IF steel for steering oil tank and preparation method of IF steel

Abstract

The invention discloses IF steel for a steering oil tank and a preparation method of the IF steel. The IF steel comprises the following components in percentage by mass: 0.0035 to 0.005 percent of C, 0 to 0.05 percent of Si, 0 to 0.4 percent of Mn, 0 to 0.015 percent of P, 0 to 0.012 percent of S, 0.02 to 0.1 percent of Al, 0.02 to 0.10 percent of Ti, 0 to 0.005 percent of N, 0.0005 to 0.0015 percent of B, more than or equal to 0 of Ti-4 * C-3. 4 * N-1. 5 * S, and the balance of Fe and other inevitable impurities, wherein the total mass of the IF steel is 100 percent. The secondary machining brittleness resistance of the IF steel can meet the stamping requirement of the steering oil tank, and the production cost of the IF steel can be reduced.

Description

Technical Field

[0001] The present application relates to the technical field of steel production, and in particular to an IF steel for a steering oil tank and a preparation method thereof. Background Art

[0002] Interstitial-free steel (IF steel) is the third generation of stamping steel. It is widely used in the manufacture of automobiles, home appliances, daily necessities, etc. due to its advantages such as low yield strength ratio, no yield platform, high elongation, and high r-value. Cold-rolled IF steel is usually produced by continuous annealing or hood annealing. The hood annealing method for producing IF steel has the advantages of low equipment investment, no specification restrictions, and flexible production, so it is widely used.

[0003] The steering oil tank of the car is mainly made of cold-rolled stamping steel. Due to its relatively deep stamping depth, the blanking disc needs to go through 2-3 stamping processes. Therefore, it is urgent to prepare an IF steel with excellent deep drawing performance. Summary of the invention

[0004] The embodiment of the present application provides an IF steel for a steering oil tank and a preparation method thereof, the IF steel has resistance to secondary processing brittleness and can meet the stamping requirements of the steering oil tank and can reduce the production cost of the IF steel.

[0005] In the first aspect, an embodiment of the present application proposes an IF steel for a steering oil tank. Taking the total mass of the IF steel as 100%, the IF steel includes the following components by mass: C: 0.0035%-0.005%, Si: 0-0.05%, Mn: 0-0.4%, P: 0-0.015%, S: 0-0.012%, Al: 0.02%-0.1%, Ti: 0.02%-0.10%, N: 0-0.005%, B: 0.0005%-0.0015%, Ti-4×C-3.4×N-1.5×S≥0, and the remainder is Fe and other inevitable impurities.

[0006] In some embodiments, the yield strength of the IF steel is 120-210 MPa, the tensile strength of the IF steel is 270-350 MPa, and the elongation of the IF steel is ≥38%.

[0007] In the second aspect, the present application embodiment proposes a method for preparing IF steel for a steering oil tank, comprising:

[0008] Provide smelted molten steel, which includes the following components by mass based on the total mass of the molten steel as 100%: C: 0.0035%-0.005%, Si: 0-0.05%, Mn: 0-0.4%, P: 0-0.015%, S: 0-0.012%, Al: 0.02%-0.1%, Ti: 0.02%-0.10%, N: 0-0.005%, B: 0.0005%-0.0015%, Ti-4×C-3.4×N-1.5×S≥0, and the balance is Fe and other inevitable impurities;

[0009] Continuously casting the molten steel to obtain a continuously cast slab;

[0010] Heating the slab after continuous casting to obtain a heated slab;

[0011] Performing finish rolling on the heated slab to obtain a finish rolled steel strip;

[0012] Coiling the finished rolled strip to obtain a coiled strip;

[0013] The coiled steel strip is cold-rolled to obtain a cold-rolled steel strip;

[0014] The cold-rolled steel strip is annealed in a full hydrogen bell furnace to obtain the annealed steel strip. The annealing temperature is 680°C-750°C.

[0015] In some embodiments, the annealing treatment includes a first insulation stage, a second insulation stage and a third insulation stage; the temperature of the first insulation stage is 390°C-410°C, and the time of the first insulation stage is 1.5-2.5h; the temperature of the second insulation stage is 670°C-680°C, and the time of the second insulation stage is 3-5h; the temperature of the third insulation stage is 680°C-750°C, and the time of the third insulation stage is 7-10h.

[0016] In some embodiments, the annealing time is 7-10 hours.

