A continuous casting and rolling production method of a 1.5mm 45 steel without Cr component

Abstract

The application discloses a continuous casting and rolling production method of Cr-free component 1.5mm 45 steel and belongs to the field of steel production, and method steps comprise: a steelmaking process, a casting and rolling process, and a slow cooling process; the casting and rolling process comprises continuous casting, rough rolling, induction heating, finish rolling, cooling and coiling; in the continuous casting, a continuous casting pulling speed is controlled to be greater than or equal to 4.8 m / min, a tundish superheat is controlled to be 12-25 DEG C, a slab cross-section temperature difference is within 50 DEG C, and an intermediate blank thickness is 12-14 mm; in the rough rolling, a rough rolling outlet temperature is 900-950 DEG C; in the induction heating, an IH induction heating furnace outlet temperature is set to 1150-1170 DEG C; in the finish rolling, a finish rolling outlet temperature is controlled to be higher than 810 DEG C; a coiling temperature is controlled to be 630-680 DEG C, and coiling is carried out by adopting a large unit tension greater than or equal to 40 Mpa. Compared with the prior art, the method can stably produce 1.5mm 45 steel.

Description

Technical Field

[0001] This invention is a divisional application of the invention patent "A method for producing thin-gauge 45 steel in a continuous casting and rolling production line" (CN2021108734573), which relates to a steel production method, particularly a method for producing 1.5mm gauge 45 steel in a continuous casting and rolling production line. Background Technology

[0002] Research indicates that the largest market segment in the hot-rolled high-carbon steel market is high-quality carbon structural steel, primarily supplied to cold-rolling enterprises. After cold rolling, it is widely used in various industries such as chains, cutting tools, measuring instruments, hardware, machinery, and automobiles. The market is characterized by high specialization, poor liquidity, and downstream products with high technical requirements, exhibiting a certain degree of rigid demand. In recent years, with the healthy development of the domestic hot-rolled steel industry and the government's and society's high emphasis on environmental protection, the materials used have gradually upgraded from initially using ordinary materials to meet basic user needs, moving towards green, environmentally friendly, thin-gauge, and high-strength materials.

[0003] With the advancement of process modernization, equipment scaling up, and production intensification, continuous casting and rolling production lines have gradually become an important component of steel production due to their advantages such as effectively reducing the costs of subsequent processes like cold rolling and annealing, and saving energy and time.

[0004] However, existing thin slab continuous casting and rolling production lines abroad have not produced steel grades with a carbon content exceeding 0.30%. The high carbon series developed by our group company achieves the "hot instead of cold" process for thin slabs by adding 0.12-0.25% Cr, which can produce steel plates with a specification of 1.5mm (such as invention patent applications CN201611258861.5 "Method for producing thin specification high carbon steel based on ESP thin slab continuous casting and rolling process" and CN201611261690.1 "Method for producing thin specification RE52Mn steel based on ESP thin slab continuous casting and rolling process"). Summary of the Invention

[0005] The technical objective of this invention is to address the shortcomings of the prior art by providing a method for producing 1.5mm specification 45 steel in a continuous casting and rolling production line, aiming to achieve "heat instead of cold" and save energy and labor time.

[0006] The technical solution of this invention to solve its technical problem is: a continuous casting and rolling production method for Cr-free 1.5mm 45 steel, the method steps including: steelmaking process, casting and rolling process, and slow cooling process; the casting and rolling process includes continuous casting, roughing rolling, induction heating, finishing rolling, cooling, and coiling; characterized in that: in the steelmaking process, the molten steel does not contain Cr; in the continuous casting process: the continuous casting speed is controlled at ≥4.8m / min; the superheat of the tundish is controlled at 12-25℃; the temperature difference of the billet cross section is controlled within 50℃; the thickness of the intermediate billet is set at 12-14mm; in the roughing rolling process: the roughing rolling exit temperature is controlled at 900-950℃; in the induction heating process: the IH induction heating furnace exit temperature is set at 1150-1170℃; in the finishing rolling process: the finishing rolling exit temperature is controlled at ≥810℃; in the coiling process: the coiling temperature is controlled at 630-680℃, and a large unit tension ≥40Mpa is used for coiling.

