A method for producing high surface quality wear-resistant steel based on extreme thermal charging process

Abstract

This invention belongs to the field of wear-resistant steel production technology and discloses a production method for high-surface-quality wear-resistant steel based on an extreme hot charging process. The production process includes: steelmaking → continuous casting → hot charging → heating → rough rolling → finish rolling → laminar flow cooling → coiling. The hot charging process has three different procedures, and the appropriate hot charging procedure is selected according to the actual temperature of the cast billet, thereby precisely controlling the temperature of the billet entering the heating furnace. This, combined with the matching heating, rolling, and cooling processes, achieves extreme hot charging of wear-resistant steel without increasing any equipment or production costs. It fully utilizes the residual heat of the continuously cast billet, achieving good energy-saving effects, while ensuring that the product is free of surface defects such as peeling and cracks, making it suitable for widespread application.

Description

Technical Field

[0001] This invention belongs to the field of wear-resistant steel production technology, specifically relating to a method for producing high surface quality wear-resistant steel based on an extreme thermal charging process. Background Technology

[0002] Statistics show that a large amount of waste heat is generated during the steel-to-finished product production process, with furnace waste heat accounting for more than 40% of the total waste heat energy in the furnace. Increasing the proportion of hot charging and direct charging of slabs can effectively reduce the release of waste heat in the heating furnace. Therefore, accelerating the application of energy-saving and emission-reduction technologies for hot charging and direct charging of slabs is key to reducing carbon emissions from hot rolling processes. Steel companies are actively promoting hot charging and direct charging processes for various steel grades, and have basically achieved hot charging and direct charging for all steel grades, with the highest slab entry temperature reaching over 800℃. However, with the increase in hot charging temperature, hot-charged wear-resistant steel slabs face the risk of surface cracking and peeling during rolling, seriously affecting rolling efficiency and the yield of the original product, thus hindering the promotion of hot charging and direct charging for related products.

[0003] Shougang Group has developed a complete set of technologies for online pretreatment equipment, processes, and control systems for hot-rolled slab surface treatment within the fan-shaped section of the casting machine to address red-charging cracking in hot-rolled slabs. By designing the optimal arrangement of high-flow-rate nozzles, they achieved crack-free red-charging of slabs to 650℃. However, this required extensive modifications to the on-site equipment and significant financial investment. Danieli suggested that slabs, small billets, and large billets after continuous casting be placed in a quenching box to reduce the surface temperature of the slabs and decrease their susceptibility to red-charging cracks. SSAB also recommended surface quenching of slabs before red-charging to ensure finer surface grains and reduce the formation of red-charging cracks. These technological measures, which address cracking by reducing the surface temperature of the slab through surface quenching, would significantly increase the energy consumption of subsequent heating furnaces.

[0004] Given the current technological level, and considering the low high-temperature plasticity of wear-resistant steel within the 600-900℃ range, it is generally introduced into the heating furnace at a lower temperature. To maintain this temperature, the high-temperature continuously cast slab is often slowly cooled in a holding pit for 10-20 hours after being removed from the production line, and then introduced into the heating furnace at a lower temperature (300-400℃) for an extended period of heating to ensure stable rolling. This method has low production efficiency and poor economic performance. Therefore, how to balance the direct loading of wear-resistant steel with high surface quality is one of the key technical challenges that urgently needs to be addressed in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing a production method for high surface quality wear-resistant steel based on an extreme hot charging process. Different hot charging procedures are adopted according to the actual temperature of the billet, the furnace temperature of the billet is precisely controlled, and the heating, rolling and cooling processes are matched. While achieving extreme hot charging of wear-resistant steel, the method ensures high surface quality of the product without surface defects such as peeling and cracks.

[0006] To solve the technical problem of this invention, this invention provides a method for producing high surface quality wear-resistant steel based on an extreme hot charging process, the process of which includes: steelmaking → continuous casting → hot charging → heating → rough rolling → finish rolling → laminar flow cooling → coiling.

[0007] In the above scheme, when the surface temperature T1 of the slab exiting the continuous casting machine meets 850≤T1≤900℃, a roller conveyor with a heat insulation cover is used to directly feed the slab to the heating furnace. The roller conveyor speed is 1.0~1.2m / s, the transmission interval is 30~40min, and the cooling rate is 2.0~2.6℃ / min, so that the surface temperature T2 of the slab entering the heating furnace meets 780≤T2≤830℃.

[0008] In the above scheme, when the surface temperature T1 of the slab exiting the continuous casting machine meets 800≤T1<850℃, a roller conveyor with a heat insulation cover is used to directly feed the slab to the heating furnace. The roller conveyor speed is 0.8~1.0m / s, the transmission interval is 50~70min, and the cooling rate is 3.0~4.1℃ / min, so that the surface temperature T2 of the slab entering the heating furnace meets 600≤T2<730℃.

