A wear-resistant steel with a duplex structure prepared by NG-TMCP technology

Abstract

The present invention provides a wear-resistant steel with a duplex structure prepared by NG-TMCP technology. The wear-resistant steel is a steel plate, and the composition of the wear-resistant steel by weight percentage is: C: 0.07 - 0.45%, Si: 0.30 - 1.20%, Mn: 0.08 - 1.60%, P: ≤0.012%, S: ≤0.002%, Ti: 0.010 - 0.040%, Alt: 0.20 - 0.60%, Nb: 0.010 - 0.040%, Cr: 0.18 - 0.40%, Mo: 0.001 - 0.45%, N: 0.002% - 0.006%, and the balance is Fe and inevitable impurities. The thickness of the finished steel plate is 10 - 60 mm. The present invention adopts reciprocating two-stage cooling to realize the regulation and preparation of the duplex structure of the wear-resistant steel, while avoiding large reduction at low temperature, reducing the load of the rolling mill, reducing energy consumption, and prolonging the service life of the rolling mill.

Description

[0001] This invention is a divisional application. The name of the parent application is: Wear-resistant steel with duplex structure prepared by NG-TMCP technology and its production method, application number: 2022105791526, application date: May 25, 2022. Technical Field

[0002] This invention relates to the technical field of wear-resistant steel manufacturing, and particularly to a wear-resistant steel with duplex structure prepared by NG-TMCP technology. Background Art

[0003] Wear-resistant steel is one of the wear-resistant materials with the largest consumption. The traditional domestic production process of high-strength wear-resistant steel adopts post-rolling heat treatment and is delivered in the quenched or quenched + tempered state. Its matrix structure is all martensite, which has high strength and high hardness while ensuring good wear resistance. However, martensite itself has high brittleness and is prone to cracking under the action of internal stress, resulting in poor formability of the steel plate. Quenching cracks are also likely to occur during the preparation process, and the preparation process flow is long, with high requirements for post-rolling heat treatment equipment, leading to high costs. Duplex structures such as bainite + martensite + retained austenite or martensite + bainite + ferrite or bainite + martensite are beneficial to the improvement of comprehensive properties. Research and development of wear-resistant steel with duplex structure have become the development direction of wear-resistant steel. Wear-resistant steel with duplex structure is generally delivered in the hot-rolled and controlled-rolling (or tempered) state, and its production process is mainly rolling → segmented cooling → coiling → (tempering). However, limited by equipment capabilities, currently, it is mainly thin-specification wear-resistant steel with duplex high strength.

[0004] The existing cooling method for wear-resistant steel is two-stage cooling. In the first stage, intensive rapid (water-cooling) cooling is adopted, with a cooling temperature of 600 - 700°C. Then, after air-cooling for 4 - 8 s, rapid (water-cooling) cooling is carried out to 100 - 200°C to obtain a duplex structure of ferrite + martensite and a small amount of retained austenite. This method requires a long cooling zone on the production line to achieve cooling in stages successively. The length of the cooling zone required for two-stage cooling plus the intermediate air-cooling is generally more than 30 meters, which greatly increases the length of the factory area. For some factory areas with limited length, it is impossible to produce wear-resistant steel.

[0005] In summary, the following problems exist in the prior art: The existing cooling method for wear-resistant steel is two-stage cooling, which requires a long cooling zone on the production line, restricting the production of wear-resistant steel. Summary of the Invention

[0006] This invention provides a wear-resistant steel and its production method, especially a wear-resistant steel with duplex structure prepared by NG-TMCP technology and its production method, to solve the problem that the existing production of wear-resistant steel requires a long cooling zone. The Chinese meaning of NG-TMCP technology is the new generation of controlled rolling and controlled cooling technology.

[0007] For this purpose, the present invention provides a production method for preparing duplex structure wear-resistant steel based on NG-TMCP technology. The wear-resistant steel is a steel plate, and the production method for preparing duplex structure wear-resistant steel based on NG-TMCP technology includes:

[0008] Rough rolling, finish rolling, pre-straightening, the first-stage ACC accelerated cooling, relaxation, the second-stage UFC ultra-fast cooling, a powerful straightening machine, and tempering;

[0009] Among them, on the production line, only one cooling zone is set after rolling. The first-stage ACC accelerated cooling and the second-stage UFC ultra-fast cooling are both in the same cooling zone, and the cooling zone is 19 m long;

[0010] The relaxation: After the first-stage ACC accelerated cooling ends, the time when the steel plate exits the cooling zone and then returns to the cooling zone is the relaxation time; that is, the time between the first-stage ACC accelerated cooling and the second-stage UFC ultra-fast cooling;

[0011] The velocity direction of the steel plate in the first-stage ACC accelerated cooling is opposite to the velocity direction in the second-stage UFC ultra-fast cooling.

