Method for preventing 82B wire rod from brittle fracture during drawing

Abstract

The invention belongs to the technical field of steel rolling production, and particularly discloses a method for preventing an 82B wire rod from brittle fracture during drawing, which comprises the following steps: optimizing a steelmaking procedure, adding V in an original component system, and adjusting the content of each component, the adjusted molten steel component proportion is as follows: 0.80-0.83% of C, 0.18-0.28% of Si, 0.60-0.80% of Mn, less than or equal to 0.015% of P, less than or equal to 0.015% of S, 0.19-0.24% of Cr and 0.015-0.025% of V; the steel rolling procedure is optimized, the temperature in a heating furnace is increased, the temperature of a soaking section is adjusted to 1180-1220 DEG C from the temperature smaller than or equal to 1150 DEG C, the temperature of a preheating section is controlled to be smaller than or equal to 750 DEG C, the temperature of a heating section is controlled to be 1170-1210 DEG C, and the load of a finishing mill is reduced; an air cooling procedure is optimized, 15 cooling fans are started, the running power of the cooling fans is increased to 100%, the temperature of the steel wire rod reaching the lap joint point of the cooling fans is controlled to be 570-590 DEG C, a whole-line roller way is divided into 9 sections, the starting speed and the increasing speed of each section of steel wire rod guide roller way are controlled, and the cooling efficiency is ensured; and different rolling speeds are set according to different wire rod specifications.

Description

Technical Field

[0001] The invention relates to the technical field of steel rolling production, and in particular to a method for preventing brittle fracture during drawing of an 82B wire rod. Background Art

[0002] SWRH82B (abbreviated as 82B) high carbon steel wire rod is an important raw material for producing high-strength, large-size prestressed steel strands and wire ropes, and is widely used in cement products, bridges, nuclear power plants, high-rise large-span houses, highways and other construction fields. 82B wire rod has the characteristics of high tensile strength and good plasticity. In recent years, it has been increasingly valued as an economical and efficient wire rod and has been widely used in various downstream industries.

[0003] However, when producing 82B steel, if the composition, production process and cooling process are not properly controlled, the proeutectoid phase in the center of the wire rod - cementite will precipitate along the austenite grain boundary to form a closed network. Cementite has high hardness, poor plasticity, almost zero elongation and impact toughness. It is a hard and brittle structure that will embrittle the grain boundary. Microcracks are easily formed here during drawing, leading to stress concentration, hindering deformation of other parts, expanding along the grain boundary, and finally causing brittle pen cone fracture. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preventing brittle fracture during drawing of 82B wire rod, so as to solve the problem that it is difficult to accurately control the mixing ratio of different gases and the calorific value and pressure fluctuations of coal gas from different sources are large during actual production operation.

[0005] To achieve the above object, the basic solution provided by the present invention is: a method for preventing brittle fracture during drawing of 82B wire rod, comprising:

[0006] Optimize the steelmaking process, add V to the original composition system, and adjust the content of each component;

[0007] Optimize the steel rolling process, increase the temperature in the heating furnace, and reduce the load on the finishing mill;

[0008] Optimize the air cooling process, adjust the wind speed, air volume and operating power of the cooling fan, and control the temperature of the wire rod reaching the overlap point of the cooling fan at 570-590℃.

[0009] The principle and beneficial effect of the present invention are as follows: adding V to the steelmaking raw material composition, V has a certain tensile strength, adjusting the temperature in the heating furnace to a suitable temperature, which is conducive to the diffusion of alloy elements, the full diffusion and dissolution of V, can play the fine grain strengthening effect of V, improve the tensile strength of the wire rod, increase the opening degree of the fan, which is conducive to further cooling the wire rod, and the increase of components and the adjustment of the proportion in the steelmaking process are conducive to improving the production quality of the wire rod. Further optimization in the steel rolling process and the air cooling process can further improve the quality of the wire rod after the optimized composition, and improve the taper rate of the wire rod.

