A steel for a raw material of a high-strength packing belt of 1000mpa or more and a production method thereof

Abstract

The application discloses a kind of high-strength packing belt raw material steels with strength above 1000MPa, which is characterized in that the chemical components are as follows: C: 0.19-0.25%, Si: 0.05-0.30%, Mn: 1.20-1.57%, P≤0.030%, S≤0.025%, Alt: 0.020-0.050%, Ca: 0.0008-0.0020%, and the balance is Fe and inevitable impurities; and a specific production method is also disclosed. The purpose of the application is to provide a kind of high-strength packing belt raw material steels with strength above 1000MPa and its production method. By adding carbon, silicon, manganese alloying elements to strengthen the design mechanism, using low-temperature controlled rolling and controlled cooling process for hot rolling, and using more than 70% high-pressure reduction ratio for pickling, a high-strength packing belt raw material steel with 1000MPa high strength and certain elongation is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to a steelmaking and rolling process for automobile structure steel, in particular to a high-strength baling belt raw material steel with a strength of 1000 MPa or more and a production method thereof. BACKGROUND

[0002] The steel belt for packaging is mainly used for industrial packaging to ensure the safety of the bundled goods during handling, transportation and storage. In the past, the steel belt for packaging was mainly the cold-rolled steel belt product of the steel plant, and in recent years, the steel belt for packaging has been developed as a steel deep processing product. The most commonly used field of the steel belt for packaging mainly includes: steel, non-ferrous metal, papermaking, glass, building material, tobacco, light textile processing and other industries. At present, the steel industry in China is the largest and most important application field of the steel belt for packaging. The steel belt for packaging is widely used in each unit of steel rolling and finished product packaging, and becomes an important material for finished product unit. With the continuous improvement of the technology of steel and other metal industries, the steel belt for packaging has developed from low strength to high strength and high toughness. In order to meet the automation needs of automatic baling equipment, a series of higher standard requirements for mechanical properties, shape, coiling and surface engineering technology are put forward for products of different strength levels. Due to the significant increase in strength, thin-gauge high-strength steel belts can replace thick-gauge low-strength steel belts, which can save a large amount of raw materials, reduce costs, improve material utilization, and realize the policy of saving and reducing consumption advocated by the state. Although China's economic growth is slowing down, its size is still huge due to the continuous increase of the base. Similarly, although the growth of China's steel market has fallen, the absolute quantity is still amazing, so the demand for the steel belt for packaging still maintains a large absolute quantity.

[0003] Retrieved patent 1: CN113621887A discloses a production method of low-cost cold-rolled steel belt raw material for baling belt. It is found that the patent adopts low-silicon and low-manganese design in component design, and the manganese content (0.3-0.5%) is different from the patent (1.2-1.4%) by an order of magnitude, and the strength design is different from the patent. The tensile strength of the retrieved patent is greater than 930 MPa, which is lower than the designed strength of 1000 MPa of the present patent. Compared with retrieved patent 1, the present patent adopts carbon, silicon and manganese alloy element strengthening design mechanism in component design. Although the alloy content of the finished product is higher than that of patent 1, the performance of the finished product after bluing and return is more stable. Compared with improving the strength of the product by water cooling, the alloy solid solution strengthening design product is better in subsequent processing and finished product stability, and is not easy to appear large range fluctuation of the strength of the finished product after annealing. The product stability is best.

[0004] Search patent 2: CN114411062A discloses "a kind of high-strength packing belt steel and its preparation method", it is found that the component design is close to the patent, the manganese content range is 1.0~1.1%, the temperature control of hot rolling process is basically consistent, the strength of finished product is slightly lower than the patent, the product elongation is slightly lower than the patent, the product processing modification ability is slightly worse than the patent, there is certain difference; compared with search patent 2, the component design of the patent adopts carbon, silicon, manganese alloy element strengthening design mechanism, the chemical composition manganese content is 0.2% higher than search patent, the finished product coil strength is about 20~40MPa higher than search patent, the elongation is about 2% higher than search patent, the product modification ability is better than search patent 2, which is beneficial to customers to replace thick gauge low strength steel belt with thin gauge high strength steel belt to realize product cost reduction and efficiency improvement, improve product market competitiveness and profitability.