[0007] In the optimized scheme, the steel composition in the above steelmaking process, by mass percentage, includes: C 0.42%-0.50%, Si 0.17%-0.35%, Mn 0.5%-0.8%, S≤0.003%, P≤0.020%, N≤80ppm, with the remainder being iron and unavoidable impurities.

[0008] The optimized solution involves casting a billet thickness of 90-110 mm in the continuous casting process described above.

[0009] The optimized solution is to use air cooling in the laminar flow cooling process described above.

[0010] Compared with the prior art, the present invention has the following outstanding advantages:

[0011] 1. The method of the present invention can stably produce 1.5mm specification 45 steel using a thin-gauge continuous casting and rolling production line, which can reduce the cost of cold rolling and annealing for customers, save energy and time, and realize "replacing cold with heat".

[0012] 2. The molten steel contains no Cr, which can effectively reduce the strength of the product during the cooling process of continuous casting and hot rolling. Combined with temperature control during the production process, it can improve the strength increase caused by excessively rapid temperature drop in air cooling, reduce the difficulty of the production process, and ensure that the final performance meets the product quality requirements.

[0013] 3. Stable production of 1.5mm ultra-thin 45 steel, with performance close to that of conventional specifications, which customers can use directly without annealing.

[0014] 4. Reduce the occurrence of problems such as unstable centerline, flat coils, and poor performance stability in thin-gauge rolling. Attached Figure Description

[0015] Figure 1 This is a metallographic image of the heart region in Embodiment 1 of the present invention.

[0016] Figure 2 This is a metallographic image of the heart portion of Embodiment 2 of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0018] This invention provides a method for producing 1.5mm specification 45 steel in a continuous casting and rolling production line. The steel composition by mass percentage includes: C 0.42%-0.50%, Si 0.17%-0.35%, Mn 0.5%-0.8%, S≤0.003%, P≤0.020%, N≤80ppm, with the remainder being iron and unavoidable impurities.

[0019] in:

[0020] C: 0.42%-0.50%. C has the effect of solid solution strengthening and is an important element for improving material strength and reducing elongation. The heat treatment method of 45 steel is generally quenching and tempering (quenching + tempering). C plays a decisive role in the strength after heat treatment. Reasonable composition design can ensure the performance of high carbon steel while minimizing production costs.

[0021] Si: 0.17%-0.35%, has a good deoxidation effect. Adding silicon as a reducing agent and deoxidizer during the steelmaking process can effectively inhibit the precipitation of carbides, reduce the critical cooling rate of steel, and improve hardenability. However, too much silicon will reduce the weldability of steel.

[0022] Mn: 0.5%-0.8%. Mn can delay the transformation of pearlite and is beneficial to the formation of bainite, but too high a concentration can coarsen the grains, increase temper brittleness, weaken the corrosion resistance of steel, and reduce weldability.

[0023] The design is free of Cr and Ni. Microalloying elements such as Cr and Ni can significantly improve the hardenability of steel and increase product strength. Downstream customers mainly use ultra-thin 45 steel for stamping various tools by "hot rolling instead of cold rolling". Stamping dies have certain requirements for the properties of raw materials. Traditional processes generally use alloying elements + cold rolling + annealing to meet these requirements. This case utilizes the characteristics of ultra-thin production process, and although no microalloying elements are added, it can meet the technical requirements of customers.

[0024] The method steps include:

[0025] 1. Steelmaking process

[0026] The raw materials are selected and then smelted in a converter and a refining furnace in sequence.