[0012] Furthermore, for rough rolling: a rolling method of vertical-horizontal-vertical is adopted.

[0013] Furthermore, for finish rolling: continuous rolling is carried out. The starting rolling temperature is 950 - 1050 °C, and the final rolling temperature of finish rolling is 860 - 910 °C. There should be no pause between passes to ensure the work hardening property of the rolled piece.

[0014] Furthermore, for the first-stage ACC accelerated cooling: the recrystallization temperature (the recrystallization temperature refers to the highest temperature reached when the heat in the core of the steel transfers outward after water cooling, causing the surface temperature of the steel to rise. Specifically in this application, the recrystallization temperature is the temperature of the steel plate in front of the straightening machine after water cooling) is the ferrite precipitation temperature, 680 °C - 780 °C.

[0015] Furthermore, for the second-stage UFC ultra-fast cooling: the steel plate directly returns to the cooling zone for the second-stage UFC ultra-fast cooling, and the recrystallization temperature is the bainite or martensite precipitation temperature, and the recrystallization temperature ≤ 350 °C.

[0016] Furthermore, the composition of the wear-resistant steel by weight percentage is C: 0.07 - 0.45%, Si: 0.30 - 1.20%, Mn: 0.08 - 1.60%, P: ≤ 0.012%, S: ≤ 0.002%, Ti: 0.010 - 0.040%, Alt: 0.20 - 0.60%, Nb: 0.010 - 0.040%, Cr: 0.18 - 0.40%, Mo: 0.001 - 0.45%, N: 0.002% - 0.006%, and the balance is Fe and unavoidable impurities.

[0017] Furthermore, the thickness of the finished steel plate is 10 - 60 mm.

[0018] Furthermore, the rough rolling starting temperature is 1150 - 1280 °C, and the rough rolling finishing temperature is ≥ 1000 °C.

[0019] The present invention also provides a duplex structure wear-resistant steel prepared by the NG-TMCP technology. The wear-resistant steel is a steel plate, and the composition of the wear-resistant steel by weight percentage is C: 0.07 - 0.45%, Si: 0.30 - 1.20%, Mn: 0.08 - 1.60%, P: ≤ 0.012%, S: ≤ 0.002%, Ti: 0.010 - 0.040%, Alt: 0.20 - 0.60%, Nb: 0.010 - 0.040%, Cr: 0.18 - 0.40%, Mo: 0.001 - 0.45%, N: 0.002% - 0.006%, and the balance is Fe and unavoidable impurities. The thickness of the finished steel plate is 10 - 60 mm, and the wear-resistant steel is made by the method described above.

[0020] Furthermore, the thickness of the finished steel plate is 20 - 40 mm, and the composition of the wear-resistant steel by weight percentage is C: 0.18%, Si: 1.14%, Mn: 1.33%, P: 0.011%, S: 0.001%, Ti: 0.02%, Alt: 0.49%, Nb: 0.02%, Cr: 0.28%, Mo: 0.30%, N: 0.0051%.

[0021] A duplex structure wear-resistant steel prepared by the NG-TMCP technology obtained by the present invention has a duplex structure, and the steel plate has good comprehensive properties. The tensile strength Rm ≥ 800 MPa, the elongation after fracture A ≥ 8%, the longitudinal impact energy AKV2 at -20 °C ≥ 24 J, and the cold bending is qualified.

[0022] After the first-stage ACC accelerated cooling in the present invention, the time in the return cooling zone is controlled to give the steel plate a certain relaxation. After the proeutectoid ferrite is precipitated, the second-stage UFC ultra-fast cooling is carried out. Without online quenching or offline quenching or a long cooling zone, the duplex structure regulation and preparation of the wear-resistant steel are realized. The present invention reduces the existing two-stage cooling zones before and after to only one cooling zone. The first-stage ACC accelerated cooling and the second-stage UFC ultra-fast cooling are both in the same cooling zone. In this way, the setting and length of the cooling zone are reduced, the production conditions of the product are relaxed, which is beneficial to the transformation on the basis of the existing plant area to produce the wear-resistant steel that could not be produced originally.

[0023] Compared with air cooling to the ferrite precipitation temperature, the present invention uses ACC to accelerate cooling to the ferrite precipitation temperature, enabling the rolled piece to quickly pass through the austenite phase region, retaining the hardened austenite structure as much as possible, achieving grain refinement and control of precipitates, and facilitating the improvement of comprehensive properties.

