance. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a heat treatment process for long bolts, comprising the following steps: ultrasonic cleaning, primary salt quenching, secondary salt quenching, and tempering.

[0006] Furthermore, the ultrasonic cleaning steps are as follows: Under normal temperature conditions, use an ultrasonic cleaner with an ultrasonic frequency of 30-40 kHz to ultrasonically clean the long rod bolt for 20-40 minutes.

[0007] Furthermore, the steps of the first salt quenching are as follows: Under the protective atmosphere of carbon monoxide, in the heating furnace of the fully automatic salt quenching equipment, the ultrasonically cleaned long rod bolt is heated to 860℃~880℃ and held for 70~90 minutes for austenitization treatment. Then it is put into the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 360~380℃ in the salt bath and held for 1~2 hours for isothermal quenching heat treatment.

[0008] Furthermore, the molten salt solution used for the first salt quenching is magnesium borate.

[0009] Furthermore, the secondary salt quenching steps are as follows: Under the protective atmosphere of carbon monoxide, in the heating furnace of the fully automatic salt quenching equipment, the long rod bolts that have undergone primary salt quenching are heated to 860℃~880℃ and held for 70~90 minutes to perform austenitizing treatment. Then, they are placed in the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 750℃~760℃ in the salt bath, and held for 4~8 hours for isothermal quenching heat treatment.

[0010] Furthermore, the molten salt solution used for the secondary salt quenching is aluminum silicate.

[0011] Furthermore, the tempering process is as follows: Under a protective atmosphere of carbon monoxide, the long bolts that have undergone secondary salt quenching are sent into a tempering furnace for heating at a temperature of 800℃~820℃ and held for 1~2 hours before being water-cooled.

[0012] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0013] The heat treatment process for long bolts provided by this invention includes ultrasonic cleaning, primary salt quenching, secondary salt quenching, and tempering; wherein the molten salt solution for primary salt quenching is magnesium borate, and the molten salt solution for secondary salt quenching is aluminum silicate.

[0014] First, ultrasonic cleaning is used on the long bolts. This not only removes residues from the surface of the long bolts but also cleans impurities from blind holes or thread gaps at the ends of high-strength bolts. The operation is simple, the cleaning effect is excellent, and the cleaning efficiency is high. During the first salt quenching, magnesium borate quickly enters the defect gaps of the long bolts, forming magnesium oxide grains that are dispersed throughout the long bolts. This pins the austenite grain boundaries, inhibits austenite grain growth, and promotes the formation of acicular ferrite, thereby enhancing the toughness of the long bolts. During the second salt quenching, aluminum silicate is introduced. The aluminum silicate combines with the boric acid on the surface of the long bolts after the first salt quenching to form a dense ceramic layer, which enhances the corrosion resistance of the long bolts. Detailed Implementation

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0016] To more clearly illustrate the method provided by the present invention, the following embodiments are provided in detail. The testing methods for various indicators of the long bolts obtained in the following embodiments are as follows:

[0017] Toughness: Long bolts of the same mass prepared in the example and comparative examples were tested on an INSTRON-450 impact testing machine. The impact energy was tested at a test temperature of 0°C to test the toughness.

[0018] Corrosion resistance: Long bolts prepared in the same mass as those in the examples and comparative examples were immersed in sodium hydroxide solution with pH 12 and nitric acid solution with pH 2 for 30 days each, and then removed to test the corrosion depth of the long bolts.

[0019] Example 1

[0020] A heat treatment process for long bolts includes the following steps: ultrasonic cleaning, primary salt quenching, secondary salt quenching, and tempering.

[0021] (1) Ultrasonic cleaning: Under normal temperature conditions, use a 30kHz ultrasonic cleaner to ultrasonically clean the long rod bolt for 20 minutes.

[0022] (2) First salt quenching: Under the protective atmosphere of carbon monoxide, in the heating furnace of the fully automatic salt quenching equipment, the ultrasonically cleaned long rod bolt is heated to 860°C and held for 70 minutes for austenitization treatment. Then it is put into the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 360°C in the salt bath for 1 hour for isothermal quenching heat treatment. The molten salt liquid of the first salt quenching is magnesium borate.

