A method for preparing a thin-gauge Nb-containing corrosion-resistant container steel

Abstract

The application discloses a preparation method of a thin-gauge Nb-containing corrosion-resistant container steel, characterized by the following chemical components in percentage by weight: C: 0.06-0.08%, Si: ≤0.25%, Mn: 1.48-1.60%, P: ≤0.016%, S: ≤0.005%, Nb: 0.035-0.045%, Ti: 0.010-0.015%, Cr: 0.030-0.040%, and the balance of Fe and inevitable impurities; and main production process steps and process parameters are also disclosed. The application aims to provide a preparation method of a thin-gauge Nb-containing corrosion-resistant container steel, which has good strength and toughness, high corrosion resistance, easy weldability, low production cost and short production cycle.

Description

Technical Field

[0001] This invention relates to the technical field of weathering steel for containers, and more particularly to a method for preparing thin-gauge Nb-containing corrosion-resistant container steel. Background Technology

[0002] Container shipping is a modern mode of transportation, characterized by its speed, safety, economy, and efficiency. With the increasing demands of the international market, container shipping plays an increasingly important role. The development of container shipping has also driven the development of the container manufacturing industry. Since the introduction of container production technology in the early 1980s, my country has become the world's largest container producer. Due to the special working environment and load-bearing conditions of containers, the market has high requirements for the steel used in containers: firstly, to extend the service life of containers and reduce operating costs, the steel used must have good resistance to atmospheric corrosion; secondly, to enhance the impact resistance of the container and reduce the degree of damage, the steel must have high strength and good toughness; thirdly, to reduce production costs and the weight of containers, the need for thinner container panels is becoming increasingly urgent. Currently, there is a trend in the field of container steel to use high-strength weathering steel to replace traditional ordinary-strength weathering steel, and the strength levels of the steel used are becoming increasingly higher. Therefore, the research and development of high-strength weathering steel for containers and the increase in market share are of great significance.

[0003] Liu Zhiwei et al. (Liu Zhiwei et al., Development of 700MPa Grade High-Strength Container Steel, Shanghai Metals, 2013, No. 4) developed a 700MPa grade container steel from Ansteel with the following composition by mass percentage: C 0.07-0.09%, Si 0.10-0.20%, Mn 1.60-1.90%, Nb+Ti+Mo ≤ 0.28%. Using the TMCP rolling method, the yield strength of the steel plate reached over 700MPa, and the tensile strength exceeded 750MPa. The addition of Mo shifts the pearlite transformation on the C-curve to the right, promoting bainite formation and playing a certain role in phase transformation strengthening. However, adding Mo alloys increases production costs.

[0004] Zhou Cong et al. (Zhou Cong et al., Microstructure and Properties of Ti Microalloyed 700MPa Grade Weathering Steel for Containers, Journal of Materials Heat Treatment, 2020, No. 8) developed a 700MPa grade container steel with the following composition by mass percentage: C 0.02-0.04%, Si 0.15-0.30%, Mn 1.38-1.50%, Cu 0.3-0.4%, Ni 0.2-0.3%, Cr 0.7-0.9%, Ti ≤0.21%. Using the TMCP rolling method, the yield strength of the steel plate reached over 700MPa, and the tensile strength exceeded 750MPa. However, the addition of metallic Ni increased production costs.

[0005] Li Wenyuan et al. (Li Wenyuan et al., Influence of Final Rolling Temperature on Microstructure and Properties of Hot-Rolled High-Strength Container Steel, Journal of Iron and Steel Research, 2015, No. 8) employed niobium-titanium composite strengthening. By controlling the rolling and cooling processes, they fully utilized the precipitation strengthening and grain refinement strengthening effects of Nb and Ti elements to obtain 700MPa grade hot-rolled high-strength container steel with excellent comprehensive mechanical properties. However, the addition of 0.1%-0.2% Ni alloy increased production costs. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing thin-gauge Nb-containing corrosion-resistant container steel, which has good strength and toughness, high corrosion resistance, easy weldability, low production cost, and short production cycle.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a method for preparing thin-gauge Nb-containing corrosion-resistant container steel. The chemical composition of the thin-gauge Nb-containing corrosion-resistant container steel, by weight percentage, is: C: 0.06-0.08%, Si: ≤0.25%, Mn: 1.48-1.60%, P: ≤0.016%, S≤0.005%, Nb: 0.035-0.045%, Ti: 0.010-0.015%, Cr: 0.030-0.040%, with the balance being Fe and unavoidable impurities.

[0009] The main production steps and process parameters are as follows:

[0010] 1) Smelting and casting

[0011] The prepared high-quality scrap steel with low phosphorus (≤0.010%), low sulfur (≤0.005%), low oxygen (≤0.0040%), and low nitrogen (≤0.0060%) and other calculated alloys are added to the vacuum smelting furnace. After vacuuming, the furnace is started for melting and smelting. After melting, the steel is cast into a rectangular steel mold to form a rectangular steel billet with dimensions of 220×250×300mm.

