A 700MPa yield grade corrosion-resistant high-strength high-plasticity steel and its manufacturing method

Abstract

The invention discloses a 700MPa yield grade corrosion-resistant high-strength and high-plasticity steel, the chemical composition of which is as follows: C: 0.05-0.07%, Si: 0.75-0.90%, Mn: 1.30-1.50%, P: ≤0.020%, S: ≤0.005%, Ti: 0.11-0.15%, Cu: 0.20-0.30%, Cr: 0.40-0.90%, and the balance is iron and inevitable impurities; the manufacturing method comprises the following steps: the casting temperature is ≥950°C, the heating temperature is controlled at 1200-1240°C, and the heating time is ≥70 min; control the rough rolling end temperature at 1080-1120°C; control the finishing temperature of fine rolling at 800-880°C; use high-pressure water cooling in the first stage, with a cooling rate of 60-200°C / s, and stop cooling to 610-650°C; use air cooling in the second stage, with a cooling time of 4-12s; use low-pressure water cooling in the third stage, with a cooling rate of 20-50°C / s; control the coiling temperature at 560-600°C; the resulting product has a yield strength of ≥700MPa, a tensile strength of 750-870MPa, an elongation A of ≥21%, and an average corrosion rate of ≤1.8g / m 2 ·h.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and in particular relates to a 700MPa yield grade corrosion-resistant high-strength and high-plasticity steel and a manufacturing method thereof. Background Art

[0002] With the trend toward lightweight commercial vehicles, the development and application of high-strength steel is becoming increasingly widespread. However, the reduced formability associated with high strength steel has become a significant constraint on its application. Furthermore, the resulting reduction in steel plate thickness often results in lightweight parts being susceptible to environmental corrosion under complex operating conditions, shortening their service life. This, in turn, restricts the widespread adoption of high-strength steel in industries such as automotive and construction.

[0003] A preliminary search revealed Chinese patent application number CN101525717A, which discloses a 700 MPa-grade Ti microalloyed ultrafine-grain hot-rolled steel and its production method. The patent's comprehensive performance is as follows: yield strength ≥ 700 MPa, tensile strength ≥ 750 MPa, elongation ≥ 14%, and impact energy absorption (Akv) ≥ 33 J for a half-size specimen (5 x 10 x 55 mm) at -20°C. However, the patent's actual elongation is relatively low, potentially posing challenges in forming complex parts. The patent also fails to address corrosion resistance.

[0004] Chinese patent application CN101538681A discloses a method for producing high-strength steel with a yield strength of 700 MPa. The steel's chemical composition (wt%) is as follows: 0.03-0.08% C, 0.20-0.50% Si, 1.4-2.0% Mn, 0.10-0.15% Ti, 0.02-0.08% Nb, 0-0.3% V, and 0.02-0.06% Al. The limiting elements S are ≤ 0.008%, N ≤ 0.008%, and P ≤ 0.04%, with the remainder consisting of Fe and unavoidable impurities. The process involves continuous casting of thin slabs, with a furnace entry temperature of 950-1050°C, a heating temperature greater than or equal to 1150°C, a furnace discharge temperature of 1080-1160°C, a final rolling temperature of 820-880°C, and, after laminar cooling, a coiling temperature of 550-620°C. The patented material does not involve corrosion resistance.

[0005] Chinese patent application number CN101921965A discloses a low-cost, non-quenched and tempered, high-strength, weather-resistant container steel with a yield strength of 700 MPa and a manufacturing method. The steel's composition is as follows: C: 0.05-0.10%; Si: ≤0.15%; Mn: 1.5-2.0%; P ≤0.015%; S ≤0.01%; Cr: 0.3-0.8%; Cu: 0.2-0.4%; Ni: 0.15-0.4%; Ti: 0.09-0.15%; Nb: 0.02-0.08%; N ≤0.005%; O ≤0.002%; the remainder being iron and unavoidable impurities. The steel has a yield strength exceeding 700 MPa, a tensile strength exceeding 800 MPa, and an elongation exceeding 18%. This patented alloy contains many elements, has high preparation cost, and has low elongation, which is not conducive to the formation of complex parts.

[0006] Chinese patent application number CN104480397A discloses a high-strength automotive steel and its manufacturing method, specifically a 700 MPa-grade hot-rolled automotive structural steel and its preparation method. The steel comprises the following chemical composition by weight: C 0.05-0.1%, Si 0.30-0.60%, Mn 0.50-1.00%, Alt 0.02-0.06%, Cr 0.60-1.00%, P ≤ 0.06%, Ti 0.05-0.10%, S ≤ 0.005%, N ≤ 0.006%, with the balance being Fe and unavoidable impurities. This invention significantly reduces costs by adding Cr, Ti, and P to the C-Si-Mn steel composition. However, the high P content is detrimental to cold forming properties, and corrosion resistance is not addressed.

