Method for producing low-yield-ratio welding bottle steel through thin slab continuous casting and rolling

Abstract

The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a method for producing low-yield-ratio welding bottle steel through thin slab continuous casting and rolling. The method comprises the following steps: primarily smelting molten steel in a top-bottom combined blowing converter, refining by blowing argon at the bottom of a steel ladle, refining in an LF furnace, continuously casting, continuously rolling, coiling and slowly cooling to prepare the welding bottle steel plates with different thicknesses. And in the continuous rolling process, the rough rolling outlet temperature is 950-1020 DEG C, and the finish rolling temperature is 885-895 DEG C. And the coiling temperature is 670-690 DEG C. And after coiling, a heat preservation box slow cooling process is adopted. The thickness of the plate strip is 2.5-3.5 mm, the hit rate of the yield ratio smaller than 0.73 is 100%, and the hit rate of the steel cylinder end socket drawing height difference smaller than or equal to 4 mm is 100%.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and in particular is a method for producing low-yield ratio welding bottle steel by continuous casting and rolling of thin slabs. Background Art

[0002] In the existing technology, the thin slab continuous casting and rolling production line has the technological advantages of short production process, low cost, energy saving and environmental protection compared with the conventional process. The development of high-performance new products using the thin slab continuous casting and rolling process is in line with productivity needs and the industry's high-quality development trend.

[0003] Welding cylinder steel generally refers to steel used to produce cylinders for liquefied petroleum gas or dissolved acetylene. Because they contain flammable and explosive liquids or gases, the parent material for manufacturing welding cylinders must have high strength and toughness indicators. The production process of welding gas cylinders mainly consists of drawing and welding. In order to ensure the smooth completion of the drawing process, the parent material welding cylinder steel must also have good cold forming properties, and the yield strength ratio ReL / Rm value (yield strength / tensile strength) is an important technical indicator for measuring the cold forming performance of steel plates. Although the national standard GB / T 6653 stipulates that the yield strength ratio ReL / Rm of welding cylinder steel is ≤0.80, users of welding cylinder steel prefer that the yield strength ratio of welding cylinder steel is less than 0.75, or even lower.

[0004] After the thin slab continuous casting and rolling process realizes short process and low-cost production of welding bottle steel, although it can meet the national standard GB / T6653 that the yield ratio of welding bottle steel ReL / Rm≤0.80, the hit rate of yield ratio less than 0.75 in actual production is less than 80%.

[0005] In the production of welding bottles, the height difference of the welded steel bottle head formed after the welding bottle steel plate is stamped is an important indicator to measure the uniformity of the stamping performance of the welding bottle steel. Users hope that the height difference of the steel bottle head is ≤4mm, which can reduce the cutting loss of the steel bottle head and improve the yield rate. The standard rate of the steel bottle head drawing height difference ≤4mm produced by conventional process is less than 85%. Summary of the invention

[0006] The purpose of the present invention is to provide a method for producing low yield ratio welding bottle steel by continuous casting and rolling of thin slabs in view of the above-mentioned shortcomings, which can solve the problems of large yield ratio fluctuations, low yield ratio hit rate, and low uniformity of stamping performance during production.

[0007] The technical solution of the present invention is: a method for producing low yield ratio welding bottle steel by continuous casting and rolling of thin slabs, including primary smelting of molten steel in a top and bottom combined blowing converter, argon refining at the bottom of a ladle, LF furnace refining, continuous casting, continuous rolling, coiling and slow cooling to form welding bottle steel plates of different thicknesses, wherein the continuous rolling includes rough rolling and finish rolling, and is characterized in that: during the smelting process, the final carbon content of the top and bottom combined blowing converter is controlled between 0.07-0.09%, the slag basicity is controlled between 3.0-3.5, the P content in the steel is lower than 0.015%, and the phosphorus content of the molten steel is less than 0.003%.

[0008] The LF furnace refining controls the slag basicity to be between 4.5 and 6.5, so as to achieve the purpose of reducing molten steel inclusions and uniform steel performance.

