Production method of low-cost rare earth Q550NHJE hot rolled steel strip for container

Abstract

The invention discloses a production method of a low-cost rare earth Q550NHJE hot rolled steel strip for a container, which comprises the following steps of: continuously casting at the speed of 1.0-1.6 m / min to obtain a slab with the thickness of 230mm; the heating temperature of the casting blank in a heating furnace is 1230 + / -20 DEG C, and heat preservation is conducted for 30-60 min; the rolling temperature is 1050 + / -10 DEG C, the finish rolling temperature is 875 + / -15 DEG C, the coiling temperature is 600 + / -15 DEG C, and the cooling mode is one-by-one cooling; meanwhile, the components are optimized and designed again. On the basis of the 2250 mm hot rolling process, the extreme cost reduction work is carried out, the cost of each ton of steel can be saved by about 200 yuan, through microstructure and performance and grain size grade analysis, all the performances of the product meet the standard requirements, and the quality and competitiveness of the product are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel materials, and in particular relates to a method for producing a low-cost rare earth Q550NHJE hot-rolled steel strip for a container. Background Art

[0002] Considering the advantages of my country's abundant Ti resources, low alloying cost, and excellent comprehensive performance of Ti microalloyed steel, a systematic study of Ti microalloying technology for 2250mm hot rolling mills was carried out to open up a new way to produce lightweight container steel at low cost. Under the premise of ensuring the weathering index requirements of product standards, the role of alloying elements Mn, Nb, and Ti elements in steel was utilized to give full play to the precipitation strengthening effect of Ti elements, and low-cost and high-strength hot-rolled coils for containers with high Ti and low Mn composition systems were developed.

[0003] After searching: the document with Chinese patent application number CN 101787487 B discloses a "Tough hot-rolled steel strip for container and its manufacturing method", which is applicable to: C 0.073-0.10, Si 0.22-0.30, Mn 1.33-1.50, P 0.010-0.020, S 0.003-0.008, Ti 0.026-0.050. The rest is Fe and unavoidable impurities. The steps of the manufacturing method of the steel strip are: A. The continuous casting billet is prepared by pre-treatment desulfurization of molten iron, top and bottom composite blowing converter smelting, LF refining and thick slab continuous casting; B. The continuous casting billet is processed into a hot-rolled steel strip by controlled rolling and controlled cooling process, the final rolling temperature is 810-850℃, and it is quickly water-cooled to 450-610℃ for coiling, and then cooled to room temperature. The steel strip processed by the tough hot-rolled steel strip manufacturing method for the container in this patent has excellent comprehensive mechanical properties, but it does not have weather resistance and does not contain Cu, Cr, and Ni elements, so its production cost is relatively low. The present invention produces a low-cost weather-resistant container, and its various performance indexes are better than those of the patent.

[0004] After searching, a document with Chinese patent application number CN 107557678 B was found, which disclosed a "Low-cost 550MPa grade hot-rolled weathering steel for containers and its manufacturing method". The method is applicable to C 0.049%~0.069%, Si 0.20%~0.30%, Mn 0.51%~0.79%, P≤0.020%, S≤0.006%, Als 0.015%~0.045%, Cr0.31%~0.41%, Ni 0.079%~0.099%, Cu 0.21%~0.29%, Ti 0.057%~0.077%, N≤0.006%, and the rest are Fe and unavoidable impurities. The thickness of the ingot is 200-230 mm, the heating temperature of the ingot is ≥1250°C, the start temperature of the finishing rolling is 1080-1100°C, the final rolling temperature of the finishing rolling is 921-949°C, laminar cooling is adopted after rolling, the cooling rate is >20°C / s, the coiling temperature is 619-649°C, and after coiling, it enters the slow cooling hood for slow cooling. If the thickness of the finished product is ≤2.0 mm, it needs to be leveled. The thickness of the steel plate is 1.5-5.0 mm. Although the alloy cost in the invention is relatively low compared with the cost of the present invention, its microstructure is observed to be coarse, its production stability needs to be considered, and the performance surplus may be small. The present invention fully meets the requirements of reduction by adding rare earth microstructure.

[0005] After searching, the document with Chinese patent application number CN 111748734 B discloses a "550MPa grade hot-rolled weathering steel for container with stable rust layer". The method is applicable to C: 0.05-0.08%, Si: 0.32-0.38%, Mn: 0.50-0.60%, Cr: 0.60-0.80%, Cu: 0.32-0.40%, Mo: 0.10-0.18%, Nb: 0.05-0.07%, Ti: 0.01-0.02%, P not exceeding 0.020%, S≤0.005%. Production method: casting into billets after converter smelting and vacuum Ca treatment; heating the billets; rough rolling; finishing rolling; laminar cooling with Na Cl solution; natural cooling; stabilization of rust layer treatment; coiling. The present invention realizes the online generation of a dense and stable rust layer with a thickness of not less than 3 μm on the surface of the steel plate under the premise of ensuring the steel plate yield strength of 550-580MPa, tensile strength of 620-650MPa, and elongation of ≥20%. The disadvantage of this patent is that although the performance index is stable, the alloy contains Mo element, which increases the alloy cost by 300-400 yuan per ton, which is not conducive to the long-term development of the enterprise. In the present invention, rare earth is used to replace the alloy, and no precious elements are added, so as to achieve the purpose of cost reduction, which meets the requirements of the green, low-carbon, and low-cost development of the enterprise. Summary of the invention

