Production method of economical easy-to-form rare earth Ti microalloyed 700MPa-grade girder steel belt

Abstract

The invention discloses a production method of an economical easy-to-form rare earth Ti microalloyed 700MPa-grade girder steel belt. The production method comprises the following steps: a steelmaking process; in the controlled rolling air cooling process, the heating temperature of the plate blank is controlled to be 1240-1270 DEG C, and the soaking time is controlled to be 20-30 min; 3 + 3 six-pass rolling is adopted for rough rolling of the plate blank, and the rolling reduction of the first pass is increased and controlled to be 35-40 mm; the temperature of an intermediate billet is controlled to be smaller than or equal to 980 DEG C, the thickness of the intermediate billet is controlled to be 55-60 mm, and the finish rolling temperature is controlled to be 830-860 DEG C; the cooling speed is controlled to be 15-30 DEG C / s, and the coiling temperature mainly considers the optimal TiC precipitation temperature and is controlled to be 590-620 DEG C; the performance of the steel strip meets the conditions that the yield strength is larger than or equal to 600 MPa, the tensile strength ranges from 700 MPa to 880 MPa, the ductility is larger than or equal to 14%, and the steel strip has good cold formability and meets the use requirements of customers.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting and rolling, and in particular relates to a method for producing an economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel strip. The product of the invention is suitable for the production and manufacture of longitudinal beams, cross beams and structural parts of light, medium and heavy trucks and other commercial vehicles. Background Art

[0002] The automobile beam carries all the weight of the car and cargo, and is one of the important parts of the car. At present, it is mainly formed by beam steel strips. With the development of lightweight automobiles, the performance of beam steel has been continuously improved, and 700MPa beam steel is the product with the highest strength for large-scale application. 700L is a low-carbon micro-alloyed high-strength steel, which obtains mechanical properties by adding micro-alloying elements and combining corresponding controlled rolling and controlled cooling processes. With the continuous upgrading of steel plant equipment and the increasing maturity of production technology, the traditional Nb-Ti composite micro-alloyed 700L beam steel widely used in the market has no technical threshold, and all steel companies have the production capacity, resulting in increasingly fierce product competition. The application of new processes and new methods to develop a 700MPa beam steel that meets the use requirements and reduces manufacturing costs is currently an urgent need for both supply and demand sides.

[0003] The alloy addition cost is an important part of the product manufacturing cost. Reducing the amount of alloy addition by adjusting the composition design is the most effective way to reduce the manufacturing cost. my country is rich in Ti element resources, and has excellent precipitation strengthening and fine grain strengthening effects. It has the potential to develop high-strength steel with a single alloy element and is a micro-alloying element with extremely high cost performance. The development of single Ti element alloyed 700L beam steel not only has the advantage of low cost, but also reduces the content of Mn and Nb in steel, saves resources, and conforms to the development concept of "green and low carbon". In contrast, single Ti micro-alloyed products have more Ti elements added, and large-sized TiN precipitation is easy to occur during smelting or cooling of ingots, which has an adverse effect on the mechanical properties and service safety of the product. Solving the problem of liquid TiN precipitation is the key to the development of single Ti micro-alloyed high-strength steel. Rare earth elements have the effects of purifying molten steel and modifying inclusions. Rare earth elements form fine rare earth oxides with oxygen and aluminum elements, which can increase the nucleation point of TiN, change the growth mode and shape of TiN, and then reduce the size of TiN, thereby reducing the adverse effect of hard phase TiN in Ti micro-alloyed steel on product quality. Combining Ti and rare earth elements to develop low-cost controlled automobile beam steel has broad application prospects.

[0004] Patent search A low temperature high toughness 700MPa high strength beam steel and its production method (application publication number: CN118389949A), the patent adopts C: 0.055-0.085%, Si: 0.05-0.18%, Mn: 1.20-1.75%, P: ≤0.014%, S≤0.004%, Als: 0.015-0.045%, Nb: 0.035-0.065%, Ti: 0.07-0.016%, Cr: 0.15-0.30%, Ni: 0.12-0.20%, N≤0.0040% composition design and combined with controlled rolling and controlled cooling process to develop 700MPa grade beam steel, the tensile properties of the product meet the requirements of national standard GB / T3273, especially with good low temperature toughness. However, this method adds expensive alloy elements such as Nb, Cr, Ni to the steel, which increases the production cost.

