Ultra-low carbon steel, preparation method thereof and steel product

Abstract

The invention relates to ultra-low carbon steel, a preparation method thereof and a steel product. The preparation method of the ultra-low carbon steel comprises the following steps: providing a casting blank; sequentially heating and hot-rolling the casting blank to obtain hot rolled steel; the hot rolling comprises rough rolling and finish rolling which are sequentially carried out, the initial rolling temperature of the rough rolling is 990-1040 DEG C, and the outlet temperature of the rough rolling is 900-940 DEG C; the initial rolling temperature of finish rolling ranges from 840 DEG C to 890 DEG C, and the final rolling temperature of finish rolling ranges from 750 DEG C to 830 DEG C; and the hot rolled steel is sequentially subjected to acid pickling, cold rolling and annealing. According to the preparation method, ferrite area low-temperature rolling is adopted, the heating energy consumption is remarkably reduced, the production efficiency is improved, the problem of scale thickening caused by traditional high-temperature rolling is avoided, the surface quality of the strip steel is more uniform, and the pickling cost is greatly reduced. Meanwhile, the ductility, the strain hardening index (n value) and the plastic strain ratio (r value) of the obtained finished product are remarkably improved, and the forming performance is excellent.

Description

Technical Field

[0001] The present application belongs to the technical field of steel preparation, and in particular relates to an ultra-low carbon steel, a preparation method thereof, and a steel product. Background Art

[0002] With the deepening of green and low-carbon development, the steel industry, as a key area of ​​high energy consumption and high carbon emissions, urgently needs to optimize production processes and efficiently utilize resources through technological innovation. Ultra-low carbon steel is widely used in precision manufacturing fields such as automotive panels, home appliance housings, and architectural decoration due to its excellent stamping and forming properties (such as high n value and r value) and good ductility. However, the preparation process of traditional ultra-low carbon steel has significant technical bottlenecks: the slab needs to be heated at a high temperature of more than 1200°C and deformed by rough rolling and finish rolling in the austenite zone. During this process, the metal surface is oxidized at high temperature to form a dense iron oxide layer with a thickness of 50-100μm, resulting in a loss of 0.3%-0.5% in yield rate and a significant increase in acid consumption in the subsequent cold rolling and pickling process. In addition, the high energy consumption and greenhouse gas emissions caused by high-temperature rolling seriously restrict the green transformation of the industry. Summary of the Invention

[0003] In view of this, the present application provides a method for preparing ultra-low carbon steel, which requires low energy consumption, has a high yield rate, and the prepared ultra-low carbon steel has good formability. Furthermore, the present application also provides ultra-low carbon steel and steel products.

[0004] In a first aspect, the present application provides a method for preparing ultra-low carbon steel, comprising the following steps:

[0005] Providing a casting billet; the casting billet comprises the following components, calculated by mass percentage: C 0.0010-0.0030%, Si ≤ 0.01%, Mn 0.10-0.20%, S ≤ 0.010%, P ≤ 0.020%, Als 0.025-0.060%, Nb ≤ 0.0020%, Ti ≤ 0.0008%, and the remainder is Fe and unavoidable impurities during smelting;

[0006] The ingot is heated and hot rolled in sequence to obtain hot rolled steel; the hot rolling includes rough rolling and finish rolling in sequence, the start rolling temperature of the rough rolling is 990℃~1040℃, the outlet temperature of the rough rolling is 900℃~940℃; the start rolling temperature of the finish rolling is 840℃~890℃, and the final rolling temperature of the finish rolling is 750℃~830℃;

[0007] The hot rolled steel is pickled, cold rolled and annealed in sequence.

[0008] The above-mentioned preparation method is to hot-roll a billet with a specific element composition ratio at a relatively low temperature, remove the iron oxide scale on the surface of the hot-rolled steel in combination with a pickling step, and then combine a cold rolling step and annealing to obtain an ultra-low carbon steel with high elongation, strain hardening index and plastic strain ratio. Furthermore, the billet with a specific composition is hot-rolled within the above-mentioned relatively low temperature range, that is, rolled in the ferrite region of the ultra-low carbon steel. Compared with the traditional rolling in the austenite region, its deformation resistance is lower, so that under the same deformation conditions, the required rolling force is smaller, thereby reducing mechanical energy consumption and heat consumption. Moreover, rolling in the ferrite region can increase the rolling rate and shorten the production cycle. In addition, hot rolling at a relatively low temperature can reduce the thickness of the iron oxide scale on the surface of the hot-rolled steel, thereby reducing product loss and improving the yield rate; it can also reduce the consumption of pickling solution in the subsequent pickling process and improve the pickling surface quality.

[0009] In summary, the above preparation method is green, environmentally friendly and has high production efficiency.

[0010] In some embodiments, the above preparation method satisfies at least one of the following conditions:

[0011] (1) The starting temperature of rough rolling is 980℃~1020℃, and the outlet temperature of rough rolling is 910℃~920℃;

[0012] (2) The starting rolling temperature of finishing rolling is 850℃~870℃, and the final rolling temperature of finishing rolling is 780℃~810℃.

