A 20mm easy-bending 460mpa steel for coal mine hydraulic support and a preparation method thereof

Abstract

This invention relates to low-alloy structural steel, specifically a 20mm flexible 460MPa steel for coal mine hydraulic supports and its preparation method. The steel is prepared from the following raw materials by mass percentage: C: 0.16-0.18%, Si: 0.20-0.30%, Mn: 1.35-1.5%, P≤0.015%, S≤0.005%, Nb: 0.020-0.025%, with the remainder being Fe and unavoidable elements. The 20mm flexible 460MPa steel for coal mine hydraulic supports provided by this invention only adds a small amount of Si, Mn, Al, and Nb alloys in its composition design, without the need for other precious alloys. Through controlled heat treatment during rolling, a 20mm 460MPa grade flexible steel for coal mine hydraulic supports is manufactured, exhibiting no cracking when bent at D=1a, and its performance is superior to the 20mm low-alloy high-strength structural steel specified in GB / T1591-2018 "Low-alloy High-strength Structural Steel".

Description

Technical Field

[0001] This invention relates to low-alloy structural steel, specifically a 20mm thick, easily bendable 460MPa steel for coal mine hydraulic supports and its preparation method. Background Technology

[0002] GB / T1591-2018, "Low-alloy High-strength Structural Steel," stipulates that 20mm thick 460MPa high-strength steel must be bent at 180° without cracking (D=3a, where the inner diameter of the bending line D is equal to three times the material thickness a). Existing materials cannot meet this requirement. With the increasing demand for larger, higher-parameter, and higher-efficiency hydraulic supports in coal mines, there is a growing need for high-strength structural steel. However, coal mine hydraulic supports are primarily manufactured using bending processes. If low-alloy high-strength structural steel manufactured according to GB / T1591-2018 is used, the edges of the workpiece are prone to cracking. Therefore, it is necessary to develop a flexible 460MPa steel for 20mm thick coal mine hydraulic supports. Summary of the Invention

[0003] To address the problems identified in the background section, the present invention aims to provide a 20mm thick easily bendable 460MPa steel for coal mine hydraulic supports and its preparation method. This method employs Nb microalloying technology and controls cooling during rolling to produce 460MPa-grade easily bendable steel for coal mine hydraulic supports, achieving a bending resistance of D=1a without cracking. This solves key technical problems such as bending cracking of high-strength steel and enables industrial application.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A type of 460MPa flexible steel for 20mm coal mine hydraulic supports, wherein the composition of the 460MPa flexible steel for 20mm coal mine hydraulic supports, by mass percentage, is: C: 0.16~0.18%, Si: 0.20~0.30%, Mn: 1.35~1.5%, P≤0.015%, S≤0.005%, Nb: 0.020~0.025%, with the remainder being Fe and unavoidable elements.

[0006] The 20mm coal mine hydraulic support uses easily bendable 460MPa steel with a yield strength greater than or equal to 460MPa and a tensile strength greater than 540MPa.

[0007] The 20mm coal mine hydraulic support uses easily bendable 460MPa steel with an elongation after fracture greater than 17%, and does not crack in the D=1a bending test.

[0008] This invention also provides a method for preparing the 460MPa flexible steel for 20mm coal mine hydraulic supports as described above, comprising the following steps performed sequentially: top and bottom blowing converter smelting, LF refining, VD vacuum refining, wide slab continuous casting, and furnace coil rolling; the top and bottom blowing converter smelting, LF refining, and VD vacuum refining steps ensure that the temperature and composition of the molten steel meet the requirements of wide slab continuous casting and product composition, and the heat treatment temperature is controlled by furnace coil rolling.

[0009] The VD vacuum refining process involves two consecutive VD vacuum refining operations.

[0010] The wide slab continuous casting adopts full-process protective pouring, and the cooling time after the slab is removed from the line is ≥48h.

[0011] The hot coil rolling process includes four controlled processes:

[0012] First-stage controlled rolling: Rolling is carried out in the recrystallization zone at a temperature range of 980–1120℃. The single-pass reduction rate in the recrystallization zone is ≥15%, and the total reduction rate is ≥40%.