[0010] Option 2, which is the preferred option of the basic option, optimizes the steelmaking process in the following ways:

[0011] The Mn content in the composition system is adjusted from 0.75-0.85% to 0.60-0.80%, and the P content is adjusted from ≤0.02% to ≤0.015%;

[0012] The adjusted composition ratio of the molten steel is: C: 0.80-0.83%, Si: 0.18-0.28%, Mn: 0.60-0.80%, P≤0.015%, S≤0.015%, Cr: 0.19-0.24%, V: 0.015-0.025%.

[0013] When the Mn content is reduced to 0.60-0.80%, the tensile strength can be guaranteed after the V grain refinement effect is exerted, and there is room for reducing Mn, which can not only reduce the alloy cost, but also alleviate the C segregation caused by the segregation of manganese.

[0014] Scheme 3, which is the optimal choice of the basic scheme, optimizes the steel rolling process in the following specific ways:

[0015] By adjusting the gas and air pipelines, the temperature inside the heating furnace is increased, the temperature of the soaking section is raised from ≤1150℃ to 1180-1220℃, the temperature of the preheating section is controlled to ≤750℃, and the temperature of the heating section is controlled to 1170-1210℃ to ensure full diffusion of alloy elements;

[0016] The temperature of the wire rod during finishing rolling is controlled at 870-900°C, and the spinning temperature of the controlled cooling process after rolling is adjusted from 870±10°C to 870-920°C.

[0017] Adjusting the temperature in the heating furnace and the finishing rolling temperature not only controls the load of the finishing mill and protects the equipment, but also helps to control the production of coarse lamellar pearlite.

[0018] Solution 4 is the preferred solution of the basic solution. When optimizing the air cooling process, the maximum power of the 1-8 machine is 200kw, and the maximum power of the 8-15 machine is 90kw. The fan inverter is used to set the speed of each cooling fan to 1450r / min, and the air volume is adjusted to 240,000m 3 / h / unit, the operating power of the cooling fans is adjusted from the original 100% for 1-6 units, 60% for 7-10 units, and 100% for 11-15 units to 100% for all 1-15 units.

[0019] Scheme 5 is the best choice of Scheme 4. The rollers of the whole line are divided into 9 sections. The starting speed and increasing speed of the rollers of each section of the wire rod guide rollers are controlled to ensure the cooling efficiency. The specific control method is as follows:

[0020] The roller start speed of the φ8.0 wire rod is set to 0.9m / s, and starting from the second section, the incremental speed of each roller section is increased by 5% based on the speed of the previous roller section;

[0021] The roller start speed of the φ10.0 wire rod is set to 0.8m / s, and starting from the second section, the incremental speed of each roller section is increased by 5% based on the speed of the previous roller section;

[0022] The roller start speed of the φ12.0 wire rod is set to 0.6m / s, and starting from the second section, the incremental speed of each roller section is increased by 6% based on the speed of the previous roller section;

[0023] The starting speed of the roller for the φ12.5 wire rod is set to 0.5 m / s, and starting from the second section, the incremental speed of each roller section is increased by 5% based on the speed of the previous roller section.

[0024] Scheme 6: This is the optimal solution for the basic scheme. Different rolling speeds are set according to different wire rod specifications. The specific setting methods are as follows:

[0025] For Φ8.0 wire rod, set the rolling speed to 68±1m / s;

[0026] For φ10.0 wire rod, set the rolling speed to 50±1m / s;

[0027] For φ12.0 wire rod, set the rolling speed to 30±1m / s;

[0028] For φ12.5 wire rod, the rolling speed is set to 24±1m / s.

