Immersion device and method for calcium and magnesium treatment of free-cutting non-quenched and tempered steel

Abstract

The invention discloses an immersion device and method for calcium and magnesium treatment of free-cutting non-quenched and tempered steel. The device comprises a shell, the shell is in a barrel cylinder shape, material releasing holes are evenly distributed in the circumferential face of the shell, and a sealing cover is arranged on the upper portion of the shell; according to the method, the calcium-magnesium alloy is put into an immersion device, and the immersion device is pressed into the bottom of a steel ladle through a pressing rod for calcium-magnesium treatment. The immersion device is arranged, so that temperature drop or secondary oxidation caused by violent turning of molten steel is avoided, the accident that the molten steel flows backwards is avoided, magnesium steam and calcium steam make more sufficient contact with the molten steel, and the yield is higher; the method disclosed by the invention has lower requirements on equipment, can ensure that magnesium and calcium are released at the bottom of the steel ladle, is higher in efficiency, reduces the production cost and improves the product quality.

Description

Technical Field

[0001] The present invention relates to the field of iron and steel metallurgy, and particularly to an immersion device and method for calcium and magnesium treatment of free-cutting non-quenched steel. Background Art

[0002] Non-quenched steel is a type of steel that achieves omission of conventional heat treatment processes through microalloying and by controlling hot working process parameters and subsequent cooling processes. It is mainly used in fields such as automobiles, machining, and oil and gas pipelines, with strong demand in the automotive field. To improve cutting performance, calcium treatment or calcium and magnesium treatment is mostly used to modify MnS in steel, making it into a composite sulfide of Mn-Ca(Mg)-S, improving its anti-deformation ability at high temperatures, and reducing the anisotropy of steel. In addition, adding magnesium to molten steel can perform composite deoxidation with oxygen control elements such as aluminum and calcium more deeply, and generate magnesium spinels with finer sizes and more dispersed distributions. These spinels will become the cores for the subsequent precipitation of Mn-Ca(Mg)-S, making the inclusions formed by encapsulation more dispersed, finer, and having a certain anti-deformation ability, thereby further improving and enhancing the properties of the steel.

[0003] However, since the solubility of Ca in steel is very low (0.0314% at 1873K), calcium treatment alone often results in incomplete modification of inclusions. And when the Ca content is too high, CaS inclusions will be formed, causing nozzle blockage. Compared with calcium treatment, magnesium treatment of molten steel has received extensive attention in recent years. However, metallic magnesium is extremely active, with a boiling point of 1107°C and a high vapor pressure (the saturated vapor pressure in molten steel at 1873K is about 2.02MPa). Direct addition of magnesium to molten steel for deoxidation is prone to explosion and splashing accidents, and the utilization rate is relatively low.

[0004] Currently, the method for magnesium treatment in domestic and foreign steel mills is to use the wire feeding method to quickly pass the magnesium alloy wire through the slag layer and feed it to the bottom of the ladle after refining deoxidation and alloying, using the hydrostatic pressure of the molten steel to overcome the high vapor pressure of magnesium to improve the recovery rate. However, due to the tight refining time, the time left for magnesium treatment in the actual refining process is extremely short, resulting in an excessive instantaneous feeding speed of the magnesium alloy wire. Since the instantaneous content of magnesium vapor in the molten steel is too high, a large amount of magnesium vapor escapes outside the ladle before it has time to react with Al 2 O 3 inclusions, and the utilization rate of magnesium vapor is low. During the magnesium treatment process, the strong evaporation and escape of magnesium cause violent tumbling and severe exposure of the molten steel in the ladle, resulting in serious loss of aluminum and nitrogen increase in the steel, polluting the molten steel. At the same time, magnesium elements will also be directly oxidized and lost by combining with oxygen in the air and weak oxygen in the slag; and the violent tumbling and severe exposure of the molten steel during the magnesium treatment process will also cause additional temperature loss of the molten steel during the magnesium treatment process, serious pollution of the on-site working environment, and overflow loss of the molten steel. Summary of the Invention