[0017] In some embodiments, the temperature of the slab after the heating treatment is 1150°C-1250°C.

[0018] In some embodiments, the finishing rolling process is performed in a single-phase austenite region.

[0019] In some embodiments, the final rolling temperature of the finishing rolling process is 890°C-940°C.

[0020] In some embodiments, the temperature of the coiling process is controlled to be 650°C-750°C.

[0021] In some embodiments, the cumulative reduction ratio of the cold rolling process is 65%-80%.

[0022] In some embodiments, the preparation method further comprises flattening the strip after annealing, and the reduction rate of the flattening is 0.8%-1.5%.

[0023] In some embodiments, the preparation method further comprises re-coiling and oiling the flattened strip and performing coil separation.

[0024] The IF steel of the embodiment of the present application adds microalloy Ti to precipitate C and N interstitial atoms in the form of two-phase particles, reducing the adverse effects of C and N on the mechanical properties of IF steel when they exist in a solid solution state, so that IF steel has excellent deep drawing forming performance. By adding the B element, the grain boundary strength of IF steel can be improved, thereby improving the resistance of IF steel plate to secondary processing brittleness. At the same time, the B element can also inhibit the segregation of P elements at the grain boundaries, eliminating the adverse effects of P element segregation at the grain boundaries on secondary processing brittleness. By controlling the C content within the range of 0.0035%-0.005%, it is conducive to the formation of a certain number of TiC precipitates, which can effectively hinder grain growth during the annealing process and improve the steel plate's resistance to secondary processing brittleness by refining the grains. Thereby, the resistance to secondary processing brittleness of IF steel meets the requirements of steering oil tank stamping, and the production cost of IF steel can also be reduced. DETAILED DESCRIPTION

[0025] The features and exemplary embodiments of various aspects of the application will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the application. However, it is obvious to those skilled in the art that the application can be implemented when some details in these specific details are not needed. The following description of the embodiments is only to provide a better understanding of the application by illustrating the example of the application.

[0026] It should be noted that, moreover, the term "comprises" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method, article, or device that includes a series of elements includes not only those elements, but also includes other elements that are not explicitly listed, or also includes elements that are inherent to such process, method, article, or device. In the absence of further restrictions, the elements defined by the sentence "comprises ..." do not exclude the presence of other identical elements in the process, method, article, or device that includes the elements.

[0027] A list of items connected by the term "one or more of" may mean any combination of the listed items. The term "plurality" means more than two.

[0028] Unless otherwise specified, the test temperature of each parameter mentioned in this application is 25°C.

[0029] Ti-IF steel produced by the hood annealing process has poor resistance to secondary processing brittleness due to clean grain boundaries and coarse grains, and its ductile-brittle transition temperature (DBTT) is usually above -40°C, which limits the application scope of hood annealed Ti-IF steel. For example, in the automotive steering oil tank mentioned in the background technology, due to the large deep drawing deformation of the steering oil tank, brittle cracking may occur during stamping when Ti-IF steel is used, which reduces the product qualification rate and increases the manufacturing cost.

[0030] In view of this, the present application provides an IF steel for a steering oil tank. Taking the total mass of the IF steel as 100%, the IF steel includes the following components by mass: C: 0.0035%-0.005%, Si: 0-0.05%, Mn: 0-0.4%, P: 0-0.015%, S: 0-0.012%, Al: 0.02%-0.1%, Ti: 0.02%-0.10%, N: 0-0.005%, B: 0.0005%-0.0015%, Ti-4×C-3.4×N-1.5×S≥0, and the balance is Fe and other inevitable impurities.

[0031] The control principles of each element in the IF steel of the embodiment of the present application are described below.

[0032] Carbon C: C is an interstitial atom. When it exists in the form of solid solution, it can significantly improve the strength of the steel plate and reduce the plasticity of the steel plate, but it needs to be combined with Ti to eliminate its adverse effects on forming. The main purpose of appropriately controlling the C content in the embodiment of the present application is to control the grain size through TiC, thereby improving the steel plate's resistance to secondary processing brittleness. When the C content is less than 0.0035%, the number of TiC precipitates formed is small, and the hindering effect on controlling the growth of the finished grains is reduced. The finished grain size is relatively large, which is not conducive to improving fatigue performance. When the C content is greater than 0.0050%, in order to meet the formula, more Ti needs to be added, which is not conducive to cost control and will also deteriorate the deep drawing performance of the steel plate.