[0013] The second stage of controlled rolling: rolling is carried out in the non-recrystallization zone, with an initial rolling temperature of 850-920℃ and a final rolling temperature of 760-830℃, and a total reduction rate of ≥60% in the non-recrystallization zone;

[0014] The third stage of controlled cooling: the initial cooling temperature is 740-800℃, and the final cooling temperature is 600-660℃;

[0015] Fourth stage: slow cooling after rolling.

[0016] The cooling rate for the third stage of controlled cooling is ≥5℃ / s.

[0017] The control method for the fourth stage is as follows: after the steel plate comes off the production line, it is stacked and cooled for ≥48 hours.

[0018] The composition design of the easily bendable 460MPa steel in this invention is based on the following:

[0019] C is one of the main elements that improve the strength of steel. As the carbon content increases, the yield strength and tensile strength of steel will increase. However, as the carbon content increases, the elongation and impact toughness of steel will decrease. Moreover, when welding steel with a high carbon content, hardening will occur in the heat-affected zone, which will exacerbate the tendency to produce cold cracks during welding. Therefore, a carbon content of 0.16 to 0.18% is adopted.

[0020] Si: It helps to improve the strength of steel, and its main function is to act as a calming agent.

[0021] Mn: is a solid solution strengthening element, which is beneficial to improving the strength of steel plates;

[0022] P: This makes the steel prone to cold brittleness; its content should be as low as possible.

[0023] S: This makes the steel prone to hot cracking; its content should be as low as possible.

[0024] Nb: The key microalloying element in the steel of this invention, which plays a role in grain refinement and precipitation strengthening.

[0025] Compared with the prior art, the present invention has the following advantages: The present invention uses Nb microalloying technology and controls the cooling during rolling to produce a 460MPa easily bendable steel for coal mine hydraulic supports. The yield strength is greater than 460MPa, the tensile strength is greater than 540MPa, the elongation after fracture is greater than 17%, and it does not crack when bent at D=1a. Attached Figure Description

[0026] Figure 1 This is a picture of the side guard plate of the coal mine hydraulic support made using the present invention when bent at 90°. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. It should be noted that 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 skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0028] The composition of the 460MPa flexible steel used in the 20mm coal mine hydraulic support in Example 1, by mass percentage, is as follows: C: 0.16%, Si: 0.24%, Mn: 1.45%, P: 0.014%, S: 0.004%, Nb: 0.022%, with the remainder being Fe and unavoidable elements.

[0029] The preparation method of Example 1 is as follows: top and bottom blowing converter smelting, LF refining, VD vacuum refining, wide slab continuous casting, and hot coil rolling; through the top and bottom blowing converter smelting, LF refining, and VD vacuum refining processes, the temperature and composition of the molten steel meet the requirements for wide slab continuous casting and product composition. The VD vacuum refining process involves two consecutive VD vacuum refining operations; the wide slab continuous casting adopts full-process protective casting, and the stacking cooling time after casting is ≥48 hours; the hot coil rolling process is divided into four controlled stages:

[0030] First stage controlled rolling: rolling in the recrystallization zone, with an initial rolling temperature of 1080℃ and a final rolling temperature of 980℃. The single-pass reduction rate in the recrystallization zone is ≥15%, and the total reduction rate in the recrystallization zone is 60%.

[0031] Second-stage controlled rolling: Rolling is carried out in the non-recrystallization zone, with an initial rolling temperature of 920℃ and a final rolling temperature of 803℃. The total reduction rate in the non-recrystallization zone is ≥60%.

[0032] The third stage of controlled cooling: the initial cooling temperature is 740-800℃, the cooling rate is ≥5℃ / s, and the final cooling temperature is 650℃.

[0033] The fourth stage is slow cooling after rolling, specifically by stacking and cooling after rolling, with a stacking and cooling time of ≥48 hours. Example 2

[0034] The composition of the 460MPa flexible steel used in the 20mm coal mine hydraulic support in Example 2, by mass percentage, is as follows: C: 0.18%, Si: 0.24%, Mn: 1.50%, P: 0.013%, S: 0.002%, Nb: 0.025%, with the remainder being Fe and unavoidable elements.

