KR100406411B1 - Method of deoxidize molten steel for hard steel wire rods at steel tapping - Google Patents

Abstract

The present invention relates to a method for refining high carbon hard steel wire having a carbon concentration of 0.5 to 0.8% by weight. The purpose of the present invention is to reduce the amount of inclusions to improve the quality of molten steel and to prevent the clogging of the nozzle during continuous casting. It is to provide a deoxidation method of molten steel in the converter steel to smooth the.

In order to achieve the above object, the present invention, while casting the molten steel of the converter in the ladle, Fe-Mn alloy, iron, Fe-Si alloy, Al deoxidizer, quicklime and fluorspar in order of C: 0.5 to 0.8 weight In the method of manufacturing a% hard steel wire, 20 to 38% of the total amount of the Al deoxidizer is first added during the tapping of the molten steel, and then the Fe-Mn alloy iron and a carbonaceous material are added, and the remaining Al deoxidizer is added. Next, the method for refining molten steel of high carbon steel wire rod comprising the step of adding quicklime and fluorspar to adjust the basicity of the ladle slag to 5-7 and the oxidation degree of the ladle slag to 1.3 wt% or less. This is a technical summary.

Description

Method of deoxidize molten steel for hard steel wire rods at steel tapping}

The present invention relates to a method for refining high carbon steel wire rods having a carbon concentration of 0.5 to 0.8% by weight, and more particularly, to reduce the inclusion source to improve the quality of molten steel and to prevent nozzle clogging during continuous casting. The present invention relates to a deoxidation method of molten steel in the converter steel for smooth operation.

In general, steelmaking industry consists of converter → secondary refining → continuous casting process. In the converter operation, molten iron and scrap are charged into the converter, and at the same time, the main lances of impurities such as C, Si, Mn, P, S, Ti, etc. A series of operations are commonly referred to as removing oxygen by oxidative refining by injecting oxygen through it. The molten steel obtained through the converter operation contains dissolved oxygen at a concentration that is in equilibrium with the converter endpoint carbon, and usually contains about 600 to 1300 ppm of dissolved oxygen (free oxygen) at the converter endpoint.

Dissolved oxygen of such molten steel is removed by deoxidation product by inputting deoxidizer such as Al when tapping into ladle in converter. However, some of these deoxidation products remain in molten steel, which not only deteriorates the quality of molten steel as harmful inclusions, but also causes clogging of nozzles when it is attached to tundish nozzles during continuous casting. have. Such nozzle clogging also occurs in the continuous casting process of hard steel wire.

When manufacturing molten steel for light steel wire, it is finished in the converter, and the Fe-Mn alloy, the carbonitizer, and the Fe-Si alloy are added to adjust the composition during the ladle, and the molten steel deoxidation Al is added. Therefore, harmful inclusions by this Al arise. After Al is added as above, quicklime and fluorspar for slag reforming are added, and when the tapping is completed, the ladle blows inert gas in a process such as gas bubbling to raise inclusions by deoxidation product into the slag layer. It is separated and the molten steel component is finely adjusted or uniformed. In addition, a certain amount of Ca-Wire is added to molten steel to form Al ₂ O ₃ , a deoxidation product, as a composite oxide of CaO + Al ₂ O ₃ , to promote flotation by slag layer, and to prevent nozzle clogging during continuous casting. It is preventing. However, this is not a fundamental solution and frequent nozzle clogging occurs.

As a solution to this, many methods have been proposed such as adding slag modifiers during and after tapping to change slag physical properties to absorb harmful inclusions such as deoxidation products in molten steel (Korean Patent No. 37363). Although this method contributes to the production of high clean steel, the addition of slag modifier or slag deoxidizer is added to about 1-10kg per ton of molten steel, so there is a drawback of increasing the slag generation as well as reducing the molten steel temperature. The slag generated is classified as a kind of waste and acts as an environmental pollution source.

As another method, after ladle bubbling process, a method of separating and casting inclusions by refluxing molten steel in an RH vacuum degassing apparatus (hereinafter simply referred to as 'RH'), and separately injecting inert gas (Ar) into the molten steel In some cases, the method of performing the bubbling process again may be performed. However, these methods require a molten steel to be pulled out of the converter subsequent to the addition of the process, and thus there is a problem that an overall production failure occurs. Therefore, in the continuous casting machine is a kind of direct processing to be cast through a bubbling operation with inert gas for a predetermined time before the main structure. Most hard steel wire rods are produced by such direct processing.