[0009] In the above scheme, when the surface temperature T1 of the slab exiting the continuous casting machine meets 700≤T1<800℃, the slab is removed from the line and slowly cooled in the heat preservation pit before being sent to the heating furnace. The heat preservation time is 2~3h, and the cooling rate is 1.6~2.5℃ / s, so that the surface temperature T2 of the slab entering the heating furnace meets 500≤T2<600℃.

[0010] In the above scheme, the heating includes a preheating section, a heating section, and a homogenizing section; the preheating section is a non-heating section, with no mixed gas flow input, and preheating of the slab is achieved through thermal radiation from the downstream section; the heating section includes a first heating section and a second heating section, with the temperature of the first heating section being 1000-1200℃ and the temperature of the second heating section being 1200-1240℃; the temperature of the homogenizing section is 1200-1240℃.

[0011] Furthermore, when the surface temperature T2 of the slab entering the heating furnace satisfies 780≤T2≤830℃, the temperature of the first heating section is 1050~1200℃; when the surface temperature T2 of the slab entering the heating furnace satisfies 600≤T2<730℃, the temperature of the first heating section is 1000~1150℃; when the surface temperature T2 of the slab entering the heating furnace satisfies 500≤T2<600℃, the temperature of the first heating section is 1050~1150℃.

[0012] Furthermore, when the surface temperature T2 of the slab entering the heating furnace satisfies 780≤T2≤830℃, the preheating period is 30-40 min; the first heating period is 30-40 min; the second heating period is 30-40 min; the total heating period is 70-80 min; and the soaking period is 20-30 min.

[0013] Furthermore, when the surface temperature T2 of the slab entering the heating furnace satisfies 600≤T2<730℃, the preheating period is 40~50min; the first heating period is 35~45min; the second heating period is 45~50min; the total heating period is 80~90min; and the soaking period is 30~40min.

[0014] Furthermore, when the surface temperature T2 of the slab entering the heating furnace satisfies 500≤T2<600℃, the preheating period is 45~60min; the first heating period is 45~50min; the second heating period is 45~50min; the total heating period is 85~100min; and the soaking period is 30~40min.

[0015] In the above scheme, the roughing is carried out sequentially on the R1 mill and the R2 mill. R1 is a single-pass rolling mill and R2 is a five-pass rolling mill. The exit temperature of the roughing mill is 1030-1070℃. The intermediate strip after roughing is fed to the finishing mill via a roller conveyor with a heat insulation cover.

[0016] Furthermore, the R1 and R2 mills are descaling. The R2 mill uses a special pass for descaling. When the roughing mill exit temperature is >1050℃, the fourth pass of the R2 mill is also descaling.

[0017] In the above scheme, the finishing rolling adopts 7-stand continuous rolling, the finishing rolling speed is 3-6m / s, and the reduction rate distribution of each pass in the continuous rolling process of F1 to F7 is 40-50%, 30-40%, 30-35%, 20-25%, 15-20%, 10-15%, and 5-10% respectively, and the final rolling temperature is 860-880℃.

[0018] Furthermore, to ensure the stability of finishing rolling, a lubrication process is adopted to reduce the rolling pressure of each pass in the finishing rolling process; during the strip threading process, the lubricating oil of each stand is turned off, and the roll gap water is turned on after a delay of 1 to 2 seconds to prevent the strip head from hitting the roll and forming roll marks. After the rolling is stable, the rolling oil of each stand is turned on.

[0019] In the above scheme, the laminar flow cooling adopts front-end cooling.

[0020] In the above scheme, the winding temperature is 650-700℃.

[0021] In the above scheme, the chemical composition of the wear-resistant steel by mass percentage is as follows: C: 0.15-0.23%, Si: 0.10-0.65%, Mn: 1.30-1.80%, P: ≤0.015%, S: ≤0.003%, Cr: 0.15-0.55%, Mo: 0.01-0.25%, Ti: 0.010-0.025%, B: 0.001-0.0025%, with the remainder being iron and unavoidable inclusions.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1) Based on the high-temperature thermoplasticity curve of wear-resistant steel, this invention designs different hot charging programs according to different billet temperatures, accurately controls the slab entry temperature into the furnace, and designs matching heating, rolling and cooling processes. Without increasing any equipment and production costs, it achieves the ultimate hot charging of wear-resistant steel, makes full use of the residual heat of the continuous casting billet, achieves good energy-saving effect, and avoids surface defects such as peeling and cracks on the product surface.