[0005] The object of the present invention is to solve the problems raised in the above-mentioned background technology, and then a submerged device and method for calcium and magnesium treatment of free-cutting non-quenched steel are proposed. By setting the submerged device, the present invention avoids the temperature drop or secondary oxidation caused by the violent tumbling of molten steel, and the accident of molten steel backflow will not occur. The contact between magnesium vapor and calcium vapor and molten steel is more sufficient, and the recovery rate is higher. The method disclosed by the present invention has low requirements for equipment, and can ensure that magnesium and calcium are released at the bottom of the ladle, with higher efficiency, lower production cost, and improved product quality.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0007] A submerged device for calcium and magnesium treatment of free-cutting non-quenched steel, including a housing. The housing is of a trough-like structure, and uniformly distributed material release holes are provided on the circumferential surface of the housing. A cover is provided above the housing. The submerged device can be made of industrial pure iron. When dealing with steel grades with strict composition requirements, the corresponding steel grades can be used as raw materials to process the submerged device, or alloys can be proportionally added during the treatment process to eliminate its influence on the composition.

[0008] Preferably, the diameter of the housing is 50 - 500 mm, and its height is 50 - 500 mm; the aperture of the internal bin of the housing is 30 - 300 mm, and its depth is 30 - 300 mm.

[0009] Preferably, the aperture of the material release hole is 1 - 20 mm, the material release holes are vertically arranged in 2 - 8 rows, with 2 - 20 in each row. The material release holes are designed to be inclined downward from the inside to the outside. During use, the internal liquid and gaseous magnesium and calcium will flow downward, further increasing the contact area and time between the magnesium and calcium metal small bubbles and the molten steel.

[0010] A method for calcium and magnesium treatment of free-cutting non-quenched steel includes the following steps:

[0011] S1. After the mixed scrap steel is subjected to slag making, deoxidation, and alloying treatments to obtain molten steel, after the molten steel is subjected to vacuum treatment in RH, the calcium-magnesium alloy is proportionally mixed and encapsulated in the submerged device. The mixing ratio of the calcium-magnesium alloy is determined according to different steel grades produced.

[0012] S2. Use a pressure rod to press the submerged device to the bottom of the ladle for calcium and magnesium treatment. The internal calcium-magnesium alloy is liquefied and gasified under the action of high temperature. The liquid and gaseous magnesium and calcium will flow downward from the material release holes and fully contact and mix with the molten steel. During the whole process, the specific surface area of the contact between the magnesium and calcium metal small bubbles diluted by the molten steel and the molten steel is greatly increased, and it can dissolve more and more fully in the molten steel before evaporating and escaping, and gradually complete the magnesium treatment of the molten steel during the relatively long alloying process.

[0013] S3. The submerged device gradually melts into the molten steel under the action of high temperature. The submerged device is a consumable item.

[0014] S4. After the immersion device and the calcium-magnesium alloy are completely melted, the calcium-magnesium treatment process for free-cutting non-quenched steel is completed.

[0015] Preferably, the mass fraction of the mixed scrap steel is not less than 40%, wherein the mass fraction of C is greater than 1.5%, the mass fraction of P is less than 0.045%, the raw material temperature is controlled to be greater than or equal to 1550 °C during the primary melting process, the continuous decarburization amount is greater than or equal to 0.30%, and the slag basicity is 2.5 - 3.5 during the oxidation process;

[0016] Preferably, the immersion device can be prepared from any one of industrial pure iron and the corresponding steel grade. For steel grades with less strict composition requirements, the immersion device can be directly prepared from industrial pure iron; for steel grades with strict composition requirements, the corresponding steel grade can be used as the raw material to process the immersion device, or alloys can be proportionally added during the treatment process to eliminate its influence on the composition.

[0017] Preferably, 1 - 10 immersion devices can be pressed into different positions simultaneously by the pressure rod to expand the reaction area, improve the recovery rate of calcium and magnesium, and improve the efficiency of calcium-magnesium treatment at the same time.

