Isothermal salt bath heat treatment production method for improving structure uniformity of bearing steel wire rod

Abstract

The invention provides an isothermal salt bath heat treatment production method for improving the structure uniformity of a bearing steel wire rod, which comprises the following steps of: performing shot blasting, flaw detection and coping on a continuous casting blank, rolling, adopting a one-heating forming process, controlling the heating temperature to be 1100-1250 DEG C, keeping the temperature for 1-3 hours, starting rolling, controlling the process temperature and the spinning temperature to be 780-870 DEG C, and after spinning, performing heat preservation for 1-3 hours. And salt bath controlled cooling is adopted, the salt bath temperature is 535-600 DEG C, the wire rod enters a heat preservation cover to be slowly cooled after being taken out of the salt bath, and the wire rod is rolled and air-cooled to the room temperature after being taken out of the cover. The molten nitrate is adopted as a cooling medium, the cooling speed of a high-temperature area is higher, especially for large-specification wires, an excellent quenching structure can be obtained, the cooling uniformity and stability are guaranteed, the temperature of the molten salt can be adjusted according to different specifications of the bearing steel wires to control the cooling speed, and therefore the cooling speed of the bearing steel wires is adjusted. And cooling is performed in an immersion manner, so that the cleaning uniformity of the wire rod is obviously superior to that of an air-cooled wire rod.

Description

Technical Field

[0001] The invention relates to the technical field of metal wire manufacturing, and in particular to an isothermal salt bath heat treatment production method for improving the uniformity of the structure of a bearing steel wire. Background Art

[0002] Bearings are an important part of mechanical equipment, and their performance directly affects the running stability and life of the machine. The quality of bearing steel wire has an important influence on the performance of bearings, among which the uniformity of the structure is an important factor affecting the quality of bearing steel wire. The carbide network is produced during the cooling process after hot rolling. As the temperature decreases, the solubility of carbon in austenite decreases, and the supersaturated carbon precipitates in the form of carbides along the austenite grain boundaries. The traditional cooling method has the problem of insufficient cooling capacity. The slower the cooling speed, the more carbides precipitate, the more uneven the distribution of carbon elements, and the more serious the network carbides. Traditional heat treatment methods often find it difficult to achieve ideal uniformity of the structure. Therefore, it is of great significance to study an effective isothermal salt bath heat treatment method to improve the uniformity of the structure of bearing steel wire.

[0003] Chinese patent CN109402356A: Controlled cooling and rolling method for controlling the carbide network of bearing steel wire rod. This patent uses EDC water bath isothermal quenching cooling. The cooling speed is slow compared to the salt bath, which can easily cause serious precipitation of network carbides.

[0004] Chinese patent CN113337693A: A heat treatment method for reducing the level of network carbides in large-size bearing steel. This patent uses quenching first and then isothermal spheroidizing annealing. The spheroidizing annealing production capacity is difficult to match with the rolling capacity, which affects production, and the insulation period is long and the production cost is high. Summary of the invention

[0005] The invention provides an isothermal salt bath heat treatment production method for improving the uniformity of the bearing steel wire structure, so as to solve the problems of slow cooling speed and serious precipitation of network carbides in the existing bearing steel heat treatment method.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: an isothermal salt bath heat treatment production method for improving the uniformity of the bearing steel wire structure, the method comprising:

[0007] The continuous casting billet is rolled after shot blasting, flaw detection and grinding. The one-fire material forming process is adopted. The heating temperature is 1000-1250℃. After keeping warm for 1-3 hours, rolling begins. The process temperature and wire drawing temperature are controlled at 780-870℃. After wire drawing, salt bath is used for controlled cooling. The salt bath temperature is 535-600℃. After leaving the salt bath, the wire enters the insulation cover for slow cooling. After leaving the cover, the wire is rolled and air-cooled to room temperature.

[0008] Preferably, the rolling speed is controlled to be 10-80 m / s.

[0009] Preferably, the salt bath cooling time is controlled to be 3-6 minutes.

[0010] Preferably, the wire enters the heat preservation cover and is slowly cooled to 460-500° C. before exiting the cover.

[0011] Preferably, the method is suitable for the production of high carbon chromium bearing steel wire rods with a diameter of Φ8mm-26mm.

[0012] Preferably, the chemical composition of the bearing steel wire to which the method is applicable is, by mass percentage: C: 0.95-1.05wt.%; Si: 0.15-0.35wt.%; Mn: 0.25-0.45wt.%; Cr: 1.40-1.65wt.%; Mo: ≤0.10wt.%; Ni: ≤0.25wt.%; Cu: ≤0.25wt.%; P: ≤0.025wt.%; S: ≤0.020wt.%; Ca: ≤0.0010wt.%; O: ≤0.0012wt.%; Ti: ≤0.0050wt.%; Al: ≤0.050wt.%; As: ≤0.04wt.%; Pb: ≤0.002wt.%; As+Sn+Sb: ≤0.075wt.%; the rest is Fe and unavoidable impurities.

[0013] Compared with the prior art, the advantages and positive effects of the present invention are:

[0014] 1. Using molten nitrate as the cooling medium is environmentally friendly and pollution-free. It has a higher heat capacity and lower temperature sensitivity. The cooling speed in the high temperature zone is faster. Especially for large-size wires, excellent quenching structure can be obtained, ensuring the uniformity and stability of cooling.

[0015] 2. According to the different specifications of the bearing steel wire, adjust the temperature of the molten salt to control the cooling rate, so as to adjust the cooling rate of the bearing steel wire.

