Steel belt for hot-based galvanized high-strength structure and production method and application of steel belt

Abstract

The invention provides a steel strip for a hot-based galvanized high-strength structure, a production method and application of the steel strip and a hot-based high-strength galvanized plate. A C-Si-Mn-Cr-Ti microalloying scheme is adopted, the mechanical property is stable, strong plasticity matching is good, meanwhile, technical measures such as controlled rolling and controlled cooling, recrystallization annealing, hot galvanizing and finishing processes are adopted in the production process, and the produced 440 MPa-grade high-strength hot-based galvanized steel plate has good mechanical property and process property. The steel plate provided by the invention is stable in mechanical property and good in strong plasticity matching, and can effectively adapt to different stamping processes (bending, stamping, flanging and the like) of users. The high-strength hot-based galvanized steel plate produced by the method is excellent in comprehensive performance, high in cost performance and good in popularization and application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot-base galvanized high-strength structural steel strip production, and relates to a steel strip for hot-base high-strength galvanized sheet, a production method and application thereof, and a hot-base high-strength galvanized sheet, and in particular to a steel strip for hot-base galvanized high-strength structure, a production method and application thereof. Background Art

[0002] my country's automobile industry has entered a period of rapid development of passenger cars. High-strength automotive materials can effectively reduce the weight of the vehicle body and reduce fuel exhaust emissions due to their good strength-plasticity matching. They are more in line with the needs of the automobile manufacturing industry for "energy saving, safety, environmental protection, and corrosion resistance" and have become one of the preferred materials for automotive steel. Low-alloy high-strength steel (HSLA) has played an important role in the development of the automotive, construction, home appliance and other industries due to its good strength-plasticity matching, good welding performance and cold forming performance. With the development of lightweight automobiles and the full life cycle of materials, low-alloy high-strength steel is also constantly developing in the direction of high strengthening and coating.

[0003] Recently, major domestic and foreign automobile manufacturers have proposed the use of high-strength galvanized steel sheets with a thickness of >2.5mm for automobiles. The limit thickness of the acid rolling-hot-dip galvanizing process of the domestic conventional production line is ≤2.5mm, and it is impossible to develop this product. The hot-based coated plate production technology, that is, the coated plate developed by the hot rolling + pickling + hot-dip galvanizing process technology, has the advantages of thick specifications, thick coatings, and low costs due to the reduction of cold rolling processes, and has good market promotion and application prospects. However, the hot-based galvanizing production process is quite different from the traditional production process, especially the hot-rolled pickling raw materials are significantly different from the cold-rolled raw materials used in the traditional acid rolling-hot-dip galvanizing process in terms of deformation storage energy and surface roughness. The deformation storage energy produced by the cold-rolled strip after large plastic deformation has a significant impact on the control of the recrystallization annealing structure in the continuous hot-dip galvanizing production process, which is directly related to the mechanical property level and uniformity of the finished product. Hot-rolled pickled raw materials lack cold working deformation energy storage, and the annealing process of direct galvanizing after pickling has no thermal history processes such as deformation structure recovery, recrystallization, and grain growth, so it is impossible to obtain the structure and texture state after conventional process annealing. Under normal conditions, the finished products obtained by ordinary processes have low plasticity and poor forming performance.

[0004] Therefore, how to find a more suitable method for producing hot-dip galvanized high-strength structural steel strip and solve the above-mentioned technical problems existing in the existing process has become one of the urgent problems to be solved by many front-line researchers in the industry. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a steel strip for hot-base high-strength galvanized sheet and its production method, application and a hot-base high-strength galvanized sheet, especially a hot-base galvanized high-strength structural steel strip. The 440MPa grade hot-base galvanized steel sheet with excellent stamping performance provided by the present invention has good room temperature mechanical properties and process performance, and fully meets the requirements of technical indicators. Moreover, the production method has simple process, good controllability, strong operability, and is more suitable for industrial promotion and application.

[0006] The present invention provides a steel strip for hot-dip high-strength galvanized sheet, which comprises, by element mass percentage:

[0007] C: 0.06wt%~0.08wt%, Si: 0~0.05wt%, Mn: 1.30wt%~1.40wt%, Cr: 0.25wt%~0.35wt%, Ti: 0.005wt%~0.015wt%, P: 0~0.015wt%, S: 0~0.010wt%, Als: 0.015wt%~0.055wt%, and the balance is Fe.

[0008] Preferably, the steel strip is a C-Si-Mn-Cr-Ti microalloyed steel;

[0009] The microstructure of the steel strip includes ferrite and pearlite;

[0010] The ferrite has a grain size of 9.5 to 10.5;

[0011] The volume fraction of the ferrite is 88% to 95%.

[0012] The present invention provides a method for producing a steel strip for a hot-dip high-strength galvanized sheet as described in any one of the above technical solutions, comprising the following steps:

[0013] 1) The molten steel is subjected to LF refining and then continuously cast to obtain a slab;

[0014] 2) The slab obtained in the above steps is heated and then hot rolled, and then cooled to obtain a steel strip.

[0015] Preferably, the smelting method includes converter smelting;

[0016] The smelting process includes pre-deoxidation and alloying steps after the furnace;

[0017] In the alloying step, raw materials including aluminum-iron alloy, metal manganese, niobium-iron alloy and iron-chromium alloy are added into the deoxidized molten steel for alloying.