[0005] Patent search: A low-brittle 700MPa grade automobile beam steel and its manufacturing method (application publication number: CN103849812A). The patent adopts the composition design of C: 0.05-0.07%, Si: ≤0.10%, Mn: 1.45-1.75%, P: ≤0.015%, S≤0.005%, Al: 0.020-0.070%, Nb: 0.035-0.050%, Ti: 0.08-0.10%, N≤0.0050%, and combines the controlled rolling and controlled cooling process to develop a 700MPa grade beam steel. The tensile performance of the product meets the requirements of the national standard GB / T3273, and the impact energy of the 10mm product at -60℃ reaches 80J, which has the characteristics of low brittleness. However, this method adds the expensive alloy element Nb to the steel, the production cost is high, and it does not have strong market competitiveness.

[0006] Patent search: A high fatigue performance 700MPa grade hot-rolled automobile beam steel strip and preparation method (application publication number: CN 113308646 A). The patent adopts the composition design of C: 0.02-0.06%, Si: ≤0.08%, Mn: 1.0-2.0%, P: ≤0.015%, S: ≤0.01%, Ti: 0.08-0.35%, N: ≤0.005%, and combines the controlled rolling and controlled cooling process to develop a 700MPa grade beam steel. The ferrite content in the product microstructure is 90-98%, and the acicular bainite content is 2-10%. In addition to the tensile performance meeting the requirements of the national standard GB / T3273, it also has good fatigue resistance. The patent uses the single Ti microalloying effect to improve the product performance, and the actual content range is as high as 0.08-0.35%, but the method does not propose a control method for controlling the liquid TiN, and the product has hidden dangers in performance and service safety. Summary of the invention

[0007] The purpose of the present invention is to provide an economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel strip production method, which adopts C+Mn+Ti composition design, eliminates Nb elements and reduces Mn elements, mainly improves performance through Ti microalloying, and achieves the purpose of reducing product alloy addition costs. At the same time, rare earth elements are used to reduce the size of liquid TiN in high-Ti high-strength steel, change the shape of liquid TiN (from irregular shape with protruding sharp edges to round shape), and improve its adverse effects on product performance and forming.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The present invention provides an economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel strip production method, comprising:

[0010] Steelmaking process:

[0011] KR desulfurization, converter, LF refining and slab continuous casting; the molten iron needs to undergo deep desulfurization operation, and the S of the molten iron after desulfurization is ≤0.002%. After desulfurization, the slag is skimmed and the slag removal area is greater than 90%. The converter tapping process requires the use of normal turnover ladles, and it is strictly forbidden to use new ladles or black ladles, and the amount of slag discharged during tapping must be strictly controlled; aluminum iron is used for deoxidation during converter tapping, and lime and synthetic slag are used for slag adjustment; the amount of aluminum iron and slag added is adjusted according to the end point C content; in the early stage of LF refining and when adjusting the composition, appropriate argon blowing intensity is used for stirring; during power transmission and refining, an appropriate amount of aluminum particles is added to strengthen the deoxidation of the slag surface, and the Als of the second sample of LF is controlled to be ≥0.050%; ferrosilicon is no longer added during LF refining; according to the in-situ sulfur content, lime is added to adjust the refining slag in time, and good fluidity of the refining slag is ensured, and the final refining slag (FeO) + (MnO) ≤ 0.5% and the white slag retention time is ≥ 20 minutes; pure calcium wire is fed during the calcium treatment process, and the calcium content of the molten steel is required to be 0.0008-0.0020%; 20-40kg of ferrocerium alloy is added after calcium treatment, and soft blowing is performed for 5 minutes. It is required that the slag surface has only slight fluctuations during soft blowing to ensure the soft blowing effect and prevent the steel liquid from being exposed;

[0012] Controlled rolling air cooling process:

[0013] The slab heating temperature is controlled at 1240-1270℃, and the soaking time is controlled at 20-30min;

[0014] The rough rolling of slab adopts 3+3 rolling, a total of 6 passes, and the reduction of the first pass is controlled at 35-40mm;

[0015] The intermediate billet temperature is controlled at ≤980℃, the intermediate billet thickness is controlled at 55-60mm, and the final rolling temperature is controlled at 830-860℃;

[0016] The cooling rate is controlled at 15-30℃ / s, and the coiling temperature is mainly considered to be the optimal temperature for TiC precipitation, which is controlled at 590-620℃;

[0017] The steel strip comprises, by mass percentage, C: 0.06-0.08%, Si: 0.03-0.10%, Mn: 1.20%-1.50%, P: ≤0.015%, S: ≤0.005%, Alt: 0.020%-0.050%, Ti: 0.070%-0.100%, N: ≤0.0060%, Ce: 0.0010-0.0030%, and the remainder is Fe and unavoidable impurities.