[0016] 3. The cooling method of immersion is adopted to avoid the disadvantage of uneven cooling of overlapping points and non-overlapping points in the traditional air cooling method, so that the uniformity of the wire rod is significantly better than that of air-cooled wire rod.

[0017] 4. Molten salt has a high heat capacity and a good temperature control system, which ensures that the temperature fluctuations of the cooling medium and the wire surface are small, thereby ensuring the temperature uniformity and stability of the wire heat treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the grades of network carbides and ribbon carbides of the product produced by the method of Example 1;

[0019] Figure 2A schematic diagram of the grades of network carbides and ribbon carbides of products produced by the method of Example 2;

[0020] Figure 3 This is a schematic diagram of the grades of network carbides and ribbon carbides in the product produced by the method of Example 3. DETAILED DESCRIPTION

[0021] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Example 1: To produce Φ15mm high carbon chromium bearing steel, the continuous casting billet is subjected to shot blasting, flaw detection and grinding before rolling, and a one-fire material forming process is adopted. The heating temperature is 1150-1250°C, and the rolling is started after keeping warm for 2h. The rolling speed is 25m / s, and the process temperature and the spinning temperature are controlled at 800-870°C. After spinning, molten nitrate is used for controlled cooling, the salt bath temperature is 580-590°C, and the salt bath cooling time is 4-5min. After exiting the salt bath, the billet enters the insulation cover and is slowly cooled to 470-480°C. After exiting the cover, the billet is rolled and air-cooled to room temperature.

[0023] The chemical composition of the product is shown in Table 1.

[0024] The carbide test results of the product are shown in Table 2.

[0025] Example 2: Production of Φ13mm high carbon chromium bearing steel test, continuous casting billet after shot blasting, flaw detection, grinding and then rolling, using a one-fire material process, heating temperature 1150 ~ 1250 ℃, insulation 2h after rolling, rolling speed 30m / s, process temperature and wire laying temperature controlled at 780-830 ℃, after laying wire using molten nitrate controlled cooling, salt bath temperature 570-600 ℃, salt bath cooling time 5-6min. After the salt tank into the insulation cover slowly cooled to 460-480 ℃, out of the cover after the coil air cooling to room temperature.

[0026] The chemical composition of the product is shown in Table 1.

[0027] The carbide test results of the product are shown in Table 2.

[0028] Example 3: Production of Φ10mm high carbon chromium bearing steel test, the continuous casting billet is rolled after shot blasting, flaw detection, grinding, using a one-fire material forming process, heating temperature 1150 ~ 1250 ℃, insulation 1.5h after rolling, rolling speed 50m / s, process temperature and spinning temperature controlled at 780-830 ℃, after spinning controlled cooling using molten nitrate, salt bath temperature 550-580 ℃, salt bath cooling time 4-5min, after the salt bath into the insulation cover slowly cooled to 480-500 ℃, out of the cover after the roll air cooling to room temperature.

[0029] The chemical composition of the product is shown in Table 1.

[0030] The carbide test results of the product are shown in Table 2.

[0031] Table 1

[0032]

[0033] Table 2

[0034]

[0035] It can be seen from Table 2 that the carbide precipitation of the high carbon chromium bearing steel produced by the method of Examples 1-3 is greatly reduced, the formed network carbides are all level 1.5, and the formed band carbides are mostly level 1.0.

[0036] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. An isothermal salt bath heat treatment production method for improving the uniformity of the bearing steel wire structure, characterized in that: The method is: The continuous casting billet is rolled after shot blasting, flaw detection and grinding. The one-fire material forming process is adopted. The heating temperature is 1000-1250℃. After keeping warm for 1-3 hours, rolling begins. The process temperature and wire drawing temperature are controlled at 780-870℃. After wire drawing, salt bath is used for controlled cooling. The salt bath temperature is 535-600℃. After leaving the salt bath, the wire enters the insulation cover for slow cooling. After leaving the cover, the wire is rolled and air-cooled to room temperature.

2. The isothermal salt bath heat treatment production method for improving the uniformity of the bearing steel wire structure according to claim 1, characterized in that: The rolling speed is controlled to be 10-80 m / s.

3. The isothermal salt bath heat treatment production method for improving the uniformity of the bearing steel wire structure according to claim 1, characterized in that: Control the salt bath cooling time to 3-6 minutes.

4. The isothermal salt bath heat treatment production method for improving the uniformity of the bearing steel wire structure according to claim 1, characterized in that: The wire enters the heat preservation cover and is slowly cooled to 460-500℃ before exiting the cover.

5. The isothermal salt bath heat treatment production method for improving the uniformity of the bearing steel wire structure according to claim 1, characterized in that: The method is suitable for the production of Φ8mm-26mm high carbon chromium bearing steel wires.

6. The isothermal salt bath heat treatment production method for improving the uniformity of the bearing steel wire structure according to claim 1, characterized in that: The chemical composition of the bearing steel wire applicable to the method is, by mass percentage: C: 0.95-1.05wt.%; Si: 0.15-0.35wt.%; Mn: 0.25-0.45wt.%; Cr: 1.40-1.65wt.%; Mo: ≤0.10wt.%; Ni: ≤0.25wt.%; Cu: ≤0.25wt.%; P: ≤0.025wt.%; S: ≤0.020wt.%; Ca: ≤0.0010wt.%; O: ≤0.0012wt.%; Ti: ≤0.0050wt.%; Al: ≤0.050wt.%; As: ≤0.04wt.%; Pb: ≤0.002wt.%; As+Sn+Sb: ≤0.075wt.%; The rest is Fe and inevitable impurities.

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