[0018] Preferably, the LF refining includes the steps of molten steel temperature adjustment, ladle bottom blowing argon treatment and alloy fine-tuning;

[0019] The pressure of the argon gas blown from the bottom of the ladle is 200-400 Pa;

[0020] The time for blowing argon from the bottom of the ladle is 4 to 6 minutes;

[0021] The LF refining time is 10 to 25 minutes;

[0022] The outlet temperature of the LF refining is 1580-1595°C.

[0023] Preferably, the continuous casting is specifically performed by using a continuous casting machine;

[0024] The continuous casting further includes a step of natural cooling;

[0025] The heating temperature is 1210-1230°C;

[0026] The soaking time of the heating is 30 to 45 minutes.

[0027] Preferably, the hot rolling includes multiple passes of rough rolling and multiple passes of finish rolling;

[0028] The initial rolling temperature of the hot rolling is 1140-1200°C;

[0029] The final rolling temperature of the hot rolling is 850-890°C;

[0030] The cooling rate of the cooling is 10-15°C / s;

[0031] The cooling step further includes the step of curling into a roll;

[0032] The cooling is to a coiling temperature of 580-620°C.

[0033] The present invention provides the use of the steel strip described in any one of the above technical solutions or the steel strip produced by the production method described in any one of the above technical solutions in the preparation of hot-base high-strength galvanized sheet.

[0034] The present invention provides a heat-based high-strength galvanized sheet, which is obtained by acid-base washing and continuous hot-dip galvanizing of a steel strip;

[0035] The continuous hot-dip galvanizing includes the steps of annealing and hot-dip galvanizing.

[0036] Preferably, the acid-alkali washing specifically includes the steps of straightening, acid washing, alkali washing and drying;

[0037] The tensile elongation of the straightening in the acid-base washing is 1.0% to 1.2%;

[0038] The annealing temperature is 850-870°C;

[0039] The annealing is specifically a continuous annealing process including preheating, recrystallization annealing, slow cooling and rapid cooling steps;

[0040] The temperature of the hot-dip galvanizing is 455-465°C;

[0041] The final cooling temperature of the cooling step after hot-dip galvanizing is ≤100°C.

[0042] The present invention provides a steel strip for hot-dip galvanized sheet, which includes, by element mass percentage: C: 0.06wt% to 0.08wt%, Si: 0 to 0.05wt%, Mn: 1.30wt% to 1.40wt%, Cr: 0.25wt% to 0.35wt%, Ti: 0.005wt% to 0.015wt%, P: 0 to 0.015wt%, S: 0 to 0.010wt%, Als: 0.015wt% to 0.055wt%, and the balance is Fe. Compared with the prior art, the present invention believes that according to the material requirements and technical conditions of major domestic automobile manufacturers, the main technical indicators of high-strength hot-dip galvanized steel sheets with a tensile strength of 440MPa and excellent formability need to meet the following requirements: R p0.2 305~390MPa, Rm≥440MPa, elongation after fracture A 50mm ≥30% (L0=50mm, b=25mm). 440MPa high-strength hot-dip galvanized steel sheet is used to process the internal structural parts of passenger cars. The main technical requirements of the steel sheet: sufficient strength and plasticity; good formability. The chemical composition of the existing 440MPa grade high-strength hot-dip galvanized steel sheet is usually designed as a C-Si-Mn-Nb-Ti micro-alloying technology route, in which the C content is ≤0.10%, the Si content is 0.10%~0.25%, the Mn content is 1.30%~1.50%, the Nb content is 0.030%~0.050%, and the Ti content is 0.005%~0.020%. The low-temperature rolling and low-temperature coiling process is adopted to obtain refined ferrite, pearlite and spherical NbC precipitation phases, which strengthens the galvanized substrate. The main production process is smelting-refining outside the furnace-continuous casting-hot rolling-pickling-hot galvanizing. Taking a 1780mm automotive plate dedicated continuous annealing production line as an example, the existing production method generally adopts two-phase zone annealing temperature (700-760℃), faster primary cooling rate (HGJC, 30℃ / S), hot dip galvanizing temperature (455-465℃) and other measures to appropriately coarsen the finished product grains, develop favorable textures, and improve the stamping performance of the finished product. However, this production process will have problems such as no deformation structure recovery, recrystallization, and grain growth during the annealing process, which are prone to mixed crystals and deterioration of performance. Therefore, how to develop a full-process production process for hot-based galvanizing without cold rolling process to obtain high-strength galvanized products with mechanical properties equivalent to cold-rolled-annealed products is the core of this technology.

[0043] Based on this, the present invention creatively designs a steel strip for hot-base high-strength galvanized sheet with a specific element composition and a specific production process. This is a 440MPa-grade high-strength hot-base galvanized steel sheet with excellent stamping performance. The present invention adopts a C-Si-Mn-Cr-Ti (C-Mn-Cr-Ti) series micro-alloying scheme, which has stable mechanical properties and good strength and plasticity matching. At the same time, the production process adopts technical measures such as controlled rolling and controlled cooling, recrystallization annealing, hot-dip galvanizing, and light finishing processes. The production inspection results show that the 440MPa-grade high-strength hot-base galvanized steel sheet produced by this method has good mechanical properties and process performance. Because the steel plate provided by the present invention has stable mechanical properties and good strength and plasticity matching, it can effectively adapt to different stamping processes of users (bending, stamping, flanging, etc.). The high-strength hot-base galvanized steel sheet produced by the present invention has excellent comprehensive performance, high cost performance, and good prospects for promotion and use.