[0033] Silicon Si: Si is both a deoxidizing element and a solid solution strengthening element. It can increase the yield strength of the steel plate and reduce the elongation. However, when the Si content is too high, it is easy to generate iron oxide scale that is difficult to pickle, affecting the surface quality of the steel plate. Therefore, the lower the Si content, the better.

[0034] Manganese Mn: Manganese is a material strengthening element like silicon, but as the Mn content increases, the material strength increases and the plasticity decreases. Therefore, the lower the Mn content, the better.

[0035] Phosphorus P: Phosphorus can improve the strength of materials, but it can also cause cold brittleness of materials, so the P content should be as low as possible.

[0036] Sulfur S: S is a harmful element in steel. The compounds formed by S and Mn and Fe elements will cause edge crack defects in steel during hot rolling, and sulfide inclusions will also deteriorate the deep drawing performance of the steel plate. At the same time, for the steel plate in the embodiment of the present application, the Ti-4×C-3.4×N-1.5×S≥0 value must be controlled. The more S, the more Ti needs to be added, which is not conducive to cost control. Therefore, the lower the mass content of S, the better.

[0037] Aluminum Al: Aluminum is added during steelmaking as a deoxidizer. When the content is less than 0.02%, the inclusions in the steel increase and the stamping performance deteriorates. However, too much Al will lead to increased production costs. Therefore, the mass content of Al should be controlled in the range of 0.02%-0.1%.

[0038] Titanium Ti: Ti is a strong carbonitride-forming element and has a strong affinity with C and N elements. When TiC and TiN precipitates are generated with C and N, the adverse effects of C and N interstitial atoms on forming can be reduced, and the stamping performance of the steel sheet can be improved. In the embodiment of the present application, fine dispersed TiC can hinder grain growth, refine grains, and improve the material's resistance to secondary processing brittleness. However, too much Ti will increase costs.

[0039] Boron B: In IF steel, since C and N are fixed, the grain boundaries are relatively clean, and P is easy to segregate to the grain boundaries, causing grain boundary embrittlement, reducing the steel plate's resistance to secondary processing brittleness. By adding the above-mentioned mass content of B, P can be prevented from segregating at the grain boundaries, and the grain boundaries can be strengthened, thereby improving the fatigue performance of the steel plate.

[0040] Nitrogen N: N, like C, is an interstitial atom. When in a solid solution state, it has a significant strengthening effect, increasing the strength of the steel plate and reducing its plasticity. Ti needs to be added to combine with it and precipitate to eliminate its adverse effects. Therefore, too much N is not conducive to cost control and should be as low as possible.

[0041] The IF steel of the embodiment of the present application adds microalloy Ti to precipitate C and N interstitial atoms in the form of two-phase particles, reducing the adverse effects of C and N on the mechanical properties of IF steel when they exist in a solid solution state, so that IF steel has excellent deep drawing forming performance. By adding the B element, the grain boundary strength of IF steel can be improved, thereby improving the resistance of IF steel plate to secondary processing brittleness. At the same time, the B element can also inhibit the segregation of P elements at the grain boundaries, eliminating the adverse effects of P element segregation at the grain boundaries on secondary processing brittleness. By controlling the C content within the range of 0.0035%-0.005%, it is conducive to the formation of a certain number of TiC precipitates, which can effectively hinder grain growth during the annealing process and improve the steel plate's resistance to secondary processing brittleness by refining the grains. Thereby, the resistance to secondary processing brittleness of IF steel meets the requirements of steering oil tank stamping, and the production cost of IF steel can also be reduced.

[0042] The IF steel of the embodiment of the present application can still achieve the IF steel's resistance to secondary processing brittleness and meet the requirements for steering oil tank stamping without adding the precious metal Nb element, thereby further reducing the production cost of the IF steel.

[0043] In some embodiments, the yield strength of the IF steel may be 120-210 MPa, the tensile strength of the IF steel may be 270-350 MPa, and the elongation of the IF steel may be ≥38%.