[0024] The present invention realizes the control and preparation of the duplex structure of wear-resistant steel through hot finish rolling + ACC accelerated cooling in the first stage + UFC ultra-fast cooling in the second stage, avoiding large reduction at low temperature, reducing the load on the rolling mill, reducing energy consumption, extending the service life of the rolling mill, and solving the difficult rolling problem caused by low-temperature finish rolling of medium-thick plates or small billets.

[0025] In addition, the present invention (1) seizes the opportunity in the high-temperature austenite range suitable for deformation to complete the strain accumulation of continuous large deformation to obtain hardened austenite; (2) enables the rolled piece to quickly pass through the austenite phase region and retain the hardened austenite structure; (3) terminates cooling at the dynamic phase transformation point of austenite to ferrite phase transformation, and then selects different cooling paths according to the needs of the material structure and properties. Based on the NG-TMCP technology, the present invention adopts reciprocating two-stage cooling to realize the control and preparation of the duplex structure of wear-resistant steel, while avoiding large reduction at low temperature, reducing the load on the rolling mill, reducing energy consumption, and extending the service life of the rolling mill. Brief Description of the Drawings

[0026] Figure 1 It is a schematic diagram of the process path of the production line of the present invention;

[0027] Figure 2 It is a schematic diagram of the process flow of the production line of the present invention;

[0028] Figure 3 It is the surface metallographic structure of Example 1 of the present invention;

[0029] Figure 4 It is the core metallographic structure of Example 1 of the present invention;

[0030] Figure 5 It is the surface metallographic structure of Example 2 of the present invention;

[0031] Figure 6 It is the core metallographic structure of Example 2 of the present invention;

[0032] Figure 7 It is the surface metallographic structure of Example 3 of the present invention;

[0033] Figure 8 It is the core metallographic structure of Example 3 of the present invention. Detailed Embodiments

[0034] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the present invention will now be described.

[0035] The present invention relates to a short process manufacturing technology (with the cooling zone reduced to 1): controlled rolling (including rough rolling and finish rolling) → pre-straightening → accelerated ACC cooling in the first stage to the ferrite precipitation temperature → relaxation → UFC ultra-fast cooling in the second stage → powerful straightening machine → tempering.

[0036] 1. Rolling:

[0037] Two-stage rolling is adopted, and rolling mill cooling water is not used throughout the process, and high-pressure descaling is performed according to the actual situation. (1) Rough rolling: The rolling method of vertical-horizontal-vertical is adopted, and austenite recrystallization rolling is carried out with high temperature and fast rolling and large reduction, so that the deformation is transferred to the core of the billet. The rough rolling finishing temperature ≥ 1000 °C, and the single-pass reduction in the intermediate pass ≥ 20 mm. The blooming thickness is 2-3 times the finished product thickness. (2) Finish rolling: The rolling start temperature is 950-1050 °C. The finish rolling finishing temperature of the steel plate is 860-910 °C, and the finishing temperature is relatively high, so the plate shape is easy to control in the cooling zone; (3) Continuous rolling, and there shall be no pause for temperature reduction between passes.

[0038] 2. Pre-straightening and accelerated ACC cooling in the first stage: (The cooling capacity of the equipment is set at 2.5 °C / S - 50 °C / S, and the water pressure is 0.2 MPa. The cooling rates for obtaining ferrite in different composition systems are different, such as 2.5 °C / S, 5 °C / S, 10 °C / S, 15 °C / S, 25 °C / S, 30 °C / S, 35 °C / S, 40 °C / S, 45 °C / S, 50 °C / S, mainly to control the return red temperature, and the water pressure of 0.2 MPa has the ability of accelerated cooling.)

[0039] The cooling start temperature is related to the finishing temperature. After leaving the finish rolling, enter the cooling zone as quickly as possible, reduce the relaxation time in the air-cooled state, avoid the merger and disappearance of dislocations, segregation of alloying elements, and change of precipitation state, and retain the hardened austenite. The return red temperature is the ferrite precipitation temperature, generally 680 °C - 780 °C, and the cooling rate is 8 °C / S - 25 °C / S (such as 8 °C / S, 10 °C / S, 15 °C / S, 18 °C / S, 20 °C / S, 25 °C / S). Through-type cooling (after entering the cooling, the steel plate goes straight forward, cools while moving forward, and then exits the cooling outlet), the water pressure is 0.2 MPa, and the upper-lower water ratio is 1.2 - 2.5. Accelerated cooling is carried out using a nozzle header for high-density fast cooling in the front section (high means high water flow rate, dense means dense nozzle layout, the diameter of the upper high-density nozzle is 3.5 mm, and the diameter of the lower high-density nozzle is 4.5 mm. After the cooling water is sprayed by the high-density fast cooling nozzle, it forms a dense water column and is evenly sprayed in the nozzle area). Increase the flow rate of the lower header to compensate for the heat transfer capacity of the lower surface.