[0018] Preferably, in S3, the calcium-magnesium alloy selects Mg-Al-Fe and Ca-Fe, the addition amount of calcium is 0.0001% - 0.02%, and the addition amount of magnesium is 0.0001% - 0.02%.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. By setting the immersion device, the present invention avoids the temperature drop or secondary oxidation caused by the violent tumbling of the molten steel, and the molten steel backflow accident will not occur. The contact between magnesium vapor and calcium vapor and the molten steel is more sufficient, and the recovery rate is higher; the method disclosed by the present invention has lower requirements for equipment, and can ensure that magnesium and calcium are released at the bottom of the ladle, with higher efficiency, lower production cost, and improved product quality.

[0021] 2. By setting the immersion device, the material release holes on the immersion device are designed to be inclined downward from the inside to the outside. During the use process, the internal liquid and gaseous magnesium and calcium will flow downward, further increasing the contact area and time between the magnesium-calcium metal small bubbles and the molten steel, improving the recovery rate, and reducing pollution.

[0022] 3. The immersion device disclosed by the present invention is a consumable, which is simple to process and replace, has low cost, and reduces the production cost.

[0023] 4. The disclosed method of the present invention does not require blowing powder into the bottom of the ladle or the tundish with argon as the carrier gas, which will not cause violent tumbling of the molten steel resulting in temperature drop or secondary oxidation, nor will there be an accident of molten steel backflow. The contact between magnesium vapor and calcium vapor and the molten steel is more sufficient, and the recovery rate is higher.

[0024] 5. Compared with the traditional wire feeding method, the disclosed method of the present invention has lower equipment requirements, that is, lower cost, and can ensure that magnesium and calcium are released at the bottom of the ladle, with higher efficiency. Brief Description of the Drawings

[0025] Figure 1 It is a schematic structural diagram of the immersion device of the disclosed device of the present invention;

[0026] Figure 2 It is a sectional view of the immersion device of the disclosed device of the present invention.

[0027] Wherein: 1. Cover; 2. Outer shell; 21. Material release hole. Detailed Description of the Invention

[0028] It should be noted that the following detailed description is illustrative and is intended to provide further description of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0029] Example 1, as Figure 1-2 shown, an immersion device for calcium and magnesium treatment of free-cutting non-quenched and tempered steel includes an outer shell 2, the outer shell 2 is in a trough shape, and uniformly distributed material release holes 21 are arranged on the circumferential surface of the outer shell 2. A cover 1 is arranged above the outer shell 2. The immersion device can be made of industrial pure iron. For steel grades with strict composition requirements, the corresponding steel grades can be used as raw materials to process the immersion device, or alloys can be proportionally added during the treatment process to eliminate its influence on the composition.

[0030] As Figure 1-2 shown, the diameter of the outer shell 2 is 50 - 500 mm, and its height is 50 - 500 mm; the aperture of the inner bin of the outer shell 2 is 30 - 300 mm, and its depth is 30 - 300 mm. The best shape of the outer shell is a cylindrical barrel, which can not only ensure the gradual release of internal magnesium and calcium metals, but also save production materials.

[0031] As Figure 1-2 shown, the aperture of the material release hole 21 is 1 - 20 mm, the material release holes 21 are arranged vertically in 2 - 8 rows, with 2 - 20 in each row. The material release holes 21 are designed to be inclined downward from the inside to the outside. During use, the internal liquid and gaseous magnesium and calcium will flow downward, further increasing the contact area and time between the magnesium and calcium metal small bubbles and the molten steel.