[0013] In some embodiments, the annealing is performed using a hood annealing method, and the hood annealing method satisfies at least one of the following conditions:

[0014] (1) The temperature of the hood annealing is 680°C to 800°C, preferably, the temperature of the hood annealing is 700°C to 740°C;

[0015] (2) The holding time of hood annealing is 750min~900min.

[0016] In some embodiments, the heating includes a heating section and a soaking section, the heating rate of the heating section is 2.2°C / min to 5.0°C / min; the temperature of the soaking section is 1010°C to 1050°C, and the total heating time of the heating section and the soaking section is 150min to 280min.

[0017] In some embodiments, the finishing rolling comprises rolling the intermediate billet obtained after the rough rolling for 7 passes;

[0018] In the 7-pass rolling, the surface roughness of the rolls in the 1st to 4th passes is independently 0.8 μm to 1.2 μm; the surface roughness of the rolls in the 5th to 7th passes is 0.2 μm to 0.6 μm lower than the highest value of the surface roughness of the rolls in the 1st to 4th passes; preferably, the surface roughness of the rolls in the 5th to 7th passes is independently 0.6 μm to 1.0 μm; and / or,

[0019] In the 7-pass rolling, roll gap lubrication is used during the 2nd to 6th passes; the oil-water ratio of the lubricant used is 0.10% to 0.25%.

[0020] In some embodiments, the above preparation method satisfies at least one of the following conditions:

[0021] (1) Rough rolling involves rolling the heated slab in 5 to 7 passes;

[0022] (2) The total reduction rate of rough rolling is 75% to 90%;

[0023] (3) The total reduction rate of finishing rolling is 85% to 95%;

[0024] (4) The rolling rate of the finishing rolling is 10m / s to 14.5m / s.

[0025] In some embodiments, the cold rolling reduction ratio is 50% to 75%.

[0026] A second aspect of the present application provides an ultra-low carbon steel, which is prepared according to the method of the first aspect.

[0027] In some embodiments, the ultra-low carbon steel satisfies at least one of the following conditions:

[0028] (1) Ultra-low carbon steel includes the following components by mass percentage: C 0.0010-0.0030%, Si≤0.01%, Mn 0.10-0.20%, S≤0.010%, P≤0.020%, Als 0.025-0.060%, Nb≤0.0020%, Ti≤0.0008%, and the remainder is Fe and unavoidable impurities during smelting;

[0029] (2) The elongation of ultra-low carbon steel is 45% to 47%;

[0030] (3) The strain hardening exponent n of ultra-low carbon steel is 0.21 to 0.25;

[0031] (4) The plastic strain ratio r of ultra-low carbon steel is 2.5~2.8.

[0032] A third aspect of the present application provides a steel product, which comprises the ultra-low carbon steel of the second aspect. DETAILED DESCRIPTION

[0033] In order to more clearly understand the above-mentioned objectives, features and advantages of the present application, the scheme of the present application will be further described below. It should be noted that, in the absence of conflict, the embodiments of the present application and the features therein can be combined with each other.

[0034] In the following description, many specific details are set forth to facilitate a full understanding of the present disclosure, but the present application may also be implemented in other ways different from those described herein; it is obvious that the embodiments in the specification are only part of the embodiments of the present application, rather than all of the embodiments.

[0035] The "ranges" disclosed herein are defined in terms of lower and upper limits, where a given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined arbitrarily, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In this application, unless otherwise indicated, the numerical range "a to b" is a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0037] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0038] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0039] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0040] Unless otherwise specified, this application adopts conventional test methods or test methods recommended by the instrument.

[0041] A method for preparing ultra-low carbon steel

[0042] In one embodiment of the present application, a method for preparing ultra-low carbon steel is provided, comprising the following steps S10 to S30:

[0043] S10. Provide a casting billet; the casting billet comprises the following components, measured by mass percentage: C 0.0010-0.0030%, Si ≤ 0.01%, Mn 0.10-0.20%, S ≤ 0.010%, P ≤ 0.020%, Als 0.025-0.060%, Nb ≤ 0.0020%, Ti ≤ 0.0008%, and the remainder is Fe and unavoidable impurities during smelting.

[0044] S20. The ingot is heated and hot-rolled in sequence to obtain hot-rolled steel; the hot rolling includes rough rolling and finish rolling in sequence, the start rolling temperature of the rough rolling is 990°C to 1040°C, and the outlet temperature of the rough rolling is 900°C to 940°C; the start rolling temperature of the finish rolling is 840°C to 890°C, and the final rolling temperature of the finish rolling is 750°C to 830°C.

[0045] S30, sequentially pickling, cold rolling and annealing the hot-rolled steel.

[0046] The above-mentioned preparation method is to hot-roll a billet with a specific element composition ratio at a relatively low temperature, remove the iron oxide scale on the surface of the hot-rolled steel in combination with a pickling step, and then combine a cold rolling step and annealing to obtain an ultra-low carbon steel with high elongation, strain hardening index and plastic strain ratio. Furthermore, the billet with a specific composition is hot-rolled within the above-mentioned relatively low temperature range, that is, rolled in the ferrite region of the ultra-low carbon steel. Compared with the traditional rolling in the austenite region, its deformation resistance is lower, so that under the same deformation conditions, the required rolling force is smaller, thereby reducing mechanical energy consumption and heat consumption. Moreover, rolling in the ferrite region can increase the rolling rate and shorten the production cycle. In addition, hot rolling at a relatively low temperature can reduce the thickness of the iron oxide scale on the surface of the hot-rolled steel, thereby reducing product loss and improving the yield rate; it can also reduce the consumption of pickling solution in the subsequent pickling process and improve the pickling surface quality.

