Electrode steel with ultra-low coefficient of thermal expansion and method for manufacturing same

Abstract

The application belongs to the technical field of electrode steel, and discloses an electrode steel with ultra-low thermal expansion coefficient and a manufacturing method thereof, wherein the chemical components and mass percentage contents of the electrode steel include C: 0.0005% to 0.0020%, Si: 0.002% to 0.005%, Mn: 0.004% to 0.008%, P≤0.006%, S≤0.004%, O≤0.0006%, and the rest is Fe and inevitable impurities. The application precisely controls the content of each component in the steel, reduces the influence of impurity elements, harmful gases and non-metallic inclusions on the increase of the thermal expansion coefficient, controls the heating, rolling and cooling steps to avoid the increase of the thermal expansion coefficient caused by the uneven structure of the finished material, regulates the grain to improve the material strength, makes up for the problem of low strength caused by low alloy content in the steel, and reduces the thermal expansion coefficient to the maximum extent while meeting the mechanical performance.

Description

Technical Field

[0001] This invention belongs to the field of electrode steel technology, specifically relating to an electrode steel with an ultra-low coefficient of thermal expansion and its manufacturing method. Background Technology

[0002] Electrode steel is used as the cathode conductive material in the electrolytic aluminum process. The electrolytic reaction temperature is as high as 950℃~970℃. The electrode steel is required to have a low coefficient of thermal expansion to ensure the dimensional and structural stability of the electrolytic cell and improve its service life.

[0003] The steel currently used for electrolytic cells is usually Q235 or Q195 low-carbon steel. When the electrolysis reaction temperature is high, the coefficient of thermal expansion of these ordinary low-carbon steels increases, which will cause problems such as poor structural stability of the electrolytic cell and reduced service life. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology by providing an electrode steel with an ultra-low coefficient of thermal expansion and a method for manufacturing the same. This method precisely controls the content of each component in the steel, reduces the influence of impurity elements, harmful gases and non-metallic inclusions on the coefficient of thermal expansion, and obtains an electrode steel with an ultra-low coefficient of thermal expansion.

[0005] To solve the technical problem proposed in this invention, this invention provides an electrode steel with an ultra-low coefficient of thermal expansion, the chemical composition and mass percentage content of which include: C: 0.0005%~0.0020%, Si: 0.002%~0.005%, Mn: 0.004%~0.008%, P≤0.006%, S≤0.004%, O≤0.0006%, with the remainder being Fe and unavoidable impurities.

[0006] Preferably, the chemical composition and mass percentage content of the electrode steel include: C: 0.0005%~0.0015%, Si: 0.002%~0.005%, Mn: 0.004%~0.008%, P≤0.005%, S≤0.003%, O≤0.0005%, with the remainder being Fe and unavoidable impurities.

[0007] In the above scheme, the electrode steel has a tensile strength ≥ 270 MPa and a resistivity ≤ 1.25 × 10⁻⁶. -7 Ω·m, coefficient of thermal expansion ≤10.5×10 -6 .

[0008] The present invention also provides a method for manufacturing electrode steel with ultra-low coefficient of thermal expansion, the steps of which include molten iron pretreatment, converter smelting, RH vacuum treatment, continuous casting, heating, rolling and cooling.

[0009] In the above scheme, the molten iron pretreatment adopts the KR desulfurization method, and the S content of the molten iron after treatment is ≤0.002%.

[0010] Furthermore, the pretreatment of molten iron uses activated lime as a desulfurizing agent, and the amount of activated lime added is 9.5 to 13.5 kg / t of molten iron.

[0011] In the above scheme, the converter smelting adopts the "double-connection method". Converter 1 is loaded with molten iron and scrap steel for deSi and deP removal. The final treatment result is Si≤0.001% and P≤0.005%. After tapping the iron and dumping the slag, the molten iron is loaded into converter 2 for deC removal. The final treatment result is C≤0.05%.

[0012] Furthermore, the slag basicity of converter 1 is 2.8 to 3.5, the FeO content in the slag is 15% to 20%, and the tapping temperature is 1465 to 1510℃.