[0044] The microstructure of the 440MPa hot-dip galvanized steel sheet provided by the present invention is ferrite + pearlite, the ferrite grain size is 9.5-10.5, the ferrite volume fraction is 88-95%, and it has good room temperature mechanical properties and process performance, and fully meets the requirements of technical indicators. The production process of the present invention adopts process measures such as controlling the chemical composition range, hot rolling soaking temperature, final rolling temperature, coiling temperature, hot dip galvanizing annealing temperature, and galvanizing temperature to obtain the hot-dip galvanized steel strip finished product: R p0.2 305~390MPa, Rm≥440MPa, A 50mm ≥30%, with excellent comprehensive performance. The present invention refines the hot-rolled microstructure, carbides and NbC particles precipitated at grain boundaries / intragranular grains to hinder the non-uniform growth of annealed grains, refine the ferrite grain size, and improve the plasticity index of the finished product, effectively overcoming the problem of mixed crystals and deteriorated performance of the finished product in the process of no deformation structure recovery, recrystallization, and grain growth in the pickling-hot-dip galvanizing technology during the annealing process. The pickling direct hot-dip galvanizing process technology adopted by the present invention omits the conventional cold rolling step, reduces the process cost, and the finished product has good physical performance, effectively adapts to the use needs of downstream users, and has good promotion value and prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The microstructure diagram of the steel plate prepared in Example 1 of the present invention;

[0046] Figure 2 The microstructure diagram of the steel plate prepared in Example 2 of the present invention;

[0047] Figure 3 This is a microstructure diagram of the steel plate prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0048] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention rather than limiting the patent claims of the present invention.

[0049] All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0050] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses industrial purity or conventional purity in the field of heat-based high-strength galvanized sheet preparation.

[0051] The brands and abbreviations of all raw materials of the present invention are conventional brands and abbreviations in the art. Each brand and abbreviation is clear and definite in the field of its related use. Those skilled in the art can purchase them from the market or prepare them by conventional methods according to the brands, abbreviations and corresponding uses.

[0052] The present invention provides a steel strip for hot-dip high-strength galvanized sheet, which comprises, by element mass percentage:

[0053] C: 0.06wt%~0.08wt%, Si: 0~0.05wt%, Mn: 1.30wt%~1.40wt%, Cr: 0.25wt%~0.35wt%, Ti: 0.005wt%~0.015wt%, P: 0~0.015wt%, S: 0~0.010wt%, Als: 0.015wt%~0.055wt%, and the balance is Fe.

[0054] In the present invention, the added amount of C is 0.06wt% to 0.08wt%, may be 0.064wt% to 0.076wt%, or may be 0.068wt% to 0.072wt%.

[0055] In the present invention, the added amount of Si is 0-0.05wt%, may be 0.01wt%-0.04wt%, may be 0.02wt%-0.03wt%.

[0056] In the present invention, the added amount of Mn is 1.30wt% to 1.40wt%, may be 1.32wt% to 1.38wt%, or may be 1.34wt% to 1.36wt%.

[0057] In the present invention, the added amount of Cr is 0.25wt% to 0.35wt%, may be 0.27wt% to 0.33wt%, or may be 0.29wt% to 0.31wt%.

[0058] In the present invention, the added amount of Ti is 0.005wt% to 0.015wt%, may be 0.007wt% to 0.013wt%, or may be 0.009wt% to 0.011wt%.

[0059] In the present invention, the added amount of P is 0-0.015wt%, may be 0.003wt%-0.012wt%, may be 0.006wt%-0.009wt%.

[0060] In the present invention, the added amount of S is 0-0.010wt%, can be 0.002-0.008wt%, can be 0.004wt%-0.006wt%.

[0061] In the present invention, the added amount of Als is 0.015wt% to 0.055wt%, can be 0.02wt% to 0.05wt%, can be 0.025wt% to 0.045wt%, can be 0.03wt% to 0.04wt%.

[0062] In the present invention, the steel strip is preferably a C-Si-Mn-Cr-Ti based microalloyed steel.

[0063] In the present invention, the microstructure of the steel strip preferably includes ferrite and pearlite.

[0064] In the present invention, the grain size of the ferrite is preferably 9.5 to 10.5, more preferably 9.7 to 10.3, and more preferably 9.9 to 10.1.

[0065] In the present invention, the volume fraction of the ferrite is preferably 88% to 95%, more preferably 89% to 94%, more preferably 90% to 93%, and more preferably 91% to 92%.

[0066] The present invention provides a method for producing a steel strip for a hot-dip high-strength galvanized sheet as described in any one of the above technical solutions, comprising the following steps:

[0067] 1) The molten steel is subjected to LF refining and then continuously cast to obtain a slab;

[0068] 2) The slab obtained in the above steps is heated and then hot rolled, and then cooled to obtain a steel strip.

[0069] The present invention firstly refines the molten steel after smelting through LF, and then continuously casts it to obtain a slab.