[0047] In summary, the above preparation method is green, environmentally friendly and has high production efficiency.

[0048] The main reason why the deformation resistance of the ferrite region of ultra-low carbon steel is significantly lower than that of the austenite region during rolling can be attributed to the synergistic effects of four aspects: first, the difference in crystal structure leads to a looser atomic arrangement in ferrite (body-centered cubic), lower slip plane resistance than in austenite (face-centered cubic), and easier dislocation movement; second, ferrite has almost no carbon solid solution strengthening effect under ultra-low carbon conditions, while the high solid solution carbon content during rolling in the austenite region significantly enhances the resistance to dislocation movement; third, the fine and uniform grains formed by rolling in the ferrite region reduce grain boundary hindrance through the Hall-Petch effect, while the complex microstructures such as pearlite and bainite and coarse grains produced by the cooling phase transformation after rolling in the austenite region are prone to stress concentration, resulting in increased strength; finally, the low dislocation density and weak pinning effect in ferrite enable smooth dislocation slip, while the carbon solid solution and face-centered structural characteristics of austenite lead to an increased dislocation entanglement density, further increasing the deformation resistance. The combined effect of these factors makes the ferrite region rolling exhibit better plastic processing properties.

[0049] As an example, the starting rolling temperature of the rough rolling may be 990°C, 995°C, 1000°C, 1005°C, 1010°C, 1015°C, 1020°C, 1025°C, 1030°C, 1035°C, or 1040°C. Furthermore, the starting rolling temperature of the rough rolling may be any value within a range consisting of any two of the above-mentioned points as end values. Preferably, the starting rolling temperature of the rough rolling is 980°C to 1020°C.

[0050] As an example, the outlet temperature of the rough rolling process may be 900°C, 905°C, 910°C, 915°C, 920°C, 925°C, 930°C, 935°C, or 940°C. Furthermore, the outlet temperature of the rough rolling process may be any value within a range consisting of any two of the above-mentioned values ​​as end values. Preferably, the outlet temperature of the rough rolling process is between 910°C and 920°C.

[0051] As an example, the starting temperature of the finishing rolling may be 840°C, 845°C, 850°C, 855°C, 860°C, 865°C, 870°C, 875°C, 880°C, 885°C or 890°C. Further, the starting temperature of the finishing rolling may be 850°C to 870°C.

[0052] As an example, the final rolling temperature of the finishing rolling can be 750℃, 755℃, 760℃, 765℃, 770℃, 775℃, 780℃, 790℃, 795℃, 800℃, 805℃, 815℃, 825℃ or 830℃; further, the final rolling temperature of the finishing rolling can be 780℃~810℃.

[0053] In some embodiments, the annealing is performed using a hood anneal.

[0054] In some embodiments, the hood annealing temperature is 680°C to 800°C. As an example, the hood annealing temperature can be 680°C, 700°C, 705°C, 710°C, 715°C, 720°C, 725°C, 730°C, 740°C, 750°C, 780°C, or 800°C, or any value within a range consisting of any two of the above values ​​as endpoints. Furthermore, the hood annealing temperature is 700°C to 740°C.

[0055] In some embodiments, the hood annealing holding time is 750 to 900 minutes. For example, the hood annealing time can be 750, 760, 770, 780, 790, 800, 810, 820, 830, 850, 890, or 900 minutes. Alternatively, the hood annealing time can be any value within a range defined by any two of the aforementioned values. By further hood annealing the cold-rolled ultra-low carbon steel and controlling the annealing temperature and holding time, the dislocation-intensive fibrous structure produced by cold rolling is replaced by equiaxed ferrite grains, eliminating work hardening, reducing hardness, and improving elongation. Furthermore, the development of the {111} texture is promoted, the plastic strain ratio (r-value) of the ultra-low carbon steel is increased, deep-drawing formability is significantly enhanced, and anisotropy is reduced.

[0056] In some embodiments, heating includes a heating stage and a soaking stage. The heating rate in the heating stage is 2.2°C / min to 5.0°C / min; the temperature in the soaking stage is 1010°C to 1050°C. The soaking stage also serves as a constant temperature holding stage. Heating the ingot before hot rolling facilitates the transition from a brittle cast titanium microstructure to a plastic workable state, providing the necessary process conditions for hot rolling and laying the foundation for the toughness and formability of the final steel.

[0057] In some embodiments, the total heating time of the temperature rising section and the soaking section is 150 min to 280 min.

[0058] In some embodiments, the rough rolling includes rolling the heated slab in 5 to 7 passes.

[0059] In some embodiments, the total reduction ratio of rough rolling is 75% to 90%.

