Preparation method of hot-dip galvanized Ti-series DX54D + Z steel strip for thin-gauge ultra-deep drawing

Abstract

The invention discloses a preparation method of a thin-gauge hot-dip galvanized Ti-series DX54D + Z steel strip for ultra-deep drawing. The preparation method comprises the following main process steps and process parameters: a smelting-continuous casting section production process flow; in the heating process, the in-furnace time is strictly controlled, and the tapping temperature is 1220 + / -20 DEG C; laminar cooling is adopted for rolling and cooling; pickling and rolling; the temperature of a heating section is 820-840 DEG C, the temperature of a soaking section is 820-840 DEG C, the temperature of a slow cooling section is 670-690 DEG C, the temperature of a rapid cooling section is 450-475 DEG C, the temperature of a zinc pot is 450-470 DEG C, the temperature of a top roller is less than or equal to 250 DEG C, the temperature of an inlet of a water quenching tank is less than or equal to 160 DEG C, and the temperature after drying is less than or equal to 40 DEG C; the finishing elongation is 0.8 + / -0.05%; the temperature of the zinc liquid is 460 + / -10 DEG C; the hot-dip galvanized Ti-series DX54D + Z steel strip has the characteristics of good extra-deep drawability, low yield ratio, good plasticity and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-dip galvanized steel strip production, and in particular relates to a method for preparing a thin-gauge hot-dip galvanized Ti-based DX54D+Z steel strip for ultra-deep drawing. Background Art

[0002] Cold-rolled hot-dip galvanized strip steel has been widely used in the construction, automobile, home appliance and other industries due to its strong corrosion resistance, good mechanical properties, excellent surface quality, high dimensional accuracy and low production cost. In particular, in recent years, hot-dip galvanizing has made great progress in technology and equipment, and its superiority in production cost and quality has made its demand increasingly greater. Deep drawing steel can be divided into commercial grade (CQ), ordinary drawing grade (DQ), deep drawing grade (DDQ), extra deep drawing grade (EDDQ) and super deep drawing grade (SUPER-EDDQ) according to the stamping level. They correspond to several stages of deep drawing steel development. The development and application of the first generation of deep drawing steel products were ordinary boiling steel in the 1950s and 1960s, which could only be used for ordinary deep drawing parts; low-carbon aluminum-killed steel was the second generation product, produced in the 1960s to 1980s, with good deep drawing performance; after the 1980s, the third generation of ultra-low carbon ultra-deep drawing steel represented by IF steel (interstitial-free steel) appeared.

[0003] Well-known steel mills at home and abroad have already upgraded their products to above DX54D+Z. Competition in the home appliance industry is becoming increasingly fierce. Many home appliance factories attract customers by changing the appearance design of home appliance products. The edges and corners of many parts are more prominent, which puts higher requirements on the deep drawing performance of raw steel strips. The automotive industry requires thick-gauge deep drawing steel to manufacture thicker and more complex parts, and the demand for manufacturing automotive parts is also gradually increasing. It is necessary to further study the mechanism and process technology, give full play to the equipment advantages of each production line, and develop a stable production process that meets the requirements of hot-dip galvanized steel strips for deep drawing. The basic characteristics of this type of steel, such as Ti-based DX54D+Z, for ultra-deep drawing, are that when steel is smelted, advanced smelting processes are used to strictly control the content of carbon, nitrogen and other elements, and some micro-alloying elements are added, so that the carbon and nitrogen atoms are dissolved into carbon and nitrogen compounds by trace alloying elements such as niobium and titanium, so that there are no interstitial atoms in the steel. It is a new generation of ultra-deep drawing steel that has emerged with the development of vacuum smelting technology and has been industrially produced. Ultra-deep drawing hot-dip galvanized steel strip has low yield point and yield strength ratio, high elongation, high n value, high r value, and no timeliness, and is suitable for deep drawing products requiring high deformation performance. The market has certain demand and broad prospects, and it is necessary to develop excellent performance and good surface quality to meet user requirements.

[0004] Huang Xiaowang (Huang Xiaowang et al., Product Development and Application of DX53D+Z Hot-dip Galvanized Fingerprint-resistant Plate, Fujian Metallurgy, Issue 2, 2023) The test steel DX53D+Z has a smoothing elongation of 1.1% and an annealing temperature of 820°C. This patent application is different from the process in document 1. It adopts a smoothing elongation of 1.0±0.05%. The smoothing process is to give the strip a small amount of deformation, mainly to improve the plate shape of the material, and a continuous annealing furnace is used. The heating section temperature is 820±5°C, the soaking section temperature is 820±5°C, the slow cooling section temperature is 680±10°C, and the fast cooling section temperature is 470±10°C.