[0027] 2. Casting and rolling process

[0028] 2.1 Continuous casting:

[0029] The thickness of the cast billet is 90-110mm;

[0030] Continuous casting speed control ≥4.8m / min; tundish superheat control 12-25℃; optimized scheme 15-20℃; thick copper plate crystallizer used to stabilize crystallizer heat flow, crystallizer liquid level fluctuation standard deviation control ≤1.5mm;

[0031] In thin slab continuous casting and rolling production lines, continuous casting and rolling are directly and rigidly connected, without the traditional heating buffer. The casting speed is the foundation of the entire thin slab continuous casting and rolling production line speed. For the production of 1.5mm thin high-carbon 45 steel, the high carbon and alloy content (C, Si, Mn) results in high resistance to hot deformation, large rolling load, and strong sensitivity to plate shape, making production difficult. However, due to the low solidification temperature and long liquid core length of 45 steel, the casting speed is limited by the length of the continuous casting sector. Therefore, while increasing the casting speed to ensure stable production and quality, it is necessary to control the superheat of the molten steel in the ladle at 12-25℃, reduce the liquid core length, and use a thick copper plate crystallizer to stabilize the heat flow in the crystallizer and ensure that the standard deviation of the liquid level fluctuation in the crystallizer is ≤1.5mm. In addition, controlling the low superheat can also improve the segregation of the billet structure, which is beneficial to the subsequent heat treatment processing of the product and improves the mechanical properties of the product.

[0032] By reducing the water volume in the horizontal section of continuous casting, the temperature difference of the billet cross section can be controlled within 50℃.

[0033] The reason this invention controls the temperature difference across the billet cross-section to within 50°C is that uneven temperature distribution across the billet cross-section directly affects uneven wear of the rolls. On one hand, this directly leads to increased rolling force deviation on both sides of the mill during slab rolling, resulting in large fluctuations in the rolling centerline. On the other hand, uneven wear on the rolls in certain areas further exacerbates the deviation of the rolling centerline, leading to rolling instability. Furthermore, it poses a quality risk of creating localized high points or ribs in the finished strip cross-section. This invention primarily utilizes the high reheat characteristic of high-carbon billets by reducing the water volume in the horizontal section of continuous casting, thereby increasing heat dissipation in the core and raising the overall surface temperature of the billet, thus controlling the temperature difference across the billet cross-section to within 50°C.

[0034] The thickness of the intermediate billet is set to 12-14mm.

[0035] The intermediate slab thickness is controlled at 12-14 mm in this invention primarily to consider the impact on the stability of roughing and finishing rolling production and surface vibration marks. If a thinner intermediate slab is selected, the roughing rolling load will increase significantly, leading to larger fluctuations in the roughing mill exit centerline. This instability in roughing will simultaneously affect the stability of the finishing and coiling areas. Conversely, if a thicker intermediate slab is selected, it will directly increase the finishing rolling load, directly affecting its stability, and may also cause vibration in the finishing mill, resulting in surface vibration marks on the strip.

[0036] 2.2 Rough rolling:

[0037] The billet is rolled through three roughing passes, with the exit temperature of the roughing roll controlled at 900-950℃.

[0038] The higher roughing mill exit temperature is to reduce the temperature rise in the IH region, thereby reducing the amount of iron oxide scale generated, mitigating the peeling behavior of CO iron oxide scale caused by the high carbon content in 45 steel, and thus avoiding module current overload faults in the IH induction heating region.

[0039] 2.3 Induction heating furnace heating:

[0040] The outlet temperature of the IH induction heating furnace is set at 1150-1170℃.

[0041] The higher IH exit and final rolling temperatures serve two purposes. First, to ensure a higher final rolling temperature, the medium- and high-carbon steel is rolled within the austenitic region throughout the rolling process, guaranteeing the accuracy of the secondary load model calculations and enhancing rolling stability. Second, to encourage dynamic recrystallization between finishing passes, softening the metal and facilitating cold rolling.

[0042] 2.4 Finish rolling:

[0043] Hot-rolled strip steel with a thickness of 1.5mm is produced by five passes of finishing rolling, with the finishing mill exit temperature controlled above 810℃.

[0044] 2.5 Laminar flow cooling:

[0045] Air cooling is used.

[0046] 2.6 Winding:

[0047] The winding temperature is controlled at 630-680℃, and a high unit tension of ≥40Mpa is used for winding.