[0060] In some embodiments, the finishing rolling comprises rolling the intermediate bar obtained after the rough rolling for 7 passes.

[0061] In some embodiments, during the finishing rolling process, the surface roughness of the rollers in the first to fourth passes is independently 0.8 μm to 1.2 μm. It is understood that, in the seven rolling passes performed during the finishing rolling process, the surface roughness of the rollers used in the first, second, third, and fourth passes is independently selected from 0.8 μm to 1.2 μm. Furthermore, the surface roughness of the rollers used in each of the first to fourth passes can be 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, or 1.2 μm, or any value within a range consisting of any two of the above-mentioned values ​​as end values.

[0062] Furthermore, the surface roughness of the rolls during the 5th to 7th rolling passes is 0.2 μm to 0.6 μm lower than the highest value of the surface roughness of the rolls during the 1st to 4th rolling passes. Controlling the surface roughness of the rolls during each of the above rolling passes is beneficial for controlling the deformation difference between the surface and core of the rolled piece during rolling. By controlling the surface roughness of the rolls during each finishing rolling pass within the above range, the uniformity of the surface and core structure of the hot-rolled strip and the finished product can be improved, while reducing the rolling force.

[0063] In some embodiments, the surface roughness of the rolls in the fifth to seventh rolling passes is independently 0.6 μm to 1.0 μm. As an example, the surface roughness of the rolls in the fifth to seventh rolling passes is independently 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or 1.0 μm; or any value within a range consisting of any two of the above values ​​as end points.

[0064] In some embodiments, roll gap lubrication is used during the second through sixth passes of the finishing rolling process. Roll gap lubrication involves spraying an oil-water mixture lubricant into the roll gap area where the rolls contact the steel plate. This reduces friction, thereby lowering rolling energy consumption and improving the surface quality of the steel plate.

[0065] Furthermore, the lubricant used for roll gap lubrication has an oil-to-water ratio of 0.10% to 0.25%. The oil-to-water ratio is calculated as follows: oil-to-water ratio = lubricating oil mass / (lubricating fluid mass) * 100%, where lubricating fluid mass = total lubricating oil mass + water mass. For example, a lubricant with an oil-to-water ratio of 0.10% to 0.25% means that 1000 liters of lubricating fluid contains only 1-2.5 liters of lubricating oil, with the remainder being water.

[0066] In some embodiments, the total reduction ratio of the finishing rolling is 85% to 95%.

[0067] In some embodiments, the rolling rate of the finishing rolling is 10m / s to 14.5m / s. Finish rolling of hot-rolled steel of a specific composition under the above-mentioned temperature conditions can achieve relatively fast rolling at the above-mentioned rolling rate; further, controlling the rolling rate of the finishing rolling within the above-mentioned range can reduce the finishing rolling time, reduce the oxidation time of the hot-rolled steel surface at high temperature, further reduce the formation of iron oxide scale on its surface, reduce the yield rate of ultra-low carbon steel, and improve its surface quality. As an example, the rolling rate of the finishing rolling is 10m / s, 10.5m / s, 11m / s, 11.5m / s, 12m / s, 12.5m / s, 13m / s, 13.5m / s, 14m / s or 14.5m / s; it can also be any value in the range value formed by any two of the above-mentioned point values ​​as end values.

[0068] In some embodiments, in step S10, the thickness of the cast billet is 230 mm.

[0069] In some embodiments, in step S20, the thickness of the intermediate billet obtained after rough rolling is 30 mm to 50 mm.

[0070] In some embodiments, in step S20, the thickness of the hot-rolled steel obtained after finish rolling is 2.5 mm to 6.0 mm.

[0071] In some embodiments, step S20 includes descaling the heated ingot before hot rolling. This descaling step can utilize conventional high-pressure descaling methods in the art, including but not limited to impacting the heated ingot surface with high-pressure water (150-300 bar). High-pressure dephosphorization can remove iron oxide scale from the ingot surface, ensuring a smooth surface during subsequent rolling and preventing rolling defects.

[0072] In some embodiments, the preparation method further comprises the steps of laminar cooling and coiling the hot rolled steel after finish rolling.

[0073] In some embodiments, the cooling rate of the laminar cooling is 8° C. / s to 20° C. / s. By controlling the laminar cooling rate, a ferrite hot-rolled steel strip structure with large and uniform grains can be obtained.

[0074] In some embodiments, the coiling temperature is 550° C. to 700° C. Coiling the hot-rolled steel is advantageous for storage.

[0075] In some embodiments, in step S30, the pickling solution used in the pickling is a pickling solution commonly used in the art, including but not limited to at least one of hydrochloric acid, sulfuric acid, and hydrofluoric acid. Preferably, the pickling solution is hydrochloric acid.

[0076] In some embodiments, in step S30, the pickling temperature is 80°C to 85°C.

[0077] In some embodiments, in step S30, the pickling speed is 150 m / min to 250 m / min.

[0078] In some embodiments, the above preparation method further includes the steps of flattening and re-coiling the annealed steel sheet.

[0079] Ultra-low carbon steel

[0080] In one embodiment of the present application, an ultra-low carbon steel is provided, which is prepared by the above method.