[0005] Zheng Zhiwang (Zheng Zhiwang, Development of Nb-Ti-IF Steel DX54D Skin-passed Hot-dip Galvanized Steel Plate, Steel Vanadium Titanium, Issue 1, 2004) trial-produced Nb+Ti-IF hot rolling raw material hot rolling adopts 1450mm four-roller 7-stand hot rolling, and the hot rolling cooling process adopts the front-end cooling method. This application patent is different from the hot rolling process of document 2, using a 2250mm hot rolling production line to produce hot rolling raw materials, and the hot rolling cooling process adopts the rear-end dispersed cooling mode.

[0006] Zheng Zhiwang (Zheng Zhiwang, Development of deep-drawn and tempered hot-dip galvanized steel sheets for home appliances, Steel Vanadium Titanium, Issue 1, 2004)

[0007] The yield strength of the galvanized steel strip is 150-220MPa, and the tensile strength is 270-350MPa. The patent application is different from the strength of the third document. It adopts the ultra-low carbon Nb+Ti-IF composition design. The yield strength of the cold-rolled steel plate is low, the yield strength ratio is low, and it has good plasticity. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing a thin-gauge hot-dip galvanized Ti-based DX54D+Z steel strip for ultra-deep drawing. The hot-dip galvanized Ti-based DX54D+Z steel strip has the characteristics of good ultra-deep drawing performance, low yield strength ratio, good plasticity, etc., and is suitable for container manufacturing, electromechanical, household appliances, automotive parts, etc.

[0009] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0010] The present invention discloses a method for preparing a thin-gauge ultra-deep drawing hot-dip galvanized Ti-based DX54D+Z steel strip, the main process steps and process parameters of which are as follows:

[0011] The production process of smelting-continuous casting section: hot metal pretreatment-converter-RH furnace-casting machine; steelmaking process control [O]≤20ppm, [N]≤30ppm;

[0012] The heating process is strictly controlled in the furnace time, and the furnace temperature is 1220±20℃;

[0013] The rolling process includes rough rolling and finishing rolling. The rough rolling process is carried out by a 2-stand rolling mill, and the finishing rolling process is carried out by a 7-stand continuous variable crown rolling mill. The starting rolling temperature of the finishing rolling is 1050±20°C, and the final rolling temperature of the finishing rolling is 900-940°C.

[0014] The cooling adopts laminar cooling, the rear dispersed cooling mode, the rear dispersed, and the coiling temperature is 700-740℃;

[0015] Pickling process: Pay attention to the concentration of acid, the matching of strip temperature and speed during pickling to prevent under-pickling or over-pickling, and check the surface quality;

[0016] Continuous hot-dip galvanizing process, the cold hard coil enters the continuous annealing furnace, the heating section temperature is 820-840℃, the soaking section temperature is 820-840℃, the slow cooling section temperature is 670-690℃, the fast cooling section temperature is 450-475℃, the zinc pot temperature is 450-470℃, the top roller is ≤250℃, the water quenching tank inlet temperature is ≤160℃, and the temperature after drying is ≤40℃; the skin-clearing elongation is 0.8±0.05%; the zinc liquid temperature is 460±10℃;

[0017] The chemical components of the hot-dip galvanized Ti-based DX54D+Z steel strip include by weight percentage: C: 0.0015-0.0025%, Si: 0.006-0.008%, Mn: 0.12-0.14%, P: ≤0.010%, S: ≤0.006%, Ti: 0.050-0.070%, and the rest are Fe and unavoidable impurities.

[0018] Furthermore, the skin-passing process is used to give the strip a small amount of deformation, mainly to improve the material shape.

[0019] Furthermore, the zinc liquid temperature is 460°C.

[0020] Furthermore, the chemical composition of the hot-dip galvanized Ti-based DX54D+Z steel strip includes, by weight percentage, C: 0.0015%, Si: 0.006%, Mn: 0.12%, P: 0.009%, S: 0.004%, Ti: 0.050%, and the remainder is Fe and unavoidable impurities.

[0021] Furthermore, the chemical composition of the hot-dip galvanized Ti-based DX54D+Z steel strip includes, by weight percentage, C: 0.0020%, Si: 0.007%, Mn: 0.13%, P: 0.008%, S: 0.003%, Ti: 0.060%, and the remainder is Fe and unavoidable impurities.

