A 700mpa grade csp short process hot-rolled high weather-resistant container steel and a production method thereof

Abstract

The application discloses a 700MPa-grade CSP short-process hot-rolled high-weather-resistance container steel and a production method thereof. The chemical components of the steel include C: 0.02-0.06%, Si: 0.20-0.65%, Mn: 1.1-1.8%, P: 0.035-0.15%, S: ≤0.008%, Cu: 0.20-0.55%, Sb: 0.02-0.25%, Ti: 0.10-0.18%, N ≤0.005%, and the balance is balanced iron and inevitable impurities, wherein the carbon equivalent CEV is controlled to be ≤0.35%. The preparation mainly includes the converter smelting, the LF ladle furnace refining, the thin slab continuous casting and rolling, the laminar cooling and the coiling steps. The container steel obtained by the application has good mechanical properties, corrosion resistance, welding performance, forming performance and cost advantage, realizes the lightweight and long service life of the container, and is suitable for popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of low-alloy high-strength steel manufacturing, specifically relating to a 700MPa grade CSP short-process hot-rolled high weather-resistant container steel and its production method. Background Technology

[0002] As a crucial piece of logistics equipment, lightweighting and extending the lifespan of shipping containers are of great significance for energy conservation, emission reduction, and environmental friendliness in their manufacturing and use. Increasing the strength of steel can reduce the container's weight, thereby lowering energy consumption and pollution emissions; improving the corrosion resistance of steel can extend the container's service life, achieving energy conservation and emission reduction throughout its lifecycle. Traditional ordinary shipping containers use SPA-H steel with a yield strength of 345MPa. This material has low strength and moderate corrosion resistance, resulting in high steel consumption, high container weight, high energy consumption during transportation, and a short service life, causing serious waste of resources and energy. Therefore, developing a high-strength, highly corrosion-resistant steel for shipping containers will create significant economic and social benefits. Summary of the Invention

[0003] This invention addresses the demand for steel used in containers by providing a 700MPa grade CSP short-process hot-rolled high weather-resistant container steel and its production method.

[0004] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0005] A 700MPa grade CSP short-process hot-rolled high weathering-resistant container steel plate is provided. The chemical composition, by mass percentage, includes C: 0.02–0.06%, Si: 0.20–0.65%, Mn: 1.1–1.8%, P: 0.035–0.15%, S: ≤0.008%, Cu: 0.20–0.55%, Sb: 0.02–0.25%, Ti: 0.10–0.18%, N ≤0.005%, with the balance being balance iron and unavoidable impurities; wherein the carbon equivalent (CEV) is controlled to ≤0.35%.

[0006] According to the above scheme, the thickness of the steel plate used for the container is 1.2 to 4.5 mm.

[0007] According to the above scheme, the steel plate for the container has a yield strength ≥700MPa, a tensile strength of 750~950MPa, and an elongation ≥20%. KV (-40℃)≥60J.

[0008] According to the above scheme, the steel plates used for containers are subjected to periodic immersion corrosion tests in accordance with the "TB / T 2375-93 Test Method for Cyclic Immersion Corrosion of Weathering Steel for Railways". The solution used is 0.01mol / L NaHSO3, the temperature is 45±2℃, the relative humidity is 70±5%, the test time is 72h, and the corrosion rate is ≤80% compared with ordinary weathering steel SPA-H for containers.

[0009] According to the above scheme, the carbon equivalent CEV = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15.

[0010] A production method for the above-mentioned 700MPa grade CSP short-process hot-rolled high weathering steel plate for containers is provided, which mainly includes converter smelting, LF ladle furnace refining, thin slab continuous casting and rolling, laminar flow cooling and coiling steps.

[0011] According to the above scheme, the specific steps of the production method are as follows:

[0012] 1) After being smelted in a converter, the molten steel enters the LF ladle furnace for refining.

