Q345qD steel for railway and preparation method of Q345qD steel

Abstract

The invention provides Q345qD steel for a railway and a preparation method of the Q345qD steel. The Q345qD steel comprises the following chemical components in percentage by mass: 0.05%-0.12% of C, 1.4%-1.6% of Mn, 0.13%-0.22% of Si, less than or equal to 0.003% of S, less than or equal to 0.009% of P, 0.02%-0.03% of Als, 0.12%-0.30% of Cr, 0.15%-0.30% of Cu, 0.45%-0.70% of N, 0.002%-0.01% of Ti and the balance of Fe and inevitable impurities. The Cu content is limited to be 0.15-0.30%, so that the gas corrosion resistance and the mechanical property of the steel are improved; the content of N is 0.45-0.70%, so that the strength and the stability of austenite are improved; the content of Ti is 0.002-0.01%, so that the strength, toughness and corrosion resistance of the steel are improved; and the content of Cr is limited to be 0.12%-0.30%, so that the hardness and strength of the alloy can be improved, and meanwhile, the situation that the toughness of the alloy is reduced due to excessive addition is avoided. Meanwhile, rough rolling and finish rolling methods are adopted, the specific rolling process is adjusted, the tempering-normalizing-tempering heat treatment mode is combined, and the comprehensive performance of the alloy is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of metal smelting, and particularly to a Q345qD steel for railways and a preparation method thereof. Background Art

[0002] Bridge steel plates are specifically used for building railway or highway bridges, and are required to have high strength, toughness, and the ability to withstand the loads and impacts of locomotives and rolling stocks. They also need to have good fatigue resistance, certain low-temperature toughness, and atmospheric corrosion resistance.

[0003] With the development of modern bridge steel structures towards large-scale, high-parameter, safety, durability, and fully welded joint steel structures, the demand for bridge steel continues to increase, and the quality requirements for bridge steel are getting higher and higher. Affected by metallurgical quality, rolling equipment, and rolling reduction ratio, for extra-thick bridge steel with a thickness greater than 100mm, it is very difficult to achieve a -20°C low-temperature impact of more than 120J while ensuring strength. At the same time, the processing performance and welding performance of the steel plate need to be considered. For steel plates with a thickness > 100mm, the previous method was to stack two steel plates to meet the requirements of extra-large thickness. However, this method has great construction difficulty, and it is difficult to ensure the welding quality, and the structural safety is not high when used in the main stress positions. Therefore, it is particularly important to develop a Q345qD steel for railways with a thickness ≥ 100mm that meets the standard mechanical property requirements and has high quality.

[0004] Patent 202110959399.6 discloses a ferrite-pearlite type Q345qD bridge steel extra-thick plate and a manufacturing method thereof. Through reasonable composition design and heat treatment process, a Q345qD bridge structure steel plate with appropriate strength, excellent high and low temperature toughness, and various performance indicators is obtained.

[0005] Patent 202210235946.0 discloses a production method of low-cost Q345q series bridge steel plates. By adopting low-temperature large reduction technology and TMCP controlled rolling and controlled cooling technology: increasing the ferrite nucleation rate, thereby refining the ferrite grains, controlling cooling after controlled rolling can improve the banded structure, refine the pearlite spheroid and reduce the pearlite lamellar spacing, giving full play to the fine grain strengthening and precipitation strengthening effects, improving the mechanical property indicators of the product, and while ensuring that the various properties of the bridge steel meet the national standards, significantly reducing the alloy cost.

[0006] However, there is still great room for improvement in the mechanical properties of the Q345q series steel plates prepared by the above technologies. How to prepare a Q345qD steel for railways with good comprehensive performance is the problem to be solved at present. Summary of the Invention

[0007] In view of this, the present invention provides a Q345qD steel for railways and a preparation method thereof. By adjusting the element composition and heat treatment steps, the present invention obtains a Q345qD steel with excellent mechanical properties.

[0008] The present invention achieves the above effects through the following technical solutions.

[0009] A Q345qD steel for railways, the chemical composition by mass percentage is:

[0010] C 0.05% - 0.12%, Mn 1.4% - 1.6%, Si 0.13% - 0.22%, S ≤ 0.003%, P ≤ 0.009%, Als 0.02% - 0.03%, Cr 0.12% - 0.30%, Cu 0.15% - 0.30%, N 0.45% - 0.70%, Ti 0.002% - 0.01%, and the rest is Fe and unavoidable impurities.