[0022] Furthermore, the chemical composition of the hot-dip galvanized Ti-based DX54D+Z steel strip includes, by weight percentage, C: 0.0025%, Si: 0.008%, Mn: 0.14%, P: 0.010%, S: 0.005%, Ti: 0.070%, and the remainder is Fe and unavoidable impurities.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are:

[0024] 1. The technical problem to be solved by the present invention is to provide a thin-gauge hot-dip galvanized Ti-based DX54D+Z steel strip for extra-deep drawing. The mechanical properties of the steel strip are characterized by low yield strength ratio, good plasticity, high plastic strain ratio, good stamping forming performance, and suitable for the needs of complex forming methods such as stamping processes. It is mainly used in the fields of container manufacturing, electromechanics, household appliances, automotive parts, etc.

[0025] 2. The yield strength of the thin-gauge ultra-deep drawing hot-dip galvanized Ti-based DX54D+Z steel strip of the present invention is distributed between 134MPa and 148MPa, the tensile strength is distributed between 288MPa and 305MPa, and the elongation A80 is distributed between 45% and 46%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be further described below in conjunction with the accompanying drawings.

[0027] Figure 1 This is the metallographic structure diagram of the steel plate according to Example 2 of the present invention. DETAILED DESCRIPTION

[0028] The present invention is described in more detail below with examples. These examples are merely descriptions of the best mode for carrying out the present invention and are not intended to limit the scope of the present invention in any way.

[0029] Example 1

[0030] The molten iron is pre-treated for desulfurization, and the top and bottom combined blown converter is used to decarbonize and dephosphorize the molten iron to obtain molten steel, and the scrap steel is added to the converter. Then the molten steel after converter smelting is subjected to RH operation, and the in-situ temperature is 1630-1660℃, and deep decarbonization treatment is carried out, with the target of 20ppm. After decarbonization, aluminum particles are added for deoxidation according to the oxygen determination, and alloys such as titanium iron and niobium iron are added to adjust the composition to ensure that [O] in the molten steel is ≤20ppm. According to the chemical composition shown in Table 1, the slab continuous casting overheat is 25℃, and the carbon-free middle package covering agent should be used in the continuous casting process to avoid carbon increase during the casting process. After that, the slab is cleaned, slowly cooled, and the quality of the continuous casting slab is checked. The slab heating temperature is 1200℃, the heating time is 240min, and the heated slab is dephosphorized by high-pressure water. The width is set by a fixed width press, and 2-stand rough rolling and 7-stand CVC finishing rolling are used. The finishing rolling start temperature is 1030℃, and the finishing rolling temperature is 900℃. Laminar cooling adopts rear-stage dispersed cooling, the coiling temperature is 700℃, and the thickness of the hot-rolled raw material is 3mm. Finally, a quality inspection is carried out, and qualified cold-rolled raw materials are obtained. After the cold-rolled raw material is uncoiled, it enters the pickling tank. The pickling process pays attention to the matching of acid concentration, strip temperature and speed to prevent under-pickling or over-pickling, and the surface quality is checked. The final thickness of the cold-rolled plate is 0.6mm. Finally, a continuous hot-dip galvanizing process is carried out. The annealing method adopts continuous annealing. The annealing heating section temperature is 820℃, the soaking section temperature is 820℃, the slow cooling section temperature is 670℃, the fast cooling section temperature is 450℃, the zinc pot (balanced section) is 450℃, the top roller (cooling tower top strip temperature) is ≤250℃, the water quenching tank inlet temperature is ≤160℃, and the temperature after drying is ≤40℃. During the continuous annealing process, the calorific value of the coal gas in the furnace must be stable, and the purity of hydrogen and nitrogen must be guaranteed. The strip steel after continuous annealing is finally skin-passed with a skin-pass elongation of 0.75%, and then coiled into a finished product. Zinc liquid temperature: 460°C.