[0012] 2) Heating and rolling:

[0013] The steel billet is loaded into a high-temperature resistance furnace using a robotic arm, and heated to 1200℃-1250℃. The total time spent in the furnace is ≥240min to ensure uniform billet temperature. Once the billet reaches the heating requirements, it is transported to a φ750×550mm experimental rolling mill using a robotic arm. The rolling process is divided into two stages. The first stage is rolling in the austenite recrystallization zone, with the first pass reduction controlled at ≥10%. The second stage is rolling in the non-recrystallization zone, with the finishing rolling starting temperature ≥950℃ and the finishing rolling temperature 900-940℃.

[0014] 3) Cooling

[0015] After controlled rolling, the steel plate enters the laminar flow cooling zone and adopts the front-stage cooling mode, with a final cooling temperature of 600-640℃.

[0016] Furthermore, the chemical composition of the thin-gauge Nb-containing corrosion-resistant container steel, by weight percentage, is C: 0.08%, Si: 0.12%, Mn: 1.55%, P: 0.010%, S: 0.0015%, Nb: 0.045%, Ti: 0.013%, Cr: 0.040%, with the balance being Fe and unavoidable impurities.

[0017] Furthermore, the chemical composition of the thin-gauge Nb-containing corrosion-resistant container steel is as follows by weight percentage: C: 0.07%, Si: 0.14%, Mn: 1.48%, P: 0.009%, S: 0.0015%, Nb: 0.035%, Ti: 0.015%, Cr: 0.035%, with the balance being Fe and unavoidable impurities.

[0018] Furthermore, the chemical composition of the thin-gauge Nb-containing corrosion-resistant container steel, by weight percentage, is C: 0.06%, Si: 0.16%, Mn: 1.60%, P: 0.010%, S: 0.0015%, Nb: 0.040%, Ti: 0.010%, Cr: 0.030%, with the balance being Fe and unavoidable impurities.

[0019] Furthermore, the mechanical properties meet the following requirements: yield strength ≥700MPa, tensile strength ≥750MPa, elongation A ≥12%, cold bending d=1.5a, and good longitudinal impact resistance at -20℃.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0021] The technical problem to be solved by this invention is to provide a method for preparing thin-gauge Nb-containing corrosion-resistant steel for containers. Through reasonable composition design, the hot-rolled steel strip adopts a C-Si-Mn-Nb-Ti composition design, adding trace amounts of the alloying element Nb to the steel. Nb can increase the recrystallization temperature of austenite and expand the non-recrystallized region, that is, to achieve rolling in the non-recrystallized region of austenite at a higher temperature, thereby enabling the rolled piece to complete rolling deformation at a higher temperature and obtaining a fine phase transformation structure. In addition, a certain amount of Ti is added, mainly relying on the precipitation of fine TiC second-phase particles in the ferrite region to inhibit dislocation movement and thus improve the yield strength.

[0022] The microstructure consists of ferrite and pearlite, with a grain size of approximately 12.0. It exhibits good strength and toughness, high corrosion resistance, and easy weldability, making it suitable for weathering steel used in containers requiring good corrosion resistance. Its mechanical and technological properties meet the requirements of yield strength ≥700MPa, tensile strength ≥750MPa, elongation A ≥12%, and wide cold bending d=1.5a. It also possesses good impact resistance at -20℃. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings.

[0024] Figure 1 This is a metallographic diagram of the steel plate in Embodiment 2 of the present invention;

[0025] Figure 2 This is a photograph showing the morphology of the TiC and NbC composite precipitates on the steel plate of Example 2 of the present invention. Detailed Implementation

[0026] The present invention will be described in more detail below with reference to examples. These examples are merely descriptions of the best mode of implementation of the invention and do not limit the scope of the invention in any way.

[0027] Example 1

[0028] The steel was smelted according to the chemical composition shown in Table 1 and cast into ingots. The ingots were heated to 1200℃ for a total furnace time of 250 minutes. The first stage of rolling, i.e., rolling in the austenite recrystallization zone, was performed on an experimental rolling mill. The first pass reduction should be greater than 10%, followed by at least one or two passes with a reduction rate controlled above 25%. The second stage of rolling, i.e., rolling in the non-recrystallization zone, was then performed. The final rolling temperature was 900℃, and the finished steel plate thickness was 3mm. After rolling, the steel plate entered the laminar flow cooling zone, with a final cooling temperature of 600℃, resulting in a fine and uniform ferrite + pearlite microstructure.

[0029] Example 2

[0030] The implementation method is the same as in Example 1. The steel ingot is heated to 1220°C, with a total furnace time of 255 minutes. The first stage of rolling, i.e., rolling in the austenite recrystallization zone, is performed on an experimental rolling mill. The reduction in the first pass should be greater than 10%, followed by at least one or two passes with a reduction rate controlled above 25%. The second stage of rolling, i.e., rolling in the non-recrystallization zone, is then performed. The final rolling temperature is 920°C, and the finished steel plate thickness is 3 mm. After rolling, the steel plate enters the laminar flow cooling zone, with a final cooling temperature of 620°C, resulting in a fine and uniform ferrite + pearlite microstructure.