[0018] Furthermore, a 2250mm hot rolling mill is used for rolling, and the thickness of the continuous casting billet is 230mm.

[0019] Furthermore, the steel strip comprises, by mass percentage, C: 0.07%, Si: 0.060%, Mn: 1.37%, P: 0.012%, S: 0.002%, Alt: 0.038%, Ti: 0.077%, N: 0.0026%, O: 0.0011%, Ce: 0.0018%, and the remainder is Fe and unavoidable impurities.

[0020] Furthermore, the steel strip comprises, by mass percentage, C: 0.07%, Si: 0.060%, Mn: 1.39%, P: 0.011%, S: 0.001%, Alt: 0.037%, Ti: 0.075%, N: 0.0045%, O: 0.0010%, Ce: 0.0012%, and the remainder is Fe and unavoidable impurities.

[0021] Furthermore, the steel strip comprises, by mass percentage, C: 0.07%, Si: 0.060%, Mn: 1.37%, P: 0.014%, S: 0.002%, Alt: 0.031%, Ti: 0.076%, N: 0.0034%, O: 0.0009%, Ce: 0.0012%, and the remainder is Fe and unavoidable impurities.

[0022] Furthermore, the steel strip comprises, by mass percentage, C: 0.07%, Si: 0.070%, Mn: 1.37%, P: 0.010%, S: 0.001%, Alt: 0.037%, Ti: 0.079%, N: 0.0032%, O: 0.0012%, Ce: 0.0016%, and the remainder is Fe and unavoidable impurities.

[0023] Furthermore, the steel strip is mainly composed of polygonal ferrite, has fine and uniform grains, and has a grain size rating of 11.

[0024] The main elements are selected for the following reasons:

[0025] C: Carbon is a cheap solid solution strengthening element and can also form hard carbides. If the content is too little, alloy elements need to be added to improve product strength, resulting in increased product manufacturing costs. If the content is too much, it will affect product forming, welding performance, impact performance and fatigue performance. This product is mainly used for processing automobile beams. It needs to have good plasticity and cold forming performance during processing. In addition to strength, it also needs to have impact toughness and fatigue resistance during service. Taking comprehensive considerations, its content is limited to 0.06-0.08%.

[0026] Si: Silicon is a deoxidizing element and has a good solid solution strengthening effect. However, if the Si content is too high, it will easily cause red oxides to form on the surface of the steel strip. The product processing beam has a painting process. If the Si content is high, it will affect the appearance of the product. After comprehensive consideration, its content is limited to 0.03-0.10%.

[0027] Mn: Manganese can be infinitely substituted with iron for solid solution, and is the most cost-effective solid solution strengthening element after C. However, if the Mn content is too high, it is easy to cause slab segregation, which is inherited to the finished product to form a harder center segregated pearlite banded structure. This problem is more serious, especially for thick specifications. The compression ratio is small and the cooling rate at the center of the thickness is low. The pearlite banded structure seriously deteriorates the formability and fatigue properties of the product. Considering all factors, its content is limited to 0.70% to 1.00%.

[0028] P, S: Phosphorus and sulfur are unavoidable harmful elements in steel. The lower their content, the better the product performance. However, too low a control will increase production costs. Taking comprehensive consideration, their contents are limited to P≤0.015% and S≤0.005% respectively.

[0029] Alt: Aluminum is added for deoxidation. When the aluminum content is insufficient, it cannot exert its effect. When the aluminum content is too high, the ductility deteriorates. Considering all factors, its content is limited to 0.020% to 0.050%.

[0030] Ti: Titanium has the effects of grain refinement and precipitation strengthening. Grain refinement is mainly achieved by fine TiN inhibiting the growth of high-temperature austenite grains, and precipitation strengthening is mainly achieved by precipitating fine TiC between phases or on the ferrite matrix to hinder dislocation movement. The comprehensive product performance requirements limit its content to 0.030-0.050%.