[0032] Example 2. A method for calcium and magnesium treatment of free-cutting non-quenched steel, comprising the following steps:

[0033] S1. After the mixed scrap steel is subjected to slag making, deoxidation and alloying treatment to obtain molten steel, after the molten steel is subjected to vacuum treatment in RH, the calcium-magnesium alloy is uniformly mixed in proportion and encapsulated in an immersion device, and the mixing ratio of the calcium-magnesium alloy is determined according to different steel grades to be produced;

[0034] S2. Use a pressure rod to press the immersion device into the bottom of the ladle for calcium and magnesium treatment. The internal calcium-magnesium alloy is liquefied and gasified under the action of high temperature. The liquid and gaseous magnesium and calcium will flow downward from the material release hole 21 and fully contact and mix with the molten steel. During the whole process, the contact specific surface area between the small magnesium-calcium metal bubbles formed by the dilution of the magnesium-calcium alloy by the molten steel and the molten steel is greatly increased, and it can dissolve more and more fully in the molten steel before evaporating and escaping, and gradually complete the magnesium treatment of the molten steel during the relatively long alloying process;

[0035] S3. The immersion device gradually melts into the molten steel under the action of high temperature, and the immersion device is a disposable consumable;

[0036] S4. After the immersion device and the calcium-magnesium alloy are completely melted, the calcium and magnesium treatment process of the free-cutting non-quenched steel is completed.

[0037] Preferably, the mass fraction of the mixed scrap steel is not less than 40%, wherein the mass fraction of C is greater than 1.5%, the mass fraction of P is less than 0.045%, the raw material temperature is controlled to be greater than or equal to 1550 °C during the primary melting process, the continuous decarburization amount is greater than or equal to 0.30%, and the slag basicity is 2.5 - 3.5 during the oxidation process;

[0038] Preferably, the immersion device can be prepared from any one of industrial pure iron and the corresponding steel grade. For steel grades with less strict composition requirements, the immersion device can be directly prepared from industrial pure iron; for steel grades with strict composition requirements, the corresponding steel grade can be used as the raw material to process the immersion device, or alloys can be proportionally added during the treatment to eliminate its influence on the composition.

[0039] Preferably, 1 - 10 immersion devices can be pressed into different positions simultaneously by the pressure rod to expand the reaction area, improve the recovery rate of calcium and magnesium, and improve the efficiency of calcium and magnesium treatment at the same time.

[0040] Preferably, in S3, the calcium-magnesium alloy selects Mg-Al-Fe and Ca-Fe, the addition amount of calcium is 0.0001% - 0.02%, and the addition amount of magnesium is 0.0001% - 0.02%.

[0041] Example 3. Taking the production of two steel grades of F45MnVS and C70S6 as examples, the method for calcium and magnesium treatment of free-cutting non-quenched steel disclosed by the present invention is introduced.

[0042] The steel grade to be produced is F45MnVS free-cutting non-quenched and tempered steel, and its designed composition includes: C 0.42 - 0.49%, Si 0.3 - 0.6%, Mn 1.0 - 1.5%, P ≤ 0.035%, S 0.35 - 0.75%, V 0.06 - 0.12, Cr ≤ 0.3%, Ni ≤ 0.3%, Cu ≤ 0.3%, N 0.008 - 0.02%. In addition, 0.002% of Mg and 0.002% of Ca are designed to be added. The 100t converter smelting process is adopted, and Si-Mn weak deoxidation is carried out after the furnace. The oxygen content in the steel is controlled at 0.015wt%. LF slag-making and heating are carried out, and Al deep deoxidation is adopted, and then ferromanganese, ferrovanadium, ferrosulfur, etc. are added for alloying. After the alloying is completed, RH is used for vacuum degassing. After the treatment is completed, the vacuum is broken, and four immersion devices filled with Mg-Al-Fe and Ca-Fe master alloys are pressed into the ladle for calcium and magnesium treatment. The Mg content in the Mg-Al-Fe master alloy is 40wt%, the Al content is 30wt%, and the Fe content is 30wt%. The Ca content in the Ca-Fe master alloy is 80wt%, and the Fe content is 20wt%. The four immersion devices are dispersedly placed at different positions at the bottom of the ladle. The immersion device is a cylindrical device processed from industrial pure iron. The outer shell is cylindrical, with a diameter of 200mm and a height of 150mm. A hole is drilled from the top of the cylinder to the center to form a bin for containing alloying materials. The hole diameter is 120mm and the depth is 100mm. Holes are drilled from the side of the cylinder along the radial direction towards the center to communicate with the internal bin. The side hole diameter is 2mm, and a total of 6 rows of holes are drilled on the side, with 8 holes in each row, and they are symmetrically distributed along the axis of the cylinder on the side. Each immersion device contains 2kg of Mg-Al-Fe master alloy and 1kg of Ca-Fe master alloy, and they are mixed evenly. After the calcium and magnesium treatment, soft blowing is carried out for 8min, and then it is cast into a square continuous casting billet of 300*300mm by the conventional continuous casting billet process. The continuous casting billet is heated in a high-temperature furnace at a heating temperature of 1200°C, and then blooming rolling is carried out.

