Thick 700MPa-grade steel produced on thin slab continuous casting and rolling production line and production method of thick 700MPa-grade steel

Abstract

The invention relates to the technical field of steel, in particular to thick 700 MPa grade steel produced on a thin slab continuous casting and rolling production line and a production method of the thick 700 MPa grade steel. The invention discloses a high-strength high-strength steel plate which comprises the following chemical components in percentage by mass: 0.02%-0.05% of C, 0.05%-0.50% of Si, 1.20%-2.0% of Mn, 0.20%-0.5% of Cr, less than or equal to 0.018% of P, less than or equal to 0.005% of S, 0.06%-0.14% of Ti and the balance of Fe and inevitable impurities. According to the high-strength high-strength high-strength high-strength steel plate, the Mn, Cr and Ti coupling strengthening technology, the high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high-strength high- The method is applied to the fields of automobile beams, high-strength pipes, machining and the like which have high requirements for obdurability, the waste heat of the casting blank can be fully utilized, and precipitation of Ti in a high-temperature section is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of steel, and in particular to a thin slab continuous casting and rolling production line for producing thick-gauge 700MPa grade steel and a production method thereof. Background Art

[0002] When the thin slab continuous casting and rolling production line produces thick specifications of 4-6mm, the problems faced are: ① Due to the limitation of continuous casting speed, the rolling speed of the final stand of the finishing rolling is (1-2) m / s, which is much different from the rolling speed of the same specification (5-10) m / s of the traditional production line. On the one hand, it affects the final rolling temperature, and on the other hand, it affects the cooling efficiency. This makes it difficult to meet the high final rolling temperature and high-level cold cooling speed required for micro-alloy high-strength steel, which is not conducive to the micro-alloy strengthening effect; especially for steel grades with a tensile strength of 700MPa. ② The compression ratio is low. The current production line design has a maximum intermediate billet of 16-20mm and a finished product specification of 4-6mm with a compression ratio of 3-4.5. The total compression ratio is low, which is not conducive to refining the structure or improving the strength.

[0003] Patent No. CN201610766506.2 introduces the composition and performance of 1.2-3.5mm specifications. The raw materials include by mass percentage: N <0.06%, C 0.1~0.40%, Si <1.75%, Mn, 0.02~0.04%, Al 0.03~0.07%, Nb 0.04~0.08%, Ti <0.08%, V <0.0020%, S <0.012%, P ≤0.005%, the rest is iron; the raw materials are successively smelted in converter, refined in LF furnace and RH furnace; the molten steel formed by RH furnace refining is passed through ESP production line to produce hot-rolled strips of different thicknesses; among which, in ESP production line, the rough rolling outlet temperature is 920~980℃, and the finishing outlet temperature is 800~870℃; the hot-rolled strip is cooled by laminar cooling front section, cooled to 530~680℃, and then enters the coiler for coiling. After the coiled strip is slowly cooled, it is flattened and coiled into storage with 1%~2.0% flattening amount. This invention uses microalloy Nb, Ti, V composite strengthening, and the production specifications are relatively thin.

[0004] On the other hand, the thin slab continuous casting and rolling production line has some advantages in the production of micro-alloy strengthened steel. The process has a high drawing speed, and the continuous casting and rolling ingot has a short cooling time and a fast speed. Compared with conventional hot rolling with low drawing speed and long slab placement, the size of TiN inclusions is significantly lower than conventional hot rolling, which brings good strength and toughness under this process. It is necessary to apply the thin slab continuous casting and rolling process products to a larger specification range. Summary of the invention

[0005] In view of the technical problems that the existing hot rolling process has low drawing speed and low compression ratio, which are not conducive to exerting the micro-alloy strengthening effect and improving the strength, the present invention provides a thin slab continuous casting and rolling production line for producing thick-gauge 700MPa grade steel and a production method thereof, which solves the problem of poor strength and toughness caused by low drawing speed and low compression ratio in the existing hot rolling.

[0006] In a first aspect, a thin slab continuous casting and rolling production line produces thick gauge 700 MPa grade steel, comprising the following chemical components in weight percentage: C 0.02%-0.05%, Si 0.05%-0.50%, Mn 1.20%-2.0%, Cr 0.20%-0.5%, P ≤0.018%, S ≤0.005%, Ti 0.06%-0.14%, the rest is Fe and unavoidable impurities, C element is the most important element to ensure the strength, hardness and wear resistance of the material, C element can be dissolved in steel to form a solid solution, which plays a role of solid solution strengthening, and is the main strengthening element of steel. It can be combined with strong carbide forming elements to form carbide precipitation, which plays a role of precipitation strengthening. C element is the element that contributes the most to the strength of steel, but with the increase of carbon content, plasticity and welding performance decrease. In the present invention, the C content is controlled at 0.02%-0.05%; Si is added as a reducing agent and deoxidizer during the steelmaking process, and Si can significantly improve the elastic limit of steel, while improving the yield strength and resistance of the material. Tensile strength, in the present invention, the Si content is controlled at 0.05%-0.50%; in addition to the role of solid solution strengthening, Mn and Cr can also reduce the phase transformation temperature, refine the size of TiC precipitation, and better play the role of precipitation strengthening; S is not good for the strength and toughness of steel, and it is easy to form MnS inclusions and Ti4C2S2. The lower its content is controlled, the better. In the present invention, the S content is controlled at ≤0.005%; Ti is the main strengthening element in the present invention. Too high Ti content is not good for toughness. In the present invention, the Ti content is controlled at 0.06%~0.14%; the continuous casting and rolling process route is adopted to make full use of the waste heat of the ingot, and the rough rolling outlet temperature is greater than 1000℃ to reduce the precipitation of Ti in the high temperature section.