[0081] In some embodiments, the ultra-low carbon steel includes the following components, calculated by mass percentage: C 0.0010-0.0030%, Si≤0.01%, Mn 0.10-0.20%, S≤0.010%, P≤0.020%, Als 0.025-0.060%, Nb≤0.0020%, Ti≤0.0008%, and the remainder is Fe and unavoidable impurities during smelting.

[0082] In some embodiments, the ultra-low carbon steel is non-IF steel.

[0083] In some embodiments, the elongation of the ultra-low carbon steel is 45% to 47%.

[0084] In some embodiments, the strain hardening exponent n of the ultra-low carbon steel is 0.21-0.25.

[0085] In some embodiments, the plastic strain ratio r of the ultra-low carbon steel is 2.5-2.8.

[0086] steel products

[0087] In one embodiment of the present application, a steel product is provided, which includes the above-mentioned oriented silicon steel.

[0088] In some embodiments, steel products include, but are not limited to, automotive panels, appliance housings, and architectural trim.

[0089] Example

[0090] The following examples describe the present disclosure in more detail and are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise indicated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further processing, and all instruments used in the examples are commercially available.

[0091] Example 1

[0092] Preparation technology of hot-rolled ultra-low carbon steel with a thickness of 4.3mm (finished product thickness 1.8mm):

[0093] (1) Providing a casting billet: Providing a casting billet with a thickness of 230, the casting billet comprising the following components (by weight): C: 0.0012%, Si: 0.006%, Mn: 0.12%, S: ≤0.010%, P: ≤0.020%, Als: 0.035%, Nb: 0.0010%, Ti: 0.0004%, and the remainder being Fe and unavoidable impurities during smelting.

[0094] (2) Heating and descaling: The ingot was placed in a heating furnace and the temperature was raised from 500°C to 1020°C at a rate of 3.5°C / min, with a total heating time of 170 min; then the ingot was taken out of the furnace and descaling was performed under high pressure.

[0095] (3) Hot rolling: The descaled ingot was subjected to 7 passes of rough rolling; wherein, the rough rolling start temperature was 1000°C, and the rough rolling outlet temperature was 910°C, to obtain an intermediate billet with a thickness of 40 mm.

[0096] After cooling, the intermediate bar was finish rolled in seven passes (i.e., F1-F7). The finishing inlet temperature was 865°C, and the final rolling temperature was 805°C. Roller gap lubrication was used for rolls F2-F6, with an oil-water ratio of 0.15%-0.25%. The surface roughness of the rolls F1-F4 was 0.8-1.0 μm, and that of the rolls F5-F7 was 0.7-0.8 μm. The rolling speed of the F7 stand was 10.5 m / s. The resulting hot-rolled strip was 4.3 mm thick and had an average scale thickness of 6.8 μm. The roll surface roughness and rolling force for each rolling pass are shown in Table 1.

[0097] (4) Laminar cooling and coiling: The hot-rolled strip after finishing is subjected to laminar cooling, and the cooling rate is controlled at 10°C / s. When the temperature of the hot-rolled strip reaches 700°C, it is coiled. The coiled steel coil is cooled naturally.

[0098] (5) Pickling and cold rolling: The hot rolled steel coil is rolled to a thickness of 1.8 mm through the pickling line.

[0099] (6) Hood annealing: annealing temperature 700°C, annealing holding time 885 minutes.

[0100] (7) After flattening and rewinding, the finished product is 1.8 mm thick. The elongation of the finished product is 45.5%, the n value is 0.21, and the r value is 2.5.

[0101] Example 2

[0102] Preparation technology of hot-rolled ultra-low carbon steel with a thickness of 3.8mm (finished product thickness 1.5mm):

[0103] (1) Providing a casting billet: Providing a casting billet with a thickness of 230 mm, the casting billet comprising the following components (by weight): C: 0.0022%, Si: 0.008%, Mn: 0.17%, S: ≤ 0.010%, P: ≤ 0.020%, Als: 0.045%, Nb: 0.0013%, Ti: 0.0005%, and the remainder being Fe and unavoidable impurities during smelting.

[0104] (2) Heating: The ingot was placed in a heating furnace and heated from 510°C to 1040°C at a rate of 3.5°C / min for a total heating time of 200 min. The ingot was then taken out of the furnace and subjected to high-pressure descaling.

[0105] (3) Hot rolling: The descaled ingot was subjected to 7 passes of rough rolling; wherein, the rough rolling start temperature was 1010°C, the rough rolling outlet temperature was 920°C, and an intermediate billet with a thickness of 38 mm was obtained.

[0106] After rough rolling, the intermediate bar was cooled and then finished rolled in seven passes (i.e., F1-F7). The finishing inlet temperature was 855°C, and the final rolling temperature was 795°C. Roll gap lubrication was used for F2-F6, with an oil-water ratio of 0.14%-0.20%. The surface roughness of the rolls for F1-F4 was 0.8-1.1 μm, and that for F5-F7 was 0.6-0.8 μm. The rolling speed for F7 was 11.5 m / s. The resulting hot-rolled strip was 3.8 mm thick and had an average scale thickness of 6.5 μm. The roll surface roughness and rolling force for each rolling pass are shown in Table 1.