[0070] In the present invention, the smelting method preferably includes converter smelting.

[0071] In the present invention, the smelting process preferably includes pre-deoxidation and alloying steps after the furnace.

[0072] In the present invention, in the alloying step, raw materials including aluminum-iron alloy, metallic manganese, niobium-iron alloy and iron-chromium alloy are preferably added into the deoxidized molten steel for alloying.

[0073] In the present invention, the LF refining preferably includes the steps of molten steel temperature adjustment, ladle bottom blowing argon treatment and alloy fine-tuning.

[0074] In the present invention, the pressure of the argon gas blown from the bottom of the ladle is preferably 200-400 Pa, more preferably 240-360 Pa, and more preferably 280-320 Pa.

[0075] In the present invention, the time for blowing argon from the bottom of the ladle is preferably 4 to 6 minutes, more preferably 4.4 to 5.6 minutes, and more preferably 4.8 to 5.2 minutes.

[0076] In the present invention, the LF refining time is preferably 10 to 25 minutes, more preferably 13 to 22 minutes, and even more preferably 16 to 19 minutes.

[0077] In the present invention, the outlet temperature of LF refining is preferably 1580-1595°C, more preferably 1583-1592°C, and more preferably 1586-1589°C.

[0078] In the present invention, the continuous casting is preferably performed by using a continuous casting machine.

[0079] In the present invention, the continuous casting preferably further includes a natural cooling step.

[0080] In the present invention, the slab obtained in the above steps is finally heated and then hot-rolled, and then cooled to obtain a steel strip.

[0081] In the present invention, the heating temperature is preferably 1210-1230°C, more preferably 1214-1226°C, and more preferably 1218-1222°C.

[0082] In the present invention, the soaking time of heating is preferably 30 to 45 minutes, more preferably 33 to 42 minutes, and more preferably 36 to 39 minutes.

[0083] In the present invention, the hot rolling preferably includes multiple passes of rough rolling and multiple passes of finish rolling.

[0084] In the present invention, the initial rolling temperature of the hot rolling is preferably 1140-1200°C, more preferably 1150-1160°C, more preferably 1160-1190°C, and more preferably 1170-1180°C.

[0085] In the present invention, the final rolling temperature of the hot rolling is preferably 850-890°C, more preferably 855-885°C, more preferably 860-880°C, and more preferably 865-875°C.

[0086] In the present invention, the cooling rate of the cooling is preferably 10 to 15°C / s, more preferably 11 to 14°C / s, and preferably 12 to 13°C / s.

[0087] In the present invention, the step of curling into a roll is preferably further included after cooling.

[0088] In the present invention, the cooling is preferably to a coiling temperature of 580 to 620°C, more preferably 585 to 615°C, more preferably 590 to 610°C, and more preferably 595 to 605°C.

[0089] The present invention provides the use of the steel strip described in any one of the above technical solutions or the steel strip produced by the production method described in any one of the above technical solutions in the preparation of hot-base high-strength galvanized sheet.

[0090] The present invention also provides a heat-based high-strength galvanized sheet, which is obtained by acid-base washing and continuous hot-dip galvanizing of a steel strip;

[0091] The continuous hot-dip galvanizing includes the steps of annealing and hot-dip galvanizing.

[0092] In the present invention, the acid-alkali washing preferably includes the steps of straightening, acid washing, alkali washing and drying.

[0093] In the present invention, the tensile elongation of the straightening in the acid-base washing is preferably 1.0% to 1.2%, more preferably 1.04% to 1.16%, and more preferably 1.08% to 1.12%.

[0094] In the present invention, the annealing temperature is preferably 850-870°C, more preferably 854-866°C, and more preferably 858-862°C.

[0095] In the present invention, the annealing is preferably a continuous annealing process including preheating, recrystallization annealing, slow cooling and rapid cooling steps.

[0096] In the present invention, the temperature of the hot-dip galvanizing is preferably 455-465°C, more preferably 457-463°C, and more preferably 459-461°C.

[0097] In the present invention, the final cooling temperature of the cooling step after hot-dip galvanizing is preferably ≤100°C, more preferably ≤90°C, and more preferably ≤80°C.

[0098] The present invention is a complete and detailed overall technical solution, which better guarantees the composition and microscopic morphology of the steel strip for hot-based high-strength galvanized sheet, and further improves the comprehensive performance of the steel strip for hot-based high-strength galvanized sheet. The above-mentioned hot-based galvanized high-strength structural steel strip and its production method, application and a hot-based high-strength galvanized sheet can specifically include the following steps:

[0099] The invention provides a 440MPa grade high-strength hot-dip galvanized steel plate with excellent stamping performance.

[0100] The chemical element range of the 440MPa grade high-strength hot-dip galvanized steel plate of the present invention is calculated on a single substance basis, and the chemical composition is (wt%): C: 0.06-0.08, Si: 0-0.05, Mn: 1.30-1.40, Cr: 0.25-0.35, Ti: 0.005-0.015, P: 0-0.015, S: 0-0.010, Als: 0.015-0.055, and the rest is Fe.