[0043] After test and detection, after the immersion device is pressed into the ladle, the calcium and magnesium treatment process is stable, without molten steel splashing and large overturning phenomena; the molten steel composition meets the control standard requirements of the steel grade chemical composition; after magnesium treatment, the non-metallic inclusions in the steel are fully modified and are distributed in a fine and dispersed state, and the modification effect of sulfides is good. Through composition detection, the recovery rate of magnesium is 35.6%, and the recovery rate of calcium is 41.5%, both of which are significantly higher than the recovery rates using traditional methods.

[0044] The steel grade produced is free-cutting non-quenched and tempered steel C70S6, and its designed composition includes: C 0.67 - 0.73%, Si 0.15 - 0.25%, Mn 0.45 - 0.55%, P ≤ 0.045%, S 0.06 - 0.07%, V 0.03 - 0.04%, Cr 0.1 - 0.2%, Ni ≤ 0.2%. In addition, 0.0015% of Mg and 0.0015% of Ca are added. The 50t electric furnace smelting process is adopted. After the furnace, Si-Mn weak deoxidation is used, and the oxygen content in the steel is controlled at 0.015wt%. LF slag-making and heating are carried out, and Al deep deoxidation is adopted, and then ferromanganese, ferrovanadium, ferrosulfur, etc. are added for alloying. After the alloying is completed, RH is used for vacuum degassing. After the treatment is completed, the vacuum is broken, and two immersion devices filled with Mg-Al-Fe and Ca-Fe master alloys are pressed into the ladle for calcium and magnesium treatment. The Mg content in the Mg-Al-Fe master alloy is 40wt%, the Al content is 30wt%, and the Fe content is 30wt%. The Ca content in the Ca-Fe master alloy is 80wt%, and the Fe content is 40wt%. The two immersion devices are dispersedly placed at different positions at the bottom of the ladle. The immersion device is a cylindrical device processed from industrial pure iron. The outer shell is cylindrical, with a diameter of 200mm and a height of 150mm. A hole is drilled from the top of the cylinder to the center to form a bunker for containing alloying materials, with a hole diameter of 100mm and a depth of 100mm. Holes are drilled from the side of the cylinder radially towards the center to communicate with the internal bunker. The side hole diameter is 2mm, and a total of 6 rows of holes are drilled on the side, 8 in each row, and they are symmetrically distributed along the axis of the cylinder on the side. Each immersion device contains 1.5kg of Mg-Al-Fe master alloy and 0.8kg of Ca-Fe master alloy, and they are mixed evenly. After the calcium and magnesium treatment, soft blowing is carried out for 8min, and then it is cast into a square continuous casting billet of 300*300mm by the conventional continuous casting billet process. The continuous casting billet is heated in a high-temperature furnace at a heating temperature of 1200°C, and then blooming rolling is carried out.

[0045] After test detection, after the immersion device is pressed into the ladle, the calcium and magnesium treatment process is stable, without molten steel splashing and large overturning phenomena; the molten steel composition meets the control standard requirements of the steel grade chemical composition; after magnesium treatment, the non-metallic inclusions in the steel are fully modified and are distributed in a fine and dispersed state, and the sulfide modification effect is good. Through composition detection, the recovery rate of magnesium is 34.7%, and the recovery rate of calcium is 39.5%, both of which are significantly higher than the recovery rates using traditional methods.

