Controlled cooling process for improving network carbide of wire rod

Abstract

The invention provides a controlled cooling process for improving network carbide of a wire rod. The controlled cooling process comprises the following steps that a wire rod is subjected to finish rolling, spinning, cooling and heat preservation; the spinning temperature ranges from 790 DEG C to 850 DEG C. According to the method, the spinning temperature after finish rolling is controlled, a large number of carbides are prevented from being separated out along the grain boundary, a few and thin carbide network is obtained in a rolled structure, and therefore the content of network carbides is reduced.

Description

Technical Field

[0001] The present application relates to the field of steel technology, and in particular to a controlled cooling process for improving wire mesh carbides. Background Art

[0002] GCr15 bearing steel is a kind of high carbon chromium bearing steel with relatively low alloy content, good performance and the most widely used. After proper quenching and tempering process, the finished product has high and uniform hardness, good wear resistance and high contact fatigue performance.

[0003] GCr15 wire is mainly used to manufacture balls or rollers. The working environment of the finished rolling element is harsh: high temperature, high pressure, and high fatigue cycle. Therefore, there are extremely high requirements for its uniformity of hardness, wear resistance, and contact fatigue performance.

[0004] In the process of GCr15 wire rolling, it is extremely important to control the appropriate metallographic structure of the finished product, and the control of network carbides is particularly important. The existence of network carbides will seriously affect its hardness uniformity and contact fatigue strength, increase the brittleness of the material, and greatly shorten its service life. Therefore, GCr15 wire has strict requirements on network carbides. Summary of the invention

[0005] The present application is made in view of the above problems, and its purpose is to provide a controlled cooling process for improving the network carbide of wire rods, wherein the content of network carbide in the wire rods produced by the controlled cooling process is low.

[0006] The present application discloses a controlled cooling process for improving wire mesh carbide, comprising the following steps:

[0007] Finish rolling, spinning, cooling and heat preservation of wire rod;

[0008] The spinning temperature is 790°C to 850°C.

[0009] According to one of the technical solutions of the controlled cooling process of the present application, at least the following beneficial effects are achieved:

[0010] Network carbides are excess secondary carbides that precipitate in a network-like distribution along the austenite grain boundaries in hypereutectoid steel. They are related to the chemical composition and degree of segregation of the steel.

[0011] The present application controls the spinning temperature after finishing rolling to prevent a large amount of carbides from precipitating along the grain boundaries, thereby obtaining a relatively small and thin carbide network in the rolled structure, thereby reducing the content of network carbides.

[0012] According to some embodiments of the present application, the finish rolling temperature is 860°C to 950°C.

[0013] According to some embodiments of the present application, the controlled cooling process further comprises rolling;

[0014] The temperature of the rolling is 1080°C to 1180°C.

[0015] According to some embodiments of the present application, the cooling rate is 4°C / s to 15°C / s.

[0016] According to some embodiments of the present application, the cooling rate is 5°C / s to 6°C / s.

[0017] The present application further reduces the precipitation of carbide networks by increasing the cooling rate.

[0018] According to some embodiments of the present application, the insulation temperature is 600°C to 690°C.

[0019] According to some embodiments of the present application, air cooling is used in the cooling process;

[0020] The control requirements for the fan and air volume during the air cooling process are as follows:

[0021] The air volume of fan No. 1 is 85% to 95%;

[0022] The air volume of fan No. 2 is 85% to 95%;

[0023] The air volume of fan No. 3 is 30% to 50%;

[0024] The air volume of fan No. 4 is 30% to 50%.

[0025] According to some embodiments of the present application, the output air volume of the fan is 250,000 m 3 / h.

[0026] According to some embodiments of the present application, the temperature of the initial rolling is 1080°C to 1120°C.

[0027] According to some embodiments of the present application, the spinning temperature is 840°C to 850°C.

[0028] According to some embodiments of the present application, the insulation temperature is 650°C to 670°C.

[0029] According to some embodiments of the present application, the finish rolling temperature is 840°C to 850°C.

[0030] According to some embodiments of the present application, the diameter of the wire is 6 mm to 18 mm.

