Method for improving compactness of square steel for deep drawing

Abstract

The invention discloses a method for improving the compactness of square steel for deep drawing, which adopts tundish induction heating and tundish temperature control within a reasonable range to ensure that the pulling speed is kept constant during casting and continuous casting at a lower degree of superheat, and adopts a continuous casting heavy pressure technology to improve the center porosity and shrinkage cavity of a casting blank; a BD cogging mill is adopted for large rolling reduction rolling, and the maximum single-pass rolling reduction is 100 mm; and isothermal operation is carried out in front of the fourth continuous rolling mill, only temperature measurement is needed, and the method is simple and easy to implement. According to the 154 mm deep drawing square steel produced through the technical scheme, the center porosity is smaller than or equal to 0.5 grade, the general porosity is 0 grade, the ingot segregation is 0 grade, and the residual shrinkage cavity is 0 grade, that is, no ingot segregation and residual shrinkage cavity exist, and ultrasonic flaw detection reaches A grade or above; and the high compactness requirement of the steel for deep drawing is met.

Description

Technical Field

[0001] The invention belongs to the technical field of deep drawing steel, and particularly relates to a method for improving the density of deep drawing square steel. Background Art

[0002] Deep drawing steel has high strength, high toughness and excellent elastic limit performance, can withstand extremely high pressure and impact loads, and has good wear resistance and corrosion resistance. In order to ensure the uniformity of deformation and surface quality of steel during deep drawing and avoid defects such as cracks and wrinkles, deep drawing steel usually requires high density; if there are defects such as looseness and pores in the steel, stress concentration will be formed during the deep drawing process, causing the steel plate to crack or deform unevenly, thus affecting the quality and performance of the product.

[0003] 154mm square steel requires a larger billet for rolling raw materials. During the solidification process of molten steel, large-sized billets have a large size, a long solidification time, and a large temperature gradient during the solidification process. The molten steel gradually solidifies from the outside to the inside, and the outside solidifies first to form a shell. When the internal molten steel solidifies later, it is easy to form defects such as looseness and shrinkage due to volume shrinkage and insufficient liquid metal supplementation, thus affecting the density. At the same time, due to the large size of 154mm square steel, the deformation force applied during the processing is difficult to evenly penetrate into the steel, resulting in insufficient densification of the internal organization and a low density pass rate. Summary of the invention

[0004] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a method for improving the density of square steel for deep drawing, so that 154mm square steel for deep drawing has no shrinkage cavity and segregation under low-magnification acid immersion inspection, and the ultrasonic flaw detection result is above Grade A.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides a method for improving the compactness of square steel for deep drawing, wherein the mass content of the components of the square steel for deep drawing is C: 0.56% to 0.61%, Si: 1.20% to 1.32%, Mn: 1.06% to 1.18%, P≤0.025%, S≤0.020%, Cr≤0.20%, Ni≤0.20%, Cu≤0.20%, and the rest is Fe and unavoidable impurities; the method comprises the following steps:

[0006] ①Continuous casting

[0007] The continuous casting process uses a 4-machine 4-stream arc continuous casting machine to continuously cast steel billets with a billet size of 390×480mm. The middle bag is inductively heated with a middle bag temperature of 1488℃~1492℃ and a casting speed of 0.40~0.50m / min. The continuous casting dynamic heavy pressure is used with a pressure reduction of 30~35mm and an actual billet size of 358×480mm.

[0008] ② Heating of ingot

[0009] It is heated by a walking beam heating furnace and adopts a cold charging process. The temperature of the preheating section is less than 650°C, the temperature of the second section is 850°C ~ 900°C, the temperature of the first section is 1190°C ~ 1220°C, the temperature of the soaking section is 1180°C ~ 1210°C, the insulation time of the soaking section is ≥ 2h, and the total heating time is ≥ 4h.

[0010] ③Rolling

[0011] High-pressure water descaling is used before rolling, and the descaling pressure is ≥28MPa; the BD billet mill adopts 9-pass reciprocating rolling, and the maximum single-pass reduction is 100mm. The rolling process is shown in Table 1.