[0046] In the description of the present invention, the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "vertical", "horizontal", etc. is based on the orientation or positional relationship shown in the drawings, and is only for describing the present invention rather than requiring the present invention to be constructed or operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. The terms "connected" and "coupled" in the present invention should be understood in a broad sense. For example, it can be a connection or a detachable connection; it can be a direct connection or an indirect connection through an intermediate component. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0047] The above is the preferred operation mode of the present invention, and the description of the specific operation mode is only for better understanding the idea of the present invention. For those of ordinary skill in the art, several improvements or equivalent replacements can be made according to the principle of the present invention, and these improvements or equivalent replacements are also regarded as falling within the protection scope of the present invention.

Claims

1. An immersion device for calcium and magnesium treatment of free-cutting non-quenched and tempered steel, characterized in that: The invention comprises an outer shell (2), wherein the outer shell (2) is a groove-shaped structure, and evenly distributed release holes (21) are arranged on the circumferential surface of the outer shell (2); and a sealing cover (1) is arranged above the outer shell (2).

2. The immersion device for calcium and magnesium treatment of free-cutting non-quenched and tempered steel according to claim 1, characterized in that: The outer shell (2) has a diameter of 50-500 mm and a height of 50-500 mm; the inner silo aperture of the outer shell (2) has a diameter of 30-300 mm and a depth of 30-300 mm.

3. The immersion device for calcium and magnesium treatment of free-cutting non-quenched and tempered steel according to claim 1, characterized in that: The diameter of the release holes (21) is 1-20 mm. The release holes (21) are arranged in 2-8 rows vertically, with 2-20 holes in each row. The release holes (21) are designed to be inclined downward from the inside to the outside.

4. A calcium-magnesium treatment method for free-cutting non-quenched and tempered steel, characterized in that An immersion device for calcium-magnesium treatment of free-cutting non-quenched and tempered steel according to any one of claims 1 to 3 comprises the following steps: S1. After the mixed scrap steel is subjected to slagging, deoxidation and alloying treatment, molten steel is obtained. After the molten steel is vacuum treated at RH, the calcium-magnesium alloy is mixed in proportion and then packaged in an immersion device; S2, using a pressure rod to press the immersion device into the bottom of the ladle for calcium-magnesium treatment, the internal calcium-magnesium alloy liquefies and vaporizes under the action of high temperature, and the liquid and gaseous magnesium and calcium flow downward from the release hole (21) and fully contact and mix with the molten steel; S3, the immersion device gradually melts into the molten steel under the action of high temperature; S4. After the immersion device and the calcium-magnesium alloy are completely melted, the calcium-magnesium treatment process of free-cutting non-quenched and tempered steel is completed.

5. The calcium-magnesium treatment method for free-cutting non-quenched and tempered steel according to claim 4, characterized in that: The mass fraction of the mixed scrap steel is not less than 40%, wherein the mass fraction of C is greater than 1.5%, the mass fraction of P is less than 0.045%, the raw material temperature is controlled to be greater than or equal to 1550°C during the primary smelting process, the continuous decarburization amount is greater than or equal to 0.30%, and the slag basicity is 2.5-3.5 during the oxidation process.

6. The calcium-magnesium treatment method for free-cutting non-quenched and tempered steel according to claim 4, characterized in that: The immersion device can be made of any one of industrial pure iron and corresponding steel grades.

7. The calcium-magnesium treatment method for free-cutting non-quenched and tempered steel according to claim 4, characterized in that: The pressure rod can press 1 to 10 immersion devices at different positions at the same time.

8. The calcium-magnesium treatment method for free-cutting non-quenched and tempered steel according to claim 4, characterized in that: The calcium-magnesium alloy in S3 is selected from Mg-Al-Fe and Ca-Fe, the addition amount of calcium is 0.0001%-0.02%, and the addition amount of magnesium is 0.0001%-0.02%.

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