[0031] Example 2

[0032] The molten iron is pre-treated for desulfurization, and the top and bottom combined blown converter is used to decarbonize and dephosphorize the molten iron to obtain molten steel, and the scrap steel is added to the converter. Then the molten steel after converter smelting is subjected to RH operation, and the in-situ temperature is 1630-1660℃, and deep decarbonization treatment is carried out, with the target of 20ppm. After decarbonization, aluminum particles are added for deoxidation according to the oxygen determination, and alloys such as titanium iron and niobium iron are added to adjust the composition to ensure that [O] in the molten steel is ≤20ppm. According to the chemical composition shown in Table 1, the slab continuous casting overheat is 25℃, and the carbon-free middle package covering agent should be used in the continuous casting process to avoid carbon increase during the casting process. After that, the slab is cleaned, slowly cooled, and the quality of the continuous casting slab is checked. The slab heating temperature is 1200℃, the heating time is 240min, and the heated slab is dephosphorized by high-pressure water. The width is set by a fixed width press, and 2-stand rough rolling and 7-stand CVC finishing rolling are used. The starting temperature of finishing rolling is 1050℃, and the final rolling temperature of finishing rolling is 920℃. Laminar cooling adopts rear-stage dispersed cooling, the coiling temperature is 720℃, and the thickness of the hot-rolled raw material is 3mm. Finally, a quality inspection is carried out, and qualified cold-rolled raw materials are obtained. After the cold-rolled raw material is uncoiled, it enters the pickling tank. The pickling process pays attention to the matching of acid concentration, strip temperature and speed to prevent under-pickling or over-pickling, and the surface quality is checked. The final thickness of the cold-rolled plate is 0.6mm. Finally, a continuous hot-dip galvanizing process is carried out. The annealing method adopts continuous annealing. The annealing heating section temperature is 830℃, the soaking section temperature is 830℃, the slow cooling section temperature is 680℃, the fast cooling section temperature is 460℃, the zinc pot (balanced section) is 460℃, the top roller (cooling tower top strip temperature) is ≤250℃, the water quenching tank inlet temperature is ≤160℃, and the temperature after drying is ≤40℃. During the continuous annealing process, the calorific value of the coal gas in the furnace must be stable, and the purity of hydrogen and nitrogen must be guaranteed. The strip steel after continuous annealing is finally subjected to skin-passing with a skin-passing elongation of 0.8%, and then coiled into a finished product. Zinc liquid temperature: 460°C. Figure 1 This is a typical microstructure diagram of the cold-rolled steel sheet prepared in this example.

[0033] Example 3

[0034] The molten iron is pre-treated for desulfurization, and the top and bottom combined blown converter is used to decarbonize and dephosphorize the molten iron to obtain molten steel, and the scrap steel is added to the converter. Then the molten steel after converter smelting is subjected to RH operation, and the in-situ temperature is 1630-1660℃, and deep decarbonization treatment is carried out, with the target of 20ppm. After decarbonization, aluminum particles are added for deoxidation according to the oxygen determination, and alloys such as titanium iron and niobium iron are added to adjust the composition to ensure that [O] in the molten steel is ≤20ppm. According to the chemical composition shown in Table 1, the slab continuous casting overheat is 25℃, and the carbon-free middle package covering agent should be used in the continuous casting process to avoid carbon increase during the casting process. After that, the slab is cleaned, slowly cooled, and the quality of the continuous casting slab is checked. The slab heating temperature is 1200℃, the heating time is 240min, and the heated slab is dephosphorized by high-pressure water. The width is set by a fixed width press, and 2-stand rough rolling and 7-stand CVC finishing rolling are used. The starting temperature of finishing rolling is 1070℃, and the final rolling temperature of finishing rolling is 940℃. Laminar cooling adopts rear-stage dispersed cooling, the coiling temperature is 740℃, and the thickness of the hot-rolled raw material is 3mm. Finally, a quality inspection is carried out, and qualified cold-rolled raw materials are obtained. After the cold-rolled raw material is uncoiled, it enters the pickling tank. The pickling process pays attention to the matching of acid concentration, strip temperature and speed to prevent under-pickling or over-pickling, and the surface quality is checked. The final thickness of the cold-rolled plate is 0.6mm. Finally, a continuous hot-dip galvanizing process is carried out. The annealing method adopts continuous annealing. The annealing heating section temperature is 840℃, the soaking section temperature is 840℃, the slow cooling section temperature is 690℃, the fast cooling section temperature is 475℃, the zinc pot (balanced section) is 470℃, the top roller (cooling tower top strip temperature) is ≤250℃, the water quenching tank inlet temperature is ≤160℃, and the temperature after drying is ≤40℃. During the continuous annealing process, the calorific value of the coal gas in the furnace must be stable, and the purity of hydrogen and nitrogen must be guaranteed. The strip steel after continuous annealing is finally skin-passed, with a skin-pass elongation of 0.85%, and then coiled into a finished product. Zinc liquid temperature: 460°C.

[0035] Table 1 Chemical composition of Examples 1 to 3 of the present invention (wt%)

[0036] Example C Si Mn P S Ti 1 0.0015 0.006 0.12 0.009 0.004 0.050 2 0.0020 0.007 0.13 0.008 0.003 0.060 3 0.0025 0.008 0.14 0.010 0.005 0.070

[0037] The mechanical properties of the cold-rolled steel sheets of Examples 1 to 3 of the present invention were tested, and the test results are shown in Table 2.