[0007] Furthermore, it has the following mechanical properties: yield strength of 688MPa-740MPa, tensile strength of 720MPa-800MPa, elongation of 16%-24%, and thickness specification of 4-6mm.

[0008] In a second aspect, the present invention provides a production method for producing thick-gauge 700 MPa grade steel by a thin slab continuous casting and rolling production line, comprising the following steps in sequence: (1) molten iron pretreatment, (2) converter smelting, (3) RH refining, (4) LF refining, (5) continuous casting, (6) rough rolling, (7) induction furnace heating, (8) finishing rolling, (9) layer cooling, (10) coiling, and (11) slow cooling storage.

[0009] Furthermore, in step (5), the rough rolling outlet temperature is greater than 1000°C.

[0010] Furthermore, in step (7), the heating temperature of the induction furnace is 1150°C ± 50°C.

[0011] Furthermore, in step (8), the finishing rolling temperature is 820°C-880°C, and the final stand compression ratio target is ≥30%.

[0012] Furthermore, in step (9), the laminar cooling is equipped with a rapid cooling device, the time from the end of rolling to the start of cooling is less than 1 second, and the cooling rate is greater than 50°C / s.

[0013] Furthermore, in step (10), the coiling temperature is 550°C-650°C.

[0014] Furthermore, in step (11), after coiling, the product is quickly put into storage and slowly cooled for ≥48 hours before being released from storage.

[0015] The beneficial effects of the present invention are: The present invention provides a thin slab continuous casting and rolling production line for producing thick-gauge 700MPa grade steel and a production method thereof. By utilizing the development of Mn, Cr, Ti coupling strengthening technology, high casting temperature, and load allocation and control of each finishing rolling frame final rolling technology, thick-gauge 700MPa grade steel can be produced at a low alloy cost, and the steel is applied to automobile beams, high-strength pipes, mechanical processing and other fields with high requirements on strength and toughness. DETAILED DESCRIPTION

[0016] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0017] Example 1 A thin slab continuous casting and rolling production line produces thick-gauge 700MPa grade steel and a production method thereof, comprising the following steps: (1) A thin slab continuous casting and rolling production line produces thick-gauge 700MPa grade steel, the chemical composition of which is designed by mass percentage: C 0.045%, Si 0.15%, Mn 1.40%, Cr 0.25%, P 0.015%, S≤0.002%, Ti 0.096%, and the rest is Fe and unavoidable impurities. The C element is the most important element to ensure the strength, hardness and wear resistance of the material. The C element can be dissolved in the steel to form a solid solution, which plays a role in solid solution strengthening. It is the main strengthening element of the steel grade. It can combine with strong carbide forming elements to form carbide precipitation, which plays a role in precipitation strengthening. The C element is the element that contributes the most to the strength of the steel, but as the carbon content increases, the plasticity and welding performance decrease. In the present invention, the C content is controlled at 0.02%-0.05%; Si is used in steelmaking. It is added as a reducing agent and deoxidizer during the process, and Si can significantly improve the elastic limit of steel, while improving the yield strength and tensile strength of the material. In the present invention, the Si content is controlled at 0.05%-0.50%; Mn and Cr, in addition to playing the role of solid solution strengthening, can also reduce the phase transition temperature, refine the TiC precipitation size, and play a precipitation strengthening role; S is not good for the strength and toughness of steel, and it is easy to form MnS inclusions and Ti4C2S2. The lower its content is controlled, the better. In the present invention, the S content is controlled at ≤0.005%; T Ti is the main strengthening element in the present invention. Too high Ti content is not good for toughness. In the present invention, Ti content is controlled at 0.06%-0.14%; the continuous casting and rolling process route is adopted to make full use of the residual heat of the ingot, and the rough rolling outlet temperature is greater than 1000°C to reduce the precipitation of Ti in the high temperature section; the chemical components are sequentially subjected to converter smelting, RH refining and LF refining, continuous casting, rough rolling, induction furnace heating, finishing rolling, layer cooling, coiling, and slow cooling storage; the rough rolling outlet temperature is greater than 1000°C, the finishing rolling temperature is controlled to be 820°C-880°C, and the layer cooling is adjusted to With rapid cooling device, the cooling time from the end of rolling to the beginning is less than 1s, the cooling rate is greater than 50℃ / s, and the coiling temperature is 550℃-650℃. By adjusting the load distribution of each finishing rolling stand, the compression ratio of the final stand is increased by ≥30%, the temperature drop of the front stand is reduced, the problems of thick specifications, slow speed and large temperature drop in the process are improved, the final rolling temperature is increased and the post-rolling structure is refined. Rapid cooling is performed after rolling to reduce the precipitation of Ti elements in the high temperature stage, and to compensate for the slow cooling rate caused by thick specifications and slow speed. After coiling, it is quickly put into storage and slowly cooled for ≥48h before being released from the storage, giving full play to the precipitation of the slow cooling process.