[0009] In the continuous casting process, the pulling speed is 3.4-3.5m / min, and a narrow range constant pulling speed control is adopted, which is conducive to obtaining a more uniform cast structure while rapidly solidifying. The specific water content is controlled at 1.6-1.7L / kg to achieve the purpose of uniform cast structure of the steel billet and uniform steel performance while rapidly cooling. The front section of the continuous casting machine fan section adopts a specific water content of 1.6-1.7L / kg for rapid cooling, and the rear section adopts a specific water content of 1.6-1.7L / kg for mist cooling, making full use of the reverse temperature field with high temperature in the core of the casting billet, reducing the deformation resistance of the steel during the rolling process of the rough rolling unit, laying a foundation for the subsequent finishing rolling unit to roll in the austenite non-crystallization zone, which is conducive to uniform structure and performance while improving the strength and toughness of the welding bottle steel.

[0010] In the continuous rolling process, the rough rolling outlet temperature is 950-1020°C, and the final rolling temperature is 885-895°C, so that part or most of the finishing rolling unit is rolled in the austenite non-crystallization zone. The coiling temperature is 670-690°C. High final rolling temperature and high coiling temperature can obtain uniform and coarse ferrite grains, which is conducive to reducing the yield strength ratio.

[0011] After coiling, the slow cooling process in the insulation chamber is adopted, and the coiled steel coil is quickly hoisted into the insulation chamber for stacking, slow cooling for 72 hours, and then hoisted out of the insulation chamber and cooled to room temperature. Slow cooling reduces the dislocation density in the steel, thereby reducing the internal stress and unevenness of the steel plate, reducing the strength of the steel and improving the plasticity of the material. Slow cooling can even out the cooling rate of the coil head, coil middle and coil tail, improve the uniformity of the organization, effectively improve the stability of the coiling performance, improve the uniformity of the stamping performance, and improve the yield strength ratio hit rate. The main structure of the insulation chamber is composed of steel columns, steel beams, steel plates, and movable cover plates, and asbestos fibers and high-aluminum brick insulation materials are pasted inside. The use of movable cover plates can improve the flexibility of lifting steel coils, and the use of asbestos fibers and high-aluminum brick insulation materials can significantly reduce the cooling rate of steel coils and improve the slow cooling effect.

[0012] Preferably, the final rolling temperature is 885°C and the coiling temperature is 670°C.

[0013] Preferably, the final rolling temperature is 890°C and the coiling temperature is 680°C.

[0014] Preferably, the final rolling temperature is 895°C and the coiling temperature is 690°C.

[0015] The present invention is based on thin slab continuous casting and rolling equipment, adopts rapid uniform solidification and continuous rolling and other process technologies, realizes grain refinement during rolling, and adopts slow cooling treatment in a heat preservation chamber after coiling. Slow cooling can make the grains more uniform, can stably control the yield strength and tensile strength of steel, improve the toughness of steel, and ensure the production of welding bottle steel products with high performance stability, good stamping performance and welding performance. The above method can realize the production of welding bottle steel with low yield ratio and high uniformity of stamping performance.

[0016] During the rolling process, the uniformity of the structure of thin-gauge strip steel after deformation is improved, the mixed crystal phenomenon caused by rolling in the two-phase region is reduced, and steel plates with uniform performance are obtained. The uneven grains caused by rapid cooling of the deformed strip steel and the poor plate shape caused by residual stress are overcome, so as to obtain better plate shape and formability, which is beneficial to improving the uniformity of stamping performance, reducing the yield strength ratio, and increasing the yield strength ratio hit rate.

[0017] The beneficial effects of the present invention are: 1. The present invention adopts a slow cooling treatment process in an insulation chamber after coiling, which is a key guarantee for reducing the yield ratio, improving the yield ratio hit rate, and obtaining uniform stamping performance. 2. The rough rolling outlet temperature in the continuous rolling process is controlled at 950-1020°C, and the final rolling temperature is 885-895°C, so that part or most of the finishing rolling unit is rolled in the austenite non-crystallization zone. The coiling temperature is controlled at 670-690°C. High final rolling temperature and high coiling temperature can obtain uniform and coarse ferrite grains, which is beneficial to reducing the yield ratio. 3. The hit rate of the yield ratio is less than 0.73 and the hit rate of the deep drawing height difference of the cylinder head ≤4mm is high, which fully meets the standards and improves the yield rate. DETAILED DESCRIPTION