[0107] (4) Laminar cooling and coiling: The hot-rolled strip after finishing is subjected to laminar cooling, and the cooling rate is controlled at 12°C / s. When the hot-rolled strip temperature reaches 680°C, it is coiled and the coiled steel is naturally cooled.

[0108] (5) Pickling and cold rolling: The hot rolled steel coil is rolled to a thickness of 1.5 mm through the pickling line.

[0109] (6) Hood annealing: annealing temperature 710°C, annealing holding time 825 minutes.

[0110] (7) After flattening and rewinding, the finished product with a thickness of 1.5 mm is produced. The elongation of the finished product is 46.5%, the n value is 0.22, and the r value is 2.6.

[0111] Example 3

[0112] Preparation technology of hot-rolled ultra-low carbon steel with a thickness of 3.8mm (finished product thickness 1.5mm):

[0113] (1) Providing a casting billet: Providing a casting billet with a thickness of 230 mm, the casting billet comprising the following components (by weight): C: 0.0025%, Si: 0.009%, Mn: 0.15%, S: ≤0.010%, P: ≤0.020%, Als: 0.040, Nb: 0.0015%, Ti: 0.0006%, and the remainder being Fe and unavoidable impurities during smelting.

[0114] (2) Heating: The ingot was placed in a heating furnace and heated from 510°C to 1050°C at a rate of 3.4°C / min for a total heating time of 190 min. The ingot was then taken out of the furnace and subjected to high-pressure descaling.

[0115] (3) Hot rolling: The descaled ingot was subjected to 7 passes of rough rolling; wherein, the rough rolling start temperature was 1030°C, the rough rolling outlet temperature was 940°C, and an intermediate billet with a thickness of 38 mm was obtained.

[0116] After rough rolling, the intermediate bar was cooled and then finished rolling was performed in seven passes (i.e., F1-F7). The finishing inlet temperature was 845°C, and the final rolling temperature was 785°C. Roller gap lubrication was used for rolls F2-F6, with an oil-water ratio of 0.15%-0.25%. The surface roughness of the rolls F1-F4 was 0.9-1.2 μm, and that of the rolls F5-F7 was 0.6-0.8 μm. The rolling speed of the F7 stand was 11.8 m / s. The resulting hot-rolled strip was 3.8 mm thick and had an average scale thickness of 6.2 μm. The roll surface roughness and rolling force for each rolling pass are shown in Table 1.

[0117] (4) Laminar cooling and coiling: The hot-rolled strip after finishing is subjected to laminar cooling, and the cooling rate is controlled at 15°C / s. When the hot-rolled strip temperature reaches 650°C, it is coiled and the coiled steel is naturally cooled.

[0118] (5) Pickling and cold rolling: The hot rolled steel coil is rolled to a thickness of 1.5 mm through the pickling line.

[0119] (6) Hood annealing: annealing temperature 710°C, annealing holding time 835 minutes.

[0120] (7) After flattening and rewinding, the finished product with a thickness of 1.5 mm is produced. The elongation of the finished product is 46.0%, the n value is 0.21, and the r value is 2.5.

[0121] Example 4

[0122] The preparation method of Example 4 is basically the same as that of Example 1, and the only difference is that the annealing temperature and holding time of the bell annealing are different. Specifically, the bell annealing temperature of this embodiment is 700° C., and the annealing holding time is 890 min.

[0123] Example 5

[0124] The preparation method of Example 5 is basically the same as that of Example 1, and the only difference is that the annealing temperature and holding time of the bell annealing are different. Specifically, the bell annealing temperature of this embodiment is 740° C., and the annealing holding time is 800 min.

[0125] Comparative Example 1

[0126] Hot rolling technology production thickness specification 4.3mm (finished product thickness 1.8mm) preparation technology:

[0127] (1) Providing a casting billet: Providing a casting billet with a thickness of 230 mm, the casting billet comprising the following components (by weight percentage): C: 0.0012%, Si: 0.006%, Mn: 0.12%, S: ≤ 0.010%, P: ≤ 0.020%, Als: 0.035%, Nb: 0.0010%, Ti: 0.0004%, and the remainder being Fe and unavoidable impurities during smelting.

[0128] (2) Heating and descaling: The ingot was placed in a heating furnace and heated from 500°C to 1190°C at a rate of 5.8°C / min, with a total heating time of 170 min; then the ingot was taken out of the furnace and descaling was performed under high pressure.

[0129] (3) Hot rolling: The descaled ingot was subjected to 7 passes of rough rolling; wherein, the rough rolling start temperature was 1170°C, the rough rolling outlet temperature was 1060°C, and an intermediate billet with a thickness of 40 mm was obtained.

[0130] After rough rolling, the intermediate bar was cooled and then finished rolling was performed in seven passes (i.e., F1-F7). The finishing inlet temperature was 1015°C, and the final rolling temperature was 905°C. Roll gap lubrication was used for F2-F6, with an oil-water ratio of 0.15%-0.25%. The surface roughness of the rolls for F1-F4 was 1.5-2.0 μm, and that for F5-F7 was 1.2-1.8 μm. The rolling speed for F7 was 7.5 m / s. The resulting hot-rolled strip was 4.3 mm thick and had an average scale thickness of 10.8 μm. The roll surface roughness and rolling force for each rolling pass are shown in Table 1.