[0013] Furthermore, the slag basicity of the converter 2 is 3.8 to 4.5, the FeO content in the slag is ≤25%, and the tapping temperature is 1620 to 1650℃.

[0014] In the above scheme, the vacuum degree of the RH vacuum treatment is ≤20Pa, the deep decarburization time is ≥18min, and the O content of the molten steel after treatment is ≤0.0006%.

[0015] In the above scheme, the cross-sectional dimensions of the continuously cast billet are 200-380mm in height and 200-420mm in width.

[0016] In the above scheme, the billet casting speed of continuous casting is 0.45 to 0.65 m / min, the superheat of molten steel in the tundish is 20 to 40°C, and the billet solidification end reduction is 12 to 16 mm.

[0017] In the above scheme, the billet heating temperature in the heating process is 1050-1150℃, and the heating time is 180-200min.

[0018] In the above scheme, the rolling process includes roughing and finishing, with the roughing start temperature ≥980℃ and the finishing finish temperature ≥900℃.

[0019] In the above scheme, the cooling is jet cooling, and the cooling rate is 3.0 to 5.0℃ / s.

[0020] The technical concept of this invention is as follows:

[0021] The reason why the main chemical components of steel are controlled to be C: 0.0005%~0.0015%, Si: 0.002%~0.005%, and Mn: 0.004%~0.008% is that reducing the content of C, Si, and Mn elements in steel can increase the melting point of steel. Correspondingly, the interatomic interaction force in steel is enhanced, and the thermal expansion coefficient of the metallic material is reduced. Setting a lower limit is to ensure that the steel has a certain strength and ensures structural stability during use.

[0022] The reason why harmful elements are controlled to P≤0.006%, S≤0.004%, and O≤0.0006% in this invention is that harmful elements will generate non-metallic inclusions with a larger coefficient of thermal expansion than metallic materials and dissolve in the material. Therefore, deeply removing the content of these elements can reduce the coefficient of thermal expansion of steel materials.

[0023] The reason why the initial rolling temperature and final rolling temperature are controlled as follows in this invention: the billet heating temperature is 1050-1150℃, the rough rolling initial rolling temperature is ≥980℃, and the finish rolling final rolling temperature is ≥900℃, is to ensure that the steel material is always at the austenitizing temperature during the rolling process, avoid rolling in the two-phase region, eliminate rolling cracking defects caused by the difference in thermal expansion coefficients of austenite and ferrite, and also avoid the problem of increased thermal expansion coefficient caused by this.

[0024] The reason why the post-rolling cooling is controlled by air jet cooling with a cooling rate of 3.0 to 5.0℃ / s is that low alloying element content in the material will affect its strength performance. Rapid cooling can make the grains finer and improve the strength of the material, making up for the problem of low strength caused by low alloying content in the steel, and giving the material better mechanical performance.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] In the design of steel composition, this invention minimizes the presence of elements other than Fe in the steel, reducing the impact of impurities, harmful gases, and non-metallic inclusions on the increase in the coefficient of thermal expansion. Furthermore, through the manufacturing method of this invention, the content of each component in the steel is precisely controlled to meet design requirements. At the same time, by controlling the heating, rolling, and cooling steps, the invention avoids the increase in the coefficient of thermal expansion caused by uneven microstructure of the finished material, and regulates the grain size to improve the material strength. This compensates for the low strength caused by low alloy content in the steel, enabling the steel to meet mechanical performance requirements while minimizing the coefficient of thermal expansion. Detailed Implementation

[0027] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0028] Example 1

[0029] An electrode steel with an ultra-low coefficient of thermal expansion has the following chemical composition and mass percentage content: C: 0.0009%, Si: 0.005%, Mn: 0.008%, P: 0.005%, S: 0.003%, O: 0.0004%, with the remainder being Fe and unavoidable impurities. Its manufacturing method includes the following steps:

[0030] 1) Hot metal pretreatment: KR desulfurization method is adopted, and active lime is added as desulfurizing agent. The amount of active lime added is 12.3 kg / t hot metal. The S content of hot metal after treatment is 0.001%.