[0013] 2) Thin slab continuous casting and rolling production of molten steel: The thickness of the cast slab is 55-85mm; then the slab is heated in a soaking furnace at a temperature of 1200-1240℃; finally, it is rolled in a 7-stand finishing mill with a finishing rolling temperature ≥1100℃, a reduction rate of ≥55% for the first three passes, a reduction rate of ≥45% for the F4 pass, and a reduction rate of ≥35% for the F5 pass. Constant speed rolling is adopted according to the thickness specification, with the rolling speed controlled at 2.5-15.0m / s, the final rolling temperature controlled at 880-930℃, and the rolled thickness 1.2-4.5mm.

[0014] 3) Laminar flow cooling: The water cooling rate is 60~110℃ / s, cooling to 660~710℃, and then cooling to 580~620℃ at a water cooling rate of ≤12℃ / s before coiling to obtain 700MPa grade CSP short-process hot-rolled high weather-resistant container steel plate.

[0015] Preferably, in step 2), when rolling is performed in a 7-stand finishing mill, the finishing mill opening temperature is 1100-1170°C, the reduction rate of the first three passes is 55-65%, the reduction rate of the F4 pass is 45-55%, and the reduction rate of the F5 pass is 35-45%.

[0016] Preferably, in step 3), the temperature is cooled to 580-620°C at a water cooling rate of 7-12°C / s before winding.

[0017] The properties of steel are determined by its composition, processing, and microstructure. This paper presents a 700MPa grade CSP short-process hot-rolled high weather-resistant container steel and its production method. The designed microstructure is ferritic, utilizing the Cu+P+Sb composite effect to significantly improve the steel's corrosion resistance. Furthermore, clean steel smelting technology and homogenized solidification control ensure the steel possesses excellent strength, toughness, and formability.

[0018] The role of each component and the main process in this invention, and the reasons for their control:

[0019] Carbon (C) is the most economical strengthening element, but excessive C content significantly deteriorates the formability and weldability of steel. It also causes peritectic reactions during casting, increasing the risk of leaks in continuous casting. Furthermore, C promotes pearlite transformation, thereby reducing the corrosion resistance of steel. This invention employs a low-C design to inhibit pearlite formation and improve the corrosion resistance, formability, and weldability of steel, limiting the C content to 0.02–0.06%.

[0020] Si: Silicon accelerates the segregation of carbon into austenite in steel, purifies ferrite, and prevents the formation of coarse carbides during cooling. At the same time, the uniform elongation of silicon in solid solution can also improve the corrosion resistance of steel. However, excessive silicon will form Fe2SiO4 during high-temperature rolling, which increases the adhesion of iron oxide scale and deteriorates the surface quality of steel plate. Therefore, the Si content should be controlled in the range of 0.20% to 0.65%.

[0021] Mn: Manganese is the most effective element for improving strength and toughness. It can lower the phase transformation temperature of austenite to ferrite, expand the austenite region in the iron-carbon phase diagram, promote the mid-temperature microstructure transformation of steel, and obtain a uniform microstructure, thereby giving the steel excellent strength and corrosion resistance. However, excessive Mn will aggravate central segregation, which is detrimental to corrosion resistance and impact toughness. Therefore, this invention controls the Mn content to 1.1-1.8%.

[0022] P is the most economical and effective corrosion-resistant element. Under atmospheric corrosion conditions, P in steel is an anodic depolarizer. It can accelerate the uniform dissolution of steel and the oxidation rate of iron, and help to form a uniform FeOOH rust layer on the steel surface, generating an amorphous dense protective film. However, P is prone to segregation in steel. Excessive P will be harmful to the impact toughness and elongation of steel. Therefore, the P content is designed to be 0.035-0.15%.

[0023] Cu is a major element for atmospheric corrosion resistance. When its content reaches 0.20% or more, it significantly improves the atmospheric corrosion resistance of steel. Cu combined with P and Sb can further improve the corrosion resistance of steel significantly. However, when the Cu content is too high, it significantly deteriorates the weldability of the steel plate and aggravates the "copper brittleness" defect on the surface of the steel plate. Therefore, the Cu content in this invention is controlled within the range of 0.20% to 0.55%.