[0023] (3) Secondary salt quenching: Under the protective atmosphere of carbon monoxide, the long rod bolts that have been salt quenched once are heated to 860°C and held for 70 minutes in the heating furnace of the fully automatic salt quenching equipment for austenitization treatment. Then they are put into the salt bath of the salt bath furnace of the fully automatic salt quenching equipment and rapidly cooled to 750°C in the salt bath for 4 hours for isothermal quenching heat treatment. The molten salt liquid of the secondary salt quenching is aluminum silicate.

[0024] (4) Tempering: Under the protective atmosphere of carbon monoxide, the long bolts that have been salt-quenched twice are sent into the tempering furnace for heating at 800℃ and held for 1 hour before being water-cooled.

[0025] Example 2

[0026] A heat treatment process for long bolts includes the following steps: ultrasonic cleaning, primary salt quenching, secondary salt quenching, and tempering.

[0027] (1) Ultrasonic cleaning: Under normal temperature conditions, use a 35kHz ultrasonic cleaner to ultrasonically clean the long rod bolt for 30 minutes.

[0028] (2) First salt quenching: Under the protective atmosphere of carbon monoxide, in the heating furnace of the fully automatic salt quenching equipment, the ultrasonically cleaned long rod bolt is heated to 870°C and held for 80 minutes for austenitization treatment. Then it is put into the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 370°C in the salt bath for 1.5 hours for isothermal quenching heat treatment. The molten salt liquid of the first salt quenching is magnesium borate.

[0029] (3) Secondary salt quenching: Under the protective atmosphere of carbon monoxide, the long rod bolts that have been salt quenched once are heated to 870°C and held for 80 minutes in the heating furnace of the fully automatic salt quenching equipment for austenitization treatment. Then they are put into the salt bath of the salt bath furnace of the fully automatic salt quenching equipment and rapidly cooled to 755°C in the salt bath for 6 hours for isothermal quenching heat treatment. The molten salt liquid of the secondary salt quenching is aluminum silicate.

[0030] (4) Tempering: Under the protective atmosphere of carbon monoxide, the long bolts that have been salt-quenched twice are sent into the tempering furnace for heating at 810℃ and held for 1.5h before being water-cooled.

[0031] Example 3

[0032] A heat treatment process for long bolts includes the following steps: ultrasonic cleaning, primary salt quenching, secondary salt quenching, and tempering.

[0033] (1) Ultrasonic cleaning: Under normal temperature conditions, use a 40kHz ultrasonic cleaner to ultrasonically clean the long rod bolt for 40 minutes.

[0034] (2) First salt quenching: Under the protective atmosphere of carbon monoxide, in the heating furnace of the fully automatic salt quenching equipment, the ultrasonically cleaned long rod bolt is heated to 880°C and held for 90 minutes for austenitization treatment. Then it is put into the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 380°C in the salt bath for 2 hours for isothermal quenching heat treatment. The molten salt liquid of the first salt quenching is magnesium borate.

[0035] (3) Secondary salt quenching: Under the protective atmosphere of carbon monoxide, the long rod bolts that have been salt quenched once are heated to 880°C and held for 90 minutes in the heating furnace of the fully automatic salt quenching equipment for austenitization treatment. Then they are put into the salt bath of the salt bath furnace of the fully automatic salt quenching equipment and rapidly cooled to 760°C in the salt bath for 8 hours for isothermal quenching heat treatment. The molten salt liquid of the secondary salt quenching is aluminum silicate.

[0036] (4) Tempering: Under the protective atmosphere of carbon monoxide, the long bolts that have been salt-quenched twice are sent into the tempering furnace for heating at 820℃ and held for 2 hours before being water-cooled.

[0037] Comparative Example 1

[0038] A heat treatment process for long bolts includes the following steps: ultrasonic cleaning, primary salt quenching, secondary salt quenching, and tempering.

[0039] (1) Cleaning: Under normal temperature conditions, clean the long bolts three times with ethanol and deionized water in sequence, and then dry them at 50°C for 2 hours.

