A high-strength and high-toughness cold-working die flat steel and its preparation method

Abstract

The present invention provides a high-strength, high-toughness cold-working die flat steel and a preparation method thereof. The high-strength, high-toughness cold-working die flat steel comprises the following chemical components by mass: C: 0.95-1.05%; Si: 0.8-1.2%; Mn: 0.3-0.6%; P≤0.03%; S≤0.005%; Cr: 8.0-9.0%; Mo: 2.0-2.3%; V: 0.2-0.4%; Cu: 0.1-0.3%; Ni: 0.1-0.3%; the remainder being Fe and unavoidable impurity elements. The preparation method of the present invention solves the flaw detection and impact problems caused by coarse and aggregated eutectic carbides in the core of thick-gauge high-strength, high-toughness cold-working die flat steel. By employing the key technologies and processes designed in the present invention, the core deformation can be significantly improved, the eutectic carbide structure can be broken up, and the flaw detection pass rate can be increased, thereby achieving certain economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of cold working die steel production, and in particular to a high-strength and high-toughness cold working die flat steel and a preparation method thereof. Background Art

[0002] Cold work die steel is a crucial component of tool steel and is widely used in blanking, stamping, cold extrusion, cold heading, drawing, and coining dies. For high-precision cold stamping dies, DC53, an improved version of Cr12MoV developed by Japan's Daido Steel Co., Ltd., and the domestically designated Cr8Mo2SiV, are highly favored. Therefore, DC53 (Cr8Mo2SiV) has long been widely used as a representative example of high-strength and high-toughness cold work die steel. However, unlike Cr12MoV, DC53's unique solidification characteristics lead to the formation of coarse, aggregated eutectic carbides. If the subsequent deformation process is not properly controlled, internal cracks can occur, resulting in point-like or continuous linear flaw detection alarms. Currently, DC53 flat steel, the primary raw material for cold stamping dies, is typically produced using die-cast ingot forging and rolling, or direct rolling from electroslag remelted ingots. This significantly increases production costs and reduces efficiency.

[0003] Patent CN115106471A discloses a method for forging titanium alloy forgings with rectangular cross-sections. The continuously cast round billet is repeatedly upset and stretched to a desired size using a flat anvil. After multiple reforging of the intermediate billet and subsequent product forging, titanium alloy flat steel with cross-sections of 60×190 and 80×190 is ultimately obtained. This patented method involves multiple upsetting of the continuously cast round billet using conventional flat anvils, followed by multiple forging of the intermediate billet. This method results in a lengthy and costly process, making it uneconomical and of limited use for DC53 flat steel production.

[0004] Patent CN114603074A discloses a forging method for large-scale forging billets of ultra-high strength and toughness TB18 titanium alloy. Specifically, the method comprises: first, forging the billet; then, forging the billet through three stages; and finally, forming forging. The method precisely controls the deformation, temperature, and forging ratio at each step throughout the process. A large fast forging unit is used to ensure sufficient forging pressure and the forgeability of the billet. Through multi-stage billet forging, the billet's aspect ratio is reduced, and double drumming generated during the forging process is effectively eliminated. A reasonable pass deformation is designed to control temperature rise and reduce deformation dead zones. Three-dimensional reversing is used to address the problem of forgeability in the middle. Flattening ensures uniformity of the billet's surface and core microstructures. Continuous remelting shortens the processing flow and preparation cycle. Through dual-operation linkage, fast feeding and reciprocating drawing are achieved. The resulting titanium alloy forging billet exhibits good high- and low-magnification microstructure uniformity, and mechanical testing shows that it fully meets the high-strength and toughness requirements of aviation equipment. This patent is mainly aimed at titanium alloy forging billets, which have high costs. However, the material properties of DC53 are significantly different from those of TB18 and do not meet the requirements of economical production. Summary of the Invention

[0005] In response to the aforementioned technical problems, a high-strength and high-toughness cold-working die flat steel and its production method are provided. Based on a continuous casting billet with a specific cross-section, the present invention designs a corresponding flat steel production process, particularly for thick flat steel with a thickness of 65-70 mm and a width of 400-450 mm. This process solves the problem of eutectic carbide fragmentation and refinement, significantly improving the flaw detection pass rate.