[0031] According to some embodiments of the present application, the method for preparing the wire rod comprises the following steps:

[0032] Hot metal pretreatment, converter smelting, CAS, LF, VD and continuous casting.

[0033] According to some embodiments of the present application, the wire rod is GCr15 wire rod.

[0034] According to some embodiments of the present application, the GCr15 bearing steel wire is mainly in the form of large coils.

[0035] According to some embodiments of the present application, the process route of the GCr15 bearing steel wire includes:

[0036] Hot metal pretreatment, converter smelting, CAS (Caustic Arc Stirring, electric arc furnace bottom blowing oxygen calcium treatment), LF (Ladle Furnace), VD (Vacuum Decarburization) furnace, continuous casting, hot delivery and coil rolling.

[0037] According to some embodiments of the present application, the hot delivery includes rapid stacking or hot loading.

[0038] According to some embodiments of the present application, the carbide network grade of the wire is below grade 2.0. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present drawings or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present drawings. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0040] Figure 1 Continuous cooling transformation curve of the experimental steel.

[0041] Figure 2 This is the metallographic diagram of the wire corresponding to Example 1.

[0042] Figure 3 This is the metallographic image of the wire corresponding to Example 3.

[0043] Figure 4 This is the metallographic diagram of the wire corresponding to Example 4.

[0044] The purpose, features and advantages of this figure will be further described in conjunction with the embodiments with reference to the accompanying drawings. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is described and illustrated below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0046] Obviously, the following descriptions are only some examples or embodiments of the present application. For ordinary technicians in this field, the present application can also be applied to other similar scenarios without creative work. In addition, it can also be understood that although the efforts made in this development process may be complicated and lengthy, for ordinary technicians in the field related to the content disclosed in this application, some changes in design, manufacturing or production based on the technical content disclosed in this application are just conventional technical means, and should not be understood as insufficient content disclosed in this application.

[0047] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0048] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0049] Network carbides are excess secondary carbides that precipitate in a network distribution along the austenite grain boundaries in hypereutectoid steel. They are related to the chemical composition and segregation degree of the steel. The relevant technology points out that the temperature range for the precipitation of GCr15 network carbides is generally 700℃~900℃, and the temperature for the precipitation of a large number of carbides is 700℃~850℃. In order to prevent the precipitation of a large number of carbides along the grain boundaries, a relatively small and thin carbide network is obtained in the rolled structure. After rolling, it is necessary to avoid staying in this temperature range as much as possible to speed up the cooling rate in this temperature range. Therefore, the process can be improved by controlling the cooling after rolling to reduce or prevent the precipitation of carbide networks.

[0050] Experimental example

[0051] The GCr15 wire sample (cut from the finished wire after rolling) was heated to 950°C at a rate of 10°C / s, kept at this temperature for 300s, and then cooled to room temperature (25°C) at different cooling rates (0.5°C / s to 20°C / s).

[0052] Based on the expansion-temperature curve collected in the experiment, the phase transition start and end temperatures at different cooling rates were determined. Based on these measurement results, the continuous cooling transformation curve (static CCT curve) of the experimental steel was drawn, see Figure 1 .

[0053] From the continuous cooling transformation curve CCT diagram ( Figure 1 ) can be seen:

[0054] 1. When the cooling rate is ≤5℃ / s, there is a high-temperature phase change zone, the starting temperature of the phase change is 690℃~667℃; the ending temperature of the phase change is 651℃~550℃; as the cooling rate increases, the phase change temperature range decreases significantly;

[0055] 2. The cooling rate is ≥8°C, the phase transformation is mainly low-temperature martensitic phase transformation, and Ms=131°C is measured.

[0056] Ac1 (Acetylene-1) indicates the starting temperature of the transformation of pearlite to austenite in steel, while Ac3 (Acetylene-3) indicates the final temperature at which all proeutectoid ferrite in steel transforms into austenite.