[0035] The preparation method of Example 2 is as follows: top and bottom blowing converter smelting, LF refining, VD vacuum refining, wide slab continuous casting, and hot coil rolling; through the top and bottom blowing converter smelting, LF refining, and VD vacuum refining processes, the temperature and composition of the molten steel meet the requirements for wide slab continuous casting and product composition. The VD vacuum refining process involves two consecutive VD vacuum refining operations; the wide slab continuous casting adopts full-process protective casting, and the stacking cooling time after casting is ≥48 hours; the hot coil rolling process is divided into four controlled stages:

[0036] First stage controlled rolling: rolling in the recrystallization zone, with an initial rolling temperature of 1089℃ and a final rolling temperature of 995℃. The single-pass reduction rate in the recrystallization zone is ≥15%, and the total reduction rate in the recrystallization zone is 60%.

[0037] Second-stage controlled rolling: Rolling is carried out in the non-recrystallization zone, with an initial rolling temperature of 915℃ and a final rolling temperature of 800℃. The total reduction rate in the non-recrystallization zone is ≥60%.

[0038] The third stage of controlled cooling: the initial cooling temperature is 740-800℃, the cooling rate is ≥5℃ / s, and the final cooling temperature is 640℃.

[0039] The fourth stage is slow cooling after rolling, specifically by stacking and cooling after rolling, with a stacking and cooling time of ≥48 hours. Example 3

[0040] The composition of the 460MPa flexible steel used in the 20mm coal mine hydraulic support in Example 3, by mass percentage, is as follows: C: 0.17%, Si: 0.25%, Mn: 1.38%, P: 0.015%, S: 0.002%, Nb: 0.025%, with the remainder being Fe and unavoidable elements.

[0041] The preparation method of Example 3 is as follows: top and bottom blowing converter smelting, LF refining, VD vacuum refining, wide slab continuous casting, and hot coil rolling; through the top and bottom blowing converter smelting, LF refining, and VD vacuum refining processes, the temperature and composition of the molten steel meet the requirements for wide slab continuous casting and product composition. The VD vacuum refining process involves two consecutive VD vacuum refining operations; the wide slab continuous casting adopts full-process protective casting, and the stacking cooling time after casting is ≥48 hours; the hot coil rolling process is divided into four controlled stages:

[0042] First stage controlled rolling: rolling in the recrystallization zone, with an initial rolling temperature of 1092℃ and a final rolling temperature of 986℃. The single-pass reduction rate in the recrystallization zone is ≥15%, and the total reduction rate in the recrystallization zone is 60%.

[0043] Second-stage controlled rolling: Rolling is carried out in the non-recrystallization zone, with an initial rolling temperature of 905℃ and a final rolling temperature of 810℃. The total reduction rate in the non-recrystallization zone is ≥60%.

[0044] The third stage of controlled cooling: the initial cooling temperature is 740-800℃, the cooling rate is ≥5℃ / s, and the final cooling temperature is 635℃.

[0045] The fourth stage is slow cooling after rolling, specifically by stacking and cooling after rolling, with a stacking and cooling time of ≥48 hours.

[0046] The composition of the steel plates produced in Examples 1-3 is shown in Table 1 below:

[0047] Table 1. Steel plate composition (wt%) for each embodiment

[0048]

[0049] The hot rolling control process for Examples 1-3 is shown in Table 2 below:

[0050] Table 2 Rolling Process

[0051]

[0052] The performance indicators of Examples 1-3 are shown in Table 3 below:

[0053] Table 3 Performance Indicators of Examples

[0054]

[0055] Comparing Examples 1, 2, and 3 in Table 3, it can be seen that: using the Nb microalloying technology disclosed in this invention, and controlling the heat treatment temperature through furnace rolling, the 460MPa easily bendable steel for coal mine hydraulic supports manufactured has a yield strength greater than or equal to 460MPa, a tensile strength greater than 540MPa, an elongation after fracture greater than 17%, and does not crack when bent at D=1a.

[0056] like Figure 1 As shown, the 20mm side guard plate for coal mine hydraulic supports made using the present invention did not crack when bent at 90°, which proves that its performance is significantly better than that of the 20mm low alloy high strength structural steel specified in GB / T1591-2018 "Low Alloy High Strength Structural Steel".