[0024] Sb can form a dense Sb2O5 protective film on the surface of steel, while promoting the enrichment of Cu and P elements in the dense inner rust layer, significantly improving the corrosion resistance of steel; however, Sb is prone to enrichment at grain boundaries, affecting the formability and toughness of steel, and Sb has a low melting point, so adding it together with Cu will aggravate the "copper embrittlement" defect; therefore, the Sb content in this invention is controlled at 0.02% to 0.25%.

[0025] Ti: Ti forms TiC second-phase particles in steel, hindering austenite grain growth, significantly refining austenite grains, increasing the austenite grain boundary area, and reducing the penetration depth of the liquid Cu-rich phase on the steel matrix surface into the austenite grain boundaries. This effectively suppresses the "copper embrittlement" defect easily caused by the combined addition of Cu and Sb in the steel of this invention. On the other hand, the addition of Ti plays a certain strengthening role. While maintaining the original strength level, the design value of C can be reduced, and the C element can be fixed as TiC, further inhibiting the transformation of C-rich austenite to pearlite, forming a single-phase ferrite structure, avoiding galvanic corrosion between different structures in conventional ferrite-pearlite steel, thereby further improving the corrosion resistance of the steel. In addition, the TiC particles formed by the addition of Ti hinder grain growth in the heat-affected zone during welding, improving the weldability of the steel. However, Ti content above 0.18% has no significant effect on further improving strength; therefore, the Ti content is designed to be 0.10–0.18%.

[0026] S and N: They easily combine with Ti in steel, affecting the strengthening effect of Ti and greatly affecting the plasticity of steel. In this invention, sulfur is controlled at ≤0.008% and nitrogen is controlled at ≤0.005%.

[0027] CEV: Carbon equivalent can predict the extent to which cold cracking (hydrogen-induced cracking) will occur in steel during welding. The higher the carbon content, the easier it is for cold cracking (hydrogen-induced cracking) to occur during welding. Therefore, this invention controls the carbon equivalent CEV = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 ≤ 0.35%, resulting in low hardenability of the steel plate and excellent weldability.

[0028] The beneficial effects of this invention are as follows:

[0029] 1. This invention provides a 700MPa grade CSP short-process hot-rolled high weather-resistant container steel plate. The composite effect of Cu+P+Sb improves the steel's corrosion resistance, avoiding the addition of expensive alloying elements such as Cr and Ni in traditional weather-resistant steel, thus significantly reducing production costs. Simultaneously, Ti effectively suppresses the "copper embrittlement" defect easily caused by the composite addition of Cu and Sb in the steel of this invention. Furthermore, it allows for a reduction in C content while ensuring strength, combining with C to form TiC, avoiding the formation of pearlite by C which affects corrosion resistance, and forming a ferrite single-phase structure, further improving corrosion resistance and weldability. The resulting container steel plate has a thickness of 1.2–4.5 mm, requiring a yield strength ≥700MPa, tensile strength 750–950MPa, elongation ≥20%, and AKV (-40℃) ≥60J. It possesses excellent mechanical properties, corrosion resistance, weldability, formability, and cost advantages, achieving lightweight and long-life containers, making it suitable for widespread application.

[0030] 2. This invention provides a method for producing 700MPa grade CSP short-process hot-rolled high weather-resistant container steel plates. The process is simple and low-cost, and the steel produced has good strength, toughness, formability and corrosion resistance, and has promising prospects for industrial application. Detailed implementation method:

[0031] The present invention will now be described in detail through specific embodiments.

[0032] Each embodiment of the present invention is produced according to the following steps:

[0033] 1) After being smelted in a converter, the molten steel enters the LF furnace for refining.