[0012] Table 1 BD slab mill large reduction rolling process

[0013] Whether to turn steel path Rolling width / mm Height of rolled piece / mm Pressing amount / mm Remark Steel turning Incoming Materials 358 480 Steel turning 1 408 421 59 2 385 350 71 Steel turning 3 365 335 50 4 384 272 63 Steel turning 5 276 370 14 6 279 360 10 7 309 260 100 Big Pressure 8 313 246 14 Steel turning 9 270 232 81

[0014] In the above technical scheme, after passing through three 850mm rolling mills, "isothermal operation" is carried out before the fourth continuous rolling mill, and the surface temperature is reduced to below 950℃ before entering the continuous rolling mill for rolling. The rolling specification is 154mm, and the steel is immediately put into the pit for insulation after leaving the cooling bed. The pit entry temperature is ≤550℃, the pit exit temperature is ≤200℃, and the insulation time is ≥48h.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] ① The present invention adopts induction heating of the tundish, and ensures that the temperature of the tundish fluctuates within the optimal range by accurately controlling the temperature of the tundish, thereby achieving casting under low superheat conditions during continuous casting. This not only improves the casting quality, but also ensures the constancy of the casting speed during continuous casting. At the same time, combined with the continuous casting heavy pressure technology, the internal structure of the ingot is effectively improved, defects such as central looseness and shrinkage holes are significantly reduced, and the overall quality of the ingot is improved.

[0017] ② In order to further optimize the rolling process of steel, the BD billet mill was used for large reduction rolling, with the maximum single-pass reduction of 100mm, which greatly improved the rolling efficiency and material density. In particular, the innovative "isothermal operation" technology was implemented in front of the fourth continuous rolling mill. The operation is simple and fast, and only temperature measurement is required to ensure the stability of steel during the rolling process, providing an ideal material basis for subsequent processing.

[0018] ③ The quality indicators of the 154mm deep-drawing square steel produced based on the above technical solution have reached a relatively high level: the central porosity level is ≤0.5, the general porosity is 0, the ingot segregation and residual shrinkage are both 0, which completely eliminates the problems of ingot segregation and residual shrinkage. The results of ultrasonic flaw detection show that the quality of the steel reaches and exceeds the A-level standard, fully meeting the strict requirements of deep-drawing steel for high density, high strength and excellent surface quality, and providing related industries with excellent performance material solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a low-magnification structural picture of the square steel for deep drawing obtained in Example 1. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with specific examples, but the present invention is not limited in any way. To avoid redundant description, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0021] A method for improving the compactness of deep-drawing square steel, wherein the mass content of the deep-drawing square steel components is C: 0.56% to 0.61%, Si: 1.20% to 1.32%, Mn: 1.06% to 1.18%, P≤0.025%, S≤0.020%, Cr≤0.20%, Ni≤0.20%, Cu≤0.20%, and the rest is Fe and unavoidable impurities; the method comprises the following steps:

[0022] ①Continuous casting: 4-machine 4-strand arc continuous casting machine is used to continuously cast steel billets with a billet size of 390×480mm;

[0023] ② Billet heating: using walking beam heating furnace for heating and cold charging process;

[0024] ③Rolling: high-pressure water descaling before rolling, descaling pressure ≥ 28MPa; BD billet mill adopts 9-pass reciprocating rolling, with the maximum single-pass reduction of 100mm.

[0025] The matters not described in the following embodiments are the same as the description of the above specific implementation methods.

[0026] Example

[0027] A method for improving the compactness of deep-drawing square steel, the mass content of the main components of the deep-drawing square steel in the embodiment is shown in Table 2; the specific process method includes the following steps:

[0028] Table 2 Chemical composition of square steel for deep drawing in Example wt%

[0029] C Si Mn P S Cr Ni Cu Example 1 0.59 1.27 1.1 0.012 0.005 0.11 0.05 0.08 Example 2 0.59 1.26 1.09 0.013 0.006 0.17 0.05 0.08 Example 3 0.58 1.26 1.1 0.012 0.005 0.12 0.05 0.08

[0030] ①Continuous casting

[0031] In continuous casting, a 4-machine 4-stream arc continuous casting machine is used to continuously cast steel billets, with a billet shape of 390×480mm. Induction heating is used in the middle bag, the middle bag temperature is 1488℃~1492℃, and the casting speed is 0.40~0.50m / min. Dynamic heavy pressure is used for continuous casting, the pressure reduction is 32mm, and the actual billet shape is 358×480mm. The continuous casting process parameters of the embodiment are shown in Table 3.