[0101] The microstructure of the 440MPa hot-dip galvanized steel sheet provided by the present invention is ferrite + pearlite, the ferrite grain size is 9.5 to 10.5, and the ferrite volume fraction is 88 to 95%. Ferrite refers to the interstitial solid solution formed by C dissolving in α-Fe, and has a body-centered cubic crystal structure. Ferrite can be measured by methods known to those skilled in the art, such as the GB / T6394 metallographic method.

[0102] The 440MPa grade hot-dip galvanized steel sheet provided by the present invention has good room temperature mechanical properties and process properties, and fully meets the requirements of technical indicators.

[0103] The present invention provides a method for preparing the above-mentioned 440MPa grade hot-dip galvanized steel sheet, which specifically includes the steps of continuous casting billet heating, hot rolling, pickling, annealing, etc. The chemical composition of the billet is (w%): C: 0.06-0.08, Si: 0-0.05, Mn: 1.30-1.40, Cr: 0.25-0.35, Ti: 0.005-0.015, P: 0-0.015, S: 0-0.010, Als: 0.015-0.055, and the rest is Fe. The soaking temperature of the steel billet heating step is 1210-1230°C, and the soaking time is 30-45min; the initial rolling temperature of the hot rolling step is 1140-1200°C, and the final rolling temperature is 850-890°C; the cooling step adopts water cooling in the front section after rolling, and the coiling temperature of the coiling step is 580-620°C; the pickling and straightening elongation is 1.0-1.2%; the hot-dip galvanizing soaking temperature is 850-870°C, the hot-dip galvanizing temperature is 455-465°C, the skin-clearing elongation is 0.8-1.20%, and the straightening elongation is 0-0.60%.

[0104] Specifically, the steel billet can be produced by methods known to those skilled in the art from molten iron in a blast furnace through converter smelting, LF refining, electric heating, and continuous casting.

[0105] Furthermore, the process flow of the production method of the 440MPa grade hot-dip galvanized steel sheet provided by the present invention is as follows:

[0106] Converter smelting → LF refining → continuous casting → hot rolling → cooling → coiling → pickling → continuous hot-dip galvanizing → skin pass → straightening → coiling → packaging → storage

[0107] Specifically, converter smelting is to smelt molten steel from blast furnace molten iron and smelting charge in a converter, and then pre-deoxidize and alloy the molten steel after the furnace; in the alloying step, aluminum-iron alloy, metal manganese, niobium-iron alloy, iron-chromium alloy, etc. are added to the deoxidized molten steel to obtain molten steel. The technology adopted in the converter smelting process is a method well known to those skilled in the art.

[0108] Specifically, the LF refining process carries out molten steel temperature adjustment, argon blowing treatment at the bottom of the ladle and alloy fine-tuning. Argon gas with a pressure of 200-400Pa is introduced into the bottom of the molten steel tank for 4-6 minutes. The argon gas flow rate is based on the condition that the molten steel does not overturn. This can avoid secondary oxidation of the molten steel and rapid temperature drop, so that the inclusions in the steel can fully float up, further improving the cleanliness of the steel.

[0109] Specifically, the LF process takes 10 to 25 minutes to process, and the exit temperature is 1580 to 1595° C. The molten steel obtained in the LF process (based on the total weight of the molten steel, calculated as wt% by single element) is C: 0.06 to 0.08, Si: 0 to 0.05, Mn: 1.30 to 1.40, Cr: 0.25 to 0.35, Ti: 0.005 to 0.015, P: 0 to 0.015, S: 0 to 0.010, Als: 0.015 to 0.055, and the rest is Fe. The technology adopted in the LF refining process is a method well known to those skilled in the art.

[0110] Specifically, the continuous casting step can adopt a method known to those skilled in the art. In the method of the present invention, the refined molten steel is cast into a pre-baked tundish, and cast into a slab by a continuous casting machine with full process protection. After casting, cooling can be performed according to conventional methods, such as natural cooling at room temperature.

[0111] Specifically, the hot rolling step is to heat the cast slab and then roll it. The purpose of rolling is to make the continuous casting slab reach the required thickness. The rolling passes of the hot rolled steel strip of the present invention are 6 rough rolling steps and 7 finishing rolling steps.

[0112] Specifically, the starting temperature of hot rolling refers to the temperature at which the billet enters the rolling mill. Heating at this temperature can fully dissolve the micro-alloying elements, eliminate the chemical element segregation caused by the dendrite bias of the ingot, and avoid the liquid precipitation of carbides to reduce the effect of micro-alloying elements in steel. The final rolling temperature of hot rolling refers to the temperature at which the steel is taken out of the finishing mill. In order to make the thickness and mechanical properties of the finished product uniform, the hot rolling intermediate billet hot coil box process technology is adopted to keep the head, middle and tail of the hot rolling intermediate billet before finishing rolling at a specific final rolling temperature.

[0113] Specifically, the temperature of the steel billet heating step of the present invention is 1210-1230°C, and the soaking time is 30-45 minutes; the initial rolling temperature of the hot rolling step is 1140-1200°C, and the final rolling temperature is 850-890°C; the temperature control during the hot rolling process can make the steel in a completely austenitic structure before the finishing rolling outlet, and avoid the austenitic structure being too coarse.