[0048] Based on the CCT dynamic cooling transformation curve of 45 steel, a layer-cooling and air-cooling strategy is adopted, controlling the coiling temperature at a relatively high level of 630-670℃. The resulting microstructure is sorbite + pearlite + ferrite. This allows for a slight reduction in strength and a slight increase in elongation, which is more beneficial for customers to further cold-rolling processes. Furthermore, due to the high coiling temperature, the strip's hot yield strength is low, and the strip is thin. The steel coil's own stiffness is insufficient to support its own weight, necessitating high-tension coiling to ensure proper coil shape.

[0049] 3. Slow cooling

[0050] After being rolled up, the coils are stacked in a slow-cooling warehouse for slow cooling.

[0051] Comparative experiments were conducted to better compare the formulation of this application with existing technologies.

[0052] The control group adopted the production method of our group for 1.5mm high carbon steel (CN201611258861.5); specifically: steelmaking → continuous casting → rough rolling → induction heating furnace → finish rolling → cooling → coiling.

[0053] Examples 1-4 employ the method of the present invention;

[0054] The composition of each group of molten steel is shown in the table below:

[0055]

[0056]

[0057] Parameter control for each group of casting and rolling processes: The thickness of the intermediate billet in each group is 12-14 mm, the IH exit temperature is set at 1150-1170℃, the finishing mill exit temperature is 845-860℃, and other parameters are as follows:

[0058]

[0059] The mechanical properties of the 45 steel produced by each group are shown in the table below:

[0060] steel grades Specifications (mm × mm) Yield strength Re (MPa) Tensile strength Rm (MPa) Elongation A% control group 1.35×1250 523 789 21.5 Example 1 1.35×1250 517 797 20.5 Example 2 1.50×1250 495 760 22.0 Example 3 1.35×1250 521 795 21.5 Example 4 1.50×1250 506 788 22.0

[0061] The results above show that the metallographic structure of the core using Examples 1 and 2 of the present invention is as follows: Figure 1 , 2 As shown, although no Cr element was added, the microstructure was S+P+F, with no abnormal microstructure and similar mechanical properties, which fully met the needs of downstream customers.

[0062]

[0063]

[0064] The results above show that while the mechanical properties of 1.5mm steel produced using the existing 1.5mm production method in the control group can be guaranteed to some extent, the centerline deviation and flattening ratio are obvious. However, the centerline deviation and flattening ratio of ultra-thin high-carbon steel produced using the method of this invention are significantly controlled.

[0065] It should be noted that the specific embodiments of the present invention have been described in detail. For those skilled in the art, various obvious changes made to it without departing from the spirit and scope of the present invention are within the protection scope of the present invention.

Claims

1. A continuous casting and rolling method for producing 1.5mm 45 steel without Cr, the method comprising the following steps: Steelmaking process, casting and rolling process, slow cooling process; In the steelmaking process, the molten steel composition by mass percentage includes: C 0.42%-0.50%, Si 0.17%-0.35%, Mn 0.5%-0.8%, S≤0.003%, P≤0.020%, N≤80ppm, with the remainder being iron and unavoidable impurities; the casting and rolling process includes continuous casting, roughing, induction heating, finishing, cooling, and coiling; characterized in that: in the steelmaking process, the molten steel composition does not include Cr; in the continuous casting: the casting speed is controlled ≥4.8m / min; the tundish superheat is controlled 12-25℃; the temperature difference of the billet cross-section is controlled within 50℃. Within ℃; using a thick copper plate crystallizer, the standard deviation of the crystallizer liquid level fluctuation is controlled ≤1.5mm; the thickness of the intermediate billet is set to 12-14mm; in the rough rolling: the rough rolling exit temperature is controlled at 900-950℃; in the induction heating: the IH induction heating furnace exit temperature is set at 1150-1170℃; in the finishing rolling: the finishing rolling exit temperature is controlled above 810℃; in the coiling: the coiling temperature is controlled at 630-680℃, and a large unit tension ≥40Mpa is used for coiling.

2. The continuous casting and rolling production method for Cr-free 1.5mm 45 steel according to claim 1, characterized in that: The thickness of the billet in the continuous casting process is 90-110 mm.

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