[0031] 2) Converter smelting: The "double-running method" is adopted. Converter 1 is charged with molten iron and scrap steel for deSi and deP removal. The slag basicity is 3.0, the FeO content in the slag is 18%, the tapping temperature is 1493℃, and the Si content at the end of the treatment is 0.001% and the P content is 0.003%. After tapping and slag removal, the molten iron is charged into Converter 2 for deC removal. The slag basicity is 3.9, the FeO content in the slag is 15%, the tapping temperature is 1645℃, and the C content at the end of the treatment is 0.03%.

[0032] 3) RH vacuum treatment: control the vacuum degree to 9Pa, the deep decarburization time to 23min, and the O content of the molten steel at the end of the treatment is 0.0003%;

[0033] 4) Continuous casting: Molten steel is continuously cast into billets with a cross-sectional dimension of 273 (height) × 385 (width) mm, a casting speed of 0.65 m / min, a superheat of molten steel in the tundish of 26℃, and a reduction of 15 mm at the end of solidification of the billet.

[0034] 5) Heating: The billet is heated to 1055℃ for 185 minutes;

[0035] 6) Rolling: including roughing and finishing rolling, with a roughing rolling start temperature of 1015℃ and a finishing rolling finish temperature of 918℃;

[0036] 7) Cooling: After rolling, the steel is cooled by air spray at a rate of 3.5℃ / s to obtain electrode steel with an ultra-low coefficient of thermal expansion.

[0037] Example 2

[0038] An electrode steel with an ultra-low coefficient of thermal expansion has the following chemical composition and mass percentage content: C: 0.0014%, Si: 0.004%, Mn: 0.006%, P: 0.004%, S: 0.002%, O: 0.0005%, with the remainder being Fe and unavoidable impurities. Its manufacturing method includes the following steps:

[0039] 1) Hot metal pretreatment: KR desulfurization method is adopted, and active lime is added as desulfurizing agent. The amount of active lime added is 11 kg / t hot metal. The S content of hot metal after treatment is 0.001%.

[0040] 2) Converter smelting: The "double process" is adopted. Converter 1 is charged with molten iron and scrap steel for deSi and deP removal. The slag basicity is 3.2, the FeO content in the slag is 19%, the tapping temperature is 1475℃, and the Si content at the end of the treatment is 0.0009% and the P content is 0.004%. After tapping and slag removal, the molten iron is charged into Converter 2 for deC removal. The slag basicity is 4.1, the FeO content in the slag is 17%, the tapping temperature is 1628℃, and the C content at the end of the treatment is 0.04%.

[0041] 3) RH vacuum treatment: control the vacuum degree at 14Pa, the deep decarburization time at 19min, and the O content of the molten steel at the end of the treatment is 0.0004%;

[0042] 4) Continuous casting: Molten steel is continuously cast into billets with a cross-sectional size of 277 (height) × 382 (width) mm, a casting speed of 0.60 m / min, a superheat of molten steel in the tundish of 28℃, and a reduction of 12 mm at the end of solidification of the billet.

[0043] 5) Heating: The billet is heated to 1095℃ for 190 minutes;

[0044] 6) Rolling: including roughing and finishing rolling, with a roughing rolling start temperature of 1024℃ and a finishing rolling finish temperature of 923℃;

[0045] 7) Cooling: After rolling, the steel is cooled by air spray at a rate of 4.0℃ / s to obtain electrode steel with an ultra-low coefficient of thermal expansion.

[0046] Example 3

[0047] An electrode steel with an ultra-low coefficient of thermal expansion has the following chemical composition and mass percentage content: C: 0.0019%, Si: 0.004%, Mn: 0.006%, P: 0.004%, S: 0.002%, O: 0.0005%, with the remainder being Fe and unavoidable impurities. Its manufacturing method includes the following steps:

[0048] 1) Hot metal pretreatment: KR desulfurization method is adopted, and active lime is added as desulfurizing agent. The amount of active lime added is 9.8 kg / t hot metal. The S content of hot metal after treatment is 0.001%.

