A method for producing thin-gauge Q355B-DX silicon controlled rectifier steel

Abstract

This invention relates to the field of steel rolling technology, specifically disclosing a method for producing thin-gauge Q355B-DX steel with controlled silicon content. The alloy composition is configured as follows: the standard composition of the billet by mass percentage is C≤0.24%, Si≤0.55%, Mn≤1.60%, P≤0.035%, S≤0.035%, Ti≤0.20%, Als≥0.010%, N≤0.012%. Billet heating is achieved using direct heating charging, with the billet placed in an insulation pit for slow cooling after finishing. Rolling parameters are set according to different billet thicknesses, including the finishing mill inlet temperature, final rolling temperature, and coiling temperature. The number of descaling passes in the roughing mill is determined, and the rolling rhythm of the hot rolls is designed. The steel produced by this invention has high strength and high toughness, good weldability, and high compositional stability, making the steel performance more stable and reliable, which helps ensure consistent product quality. It also improves product surface quality and reduces cost waste caused by defective products.

Description

Technical Field

[0001] This invention relates to the field of steel rolling technology, specifically to a method for producing thin-gauge Q355B-DX steel with silicon controlled oxidation. Background Technology

[0002] Q355B-DX steel is a widely used and representative low-alloy high-strength structural steel. Positioned as a medium-strength structural steel with good comprehensive properties (including strength, plasticity, weldability, and toughness), it serves as an important bridge between ordinary steel and higher-strength special steels, and is widely used in construction engineering, machinery manufacturing, shipbuilding, and other fields. The existing smelting processes for Q355B-DX steel mainly include:

[0003] 1. Ingredient design technology:

[0004] The composition and heating conditions are as follows: In terms of composition, the silicon content (0.029%) exceeds the target value (≤0.02%), and the silicon content is close to the upper limit of control. In terms of heating, the furnace temperature of the first heating and soaking sections is around 1290℃. The furnace time for the first 3 rolls is 230-240 minutes, and the furnace time for the 12 rolls after the F2 roll change is about 280-300 minutes.

[0005] 2. Production process technology:

[0006] The existing rolling process uses a hot coil box. The FET temperature of the first 2.0mm coil is too low, at 1000-1020℃. In addition, the F2 reduction rate of the 2.3mm Q355B hot roll material in the front is relatively large, which leads to severe resonance. As a result, the first 3 coils of Q355B-DX with 2.0mm specification have continuous operation side vibration marks.

[0007] 3. Limiting specifications, finishing rolling reduction, speed and rolling force: The first coil of 2.0*1421mm F2 has a reduction of 7.95mm, a reduction rate of 52.7%, and severe resonance.

[0008] Existing rolling processes result in unsatisfactory control of silicon content in Q355B-DX steel, leading to poor surface quality and affecting the steel's strength, toughness, and weldability. Therefore, it is necessary to explore a production method for thin-gauge Q355B-DX steel with controlled silicon content to address the issues of poor compositional stability and surface quality in existing Q355B-DX steel products. Summary of the Invention

[0009] To address the problems existing in the prior art, the purpose of this invention is to provide a method for producing thin-gauge Q355B-DX silicon controlled rectifier steel.

[0010] The technical solution adopted by this invention to solve its technical problem is: a method for producing thin-gauge Q355B-DX silicon controlled refractor steel, comprising the following steps:

[0011] S1. Alloy composition configuration: The standard composition of the billet by mass percentage is C≤0.24%, Si≤0.55%, Mn≤1.60%, P≤0.035%, S≤0.035%, Ti≤0.20%, Als≥0.010%, N≤0.012%;

[0012] S2. Steel billet heating: Direct heating is adopted, and the billet is placed in an insulation pit for slow cooling after it comes off the line;

[0013] S3. Rolling parameters: Set the finishing mill inlet temperature, finishing mill temperature and coiling temperature for steel billets according to different thickness specifications, determine the number of descaling passes in roughing mill, and design the rolling rhythm of hot rolls.

[0014] Specifically, the internal control standard for the mass percentage of the chemical composition of the steel billet in step S1 is: C: 0.14-0.18%, Si≤0.03%, Mn: 0.50-0.70%, P≤0.010%, S≤0.015%, Ti: 0.035-0.050%, Als: 0.015-0.045%, N≤0.0060%.

[0015] Specifically, in step S2, when the thickness of the steel billet is 1.5-8.0mm and the thickness of the steel billet is 1.5-3.6mm, the preheating section temperature of the heating furnace is 950±20℃, the third heating section temperature is 1080±20℃, the second heating section temperature is 1180±20℃, the first heating section temperature is 1290±20℃, the soaking section temperature is 1280±20℃, and the target tapping temperature is 1250±20℃.