[0031] Example 3

[0032] The implementation method is the same as in Example 1, except that the heating temperature is 1250℃, the total furnace time is 260 minutes, and the first stage rolling (rolling in the austenite recrystallization zone) is performed on an experimental rolling mill. The reduction in the first pass should be greater than 10%, and at least one or two subsequent passes should have a reduction rate controlled above 25% for the second stage rolling (rolling in the non-recrystallization zone of austenite). The final rolling temperature is 940℃, and the thickness of the finished steel plate is 3mm. After rolling, the steel plate enters the laminar flow cooling zone, and the final cooling temperature is 640℃, resulting in a fine and uniform ferrite + pearlite microstructure.

[0033] Table 1. Chemical composition (wt%) of Examples 1-3 of the present invention

[0034]

[0035]

[0036] Table 2 Mechanical properties of the heat-treated steel plates from Examples 1-3 of this invention

[0037]

[0038] As shown in Table 2, the method for preparing thin-gauge Nb-containing corrosion-resistant steel for containers provided by this invention achieves the following mechanical and technological properties: yield strength ≥ 700 MPa, tensile strength ≥ 750 MPa, elongation A ≥ 12%, cold bending d = 1.5a, and good longitudinal impact resistance at -20℃. The results from the above embodiments demonstrate that the thin-gauge Nb-containing corrosion-resistant steel for containers of this invention possesses excellent mechanical properties, especially its low-temperature toughness, while also exhibiting good corrosion resistance.

[0039] In the laboratory, a controlled rolling and controlled cooling process was used on a φ750×550mm rolling mill to obtain a metallographic structure dominated by fine ferrite and pearlite, resulting in good strength, toughness, high corrosion resistance, and easy weldability. This provides technical support for on-site industrial trials.

[0040] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for manufacturing a thin-gauge Nb-containing corrosion-resistant container steel, characterized by, The chemical composition of the thin-gauge Nb-containing corrosion-resistant container steel contains, by weight percent, C: 0.06-0.08%, Si: ≤0.25%, Mn: 1.48-1.60%, P: ≤0.016%, S ≤0.005%, Nb: 0.035-0.045%, Ti: 0.010-0.015%, Cr: 0.030-0.040%, and the balance of Fe and inevitable impurities. The main production process steps and process parameters are as follows: 1) Smelting and casting The prepared low-phosphorus, low-sulfur, low-oxygen, low-nitrogen high-quality scrap steel and the calculated other alloys are added to a vacuum smelting furnace, and after vacuumizing, melting smelting is started, and after melting, the steel is cast into a rectangular steel mold to form a rectangular billet; 2) Heating and rolling: The billet is loaded into a high-temperature resistance furnace by a mechanical hand, the heating temperature is 1200-1250℃, the total furnace time is ≥240min, and the billet temperature is uniform, and when the billet reaches the heating requirement, the billet is sent to the rolling mill by a mechanical hand; rolling is divided into two stages, the first stage is rolled in the austenite recrystallization zone, the first pass reduction rate is controlled to be more than 10%, and the second stage is rolled in the austenite non-recrystallization zone, the rough rolling starting temperature is ≥950℃, and the finish rolling temperature is 900-940℃; 3) Cooling After the rolling is completed, the steel plate enters the laminar cooling area, adopts the front cooling mode, and the final cooling temperature is 600-640℃; The mechanical properties meet the requirements of yield strength ≥700MPa, tensile strength ≥750MPa, elongation A ≥12%, cold bending d=1.5a, and good longitudinal impact energy at-20℃; the microstructure is ferrite+pearlite, and the grain size is 12.0 grade.

2. The method of claim 1, wherein the method further comprises, after the annealing, cold rolling the steel sheet to a thickness of 1.5 mm or less. The chemical composition of the thin-gauge Nb-containing corrosion-resistant container steel contains, by weight percent, C: 0.08%, Si: 0.12%, Mn: 1.55%, P: 0.010%, S: 0.0015%, Nb: 0.045%, Ti: 0.013%, Cr: 0.040%, and the balance of Fe and inevitable impurities.

3. The method of claim 1, wherein the method further comprises, after the annealing, cold rolling the steel sheet to a thickness of 1.5 mm or less. The chemical composition of the thin-gauge Nb-containing corrosion-resistant container steel contains, by weight percent, C: 0.07%, Si: 0.14%, Mn: 1.48%, P: 0.009%, S: 0.0015%, Nb: 0.035%, Ti: 0.015%, Cr: 0.035%, and the balance of Fe and inevitable impurities.

4. The method for preparing thin-gauge Nb-containing corrosion-resistant container steel according to claim 1, characterized in that, The chemical composition of the thin-gauge Nb-containing corrosion-resistant container steel contains, by weight percent, C: 0.06%, Si: 0.16%, Mn: 1.60%, P: 0.010%, S: 0.0015%, Nb: 0.040%, Ti: 0.010%, Cr: 0.030%, and the balance of Fe and inevitable impurities.

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