[0040] 3. Relaxation

[0041] After the first-stage ACC accelerated cooling ends, the time for the steel plate to return to the cooling zone after leaving the cooling zone is the relaxation time. Adjust the roller speed to control the relaxation time so as to precipitate ferrite, generally 30s to 70s. The ferrite precipitation ratio is 10% to 35%, and the influence of the cooling and rolling rhythms in the front and back sections can be flexibly controlled. The ferrite precipitation ratio is affected by the relaxation time.

[0042] 4. Second-stage UFC ultra-fast cooling

[0043] The steel plate relaxes for a certain time, for example: 30 - 70s. (The length of the relaxation time affects (1) the precipitation of ferrite structure. If the relaxation time is too long, more ferrite precipitates, softening the material and reducing the strength; if the relaxation time is too short and the precipitation amount is small, the plasticity of the material will be reduced. (2) For thin plates, a long relaxation time will affect the temperature of the steel plate, resulting in changes in the structure and unable to be controlled as expected.) Return to the cooling zone and directly perform the second-stage UFC ultra-fast cooling (the cooling capacity of the equipment is set at a cooling rate of 6 - 120°C / S). The recrystallization temperature is the bainite or martensite precipitation temperature, the recrystallization temperature ≤ 350°C, and the cooling rate ≥ 30°C / S. To ensure cooling uniformity, use through-type cooling, with a water pressure of 0.5MPa, an upper and lower water ratio of 1.2 - 2.5, and use slot nozzles + high-density fast-cooling nozzles for ultra-fast cooling. If the steel plate is thick and the cooling zone is short, to ensure the temperature drop at the core, appropriately increase the number of ultra-fast cooling passes.

[0044] 5. Powerful straightening machine

[0045] After cooling is completed, straighten it through a powerful straightening machine to ensure the flatness of the plate shape. For example, use a straightening force of 3000KN and straighten for 2 passes.

[0046] 6. Tempering

[0047] Low-temperature tempering or high-temperature tempering is used for tempering. According to user requirements, performance, or plate shape, perform tempering heat treatment to improve plasticity and plate shape. For example, the tempering temperature is 450°C ± 5°C, and the tempering time is 1.5 times the thickness.

[0048] Example: The duplex structure wear-resistant steel prepared based on the NG-TMCP technology adopts the following component ratios and specific processes. Among them, Table 1 shows the components of the steel in each example (by weight percentage). Tables 2 and 3 are the rolling and cooling process parameters corresponding to the components of the examples described in Table 1, and Table 4 shows the mechanical properties and structures corresponding to each example. Figures 3 to 6 It is the metallographic structure corresponding to the example.

[0049] Table 1: Chemical composition of the product (wt%)

[0050] Example C Si Mn P S Alt Nb Ti Cr Mo N Example 1 0.18 1.14 1.33 0.011 0.001 0.49 0.02 0.02 0.28 0.30 0.0051 Example 2 0.12 0.90 1.55 0.009 0.0015 0.32 0.03 0.03 0.32 0.38 0.0040 Example 3 0.13 1.10 1.53 0.009 0.001 0.25 0.015 0.022 0.36 0.27 0.0045

[0051] Table 2: Specific rolling process parameters for each example

[0052] The rough rolling adopts the longitudinal-transverse-longitudinal continuous rolling method to improve the transverse performance and reduce anisotropy. The finish rolling is carried out by longitudinal rolling for 8 passes continuously. The width of the intermediate billet is the width of the finished steel plate. The rough rolling starting temperature: 1150 - 1280 °C, and the rough rolling finishing temperature: 1000 °C - 1080 °C.

[0053]

[0054] Table 3: Specific cooling process parameters of each embodiment

[0055] Cooling is carried out in stages. After ACC accelerated cooling, using the time in the return cooling zone, a certain relaxation is given to the steel plate to precipitate proeutectoid ferrite and then ultra-fast cooling is carried out.

[0056]

[0057]

[0058] Table 4: Mechanical properties obtained in each embodiment

[0059]

[0060] The present invention has a good cooling effect on steel plates including medium and heavy plates, and is applicable to steel plates with a thickness of 10 - 60 mm.

