980MPa-grade hot-dip galvanized DH steel and production process thereof

Abstract

The invention discloses 980MPa-grade hot-dip galvanized DH steel and a production process thereof. The DH steel comprises the following main chemical components in percentage by mass: 0.17%-0.21% of C, 0.4%-0.7% of Si, 1.8%-2.2% of Mn, 0.01%-0.02% of Nb, 0.01%-0.02% of Ti, 0.4%-0.6% of Cr, 0.14%-0.9% of Als and the balance of Fe. The microscopic structure comprises the following components in percentage by volume: 20-40% of ferrite, 40-65% of martensite, 3-12% of retained austenite and 3-15% of bainite; through the precise alloy component proportion and the optimized technological process, perfect combination of high strength and good formability of the steel is successfully achieved, and the surface quality of the hot-dip galvanized DH steel is jointly improved by combining the design of low Si and Mn content and the oxidation-reduction process; the optimized heating temperature and rolling technology are beneficial to reducing energy consumption and reducing carbon emission in the production process.

Description

Technical Field

[0001] The invention belongs to the technical field of high-strength steel, and specifically relates to a 980MPa grade hot-dip galvanized DH steel and a production process. Background Art

[0002] With the acceleration of global industrialization, the demand for high-strength steel is growing, especially in key areas such as automobiles, construction and energy. This type of steel is not only required to have excellent mechanical properties to meet the needs of structural strength and durability, but also needs to have good surface quality to ensure the aesthetics and corrosion resistance of the product. However, traditional steel production methods are often accompanied by high carbon emissions and high costs while pursuing high strength and high surface quality. Traditional high-strength steels, such as certain types of DP steel, usually contain a higher carbon content in order to achieve the required mechanical strength. However, the high carbon content not only reduces the plasticity and toughness of the steel, affecting the safety and service life of the product, but also increases carbon emissions during production and use; especially during the hot-dip galvanizing process, high-carbon steel is prone to carbide precipitation, resulting in uneven galvanizing, affecting the appearance and corrosion resistance of the product.

[0003] At the same time, the market has increasingly stringent requirements for the surface quality of steel. Traditional steel production processes, especially hot-dip galvanizing processes, often make it difficult to achieve high surface quality while ensuring strength. Defects on the surface of steel not only affect the aesthetics of the product, but may also reduce its corrosion resistance and service life, thereby increasing maintenance and replacement costs. In addition, traditional steel production processes are usually complex and energy-intensive, resulting in high production costs, which limits the application of high-strength steel in a wider range of fields. Summary of the invention

[0004] In order to overcome the defects of the above-mentioned prior art, the composition design of the present invention is based on low Si and low Mn, focusing on using Cr to partially or completely replace precious Mo, Ni, Cu, V and other elements, and matching with a suitable oxidation-reduction process. Through innovative process methods, low carbon, high surface quality and low cost production are achieved.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides a 980MPa grade hot-dip galvanized DH steel, wherein the chemical composition mass content of the hot-dip galvanized DH steel is C: 0.17% ~ 0.21%, Si: 0.4% ~ 0.7%, Mn: 1.8% ~ 2.2%, Nb: 0.01% ~ 0.02%, Ti: 0.01% ~ 0.02%, Cr: 0.4% ~ 0.6%, Als: 0.14% ~ 0.90%, and the balance is iron and unavoidable impurities.

[0006] The present invention fully considers the role and influence of each element when designing the steel composition to ensure that the comprehensive performance of the steel reaches the best.

[0007] First, an appropriate amount of carbon (C) is selected as a strengthening element, and its content is controlled at 0.17% to 0.21%. Carbon can not only form interstitial solid solutions, but also combine with alloy elements to form carbides, thereby increasing the strength of steel; however, too high a carbon content will damage the toughness of the material.

[0008] At the same time, silicon (Si) is added, and its content is controlled at 0.4% to 0.7%. Silicon has a solid solution strengthening effect and can improve hardenability; but it should be noted that too high a silicon content will reduce the plasticity and toughness of the steel, and may even cause cold brittleness.