[0018] A method for producing low-yield ratio welded steel by continuous casting and rolling of thin slabs, the process flow is: blast furnace molten iron smelting, molten iron pretreatment, top and bottom combined blowing converter primary smelting, ladle bottom blowing argon refining, LF molten steel refining, thin slab continuous casting and rolling mill assembly to make steel billets. The specific method includes narrower range control of C, Mn, Si, P, S, and Als content during smelting, and its chemical composition, by mass percentage, C: 0.16-0.17%, Mn: 0.70-0.75%, Si≤0.08%, P≤0.015%, S≤0.003%, Als: 0.017-0.019%, and the rest is Fe. It also includes top and bottom combined blowing converter endpoint control, refining slag basicity control, continuous casting machine constant pulling speed, specific water content control, etc. during smelting, and final rolling temperature, coiling temperature, steel plate width, and thickness control during rolling, as follows: Example 1

[0019] The molten iron after slag removal and desulfurization is poured into the top and bottom double-blown converter mixed with scrap steel through the overhead crane for smelting, and molten steel with a final carbon content of 0.07%, a basicity of 3.3, and a phosphorus content of 0.012% is obtained. During the smelting period, a slide plate is used to block the slag and achieve slag-free steelmaking, which is beneficial to reduce the inclusion content in the molten steel and stabilize the performance of the steel.

[0020] Furthermore, the ladle filled with molten steel is hoisted to the LF refining furnace by the overhead crane. The charging data of the LF refining furnace is based on the amount of steel added per ton, and the amount of steel is calculated as 145t. 2.5kg / t of aluminum wire is added for deoxidation. After deoxidation, 19kg / t of lime is added for desulfurization, and 9.5kg / t of high-carbon manganese iron alloy is added to obtain molten steel with a C content of 0.16%, a Mn content of 0.73%, a Si content of 0.06%, a S content of 0.003%, and an Als content of 0.0185%. During the treatment process, the basicity of the refined slag is 4.8, and the soft blowing time before the molten steel leaves the station is more than 15min to ensure that the inclusions float fully.

[0021] Furthermore, the ladle filled with qualified molten steel is hoisted by a crane to the thin slab continuous casting unit for casting to form billets, which are directly transported to the heating furnace and to the continuous rolling unit without secondary heating. During the billet casting, the superheat is 18°C, the pulling speed is 3.4m / min, and the specific water content is 1.60L / kg.

[0022] Furthermore, the steel billet enters the thin slab continuous rolling mill through the heating furnace for rolling, and the final rolling temperature is controlled at 885°C during the rolling process. The coiling temperature is controlled at 670°C. The steel plate width tolerance is controlled at 11mm, and the steel plate thickness tolerance is controlled between -0.06mm and -0.03mm.

[0023] Furthermore, the steel billet is rolled into a 2.8 mm hot-rolled coil by a thin slab continuous casting and rolling mill and then enters a heat preservation chamber for slow cooling to room temperature for 72 hours. Example 2

[0024] The molten iron after slag removal and desulfurization is poured into the top and bottom double-blown converter mixed with scrap steel through the overhead crane for smelting, and molten steel with an end carbon content of 0.073%, basicity of 3.2, and phosphorus content of 0.013% is obtained. During the smelting period, the slide plate is used to block the slag and achieve slag-free steelmaking, which is conducive to reducing the inclusion content in the molten steel and stabilizing the performance of the steel.

[0025] Furthermore, the ladle filled with molten steel is hoisted to the LF refining furnace by a crane. The charging data of the refining furnace is based on the amount of steel added per ton, and the amount of steel is calculated as 145t. 2.7kg / t of aluminum wire is added for deoxidation. After deoxidation, 22kg / t of lime is added for desulfurization, and 9.2kg / t of high-carbon manganese iron alloy is added to obtain molten steel with a C content of 0.163%, a Mn content of 0.75%, a Si content of 0.06%, an Als content of 0.0173%, and a S content of 0.0025%. During the treatment process, the basicity of the refined slag is 5.2, and the soft blowing time before the molten steel leaves the station is more than 15min to ensure that the inclusions float fully.