[0044] [Preparation method of IF steel for steering oil tank]

[0045] The present application also provides a method for preparing IF steel for a steering oil tank, comprising:

[0046] Provide smelted molten steel, which includes the following components by mass based on the total mass of the molten steel as 100%: C: 0.0035%-0.005%, Si: 0-0.05%, Mn: 0-0.4%, P: 0-0.015%, S: 0-0.012%, Al: 0.02%-0.1%, Ti: 0.02%-0.10%, N: 0-0.005%, B: 0.0005%-0.0015%, Ti-4×C-3.4×N-1.5×S≥0, and the balance is Fe and other inevitable impurities;

[0047] Continuously casting the molten steel to obtain a continuously cast slab;

[0048] Heating the slab after continuous casting to obtain a heated slab;

[0049] Performing finish rolling on the heated slab to obtain a finish rolled steel strip;

[0050] Coiling the finished rolled strip to obtain a coiled strip;

[0051] The coiled steel strip is cold-rolled to obtain a cold-rolled steel strip;

[0052] The cold-rolled steel strip is annealed in a full hydrogen bell furnace to obtain the annealed steel strip. The annealing temperature is 680°C-750°C.

[0053] The purpose of annealing is to eliminate the work hardening effect of cold rolling and make the steel plate have excellent plastic forming properties, but too high annealing temperature will increase energy consumption. Therefore, by controlling the annealing temperature within the above range, the work hardening effect of cold rolling can be eliminated and the steel plate can have excellent plastic forming properties.

[0054] The embodiment of the present application improves the grain boundary state and grain size of IF steel prepared by the hood annealing process through the design of IF steel composition, reduces the ductile-brittle transition temperature (DBTT) of IF steel, and improves the IF steel's resistance to secondary processing brittleness, so that the IF steel meets the requirements of steering oil tank stamping manufacturing.

[0055] In some embodiments, the annealing treatment may include a first insulation stage, a second insulation stage and a third insulation stage; the temperature of the first insulation stage may be 390°C-410°C, and the time of the first insulation stage may be 1.5-2.5h; the temperature of the second insulation stage may be 670°C-680°C, and the time of the second insulation stage may be 3-5h; the temperature of the third insulation stage may be 680°C-750°C, and the time of the third insulation stage may be 7-10h.

[0056] The embodiment of the present application does not limit the heating rate in the annealing process, and free heating can be adopted.

[0057] By setting the annealing conditions within the above range, that is, adopting a staged annealing process, the work hardening can be eliminated and the steel sheet can be completely recrystallized and homogenized, thereby improving the stamping formability and performance uniformity.

[0058] In some embodiments, the temperature of the slab after the heat treatment may be 1150°C-1250°C.

[0059] By setting the temperature of the slab after the heat treatment within the above range, the slab can be completely austenitized, thereby ensuring that the final rolling temperature is within the austenitizing temperature range, which not only reduces the finishing rolling force but also improves the uniformity of the structure.

[0060] In some embodiments, the finishing rolling process is performed in a single-phase austenite region.

[0061] In some embodiments, the final rolling temperature of the finishing rolling process may be 890°C-940°C.

[0062] If the final rolling temperature of the finishing rolling treatment is too high, serious iron oxide scale will appear, making it difficult to pickle, affecting the surface quality of the steel plate. If the final rolling temperature of the finishing rolling treatment is too low, the steel plate will enter the two-zone rolling and mixed crystals will appear, and snowflake defects will be generated during stamping, affecting the appearance of the product. By controlling the final rolling temperature of the finishing rolling treatment within the above range, the final rolling temperature of the finishing rolling treatment can be made higher than the austenite zone temperature of Ar3, and the surface quality of the steel plate can also be improved.

[0063] In some embodiments, the temperature of the coiling process may be controlled at 650°C-750°C.

[0064] The coiling temperature is greater than 650℃, which is conducive to the dispersion and precipitation of TiC precipitates. However, too high a coiling temperature will cause serious iron scale on the surface of the steel plate and make it difficult to pickle, affecting the quality of the steel plate. By controlling the coiling temperature within the above range, it is not only conducive to the dispersion and precipitation of TiC precipitates, but also can improve the quality of the steel plate.

[0065] In some embodiments, the cumulative reduction ratio of the cold rolling process may be 65%-80%.

[0066] The cumulative reduction rate of the cold rolling process reflects the deformation of the steel plate during cold rolling. A larger cold rolling deformation can increase the strength of the favorable texture in the IF steel and improve the stamping performance of the IF steel. However, too much deformation will increase the difficulty of the cold rolling process. Therefore, the cumulative reduction rate of the cold rolling process is controlled within the range of 65%-80% in the embodiment of the present application.