[0016] When the thickness of the steel billet is 3.61-8.0mm, the preheating section temperature of the heating furnace is 920±30℃, the third heating section temperature is 1040±30℃, the second heating section temperature is 1150±30℃, the first heating section temperature is 1260±30℃, the soaking section temperature is 1240±30℃, and the target tapping temperature is 1220±20℃.

[0017] Specifically, the furnace time for cold billets is 160-240 minutes, with a soaking time of ≥24 minutes; the furnace time for hot billets is 120-240 minutes, with a soaking time of ≥20 minutes.

[0018] Specifically, in step S3, when the thickness of the steel billet is 1.5-3.6mm, the finishing rolling entry temperature is 1040±20℃, the final rolling temperature is 860±20℃, the coiling temperature is 640±20℃, and the cooling strategy adopts ultra-fast sparse cooling.

[0019] When the thickness of the steel billet is 3.61-8.0mm, the finishing rolling inlet temperature is 1010±20℃, the final rolling temperature is 840±20℃, the coiling temperature is 630±20℃, and the cooling strategy adopts ultra-fast sparse cooling.

[0020] Specifically, in step S3, the descaling passes in the rough rolling process are 3+3, with R1 and R2 each guaranteed at least one pass, and 1+5 guaranteed at least 3 passes for descaling. Before finishing rolling, the descaling box with a thickness ≤3mm uses one set, and with a thickness >3mm, it uses two sets.

[0021] Specifically, in step S3, the rolling rhythm of the hot-rolled materials is 240s for the first 5 hot-rolled materials and 200s for the last 5 hot-rolled materials. F1_x0010_F4 anti-stripping water is used throughout the process to track the iron oxide scale of the finished product in a timely manner. After production, samples are immediately taken for pickling and inspection. The flatness is also inspected and sampled for pickling and inspection. The morphology of the roll surface and plate surface is tracked in real time.

[0022] Specifically, there are 2-3 gaps between each heat before the rolling process. The vertical roll beam of the finishing mill is polished and the rolls are quickly changed. The surface elevation of the F1 roll of the finishing mill is ≥ +5mm.

[0023] The present invention has the following beneficial effects:

[0024] The present invention discloses a method for producing thin-gauge Q355B-DX steel with silicon control. The produced steel has high strength and high toughness. By adding trace amounts of alloying elements such as manganese and silicon, the strength of the steel can be increased by more than 30% compared with ordinary carbon steel, while maintaining good toughness, which can better meet the usage requirements of engineering structures such as buildings and bridges.

[0025] The present invention discloses a method for producing thin-gauge Q355B-DX steel with silicon controlled rectifier. The produced steel has good weldability. Thin-gauge Q355B-DX steel generally has good weldability, is easy to process and manufacture, and is widely used in modern construction, urban pipeline networks, new energy photovoltaic brackets and other fields. It can reduce welding defects and improve project quality and construction efficiency.

[0026] The present invention relates to a production method for thin-gauge Q355B-DX steel, which produces steel with high compositional stability. By real-time monitoring and fine-tuning of alloying elements, the compositional stability is improved to 99.5%, making the steel performance more stable and reliable, and thus helping to ensure the consistency of product quality.

[0027] The present invention relates to a production method for thin-gauge Q355B-DX steel, which improves product surface quality and reduces cost waste caused by defective products by standardizing the plate inspection mechanism and modifying spare parts. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be described clearly, completely, and in further detail below. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0029] 1. Process parameters

[0030] 1.1 Composition standards are shown in Table 1.

[0031] Table 1. Chemical composition of steel billet (wt%) by mass

[0032]

[0033] 1.2 Heating Process

[0034] This steel grade uses direct heating charging, and directly heated billets must undergo surface inspection. First and last billets, as well as billets not directly heated, must undergo cold inspection; any defects found must be cleaned. Billets leaving the production line must be placed in an insulated pit for slow cooling. The required heating temperatures for the billets are shown in Table 2.

[0035] Table 2 Temperature requirements for billet heating (°C)

[0036]

[0037] If the furnace time exceeds 240 minutes, notify technical personnel to develop a solution on-site. The residual oxygen content inside the furnace should be controlled below 0.5%.

[0038] 1.3 Rolling process parameters

[0039] The rolling temperature of the steel billet is set according to different thickness specifications, as shown in Table 3 below.

[0040] Table 3 Temperature requirements for billet rolling (°C)

[0041]

[0042] (1) The descaling passes of rough rolling shall be 3+3. R1 and R2 shall each be guaranteed at least once, and 1+5 shall be guaranteed at least 3 descaling passes. Before finishing rolling, the descaling box with a thickness ≤3mm shall use one set, and the thickness >3mm shall use two sets.