[0024] 2) The method of this invention is highly versatile, and the control concept can be basically referenced for direct loading and extreme hot delivery loading of other steel grades. The control method is flexible and efficient, with low cost, and can be widely promoted and applied. Attached Figure Description

[0025] Figure 1 Macroscopic morphology of surface peeling defects in wear-resistant steel produced by conventional methods. Detailed Implementation

[0026] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0027] Examples 1-10

[0028] The chemical composition and weight percentage of the wear-resistant steel in Examples 1-10 are shown in Table 1.

[0029] Table 1 Chemical composition of wear-resistant steel in various embodiments of the present invention

[0030]

[0031] The production method of wear-resistant steel in Examples 1-10 includes the following steps:

[0032] 1) Steelmaking: Smelting molten steel to obtain molten steel with the target composition;

[0033] 2) Continuous casting: Molten steel is continuously cast to form slabs;

[0034] 3) Hot charging: Select the appropriate hot charging program based on the surface temperature T1 of the slab exiting the continuous casting machine;

[0035] ① When 850≤T1≤900℃, a roller conveyor with a heat insulation cover is used to directly feed the slab into the heating furnace. The roller conveyor speed is 1.0~1.2m / s, the transmission time is 30~40min, and the cooling rate is 2.0~2.6℃ / min, so that the surface temperature T2 of the slab entering the heating furnace meets 780≤T2≤830℃;

[0036] ② When 800≤T1<850℃, a roller conveyor with a heat insulation cover is used to directly feed the slab into the heating furnace. The roller conveyor speed is 0.8~1.0m / s, the transmission time is 50~70min, and the cooling rate is 3.0~4.1℃ / min, so that the surface temperature T2 of the slab entering the heating furnace meets 600≤T2<730℃;

[0037] ③ When 700≤T1<800℃, the slab is removed from the production line and placed in the heat preservation pit for slow cooling before being sent to the heating furnace. The heat preservation time is 2~3h, and the cooling rate is 1.6~2.5℃ / s, so that the surface temperature T2 of the slab entering the heating furnace meets 500≤T2<600℃.

[0038] 4) Heating: Slab heating includes a preheating section, a heating section, and a soaking section; the preheating section is a non-heating section; the heating section includes a first heating section and a second heating section, with the temperature of the first heating section being 1000–1200℃ and the temperature of the second heating section being 1200–1240℃; the temperature of the soaking section is 1200–1240℃; the temperature of the first heating section and the time for each section are further determined based on the surface temperature T2 of the slab entering the heating furnace.

[0039] ① When 780≤T2≤830℃, the preheating time is 30~40min; the temperature of the first heating section is 1050~1200℃, the first heating time is 30~40min, the second heating time is 30~40min, the total heating time is 70~80min; the soaking time is 20~30min.

[0040] ② When 600≤T2<730℃, the preheating time is 40~50min; the temperature of the first heating section is 1000~1150℃, the first heating time is 35~45min, the second heating time is 45~50min, and the total heating time is 80~90min; the soaking time is 30~40min.

[0041] ③ When 500≤T2<600℃, the preheating time is 45~60min; the temperature of the first heating section is 1050~1150℃, the first heating time is 45~50min, the second heating time is 45~50min, the total heating time is 85~100min; the soaking time is 30~40min.

[0042] 5) Rough rolling: Rough rolling is carried out sequentially on R1 and R2 mills. R1 mill has 1 pass and R2 mill has 5 passes. Descaling is started on R1 mill and descaling is done on R2 mill with an extra pass. The exit temperature of rough rolling is 1030-1070℃. When the exit temperature of rough rolling is >1050℃, descaling is also started on the 4th pass of R2 mill. The intermediate strip after rough rolling is sent to finish rolling via a roller conveyor with heat insulation cover.

[0043] 6) Finishing rolling: 7-stand continuous rolling is adopted, and the finishing rolling speed is 3-6 m / s. During the continuous rolling process of F1 to F7, the reduction rate of each pass is distributed as follows: 40-50%, 30-40%, 30-35%, 20-25%, 15-20%, 10-15%, and 5-10%, respectively. The final rolling temperature is 860-880℃.

[0044] 7) Laminar flow cooling: Front-end cooling is used;

[0045] 8) Winding: The winding temperature is 650-700℃.

[0046] Table 2. Thermal charging parameters of various embodiments of the present invention

[0047]

[0048]

[0049] Table 3 Heating parameters of various embodiments of the present invention

[0050]

[0051] Table 4. Roughing, final rolling, cooling, and coiling parameters of various embodiments of the present invention.

[0052]

[0053] As can be seen from the above embodiments, by adopting the production method of the present invention, different hot charging procedures are adopted according to the actual temperature of the billet, the furnace temperature of the billet is precisely controlled, and the heating, rolling and cooling processes are matched. While achieving the ultimate hot charging of wear-resistant steel, the product is guaranteed to be free of surface defects such as peeling and cracks.