[0131] (4) Laminar cooling and coiling: The hot-rolled strip after finishing is subjected to laminar cooling, with the cooling rate controlled at 10°C / s. Coiling is performed when the hot-rolled strip temperature reaches 680°C, and the coiled steel coil is naturally cooled.

[0132] (5) Pickling and cold rolling: The hot rolled steel coil is rolled to a thickness of 1.8 mm through the pickling line.

[0133] (6) Hood annealing: annealing temperature 700℃, annealing holding time 890 minutes.

[0134] (7) After flattening and rewinding, the finished product has a thickness of 1.8 mm. The elongation of the finished product is 42.5%, the n value is 0.19, and the r value is 1.8.

[0135] Comparative Example 2

[0136] Hot rolling technology production thickness specification 3.8mm (finished product thickness 1.5mm) preparation technology:

[0137] (1) Providing a casting billet: Providing a casting billet with a thickness of 230 mm, the casting billet comprising the following components (by weight): C: 0.0022%, Si: 0.008%, Mn: 0.17%, S: ≤ 0.010%, P: ≤ 0.020%, Als: 0.045%, Nb: 0.0013%, Ti: 0.0005%, and the remainder being Fe and unavoidable impurities during smelting.

[0138] (2) Heating and descaling: The ingot was placed in a heating furnace and the temperature was raised from 510°C to 1210°C at a rate of 5.1°C / s for a total heating time of 200 min. The ingot was then taken out of the furnace and descaled under high pressure.

[0139] (3) Hot rolling: The descaled ingot is subjected to 7 passes of rough rolling in a rough rolling mill; wherein, the rough rolling start temperature is 1190°C, the rough rolling outlet temperature is 1070°C, and an intermediate billet with a thickness of 38 mm is obtained.

[0140] After rough rolling, the intermediate bar was cooled and then finished rolling was performed in seven passes (i.e., F1-F7). The finishing inlet temperature was 1025°C, and the final rolling temperature was 900°C. Roll gap lubrication was used for F2-F6, with an oil-water ratio of 0.15%-0.25%. The surface roughness of the rolls for F1-F4 was 1.5-2.0 μm, and that for F5-F7 was 1.2-1.8 μm. The rolling speed for F7 was 8.5 m / s. The resulting hot-rolled strip was 3.8 mm thick and had an average scale thickness of 9.0 μm. The roll surface roughness and rolling force for each rolling pass are shown in Table 1.

[0141] (4) Laminar cooling and coiling: The hot-rolled strip after finishing is subjected to laminar cooling, and the cooling rate is controlled at 15°C / s. When the temperature of the hot-rolled strip reaches 680°C, it is coiled. The coiled steel coil is cooled naturally.

[0142] (5) Pickling and cold rolling: The hot rolled steel coil is rolled to a thickness of 1.5 mm through the pickling line.

[0143] (6) Hood annealing: annealing temperature 730℃, annealing holding time 780 minutes.

[0144] (7) After flattening and rewinding, the finished product with a thickness of 1.5 mm is produced. The elongation of the finished product is 43.0%, the n value is 0.19, and the r value is 1.9.

[0145] The preparation conditions of each embodiment and comparative example are shown in Table 1.

[0146] Table 1

[0147]

[0148]

[0149] Performance Testing

[0150] Elongation: The elongation of the ultra-low carbon steel prepared in each embodiment and comparative example was tested according to the method specified in GB / T 228.1-2021 "Tensile test of metallic materials Part 1: Room temperature test method".

[0151] Strain hardening index n: The strain hardening index n of the ultra-low carbon steel prepared in each embodiment and comparative example was tested according to the method specified in GB / T 5028-2008 "Determination of tensile strain hardening index (n value) of metal sheets and strips".

[0152] Plastic strain ratio r: The plastic strain ratio r of the ultra-low carbon steel prepared in each embodiment and comparative example was tested according to the method specified in GB / T 5027-2016 "Determination of plastic strain ratio (r-value) of metal sheets and strips".

[0153] The preparation conditions and performance test results of each embodiment and comparative example are shown in Table 2 below:

[0154] Table 2

[0155] Elongation / % Strain hardening exponent n Plastic strain ratio r Example 1 45.5 0.21 2.5 Example 2 46.5 0.22 2.6 Example 3 46.0 0.21 2.5 Example 4 47.0 0.21 2.7 Example 5 46.3 0.22 2.6 Comparative Example 1 42.5 0.19 1.8 Comparative Example 2 43.0 0.19 1.9

[0156] As can be seen from the data in Table 2, the ultra-low carbon steels prepared using the technical solutions of this application in Examples 1-5 exhibit high elongation, strain hardening exponent n, and plastic strain r, demonstrating excellent processability. Furthermore, Examples 1-5 can be rolled relatively quickly to obtain hot-rolled plates of the desired thickness, while requiring relatively low rolling forces. The resulting hot-rolled plates have a relatively thin surface thickness after oxidation, which can, to a certain extent, reduce production energy consumption and improve yield rates.