[0031] O: Titanium is chemically active and reacts with O first to produce compounds. The more O content in steel, the more Ti is consumed, which reduces the effective titanium content for γ→α phase transformation or precipitation of TiC on the ferrite matrix, weakening the precipitation strengthening effect of titanium. Taking all factors into consideration, its content is limited to ≤0.0060%.

[0032] N: Titanium is chemically active and reacts with N first to form compounds. The higher the N content in steel, the more Ti is consumed. On the one hand, the effective titanium content for TiC precipitation in the γ→α phase transformation or on the ferrite matrix is ​​reduced, weakening the precipitation strengthening effect of titanium; on the other hand, the TiN formed during the smelting process is large in size and has sharp edges, which has an adverse effect on performance. However, controlling the N element requires increasing the smelting cost, and considering comprehensively, its content is limited to ≤0.0020%.

[0033] Ce: Rare earth Ce has active chemical properties. When rare earth is added to steel, fine CeAl 2 O 3 The production of composite oxide increases the nucleation point of TiN and changes the aggregation mode of Ti and N, thereby reducing the size and shape of TiN, which helps to improve the adverse effect of TiN in Ti-containing steel on product performance. Taking into account the role of rare earth Ce and the smooth progress of industrial production, the Ce content in steel is controlled at 0.0010-0.0030%.

[0034] Compared with the prior art, the beneficial technical effects of the present invention are:

[0035] The special feature of the technical solution of the present invention is that the method successfully develops an economical 700MPa grade beam steel by using a single Ti microalloying method and reasonably setting its content in combination with a corresponding controlled rolling and controlled cooling process, and at the same time utilizes rare earth elements to modify the liquid TiN inclusions in the steel, thereby reducing their adverse effects on the service performance and safety of the product.

[0036] The 700MPa-grade beam steel manufacturing method provided by the present invention reduces the manufacturing cost of the product and improves the product's profit-creating ability. The 700MPa-grade beam steel gradually becomes the main grade of steel for beams, which can create objective economic benefits for enterprises.

[0037] Ti is the most cost-effective fine-grain strengthening element and has great advantages in the development of microalloyed high-strength steel. The application of rare earth in the present invention solves the technical problem that the liquid precipitation of TiN in Ti microalloyed high-strength steel seriously harms the performance and safety to a certain extent. The disclosed technology of combining Ti and rare earth application will become the development direction of low-cost controlled microalloyed high-strength steel.

[0038] This method adopts C+Mn+Ti composition design, eliminates Nb element and reduces Mn element, mainly improves performance through Ti microalloying, and achieves the purpose of reducing product alloy addition cost. At the same time, rare earth elements are used to reduce the size of liquid TiN in high-Ti high-strength steel, change the shape of liquid TiN (from irregular shape with protruding sharp edges to round shape), and improve its adverse effects on product performance and forming. Rare earth Ti microalloyed 700MPa grade beam steel has uniform and refined structure, and its performance meets: yield strength ≥600MPa, tensile strength: 700-880MPa, elongation ≥14%, and has good cold formability, meeting customer requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be further described below in conjunction with the accompanying drawings.

[0040] Figure 1 The metallographic structure of the steel strip at 1 / 4 and 1 / 2 of the thickness direction is shown in the embodiment of the present invention. The product is mainly polygonal ferrite, with fine and uniform grains and a grain size rating of 11.

[0041] Figure 2 The TiN morphology in the embodiment is round, has no protruding sharp edges, and the size is controlled at 5 μm. DETAILED DESCRIPTION

[0042] An economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel strip manufacturing method, the method adopts C+Mn+Ti composition design, eliminates Nb element and reduces Mn element, mainly improves performance through Ti microalloying, and achieves the purpose of reducing product alloy addition cost. At the same time, rare earth elements are used to reduce the size of liquid TiN in high-Ti high-strength steel, change the shape of liquid TiN (from irregular shape with protruding sharp edges to round shape), and improve its adverse effects on product performance and forming. The rare earth Ti microalloyed 700MPa grade beam steel has uniform and refined structure, yield strength ≥600MPa, tensile strength: 700-880MPa, elongation ≥14%, good cold formability, and meets customer requirements.