[0018] The product obtained in this embodiment has the following performance parameters: thickness specification is 4.5mm, yield strength is 688MPa, tensile strength is 747MPa, and elongation is 21%; the present invention utilizes the development of Mn, Cr, Ti coupling strengthening technology, high casting temperature, finishing rolling frame load allocation and control final rolling technology, and post-rolling rapid cooling technology to produce thick specification 700MPa grade steel at low alloy cost, which is applied to automobile beams, high-strength pipes, mechanical processing and other fields with high strength and toughness requirements.

[0019] Example 2 The difference between Example 2 and Example 1 is that the obtained product has the following performance parameters: thickness specification is 5.5mm, chemical composition by mass percentage is C 0.042%, Si 0.38%, Mn 1.71%, Cr 0.38%, P 0.011%, S ≤0.002%, Ti 0.012%, the rest is Fe and unavoidable impurities, the rough rolling outlet temperature is 1025℃, the final stand reduction rate is 32%, the final rolling temperature is 815℃, rapid cooling after rolling, cooling rate>50℃ / s, coiling temperature is 610℃, and slow cooling is ≥48h before delivery; the yield strength is 700MPa, the tensile strength is 767MPa, and the elongation is 22%.

[0020] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and such changes or substitutions shall be within the scope of protection of the present invention.

Claims

1. A thin slab continuous casting and rolling production line for producing thick-gauge 700MPa grade steel, characterized in that: The chemical composition includes the following weight percentages: C 0.02%-0.05%, Si 0.05%-0.50%, Mn1.20%-2.0%, Cr 0.20%-0.5%, P ≤0.018%, S ≤0.005%, Ti 0.06%-0.14%, and the rest are Fe and unavoidable impurities.

2. A method for producing thick-gauge 700MPa grade steel by continuous casting and rolling of thin slabs as claimed in claim 1, characterized in that: It has the following mechanical properties: yield strength of 688MPa-740MPa, tensile strength of 720MPa-800MPa, elongation of 16%-24%, and thickness specification of 4-6mm.

3. The method for producing thick-gauge 700MPa grade steel by continuous casting and rolling of thin slabs as claimed in claim 1, characterized in that: The process includes the following steps in sequence: (1) molten iron pretreatment, (2) converter smelting, (3) RH refining, (4) LF refining, (5) continuous casting, (6) rough rolling, (7) induction furnace heating, (8) finishing rolling, (9) layer cooling, (10) coiling, and (11) slow cooling storage.

4. The method for producing thick-gauge 700MPa grade steel by a thin slab continuous casting and rolling production line as claimed in claim 3, characterized in that: In step (6), the rough rolling outlet temperature is greater than 1000°C.

5. The method for producing thick-gauge 700MPa grade steel by a thin slab continuous casting and rolling production line as claimed in claim 3, characterized in that: In step (7), the heating temperature of the induction furnace is 1150°C ± 50°C.

6. The method for producing thick-gauge 700MPa grade steel by a thin slab continuous casting and rolling production line as claimed in claim 3, characterized in that: In step (8), the finishing rolling temperature is 820°C-880°C, and the final stand compression ratio target is ≥30%.

7. The method for producing thick-gauge 700MPa grade steel by a thin slab continuous casting and rolling production line as claimed in claim 3, characterized in that: In step (9), the laminar cooling is equipped with a rapid cooling device, the time from the end of rolling to the start of cooling is less than 1s, and the cooling rate is greater than 50°C / s.

8. The method for producing thick-gauge 700MPa grade steel by a thin slab continuous casting and rolling production line as claimed in claim 3, characterized in that: In step (10), the coiling temperature is 550°C-650°C.

9. The method for producing thick-gauge 700MPa grade steel by a thin slab continuous casting and rolling production line as claimed in claim 3, characterized in that: In step (11), after coiling, the product is quickly put into storage and slowly cooled for ≥48 hours before being released from storage.