[0006] The technical means adopted in the present invention are as follows:

[0007] A high-strength and high-toughness cold-working die flat steel, wherein the high-strength and high-toughness cold-working die flat steel is composed of the following chemical components by mass percentage:

[0008] C: 0.95~1.05%; Si: 0.8~1.2%; Mn: 0.3~0.6%; P≤0.03%; S≤0.005%; Cr: 8.0~9.0%; Mo: 2.0~2.3%; V: 0.2~0.4%; Cu: 0.1~0.3%; Ni: 0.1~0.3%; the balance is Fe and unavoidable impurity elements.

[0009] Furthermore, the high-strength and high-toughness cold-working die flat steel has a thickness of 65-70 mm and a width of 400-450 mm.

[0010] The present invention also provides a method for preparing high-strength and high-toughness cold-working die flat steel, comprising the following steps:

[0011] S1. Design and process the drawing die;

[0012] S2, feeding the continuous casting billet into a walking beam heating furnace and heating it in a two-stage heating method;

[0013] S3. After the continuous casting billet is heated and discharged from the furnace, the continuous casting billet is fed into the first half anvil, the cross-sectional shape of the drawing die is adjusted, the width of the drawing die is adjusted, and the continuous casting billet is drawn for the first time using the drawing die;

[0014] S4, rotating the continuous casting billet obtained in step S3 by 90 degrees, feeding the billet with a full anvil for a second time, adjusting the cross-sectional shape and width of the drawing die, and using the drawing die to draw the continuous casting billet for a second time;

[0015] S5, the continuous casting billet obtained in step S4 is not rotated, and the continuous casting billet is fed for the third time, between the half anvil and the full anvil, with a feeding amount of 240-250 mm, and the cross-sectional shape and width of the drawing die are adjusted, and the continuous casting billet is drawn for the third time using the drawing die to obtain an intermediate billet;

[0016] S6. Return the intermediate billet to the furnace, i.e., send it into a walking beam heating furnace for heating; replace the electro-hydraulic hammer with a flat anvil;

[0017] S7, after the intermediate blank is heated in step S6, it is taken out of the furnace and the intermediate blank is directly stretched on the wide side using a flat anvil, with a feed amount of 200-300 mm and a reduction amount of 40-45 mm, and the width is freely widened;

[0018] S8, the intermediate blank obtained in step S7 is stretched for the second time, the intermediate blank is not turned over, the feed amount is 200-250mm, the pressing amount is 25-35mm, and the width is freely widened;

[0019] S9. Finally, high-strength and high-toughness cold-working die flat steel with a thickness of 65-70mm and a width of 400-450mm is obtained.

[0020] Furthermore, in step S1, the drawing die is a combined die, comprising an upper hammer head and a lower hammer head that are symmetrical in the upper and lower directions, each hammer head is U-shaped, and the two hammer heads can be moved left and right through an electric worm gear mechanism to achieve left and right width adjustment.

[0021] Furthermore, in step S1, the width adjustment range of the drawing die is 150 to 260 mm; and the length of the hammer head working area is 300 mm.

[0022] Furthermore, in step S2, the width and height of the continuous casting billet are both 170 mm, the radius of the four fillets is 60 mm, the side length is 50 mm, and the fixed length of the continuous casting billet is 5 to 7 meters.

[0023] Furthermore, in step S2, the two-stage heating method is: first perform the first stage heating, i.e., the preheating stage, with a heating temperature of 1130-1140°C and a heating time of 2-3 hours; then perform the second stage heating, i.e., the soaking stage, with a heating temperature of 1145±5°C and a heating time of 1-1.5 hours.

[0024] Furthermore, in step S3, the cross-sectional shape of the drawing die is adjusted to meet the requirement of 40-50 mm for a single hammer pressing amount, and the width of the drawing die is adjusted to 210-220 mm;

[0025] In step S4, the cross-sectional shape and width of the drawing die are adjusted to: the width is 150-160 mm, and the single hammer pressing amount is 25-30 mm;

[0026] In step S5, the cross-sectional shape and width of the drawing die are adjusted to: the width is 240-260 mm, and the single hammer pressing amount is 60-70 mm.