[0011] The preparation method of the Q345qD steel for railways described in the present invention includes the following steps:

[0012] (1) Smelting process: The molten steel undergoes desulfurization pretreatment, converter smelting, LF refining, RH vacuum treatment, and then is continuously cast and cooled to obtain a continuous casting billet;

[0013] (2) Heating of the continuous casting billet: The billet is heated in a heating furnace and then descaled;

[0014] (3) Rolling process: The continuously cast billet after heat treatment is hot-rolled to obtain a hot-rolled steel plate; the rolling includes rough rolling and finish rolling;

[0015] (4) Post-rolling heat treatment: The steel plate is subjected to the first tempering treatment and air-cooled to room temperature, then normalized, and then subjected to the second tempering treatment to obtain the Q345qD steel for railways.

[0016] Preferably, the thickness of the continuous casting billet in step (1) is ≥ 250 mm.

[0017] Preferably, the specific method of the heat treatment in step (2) is to first heat the continuous casting billet to 200 - 300 °C, hold for 1 - 1.5 h, then heat it to 700 - 900 °C for the second time, hold for 3 - 3.5 h, and finally heat it to 1300 - 1350 °C for the third time, hold for 2 - 5 h.

[0018] More preferably, the heating rate of the first heating is 5 - 10 °C / min; the heating rate of the second heating is 5 - 10 °C / min; the heating rate of the third heating is 10 - 15 °C / min.

[0019] Preferably, the rolling temperature in step (3) of rough rolling is 1150 - 1300 °C, and single-pass rolling is adopted in the rough rolling with a reduction ratio of ≥ 30%.

[0020] Preferably, the starting rolling temperature in step (3) of finish rolling is 800 - 900 °C, and the finishing rolling temperature is 600 - 750 °C.

[0021] Preferably, multi-pass rolling is adopted in step (3) of finish rolling, the number of rolling passes is 4 - 5 times, and the reduction ratio for each pass is 3 - 15%.

[0022] Preferably, the temperature of the first tempering in step (4) is 200 - 300 °C, and the treatment time is 2 - 5 h; the temperature of the second tempering is 200 - 350 °C, and the treatment time is 2 - 5 h.

[0023] Preferably, the temperature of normalizing in step (4) is 800 - 850 °C, and the treatment time is 30 - 40 min.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides a Q345qD steel and its preparation method. By adjusting the element composition and heat treatment steps, a Q345qD steel with excellent mechanical properties is obtained. The present invention limits the Cu content to 0.15% - 0.30% to improve the corrosion resistance and mechanical properties of the steel; the N content to 0.45% - 0.70% to improve the strength and stability of austenite; the Ti content to 0.002% - 0.01% to improve the strength, toughness and corrosion resistance of the steel; and limits the Cr content to 0.12% - 0.30%, which can improve the hardness and strength of the alloy while avoiding a decrease in the toughness of the alloy due to excessive addition. At the same time, the present invention adopts the methods of rough rolling and finish rolling, adjusts the specific rolling process, and combines the heat treatment method of tempering - normalizing - tempering to improve the comprehensive performance of the alloy. Detailed Embodiments

[0026] The present invention provides a Q345qD steel for railway use, and its chemical composition by mass percentage is as follows:

[0027] C 0.05% - 0.12%, Mn 1.4% - 1.6%, Si 0.13% - 0.22%, S ≤ 0.003%, P ≤ 0.009%, Als 0.02% - 0.03%, Cr 0.12% - 0.30%, Cu 0.15% - 0.30%, N 0.45% - 0.70%, Ti 0.002% - 0.01%, and the rest is Fe and unavoidable impurities.

[0028] The preparation method of the Q345qD steel for railway use comprises the following steps:

[0029] (1) Smelting process: The molten steel undergoes desulfurization pretreatment, converter smelting, LF refining, RH vacuum treatment, and then is continuously cast and cooled to obtain a continuous casting billet with a thickness of ≥250 mm;

[0030] (2) Heating of continuous casting billet: The casting billet is heated in a heating furnace and then descaled using a conventional method;

[0031] The heat treatment method is to first heat the continuous casting billet to 200 - 300 °C and hold for 1 - 1.5 h, then heat it to 700 - 900 °C for the second time and hold for 3 - 3.5 h, and finally heat it to 1300 - 1350 °C for the third time and hold for 2 - 5 h; the heating rate for the first heating is 5 - 10 °C / min; the heating rate for the second heating is 5 - 10 °C / min; the heating rate for the third heating is 10 - 15 °C / min;

[0032] (3) Rolling process: The heated continuous casting billet is hot-rolled (including rough rolling and finish rolling) to obtain a hot-rolled steel plate; the rolling temperature for rough rolling is 1150 - 1300 °C, single-pass rolling is used, and the reduction ratio is ≥30%; the starting rolling temperature for finish rolling is 800 - 900 °C, the finishing rolling temperature is 600 - 750 °C, multi-pass rolling is used, the number of rolling passes is 4 - 5 times, and the reduction ratio for each pass is 3 - 15%; after rough rolling, the surface of the steel plate is subjected to skin pass treatment;

[0033] (4) Post-rolling heat treatment: The steel plate is treated at 200 - 300 °C for 2 - 5 h for the first tempering and air-cooled to room temperature, then treated at 800 - 850 °C for 30 - 40 min for normalizing heat treatment, and then treated at 200 - 350 °C for 2 - 5 h for the second tempering to obtain the Q345qD steel for railways.