[0007] Chinese patent application number CN101568659A discloses a high-strength hot-rolled steel plate with excellent weather resistance for use in containers. The plate contains, by weight, 0.05-0.07% C, 2.5% or less Mn, 0.04-0.06% Nb, 0.08-0.10% Ti, 0.30-0.60% Cu, 0.5-1.0% Cr, and 0.15-0.30% Ni, with the remainder being Fe and other unavoidable impurities. A method for manufacturing the hot-rolled steel plate is also provided. According to one aspect of the present invention, the hot-rolled steel plate is weather-resistant by adding Cu, Cr, and Ni, and exhibits material properties such as a tensile strength in the range of 800-900 MPa and a yield strength in the range of 700-800 MPa.

[0008] How to ensure high plasticity and good corrosion resistance while using economical components to ensure the steel yield level of 700MPa has become a technical problem that needs to be solved urgently. Summary of the Invention

[0009] The present invention aims to provide a high-strength and high-plasticity steel with a yield strength of 700 MPa and atmospheric corrosion resistance, and a method for manufacturing the same. The high-strength steel produced has a thickness of 1.2 to 16 mm, a yield strength of ≥ 700 MPa, a tensile strength of 750 to 870 MPa, an elongation A of ≥ 21%, and an average corrosion rate of ≤ 1.8 g / m 2 ·h.

[0010] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0011] Disclosed is a 700MPa yield grade corrosion-resistant high-strength and high-plasticity steel. Its chemical composition, by mass percentage, includes C: 0.05-0.07%, Si: 0.75-0.90%, Mn: 1.30-1.50%, P: ≤0.020%, S: ≤0.005%, Ti: 0.11-0.15%, Cu: 0.20-0.30%, Cr: 0.40-0.90%, and the balance being iron and unavoidable impurities.

[0012] According to the above solution, the mass percentage of Cu is 0.22-0.28%.

[0013] According to the above solution, the mass percentage of Cr is 0.50-0.79%.

[0014] The method for manufacturing the above-mentioned 700MPa yield grade corrosion-resistant high-strength and high-plasticity steel comprises the following steps:

[0015] 1) Heating the ingot: the ingot temperature is ≥950℃, the heating temperature is controlled at 1200~1240℃, and the heating time is ≥70min;

[0016] 2) Rough rolling the heated ingot: the rough rolling end temperature is controlled at 1080-1120°C;

[0017] 3) Finish rolling the slab after rough rolling: control the finishing rolling temperature at 800-880°C;

[0018] 4) The steel plate after rolling is cooled by different media: the first stage uses high-pressure water cooling, the cooling rate of the steel plate is 60-200℃ / s, and the cooling stops when the temperature reaches 610-650℃; the second stage uses air cooling, the cooling time is 4-12s; the third stage uses low-pressure water cooling, the cooling rate is 20-50℃ / s;

[0019] 5) Coil the cooled steel plate: control the coiling temperature at 560-600°C.

[0020] According to the above scheme, the heating temperature in step 1 is controlled at 1200-1230°C.

[0021] According to the above scheme, in step 4, the first cooling rate is 80-160°C / s to cool to 620-645°C; the second air cooling time is 6-11s; and the third cooling rate is 25-45°C / s.

[0022] According to the above scheme, the product has a yield strength of ≥700MPa, a tensile strength of 750-870MPa, an elongation A of ≥21%, and an average corrosion rate of steel of ≤1.8g / m 2 ·h.

[0023] The role and reasons for control of the main components and processes in the present invention:

[0024] Carbon: Carbon is an inexpensive solid solution strengthening element. This steel grade is primarily used for forming automotive and construction parts, typically processed by stamping, which places high demands on formability. A carbon content below 0.05% fails to meet strength requirements, while a content above 0.07% fails to provide adequate formability. Therefore, its content is limited to 0.05-0.07%.

[0025] Silicon: Silicon accelerates carbon segregation toward austenite in steel, purifies ferrite, and prevents the formation of coarse carbides during cooling. Solid-solution silicon also helps even out elongation, so the lower limit for silicon is 0.75%. However, excessive silicon content can form Fe2SiO4 during high-temperature rolling, increasing the adhesion of oxide scale and deteriorating the surface quality of the steel plate. Therefore, the upper limit of silicon content must be controlled. Therefore, the content is limited to 0.75 < C < 0.90%.