[0027] Furthermore, in step S6, the heating temperature is 1140-1145° C., and the insulation time is 2.5-3 hours.

[0028] Furthermore, in step S6, the anvil width of the flat anvil is 400 mm, the anvil length is 600 mm, and the chamfer radius is 10 mm.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] The high-strength and high-toughness cold-working die flat steel and its preparation method provided by the present invention solve the flaw detection and impact problems caused by the coarse and aggregated eutectic carbides in the core of thick-gauge high-strength and high-toughness cold-working die flat steel. The key technologies and processes designed by the present invention can significantly improve the core deformation, break the eutectic carbide structure, and improve the flaw detection pass rate, which has certain economic benefits.

[0031] Based on the above reasons, the present invention can be widely promoted in the fields of preparation of cold working die steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0033] Figure 1 It is a process flow chart of the present invention.

[0034] Figure 2 It is a schematic diagram of the cross-sectional shape of the continuous casting billet of the present invention.

[0035] Figure 3 It is a schematic cross-sectional view of the hammer head of the present invention.

[0036] Figure 4 It is a three-dimensional schematic diagram of the hammer head of the present invention.

[0037] Figure 5 This is the edge structure diagram of Example 1 of the present invention (the eutectic carbide rating is level 1).

[0038] Figure 6 This is the core structure diagram of Example 1 of the present invention (the eutectic carbide rating is 1.5).

[0039] Figure 7 This is the edge microstructure diagram of Example 2 of the present invention (the eutectic carbide rating is level 1).

[0040] Figure 8 This is the core structure diagram of Example 2 of the present invention (the eutectic carbide rating is 1.5). DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0043] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0044] Unless otherwise specifically stated, the relative arrangement of the parts and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following figures, and therefore, once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0045] In order to solve the above problems, Figure 1 As shown, the present invention is based on a continuous casting billet with a specific cross-section shape and designs a flat steel production process that matches it, especially a production process for thick flat steel with a thickness of 65-70 mm and a width of 400-450 mm.

[0046] The purpose of the present invention is to provide a method for preparing high-strength and high-toughness cold-working die flat steel. A forging process is designed for continuous casting billets with special cross-sections. The finished product has a thickness of 65-70 mm and a width of 400-450 mm. The problem of eutectic carbide crushing and refinement is solved, and the flaw detection pass rate is significantly improved.

[0047] In order to achieve the above object, the technical solution of the present invention is as follows:

[0048] (1) The high-strength and high-toughness cold working die steel involved is DC53 (Cr8Mo2SiV). Based on the requirements of national standards, the preferred chemical composition of the present invention is: C: 0.95-1.05%; Si: 0.8-1.2%; Mn: 0.3-0.6%; P≤0.03%; S≤0.005%; Cr: 8.0-9.0%; Mo: 2.0-2.3%; V: 0.2-0.4%; Cu: 0.1-0.3%; Ni: 0.1-0.3%; the balance is Fe and unavoidable impurity elements.

[0049] (2) Specific continuous casting billet cross section as shown in the attached Figure 2 As shown, the width W and height H are both 170 mm, the radii R of the four corners are 60 mm, and the side lengths L are all 50 mm.

[0050] (3) The present invention designs a special drawing die, which is a modular die with adjustable width on the left and right (adjustable between 150 and 260 mm) and vertical symmetry (the drawing die includes an upper hammer head and a lower hammer head that are vertically symmetrical, each hammer head is U-shaped, and the two hammer heads can be moved left and right by an electric worm mechanism to achieve left and right width adjustment). The specific dimensions are shown in the schematic diagram. Figure 3 , see the three-dimensional schematic diagram Figure 4 .

[0051] (4) The length of the hammer head working area is 300mm.

[0052] (5) The continuous casting billet has a fixed length of 5 to 7 meters and is directly fed into a walking beam heating furnace for heating in two sections. The first section is the preheating section with a heating temperature of 1130 to 1140°C and a heating time of 2 to 3 hours; the second section is the soaking section with a heating temperature of 1145 ± 5°C and a heating time of 1 to 1.5 hours.