[0034] 2) Subsequently, the molten steel is continuously cast and rolled into thin slabs: the thickness of the cast slabs is 55-85mm; the slabs are heated in a soaking furnace at a temperature controlled at 1200-1240℃; they are rolled in a 7-stand finishing mill at a starting temperature ≥1100℃, a reduction rate of ≥55% for the first three passes, a reduction rate of ≥45% for the F4 pass, and a reduction rate of ≥35% for the F5 pass. Constant speed rolling is adopted according to the thickness specification, with the rolling speed controlled at 2.5-15.0m / s, the final rolling temperature controlled at 880-930℃, and the rolled thickness 1.2-4.5mm.

[0035] 3) Laminar flow cooling: The water cooling rate is 60-110℃ / s, cooling to 660-710℃, and then cooling to 580-620℃ at a water cooling rate of ≤12℃ / s before winding.

[0036] Table 1 shows the chemical composition values ​​of each embodiment and comparative example of the present invention; the comparative example is SPA-H, the most commonly used steel plate for containers.

[0037] Table 2 is a list of the main process parameters for each embodiment of the present invention;

[0038] Table 3 is a list of mechanical properties of various embodiments and comparative examples of the present invention;

[0039] Table 4 shows the corrosion resistance test results of the steel obtained in the embodiments of the present invention and the comparative examples.

[0040] Table 1 Chemical composition (mass fraction, %) of the examples

[0041] Example C Si Mn P S Cu Cr Ni Sb Ti N CEV 1 0.031 0.436 1.32 0.039 0.007 0.38 / / 0.057 0.172 0.004 0.28 2 0.022 0.335 1.13 0.141 0.005 0.22 / / 0.028 0.123 0.003 0.23 3 0.051 0.231 1.77 0.072 0.003 0.53 / / 0.235 0.157 0.004 0.38 4 0.046 0.576 1.42 0.096 0.004 0.41 / / 0.104 0.118 0.002 0.31 5 0.039 0.457 1.62 0.128 0.006 0.48 / / 0.167 0.162 0.003 0.34 6 0.056 0.483 1.58 0.058 0.005 0.33 / / 0.083 0.141 0.004 0.34 Comparative Example 0.128 0.303 0.53 0.085 0.012 0.31 0.42 0.12 / / 0.008 0.329

[0042] Table 2. List of main process parameters for each embodiment of the present invention.

[0043]

[0044] Table 3 Mechanical properties and microstructure of each embodiment

[0045]

[0046] To demonstrate the superior corrosion resistance of the steel of this invention, corrosion tests were conducted under the following conditions:

[0047] The cyclic immersion corrosion test was conducted in accordance with the "TB / T 2375-93 Test Method for Cyclic Immersion Corrosion of Weathering Steel for Railways". The solution used was 0.01 mol / L NaHSO3, the temperature was 45±2℃, the relative humidity was 70±5%, and the test time was 72h. The test results are shown in Table 4 below.

[0048] Table 4 Results of the periodic immersion corrosion test (72h)

[0049] Sample <![CDATA[Corrosion rate (g / m 2 ·h)]]> Example / Comparative Example (%) Example 1 4.512 78.44 Example 2 4.101 71.30 Example 3 4.472 77.75 Example 4 4.152 72.18 Example 5 3.987 69.32 Example 6 4.246 73.82 Comparative Example 5.752 100

[0050] As shown in Table 3, the steel in the embodiments of the present invention has a yield strength ≥700MPa, a tensile strength of 750~950MPa, and an elongation ≥20%. KV (-40℃) ≥60J, demonstrating the excellent mechanical properties of the steel of this invention, especially its good toughness and plasticity. Table 4 shows that the corrosion rate of the steel in the example in the immersion test in 0.01mol / L solution is ≤80% compared with ordinary weathering steel SPA-H, and its corrosion resistance is significantly improved compared with SPA-H, exhibiting excellent corrosion resistance in atmospheric environment.

[0051] The above is a detailed description of the process steps of the preferred embodiment of the present invention. Those skilled in the art can make non-substantial changes in form and content based on the above steps without departing from the scope of substantive protection of the present invention. Therefore, the present invention is not limited to the specific implementation examples described above.