[0067] In some embodiments, the preparation method further comprises flattening the strip after annealing, and the reduction rate of the flattening can be 0.8%-1.5%.

[0068] Flattening can eliminate the yield platform of steel plates and reduce the tensile strain mark defects produced during the stamping process, which affects the appearance quality of enamel products. However, if the reduction rate of flattening is too low, the yield platform of steel plates cannot be eliminated; if the reduction rate of flattening is too high, it will lead to work hardening, reduce the elongation of the final steel, and reduce the plastic processing performance of steel. Therefore, the reduction rate of flattening is controlled within the range of 0.8%-1.2%.

[0069] In some embodiments, the preparation method further comprises re-coiling and oiling the flattened strip and performing coil separation.

[0070] The embodiment of the present application adopts reasonable formula design and process control to realize the IF steel prepared by the hood annealing process of the Ti-IF component system, and the steel plate has excellent resistance to secondary processing brittleness, excellent deep drawing performance and good surface quality. And without adding the precious metal Nb element, through the precise control of C and the staged annealing process design, the resistance to secondary processing brittleness of IF steel is improved and the production cost is reduced.

[0071] Example

[0072] The following examples describe the disclosure of the present application in more detail, and these examples are for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present application are apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are commercially available.

[0073] Example 1

[0074] The smelted molten steel is provided, and based on the total mass of the molten steel being 100%, the molten steel includes components in the following mass contents: C: 0.0037%, Si: 0.0065%, Mn: 0.052%, P: 0.0129%, S: 0.0091%, Al: 0.0518%, Ti: 0.0594%, N: 0.0029%, B: 0.0009%, Ti-4×C-3.4×N-1.5×S=0.021, and the rest is iron and unavoidable impurities.

[0075] The molten steel is continuously cast into slabs; the slabs are heated in a heating furnace and taken out of the heating furnace at 1231°C; the slabs are rough rolled and then enter the finishing mill, the final rolling temperature of the finishing rolling is 934°C, the coiling temperature is 665°C, and the slabs are rolled into 5.0mm thick hot-rolled coils; the hot-rolled coils are cold-rolled and acid-rolled into 1.5mm thick hard-rolled coils, with a cold rolling reduction of 70%; the hard-rolled coils are placed in a bell-type annealing furnace, annealed at 720°C for 8 hours, and then cooled and leveled in a leveling mill with a leveling reduction of 1.0%, and then oiled in a rewinding line. The yield strength of the steel plate is 167MPa, the tensile strength is 298MPa, the elongation is 42.5%, the r value is 2.56, and the n value is 0.21.

[0076] Example 2

[0077] The smelted molten steel is provided, and based on the total mass of the molten steel being 100%, the molten steel includes components in the following mass contents: C: 0.0046%, Si: 0.0103%, Mn: 0.157%, P: 0.0085%, S: 0.0104%, Al: 0.0425%, Ti: 0.0643%, N: 0.0041%, B: 0.0008%, Ti-4×C-3.4×N-1.5×S=0.016, and the rest is iron and unavoidable impurities.

[0078] The molten steel is continuously cast into slabs; the slabs are heated in a heating furnace and taken out of the heating furnace at 1205℃; the slabs are rough rolled and then enter the finishing mill, the final rolling temperature of the finishing rolling is 918℃, the coiling temperature is 685℃, and the slabs are rolled into 4.8mm thick hot-rolled coils; the hot-rolled coils are cold-rolled and acid-rolled into 1.5mm thick hard-rolled coils, with a cold rolling reduction of 68.7%; the hard-rolled coils are placed in a bell-type annealing furnace, annealed at 710℃ for 10 hours, and then cooled and leveled in a leveling mill with a leveling reduction of 0.8%, and then oiled in a rewinding line. The yield strength of the steel plate is 159MPa, the tensile strength is 292MPa, the elongation is 41%, the r value is 2.38, and the n value is 0.21.

[0079] Example 3

[0080] The smelted molten steel is provided, and based on the total mass of the molten steel being 100%, the molten steel includes components in the following mass contents: C: 0.0041%, Si: 0.0075%, Mn: 0.098%, P: 0.0057%, S: 0.0044%, Al: 0.0432%, Ti: 0.0474%, N: 0.0033%, B: 0.0012%, Ti-4×C-3.4×N-1.5×S=0.013, and the rest is iron and unavoidable impurities.