[0053] (6) After the continuous casting billet is removed from the furnace, the first half anvil is fed in, and the cross-sectional shape of the die is adjusted to meet the single hammer pressure of 40-50mm and the die width is adjusted to 210-220mm. The continuous casting billet is stretched for the first time using the stretching die.

[0054] (7) In the second run, the continuous casting billet is rotated 90° and fed through the full anvil. The cross-sectional shape of the die is adjusted to 150-160 mm in width and 25-30 mm in single hammer reduction. The continuous casting billet is stretched for the second time using the stretching die.

[0055] (8) During the third feed, the continuous casting billet is not rotated and the feed amount is 240-250 mm. The cross-section of the die is adjusted between half anvil and full anvil: the width is 240-260 mm and the single hammer pressure is 60-70 mm. The continuous casting billet is stretched for the third time using the stretching die to obtain the intermediate billet.

[0056] (9) The intermediate billet is returned to the furnace, that is, sent to a step-beam heating furnace for heating at a temperature of 1140-1145°C for 2.5-3 hours. The press electro-hydraulic hammer is replaced with a flat anvil (conventional hammer head directly), with an anvil width of 400mm, anvil length of 600mm, and a chamfer radius of 10mm.

[0057] (10) The intermediate billet is taken out of the furnace and the wide surface is directly stretched using a flat anvil, with a feed amount of 200-300mm and a reduction amount of 40-45mm, and the width is freely widened.

[0058] (11) In the second stretching, the intermediate blank is not turned over, the feed amount is 200-250mm, the press amount is 25-35mm, and the width is freely widened.

[0059] The above-mentioned half anvil and full anvil refer to the feed amount of the blank.

[0060] The application of the present invention solves the flaw detection and impact problems caused by the coarse and aggregated eutectic carbides in the core of thick-gauge, high-strength and high-toughness cold-working die flat steel. The key technologies and processes designed by the present invention can significantly improve the core deformation, break the eutectic carbide structure, and improve the flaw detection pass rate, which has certain economic benefits.

[0061] The invention has been implemented within the company and can be extended to similar products or businesses.

[0062] Example 1

[0063] This embodiment is produced using the die section and forging process designed by the present invention.

[0064] The details are as follows:

[0065] (1) The chemical composition of the cold working die steel used in the production of continuous casting billets is as follows: C: 0.98%; Si: 1.0%; Mn: 0.5%; P: 0.02%; S: 0.002%; Cr: 8.8%; Mo: 2.3%; V: 0.4%; Cu: 0.3%; Ni: 0.28%; the rest is Fe and unavoidable impurity elements.

[0066] (2) The width and height of the continuous casting billet (crystallizer) are both 170 mm, the radius of the four fillets is 60 mm, the side length is 50 mm, and the total length of the crystallizer is 1500 mm.

[0067] (3) The continuous casting billet has a fixed length of 5 meters and is directly fed into a walking beam heating furnace for heating in two sections. The first section is a preheating section with a heating temperature of 1140°C and a heating time of 2.5 hours; the second section is a soaking section with a heating temperature of 1145°C and a heating time of 1.2 hours.

[0068] (4) After the continuous casting billet leaves the heating furnace, the first half anvil is fed in, and the cross-sectional shape of the mold is adjusted to meet the single hammer pressing amount of 45 mm and the mold width is adjusted to 220 mm.

[0069] (5) In the second run, the continuous casting billet is rotated 90° and fed into the full anvil. The cross-sectional shape of the mold is adjusted: the width is 160 mm and the single hammer pressing amount is 28 mm.

[0070] (6) During the third feed, the continuous casting billet is not rotated and the feed amount is 240 mm. The cross-section of the die is adjusted between half anvil and full anvil: the width is 260 mm and the single hammer pressure is 70 mm. The intermediate billet is obtained.

[0071] (7) The intermediate billet is returned to the furnace, heated to 1145℃, kept warm for 3h, and the electro-hydraulic hammer is replaced with a flat anvil with an anvil width of 400mm, anvil length of 600mm, and chamfer radius of 10mm.