[0038] Table 2 Mechanical properties of the steel plates of Examples 1 to 3 of the present invention

[0039]

[0040] It can be seen from the data in Table 2 that the present invention provides a thin-gauge hot-dip galvanized Ti-based DX54D+Z steel strip for ultra-deep drawing, and the mechanical properties of the cold-rolled plate meet the requirements of yield strength of 120-180 MPa, tensile strength of 260-330 MPa, elongation A≥38%, n≥0.18, and r≥1.6.

[0041] It can be seen from the results of the above embodiments that the thin-gauge hot-dip galvanized Ti-based DX54D+Z steel strip for ultra-deep drawing of the present invention has the characteristics of good ultra-deep drawing performance, low yield strength ratio, good plasticity, etc.

[0042] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a thin-gauge ultra-deep drawing hot-dip galvanized Ti-based DX54D+Z steel strip, characterized in that: The main process steps and process parameters are as follows: The production process of smelting-continuous casting section: hot metal pretreatment-converter-RH furnace-casting machine; steelmaking process control [O]≤20ppm, [N]≤30ppm; The heating process is strictly controlled in the furnace time, and the furnace temperature is 1220±20℃; The rolling process includes rough rolling and finishing rolling. The rough rolling process is carried out by a 2-stand rolling mill, and the finishing rolling process is carried out by a 7-stand continuous variable crown rolling mill. The starting rolling temperature of the finishing rolling is 1050±20°C, and the final rolling temperature of the finishing rolling is 900-940°C. The cooling adopts laminar cooling, the rear dispersed cooling mode, the rear dispersed, and the coiling temperature is 700-740℃; Pickling process: Pay attention to the concentration of acid, the matching of strip temperature and speed during pickling to prevent under-pickling or over-pickling, and check the surface quality; Continuous hot-dip galvanizing process, the cold hard coil enters the continuous annealing furnace, the heating section temperature is 820-840℃, the soaking section temperature is 820-840℃, the slow cooling section temperature is 670-690℃, the fast cooling section temperature is 450-475℃, the zinc pot temperature is 450-470℃, the top roller is ≤250℃, the water quenching tank inlet temperature is ≤160℃, and the temperature after drying is ≤40℃; the skin-clearing elongation is 0.8±0.05%; the zinc liquid temperature is 460±10℃; The chemical components of the hot-dip galvanized Ti-based DX54D+Z steel strip include by weight percentage: C: 0.0015-0.0025%, Si: 0.006-0.008%, Mn: 0.12-0.14%, P: ≤0.010%, S: ≤0.006%, Ti: 0.050-0.070%, and the rest are Fe and unavoidable impurities.

2. The method for preparing a thin-gauge ultra-deep drawing hot-dip galvanized Ti-based DX54D+Z steel strip according to claim 1, characterized in that: The skin-passing process is used to give the strip a small amount of deformation, mainly to improve the material shape.

3. The method for preparing a thin-gauge ultra-deep drawing hot-dip galvanized Ti-based DX54D+Z steel strip according to claim 1, characterized in that: Zinc liquid temperature: 460℃.

4. The method for preparing a thin-gauge ultra-deep drawing hot-dip galvanized Ti-based DX54D+Z steel strip according to claim 1, characterized in that: The chemical components of the hot-dip galvanized Ti-based DX54D+Z steel strip include, by mass percentage, C: 0.0015%, Si: 0.006%, Mn: 0.12%, P: 0.009%, S: 0.004%, Ti: 0.050%, and the rest are Fe and unavoidable impurities.

5. The method for preparing a thin-gauge ultra-deep drawing hot-dip galvanized Ti-based DX54D+Z steel strip according to claim 1, characterized in that: The chemical components of the hot-dip galvanized Ti-based DX54D+Z steel strip include, by mass percentage, C: 0.0020%, Si: 0.007%, Mn: 0.13%, P: 0.008%, S: 0.003%, Ti: 0.060%, and the rest are Fe and unavoidable impurities.

6. The method for preparing a thin-gauge ultra-deep drawing hot-dip galvanized Ti-based DX54D+Z steel strip according to claim 1, characterized in that: The chemical components of the hot-dip galvanized Ti-based DX54D+Z steel strip include, by mass percentage, C: 0.0025%, Si: 0.008%, Mn: 0.14%, P: 0.010%, S: 0.005%, Ti: 0.070%, and the rest are Fe and unavoidable impurities.

Images