980mpa grade hot-dip galvanizing dh steel and production process

Abstract

The application discloses a 980MPa-grade hot-dip galvanizing DH steel and a production process, the main chemical component mass content of the DH steel is as follows: 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%, and Als: 0.14-0.9%; the microstructure contains 20-40% ferrite, 40-65% martensite, 3-12% residual austenite and 3-15% bainite in percentage by volume; through accurate alloy component proportioning and an optimized process flow, perfect combination of high strength and good formability of the steel is successfully realized, the surface quality of the hot-dip galvanizing DH steel is improved by combining the design of low Si and Mn contents and the oxidation-reduction process; and the optimized heating temperature and rolling process are helpful to reduce energy consumption and carbon emission in the production process.

Description

Technical Field

[0001] This invention belongs to the field of high-strength steel technology, specifically relating to a 980MPa grade hot-dip galvanized DH steel and its production process. Background Technology

[0002] With the acceleration of global industrialization, the demand for high-strength steel is increasing, especially in key sectors such as automotive, construction, and energy. This type of steel not only requires excellent mechanical properties to meet structural strength and durability requirements, but also good surface quality to ensure product aesthetics and corrosion resistance. However, traditional steel production methods, while pursuing high strength and high surface quality, often come at the cost of high carbon emissions and high costs. Traditional high-strength steels, such as certain types of DP steel, typically contain high carbon content to achieve the required mechanical strength. However, high carbon content not only reduces the steel's plasticity and toughness, affecting product safety and service life, but also increases carbon emissions during production and use; particularly during hot-dip galvanizing, high-carbon steel is prone to carbide precipitation, leading to uneven galvanized layers and affecting the product's appearance and corrosion resistance.

[0003] Meanwhile, market demands for steel surface quality are becoming increasingly stringent. Traditional steel production processes, especially hot-dip galvanizing, often struggle to achieve high surface quality while maintaining strength. Surface defects in steel not only affect the product's aesthetics but can also reduce its corrosion resistance and service life, thereby increasing maintenance and replacement costs. Furthermore, traditional steel production processes are typically complex and energy-intensive, resulting in high production costs and limiting the wider application of high-strength steel. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention is designed with low Si and low Mn content, focusing on using Cr to partially or completely replace expensive elements such as Mo, Ni, Cu, and V, coupled with a suitable oxidation-reduction process. Through innovative processing methods, low-carbon, high-surface-quality, and low-cost production is achieved.

[0005] To achieve the above-mentioned objective, this invention provides a 980MPa grade hot-dip galvanized DH steel, wherein the chemical composition of the hot-dip galvanized DH steel is as follows (mass content): 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%, with the balance being iron and unavoidable impurities.

[0006] This invention fully considers the role and influence of each element when designing the steel composition to ensure that the overall performance of the steel reaches the optimal level.

[0007] First, an appropriate amount of carbon (C) was selected as a strengthening element, with its content controlled between 0.17% and 0.21%. Carbon can not only form interstitial solid solutions, but also combine with alloying elements to form carbides, thereby improving the strength of steel; however, excessive carbon content will impair the toughness of the material.

[0008] Meanwhile, silicon (Si) was added, with its content controlled between 0.4% and 0.7%. Silicon has a solid solution strengthening effect and can improve hardenability; however, it should be noted that excessive silicon content will reduce the plasticity and toughness of steel, and may even cause cold brittleness.

[0009] To increase austenite stability and improve hardenability, manganese (Mn) was added, with its content controlled between 1.8% and 2.2%. Manganese also has a solid solution strengthening effect, but excessive manganese content may lead to segregation problems and affect welding performance.

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

[0011] The addition of titanium (Ti) is also to strengthen 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 steel.

[0012] Chromium (Cr) is added to compensate for the strength loss caused by the reduction of other elements and to improve austenite stability and hardenability. The chromium content is controlled at 0.4% to 0.6%, which can improve the corrosion resistance of steel while avoiding adverse effects on weldability and plasticity.

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

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

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

[0016] A production process for the aforementioned 980MPa grade hot-dip galvanized DH steel includes the following steps: converter smelting, slab continuous casting, removal of edge defects from the cast slab, hot rolling, pickling and cold rolling, preheating, heating, annealing, slow cooling, rapid cooling, and galvanizing after rapid cooling; wherein...

[0017] Converter smelting: The sulfur content of the pretreated molten iron entering the furnace is ≤0.003%, and the slag removal rate is ≥94%;

[0018] Scrap steel is added to the converter, accounting for 15%–18% of the total steel content, while molten iron accounts for 82%–85%. The converter bottom blowing adopts a continuous argon blowing mode, with the final oxygen level controlled to ≤650ppm. A refining LF path is employed: 30–40 kg of slag is added; vacuum decarburization is performed, with a vacuum degree ≤150Pa and a decarburization time of 18–25 min; vacuum deoxidation and alloying is then performed, adding ferrosilicon, ferromanganese, aluminum granules, and ferroniobium, in the Al-Mn-Nb alloying sequence.

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

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

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

[0022] Galvanizing: The strip steel 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 830℃~850℃, slow cooling outlet temperature 690℃~740℃, fast cooling outlet temperature 435℃~460℃, after galvanizing, the strip steel is first air-cooled to 400℃~420℃; the finishing elongation rate during the finishing process is controlled within the range of 0.5%~1.0%.