[0054] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for producing high surface quality wear-resistant steel based on an extreme thermal charging process, the process comprising: Steelmaking → Continuous casting → Hot charging → Heating → Rough rolling → Finish rolling → Laminar flow cooling → Coiling, characterized in that the appropriate hot charging program is selected according to the surface temperature T1 of the slab exiting the continuous casting machine: 1) When 850≤T1≤900 ℃, the slab is directly fed into the heating furnace using a roller conveyor with a heat insulation cover. The roller conveyor speed is 1.0~1.2 m / s, the conveying time is 30~40 min, and the cooling rate is 2.0~2.6 ℃ / min, so that the surface temperature T2 of the slab entering the heating furnace meets 780≤T2≤830 ℃; 2) When 800≤T1<850 ℃, the slab is directly fed to the heating furnace using a roller conveyor with a heat insulation cover. The roller conveyor speed is 0.8~1.0 m / s, the conveying time is 50~70 min, and the cooling rate is 3.0~4.1 ℃ / min, so that the surface temperature T2 of the slab entering the heating furnace meets 600≤T2<730 ℃; 3) When 700≤T1<800 ℃, the slab is removed from the production line and placed in the heat preservation pit for slow cooling before being sent to the heating furnace. The heat preservation time is 2~3 h and the cooling rate is 1.6~2.5 ℃ / min, so that the surface temperature T2 of the slab entering the heating furnace meets 500≤T2<600 ℃. The chemical composition of the wear-resistant steel, by mass percentage, is as follows: C: 0.15~0.23%, Si: 0.10~0.65%, Mn: 1.30~1.80%, P: ≤0.015%, S: ≤0.003%, Cr: 0.15~0.55%, Mo: 0.01~0.25%, Ti: 0.010~0.025%, B: 0.001~0.0025%, with the remainder being iron and unavoidable inclusions.

2. The method for producing high surface quality wear-resistant steel based on the ultimate thermal charging process according to claim 1, characterized in that, The heating process includes a preheating section, a heating section, and a heat equalization section; the preheating section is a non-heating section; the heating section includes a first heating section and a second heating section, the temperature of the first heating section is 1000~1200 ℃, the temperature of the second heating section is 1200~1240 ℃; and the temperature of the heat equalization section is 1200~1240 ℃.

3. The method for producing high surface quality wear-resistant steel based on the ultimate thermal charging process according to claim 2, characterized in that, When 780≤T2≤830 ℃, the temperature of the first heating section is 1050~1200 ℃; when 600≤T2<730 ℃, the temperature of the first heating section is 1000~1150 ℃; when 500≤T2<600 ℃, the temperature of the first heating section is 1050~1150 ℃.

4. The method for producing high surface quality wear-resistant steel based on the ultimate thermal charging process according to claim 2, characterized in that, When 780≤T2≤830 ℃, the preheating time is 30~40 min; the first heating time is 30~40 min, the second heating time is 30~40 min, the total heating time is 70~80 min; and the soaking time is 20~30 min.

5. The method for producing high surface quality wear-resistant steel based on the ultimate thermal charging process according to claim 2, characterized in that, When 600≤T2<730 ℃, the preheating time is 40~50 min; the first heating time is 35~45 min; the second heating time is 45~50 min; the total heating time is 80~90 min; and the soaking time is 30~40 min.

6. The method for producing high surface quality wear-resistant steel based on the ultimate thermal charging process according to claim 2, characterized in that, When 500≤T2<600 ℃, the preheating time is 45~60 min; the first heating time is 45~50 min; the second heating time is 45~50 min; the total heating time is 85~100 min; and the soaking time is 30~40 min.

7. The method for producing high surface quality wear-resistant steel based on the ultimate thermal charging process according to claim 1, characterized in that, The roughing is carried out sequentially on the R1 and R2 mills. The R1 mill has one pass and the R2 mill has five passes. The R1 mill starts descaling, and the R2 mill uses an odd-pass descaling. The roughing mill exit temperature is 1030~1070 ℃. When the roughing mill exit temperature is >1050 ℃, the fourth pass of the R2 mill also starts descaling.

8. The method for producing high surface quality wear-resistant steel based on the ultimate thermal charging process according to claim 1, characterized in that, The finishing mill adopts a 7-stand continuous rolling process with a finishing mill speed of 3~6 m / s. The reduction rate of each pass during the continuous rolling process of F1~F7 is distributed as follows: 40~50%, 30~40%, 30~35%, 20~25%, 15~20%, 10~15%, and 5~10%, respectively. The final rolling temperature is 860~880 ℃.

9. The method for producing high surface quality wear-resistant steel based on the ultimate thermal charging process according to claim 1, characterized in that, The laminar flow cooling adopts front-end cooling; the winding temperature is 650~700 ℃.

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