[0005] Search patent 3: CN111850410A discloses "a kind of packing belt cold hard coil plate and its preparation method", it is found that the patent adopts low silicon and low manganese design in component design, the manganese content (0.4~0.5%) and the patent (1.2~1.4%) exist order of magnitude difference, the strength design and the patent exist level difference, the design tensile strength is greater than 930MPa, which is about 1000MPa lower than the strength of the patent; compared with search patent 3, the component design of the patent adopts carbon, silicon, manganese alloy element strengthening design mechanism, although the finished product alloy content is slightly higher than patent 3, but the performance is more stable after bluing return, compared with water cooling to improve product strength, alloy solid solution strengthening design product is better in subsequent processing and finished product stability, and it is not easy to appear that the strength of finished product after annealing fluctuates in a large range, the product stability is best. SUMMARY

[0006] The purpose of the present application is to provide a kind of high-strength packing belt raw material steel and its production method with strength above 1000MPa, by adding carbon, silicon, manganese alloy element strengthening design mechanism, hot rolling adopts low temperature controlled rolling and controlled cooling process, acid rolling adopts more than 70% high pressure rate, etc. Measures, a kind of high-strength packing belt raw material steel with 1000MPa higher strength and certain elongation is obtained.

[0007] To solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0008] The present application provides a kind of high-strength packing belt raw material steel with strength above 1000MPa, the chemical composition is as follows: C: 0.19~0.25%, Si: 0.05~0.30%, Mn: 1.20~1.57%, P≤0.030%, S≤0.025%, Alt: 0.020~0.050%, Ca: 0.0008~0.0020%, the balance is Fe and inevitable impurities.

[0009] Further, its chemical composition is C: 0.22%, Si: 0.07%, Mn: 1.31%, P: 0.011%, S: 0.005%, Alt: 0.027%, Ca: 0.0013% by weight percentage, the balance being Fe and unavoidable impurities.

[0010] Further, its chemical composition is C: 0.23%, Si: 0.08%, Mn: 1.29%, P: 0.015%, S: 0.004%, Alt: 0.026%, Ca: 0.0010% by weight percentage, the balance being Fe and unavoidable impurities.

[0011] A production method of a high-strength steel for a 1000 MPa grade or more high-strength packing belt raw material, main steps are:

[0012] (1) KR desulfurization → converter smelting → LF refining → slab continuous casting;

[0013] (2) slab heating → high-pressure water descaling → width setting press → E1R1 rough rolling mill rolling → E2R2 rough rolling mill rolling → heat preservation cover → flying shear cutting head and tail → high-pressure water descaling → F1-F7 finishing rolling mill rolling → densification type laminar cooling → coiling → pallet transportation system → weighing → warehousing;

[0014] (3) pickling uncoiling → welding → tension leveling → pickling → rinsing → drying → edge cutting → rolling → coiling → weighing → marking → baling → warehousing;

[0015] Key process points are as follows:

[0016] First step: in order to ensure low sulfur of molten iron and low sulfur content at the end point, deep desulfurization operation is adopted in KR desulfurization treatment, the sulfur content in molten iron at the end of desulfurization should be ≤0.010%, and the slag scraping ratio on the surface of molten iron tank should be ≥90%;

[0017] Second step: in order to improve the cleanliness of molten steel, the carbon content at the end of converter smelting needs to be controlled to be ≥0.04%, the point blowing operation number at the end of converter is ≤1 times per furnace, the converter tapping temperature is controlled to be ≥1620℃, the sliding plate slag stopping operation is adopted at the beginning and end of tapping to prevent the converter slag from entering the ladle, and the molten steel is subjected to one-time deoxidation alloying operation during tapping process, aluminum iron, silicon iron, manganese iron alloy and carbon additive are added during deoxidation alloying process, so as to realize one-time deoxidation alloying operation of molten steel.