[0081] The molten steel is continuously cast into slabs; the slabs are heated in a heating furnace and taken out of the heating furnace at 1188℃; the slabs are rough rolled and then enter the finishing mill, the final rolling temperature of the finishing rolling is 923℃, the coiling temperature is 671℃, and the slabs are rolled into 5.0mm thick hot-rolled coils; the hot-rolled coils are cold-rolled and acid-rolled into 1.5mm thick hard-rolled coils, with a cold rolling reduction of 70%; the hard-rolled coils are placed in a bell-type annealing furnace, annealed at 730℃ for 7 hours, and then leveled with a 1.0% leveling reduction rate on a leveling mill after being cooled out of the furnace, and oiled on a rewinding line. The yield strength of the steel plate is 170MPa, the tensile strength is 302MPa, the elongation is 43%, the r value is 2.61, and the n value is 0.20.

[0082] Example 4

[0083] The smelted molten steel is provided, and based on the total mass of the molten steel being 100%, the molten steel includes components in the following mass contents: C: 0.0043%, Si: 0.0152%, Mn: 0.174%, P: 0.0129%, S: 0.0097%, Al: 0.0625%, Ti: 0.0731%, N: 0.0025%, B: 0.0007%, Ti-4×C-3.4×N-1.5×S=0.033, and the rest is iron and unavoidable impurities.

[0084] The molten steel is continuously cast into slabs; the slabs are heated in a heating furnace and taken out of the heating furnace at 1228℃; the slabs are rough rolled and then enter the finishing mill, the final rolling temperature of the finishing rolling is 929℃, the coiling temperature is 695℃, and the slabs are rolled into 4.8mm thick hot-rolled coils; the hot-rolled coils are cold-rolled and acid-rolled into 1.5mm thick hard-rolled coils, with a cold rolling reduction of 68.7%; the hard-rolled coils are placed in a bell-type annealing furnace, annealed at 715℃ for 10 hours, and then leveled with a 0.8% leveling reduction rate on a leveling mill after being cooled out of the furnace, and oiled on a rewinding line. The yield strength of the steel plate is 164MPa, the tensile strength is 293MPa, the elongation is 40.5%, the r value is 2.41, and the n value is 0.21.

[0085] Comparative Example 1

[0086] The smelted molten steel is provided, and based on the total mass of the molten steel being 100%, the molten steel includes components with the following mass contents: C: 0.0011%, Si: 0.0062%, Mn: 0.134%, P: 0.0105%, S: 0.0073%, Al: 0.0507%, Ti: 0.0581%, N: 0.0032%, and the rest being iron and unavoidable impurities.

[0087] The molten steel is continuously cast into slabs; the slabs are heated in a heating furnace and taken out of the heating furnace at 1236℃; the slabs are rough rolled and then enter the finishing mill, the final rolling temperature of the finishing rolling is 924℃, the coiling temperature is 678℃, and the slabs are rolled into 5.0mm thick hot-rolled coils; the hot-rolled coils are cold-rolled and acid-rolled into 1.5mm thick hard-rolled coils, with a cold rolling reduction of 70%; the hard-rolled coils are placed in a bell-type annealing furnace, annealed at 730℃ for 8 hours, and then cooled and leveled in a leveling mill with a leveling reduction of 1.0%, and then oiled in a rewinding line. The yield strength of the steel plate is 142MPa, the tensile strength is 283MPa, the elongation is 44%, the r value is 2.71, and the n value is 0.23.

[0088] Comparative Example 2

[0089] The smelted molten steel is provided, and based on the total mass of the molten steel being 100%, the molten steel includes components with the following mass contents: C: 0.0021%, Si: 0.0114%, Mn: 0.0716%, P: 0.0089%, S: 0.0052%, Al: 0.0381%, Ti: 0.0676%, N: 0.0023%, and the rest being iron and unavoidable impurities.