[0043] To achieve the above object, the technical solution of the present invention is as follows:

[0044] 1. Ingredient Design

[0045] The composition of an economical and easy-to-form rare earth Ti microalloyed 510MPa grade beam steel is as follows: C: 0.06-0.08%, Si: 0.03-0.10%, Mn: 1.20%-1.50%, P: ≤0.015%, S: ≤0.005%, Alt: 0.020%-0.050%, Ti: 0.070%-0.100%, N: ≤0.0060%, O: ≤0.0020%, Ce: 0.0010-0.0030%, and the balance is Fe and unavoidable impurities.

[0046] The main elements are selected for the following reasons:

[0047] C: Carbon is a cheap solid solution strengthening element and can also form hard carbides. If the content is too little, alloy elements need to be added to improve product strength, resulting in increased product manufacturing costs. If the content is too much, it will affect product forming, welding performance, impact performance and fatigue performance. This product is mainly used for processing automobile beams. It needs to have good plasticity and cold forming performance during processing. In addition to strength, it also needs to have impact toughness and fatigue resistance during service. Taking comprehensive considerations, its content is limited to 0.06-0.08%.

[0048] Si: Silicon is a deoxidizing element and has a good solid solution strengthening effect. However, if the Si content is too high, it will easily cause red oxides to form on the surface of the steel strip. The product processing beam has a painting process. If the Si content is high, it will affect the appearance of the product. After comprehensive consideration, its content is limited to 0.03-0.10%.

[0049] Mn: Manganese can be infinitely substituted with iron for solid solution, and is the most cost-effective solid solution strengthening element after C. However, if the Mn content is too high, it is easy to cause slab segregation, which is inherited to the finished product to form a harder center segregated pearlite banded structure. This problem is more serious, especially for thick specifications. The compression ratio is small and the cooling rate at the center of the thickness is low. The pearlite banded structure seriously deteriorates the formability and fatigue properties of the product. Considering all factors, its content is limited to 0.70% to 1.00%.

[0050] P, S: Phosphorus and sulfur are unavoidable harmful elements in steel. The lower their content, the better the product performance. However, too low a control will increase production costs. Taking comprehensive consideration, their contents are limited to P≤0.015% and S≤0.005% respectively.

[0051] Alt: Aluminum is added for deoxidation. When the aluminum content is insufficient, it cannot exert its effect. When the aluminum content is too high, the ductility deteriorates. Considering all factors, its content is limited to 0.020% to 0.050%.

[0052] Ti: Titanium has the effects of grain refinement and precipitation strengthening. Grain refinement is mainly achieved by fine TiN inhibiting the growth of high-temperature austenite grains, and precipitation strengthening is mainly achieved by precipitating fine TiC between phases or on the ferrite matrix to hinder dislocation movement. The comprehensive product performance requirements limit its content to 0.030-0.050%.

[0053] O: Titanium is chemically active and reacts with O first to produce compounds. The more O there is in the steel, the more Ti is consumed, which reduces the effective titanium content for the γ→α phase transformation or the precipitation of TiC on the ferrite matrix, weakening the precipitation strengthening effect of titanium. Taking all factors into consideration, its content is limited to ≤0.0020%.

[0054] N: Titanium is chemically active and reacts with N first to form compounds. The higher the N content in steel, the more Ti is consumed. On the one hand, the effective titanium content for TiC precipitation in the γ→α phase transformation or on the ferrite matrix is ​​reduced, weakening the precipitation strengthening effect of titanium; on the other hand, the TiN formed during the smelting process is large in size and has sharp edges, which has an adverse effect on performance. However, controlling the N element requires increasing the smelting cost, and considering comprehensively, its content is limited to ≤0.0020%.

[0055] Ce: Rare earth Ce has active chemical properties. When rare earth is added to steel, fine CeAl 2 O 3 The production of composite oxide increases the nucleation point of TiN and changes the aggregation mode of Ti and N, thereby reducing the size and shape of TiN, which helps to improve the adverse effect of TiN in Ti-containing steel on product performance. Taking into account the role of rare earth Ce and the smooth progress of industrial production, the Ce content in steel is controlled at 0.0010-0.0030%.