[0009] In order to increase austenite stability and improve hardenability, manganese (Mn) is added and its content is controlled at 1.8% to 2.2%. Manganese also has a solid solution strengthening effect, but too high a manganese content may cause segregation problems and affect welding performance.

[0010] In addition, a small amount of niobium (Nb) is introduced, with the content controlled at 0.01% to 0.02%. Niobium has a significant solid solution strengthening effect, and can refine the grains and improve the strength of steel. However, too high a niobium content may impair welding performance and increase production costs.

[0011] Titanium (Ti) is also added to strengthen the steel, and its content is controlled at 0.01% to 0.02%. Titanium can form high-melting-point carbonitrides, effectively controlling the amount of free nitrogen, thereby improving the strength and stability of the steel.

[0012] Chromium (Cr) is added to compensate for the strength loss caused by the reduction of other elements and to improve the stability and hardenability of austenite. The chromium content is controlled at 0.4% to 0.6%, which can not only improve the corrosion resistance of steel, but also avoid adverse effects on welding performance and plasticity.

[0013] Finally, an appropriate amount of aluminum (Al) is added, and its acid-soluble aluminum content is controlled at 0.14% to 0.9%. In addition to being a deoxidizing element, aluminum can also effectively reduce inclusions in steel and improve the surface quality of galvanized steel.

[0014] In the above technical solution, further, the microstructure of the hot-dip galvanized DH steel contains 20% to 40% ferrite, 40% to 65% martensite, 3% to 12% residual austenite, and 3% to 15% bainite by volume percentage.

[0015] Furthermore, the yield strength of the hot-dip galvanized DH steel perpendicular to the rolling direction is ≥550MPa, the tensile strength is ≥980MPa, and the 80 The elongation after fracture is 15% to 23%, the thickness is 1.0 to 2.5 mm, and the hole expansion rate is ≥20%.

[0016] A production process of the above-mentioned 980MPa grade hot-dip galvanized DH steel, the production process includes the steps of converter smelting, slab continuous casting, removing defects on the edge of the ingot, hot rolling, pickling and cold rolling, preheating, heating, annealing, slow cooling, rapid cooling and galvanizing after rapid cooling; wherein,

[0017] Converter smelting: S of hot metal after pretreatment is ≤0.003%, and slag removal rate is ≥94%;

[0018] Scrap steel is added to the converter, with scrap steel accounting for 15% to 18% and molten iron accounting for 82% to 85%; the converter bottom blowing adopts the full-process argon blowing mode, and the terminal oxygen is controlled to be ≤650ppm. The refining LF path is adopted: the slag addition amount is 30 to 40kg; vacuum decarburization treatment, vacuum degree ≤150Pa, decarburization time 18 to 25min; vacuum deoxidation alloying treatment, deoxidation alloying adds ferrosilicon, silicon manganese, aluminum particles, ferroniobium, and the alloying sequence is Al-Mn-Nb.

[0019] Slab continuous casting: The continuous casting superheat is controlled at 17℃~27℃; the continuous casting maintains a constant pulling speed of 1.0~1.3m / min, and dynamic light pressure is adopted. The edge defects of the slab need to be removed after continuous casting.

[0020] Hot rolling: billet heating temperature 1230℃~1250℃, start rolling temperature 1020℃~1160℃, final rolling temperature 880℃~900℃, coiling temperature 550℃~570℃.

[0021] Pickling cold rolling: cold rolling reduction rate is 60% to 80%;

[0022] Galvanizing: The strip is equipped with a pre-oxidation chamber in the heating section. The pre-oxidation temperature is 450℃~550℃, the dew point of the pre-oxidation chamber is -15℃~-10℃, the oxygen (volume) content is 1.0%~1.5%, and the air flow rate is 30~50Nm 3 / h. Annealing temperature is 830℃~850℃, slow cooling outlet temperature is 690℃~740℃, fast cooling outlet temperature is 435℃~460℃, after galvanizing, the strip is first air-knife cooled to 400℃~420℃; the skin-pass elongation of the skin-pass process is controlled within the range of 0.5%~1.0%.