[0072] (8) The intermediate billet is taken out of the furnace and the wide surface is directly stretched using a flat anvil. The feed amount is 280 mm, the reduction amount is 45 mm, and the width is freely widened.

[0073] (9) In the second stretching, the intermediate blank is not turned over, the feed amount is 240mm, the pressing amount is 30mm, and the width is freely expanded.

[0074] (10) The final cross-sectional dimensions of the high-strength and high-toughness cold-working die flat steel product are: 65 mm (thickness) × 430 mm (width).

[0075] (11) The structure of the edge and center of the finished product is as follows Figure 5 and Figure 6 shown.

[0076] Example 2

[0077] This embodiment is produced using the die section and forging process designed by the present invention.

[0078] The details are as follows:

[0079] (1) The chemical composition of the cold working die steel used in the production of continuous casting billets is as follows: C: 0.95%; Si: 0.81%; Mn: 0.3%; P: 0.01%; S: 0.005%; Cr: 81%; Mo: 2.0%; V: 0.22%; Cu: 0.12%; Ni: 0.15%; the rest is Fe and unavoidable impurity elements.

[0080] (2) The width and height of the crystallizer are both 170 mm, the radius of the four corners is 60 mm, the side length is 50 mm, and the total length of the crystallizer is 1500 mm.

[0081] (3) The continuous casting billet has a fixed length of 7 meters and is directly fed into a walking beam heating furnace for heating in two sections. The first section is a preheating section with a heating temperature of 1135°C and a heating time of 3 hours. The second section is a soaking section with a heating temperature of 1143°C and a heating time of 1 hour.

[0082] (4) After the continuous casting billet leaves the heating furnace, the first half anvil is fed in, and the cross-sectional shape of the mold is adjusted to meet the single hammer pressing amount of 40 mm and the mold width is adjusted to 210 mm.

[0083] (5) In the second run, the continuous casting billet is rotated 90° and fed into the full anvil. The cross-sectional shape of the mold is adjusted: the width is 150 mm and the single hammer pressing amount is 25 mm.

[0084] (6) During the third feed, the continuous casting billet is not rotated and the feed amount is 250 mm. Between the half anvil and the full anvil, the cross-section of the mold is adjusted to 240 mm in width and 60 mm in single hammer reduction. The intermediate billet is obtained.

[0085] (7) The intermediate billet is returned to the furnace, heated to 1141 °C, kept warm for 3 h, and the electro-hydraulic hammer is replaced with a flat anvil with an anvil width of 400 mm, anvil length of 600 mm, and chamfer radius of 10 mm.

[0086] (8) The intermediate billet is taken out of the furnace and the wide surface is directly stretched using a flat anvil. The feed amount is 200 mm, the reduction amount is 40 mm, and the width is freely widened.

[0087] (9) In the second stretching, the intermediate blank is not turned over, the feed amount is 200mm, the pressing amount is 25mm, and the width is freely widened.

[0088] (10) The final cross-sectional dimensions of the high-strength and high-toughness cold-working die flat steel product are: 70 mm (thickness) × 405 mm (width).

[0089] (11) The structure of the edge and center of the finished product is as follows Figure 7 and Figure 8 shown.