[0043] (2) The rolling rhythm of the hot-rolled materials during the rolling process is 240s for the first 5 hot-rolled materials and 200s for the last 5 hot-rolled materials. F1_x0010_F4 anti-stripping water is used throughout the process. The condition of the finished product's iron oxide scale is monitored in a timely manner. Immediately after production, samples are taken for pickling and inspection. The surface finish is also inspected and sampled for pickling. Iron oxide scale must be strictly controlled, and any defects must be reported immediately. A dedicated production person is assigned to follow up and compile a summary, tracking the morphology of the roll surface and plate surface in real time.

[0044] (3) Before the Q355-DX rolling process, there should be 2-3 gaps between each heat. The vertical roll beam of the finishing mill should be polished and the rolls should be changed quickly. The surface elevation of the F1 roll of the finishing mill should be ≥ +5mm.

[0045] Example 1

[0046] A method for producing thin-gauge Q355B-DX1 silicon controlled rectifier steel includes the following steps:

[0047] 1. Alloy composition configuration: The chemical composition of the steel billet by mass percentage is C: 0.18%, Si: 0.03%, Mn: 0.70%, P: 0.010%, S: 0.015%, Ti: 0.050%, Als: 0.045%, N: 0.0060%.

[0048] 2. Billet Heating: Direct heating is adopted, and the billets are placed in an insulated pit for slow cooling after being removed from the furnace. The billet thickness is 8.0mm. The preheating section temperature of the heating furnace is 950℃, the third heating section temperature is 1070℃, the second heating section temperature is 1180℃, the first heating section temperature is 1290℃, the soaking section temperature is 1270℃, and the target tapping temperature is 1240℃. The billet is placed in the furnace as a cooled billet for 240 minutes, and the soaking section residence time is 24 minutes.

[0049] 3. Rolling parameters: When the thickness of the billet is 8.0mm, the finishing mill inlet temperature is 1030℃, the finishing mill temperature is 860℃, the coiling temperature is 650℃, and the cooling strategy adopts ultra-fast sparse cooling.

[0050] The roughing mill uses a 3+3 descaling pass system, with at least one pass each for R1 and R2, and at least three passes for 1+5. Before finishing milling, one set of descaling boxes is used for thicknesses ≤3mm, and two sets are used for thicknesses >3mm. The rolling rhythm for the first five hot rolls is 240s, and for the next five hot rolls, it is 200s. F1_x0010_F4 anti-stripping water is used throughout the process, and the condition of the finished product's iron oxide scale is monitored closely. Immediately after production, samples are taken for pickling and inspection. Leveling is also inspected and samples are taken for pickling. The morphology of the roll surface and plate surface is monitored in real time. For Q355B-DX1, there are 2-3 gaps between each heat before the rolling cycle. During finishing milling, the vertical roll beams are inspected for grinding, and rolls are quickly changed. The surface elevation of the F1 rolls on the finishing mill is ≥+5mm.

[0051] Example 2

[0052] A method for producing thin-gauge Q355B-DX2 silicon controlled rectifier steel includes the following steps:

[0053] 1. Alloy composition configuration: The chemical composition of the steel billet by mass percentage is C: 0.16%, Si: 0.02%, Mn: 0.60%, P: 0.010%, S: 0.008%, Ti: 0.040%, Als: 0.020%, N: 0.0045%.

[0054] 2. Billet heating: Direct heating is adopted, and the billet is placed in the heat preservation pit for slow cooling after it comes off the line; when the thickness of the billet is 3.6mm, the temperature of the preheating section of the heating furnace is 950℃, the temperature of the third heating section is 1080℃, the temperature of the second heating section is 1180℃, the temperature of the first heating section is 1290℃, the temperature of the soaking section is 1280℃, and the target tapping temperature is 1250℃; the billet is put into the furnace as a hot billet and the time in the furnace is 200 minutes, and the residence time in the soaking section is 20 minutes.

[0055] 3. Rolling parameters: When the thickness of the steel billet is 3.6mm, the finishing mill inlet temperature is 1040℃, the finishing mill temperature is 860℃, the coiling temperature is 640℃, and the cooling strategy adopts ultra-fast sparse cooling.