[0023] The dew point of the annealing section and the slow cooling section is -40°C to -30°C, and the hydrogen (volume) content is 3% to 5%.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention successfully achieves the perfect combination of high strength and good formability of steel through precise alloy composition ratio and optimized process flow, meeting the stringent requirements of modern industry on material performance. By optimizing the composition ratio, especially the optimized use of chromium and manganese elements, high performance is achieved while cost control is fully carried out, with good economic benefits. The design of low C and Mn content combined with the oxidation-reduction process jointly improves the surface quality of hot-dip galvanized DH steel; the optimized heating temperature and rolling process help reduce energy consumption and reduce carbon emissions in the production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The stress-strain curve of 980MPa grade hot-dip galvanized DH steel obtained in Example 1;

[0027] Figure 2 The microstructure morphology of the 980MPa grade hot-dip galvanized DH steel obtained in Example 1;

[0028] Figure 3 This is a surface diagram of the galvanized sheet of 980MPa grade hot-dip galvanized DH steel prepared in Example 1. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with specific examples, but the present invention is not limited in any way. To avoid redundant description, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0030] A 980MPa grade hot-dip galvanized DH steel, wherein the chemical composition mass content of the hot-dip galvanized DH steel is C: 0.17%-0.21%, Si: 0.4%-0.7%, Mn: 1.8%-2.2%, Nb: 0.01%-0.02%, Ti: 0.01%-0.02%, Cr: 0.4%-0.6%, Als: 0.14%-0.9%, and the balance is iron and unavoidable impurities.

[0031] A production process of the above-mentioned 980MPa grade hot-dip galvanized DH steel includes the steps of converter smelting, slab continuous casting, hot rolling, pickling and cold rolling, preheating, heating, annealing, slow cooling, rapid cooling, and galvanizing after rapid cooling.

[0032] The matters not described in the following embodiments are the same as the description of the above specific implementation methods.

[0033] Example

[0034] A 980MPa grade hot-dip galvanized DH steel, the specific chemical composition of the hot-dip galvanized DH steel described in Examples 1-10 is shown in Table 1.

[0035] Table 1 Chemical composition of hot-dip galvanized DH steel in the embodiment (wt%)

[0036]

[0037]

[0038] A production process of 980MPa grade hot-dip galvanized DH steel. The specific process flow of Examples 1-10 is as follows. Table 2 shows the hot rolling process parameters; the billet heating temperature is 1230°C to 1250°C, the start rolling temperature is 1020°C to 1160°C, the final rolling temperature is 880°C to 900°C, and the coiling temperature is 550°C to 570°C.

[0039] Table 2 Hot rolling process parameters of the production process of the embodiment

[0040]

[0041] Table 3 lists the process parameters of cold rolling and hot-dip galvanizing of the example steel. Pickling cold rolling: cold rolling reduction rate is 60% to 80%. Galvanizing: annealing temperature 830℃ to 850℃, slow cooling outlet temperature 690℃ to 740℃, rapid cooling outlet temperature 435℃ to 460℃. After galvanizing, the strip is first air-knife cooled to 400℃ to 420℃; the skin-finishing elongation of the skin-finishing process is controlled within the range of 0.5% to 1.0%. The dew point of the annealing section and the slow cooling section is -40℃ to -30℃, and the hydrogen content is 3% to 5%. The pre-oxidation temperature is 450℃ to 550℃, the dew point of the pre-oxidation chamber is -15℃ to -10℃, the oxygen content is 1.0% to 1.5%, and the air flow rate is 30 to 50Nm 3 / h.