[0032] Table 3 Continuous casting process parameters of the embodiment

[0033] Middle package temperature ℃ Pulling speed m / min Press down amount (mm) Example 1 1489～1492 0.45 32 Example 2 1488～1492 0.45 32 Example 3 1488～1492 0.45 32

[0034] ② Heating of ingot

[0035] The heating is carried out by a walking beam heating furnace, and the cold charging process is adopted, the preheating section temperature is less than 650°C, the second section temperature is 850°C to 900°C, the first section temperature is 1190°C to 1220°C, the soaking section temperature is 1180°C to 1210°C, the soaking section holding time is ≥2h, and the total heating time is ≥4h. The heating process parameters of the embodiment are shown in Table 4.

[0036] Table 4 Heating process parameters of the embodiment

[0037]

[0038] ③Rolling

[0039] High pressure water descaling is used before rolling, and the descaling pressure is ≥28MPa. The BD blanking mill adopts 9-pass reciprocating rolling, and the maximum single-pass reduction is 100mm; the rolling process is shown in Table 1. The rolling process parameters of the embodiment are shown in Table 5.

[0040] Table 5 Rolling process parameters of the embodiment

[0041] High-pressure water descaling pressure MPa Surface temperature after isothermal treatment ℃ Example 1 29 926 Example 2 29 932 Example 3 29 922

[0042] After passing through three 850mm rolling mills, the steel is subjected to "isothermal operation" in front of the fourth continuous rolling mill, and when the surface temperature drops below 950℃, it is rolled in the continuous rolling mill. The rolling specification is 154mm square, and the steel is immediately put into the pit for insulation after leaving the cooling bed. The exit temperature is ≤550℃, the exit temperature is ≤200℃, and the insulation time is ≥48h.

[0043] The ultrasonic test results of the deep drawing square steels obtained in Examples 1 to 3 are shown in Table 6. The macroscopic structure picture of the deep drawing square steel obtained in Example 1 is as follows: Figure 1 As shown, the central looseness is level 0.5, and the general looseness, ingot-shaped segregation and central segregation are all level 0.

[0044] Table 6 Ultrasonic test results of deep drawing square steel obtained in Examples 1 to 3

[0045]

[0046] For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for improving the density of square steel for deep drawing, characterized in that: The deep drawing square steel component mass content is C: 0.56% to 0.61%, Si: 1.20% to 1.32%, Mn: 1.06% to 1.18%, P≤0.025%, S≤0.020%, Cr≤0.20%, Ni≤0.20%, Cu≤0.20%, and the rest is Fe and unavoidable impurities; the method comprises the following steps: ①Continuous casting: 4-machine 4-strand arc continuous casting machine is used to continuously cast steel billets with a billet size of 390×480mm; ② Billet heating: using walking beam heating furnace for heating and cold charging process; ③Rolling: high-pressure water descaling before rolling, descaling pressure ≥ 28MPa; BD billet mill adopts 9-pass reciprocating rolling, with the maximum single-pass reduction of 100mm.

2. The method according to claim 1, characterized in that In step ①, the continuous casting adopts tundish induction heating, the tundish temperature is 1488°C to 1492°C, and the casting speed is 0.40 to 0.50 m / min.

3. The method according to claim 1, characterized in that The continuous casting in step ① adopts continuous casting dynamic heavy pressure, the pressure reduction is 30-35 mm, and the actual billet shape is 358×480 mm.

4. The method according to claim 1, characterized in that: In step ②, the preheating section temperature of the ingot is less than 650°C, the second section temperature is 850°C to 900°C, the first section temperature is 1190°C to 1220°C, the soaking section temperature is 1180°C to 1210°C, the soaking section insulation time is ≥2h, and the total heating time is ≥4h.

5. The method according to claim 1, characterized in that In step ③, after passing through three 850mm rolling mills, "isothermal operation" is performed before the fourth continuous rolling mill. When the surface temperature drops below 950°C, the steel sheet enters the continuous rolling mill for rolling.

6. The method according to claim 1, characterized in that In step ③, the rolling specification is 154mm, the steel is put into the pit for insulation after being put down from the cooling bed, the pit entry temperature is ≤550°C, the pit exit temperature is ≤200°C, and the insulation time is ≥48h.

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