[0029] Large diameter wire rods dissipate heat relatively slowly and have good temperature stability, allowing the rolling speed to be increased to improve production efficiency. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below through specific embodiments:

[0031] Example

[0032] A method for preventing brittle fracture of 82B wire rod during drawing, comprising:

[0033] Optimize the steelmaking process, add V to the original component system, adjust the content of each component, and optimize the steelmaking process in the following specific ways:

[0034] The content of Mn in the composition system is adjusted from 0.75-0.85% to 0.60-0.80%, and the content of P is adjusted from ≤0.02% to ≤0.015%;

[0035] The adjusted composition ratio of molten steel is: C: 0.80-0.83%, Si: 0.18-0.28%, Mn: 0.60-0.80%, P≤0.015%, S≤0.015%, Cr: 0.19-0.24%, V: 0.015-0.025%:

[0036] Optimize the steel rolling process, increase the temperature in the heating furnace, reduce the load of the finishing mill, and optimize the steel rolling process in the following specific ways:

[0037] By adjusting the gas and air pipelines, the temperature inside the heating furnace is increased, the temperature of the soaking section is adjusted from ≤1150℃ to 1180-1220℃, the temperature of the preheating section is controlled to ≤750℃, and the temperature of the heating section is controlled to 1170-1210℃ to ensure full diffusion of alloy elements;

[0038] The temperature of the wire rod during finishing rolling is controlled at 870-900℃, and the wire drawing temperature of the controlled cooling process after rolling is adjusted from 870±10℃ to 870-920℃;

[0039] Optimize the air cooling process, adjust the wind speed, air volume and operating power of the cooling fan, and control the temperature of the wire rod reaching the overlap point of the cooling fan at 570-590℃. When optimizing the air cooling process, the maximum power of the 1-8 machine is 200kw, and the maximum power of the 8-15 machine is 90kw. Use the fan inverter to set the speed of each cooling fan to 1450r / min, and the air volume is adjusted to 240,000m 3 / h / unit, the operating power of cooling fans was adjusted from 100% for 1-6 units, 60% for 7-10 units, and 100% for 11-15 units to 100% for all 1-15 units;

[0040] The rollers of the whole line are divided into 9 sections, and the starting speed and increasing speed of the rollers of each section of the wire rod guide rollers are controlled to ensure the cooling efficiency. The specific control method is as follows:

[0041] The roller start speed of the φ8.0 wire rod is set to 0.9m / s, and starting from the second section, the incremental speed of each roller section is increased by 5% based on the speed of the previous roller section;

[0042] The roller start speed of the φ10.0 wire rod is set to 0.8m / s, and starting from the second section, the incremental speed of each roller section is increased by 5% based on the speed of the previous roller section;

[0043] The roller start speed of the φ12.0 wire rod is set to 0.6m / s, and starting from the second section, the incremental speed of each roller section is increased by 6% based on the speed of the previous roller section;

[0044] The roller start speed of the φ12.5 wire rod is set to 0.5m / s, and starting from the second section, the incremental speed of each roller section is increased by 5% based on the speed of the previous roller section;

[0045] Different rolling speeds are set according to different wire rod specifications. The specific setting methods are as follows:

[0046] For Φ8.0 wire rod, set the rolling speed to 68±1m / s;

[0047] For φ10.0 wire rod, set the rolling speed to 50±1m / s;

[0048] For φ12.0 wire rod, set the rolling speed to 30±1m / s;

[0049] For φ12.5 wire rod, the rolling speed is set to 24±1m / s.

[0050] The specific implementation of this embodiment:

[0051] Through metallographic and electron microscope analysis of 82B wire rod broken samples, review of process documents, face-to-face communication, on-site process execution record review, etc., it is concluded that the main process and quality problems of 82B wire rod pen tip breaking are that the net C detected in the three broken samples is level 3, level 3.5 and level 4 respectively. Among them, the electron microscope analysis of one broken sample contains more Ca, Mg, Na, and K, indicating that there is slag rolling in continuous casting, and the abnormal billet is not removed. The metallographic analysis results show that the main reason for the wire rod cold drawing pen tip breaking is that the net carbon level is too high, so a method to prevent brittle fracture during 82B wire rod drawing is introduced as follows:

[0052] 1. Optimize the steelmaking process, add V to the original component system, adjust the content of each component, and optimize the steelmaking process in the following specific ways:

[0053] The Mn content in the composition system is adjusted from 0.75-0.85% to 0.60-0.80%, and the P content is adjusted from ≤0.02% to ≤0.015%;

[0054] The adjusted composition ratio of molten steel is: C: 0.80-0.83%, Si: 0.18-0.28%, Mn: 0.60-0.80%, P≤0.015%, S≤0.015%, Cr: 0.19-0.24%, V: 0.015-0.025%. Low N carburizer is used in steelmaking, and N≤0.005% is specified. N will reduce the drawing performance of wire rod and extend the aging time. Controlling N is beneficial to improving the drawing performance of wire rod. Further reducing the upper limit of P will increase the cold brittleness of steel. Controlling P is beneficial to the drawing performance of wire rod in winter.