[0114] Specifically, the cooling step can adopt various conventional methods. Usually, the hot-rolled thin strip steel is cooled to adjust the internal structure of the steel, and then it is coiled into a coil. In order to meet the strength-plasticity matching of the finished hot-dip galvanized steel plate, the present invention controls the ferrite grain size in the microstructure of the strip steel after hot rolling to about 11 levels, and because the precipitation of NbC and Cr carbides inhibits the non-uniform growth of ferrite in the high temperature zone, the hot-rolled substrate structure is fine and uniform. The layer cooling step is the front-stage cooling, and the cooling rates of the upper and lower manifolds are 75% and 50% respectively, the cooling rate is 10-15°C / s, and it is cooled to a coiling temperature of 580-620°C.

[0115] Specifically, the pickling step can adopt various conventional methods. Usually, the thin steel strips rolled by hot rolling are welded at the head of the pickling unit to form a continuous steel strip, and then supplied to the hot-dip galvanizing unit for production after straightening, pickling, alkali washing and drying. The pickling straightening elongation is 1.0-1.2%. After pickling, the surface oxide scale of the steel plate is washed away and the surface quality is improved. The pickling step can adopt methods and techniques known to those skilled in the art.

[0116] Specifically, the continuous hot-dip galvanizing step can adopt various conventional methods. After pickling, the thin steel strip is welded at the entrance of the hot-dip galvanizing unit to form a continuous steel strip. After continuous surface cleaning and drying, it is annealed + galvanized in a continuous hot-dip galvanizing unit. The cleaning process is a method known to those skilled in the art. The annealing process is a continuous annealing method. The steel strip is preheated, recrystallized annealed, slowly cooled, quickly cooled, hot-dip galvanized, and cooled after plating in an annealing unit, followed by online skin-passing, straightening, online inspection, and coiling. The annealing temperature is 850-870°C, the hot-dip galvanizing temperature is 455-465°C, the secondary cooling final cooling temperature is ≤100°C, the skin-pass elongation is 0.80-1.20%, and the straightening elongation is 0-0.60%. The steps can adopt methods and techniques known to those skilled in the art.

[0117] The above content of the present invention provides a hot-base galvanized high-strength structural steel strip and its production method, application and a hot-base high-strength galvanized sheet. The hot-base high-strength galvanized sheet steel strip designed by the present invention with a specific element composition and a specific production process is a 440MPa grade high-strength hot-base galvanized steel sheet with excellent stamping performance. The present invention adopts a C-Si-Mn-Cr-Ti system micro-alloying scheme, with stable mechanical properties and good strength and plasticity matching. At the same time, the production process adopts technical measures such as controlled rolling and controlled cooling, recrystallization annealing, hot-dip galvanizing, and light finishing processes. The production inspection results show that the 440MPa grade high-strength hot-base galvanized steel sheet produced by this method has good mechanical properties and process performance. Because the steel plate provided by the present invention has stable mechanical properties and good strength and plasticity matching, it can effectively adapt to different stamping processes of users (bending, stamping, flanging, etc.). The high-strength hot-base galvanized steel sheet produced by the present invention has excellent comprehensive performance, high cost performance, and good prospects for promotion and use.

[0118] The microstructure of the 440MPa hot-dip galvanized steel sheet provided by the present invention is ferrite + pearlite, the ferrite grain size is 9.5-10.5, the ferrite volume fraction is 88-95%, and it has good room temperature mechanical properties and process performance, and fully meets the requirements of technical indicators. The production process of the present invention adopts process measures such as controlling the chemical composition range, hot rolling soaking temperature, final rolling temperature, coiling temperature, hot dip galvanizing annealing temperature, and galvanizing temperature to obtain the hot-dip galvanized steel strip finished product: R p0.2 305~390MPa, Rm≥440MPa, A 50mm≥30%, with excellent comprehensive performance. The present invention refines the hot-rolled microstructure, carbides and NbC particles precipitated at grain boundaries / intragranular grains to hinder the non-uniform growth of annealed grains, refine the ferrite grain size, and improve the plasticity index of the finished product, effectively overcoming the problem of mixed crystals and deteriorated performance of the finished product in the process of no deformation structure recovery, recrystallization, and grain growth in the pickling-hot-dip galvanizing technology during the annealing process. The pickling direct hot-dip galvanizing process technology adopted by the present invention omits the conventional cold rolling step, reduces the process cost, and the finished product has good physical performance, effectively adapts to the use needs of downstream users, and has good promotion value and prospects.

[0119] In order to further illustrate the present invention, a steel strip for hot-base high-strength galvanized sheet and its production method, application and a hot-base high-strength galvanized sheet provided by the present invention are described in detail in combination with the embodiments below. However, it should be understood that these embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating processes are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following embodiments.

[0120] The chemical composition detection methods in the present invention are respectively spark source atomic emission spectrometry analysis methods for carbon steel and medium and low alloy steel, and the national standard is GB / T4336; Determination of low carbon content in non-alloy steel Part 2: Infrared absorption method after combustion in an induction furnace (preheated), and the national standard is GB / T 20126-2006.

[0121] Example 1

[0122] a. Molten steel smelting: The smelting equipment is a top-blown converter. The semi-steel after vanadium extraction from blast furnace molten iron is used as raw material. The temperature is 1345℃. Steelmaking auxiliary materials are added to melt to 1660℃ and the steel is tapped into the molten steel tank. When 1 / 3 of the steel is tapped, aluminum iron, low-carbon manganese iron, chromium iron, etc. are added to the ladle for pre-deoxidation and alloying. Subsequently, argon gas is blown from the bottom of the molten steel tank on a small platform outside the furnace. The argon gas pressure is 200-400Pa and the time is 4 minutes.