[0049] 2) Converter smelting: The "double process" is adopted. Converter 1 is charged with molten iron and scrap steel for deSi and deP removal. The slag basicity is 3.3, the FeO content in the slag is 17%, the tapping temperature is 1479℃, and the Si content at the end of the treatment is 0.001% and the P content is 0.003%. After tapping and slag removal, the molten iron is charged into Converter 2 for deC removal. The slag basicity is 4.2, the FeO content in the slag is 15%, the tapping temperature is 1635℃, and the C content at the end of the treatment is 0.03%.

[0050] 3) RH vacuum treatment: control the vacuum degree to 5Pa, the deep decarburization time to 20min, and the O content of the molten steel at the end of the treatment is 0.0004%;

[0051] 4) Continuous casting: Molten steel is continuously cast into billets with a cross-sectional dimension of 274 (height) × 384 (width) mm, a casting speed of 0.62 m / min, a superheat of molten steel in the tundish of 30℃, and a reduction of 14 mm at the end of solidification of the billet.

[0052] 5) Heating: The billet is heated to 1107℃ for 195 minutes;

[0053] 6) Rolling: including roughing and finishing rolling, with a roughing rolling start temperature of 1035℃ and a finishing rolling finish temperature of 931℃;

[0054] 7) Cooling: After rolling, the steel is cooled by air spray at a rate of 3.6℃ / s to obtain electrode steel with an ultra-low coefficient of thermal expansion.

[0055] Example 4

[0056] An electrode steel with an ultra-low coefficient of thermal expansion has the following chemical composition and mass percentage content: C: 0.0012%, Si: 0.003%, Mn: 0.005%, P: 0.006%, S: 0.004%, O: 0.0006%, with the remainder being Fe and unavoidable impurities. Its manufacturing method includes the following steps:

[0057] 1) Hot metal pretreatment: KR desulfurization method is adopted, and active lime is added as desulfurizing agent. The amount of active lime added is 13.2 kg / t hot metal. The S content of hot metal after treatment is 0.001%.

[0058] 2) Converter smelting: The "double process" is adopted. Converter 1 is charged with molten iron and scrap steel for deSi and deP removal. The slag basicity is 3.1, the FeO content in the slag is 15%, the tapping temperature is 1503℃, and the Si content at the end of the treatment is 0.001% and the P content is 0.005%. After tapping and slag removal, the molten iron is charged into Converter 2 for deC removal. The slag basicity is 4.0, the FeO content in the slag is 18%, the tapping temperature is 1637℃, and the C content at the end of the treatment is 0.02%.

[0059] 3) RH vacuum treatment: control the vacuum degree to 8Pa, the deep decarburization time to 24min, and the O content of the molten steel at the end of the treatment is 0.0005%;

[0060] 4) Continuous casting: Molten steel is continuously cast into billets with a cross-sectional dimension of 275 (height) × 383 (width) mm, a casting speed of 0.62 m / min, a superheat of molten steel in the tundish of 30℃, and a reduction of 13 mm at the end of solidification of the billet.

[0061] 5) Heating: The billet is heated to 1075℃ for 186 minutes;

[0062] 6) Rolling: including roughing and finishing rolling, with a roughing rolling start temperature of 1013℃ and a finishing rolling finish temperature of 914℃;

[0063] 7) Cooling: After rolling, the steel is cooled by air spray at a rate of 3.4℃ / s to obtain electrode steel with an ultra-low coefficient of thermal expansion.

[0064] Comparative Example 1

[0065] Comparative Example 1 is Q195 low-carbon steel, whose chemical composition and mass percentage content include: C: 0.15%, Si: 0.39%, Mn: 0.23%, P: 0.012%, S: 0.009%.

[0066] Comparative Example 2

[0067] Comparative Example 2 is Q195 low-carbon steel, whose chemical composition and mass percentage content include: C: 0.16%, Si: 0.24%, Mn: 0.43%, P: 0.014%, S: 0.012%.

[0068] The tensile strength, resistivity, and coefficient of thermal expansion of the steels in Examples 1-4 and Comparative Examples 1-2 were tested. The coefficient of thermal expansion was measured as the average linear expansion coefficient at 20-950℃ after the steels were rolled into 160×160mm square steel. The results are shown in Table 1.