[0061] The above are only the schematic specific embodiments of the present invention, and are not intended to limit the scope of the present invention. The components of the present invention can be combined with each other under the condition of no conflict. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principle of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A duplex structure wear-resistant steel prepared by NG-TMCP technology, characterized in that, The wear-resistant steel is a steel plate. The composition of the wear-resistant steel by weight percentage is C: 0.07 - 0.45%, Si: 0.30 - 1.20%, Mn: 0.08 - 1.60%, P: ≤0.012%, S: ≤0.002%, Ti: 0.010 - 0.040%, Alt: 0.20 - 0.60%, Nb: 0.010 - 0.040%, Cr: 0.18 - 0.40%, Mo: 0.001 - 0.45%, N: 0.002% - 0.006%. The balance is Fe and inevitable impurities. The thickness of the finished steel plate is 10 - 60 mm. The wear-resistant steel is made by a production method of preparing a duplex structure wear-resistant steel based on the NG-TMCP technology; The production method of preparing a duplex structure wear-resistant steel based on the NG-TMCP technology includes: Rough rolling, finish rolling, pre-straightening, the first-stage ACC accelerated cooling, relaxation, the second-stage UFC ultra-fast cooling, a powerful straightening machine, tempering; The rough rolling finishing temperature ≥ 1000°C, the single-pass reduction in the intermediate pass ≥ 20 mm, and the blooming thickness is 2 - 3 times the finished thickness; Finish rolling: The rolling start temperature is 950 - 1050°C, and the finish rolling temperature of the steel plate is 860 - 910°C; Among them, on the production line, there is only one cooling zone after rolling. Both the first-stage ACC accelerated cooling and the second-stage UFC ultra-fast cooling are in the same cooling zone; The relaxation: After the first-stage ACC accelerated cooling ends, the time when the steel plate returns to the cooling zone after leaving the cooling zone is the relaxation time; that is, the time between the first-stage ACC accelerated cooling and the second-stage UFC ultra-fast cooling; The speed direction of the steel plate in the first-stage ACC accelerated cooling is opposite to the speed direction in the second-stage UFC ultra-fast cooling; The first-stage ACC accelerated cooling: The recrystallization temperature is the ferrite precipitation temperature, 680°C - 780°C; The cooling rate is 8°C / s - 25°C / s; The second-stage UFC ultra-fast cooling: The steel plate directly enters the second-stage UFC ultra-fast cooling after returning to the cooling zone. The recrystallization temperature is the bainite or martensite precipitation temperature, and the recrystallization temperature ≤ 350°C; The cooling rate ≥ 30°C / s; The microstructure is: F + M; or F + M + B; or F + M + B + P.

2. The duplex structure wear-resistant steel according to claim 1, characterized in that, The thickness of the finished steel plate is 20 - 40 mm. The composition of the wear-resistant steel by weight percentage is C: 0.18%, Si: 1.14%, Mn: 1.33%, P: 0.011%, S: 0.001%, Ti: 0.02%, Alt: 0.49%, Nb: 0.02%, Cr: 0.28%, Mo: 0.30%, N: 0.0051%.

3. The duplex structure wear-resistant steel according to claim 1, characterized in that, The thickness of the finished steel plate is 20 mm, 40 mm or 60 mm.

4. The duplex structure wear-resistant steel according to claim 1, characterized in that, The composition of the wear-resistant steel by weight percentage is C: 0.12%, Si: 0.90%, Mn: 1.55%, P: 0.009%, S: 0.0015%, Ti: 0.03%, Alt: 0.32%, Nb: 0.03%, Cr: 0.32%, Mo: 0.38%, N: 0.0040%.

5. The duplex structure wear-resistant steel according to claim 1, characterized in that, The composition of the wear-resistant steel is by weight percentage: C: 0.13%, Si: 1.10%, Mn: 1.53%, P: 0.009%, S: 0.001%, Ti: 0.022%, Alt: 0.25%, Nb: 0.015%, Cr: 0.36%, Mo: 0.27%, N: 0.0045%.

6. The duplex structure wear-resistant steel according to claim 1, characterized in that, The microstructure is: F + M; the proportion of F is 38%.

7. The duplex structure wear-resistant steel according to claim 1, characterized in that, The microstructure is: F + M + B; the proportion of F is 28%.

8. The duplex structure wear-resistant steel according to claim 1, characterized in that, The microstructure is: F + M + B + P, and the proportion of F is 35%.

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