[0057] The preparation method of GCr15 wire rod in this embodiment consists of the following steps:

[0058] Hot metal pretreatment, converter smelting, CAS (Caustic Arc Stirring, electric arc furnace bottom blowing oxygen calcium treatment), LF (Ladle Furnace), VD (Vacuum Decarburization) furnace, continuous casting, hot delivery.

[0059] Hot metal pretreatment: Use low-Ti hot metal, Ti≤0.02% of hot metal entering the furnace. Use granular magnesium injection for desulfurization, target [S]≤0.030%; slag removal after desulfurization.

[0060] Converter smelting: strictly control the number of post-blowing times ≯ 2 times.

[0061] Smelting endpoint control targets: [C] ≥ 0.05%, [P] ≤ 0.015%, [S] ≤ 0.030%.

[0062] The slag stopper balls and slide plates are used together for steel tapping from the converter, and the slag layer in the ladle is controlled to be ≤50mm.

[0063] CAS station composition target requirements: C: 0.90%-0.97%, Mn: 0.25%-0.35%;

[0064] CAS: Measure the temperature of molten steel within 2 minutes after it enters the station, take samples after 2 minutes of normal argon blowing, and the target pressure of argon is 1.0~1.5Mpa.

[0065] Adjust the C content in the molten steel to 0.90% to 0.95% (target value 0.93%).

[0066] LF: Control the smelting rhythm of molten steel in LF furnace: power supply time ≥ 25min, station time 40min.

[0067] Carbon is adjusted by carbon line (except abnormal conditions), and the outgoing station [C] is controlled at the target value of 0.97%-0.99%. The total amount of refined slag material added is 750kg~800kg of lime. The viscosity and color change of refined slag are observed during the process, and the white slag retention time is ≥10min.

[0068] VD: When the molten steel enters the VD furnace, the whole process of argon blowing is started, and the total argon blowing time in the VD furnace is 35 minutes. The vacuum target is below 67Pa, and the vacuum time is maintained for 15 minutes.

[0069] The outgoing hydrogen target is ≤1.5ppm.

[0070] Continuous casting: Use alkaline covering agent + carbonized rice husk for covering.

[0071] The superheat of molten steel in the tundish is controlled at ≤30℃ for the initial pouring furnace and ≤25℃ for the continuous pouring furnace.

[0072] Billet drawing system (theoretical liquidus temperature of steel grade is 1450℃):

[0073] Middle package temperature ℃ ＜1470 1470～1480 ＞1480 Pulling speed m / min 2.40 2.35～2.25 2.20

[0074] Electromagnetic stirring parameters:

[0075] - Frequency (Hz) Current (A) Electromagnetic stirring of crystallizer 3.0 340 Electromagnetic stirring at the end 16 340

[0076] Example 1

[0077] This embodiment is a controlled cooling process for improving the wire mesh carbide, which comprises the following steps:

[0078] The wire rod is rolled, finished (pre-FRS temperature), wired, cooled and kept warm;

[0079] The rolling temperature is 1150℃±30℃;

[0080] Finishing rolling temperature is 915℃±15℃;

[0081] The spinning temperature is 845℃±5℃;

[0082] During cooling:

[0083] 90% of the air volume of fans No. 1 and No. 2 (250,000 m 3 / h*0.9=225,000m 3 / h), the air volume of fans 3 and 4 is 50% (250,000 m 3 / h*0.5=125,000m 3 / h), the rest are closed;

[0084] At this air volume, the average cooling rate is 5℃ / s.

[0085] The insulation temperature is 660℃±10℃.

[0086] Example 2

[0087] This embodiment is a controlled cooling process for improving the wire mesh carbide, and the difference from the embodiment 1 is:

[0088] The rolling temperature is 1100℃±20℃.

[0089] Example 3

[0090] This embodiment is a controlled cooling process for improving the wire mesh carbide, which comprises the following steps:

[0091] The wire rod is rolled, finished (pre-FRS temperature), wired, cooled and kept warm;

[0092] The rolling temperature is 1110℃±20℃;

[0093] Finishing rolling temperature is 940℃±10℃;

[0094] The spinning temperature is 885℃±5℃;

[0095] During cooling:

[0096] 90% of the air volume of fans No. 1 and No. 2 (250,000 m 3 / h*0.9=225,000m 3 / h), the air volume of fans 3 and 4 is 70% (250,000 m 3 / h*0.7=175,000m 3 / h), the rest are closed;

[0097] At this air volume, the average cooling rate is 10.5℃ / s.