[0040] (2) First salt quenching: Under the protective atmosphere of carbon monoxide, the cleaned long rod bolts are heated to 870°C and held for 80 minutes in the heating furnace of the fully automatic salt quenching equipment for austenitization treatment. Then, they are put into the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 370°C in the salt bath for 1.5 hours for isothermal quenching heat treatment. The molten salt liquid of the first salt quenching is magnesium borate.

[0041] (3) Secondary salt quenching: Under the protective atmosphere of carbon monoxide, the long rod bolts that have been salt quenched once are heated to 870°C and held for 80 minutes in the heating furnace of the fully automatic salt quenching equipment for austenitization treatment. Then they are put into the salt bath of the salt bath furnace of the fully automatic salt quenching equipment and rapidly cooled to 755°C in the salt bath for 6 hours for isothermal quenching heat treatment. The molten salt liquid of the secondary salt quenching is aluminum silicate.

[0042] (4) Tempering: Under the protective atmosphere of carbon monoxide, the long bolts that have been salt-quenched twice are sent into the tempering furnace for heating at 810℃ and held for 1.5h before being water-cooled.

[0043] Comparative Example 2

[0044] A heat treatment process for long bolts includes the following steps: ultrasonic cleaning, primary salt quenching, secondary salt quenching, and tempering.

[0045] (1) Ultrasonic cleaning: Under normal temperature conditions, use a 35kHz ultrasonic cleaner to ultrasonically clean the long rod bolt for 30 minutes.

[0046] (2) First salt quenching: Under the protective atmosphere of carbon monoxide, in the heating furnace of the fully automatic salt quenching equipment, the ultrasonically cleaned long rod bolt is heated to 870°C and held for 80 minutes for austenitization treatment. Then it is put into the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 755°C in the salt bath for 6 hours for isothermal quenching heat treatment. The molten salt liquid of the first salt quenching is aluminum silicate.

[0047] (3) Tempering: Under the protective atmosphere of carbon monoxide, the long bolts that have been salt-quenched twice are sent into the tempering furnace for heating at 810℃ and held for 1.5h before being water-cooled.

[0048] Comparative Example 3

[0049] A heat treatment process for long bolts includes the following steps: ultrasonic cleaning, primary salt quenching, secondary salt quenching, and tempering.

[0050] (1) Ultrasonic cleaning: Under normal temperature conditions, use a 35kHz ultrasonic cleaner to ultrasonically clean the long rod bolt for 30 minutes.

[0051] (2) First salt quenching: Under the protective atmosphere of carbon monoxide, in the heating furnace of the fully automatic salt quenching equipment, the ultrasonically cleaned long rod bolt is heated to 870°C and held for 80 minutes for austenitization treatment. Then it is put into the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 370°C in the salt bath for 1.5 hours for isothermal quenching heat treatment. The molten salt liquid of the first salt quenching is magnesium borate.

[0052] (4) Tempering: Under the protective atmosphere of carbon monoxide, the long bolts that have been salt-quenched once are sent into the tempering furnace for heating at 810℃ and held for 1.5h before being water-cooled.

[0053] Comparative Example 4

[0054] A heat treatment process for long bolts includes the following steps: ultrasonic cleaning, primary salt quenching, secondary salt quenching, and tempering.

[0055] (1) Ultrasonic cleaning: Under normal temperature conditions, use a 35kHz ultrasonic cleaner to ultrasonically clean the long rod bolt for 30 minutes.

[0056] (2) First quenching: Under the protective atmosphere of carbon monoxide, in the heating furnace of the fully automatic salt quenching equipment, the ultrasonically cleaned long rod bolt is heated to 870°C and held for 80 minutes for austenitization treatment. Then it is put into the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 370°C in the salt bath for 1.5 hours for isothermal quenching heat treatment. The quenching medium for the first quenching is oil.

[0057] (3) Secondary salt quenching: Under the protective atmosphere of carbon monoxide, the long rod bolts that have been salt quenched once are heated to 870°C and held for 80 minutes in the heating furnace of the fully automatic salt quenching equipment for austenitization treatment. Then they are put into the salt bath of the salt bath furnace of the fully automatic salt quenching equipment and rapidly cooled to 755°C in the salt bath for 6 hours for isothermal quenching heat treatment. The molten salt liquid of the secondary salt quenching is aluminum silicate.