[0034] The present invention will be further described below in conjunction with embodiments. In the specific embodiments of the present invention, unless otherwise specified, conventional methods are used for treatment.

[0035] Example 1

[0036] A Q345qD steel for railways, the mass percentages of chemical components are shown in Table 1.

[0037] The preparation method of the Q345qD steel for railways is as follows:

[0038] (1) Smelting process: The molten steel undergoes desulfurization pretreatment, converter smelting, LF refining, RH vacuum treatment, and then is continuously cast and cooled to obtain a continuous casting billet with a thickness of 400 mm;

[0039] (2) Heating of continuous casting billet: The casting billet is heated in a heating furnace and then descaled using a conventional method;

[0040] The method of the heat treatment is to first heat the continuous casting billet to 290°C and hold for 1.2 h, then heat it to 880°C for the second time and hold for 3 h, and finally heat it to 1320°C for the third time and hold for 4.5 h; the heating rate for the first heating is 6°C / min, the heating rate for the second heating is 8°C / min, and the heating rate for the third heating is 11°C / min;

[0041] (3) Rolling process: Rough rolling and finish rolling are carried out on the heat-treated continuous casting billet; the rolling temperature for the rough rolling is 1260°C, single-pass rolling is adopted, and the reduction is 45%, obtaining a slab with a thickness of 220 mm; the starting rolling temperature for the finish rolling is 870°C, the finishing rolling temperature is 720°C, multi-pass rolling is adopted, and the number of rolling passes is 5 times, with the reduction per pass being 5-15%, obtaining a steel plate with a thickness of 110 mm;

[0042] (4) Post-rolling heat treatment: The steel plate is tempered at 270°C for 4 h and then air-cooled to room temperature, then normalized at 820°C for 25 min, and then tempered at 290°C for 4 h for the second time to obtain the Q345qD steel for railways.

[0043] Example 2-3

[0044] A Q345qD steel for railways, the mass percentages of the chemical components are as shown in Table 1, and the preparation method is the same as that in Example 1.

[0045] Example 4

[0046] A Q345qD steel for railways, the mass percentage content of the chemical components is as shown in Table 1,

[0047] The preparation method of the Q345qD steel for railways is as follows:

[0048] (1) Smelting process: The molten steel is subjected to desulfurization pretreatment, converter smelting, LF refining, RH vacuum treatment, and then cast by continuous casting and cooled to obtain a continuous casting billet with a thickness of 400 mm;

[0049] (2) Heating of continuous casting billet: The cast billet is heated in a heating furnace and then descaled, and the descaling is carried out by a conventional method;

[0050] The method of the heat treatment is to first heat the continuous casting billet to 270°C and hold for 1.5 h, then heat it to 850°C for the second time and hold for 3.5 h, and finally heat it to 1310°C for the third time and hold for 4.5 h. The heating rate for the first heating is 6°C / min; the heating rate for the second heating is 8°C / min; the heating rate for the third heating is 11°C / min;

[0051] (3) Rolling process: Rough rolling and finish rolling are carried out on the continuously cast billet after heat treatment; the rolling temperature of the rough rolling is 1260 °C, single-pass rolling is adopted, the reduction is 50%, and a slab with a thickness of 200 mm is obtained; the starting rolling temperature of the finish rolling is 870 °C, the finishing rolling temperature is 720 °C, multi-pass rolling is adopted, the number of rolling passes is 4 times, and the reduction per pass is 7-15%, obtaining a steel plate with a thickness of 110 mm;

[0052] (4) Post-rolling heat treatment: The steel plate is tempered at 270 °C for 4 h and then air-cooled to room temperature, then normalized at 820 °C for 25 min, and then tempered at 270 °C for 4 h for the second time to obtain the Q345qD steel for railways.

[0053] Table 1

[0054]

[0055] Comparative Examples 1-5

[0056] A Q345qD steel for railways, the mass percentages of the chemical components are as shown in Table 2, and the preparation method is the same as that of Example 1.

[0057] Table 2

[0058]

[0059]

[0060] Comparative Example 6

[0061] A Q345qD steel for railways, the chemical components and the preparation method are the same as those of Example 1, except that the continuously cast billet of Comparative Example 6 is directly heated to 1320 °C.

[0062] Comparative Example 7

[0063] A Q345qD steel for railways, the chemical components and the preparation method are the same as those of Example 1, except that the steel plate in step (4) of Comparative Example 7 does not undergo the first tempering.