[0026] Furthermore, the ladle filled with qualified molten steel is hoisted by a crane to the thin slab continuous casting unit for casting to form billets, which are directly transported to the heating furnace and to the continuous rolling unit without secondary heating. During the billet casting, the superheat is 22°C, the pulling speed is 3.5m / min, and the specific water content is 1.68L / kg.

[0027] Furthermore, the steel billet enters the thin slab continuous rolling mill through the heating furnace for rolling, and the final rolling temperature is controlled at 890°C during the rolling process. The coiling temperature is controlled at 680°C. The steel plate width tolerance is controlled at 13mm, and the steel plate thickness tolerance is controlled between -0.05mm and -0.02mm.

[0028] Furthermore, the steel billet is rolled into a 3.0 mm hot-rolled coil by a thin slab continuous casting and rolling mill and then enters a heat preservation chamber for slow cooling to room temperature for 72 hours. Example 3

[0029] The molten iron after slag removal and desulfurization is poured into the top and bottom double-blown converter mixed with scrap steel through the overhead crane for smelting, and molten steel with a final carbon content of 0.08%, a basicity of 3.5, and a phosphorus content of 0.009% is obtained. During the smelting period, a slide plate is used to block the slag and achieve slag-free steelmaking, which is beneficial to reduce the inclusion content in the molten steel and stabilize the performance of the steel.

[0030] Furthermore, the ladle filled with molten steel is hoisted to the LF refining furnace by the overhead crane. The charging data of the refining furnace is based on the amount of steel added per ton, and the amount of steel is calculated as 145t. 2.3kg / t of aluminum wire is added for deoxidation. After deoxidation, 25kg / t of lime is added for desulfurization, and 9.0kg / t of high-carbon manganese iron alloy is added to obtain molten steel with a C content of 0.161%, a Mn content of 0.73%, a Si content of 0.06%, an Als content of 0.0187%, and a S content of 0.0028%. During the treatment process, the basicity of the refined slag is 5.5, and the soft blowing time before the molten steel leaves the station is more than 15min to ensure that the inclusions are fully floated.

[0031] Furthermore, the ladle filled with qualified molten steel is hoisted by a crane to the thin slab continuous casting unit for casting to form billets, which are directly transported to the heating furnace and to the continuous rolling unit without secondary heating. During the billet casting, the superheat is 20°C, the pulling speed is 3.4m / min, and the specific water content is 1.62L / kg.

[0032] Furthermore, the steel billet enters the thin slab continuous rolling mill through the heating furnace for rolling, and the final rolling temperature is controlled at 895°C during the rolling process. The coiling temperature is controlled at 690°C. The steel plate width tolerance is controlled at 11mm, and the steel plate thickness tolerance is controlled between -0.05mm and -0.02mm.

[0033] Furthermore, the steel billet is rolled into a 2.8 mm hot-rolled coil by a thin slab continuous casting and rolling mill and then enters a heat preservation chamber for slow cooling to room temperature for 72 hours. Example 4

[0034] The molten iron after slagging and desulfurization is poured into the top and bottom double-blown converter mixed with scrap steel through the overhead crane for smelting, and the molten steel with the final carbon content of 0.09%, basicity of 3.2 and phosphorus content of 0.011% is obtained. During the smelting period, the slide plate is used to block the slag and achieve slag-free steelmaking.

[0035] Furthermore, the ladle filled with molten steel is hoisted to the LF refining furnace by a crane. The charging data of the refining furnace is based on the amount of steel added per ton, and the amount of steel is calculated as 145t. 2.3kg / t of aluminum wire is added for deoxidation. After deoxidation, 25kg / t of lime is added for desulfurization, and 9.5kg / t of high-carbon ferromanganese alloy is added to obtain molten steel with a C content of 0.165%, a Mn content of 0.75%, a Si content of 0.05%, an Als content of 0.018%, and a S content of 0.003%. During the treatment process, the basicity of the refined slag is 4.5, and the soft blowing time before the molten steel leaves the station is more than 15min to ensure that the inclusions float fully.

[0036] Furthermore, the ladle filled with qualified molten steel is hoisted by a crane to the thin slab continuous casting unit for casting to form billets, which are directly transported to the heating furnace and to the continuous rolling unit without secondary heating. During the billet casting, the superheat is 28°C, the pulling speed is 3.4m / min, and the specific water content is 1.62L / kg.