[0090] The molten steel is continuously cast into slabs; the slabs are heated in a heating furnace and taken out of the heating furnace at 1225℃; the slabs are rough rolled and then enter the finishing mill, the final rolling temperature of the finishing rolling is 933℃, the coiling temperature is 692℃, and the slabs are rolled into 5.0mm thick hot-rolled coils; the hot-rolled coils are cold-rolled and acid-rolled into 1.5mm thick hard-rolled coils, with a cold rolling reduction of 70%; the hard-rolled coils are placed in a bell-type annealing furnace, annealed at 715℃ for 10 hours, and then cooled and leveled in a leveling mill with a leveling reduction of 0.9%, and then oiled in a rewinding line. The yield strength of the steel plate is 136MPa, the tensile strength is 283MPa, the elongation is 45%, the r value is 2.84, and the n value is 0.23.

[0091] Test Section

[0092] Ductile-brittle transition temperature: The detection method of ductile-brittle transition temperature (DBTT) refers to GB / T24173-2016 "Test method for embrittlement of secondary processing of steel plates".

[0093] The performance test results of the steel plates of Examples 1-4 and Comparative Examples 1-2 are shown in Table 1.

[0094] Table 1

[0095]

[0096]

[0097] It can be seen from the embodiments and comparative examples that the molten steel composition of the embodiments of the present application can reduce the ductile-brittle transition temperature, obtain a steel plate with qualified stamping forming and excellent comprehensive evaluation grade, and improve the steel plate's resistance to secondary processing brittleness so that it can meet the requirements of steering tank stamping.

[0098] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and the same effect as the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An IF steel for a steering oil tank, characterized in that: Taking the total mass of the IF steel as 100%, the IF steel includes the following components by mass: C: 0.0035%-0.005%, Si: 0-0.05%, Mn: 0-0.4%, P: 0-0.015%, S: 0-0.012%, Al: 0.02%-0.1%, Ti: 0.02%-0.10%, N: 0-0.005%, B: 0.0005%-0.0015%, Ti-4×C-3.4×N-1.5×S≥0, and the balance is Fe and other inevitable impurities.

2. The IF steel for steering oil tank according to claim 1, characterized in that: The yield strength of the IF steel is 120-210 MPa, the tensile strength of the IF steel is 270-350 MPa, and the elongation of the IF steel is ≥38%.

3. A method for preparing IF steel for steering oil tank, characterized in that: include: Providing smelted molten steel, which comprises the following components by mass based on the total mass of the molten steel as 100%: C: 0.0035%-0.005%, Si: 0-0.05%, Mn: 0-0.4%, P: 0-0.015%, S: 0-0.012%, Al: 0.02%-0.1%, Ti: 0.02%-0.10%, N: 0-0.005%, B: 0.0005%-0.0015%, Ti-4×C-3.4×N-1.5×S≥0, and the balance is Fe and other inevitable impurities; Continuously casting the molten steel to obtain a continuously cast slab; Heating the slab after continuous casting to obtain a heated slab; Performing finish rolling on the heated slab to obtain a finish rolled steel strip; Coiling the finish-rolled steel strip to obtain a coiled steel strip; cold rolling the coiled steel strip to obtain a cold rolled steel strip; The cold-rolled steel strip is annealed in a full hydrogen bell furnace to obtain an annealed steel strip, wherein the annealing temperature is 680°C-750°C.

4. The preparation method according to claim 3, characterized in that: The annealing treatment includes a first heat preservation stage, a second heat preservation stage and a third heat preservation stage; The temperature of the first insulation stage is 390°C-410°C, and the time of the first insulation stage is 1.5-2.5h; The temperature of the second insulation stage is 670°C-680°C, and the time of the second insulation stage is 3-5h; The temperature of the third insulation stage is 680° C.-750° C., and the time of the third insulation stage is 7-10 hours.

5. The preparation method according to claim 3, characterized in that: The temperature of the slab after the heating treatment is 1150°C-1250°C.

6. The preparation method according to claim 3, characterized in that: The finishing rolling is carried out in a single-phase austenite region; and / or, The final rolling temperature of the finishing rolling process is 890°C-940°C.

7. The preparation method according to claim 3, characterized in that: The temperature of the coiling process is 650°C-750°C.

8. The preparation method according to claim 3, characterized in that: The cumulative reduction rate of the cold rolling process is 65%-80%.

9. The preparation method according to claim 3, characterized in that: The preparation method further comprises flattening the strip steel after the annealing treatment, wherein the reduction rate of the flattening treatment is 0.8%-1.5%.

10. The preparation method according to claim 9, characterized in that: The preparation method also includes re-coiling and oiling the flattened strip and performing coil separation.

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