[0026] Copper: Copper, through cathodic contact between steel and secondary Cu deposited on its surface, promotes anodic passivation of the steel, forming a rust layer that protects the steel matrix, significantly improving the steel's corrosion resistance. It also provides solid solution and precipitation strengthening. However, when the Cu content exceeds 0.30%, copper embrittlement may occur on the steel plate surface. Therefore, the present invention controls the Cu content to 0.20% to 0.30%.

[0027] Chromium: Chromium forms a dense oxide film on the steel surface, improving the steel's passivation ability and thus enhancing corrosion resistance. Chromium also helps refine ferrite grains and precipitates, improving the steel's strength and formability. Therefore, the present invention limits the Cr content to 0.4% to 0.9%.

[0028] Manganese: Manganese is the most effective element for improving strength and toughness. If its content is less than 1.30%, the material's strength requirements cannot be met. However, adding too much manganese increases the steel's hardenability, leading to increased crack sensitivity due to the formation of a weld hardened layer, and increases the alloying cost of the steel. For this reason, the upper limit is set at 1.50%, and the content is therefore limited to the range of 1.30-1.50%.

[0029] Titanium: Titanium is one of the most economical elements for increasing steel strength. By combining appropriate processes to maximize TiC precipitation, steel can achieve the designed strength level. If the titanium content is less than 0.11%, insufficient precipitation will result in strength failing to meet the designed lower limit. If the titanium content exceeds 0.15%, the tensile strength will exceed the upper limit. Therefore, the titanium content is limited to 0.11-0.15%.

[0030] After rolling, the coils are cooled using different cooling media to adjust the steel's microstructure, achieving a suitable balance between high strength and high ductility, enhancing material strength through precipitation strengthening, and improving formability. The first high cooling rate ensures that the steel retains a fine grain size and deformation substructure after rolling, improving strength. The second air cooling stage aims to achieve appropriate microstructural transformation and enhance ductility. The third, even higher cooling rate, further enhances and maintains strength, avoiding strength degradation caused by prolonged air cooling at excessively high temperatures.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] Compared with the prior art, the high-strength and high-plasticity steel produced by the present invention not only meets the requirements of high strength and high elongation, but also has good atmospheric corrosion resistance, thereby increasing the service life of lightweight parts.

[0033] The steel obtained by the present invention has a yield strength of ≥700MPa, a tensile strength of 750-870MPa, an elongation A of ≥21%, and an average corrosion rate of ≤1.8g / m 2 ·h, thereby improving the corrosion resistance of steel. DETAILED DESCRIPTION

[0034] The following examples further illustrate the technical solutions of the present invention but are not intended to limit the scope of protection of the present invention.

[0035] A specific embodiment provides a 700MPa yield grade corrosion-resistant high-strength and high-plasticity steel, whose chemical composition is, by mass percentage, C: 0.05-0.07%, Si: 0.75-0.90%, Mn: 1.30-1.50%, P: ≤0.020%, S: ≤0.005%, Ti: 0.11-0.15%, Cu: 0.20-0.30%, Cr: 0.40-0.90%, and the balance is balanced iron and unavoidable impurities.

[0036] In the optimized solution, the mass percentage of Cu is 0.22-0.28%.

[0037] In the optimized solution, the mass percentage of Cr is 0.50-0.79%.

[0038] The specific embodiment also provides a method for manufacturing the above-mentioned 700 MPa yield grade corrosion-resistant high-strength and high-plasticity steel, comprising the following steps:

[0039] 1) Heating the ingot: the ingot temperature is ≥950℃, the heating temperature is controlled at 1200~1240℃, and the heating time is ≥70min;

[0040] 2) Rough rolling the heated ingot: the rough rolling end temperature is controlled at 1080-1120°C;

[0041] 3) Finish rolling the slab after rough rolling: control the finishing rolling temperature at 800-880°C;

[0042] 4) The steel plate after rolling is cooled by different media: the first stage uses high-pressure water cooling, the cooling rate of the steel plate is 60-200℃ / s, and the cooling stops when the temperature reaches 610-650℃; the second stage uses air cooling, the cooling time is 4-12s; the third stage uses low-pressure water cooling, the cooling rate is 20-50℃ / s;

[0043] 5) Coil the cooled steel plate: control the coiling temperature at 560-600°C.

[0044] In the optimized solution, the heating temperature in step 1 is controlled at 1200-1230°C.