[0055] 2. Optimize the steel rolling process, increase the temperature in the heating furnace, and reduce the load of the finishing mill. The specific ways to optimize the steel rolling process are as follows:

[0056] By adjusting the gas and air pipelines, the temperature inside the heating furnace is increased, the temperature of the soaking section is adjusted from ≤1150℃ to 1180-1220℃, the temperature of the preheating section is controlled to ≤750℃, and the temperature of the heating section is controlled to 1170-1210℃ to ensure full diffusion of alloy elements;

[0057] The finishing rolling temperature is controlled at 870-900℃, and the wire drawing temperature of the post-rolling controlled cooling process is adjusted from 870±10℃ to 870-920℃; higher temperature is conducive to the diffusion of alloy elements. Full diffusion and dissolution of V can play the role of V in fine grain strengthening and improve the tensile strength of wire rod; full diffusion of manganese elements makes the composition uniform, prevents C segregation caused by manganese segregation, and reduces the C level of the mesh.

[0058] 3. Optimize the air cooling process, adjust the wind speed, air volume and operating power of the cooling fan, and control the temperature of the wire rod reaching the overlap point of the cooling fan at 570-590℃. The specific optimization process is as follows:

[0059] The fan opening state is divided into two states: summer state and winter state. 15 fans are set, the maximum power of fans 1-8 is 200kw, and the maximum power of fans 8-15 is 90kw. The fan inverter is used to set the speed of each cooling fan to 1450r / min, and the air volume is adjusted to 240,000m 3 / h / unit. In summer, the operating power of the cooling fans is adjusted from the original 1-6 units at 100%, 7-10 units at 60%, and 11-15 units at 100% to 1-15 units at 100%. In winter, due to the low outside temperature, units 14 and 15 can be closed, and units 1-6 can be opened at 100%, units 7-10 at 60%, and units 11-13 at 100%. When controlling the outlet fan, the overlap point temperature range can be 570-590℃.

[0060] The rollers of the whole line are arranged by a series of high temperature resistant cast iron rollers and installed on the bearing seat. The whole line is divided into 9 sections with a length of 101 meters. Each section of the roller can be driven separately. According to the different properties of steel, it can be transported and cooled at different speeds. There are 18 roller motors with a motor power of 22kw and a speed of 1470r / min. The starting speed and the increasing speed of the rollers of each section of the wire rod guide roller are controlled to ensure the cooling efficiency, and different rolling speeds are set according to different wire rod specifications. The specific control method is shown in Table 1:

[0061] Table 1: Speed ​​setting standards for wire rods of different specifications

[0062] Specifications (mm) Roller start speed Roller increasing speed Rolling speed φ8.0 0.9m / s 5％ 68±1m / s φ10.0 0.8m / s 5％ 50±1m / s φ12.0 0.6m / s 6％ 30±1m / s φ12.5 0.5m / s 5％ 24±1m / s

[0063] The roller start speed of the φ8.0 wire rod is set to 0.9m / s. Starting from the second section, the incremental speed of each roller section is increased by 5% based on the speed of the previous roller section, and the rolling speed is set to 68±1m / s.

[0064] The roller start speed of the φ10.0 wire rod is set to 0.8m / s. Starting from the second section, the incremental speed of each roller section is increased by 5% based on the speed of the previous roller section, and the rolling speed is set to 50±1m / s.