[0006] In order to solve the above technical problems, the purpose of the present invention is to provide a low-cost rare earth Q550NHJE container hot-rolled steel strip production method.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The invention discloses a method for producing a low-cost rare earth Q550NHJE hot-rolled steel strip for a container. The chemical components and weight percentages of the Q550NHJE after cost reduction are: C: 0.06-0.08%, Si: 0.37-0.47%, Mn: 0.65-0.75%, P: 0.015-0.025%, S≤0.005%, Cu: 0.30-0.40%, Cr: 0.30-0.40%, Ti: 0.035-0.045%, Ni: 0.05-0.13%, and the balance is Fe and incidental inclusions. The production method comprises:

[0009] The continuous casting billet drawing speed is 1.0m-1.6m / min, and the slab with a thickness of 230mm is obtained;

[0010] The casting is heated in a heating furnace to a temperature of 1230±20°C and kept warm for 30-60 minutes;

[0011] The rolling temperature is 1050±10℃, the final rolling temperature is 875±15℃, the coiling temperature is 600±15℃, and the cooling mode is alternate one-on-one.

[0012] Furthermore, the chemical composition and weight percentage of Q550NHJE after cost reduction are: C: 0.07%, Si: 0.40%, Mn: 0.70%, P: 0.020%, S: 0.003%, Cu: 0.35%, Cr: 0.35%, Ti: 0.040%, Ce: 0.0020%, and the balance is Fe and incidental inclusions.

[0013] Furthermore, the continuous casting billet drawing speed is 1.0 m / min, and a slab with a thickness of 230 mm is obtained; the billet is heated to 1233°C in a heating furnace and kept warm for 47 minutes; the starting rolling temperature is 1048°C, the final rolling temperature is 855°C, the coiling temperature is 578°C, and the cooling mode adopts alternate-open-one.

[0014] Furthermore, its production process includes: slab heating - high-pressure water descaling - fixed width press - E1 R1 roughing mill rolling - E2R2 roughing mill rolling - flying shear - high-pressure water descaling - F1-F7 finishing mill rolling - encrypted laminar cooling - coiling.

[0015] Furthermore, the thickness of the hot rolled plate is 6 mm.

[0016] Furthermore, the atmospheric corrosion resistance index is I=6.0-6.8.

[0017] Compared with the prior art, the beneficial technical effects of the present invention are:

[0018] Based on the 2250mm hot rolling process, the present invention carries out extreme cost reduction work under the dual carbon background, which can save about 200 yuan per ton of steel. Through the analysis of microstructure, performance and grain size grade, the performance of the product meets the standard requirements, thereby improving the quality and competitiveness of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below in conjunction with the accompanying drawings.

[0020] Figure 1 Example 1: Metallographic structure diagram of Q550NHJE before cost reduction (without adding rare earth).

[0021] Figure 2 Example 3: Metallographic structure diagram of Q550NHJE after cost reduction (without adding rare earth).

[0022] Figure 3 Example 4: Metallographic structure diagram of Q550NHJE after cost reduction (with rare earth added). DETAILED DESCRIPTION

[0023] The present invention is described in more detail below with reference to examples. These examples are merely descriptions of the best mode for carrying out the present invention and do not impose any limitation on the scope of the present invention.

[0024] Example 1

[0025] (1) In view of the high cost of Q550NHJE for containers, the formula was designed and developed before cost reduction, including the following chemical components in percentage by weight: C: 0.07, Si: 0.43, Mn: 0.75, P: 0.020, S: 0.003, Cu: 0.35, Cr: 0.35, Ti: 0.079, Ni: 0.08, and the balance is Fe and accompanying inclusions.

[0026] (2) The continuous casting billet drawing speed is 1.0 m / min, and the obtained billet has a thickness of 230 mm. The process conditions are: the billet is heated to 1230°C in a heating furnace and kept warm for 45 minutes. The starting rolling temperature is 1055°C, the final rolling temperature is 875°C, the coiling temperature is 600°C, and the cooling mode is one-on-one.

[0027] Example 2

[0028] (1) In view of the high cost of Q550NHJE for containers, its formula was developed and designed before cost reduction, including the following chemical components in weight percentage: C: 0.07, Si: 0.44, Mn: 0.74, P: 0.022, S: 0.003, Cu: 0.33, Cr: 0.34, Ti: 0.078, Ni: 0.08, and the balance is Fe and accompanying inclusions.

[0029] (2) The continuous casting billet drawing speed is 1.0 m / min, and the obtained billet has a thickness of 230 mm. The process conditions are: the billet is heated to 1233°C in a heating furnace and kept warm for 48 minutes. The starting rolling temperature is 1050°C, the final rolling temperature is 870°C, the coiling temperature is 595°C, and the cooling mode is one-on-one.