[0157] When preparing ultra-low carbon steel in Comparative Examples 1 and 2, both were rough rolled at relatively high temperatures (nearly 1200°C) and then finish rolled at temperatures near 1000°C. This means that both were rolled in the austenite region. To achieve the same rolling thickness as Examples 1 and 2, greater rolling forces and mechanical energy were required. Furthermore, the rolling rate was slower, resulting in a longer production cycle. The final product exhibited lower elongation, strain hardening exponent n, and plastic strain r, and its formability was inferior to that of Examples 1 and 2.

[0158] The above description is only a specific embodiment of the present application. Those skilled in the art will clearly understand that for the convenience and brevity of description, the specific working processes of the systems, modules and units described above can refer to the corresponding processes in the aforementioned method embodiments, and will not be repeated here. It should be understood that the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the scope of protection of the present application.

Claims

1. A method for preparing ultra-low carbon steel, characterized in that: The steps include: Providing a casting billet; the casting billet comprises the following components, calculated by mass percentage: C 0.0010-0.0030%, Si ≤ 0.01%, Mn 0.10-0.20%, S ≤ 0.010%, P ≤ 0.020%, Als 0.025-0.060%, Nb ≤ 0.0020%, Ti ≤ 0.0008%, and the remainder is Fe and unavoidable impurities during smelting; The cast steel is sequentially heated and hot-rolled to obtain hot-rolled steel; the hot rolling includes sequentially performing rough rolling and finishing rolling, wherein the starting rolling temperature of the rough rolling is 990° C. to 1040° C., and the outlet temperature of the rough rolling is 900° C. to 940° C.; the starting rolling temperature of the finishing rolling is 840° C. to 890° C., and the finishing rolling temperature is 750° C. to 830° C.; The hot-rolled steel is pickled, cold-rolled and annealed in sequence.

2. The preparation method according to claim 1, characterized in that The preparation method satisfies at least one of the following conditions: (1) The starting rolling temperature of the rough rolling is 980°C to 1020°C, and the outlet temperature of the rough rolling is 910°C to 920°C; (2) The starting rolling temperature of the finishing rolling is 850°C to 870°C, and the final rolling temperature of the finishing rolling is 780°C to 810°C.

3. The preparation method according to claim 1, characterized in that The annealing is performed by hood annealing, and the hood annealing satisfies at least one of the following conditions: (1) The temperature of the bell annealing is 680°C to 800°C, preferably, the temperature of the bell annealing is 700°C to 740°C; (2) The hood annealing holding time is 750 min to 900 min.

4. The preparation method according to claim 1, characterized in that The heating includes a heating section and a soaking section, the heating rate of the heating section is 2.2°C / min to 5.0°C / min; the temperature of the soaking section is 1010°C to 1050°C, and the total heating time of the heating section and the soaking section is 150min to 280min.

5. The preparation method according to any one of claims 1 to 4, characterized in that The finishing rolling comprises rolling the intermediate billet obtained after the rough rolling for 7 passes; In the 7 rolling passes, the surface roughness of the rolls in the 1st to 4th rolling passes is independently 0.8 μm to 1.2 μm; the surface roughness of the rolls in the 5th to 7th rolling passes is 0.2 μm to 0.6 μm lower than the highest value of the surface roughness of the rolls in the 1st to 4th rolling passes; preferably, the surface roughness of the rolls in the 5th to 7th rolling passes is independently 0.6 μm to 1.0 μm; and / or, In the seven rolling passes, roll gap lubrication is used during the second to sixth rolling passes; the oil-water ratio of the lubricant used is 0.10% to 0.25%.

6. The preparation method according to any one of claims 1 to 4, characterized in that The preparation method satisfies at least one of the following conditions: (1) The rough rolling includes rolling the heated ingot for 5 to 7 passes; (2) the total reduction rate of the rough rolling is 75% to 90%; (3) the total reduction rate of the finish rolling is 85% to 95%; (4) The rolling rate of the finish rolling is 10 m / s to 14.5 m / s.

7. The preparation method according to any one of claims 1 to 4, characterized in that The cold rolling reduction ratio is 50% to 75%.

8. An ultra-low carbon steel, characterized in that: The ultra-low carbon steel is prepared according to the method according to any one of claims 1 to 7.

9. The ultra-low carbon steel according to claim 8, characterized in that The ultra-low carbon steel meets at least one of the following conditions: (1) The ultra-low carbon steel comprises the following components, measured by mass percentage: C 0.0010-0.0030%, Si ≤ 0.01%, Mn 0.10-0.20%, S ≤ 0.010%, P ≤ 0.020%, Als 0.025-0.060%, Nb ≤ 0.0020%, Ti ≤ 0.0008%, and the remainder is Fe and unavoidable impurities during smelting; (2) The elongation of the ultra-low carbon steel is 45% to 47%; (3) The strain hardening exponent n of the ultra-low carbon steel is 0.21 to 0.25; (4) The plastic strain ratio r of the ultra-low carbon steel is 2.5 to 2.

8.

10. A steel product, characterized in that: The steel product comprises the ultra-low carbon steel according to claim 9.

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