[0018] Third step: in order to reduce the sulfur content of molten steel, LF refining process adopts slagging desulfurization operation, adding lime in ladle to improve the basicity of molten steel top slag in ladle, and adding aluminum-iron alloy to improve the argon stirring at the bottom of ladle, and at the same time, arc electric heating is carried out on molten steel to promote the sulfur content in molten steel to enter the slag in the form of sulfide, so as to reduce the sulfuration of molten steel, and the LF refining slag should achieve white slag effect, and the content of (FeO+MnO) in the slag should be less than 1.5%; in order to avoid nitrogen increase, the speed of dust removal fan needs to be adjusted to ensure that the pressure in the smoke hood during LF refining and heating process is in a slight positive pressure state, so as to avoid the contact between external air and molten steel; LF off-site ensures that the S content in molten steel is less than or equal to 0.015%; calcium treatment is carried out after LF refining treatment, the feeding speed of high calcium wire during calcium treatment process is 200-300 m, the feeding speed of wire during calcium treatment process is controlled to be 3-3.5 m / s, the soft blowing time of molten steel after calcium treatment is greater than or equal to 8 min, and the temperature and chemical composition of molten steel at the end of LF refining treatment should meet the control requirements of casting process;

[0019] Fourth step: argon protection is adopted during ladle casting process, the slag detection equipment is started during tundish casting process, and the slag in ladle is prevented from flowing into tundish at the end of ladle casting; constant speed control is adopted during casting process, the speed setting range is 1.0-1.8 m / min according to different casting sections; the superheat degree during tundish casting is controlled to be 20-35℃; in order to improve the central segregation of internal quality of casting blank, the superheat degree during casting process is executed according to the temperature requirement offline range, light pressing process is adopted during casting process, the pressing amount of liquid core solidification end of casting blank is greater than or equal to 4 mm, and the central segregation of macrostructure test piece of continuous casting blank should not be greater than B class 2.0 level;

[0020] Fifth step: after the slab is cooled for 36 hours and the macrostructure test is qualified, the slab is released, the slab is loaded into hot rolling heating furnace, and appropriate process parameters are selected according to the thickness of product in heating furnace process; the heating temperature is 1210-1230℃, the time in furnace is 150-220 min, the soaking temperature is 25-55 min, and the out-of-furnace temperature is 1210-1250℃ when the thickness is less than or equal to 3.0 mm; the heating temperature is 1200-1220℃, the time in furnace is 150-220 min, the soaking temperature is 25-55 min, and the out-of-furnace temperature is 1190-1230℃ when the thickness is greater than 3.0 mm;

[0021] Sixth step: rolling includes rough rolling and finish rolling, the rough rolling adopts 2-stand rough rolling mill, the finish rolling adopts 7-stand continuous variable crown rolling mill, the finish rolling temperature is 875-905℃, the cooling adopts laminar flow continuous cooling equipment, the cooling code is set to 11 mode, the upper end cooling nozzle is opened every other one, the lower end cooling nozzle is opened every other two, and the coiling temperature is controlled to be 560-600℃ according to different thickness;

[0022] Seventh step: the surface quality, thickness tolerance, surface roughness requirement of acid pickling process is strict operation procedure is executed, wherein the acid concentration of tail acid tank is greater than or equal to 160g / L, the ferrous ion concentration is not greater than 30g / L, the rolling speed of strip steel in acid pickling process is 90-210m / min (target value 160m / min) ; reasonable total compression ratio and deformation pass are effective means for work hardening to improve the toughness of cold hard coil, and the actual control range of total reduction of acid pickling process is greater than 70%-80%.

[0023] Further, the performance of the produced high-strength packing belt raw material steel meets: yield strength is greater than 900MPa, yield strength is greater than 1000MPa

[0024] Compared with the prior art, the beneficial technical effects of the present application are:

[0025] The present application can realize a kind of strength 1000MPa grade above high-strength packing belt raw material steel output by reasonable chemical composition design, rolling process and larger acid pickling reduction etc.Measures, since the product has higher strength, can realize the thin gauge high-strength steel belt instead of thick gauge low-strength steel belt, so that a large amount of raw materials can be saved, cost is reduced, material utilization is improved, the saving of energy consumption advocated by the country can be realized. BRIEF DESCRIPTION OF DRAWINGS

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

[0027] Figure 1 It is the microstructure diagram of example 1;

[0028] Figure 2 It is the microstructure diagram of example 2. DETAILED DESCRIPTION

[0029] The present application will be further described below in conjunction with the drawings.