[0030] Example 3

[0031] (1) The composition of Q550NHJE for containers was adjusted, and the formula was developed and designed after cost reduction to include the following chemical components in percentage by weight: C: 0.07, Si: 0.40, Mn: 0.70, P: 0.020, S: 0.003, Cu: 0.35, Cr: 0.35, Ti: 0.040, Ce: 0.0020, and the balance was Fe and incidental inclusions.

[0032] (2) The continuous casting billet drawing speed is 1.0 m / min, and the obtained billet has a thickness of 230 mm. The process conditions are: the billet is heated to 1233°C in a heating furnace and kept warm for 47 minutes. The starting rolling temperature is 1048°C, the final rolling temperature is 859°C, the coiling temperature is 580°C, and the cooling mode is one-on-one.

[0033] Example 4

[0034] (1) The composition of Q550NHJE for containers was adjusted, and the formula was developed and designed after cost reduction to include the following chemical components in percentage by weight: C: 0.07, Si: 0.40, Mn: 0.70, P: 0.020, S: 0.003, Cu: 0.35, Cr: 0.35, Ti: 0.040, Ce: 0.0020, and the balance was Fe and incidental inclusions.

[0035] (2) The continuous casting billet drawing speed is 1.0 m / min, and the obtained billet has a thickness of 230 mm. The process conditions are: the billet is heated to 1233°C in a heating furnace and kept warm for 47 minutes. The starting rolling temperature is 1048°C, the final rolling temperature is 855°C, the coiling temperature is 578°C, and the cooling mode is one-on-one.

[0036] The production method of process 3 and 4 of the above-mentioned examples can solve the problem of high cost of Q550NHJE container steel. On the basis of reducing the component alloy, rare earth alloys are added to refine the inclusion morphology and grain size to ensure that the mechanical properties and corrosion resistance of the product meet the requirements. At the same time, the product performance has a certain margin by reducing the final rolling and coiling temperature. The hot-rolled microstructure is ferrite and pearlite. The microstructure morphology is consistent before and after cost reduction, and the grain size is close to level 9. From the feedback of the performance results of the chemical inspection, as shown in Table 1, the tensile test and -40℃ impact test meet the standard requirements before and after cost reduction, and the cost reduction goal is fully achieved.

[0037] Table 1 Q550NHJE performance distribution

[0038]

[0039]

[0040] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing low-cost rare earth Q550NHJE hot-rolled steel strip for container, characterized in that: The chemical composition and weight percentage of Q550NHJE after cost reduction are: C: 0.06-0.08%, Si: 0.37-0.47%, Mn: 0.65-0.75%, P: 0.015-0.025%, S≤0.005%, Cu: 0.30-0.40%, Cr: 0.30-0.40%, Ti: 0.035-0.045%, Ni: 0.05-0.13%, and the balance is Fe and incidental inclusions; The production method includes: The continuous casting billet drawing speed is 1.0m-1.6m / min, and the slab with a thickness of 230mm is obtained; The casting is heated in a heating furnace to a temperature of 1230±20°C and kept warm for 30-60 minutes; The rolling temperature is 1050±10℃, the final rolling temperature is 875±15℃, the coiling temperature is 600±15℃, and the cooling mode is alternate one-on-one.

2. The method for producing low-cost rare earth Q550NHJE hot-rolled steel strip for container according to claim 1, characterized in that: After cost reduction, the chemical composition and weight percentage of Q550NHJE are: C: 0.07%, Si: 0.40%, Mn: 0.70%, P: 0.020%, S: 0.003%, Cu: 0.35%, Cr: 0.35%, Ti: 0.040%, Ce: 0.0020%, and the balance is Fe and incidental inclusions.

3. The method for producing low-cost rare earth Q550NHJE hot-rolled steel strip for container according to claim 2, characterized in that: The continuous casting billet drawing speed is 1.0m / min, and the resulting billet has a thickness of 230mm. The billet is heated to 1233°C in a heating furnace and kept warm for 47min. The starting rolling temperature is 1048°C, the final rolling temperature is 855°C, the coiling temperature is 578°C, and the cooling mode is alternate-open-one.

4. The method for producing low-cost rare earth Q550NHJE hot-rolled steel strip for container according to claim 1, characterized in that: The production process includes: slab heating - high-pressure water descaling - fixed-width press - E1 R1 roughing mill rolling - E2R2 roughing mill rolling - flying shear - high-pressure water descaling - F1-F7 finishing mill rolling - encrypted laminar cooling - coiling.

5. The method for producing low-cost rare earth Q550NHJE hot-rolled steel strip for container according to claim 1, characterized in that: The thickness of the hot rolled plate is 6 mm.

6. The method for producing low-cost rare earth Q550NHJE hot-rolled steel strip for container according to claim 1, characterized in that: Atmospheric corrosion resistance index I = 6.0-6.8.

Images