[0056] 2. Steelmaking Process

[0057] An economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel production process involves KR desulfurization, converter, LF refining and slab continuous casting. The molten iron needs to be deeply desulfurized, and the molten iron S after desulfurization is ≤0.002%. After desulfurization, the slag is removed, and the slag removal area (bright surface) is greater than 90%. The converter tapping process requires the use of normal turnover ladles, and it is strictly forbidden to use new ladles and black ladles, and the amount of slag removed during tapping is strictly controlled. Aluminum iron is used for deoxidation during converter tapping, and lime and synthetic slag are used for slag adjustment. The amount of aluminum iron and slag added is adjusted according to the end C content. In the early stage of LF refining and when adjusting the composition, appropriate argon blowing intensity is used for stirring (the molten steel is not overturned and exposed). During the power transmission and refining process, an appropriate amount of aluminum particles is added to strengthen the deoxidation of the slag surface, and the Als of the second sample of LF is controlled to be ≥0.050%. No more ferrosilicon is added during LF refining. According to the sulfur content in place, add lime to adjust the refined slag in time and ensure good fluidity of the refined slag. The final refined slag (FeO) + (MnO) ≤ 0.5% and the white slag retention time ≥ 20 minutes. During the calcium treatment process, feed pure calcium wire, and the calcium content of molten steel is required to be 0.0008-0.0020%. After calcium treatment, add 20-40kg ferrocerium alloy and soft blow for 5 minutes. It is required that the slag surface has only slight fluctuations during soft blowing to ensure the soft blowing effect and prevent the steel liquid from being exposed.

[0058] 3. Controlled rolling air cooling process

[0059] The steel is rolled using a 2250mm hot rolling mill. The thickness of the continuous casting billet is 230mm.

[0060] The heating of the slab should consider both the full solid solution of the alloy elements and the prevention of excessive grain coarsening. Therefore, the heating temperature of the slab is controlled at 1240-1270℃ and the soaking time is controlled at 20-30min.

[0061] The slab temperature is high during the rough rolling stage and is in the complete recrystallization zone. It is an important process for refining the coarse grains of the slab and a key link in achieving uniformity of the product thickness. The two necessary conditions for using recrystallization to refine the grain size are high temperature and large deformation. Therefore, the rough rolling of the slab adopts 3+3 rolling for a total of 6 passes, and the first pass reduction is controlled at 35-40mm.

[0062] In the finishing rolling stage, the partial recrystallization zone is avoided and the rolling is controlled in the non-recrystallization zone. The partial recrystallization zone is prone to mixed crystal structure, and the thickness center problem is more serious. Rolling in the non-recrystallization zone can lengthen the grain size, increase the grain boundary area, and provide more nucleation points for subsequent phase transformation, thereby achieving the purpose of refining the grain size. Increasing the reduction in the finishing rolling stage and the lower final rolling temperature are also helpful to increase the grain boundary area and nucleation points. Therefore, the intermediate billet temperature is controlled at ≤980℃, the intermediate billet thickness is controlled at 55-60mm, and the final rolling temperature is controlled at 830-860℃.

[0063] If the cooling speed of the steel coil is too slow, the size of the refined grains will grow. If the cooling speed is too fast, the "red return" problem will occur. To prevent such problems, the cooling speed is controlled at 15-30℃ / s, and the coiling temperature is mainly considered to be the optimal temperature for TiC precipitation, which is controlled at 590-620℃.

[0064] The special feature of the technical solution of the present invention is that the method successfully develops an economical 700MPa grade beam steel by using a single Ti microalloying method and reasonably setting its content in combination with a corresponding controlled rolling and controlled cooling process, and at the same time utilizes rare earth elements to modify the liquid TiN inclusions in the steel, thereby reducing their adverse effects on the service performance and safety of the product.

[0065] The following examples are used to specifically illustrate the present invention. These examples are only general descriptions of the present invention and do not limit the present invention.

[0066] In order to further understand the present invention, 4 groups of economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel strip embodiments of the present invention are provided. The chemical composition control of the embodiments is shown in Table 1, the heating-rolling-cooling parameter control of the embodiments is shown in Table 2, and the mechanical properties of the embodiments are shown in Table 3.

[0067] Table 1 Chemical composition of steel in the example (wt%)

[0068]

[0069]

[0070] Table 2 Example steel process system

[0071]

[0072] Table 3 Mechanical properties of example steel

[0073]

[0074] It can be seen from the examples that the yield strength, tensile strength and elongation of the steel strip of the present invention meet the requirements of the national standard GB / T3273, especially the elongation margin is large, so that the product has good cold formability.