[0123] b. LF refining: Argon gas of a certain pressure (200-400Pa) is introduced into the bottom of the molten steel tank for 4 minutes, and the argon gas flow rate is based on the condition that the molten steel does not overturn; LF is used for heating, Ti microalloying and alloy fine-tuning, and the LF treatment termination temperature is 1595℃. The molten steel obtained (based on the total weight of the molten steel, calculated as a single substance, wt, %) is C: 0.06, Si: 0.02, Mn: 1.35, Cr: 0.31, Ti: 0.012, P: 0.010, S: 0.003, Als: 0.040, and the rest is Fe.

[0124] c. Continuous casting: The molten steel tank is transported to the casting position, and the bottom of the molten steel tank slides the Al stopper rod, and the molten steel automatically flows into the tundish, passes through the Al stopper rod, and is drained to the crystallizer for continuous casting. The whole process uses protective slag for protective casting, and after casting, it is cooled into hot-rolled plate billets.

[0125] d. Hot rolling: the slab soaking temperature is 1220℃, the rough rolling temperature is 1165℃, and the finishing rolling temperature is 880℃; the rough rolling steps are 6 and the finishing rolling steps are 7; the cooling method adopts water cooling in the front section after rolling, and the cooling rates of the upper and lower headers are 75% and 50% respectively, and the cooling rate is 15℃ / s; the coiling temperature is 590℃. The thickness of the strip after rolling is 2.90 mm.

[0126] e. Pickling: The elongation of pickling and straightening is 1.2%.

[0127] f. Hot-dip galvanizing: The recrystallization annealing temperature of hot-dip galvanizing steel strip is 870℃, the hot-dip galvanizing temperature is 460℃, the final cooling temperature of the secondary cooling section is 90℃, the skin-clearing elongation is 1.10%, and the tensile elongation is 0.2%.

[0128] The prepared coils were subjected to mechanical property tests, and the yield strength Rp0.2, tensile strength Rm, and elongation A50mm at room temperature were tested. The tensile properties were tested in accordance with GB / T228 room temperature tensile test method for metal materials. The finished product had a yield strength (Rp0.2) of 352MPa, a tensile strength (Rm) of 486MPa, and an elongation (A50mm) of 37%, which met the technical requirements of 440MPa grade high-strength hot-dip galvanized structural steel plates.

[0129] See also Figure 1 , Figure 1 This is a microstructure diagram of the steel plate prepared in Example 1 of the present invention. Figure 1 Among them, the volume proportion of ferrite structure is 92%, and the volume proportion of pearlite structure is 8%.

[0130] Example 2

[0131] The preparation method is basically the same as that of Example 1, except that the molten steel obtained by converter smelting has the following components: C: 0.08, Si: 0.03, Mn: 1.38, Cr: 0.32, Ti: 0.010, P: 0.008, S: 0.005, Als: 0.034, and the rest is Fe (Wt,%). The hot-rolled steel sheet produced by the above molten steel has a slab soaking temperature of 1215°C, a final rolling temperature of 885°C, a coiling temperature of 610°C, a hot-rolled thickness of 3.0 mm, an pickling straightening elongation of 1.2%, a hot-dip galvanizing annealing temperature of 865°C, a hot-dip galvanizing temperature of 458°C, a secondary cooling section final cooling temperature of 90°C, a skin-pass elongation of 1.2%, and a straightening elongation of 0.2%.

[0132] The prepared coils were subjected to mechanical property tests, and the yield strength Rp0.2, tensile strength Rm, and elongation A50mm at room temperature were tested. The tensile properties were tested in accordance with GB / T228 room temperature tensile test method for metal materials. The finished product had a yield strength (Rp0.2) of 370MPa, a tensile strength (Rm) of 494MPa, and an elongation (A50mm) of 34%, which met the technical requirements of 440MPa grade high-strength hot-dip galvanized structural steel plates.

[0133] See also Figure 2 , Figure 2 This is a microstructure diagram of the steel plate prepared in Example 2 of the present invention. Figure 2 Among them, the volume proportion of ferrite structure is 90%, and the volume proportion of pearlite structure is 10%.

[0134] Comparative Example 1

[0135] The preparation method is basically the same as that of Example 1, except that the composition of the molten steel obtained by converter smelting is C: 0.08%, Si: 0.02%, Mn: 1.30, Nb: 0.035, Ti: 0.010, P: 0.012, S: 0.003, Als: 0.045, and the rest is Fe, (Wt,%). The hot-rolled steel plate produced by the above-mentioned molten steel has a slab furnace temperature of 1225°C, a final rolling temperature of 870°C, a coiling temperature of 600°C, a hot rolling thickness of 3.0mm, and an acid pickling straightening elongation of 1.4%. The hot-dip galvanizing annealing temperature is 760°C, the hot-dip galvanizing temperature is 460°C, the final cooling temperature of the secondary cooling section is 94°C, the skin-clearing elongation is 1.2%, and the straightening elongation is 0%.