[0069] Table 1

[0070] Item Coefficient of thermal expansion Resistivity (Ω·m) Tensile strength (MPa) Example 1 10.4 x 10 -6 ]] 1.17 x 10 -7 ]] 287 Example 2 9.6 x 10 -6 ]] 1.09 x 10 -7 ]] 292 Example 3 9.8 x 10 -6 ]] 1.12 x 10 -7 ]] 286 Example 4 9.9 x 10 -6 ]] 1.14 x 10 -7 ]]> 289 Comparative Example 1 13.6 x 10 -6 ]]> 1.54 x 10 -7 ]]> 381 Comparative Example 2 14.1 x 10 -6 ]] 1.56 x 10 -7 ]] 379

[0071] Table 1 shows that the electrode steel of the present invention has a tensile strength of ≥270MPa, which meets the mechanical performance requirements of electrode steel. On this basis, the coefficient of thermal expansion is reduced by about 30% compared with Q195 low carbon steel, which improves the structural stability during use. At the same time, the resistivity is also significantly reduced, and the conductivity is further improved.

[0072] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing electrode steel with an ultra-low coefficient of thermal expansion, characterized in that, Includes the following steps: 1) Hot metal pretreatment: KR desulfurization method is adopted, and the sulfur content of the hot metal after treatment is ≤0.002%; 2) Converter smelting: A double-unit method is adopted. In converter 1, molten iron and scrap steel are charged for deSi and deP removal. The slag basicity is 2.8~3.5, the FeO content in the slag is 15%~20%, and the tapping temperature is 1465~1510℃. The final treatment result is Si≤0.001% and P≤0.005%. After tapping and slag removal, the molten iron is charged into converter 2 for deC removal. The slag basicity is 3.8~4.5, the FeO content in the slag is ≤25%, and the tapping temperature is 1620~1650℃. The final treatment result is C≤0.05%. 3) RH vacuum treatment: vacuum degree ≤20Pa, deep decarburization time ≥18min, and O in molten steel after treatment ≤0.0006%; 4) Continuous casting and heating: molten steel is continuously cast into billets, with a casting speed of 0.45~0.65m / min, a superheat of molten steel in the tundish of 20~40℃, and a reduction of 12~16mm at the end of solidification of the billet; the billet is heated at a temperature of 1050~1150℃ for a time of 180~200min. 5) Rolling: including roughing and finishing rolling, with a roughing rolling start temperature ≥980℃ and a finishing rolling finish temperature ≥900℃; 6) Cooling: After rolling, air is sprayed for cooling at a rate of 3.0~5.0℃ / s to obtain electrode steel with an ultra-low coefficient of thermal expansion; The chemical composition and mass percentage content of the electrode steel include: C: 0.0005%~0.0020%, Si: 0.002%~0.005%, Mn: 0.004%~0.008%, P≤0.006%, S≤0.004%, O≤0.0006%, with the remainder being Fe and unavoidable impurities; The electrode steel has a tensile strength ≥270MPa and a resistivity ≤1.25×10⁻⁶. -7 Ω·m, coefficient of thermal expansion ≤10.5×10 -6 .

2. The method for preparing the electrode steel with an ultra-low coefficient of thermal expansion according to claim 1, characterized in that, The chemical composition and mass percentage content of the electrode steel include: C: 0.0005%~0.0015%, Si: 0.002%~0.005%, Mn: 0.004%~0.008%, P≤0.005%, S≤0.003%, O≤0.0005%, with the remainder being Fe and unavoidable impurities.

3. The method for preparing electrode steel with an ultra-low coefficient of thermal expansion according to claim 1, characterized in that, The cross-sectional dimensions of the continuously cast billet are 200~380mm in height and 200~420mm in width.

4. The method for preparing electrode steel with an ultra-low coefficient of thermal expansion according to claim 1, characterized in that, The pretreatment of molten iron uses active lime as a desulfurizing agent, with an addition amount of 9.5~13.5 kg / t of molten iron.