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0058] The parts of this invention not described in detail are prior art.

Claims

1. A type of easily bendable 460MPa steel for 20mm thick hydraulic supports in coal mines, characterized in that... The composition of the 460MPa flexible steel for the 20mm coal mine hydraulic support, by mass percentage, is as follows: C: 0.16-0.18%, Si: 0.20-0.30%, Mn: 1.35-1.5%, P≤0.015%, S≤0.005%, Nb: 0.020-0.025%, with the remainder being Fe and unavoidable elements; furthermore, the 460MPa flexible steel for the 20mm coal mine hydraulic support does not crack in the D=1a bending test; The preparation method of the 20mm coal mine hydraulic support using easily bendable 460MPa steel includes the following sequential steps: top and bottom blowing converter smelting, LF refining, VD vacuum refining, wide slab continuous casting, and furnace coil rolling; the top and bottom blowing converter smelting, LF refining, and VD vacuum refining steps ensure that the temperature and composition of the molten steel meet the requirements of wide slab continuous casting and product composition, and the heat treatment temperature is controlled by furnace coil rolling; the furnace coil rolling includes a four-stage control process: First-stage controlled rolling: Rolling is carried out in the recrystallization zone at a temperature range of 980–1120℃. The single-pass reduction rate in the recrystallization zone is ≥15%, and the total reduction rate is ≥40%. The second stage of controlled rolling: rolling is carried out in the non-recrystallization zone, with an initial rolling temperature of 850-920℃ and a final rolling temperature of 760-830℃, and a total reduction rate of ≥60% in the non-recrystallization zone; The third stage of controlled cooling: the initial cooling temperature is 740-800℃, and the final cooling temperature is 600-660℃; the cooling rate is ≥5℃ / s. Fourth stage: slow cooling after rolling; The control method for the fourth stage is as follows: after the steel plate comes off the production line, it is stacked and cooled for ≥48 hours.

2. The easily bendable 460MPa steel for a 20mm thick hydraulic support in a coal mine according to claim 1, characterized in that, The 20mm coal mine hydraulic support uses easily bendable 460MPa steel with a yield strength greater than or equal to 460MPa and a tensile strength greater than 540MPa.

3. The easily bendable 460MPa steel for a 20mm thick hydraulic support in a coal mine according to claim 1, characterized in that, The 20mm coal mine hydraulic support uses easily bendable 460MPa steel with an elongation after fracture greater than 17%.

4. A method for preparing 20mm thick easily bendable 460MPa steel for coal mine hydraulic supports as described in any one of claims 1-3, characterized in that, The process includes the following steps performed sequentially: top and bottom blowing converter smelting, LF refining, VD vacuum refining, wide slab continuous casting, and coil rolling; the top and bottom blowing converter smelting, LF refining, and VD vacuum refining processes ensure that the temperature and composition of the molten steel meet the requirements for wide slab continuous casting and product composition, and the heat treatment temperature is controlled by coil rolling; the coil rolling process includes four controlled stages: First-stage controlled rolling: Rolling is carried out in the recrystallization zone at a temperature range of 980–1120℃. The single-pass reduction rate in the recrystallization zone is ≥15%, and the total reduction rate is ≥40%. The second stage of controlled rolling: rolling is carried out in the non-recrystallization zone, with an initial rolling temperature of 850-920℃ and a final rolling temperature of 760-830℃, and a total reduction rate of ≥60% in the non-recrystallization zone; The third stage of controlled cooling: the initial cooling temperature is 740-800℃, and the final cooling temperature is 600-660℃; the cooling rate is ≥5℃ / s. Fourth stage: slow cooling after rolling; The control method for the fourth stage is as follows: after the steel plate comes off the production line, it is stacked and cooled for ≥48 hours.

5. The preparation method according to claim 4, characterized in that, The VD vacuum refining process involves two consecutive VD vacuum refining operations.

6. The preparation method according to claim 4, characterized in that, The wide slab continuous casting adopts full-process protective pouring, and the cooling time after the slab is removed from the line is ≥48h.

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