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

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention achieves a perfect combination of high strength and good formability in steel through precise alloy composition and optimized process flow, meeting the stringent requirements of modern industry for material performance. By optimizing the composition, particularly the use of chromium and manganese, high performance is achieved while simultaneously controlling costs, resulting in good economic benefits. The combination of a low C and Mn content design and an oxidation-reduction process further enhances the surface quality of hot-dip galvanized DH steel; optimized heating temperature and rolling process help reduce energy consumption and carbon emissions during production. Attached Figure Description

[0026] Figure 1 The stress-strain curve of the 980MPa grade hot-dip galvanized DH steel prepared in Example 1 is shown.

[0027] Figure 2 The image shows the microstructure of the 980MPa grade hot-dip galvanized DH steel prepared in Example 1.

[0028] Figure 3 The image shows the surface of the galvanized sheet of 980MPa grade hot-dip galvanized DH steel prepared in Example 1. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments, but this does not limit the invention in any way. To avoid redundancy, unless otherwise specified, the raw materials used in the following embodiments are all commercially available products, and the methods used are all conventional methods unless otherwise specified.

[0030] A 980MPa grade hot-dip galvanized DH steel, wherein the chemical composition of the hot-dip galvanized DH steel is as follows (mass content): 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%, with the balance being iron and unavoidable impurities.

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

[0032] Any aspects not described in the following embodiments are the same as those described in the specific embodiments above.

[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 (wt%) of hot-dip galvanized DH steel in the examples.

[0036]

[0037]

[0038] A production process for 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: billet heating temperature 1230℃~1250℃, initial rolling temperature 1020℃~1160℃, final rolling temperature 880℃~900℃, coiling temperature 550℃~570℃.

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

[0040]

[0041] Table 3 lists the process parameters for cold rolling and hot-dip galvanizing of the steel in the examples. For pickling and cold rolling: the cold rolling reduction rate is 60%–80%. For galvanizing: annealing temperature 830℃–850℃, slow cooling exit temperature 690℃–740℃, rapid cooling exit temperature 435℃–460℃, after galvanizing, the strip is first cooled to 400℃–420℃ by air knife; the finishing elongation rate during the finishing process is controlled within the range of 0.5%–1.0%. The dew point in the annealing and slow cooling sections is -40℃ to -30℃, and the hydrogen content is 3%–5%. The pre-oxidation temperature is 450℃–550℃, the dew point in the pre-oxidation chamber is -15℃ to -10℃, the oxygen content is 1.0%–1.5%, and the air flow rate is 30–50 Nm³. 3 / h.

[0042] Table 3. Process parameters for cold rolling and hot-dip galvanizing in the embodiments.

[0043]

[0044]

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

[0046] Table 4. Performance parameters of 980MPa grade hot-dip galvanized DH steel prepared in the examples.

[0047]

[0048] For anyone skilled in the art, many possible variations and modifications can be made to the technical solutions of this invention, or equivalent embodiments can be modified based on the disclosed technical content, without departing from the scope of the technical solutions of this invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this invention without departing from the content of the technical solutions of this invention should still fall within the protection scope of the technical solutions of this invention.

Claims

1. A 980MPa grade hot-dip galvanized DH steel, characterized in that, The hot-dip galvanized DH steel has the following chemical composition by mass: 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%, with the balance being iron and unavoidable impurities. The microstructure of the hot-dip galvanized DH steel contains, by volume percentage, 20%–40% ferrite, 40%–65% martensite, 3%–12% retained austenite, and 3%–15% bainite. The hot-dip galvanized DH steel has a yield strength ≥550MPa and a tensile strength ≥980MPa along the direction perpendicular to the rolling direction. 80 Elongation after fracture is 15%–23%, thickness is 1.0–2.5 mm, and porosity is ≥20%; The production process of the 980MPa grade hot-dip galvanized DH steel includes the following steps: converter smelting, slab continuous casting, hot rolling, pickling and cold rolling, preheating, heating, annealing, slow cooling, rapid cooling, and galvanizing. in, Converter smelting: The sulfur content of the pretreated molten iron entering the furnace is ≤0.003%, and the slag removal rate is ≥94%; during the converter smelting process, the proportion of scrap steel is 15%~18%, and the proportion of molten iron is 82%~85%; the converter bottom blowing adopts the full-process argon blowing mode, and the oxygen control at the end point is ≤650ppm; the refining LF path is adopted, and the slag addition amount is 30~40kg; vacuum decarburization treatment is carried out, with a vacuum degree ≤150Pa and a decarburization time of 18~25min; During the continuous casting of slabs, the superheat of continuous casting is controlled at 17℃~27℃; the continuous casting speed is kept constant at 1.0~1.3m / min, and dynamic light reduction is adopted. After continuous casting, edge defects of the slab are removed. Hot rolling: billet heating temperature 1230℃~1250℃, initial rolling temperature 1020℃~1160℃, final rolling temperature 880℃~900℃, coiling temperature 550℃~570℃; The heating process includes a pre-oxidation chamber with a pre-oxidation temperature of 450℃~550℃, a dew point of -15℃~-10℃, an oxygen content of 1.0%~1.5%, and an air flow rate of 30~50Nm. 3 / h; Pickling and cold rolling: cold rolling reduction rate is 60% to 80%; Galvanizing: Annealing temperature 830℃~850℃, slow cooling exit temperature 690℃~740℃, fast cooling exit temperature 435℃~460℃, after galvanizing, the strip is cooled to 400℃~420℃ by air knife; the finishing elongation during the finishing process is controlled within the range of 0.5%~1.0%. The dew point of the annealing and slow cooling sections is -40℃ to -30℃, and the hydrogen content is 3% to 5%.

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