[0090] The DC53 continuous casting method described in this invention is rarely reported publicly domestically or internationally. It represents a novel approach, encompassing the design of the cross-sectional shape of the continuous casting billet, the design of the forging tool, and the forging process. Its benefits include high continuous casting efficiency and high solidification quality, which is beneficial for flaw detection. The forging intermediate billet is simply lengthened and combined with an anvil, further improving internal quality.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing high-strength and high-toughness cold-working die flat steel, characterized in that: The high-strength and high-toughness cold-working die flat steel is composed of the following chemical components by mass percentage: C: 0.95~1.05%; Si: 0.8~1.2%; Mn: 0.3~0.6%; P≤0.03%; S≤0.005%; Cr: 8.0~9.0%; Mo: 2.0~2.3%; V: 0.2~0.4%; Cu: 0.1~0.3%; Ni: 0.1~0.3%; the balance is Fe and unavoidable impurity elements; The method for preparing the high-strength and high-toughness cold-working die flat steel comprises the following steps: S1. Design and process the drawing die; S2, feeding the continuous casting billet into a walking beam heating furnace and heating it in a two-stage heating method; S3. After the continuous casting billet is heated and discharged from the furnace, the continuous casting billet is fed into the first half anvil, the cross-sectional shape of the drawing die is adjusted, the width of the drawing die is adjusted, and the continuous casting billet is drawn for the first time using the drawing die; S4, rotating the continuous casting billet obtained in step S3 by 90 degrees, feeding the billet with a full anvil for a second time, adjusting the cross-sectional shape and width of the drawing die, and using the drawing die to draw the continuous casting billet for a second time; S5, the continuous casting billet obtained in step S4 is not rotated, and the continuous casting billet is fed for the third time, with a feeding amount of 240-250 mm. The cross-sectional shape and width of the drawing die are adjusted between the half anvil and the full anvil, and the continuous casting billet is drawn for the third time using the drawing die to obtain an intermediate billet; S6. Return the intermediate billet to the furnace, i.e., send it into a walking beam heating furnace for heating; replace the electro-hydraulic hammer with a flat anvil; S7, after the intermediate blank is heated in step S6, it is taken out of the furnace and the intermediate blank is directly stretched on the wide side using a flat anvil, with a feed amount of 200-300 mm and a reduction amount of 40-45 mm, and the width is freely widened; S8, the intermediate blank obtained in step S7 is stretched for the second time, the intermediate blank is not turned over, the feed amount is 200-250mm, the pressing amount is 25-35mm, and the width is freely widened; S9. Finally, high-strength and high-toughness cold-working die flat steel with a thickness of 65-70mm and a width of 400-450mm is obtained.

2. The method for preparing high-strength and high-toughness cold-working die flat steel according to claim 1, characterized in that: In step S1, the drawing die is a combined die, including an upper hammer head and a lower hammer head that are symmetrical in the upper and lower directions. Each hammer head is U-shaped, and the two hammer heads can be moved left and right by an electric worm mechanism to adjust the width left and right.

3. The method for preparing high-strength and high-toughness cold-working die flat steel according to claim 1 or 2, characterized in that: In step S1, the width adjustment range of the drawing die is 150-260 mm; the length of the hammer head working area is 300 mm.

4. The method for preparing high-strength and high-toughness cold-working die flat steel according to claim 1, characterized in that: In step S2, the width and height of the continuous casting billet are both 170 mm, the radius of the four fillets is 60 mm, the side length is 50 mm, and the fixed length of the continuous casting billet is 5 to 7 meters.

5. The method for preparing high-strength and high-toughness cold-working die flat steel according to claim 1 or 4, characterized in that: In step S2, the two-stage heating method is: first perform the first stage heating, i.e., the preheating stage, with a heating temperature of 1130~1140℃ and a heating time of 2-3h; then perform the second stage heating, i.e., the soaking stage, with a heating temperature of 1145±5℃ and a heating time of 1-1.5h.

6. The method for preparing high-strength and high-toughness cold-working die flat steel according to claim 1, characterized in that: In step S3, the cross-sectional shape of the drawing die is adjusted to meet the requirement of 40-50 mm for a single hammer press, and the width of the drawing die is adjusted to 210-220 mm; In step S4, the cross-sectional shape and width of the drawing die are adjusted to: the width is 150-160 mm, and the single hammer pressing amount is 25-30 mm; In step S5, the cross-sectional shape and width of the drawing die are adjusted to: the width is 240-260 mm, and the single hammer pressing amount is 60-70 mm.

7. The method for preparing high-strength and high-toughness cold-working die flat steel according to claim 1, characterized in that: In step S6, the heating temperature is 1140-1145° C., and the heat preservation time is 2.5-3 hours.

8. The method for preparing high-strength and high-toughness cold-working die flat steel according to claim 1 or 7, characterized in that: In step S6, the anvil width of the flat anvil is 400 mm, the anvil length is 600 mm, and the chamfer radius is 10 mm.

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