[0058] (4) Tempering: Under the protective atmosphere of carbon monoxide, the long bolts that have been salt-quenched twice are sent into the tempering furnace for heating at 810℃ and held for 1.5h before being water-cooled.

[0059] Comparative Example 5

[0060] A heat treatment process for long bolts includes the following steps: ultrasonic cleaning, primary salt quenching, secondary salt quenching, and tempering.

[0061] (1) Ultrasonic cleaning: Under normal temperature conditions, use a 35kHz ultrasonic cleaner to ultrasonically clean the long rod bolt for 30 minutes.

[0062] (2) First salt quenching: Under the protective atmosphere of carbon monoxide, in the heating furnace of the fully automatic salt quenching equipment, the ultrasonically cleaned long rod bolt is heated to 870°C and held for 80 minutes for austenitization treatment. Then it is put into the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 370°C in the salt bath for 1.5 hours for isothermal quenching heat treatment. The molten salt liquid of the first salt quenching is magnesium borate.

[0063] (3) Secondary quenching: Under the protective atmosphere of carbon monoxide, the long rod bolts that have been salt-quenched once are heated to 870°C and held for 80 minutes in the heating furnace of the fully automatic salt quenching equipment for austenitization treatment. Then they are put into the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 755°C in the salt bath for 6 hours for isothermal quenching heat treatment. The quenching medium for the secondary quenching is oil.

[0064] (4) Tempering: Under the protective atmosphere of carbon monoxide, the long bolts that have been salt-quenched twice are sent into the tempering furnace for heating at 810℃ and held for 1.5h before being water-cooled.

[0065] Example of effect

[0066] Table 1 below presents the analysis results of the toughness and corrosion resistance of the long bolts prepared using Examples 1 to 3 and Comparative Examples 1 to 4 of the present invention.

[0067] Table 1

[0068]

[0069] Table 1 shows that the long bolts prepared in Examples 1, 2, and 3 have good toughness and corrosion resistance. A comparison of the experimental data from Examples 1, 2, and 3 and Comparative Example 1 shows that the long bolts prepared using ultrasonic cleaning have good toughness. The experimental data from Examples 1, 2, and 3 and Comparative Examples 2 and 4 show that the long bolts prepared using magnesium borate with a single salt quenching have good toughness and corrosion resistance. The experimental data from Examples 1, 2, and 3 and Comparative Examples 3 and 5 show that the long bolts prepared using aluminum silicate with a double salt quenching have good corrosion resistance.

[0070] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A heat treatment process for long bolts, characterized in that, The process includes the following steps: ultrasonic cleaning, primary salt quenching, secondary salt quenching, and tempering. At room temperature, use an ultrasonic cleaner with a frequency of 30-40 kHz to ultrasonically clean the long rod bolts for 20-40 minutes. Under a protective atmosphere of carbon monoxide, in the heating furnace of a fully automatic salt quenching equipment, the ultrasonically cleaned long rod bolts are heated to 860℃~880℃ and held for 70~90 minutes for austenitization treatment. Then they are put into the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 360~380℃ in the salt bath and held for 1~2 hours for isothermal quenching heat treatment. The molten salt solution used in the first salt quenching is magnesium borate; Under the protective atmosphere of carbon monoxide, in the heating furnace of the fully automatic salt quenching equipment, the long rod bolts that have been salt quenched once are heated to 860℃~880℃ and held for 70~90 minutes to perform austenitization treatment. Then they are put into the salt bath of the fully automatic salt quenching equipment and rapidly cooled to 750℃~760℃ in the salt bath and held for 4~8 hours for isothermal quenching heat treatment. The molten salt solution used in the secondary salt quenching is aluminum silicate; Under a protective atmosphere of carbon monoxide, the long bolts that have undergone secondary salt quenching are sent into a tempering furnace for heating at a temperature of 800℃~820℃ and held for 1~2 hours before being water cooled.

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