[0030] Example 1

[0031] The hot metal is pretreated by desulphurization, the desulphurized KR hot metal S content is 0.004%, the desulphurizer addition amount in the treatment process is 0.5 tons, the stirring time is 15 min, the slagging frequency is more than 1 time, the slagging rate is more than 90%, and the hot metal off-site temperature T is 1312°C; the hot metal is decarburized and dephosphorized by top and bottom combined blowing converter smelting to obtain molten steel, the converter smelting is blown with argon all the way, the weight of scrap steel added into the converter is 39.1 tons, the weight of hot metal added into the converter is 269 tons, the converter tapping temperature is 1623°C, the tapping carbon content is 0.041%, the deoxidization and alloying treatment is carried out during the tapping process, the sliding plate slag stopping tapping operation is used before and after the tapping to prevent slagging, 3800 kg of manganese iron alloy, 1300 kg of aluminum iron are added during the deoxidization and alloying process. Then the molten steel after the converter smelting is subjected to LF furnace refining, the refining on-site temperature is 1575°C, the LF refining slagging desulphurization is carried out, and the composition temperature is adjusted, the alloying treatment is carried out in the early stage of the LF treatment, 800 kg of manganese iron, 500 kg of aluminum iron, and 2400 kg of silicon iron are added, 360 meters of calcium line is fed for calcium treatment, the calcium treatment is carried out after the white slag is formed after the alloying is completed, the soft blowing is carried out for 10 min, the steel liquid bare leakage is avoided during the soft blowing process, the LF refining off-site temperature is 1557°C. The chemical composition shown in Table 1 is provided for the casting machine. The casting machine is poured with a superheat of 20°C, the withdrawal speed is 1.10 m / min, the tundish pouring is completed to open the slag detection automatic closing water gap sliding plate operation to avoid tundish slagging and ensure that the light pressing equipment at the end of the casting blank solidification is normally opened. Then the slab slow cooling and the continuous casting blank quality inspection are carried out. The hot-rolled slab thickness is 2.9 mm, the discharge temperature is 1220°C, the heating time is 180 min, the high-pressure water desulphurization is carried out on the heated slab. The width is fixed by a fixed-width press, 2-stand rough rolling (3+5 mode is adopted for rough rolling), 7-stand CVC finishing rolling, and the finishing rolling final rolling temperature is 885°C. The laminar flow cooling adopts continuous cooling mode 11, and the coiling temperature is 574°C. The pickling process rolls the thickness of 0.8 mm, the pickling pickling reduction rate is actually 72%, and other processes are carried out according to the pickling process operation requirements. The corresponding finished product mechanical properties are shown in Table 2.

[0032] Example 2

[0033] The molten iron is pretreated by desulphurization, the desulphurized KR off-site molten iron S content is 0.001%, the desulphurizer addition amount in the treatment process is 0.7 tons, the stirring time is 7 min, the slagging frequency is greater than 1 time, the slagging rate is greater than 90%, and the molten iron off-site temperature T is 1330℃; the molten iron is decarburized and dephosphorized by top and bottom combined blowing converter smelting to obtain molten steel, the whole process of converter smelting is blown by argon, the weight of scrap steel added into the converter is 36.85 tons, the weight of molten iron added into the converter is 276 tons, the converter tapping temperature is 1648℃, the tapping carbon content is 0.037%, the deoxidization and alloying treatment is carried out during the tapping process, the sliding plate slag stopping tapping operation is adopted before and after the tapping, and the slag is prevented from falling, 4000 kg of manganese iron alloy, 1300 kg of aluminum iron, and 600 kg of silicon manganese alloy are added during the deoxidization and alloying process. Then the molten steel after the converter smelting is subjected to LF furnace external refining, the refining on-site temperature is 1549℃, the LF refining slagging desulphurization is carried out, and the composition temperature is adjusted, the alloying treatment is carried out in the early stage of the LF treatment, 450 kg of manganese iron, 200 kg of silicon iron, and 240 meters of calcium line are fed for calcium treatment, the calcium treatment is carried out after the white slag is formed after the alloying is completed, the soft blowing is carried out for 8 min, the steel liquid is prevented from being exposed to the air during the soft blowing process, the LF refining off-site temperature is 1591℃. The chemical composition shown in Table 1 is provided for the casting machine. The casting machine is poured at a superheat of 24℃, the withdrawal speed is 1.20 m / min, the tundish pouring is completed, the slag is detected, and the water gap sliding plate operation is automatically closed to avoid the tundish slagging and ensure that the light pressing equipment at the end of the casting blank solidification is normally opened. Then the slab slow cooling and the continuous casting blank quality inspection are carried out. The hot-rolled plate blank thickness is 2.9 mm, the discharge temperature is 1222℃, the heating time is 174 min, and the high-pressure water is used for desulphurization after the heated plate blank is desulphurized. The width is fixed by a fixed-width press, 2 racks of rough rolling (the rough rolling adopts a 3+5 mode), 7 racks of CVC finishing rolling, and the finishing rolling final rolling temperature is 891℃. The laminar flow cooling adopts a continuous cooling mode 11, and the coiling temperature is 591℃. The pickling process is rolled to a thickness of 0.9 mm, the pickling rolling reduction rate is actually 70%, and other processes are carried out according to the pickling process operation requirements. The corresponding finished product mechanical properties are shown in Table 2. According to the chemical composition actual value in Table 1 and the finished product coil mechanical property detection value in Table 2, the steel coil chemical composition and mechanical properties produced by the case implementation 1 and 2 meet the user requirements.