[0064] Comparative Example 8

[0065] A Q345qD steel for railways, the chemical components and the preparation method are the same as those of Example 1, except that the steel plate in step (4) of Comparative Example 8 does not undergo the second tempering.

[0066] Comparative Example 9

[0067] A Q345qD steel for railways, the chemical components and the preparation method are the same as those of Example 1, except that the steel plate in step (4) of Comparative Example 9 does not undergo tempering.

[0068] Comparative Example 10

[0069] A Q345qD steel for railways, with the chemical composition and preparation method being the same as those in Example 1, except that the rolling process of Comparative Example 10 is as follows:

[0070] The continuously cast billet after heat treatment is subjected to rough rolling and finish rolling; the rolling temperature of the rough rolling is 1260 °C, single-pass rolling is adopted, and the reduction is 50%, obtaining a slab with a thickness of 200 mm; the starting rolling temperature of the finish rolling is 870 °C, and the finishing rolling temperature is 720 °C. Multi-pass rolling is adopted, with the number of rolling passes being 3 times, and the reduction per pass being 15 - 25%, obtaining a steel plate with a thickness of 110 mm.

[0071] The Q345qD steels prepared in Examples 1 - 4 and Comparative Example 9 were subjected to performance testing according to the methods of GB / T714 - 2015 (yield strength, tensile strength, elongation after fracture, impact absorption energy) and the 72-hour cyclic immersion corrosion test (relative corrosion rate) of TB / T2375. The results are shown in Table 3.

[0072] Table 3

[0073]

[0074]

[0075] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A Q345qD steel for railways, characterized in that, The chemical composition by mass percentage is as follows: C 0.05% - 0.12%, Mn 1.4% - 1.6%, Si 0.13% - 0.22%, S ≤ 0.003%, P ≤ 0.009%, Als 0.02% - 0.03%, Cr 0.12% - 0.30%, Cu 0.15% - 0.30%, N 0.45% - 0.70%, Ti 0.002% - 0.01%, and the balance is Fe and inevitable impurities.

2. The preparation method of the Q345qD steel for railways according to claim 1, characterized in that, It includes the following steps: (1) Smelting process: The molten steel undergoes desulfurization pretreatment, converter smelting, LF refining, RH vacuum treatment, and then is continuously cast and cooled to obtain a continuous casting billet. (2) Heating of the continuous casting billet: The billet is heated in a heating furnace and then descaled. (3) Rolling process: The heat-treated continuous casting billet is hot-rolled to obtain a hot-rolled steel plate; the rolling includes rough rolling and finish rolling. (4) Post-rolling heat treatment: The hot-rolled steel plate is subjected to the first tempering treatment and air-cooled to room temperature, then normalized, and then subjected to the second tempering treatment to obtain the Q345qD steel for railways.

3. A preparation method of the Q345qD steel for railways according to claim 2, characterized in that, The thickness of the continuous casting billet in step (1) is ≥ 250 mm.

4. A preparation method of the Q345qD steel for railways according to claim 2, characterized in that, The specific method of the heating treatment in step (2) is to first heat the continuous casting billet to 200 - 300 °C, hold for 1 - 1.5 h, then heat it to 700 - 900 °C for the second time, hold for 3 - 3.5 h, and finally heat it to 1300 - 1350 °C for the third time, hold for 2 - 5 h.

5. A preparation method of the Q345qD steel for railways according to claim 4, characterized in that, The heating rate of the first heating is 5 - 10 °C / min; the heating rate of the second heating is 5 - 10 °C / min; the heating rate of the third heating is 10 - 15 °C / min.

6. A preparation method of the Q345qD steel for railways according to claim 2, characterized in that, The rolling temperature of the rough rolling in step (3) is 1150 - 1300 °C, the rough rolling adopts single-pass rolling, and the reduction ratio is ≥ 30%.

7. A preparation method of the Q345qD steel for railways according to claim 2, characterized in that, The starting rolling temperature of the finish rolling in step (3) is 800 - 900 °C, and the final rolling temperature is 600 - 750 °C.

8. A preparation method of Q345qD steel for railways according to claim 2, characterized in that, The finish rolling in step (3) adopts multi-pass rolling, the number of rolling passes is 4 - 5 times, and the reduction ratio per pass is 3 - 15%.

9. A preparation method of the Q345qD steel for railways according to claim 2, characterized in that, The temperature of the first tempering in step (4) is 200 - 300 °C, and the treatment time is 2 - 5 h; the temperature of the second tempering is 200 - 350 °C, and the treatment time is 2 - 5 h.

10. A preparation method of Q345qD steel for railways according to claim 2, characterized in that, The temperature of the normalizing in step (4) is 800 - 850 °C, and the treatment time is 30 - 40 min.

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