[0098] The insulation temperature is 685℃±5℃.

[0099] Example 4

[0100] This embodiment is a controlled cooling process for improving the wire mesh carbide, which comprises the following steps:

[0101] The wire rod is rolled, finished (pre-FRS temperature), wired, cooled and kept warm;

[0102] The rolling temperature is 1110℃±20℃;

[0103] Finishing rolling temperature is 875℃±15℃;

[0104] The spinning temperature is 800℃±10℃;

[0105] During cooling:

[0106] The air volume of fans No. 1 and No. 2 is 90%, the air volume of fans No. 3 and No. 4 is 30%, and the rest are closed;

[0107] The insulation temperature is 610℃±10℃.

[0108] Example 5

[0109] This embodiment is a controlled cooling process for improving the wire mesh carbide, and the difference from the embodiment 4 is that:

[0110] The rolling temperature is 1150℃±30℃.

[0111] The similarities and differences of the metallographic structures of GCr15 wire under different controlled cooling processes are analyzed and compared, especially the precipitation of network carbides. The specific organizational structure is shown in Table 1 below (S is troostite and P is pearlite).

[0112] Table 1

[0113]

[0114] After the high-temperature phase change interval of GCr15 wire was tested by thermal simulation, the cooling control parameter setting of Example 1 was more reasonable according to the comparison of various embodiments. The spinning temperature was controlled at 845°C ± 5°C by controlling the temperature of the finishing mill FRS. After spinning the wire onto the LCC roller, the front fans No. 1 and No. 2 were fully turned on to increase the cooling speed, and the cooling of fans No. 3 and No. 4 was used to avoid the precipitation of a large amount of network carbides. The network level of carbides in Example 1 is below level 2.0.

[0115] The design idea in the embodiment is to reduce the time of the temperature range where carbide network is precipitated in large quantities, increase the fan air volume in the temperature range where network carbide is easy to precipitate to speed up the cooling speed appropriately to avoid its large-scale precipitation. At the same time, it is also necessary to avoid excessive increase in cooling speed. Too fast cooling speed will lead to the formation of brittle quenching martensite structure, which greatly affects the mechanical properties of GCr15 wire.

[0116] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A controlled cooling process for improving wire mesh carbide, characterized in that: The following steps are involved: Finish rolling, spinning, cooling and heat preservation of wire rod; The spinning temperature is 790°C to 850°C.

2. The controlled cooling process according to claim 1, characterized in that: The temperature of the finish rolling is 860°C to 950°C.

3. The controlled cooling process according to claim 1, characterized in that: It also includes open rolling; The temperature of the rolling is 1080°C to 1180°C.

4. The controlled cooling process according to claim 1, characterized in that: The cooling speed is 4°C / s to 15°C / s.

5. The controlled cooling process according to claim 4, characterized in that: The insulation temperature is 600°C to 690°C.

6. The controlled cooling process according to claim 4, characterized in that: Air cooling is adopted in the cooling process; The control requirements for the fan and air volume during the air cooling process are as follows: The air volume of fan No. 1 is 85% to 95%; The air volume of fan No. 2 is 85% to 95%; The air volume of fan No. 3 is 30% to 50%; The air volume of fan No. 4 is 30% to 50%.

7. The controlled cooling process according to claim 1, characterized in that: The diameter of the wire material is 6 mm to 18 mm.

8. The controlled cooling process according to claim 1, characterized in that: The method for preparing the wire rod comprises the following steps: Hot metal pretreatment, converter smelting, CAS, LF, VD and continuous casting.

9. The controlled cooling process according to claim 1, characterized in that: The wire rod is GCr15 wire rod.

10. The controlled cooling process according to claim 1, characterized in that: The carbide mesh grade of the wire material is below grade 2.0.

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