[0045] In the optimized solution, in step 4, the first cooling rate is 80-160°C / s to cool to 620-645°C; the second air cooling time is 6-11s; and the third cooling rate is 25-45°C / s.

[0046] The chemical composition designs of the specific embodiments and comparative examples are shown in Table 1. The process parameter values ​​of the specific embodiments and comparative examples are shown in Table 2.

[0047] The performance parameters of the specific examples and comparative examples are shown in Table 3.

[0048] Table 1

[0049] Example C Mn Si Cu Cr Ti P S 1 0.056 1.35 0.75 0.2 0.55 0.130 0.009 0.003 2 0.063 1.31 0.9 0.28 0.90 0.150 0.008 0.001 3 0.070 1.30 0.85 0.23 0.49 0.125 0.01 0.002 4 0.068 1.42 0.88 0.29 0.50 0.110 0.007 0.003 5 0.055 1.50 0.78 0.22 0.81 0.119 0.006 0.002 6 0.061 1.45 0.82 0.27 0.65 0.135 0.018 0.002 7 0.050 1.39 0.83 0.25 0.72 0.145 0.015 0.001 8 0.058 1.41 0.79 0.21 0.40 0.128 0.012 0.003 Comparative Example 1 0.06 1.63 0.12 0 0 0.145 0.022 0.007 Comparative Example 2 0.07 1.65 0.11 0 0 0.125 0.018 0.005

[0050] Table 2

[0051]

[0052] Table 3

[0053]

[0054]

[0055] The atmospheric corrosion resistance test used 700MPa yield-grade high-strength steel as a control sample. Cyclic immersion corrosion tests were conducted for 72 hours according to the cyclic immersion test method for weathering structural steel (GB / T 4171-2008). The corrosion method was: 10% H2SO4 + 3.5% NaCl, immersion temperature 23±2°C, 72 hours. The average corrosion rate was calculated by calculating the corrosion weight loss per unit area of ​​the sample.

[0056] It can be seen from the results in Tables 2 and 3 above that the steel of the present invention has a yield strength of ≥700 MPa, a tensile strength of 750-870 MPa, an elongation A of ≥21%, and good atmospheric corrosion resistance.

Claims

1. A 700MPa yield grade corrosion resistant high strength and high plasticity steel, characterized by Chemical composition by mass percentage: C: 0.05~0.07%, Si: 0.75~0.90%, Mn: 1.30~1.50%, P: ≤0.020%, S: ≤0.005%, Ti: 0.11~0.15%, Cu: 0.20~0.30%, Cr: 0.40~0.90%, the balance is iron and unavoidable impurities; The method for manufacturing the 700MPa yield grade corrosion-resistant high-strength and high-plasticity steel comprises the following steps: 1) Heating the ingot: the ingot temperature should be ≥950℃, the heating temperature should be controlled between 1200℃ and 1240℃, and the heating time should be ≥70min; 2) Rough rolling of the heated ingot: the end temperature of rough rolling is controlled at 1080~1120℃; 3) Finish rolling the slab after rough rolling: control the finishing rolling temperature at 800~880℃; 4) Use different media to cool the rolled steel plate: the first stage uses high-pressure water cooling, with a cooling rate of 60~200℃ / s, and stops when the cooling reaches 610~650℃; the second stage uses air cooling, with a cooling time of 4~12s; the third stage uses low-pressure water cooling, with a cooling rate of 20~50℃ / s; 5) Coil the cooled steel plate: control the coiling temperature at 560~600℃.

2. The 700MPa yield grade corrosion-resistant high-strength and high-plasticity steel as claimed in claim 1, characterized in that The mass percentage of Cu is 0.22-0.28%.

3. The 700MPa yield grade corrosion-resistant high-strength and high-plasticity steel as claimed in claim 1, characterized in that The mass percentage of Cr is 0.50-0.79%.

4. The method for manufacturing the 700MPa yield grade corrosion-resistant high-strength and high-plasticity steel according to claim 1, characterized in that In step 1, the heating temperature is controlled at 1200-1230°C.

5. The method for manufacturing the 700MPa yield grade corrosion-resistant high-strength and high-plasticity steel according to claim 1, characterized in that In step 4, the first cooling period is 80-160°C / s to 620-645°C; the second air cooling period is 6-11s; and the third cooling period is 25-45°C / s.

6. The method for manufacturing the 700MPa yield grade corrosion-resistant high-strength and high-plasticity steel according to claim 1, characterized in that The yield strength of the obtained product is ≥700MPa, the tensile strength is 750~870MPa, the elongation A is ≥21%, and the average corrosion rate of the steel is ≤1.8g / m 2 ·h.

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