[0042] Table 3 Cold rolling and hot dip galvanizing process parameters of the production process of the embodiment

[0043]

[0044]

[0045] The mechanical properties and key parameters of the 980MPa grade hot-dip galvanized DH steel obtained in Example 1-10 are shown in Table 4. The yield strength of the hot-dip galvanized DH steel perpendicular to the rolling direction is ≥550MPa, the tensile strength is ≥980MPa, and the A 80 The elongation after fracture is 15% to 23%, the thickness is 1.0 to 2.5 mm, and the hole expansion rate is ≥ 20%. The stress-strain curve of the 980MPa grade hot-dip galvanized DH steel obtained in Example 1 is as follows: Figure 1 As shown; microstructure morphology, such as Figure 2 As shown; the surface condition of the galvanized sheet, such as Figure 3 shown.

[0046] Table 4 Performance parameters of 980MPa grade hot-dip galvanized DH steel obtained in Example

[0047]

[0048] For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A 980MPa grade hot-dip galvanized DH steel, characterized in that: The chemical composition mass content of the hot-dip galvanized DH steel is C: 0.17%-0.21%, Si: 0.4%-0.7%, Mn: 1.8%-2.2%, Nb: 0.01%-0.02%, Ti: 0.01%-0.02%, Cr: 0.4%-0.6%, Als: 0.14%-0.9%, and the balance is iron and unavoidable impurities.

2. The hot-dip galvanized DH steel according to claim 1, characterized in that: The microstructure of the hot-dip galvanized DH steel contains, by volume percentage, 20% to 40% ferrite, 40% to 65% martensite, 3% to 12% residual austenite, and 3% to 15% bainite.

3. The hot-dip galvanized DH steel according to claim 1, characterized in that: The yield strength of the hot-dip galvanized DH steel perpendicular to the rolling direction is ≥550MPa, the tensile strength is ≥980MPa, and the 80 The elongation after fracture is 15% to 23%, the thickness is 1.0 to 2.5 mm, and the hole expansion rate is ≥20%.

4. A production process for 980MPa grade hot-dip galvanized DH steel as claimed in claim 1, characterized in that: The production process includes the following steps: converter smelting, slab continuous casting, hot rolling, pickling and cold rolling, preheating, heating, annealing, slow cooling, fast cooling, and galvanizing; in, Converter smelting: S of hot metal after pretreatment is ≤0.003%, and slag removal rate is ≥94%; Hot rolling: billet heating temperature 1230℃~1250℃, start rolling temperature 1020℃~1160℃, final rolling temperature 880℃~900℃, coiling temperature 550℃~570℃; The heating process is equipped with a pre-oxidation chamber, the pre-oxidation temperature is 450℃~550℃, the dew point of the pre-oxidation chamber is -15℃~-10℃, the oxygen content is 1.0%~1.5%, and the air flow rate is 30~50Nm 3 / h; Pickling cold rolling: cold rolling reduction rate is 60% to 80%; Galvanizing: annealing temperature 830℃~850℃, slow cooling outlet temperature 690℃~740℃, fast cooling outlet temperature 435℃~460℃, after galvanizing, the strip is cooled to 400℃~420℃ by air knife; the skin-clearing elongation of the skin-clearing process is controlled within the range of 0.5%~1.0%; The dew point of the annealing section and the slow cooling section is -40°C to -30°C, and the hydrogen content is 3% to 5%.

5. The production process of hot-dip galvanized DH steel according to claim 4, characterized in that: During the converter smelting process, scrap steel accounts for 15% to 18%, and molten iron accounts for 82% to 85%; the converter bottom blowing adopts the full-process argon blowing mode, and the end point oxygen is controlled ≤650ppm; the refining LF path is adopted, and the slag addition amount is 30 to 40kg; vacuum decarburization treatment, vacuum degree ≤150Pa, decarburization time 18 to 25min.

6. The production process of hot-dip galvanized DH steel according to claim 4, characterized in that: During the continuous casting of the slab, the continuous casting superheat is controlled at 17℃~27℃; the continuous casting maintains a constant pulling speed of 1.0~1.3m / min, and dynamic light pressure is adopted to remove edge defects of the cast slab after continuous casting.

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