[0136] The prepared coils were subjected to mechanical property tests, and the yield strength Rp0.2, tensile strength Rm, and elongation A50mm at room temperature were tested. The tensile properties were tested in accordance with GB / T228 room temperature tensile test method for metal materials. The finished product yield strength (Rp0.2) was 405MPa, the tensile strength (Rm) was 516MPa, and the elongation (A50mm) was 26%. The mechanical properties did not meet the technical requirements of 440MPa grade high-strength hot-dip galvanized structural steel plates.

[0137] See also Figure 3 , Figure 3 This is a microstructure diagram of the steel plate prepared in Comparative Example 1 of the present invention. Figure 3 In the sample, the volume proportion of ferrite structure is 87%, the volume proportion of pearlite structure is 13%, and there are obvious ferrite structure mixed crystals.

[0138] The 440MPa grade hot-dip galvanized high-strength structural steel strip production technology provided by the present invention has been successfully applied to industrial production. The product is one of the important products of Panzhihua Iron and Steel (Group) Company, mainly used for punching internal structural parts of passenger cars. According to the previous industrial production performance and user use effects, the actual surface quality of the steel plate is good, the parts have small stamping rebound, and the forming performance is excellent, which meets the user's use requirements.

[0139] Under the current external demand conditions of "energy saving, safety, environmental protection and corrosion resistance" in the domestic automobile manufacturing industry, compared with the materials used by users in the early stage, the manufacturing process of 440MPa grade hot-dip galvanized high-strength structural steel strip omits the cold rolling process. In addition to maintaining certain stamping performance, it also has certain corrosion resistance. It can effectively adapt to the needs of the automobile manufacturing industry and has good promotion prospects.

[0140] The above is a detailed introduction to a hot-dip galvanized high-strength structural steel strip provided by the present invention and its production method and application. The principle and implementation method of the present invention are described in detail using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention, including the best mode, and also enables any technician in the field to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A steel strip for hot-dip high-strength galvanized sheet, characterized in that: Measured by element mass percentage, including: C: 0.06wt%~0.08wt%, Si: 0~0.05wt%, Mn: 1.30wt%~1.40wt%, Cr: 0.25wt%~0.35wt%, Ti: 0.005wt%~0.015wt%, P: 0~0.015wt%, S: 0~0.010wt%, Als: 0.015wt%~0.055wt%, and the balance is Fe.

2. The steel strip according to claim 1, characterized in that The steel strip is a C-Si-Mn-Cr-Ti series microalloy steel; The microstructure of the steel strip includes ferrite and pearlite; The ferrite has a grain size of 9.5 to 10.5; The volume fraction of the ferrite is 88% to 95%.

3. A method for producing a steel strip for hot-dip galvanized sheet according to any one of claims 1 to 2, characterized in that: The following steps are involved: 1) The molten steel is subjected to LF refining and then continuously cast to obtain a slab; 2) The slab obtained in the above steps is heated and then hot rolled, and then cooled to obtain a steel strip.

4. The production method according to claim 3, characterized in that: The smelting method includes converter smelting; The smelting process includes pre-deoxidation and alloying steps after the furnace; In the alloying step, raw materials including aluminum-iron alloy, metal manganese, niobium-iron alloy and iron-chromium alloy are added into the deoxidized molten steel for alloying.

5. The production method according to claim 3, characterized in that: The LF refining includes the steps of molten steel temperature adjustment, ladle bottom blowing argon treatment and alloy fine adjustment; The pressure of the argon gas blown from the bottom of the ladle is 200-400 Pa; The time for blowing argon from the bottom of the ladle is 4 to 6 minutes; The LF refining time is 10 to 25 minutes; The outlet temperature of the LF refining is 1580-1595°C.

6. The production method according to claim 3, characterized in that: The continuous casting is specifically performed by using a continuous casting machine; The continuous casting further includes a step of natural cooling; The heating temperature is 1210-1230°C; The soaking time of the heating is 30 to 45 minutes.

7. The production method according to claim 3, characterized in that: The hot rolling includes multiple passes of rough rolling and multiple passes of finish rolling; The initial rolling temperature of the hot rolling is 1140-1200°C; The final rolling temperature of the hot rolling is 850-890°C; The cooling rate of the cooling is 10-15°C / s; The cooling step further includes the step of curling into a roll; The cooling is to a coiling temperature of 580-620°C.

8. Use of the steel strip according to any one of claims 1 to 2 or the steel strip produced by the production method according to any one of claims 3 to 7 in the preparation of hot-base high-strength galvanized sheet.

9. A thermally-based high-strength galvanized sheet, characterized in that: The galvanized sheet is obtained by acid-base washing and continuous hot-dip galvanizing of the steel strip; The continuous hot-dip galvanizing includes the steps of annealing and hot-dip galvanizing.

10. The thermally-based high-strength galvanized sheet according to claim 9, characterized in that: The acid-alkali washing specifically includes the steps of straightening, acid washing, alkali washing and drying; The tensile elongation of the straightening in the acid-base washing is 1.0% to 1.2%; The annealing temperature is 850-870°C; The annealing is specifically a continuous annealing process including preheating, recrystallization annealing, slow cooling and rapid cooling steps; The temperature of the hot-dip galvanizing is 455-465°C; The final cooling temperature of the cooling step after hot-dip galvanizing is ≤100°C.

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