Claims

1. A 700MPa grade CSP short-process hot-rolled high weather-resistant container steel plate, characterized in that, By mass percentage, the chemical composition includes C: 0.02~0.039%, Si: 0.335~0.65%, Mn: 1.32~1.8%, P: 0.035~0.15%, S: ≤0.008%, Cu: 0.38~0.55%, Sb: 0.02~0.25%, Ti: 0.10~0.18%, N≤0.005%, with the balance being balance iron and unavoidable impurities; wherein the carbon equivalent (CEV) is controlled to be ≤0.35% and not less than 0.23%. The steel plates used for containers have a yield strength ≥700MPa, a tensile strength of 750~950MPa, and an elongation ≥20%. KV (-40℃) ≥60J; The steel plate for the container is subjected to a periodic immersion corrosion test in accordance with "TB / T 2375-93 Test Method for Periodic Immersion Corrosion of Weathering Steel for Railway", and the corrosion rate is ≤80% compared with ordinary weathering steel SPA-H for containers; The production method of the steel plate for containers mainly includes converter smelting, LF ladle furnace refining, thin slab continuous casting and rolling, laminar flow cooling and coiling steps, wherein: 1) After being smelted in a converter, the molten steel enters the LF ladle furnace for refining. 2) Thin slab continuous casting and rolling production of molten steel: The thickness of the cast slab is 55~85mm; then the slab is heated in a soaking furnace, and the heating temperature is controlled at 1200~1240℃; finally, it is rolled in a 7-stand finishing mill, with a finishing rolling temperature ≥1100℃, a reduction rate of ≥55% for the first three passes, a reduction rate of ≥45% for the F4 pass, and a reduction rate of ≥35% for the F5 pass. Constant speed rolling is adopted according to the thickness specification, with the rolling speed controlled at 2.5~15.0m / s, the final rolling temperature controlled at 880~930℃, and the rolled thickness 1.2~4.5mm; 3) Laminar flow cooling: The water cooling rate is 60~110℃ / s, cooling to 660~710℃, and then cooling to 580~620℃ at a water cooling rate of ≤12℃ / s before coiling to obtain 700MPa grade CSP short-process hot-rolled high weather-resistant container steel plate.

2. The steel plate for containers according to claim 1, characterized in that, The thickness of the steel plates used for the containers is 1.2~4.5mm.

3. A method for producing 700MPa grade CSP short-process hot-rolled high weathering-resistant container steel plate as described in claim 1, characterized in that, The main processes include converter smelting, LF ladle furnace refining, thin slab continuous casting and rolling, laminar flow cooling, and coiling. 1) After being smelted in a converter, the molten steel enters the LF ladle furnace for refining. 2) Thin slab continuous casting and rolling production of molten steel: The thickness of the cast slab is 55~85mm; then the slab is heated in a soaking furnace, and the heating temperature is controlled at 1200~1240℃; finally, it is rolled in a 7-stand finishing mill, with a finishing rolling temperature ≥1100℃, a reduction rate of ≥55% for the first three passes, a reduction rate of ≥45% for the F4 pass, and a reduction rate of ≥35% for the F5 pass. Constant speed rolling is adopted according to the thickness specification, with the rolling speed controlled at 2.5~15.0m / s, the final rolling temperature controlled at 880~930℃, and the rolled thickness 1.2~4.5mm; 3) Laminar flow cooling: The water cooling rate is 60~110℃ / s, cooling to 660~710℃, and then cooling to 580~620℃ at a water cooling rate of ≤12℃ / s before coiling to obtain 700MPa grade CSP short-process hot-rolled high weather-resistant container steel plate.

4. The production method according to claim 3, characterized in that, In step 2), when rolling is performed on a 7-stand finishing mill, the finishing mill opening temperature is 1100~1170℃, the reduction rate of the first three passes is 55~65%, the reduction rate of the F4 pass is 45~55%, and the reduction rate of the F5 pass is 35~45%.

5. The production method according to claim 3, characterized in that, In step 3), the temperature is cooled to 580-620°C at a water cooling rate of 7-12°C / s before winding.

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