[0075] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for producing an economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel strip, characterized in that: include: Steelmaking process: KR desulfurization, converter, LF refining and slab continuous casting; the molten iron needs to undergo deep desulfurization operation, and the S of the molten iron after desulfurization is ≤0.002%. After desulfurization, the slag is skimmed and the slag removal area is greater than 90%. The converter steel-making process requires the use of normal turnover ladles, and it is strictly forbidden to use new ladles or black ladles, and the amount of slag discharged during steel-making is strictly controlled; aluminum iron is used for deoxidation during converter steel-making, and lime and synthetic slag are used for slag adjustment; the amount of aluminum iron and slag added is adjusted according to the end point C content; in the early stage of LF refining and when adjusting the composition, appropriate argon blowing intensity is used for stirring; during power transmission and refining, an appropriate amount of aluminum particles is added to strengthen the deoxidation of the slag surface, and the Als of the second sample of LF is controlled to be ≥0.050%; no ferrosilicon is added during LF refining; according to the in-situ sulfur content, lime is added to adjust the refining slag in time, and the refining slag has good fluidity, and the final refining slag FeO+MnO≤0.5% and the white slag retention time is ≥20 minutes; During the calcium treatment, pure calcium wire is fed, and the calcium content of molten steel is required to be 0.0008-0.0020%. After calcium treatment, 20-40kg of ferrocerium alloy is added, and soft blowing is performed for 5 minutes. It is required that the slag surface has only slight fluctuations during soft blowing to ensure the soft blowing effect and prevent the molten steel from being exposed. Controlled rolling air cooling process: The slab heating temperature is controlled at 1240-1270℃, and the soaking time is controlled at 20-30min; The rough rolling of slab adopts 3+3 rolling, a total of 6 passes, and the reduction of the first pass is controlled at 35-40mm; The intermediate billet temperature is controlled at ≤980℃, the intermediate billet thickness is controlled at 55-60mm, and the final rolling temperature is controlled at 830-860℃; The cooling rate is controlled at 15-30℃ / s, and the coiling temperature is mainly considered to be the optimal temperature for TiC precipitation, which is controlled at 590-620℃; The steel strip comprises, by mass percentage, C: 0.06-0.08%, Si: 0.03-0.10%, Mn: 1.20%-1.50%, P: ≤0.015%, S: ≤0.005%, Alt: 0.020%-0.050%, Ti: 0.070%-0.100%, N: ≤0.0060%, O≤0.0020%, Ce: 0.0010-0.0030%, and the remainder is Fe and unavoidable impurities.

2. The method for producing an economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel strip according to claim 1, characterized in that: The steel is rolled using a 2250mm hot rolling mill, and the thickness of the continuous casting billet is 230mm.

3. The method for producing an economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel strip according to claim 1, characterized in that: The steel strip is calculated by mass percentage as follows: C: 0.07%, Si: 0.060%, Mn: 1.37%, P: 0.012%, S: 0.002%, Alt: 0.038%, Ti: 0.077%, N: 0.0026%, O: 0.0011%, Ce: 0.0018%, and the balance is Fe and inevitable impurities.

4. The method for producing an economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel strip according to claim 1, characterized in that: The steel strip comprises, by mass percentage, C: 0.07%, Si: 0.060%, Mn: 1.39%, P: 0.011%, S: 0.001%, Alt: 0.037%, Ti: 0.075%, N: 0.0045%, O: 0.0010%, Ce: 0.0012%, and the remainder is Fe and unavoidable impurities.

5. The method for producing an economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel strip according to claim 1, characterized in that: The steel strip comprises, by mass percentage, C: 0.07%, Si: 0.060%, Mn: 1.37%, P: 0.014%, S: 0.002%, Alt: 0.031%, Ti: 0.076%, N: 0.0034%, O: 0.0009%, Ce: 0.0012%, and the remainder is Fe and unavoidable impurities.

6. The method for producing an economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel strip according to claim 1, characterized in that: The steel strip comprises, by mass percentage, C: 0.07%, Si: 0.070%, Mn: 1.37%, P: 0.010%, S: 0.001%, Alt: 0.037%, Ti: 0.079%, N: 0.0032%, O: 0.0012%, Ce: 0.0016%, and the remainder is Fe and unavoidable impurities.

7. The method for producing an economical and easy-to-form rare earth Ti microalloyed 700MPa grade beam steel strip according to claim 1, characterized in that: The steel strip is mainly composed of polygonal ferrite, with fine and uniform grains and a grain size rating of 11 levels.

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