[0056] The roughing mill uses a 3+3 descaling pass system, with at least one pass each for R1 and R2, and at least three passes for 1+5. Before finishing milling, one set of descaling boxes is used for thicknesses ≤3mm, and two sets are used for thicknesses >3mm. The rolling rhythm for the first five hot rolls is 240s, and for the next five hot rolls, it is 200s. F1_x0010_F4 anti-stripping water is used throughout the process, and the condition of the finished product's iron oxide scale is monitored closely. Immediately after production, samples are taken for pickling and inspection. Leveling is also inspected and samples are taken for pickling. The morphology of the roll surface and plate surface is monitored in real time. For Q355B-DX1, there are 2-3 gaps between each heat before the rolling cycle. During finishing milling, the vertical roll beams are inspected for grinding, and rolls are quickly changed. The surface elevation of the F1 rolls on the finishing mill is ≥+5mm.

[0057] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

[0058] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A method for producing thin-gauge Q355B-DX steel with silicon controlled rectifier, characterized in that, Includes the following steps: S1. Alloy composition configuration: The standard composition of the billet by mass percentage is C≤0.24%, Si≤0.55%, Mn≤1.60%, P≤0.035%, S≤0.035%, Ti≤0.20%, Als≥0.010%, N≤0.012%; S2. Steel billet heating: Direct heating is adopted, and the billet is placed in an insulation pit for slow cooling after it comes off the line; S3. Rolling parameters: Set the finishing mill inlet temperature, finishing mill temperature and coiling temperature for steel billets according to different thickness specifications, determine the number of descaling passes in roughing mill, and design the rolling rhythm of hot rolls.

2. The method for producing thin-gauge Q355B-DX steel according to claim 1, characterized in that, The internal control standard for the mass percentage of chemical composition of the steel billet in step S1 is as follows: C: 0.14-0.18%, Si≤0.03%, Mn: 0.50-0.70%, P≤0.010%, S≤0.015%, Ti: 0.035-0.050%, Als: 0.015-0.045%, N≤0.0060%.

3. The method for producing thin-gauge Q355B-DX steel according to claim 1, characterized in that, In step S2, when the thickness of the steel billet is 1.5-8.0 mm, and the thickness of the steel billet is 1.5-3.6 mm, the preheating section temperature of the heating furnace is 950±20℃, the third heating section temperature is 1080±20℃, the second heating section temperature is 1180±20℃, the first heating section temperature is 1290±20℃, the soaking section temperature is 1280±20℃, and the target tapping temperature is 1250±20℃. When the thickness of the steel billet is 3.61-8.0mm, the preheating section temperature of the heating furnace is 920±30℃, the third heating section temperature is 1040±30℃, the second heating section temperature is 1150±30℃, the first heating section temperature is 1260±30℃, the soaking section temperature is 1240±30℃, and the target tapping temperature is 1220±20℃.

4. The method for producing thin-gauge Q355B-DX steel according to claim 3, characterized in that, The furnace time for steel billets entering the furnace as cooled billets is 160-240 minutes, with a soaking time of ≥24 minutes. The furnace time for steel billets entering the furnace as hot billets is 120-240 minutes, with a soaking time of ≥20 minutes.

5. The method for producing thin-gauge Q355B-DX steel according to claim 3, characterized in that, In step S3, when the thickness of the steel billet is 1.5-3.6mm, the finishing rolling entry temperature is 1040±20℃, the final rolling temperature is 860±20℃, the coiling temperature is 640±20℃, and the cooling strategy adopts ultra-fast sparse cooling. When the thickness of the steel billet is 3.61-8.0mm, the finishing rolling inlet temperature is 1010±20℃, the final rolling temperature is 840±20℃, the coiling temperature is 630±20℃, and the cooling strategy adopts ultra-fast sparse cooling.

6. The method for producing thin-gauge Q355B-DX steel according to claim 1, characterized in that, In step S3, the roughing descaling passes adopt a 3+3 roughing descaling pass, with R1 and R2 each guaranteed at least one pass, and 1+5 guaranteed at least 3 descaling passes. Before finishing rolling, the descaling box thickness is ≤3mm and uses one set, and the thickness is >3mm and uses two sets.

7. The method for producing thin-gauge Q355B-DX steel according to claim 1, characterized in that, In step S3, the rolling rhythm of the hot-rolled materials is 240s for the first 5 hot-rolled materials and 200s for the last 5 hot-rolled materials. F1_x0010_F4 anti-stripping water is used throughout the process to track the iron oxide scale of the finished product in a timely manner. After production, samples are immediately taken for pickling and inspection. The flatness is also inspected and sampled for pickling and inspection. The morphology of the roll surface and plate surface is tracked in real time.

8. The method for producing thin-gauge Q355B-DX steel according to claim 7, characterized in that, Before each rolling stroke, there should be 2-3 gaps between each heat. During the finishing mill, the vertical roll beams should be polished and the rolls should be changed quickly. The surface elevation of the F1 roll of the finishing mill should be ≥ +5mm.

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