[0037] Furthermore, the steel billet enters the thin slab continuous rolling mill through the heating furnace for rolling, and the final rolling temperature is controlled at 870°C during the rolling process. The coiling temperature is controlled at 650°C. The steel plate width tolerance is controlled at 12mm, and the steel plate thickness tolerance is controlled between -0.06mm and -0.03mm.

[0038] Further, the steel billet is rolled into a 2.8 mm hot rolled coil by a thin slab continuous casting and rolling mill, and naturally cooled to room temperature. Example 5

[0039] The molten iron after slagging and desulfurization is poured into the top and bottom double-blown converter mixed with scrap steel through the overhead crane for smelting, and the molten steel with the final carbon content of 0.075%, basicity of 3.1 and phosphorus content of 0.014% is obtained. During the smelting period, the slide plate is used to block the slag and achieve slag-free steelmaking.

[0040] Furthermore, the ladle filled with molten steel is hoisted to the LF refining furnace by the overhead crane. The charging data of the refining furnace is based on the amount of steel added per ton, and the amount of steel is calculated as 145t. 2.3kg / t of aluminum wire is added for deoxidation. After deoxidation, 25kg / t of lime is added for desulfurization, and 10.05kg / t of high-carbon manganese iron alloy is added to obtain molten steel with a C content of 0.17%, a Mn content of 0.75%, a Si content of 0.06%, an Als content of 0.0175%, and a S content of 0.0028%. During the treatment process, the basicity of the refined slag is 4.7, and the soft blowing time before the molten steel leaves the station is more than 15min to ensure that the inclusions float fully.

[0041] Furthermore, the ladle filled with qualified molten steel is hoisted by a crane to the thin slab continuous casting unit for casting to form billets, which are directly transported to the heating furnace and to the continuous rolling unit without secondary heating. During the billet casting, the superheat is 23°C, the pulling speed is 3.4m / min, and the specific water content is 1.61L / kg.

[0042] Furthermore, the steel billet enters the thin slab continuous rolling mill through the heating furnace for rolling, and the final rolling temperature is controlled at 900°C during the rolling process. The coiling temperature is controlled at 700°C. The steel plate width tolerance is controlled at 11mm, and the steel plate thickness tolerance is controlled between -0.05mm and -0.02mm.

[0043] Furthermore, the steel billet is rolled into a 2.8 mm hot-rolled coil by a thin slab continuous casting and rolling mill and then enters a chamber for slow cooling for 24 hours to cool to room temperature. Example 6

[0044] The molten iron after slagging and desulfurization is poured into the top and bottom double-blown converter mixed with scrap steel through the overhead crane for smelting, and the molten steel with the final carbon content of 0.085%, basicity of 3.4 and phosphorus content of 0.012% is obtained. During the smelting period, the slide plate is used to block the slag and achieve slag-free steelmaking.

[0045] Furthermore, the ladle filled with molten steel is hoisted to the LF refining furnace by the overhead crane. The charging data of the refining furnace is based on the amount of steel added per ton, and the amount of steel is calculated as 145t. 2.3kg / t of aluminum wire is added for deoxidation. After deoxidation, 25kg / t of lime is added for desulfurization, and 9.75kg / t of high-carbon manganese iron alloy is added to obtain molten steel with a C content of 0.168%, a Mn content of 0.73%, a Si content of 0.05%, an Als content of 0.019%, and a S content of 0.003%. During the treatment process, the basicity of the refined slag is 5.2, and the soft blowing time before the molten steel leaves the station is more than 15min to ensure that the inclusions float fully.

[0046] Furthermore, the ladle filled with qualified molten steel is hoisted by a crane to the thin slab continuous casting unit for casting to form billets, which are directly transported to the heating furnace and to the continuous rolling unit without secondary heating. During the billet casting, the superheat is 20°C, the pulling speed is 3.5m / min, and the specific water content is 1.69L / kg.