[0034] Table 1 Finished product chemical composition (%)

[0035] C Si Mn P S Alt Ca Example 1 0.22 0.07 1.31 0.011 0.005 0.027 0.0013 Example 2 0.23 0.08 1.29 0.015 0.004 0.026 0.0010

[0036] Table 2 Finished product mechanical properties corresponding to the implementation case

[0037] Yield strength / MPa Tensile strength / MPa Elongation / % Example 1 938 1039 10.0 Example 2 Yield strength / MPa Tensile strength / MPa Elongation / % 948 1063 9.0

[0038] The above described embodiments are only to illustrate the preferred modes of the present application, and are not intended to limit the scope of the present application. Any modification and improvement made by those skilled in the art to the technical solutions of the present application without departing from the design spirit of the present application shall fall within the protection scope of the present application.

Claims

1. A type of high-strength steel for strapping materials with a strength of 1000 MPa or higher, characterized in that, Its chemical composition by weight percentage is C: 0.19-0.25%, Si: 0.05-0.30%, Mn: 1.20-1.57%, P≤0.030%, S≤0.025%, Alt: 0.020-0.050%, Ca: 0.0008-0.0020%, with the balance being Fe and unavoidable impurities; Its production method mainly involves the following steps: (1) KR desulfurization → converter smelting → LF refining → slab continuous casting; (2) Slab heating → high pressure water descaling → fixed width press → E1R1 roughing mill rolling → E2R2 roughing mill rolling → heat insulation cover → flying shear head and tail → high pressure water descaling → F1-F7 finishing mill rolling → dense laminar flow cooling → coiling → pallet transport system → weighing → warehousing; (3) Pickling and uncoiling → welding → tension leveling → pickling → rinsing → drying → trimming → rolling → coiling → weighing → marking → bundling → warehousing; The key process points are as follows: Step 1: To ensure low sulfur content in molten iron and control of sulfur content at the final stage, KR desulfurization treatment adopts deep desulfurization operation. At the end of desulfurization, the sulfur content in molten iron should be ≤0.010%, and the slag removal ratio on the surface of the molten iron ladle should be ≥90%. Step 2: To improve the cleanliness of molten steel, the carbon content of the final component of the converter smelting is controlled to be ≥0.04%, the number of point blowing operations at the end of the converter is ≤1 time / furnace, the converter tapping temperature is controlled to be ≥1620℃, and the slag blocking operation is carried out by sliding plate at the beginning and end of the converter tapping to prevent converter slag from entering the ladle. During the tapping process, the molten steel is deoxidized and alloyed once. In the deoxidation and alloying process, aluminum ferroalloy, silicon ferroalloy, manganese ferroalloy and carbon raiser are added to achieve the deoxidation and alloying operation of the molten steel in one step. Step 3: To reduce the sulfur content of molten steel, the LF refining process employs slag-forming desulfurization. Quicklime is added to the ladle to increase the basicity of the top slag in the ladle furnace, and aluminum-iron alloys are added. Argon gas is blown from the bottom of the ladle for stirring, and the molten steel is simultaneously heated by electric arc heating. This promotes the conversion of sulfur in the molten steel into sulfides generated by the reaction, thereby reducing the amount of sulfur in the molten steel. The LF refining slag should achieve a white slag effect, meaning the (FeO+MnO) content in the slag should be less than 1.5%. Simultaneously, to avoid nitrogen increase during the LF heating process, the nitrogen removal process needs to be adjusted... The speed of the dust blower is adjusted to ensure that the pressure inside the fume hood is slightly positive during the LF refining heating process, preventing outside air from entering the fume hood and coming into contact with the molten steel; the LF is positioned to ensure that the S content in the molten steel is ≤0.015%; after the LF refining process, calcium treatment is carried out, during which 200-300m of high-calcium wire is fed in, and the wire feeding speed is controlled at 3m / s-3.5m / s; after the calcium treatment, the soft blowing time of the molten steel is ≥8min; at the end of the LF refining process, the temperature and chemical composition of the molten steel must meet the control requirements of the casting machine pouring process. Step 4: Argon gas is used for protection throughout the casting process. The slag detection equipment is turned on during the ladle pouring process, and slag from the ladle is prevented from flowing into the tundish at the end of the ladle pouring. The casting process adopts constant casting speed control, with the casting speed set in the range of 1.0m / min to 1.8m / min according to different casting sections. The superheat of the tundish pouring is controlled between 20℃ and 35℃. In order to improve the segregation of the center of mass inside the billet, the superheat of the pouring process shall be within the lower limit of the temperature requirement. The casting process shall adopt a light pressure process, and the reduction at the end of the solidification of the liquid core of the billet shall be ≥4mm. The center segregation of the continuous casting billet in the low magnification microstructure test piece shall not be greater than Class B 2.