[0065] The roller start speed of the φ12.0 wire rod is set to 0.6m / s. Starting from the second section, the incremental speed of each roller section is increased by 6% based on the speed of the previous roller section, and the rolling speed is set to 30±1m / s.

[0066] The roller starting speed of the φ12.5 wire rod is set to 0.5m / s. Starting from the second section, the incremental speed of each roller section is increased by 5% based on the speed of the previous roller section, and the rolling speed is set to 24±1m / s.

[0067] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preventing brittle fracture of 82B wire rod during drawing, characterized in that: include: Optimize the steelmaking process, add V to the original composition system, and adjust the content of each component; Optimize the steel rolling process, increase the temperature in the heating furnace, and reduce the load on the finishing mill; Optimize the air cooling process, adjust the wind speed, air volume and operating power of the cooling fan, and control the temperature of the wire rod reaching the overlap point of the cooling fan at 570-590℃.

2. A method for preventing brittle fracture of 82B wire rod during drawing according to claim 1, characterized in that: The specific ways to optimize the steelmaking process are as follows: The Mn content in the composition system is adjusted from 0.75-0.85% to 0.60-0.80%, and the P content is adjusted from ≤0.02% to ≤0.015%; The adjusted composition ratio of the molten steel is: C: 0.80-0.83%, Si: 0.18-0.28%, Mn: 0.60-0.80%, P≤0.015%, S:≤0.015%, Cr: 0.19-0.24%, V: 0.015-0.025%.

3. A method for preventing brittle fracture of 82B wire rod during drawing according to claim 1, characterized in that: The specific ways to optimize the steel rolling process are as follows: By adjusting the gas and air pipelines, the temperature inside the heating furnace is increased, the temperature of the soaking section is adjusted from ≤1150℃ to 1180-1220℃, the temperature of the preheating section is controlled to ≤750℃, and the temperature of the heating section is controlled to 1170-1210℃ to ensure full diffusion of alloy elements; The temperature of the wire rod during finishing rolling is controlled at 870-900°C, and the spinning temperature of the controlled cooling process after rolling is adjusted from 870±10°C to 870-920°C.

4. A method for preventing brittle fracture of 82B wire rod during drawing according to claim 1, characterized in that: When optimizing the air cooling process, the maximum power of the 1-8 machine is 200kw, and the maximum power of the 8-15 machine is 90kw. The fan inverter is used to set the speed of each cooling fan to 1450r / min, and the air volume is adjusted to 240,000m 3 / h / unit, the operating power of the cooling fans is adjusted from the original 100% for 1-6 units, 60% for 7-10 units, and 100% for 11-15 units to 100% for all 1-15 units.

5. A method for preventing brittle fracture of 82B wire rod during drawing according to claim 4, characterized in that: The rollers of the whole line are divided into 9 sections, and the starting speed and increasing speed of the rollers of each section of the wire rod guide rollers are controlled to ensure the cooling efficiency. The specific control method is as follows: The roller start speed of the φ8.0 wire rod is set to 0.9m / s, and starting from the second section, the incremental speed of each roller section is increased by 5% based on the speed of the previous roller section; The roller start speed of the φ10.0 wire rod is set to 0.8m / s, and starting from the second section, the incremental speed of each roller section is increased by 5% based on the speed of the previous roller section; The roller start speed of the φ12.0 wire rod is set to 0.6m / s, and starting from the second section, the incremental speed of each roller section is increased by 6% based on the speed of the previous roller section; The starting speed of the roller for the φ12.5 wire rod is set to 0.5 m / s, and starting from the second section, the incremental speed of each roller section is increased by 5% based on the speed of the previous roller section.

6. A method for preventing brittle fracture of 82B wire rod during drawing according to claim 1, characterized in that: Different rolling speeds are set according to different wire rod specifications. The specific setting methods are as follows: For Φ8.0 wire rod, set the rolling speed to 68±1m / s; For φ10.0 wire rod, set the rolling speed to 50±1m / s; For φ12.0 wire rod, set the rolling speed to 30±1m / s; For φ12.5 wire rod, the rolling speed is set to 24±1m / s.