[0047] Furthermore, the steel billet enters the thin slab continuous rolling mill through the heating furnace for rolling, and the final rolling temperature is controlled at 860°C during the rolling process. The coiling temperature is controlled at 660°C. The width tolerance of the steel plate is controlled at 11mm, and the thickness tolerance of the steel plate is controlled between -0.05mm and -0.02mm.

[0048] Furthermore, the steel billet is rolled into a 3.0 mm hot-rolled coil by a thin slab continuous casting and rolling mill and then enters a chamber for slow cooling for 48 hours to cool to room temperature.

[0049] Table 1: Performance indicators of Examples 1-6 Rolling specification mm Yield strength MPa Tensile strength MPa Elongation% Yield-to-strength ratio Example 1 2.8 330 472 38 0.69 Example 2 3.0 345 476 28 0.72 Example 3 2.8 340 478 30 0.71 Example 4 2.8 350 433 28 0.80 Example 5 2.8 338 428 32 0.79 Example 6 3.0 360 440 30 0.82 As shown in Table 1, the yield strength of the welding bottle steel produced by the method provided by the present invention in Examples 1-3 is controlled between 330-345MPa, the tensile strength is controlled between 472-478MPa, the elongation is controlled between 28-38%, the yield strength ratio is controlled between 0.69-0.72, and the hit rate is 100% when the yield strength ratio is less than 0.73. The steelmaking method of Examples 4-6 is basically the same as that of Examples 1-3, but the rolling process and slow cooling time are different, the yield strength ratio is controlled between 0.79-0.82, and the yield strength ratio exceeds the national standard requirements, and the hit rate is "zero" when the yield strength ratio is less than 0.73.

[0050] The effects of Examples 1-6 on the hit rate of the yield strength ratio and the compliance rate of the steel cylinder head drawing height difference ≤4mm are shown in Table 2.

[0051] Table 2 Yield-to-strength ratio Height difference ≤4mm compliance rate Example 1 0.69 100% Example 2 0.72 100% Example 3 0.71 100% Example 4 0.80 44.46% Example 5 0.79 52.45% Example 6 0.82 25.88% As shown in Table 2, in Examples 4-6, since the yield strength ratio is higher than 0.73, the compliance rate of the steel cylinder head drawing height difference ≤4mm is controlled below 52.45%, while in Examples 1-3, since the yield strength ratio is lower than 0.73, the compliance rate of the steel cylinder head drawing height difference ≤4mm reaches 100%.

[0052] The above description is only a specific implementation mode of the present invention, and various examples do not constitute a limitation on the essential content of the present invention.

Claims

1. A method for producing low yield ratio welding steel by continuous casting and rolling of thin slabs, comprising primary refining of molten steel in a top and bottom combined blowing converter, refining with argon gas at the bottom of a ladle, refining in an LF furnace, continuous casting, continuous rolling, coiling and slow cooling to produce welding steel plates of different thicknesses, wherein the continuous rolling includes rough rolling and finishing rolling, and is characterized in that: In the smelting process, the final carbon content of the top and bottom combined blowing converter is controlled between 0.07-0.09%, the slag basicity is controlled between 3.0-3.5, the P content in the steel is less than 0.015%, and the phosphorus content of the molten steel is less than 0.003%; The LF furnace refining controls the slag basicity to be between 4.5 and 6.5; In the continuous casting process, the casting speed is 3.4-3.5 m / min, and the specific water content is 1.6-1.7 L / kg; In the continuous rolling process, the rough rolling outlet temperature is 950-1020°C, the final rolling temperature is 885-895°C, and the coiling temperature is 670-690°C; After coiling, the steel coil is quickly hoisted into the insulation chamber for stacking, slowly cooled for 72 hours, and then hoisted out of the insulation chamber to cool to room temperature.

2. The method for producing low yield ratio welding bottle steel by continuous casting and rolling of thin slab according to claim 1, characterized in that The final rolling temperature is 885°C and the coiling temperature is 670°C.

3. The method for producing low yield ratio welding bottle steel by continuous casting and rolling of thin slab according to claim 1, characterized in that The final rolling temperature is 890°C and the coiling temperature is 680°C.

4. The method for producing low yield ratio welding bottle steel by continuous casting and rolling of thin slab according to claim 1, characterized in that The final rolling temperature is 895°C and the coiling temperature is 690°C.