0. Step 5: After the slabs have been cooled for 36 hours and passed a low-magnification inspection, they are released and loaded into the hot rolling furnace. The furnace process selects appropriate process parameters according to the product thickness specifications: for thickness ≤ 3.0mm, the heating temperature is 1210-1230℃, the furnace time is 150-220min, the soaking temperature is 25-55min, and the furnace exit temperature is 1210-1250℃; for thickness > 3.0mm, the heating temperature is 1200-1220℃, the furnace time is 150-220min, the soaking temperature is 25-55min, and the furnace exit temperature is 1190-1230℃. Step 6: Rolling includes roughing and finishing. Roughing is done on a 2-stand mill, and finishing is done on a 7-stand continuous variable crown mill. The finishing temperature is 875-905℃. Cooling is done on a laminar flow continuous cooling system. The upper cooling nozzles are alternately opened, and the lower cooling nozzles are alternately opened. The coiling temperature is controlled within the range of 560-600℃ depending on the thickness. Step 7: The pickling and rolling process requires strict adherence to operating procedures regarding surface quality, thickness tolerance, and surface roughness. Specifically, the acid concentration in the tail pickling bath must be ≥160g / L, and the ferrous ion concentration must not exceed 30g / L. The strip rolling speed in the pickling and rolling process is 90-210m / min. A reasonable total reduction ratio and deformation passes are effective means of work hardening to improve the strength and toughness of cold-rolled coils. Currently, the actual control range of the total reduction rate in the pickling and rolling process is 70%-80%.

2. The high-strength packing strap raw material steel with a strength of 1000MPa or higher as described in claim 1, characterized in that, Its chemical composition by weight percentage is C: 0.22%, Si: 0.07%, Mn: 1.31%, P: 0.011%, S: 0.005%, Alt: 0.027%, Ca: 0.0013%, with the balance being Fe and unavoidable impurities.

3. The high-strength packing strap raw material steel with a strength of 1000MPa or higher as described in claim 1, characterized in that, Its chemical composition by weight percentage is C: 0.23%, Si: 0.08%, Mn: 1.29%, P: 0.015%, S: 0.004%, Alt: 0.026%, Ca: 0.0010%, with the balance being Fe and unavoidable impurities.

4. The high-strength packing strap raw material steel with a strength of 1000MPa or higher as described in claim 1, characterized in that, The steel used in the production of high-strength packing straps meets the following performance requirements: yield strength greater than 900MPa and tensile strength greater than 1000MPa.

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