As described above, in the conventional manufacturing technology of hard steel wire rods, in order to manufacture high-clean steel without clogging nozzles, RH refining or a separate bubbling process is adopted, or a large amount of slag is generated, as well as reducing molten steel temperature. It is being overlooked and adopted as a method of injecting slag modifiers.

The present invention does not perform a separate RH or bubbling process in the manufacturing method of the hard steel wire, as well as providing a method for producing a high-purity hard steel wire without causing a large amount of slag, an object thereof. The present invention was completed by metallurgically grasping the root cause of the nozzle clogging in the refining process of hard steel wire rod and deriving a solution, solving the problem by improving the conventional method of adding ferroalloy and deoxidizer.

1 is a graph showing the relationship between the basicity and slag oxidation degree of the ladle slag on clogging the tundish nozzle in the continuous casting process.

Figure 2 is a comparison of the method of adding ferroalloy and deoxidizer and secondary raw materials in the present invention and the conventional method

Figure 3 is a _{CaO-SiO 2 -Al 2 O 3} 3 binary state of the ladle slag in the present invention and the conventional method.

In order to achieve the above object, the present invention, while casting the molten steel of the converter into the ladle, Fe-Mn alloy iron, a briquette material, Fe-Si alloy iron, Al deoxidizer, CaO, CaF _{2 in} the order of C: 0.5 ~ 0.8 In the method of manufacturing a weight% hard steel wire, 20 to 40% of the total amount of the Al deoxidizer is first added during the tapping of the molten steel, and then the remaining Al deoxidizer is added after the Fe-Mn alloy iron and the carbonaceous material are added. Then, CaO and CaF ₂ are added to adjust the basicity of the ladle slag to 5 to 7, and the oxidation degree of the ladle slag to 1.3% by weight or less.

Hereinafter, the present invention will be described in detail.

The present inventors traced various possible conditions to find the cause of nozzle clogging in hard wire molten steel, and found the cause in the ladle slag. That is, as a result of investigating the properties of the ladle slag when the nozzle was clogged during the continuous casting and the casting was normally completed (FIG. 1), the relationship between the degree of oxidation (T.Fe + MnO) of the ladle slag and the basicity of the ladle slag was directly It was found to affect. As can be seen in Figure 1, in order to prevent the nozzle clogging to complete the casting normally it can be seen that the basicity is maintained at 5.0 or more while maintaining the oxidation degree of the ladle slag to about 1.0% or less.

Based on these experimental results, the cause of the poor management of the basicity and oxidation degree of the conventional ladle slag was examined. Conventionally, when tapping the molten steel refined in the converter, the input of carbonaceous material and ferroalloy for component adjustment. At this time, the order of addition is in the order of Fe-Mn → charcoal material → Fe-Si alloy iron → Al → CaO → CaF ₂ .

The inventors have paid attention to the order of input of such ferroalloy, deoxidizer, and subsidiary materials. In other words, the concentration of dissolved oxygen in molten steel is high during tapping.In this case, when Fe-Mn, carbonaceous material, and Fe-Si are added, oxygen of molten steel reacts with carbon in the injected carbonaceous material as shown in Equation 1 below. Generate. In addition, Mn in the Fe—Mn alloy iron is oxidized to form MnO as in Scheme 2, thereby increasing the oxidation degree of slag. In addition, Si in the Fe-Si alloy iron is oxidized as in Scheme 3 to increase the SiO ₂ concentration in the slag.

O + [C] = CO (g)

O + [Mn] = (MnO)

2O + [Si] = (SiO ₂ )

Of course, the addition of CaO in addition to the increase in the amount of SiO ₂ was thought to be able to control the basicity, but the addition of 500kg CaO it was difficult to increase the slag basicity to the target level. Because of the increased CaO, fluorite (CaF ₂ ) to promote its dissolution must also be increased. Dissolution of slag is promoted by the addition of fluorspar, but due to SiO ₂ contained in about 15-20% of fluorspar, the increase in basicity decreases and the temperature drop is increased. Therefore, it was found that the phenomenon that the tundish nozzle was clogged during the continuous casting and frequently failed to complete the casting.

Therefore, in the present invention, as a result of solving the problem that the basicity and oxidation degree of the ladle slag cannot be controlled by the reaction of Mn and Si in the dissolved oxygen and ferroalloy, the order of addition of ferroalloy and Al deoxidizer and In experiments, it was found that the solution could be solved by adjusting the amount of Al deoxidizer.

The present invention is characterized by adjusting the degree of basicity and oxidation aimed at ladle slag without increasing the input amount of quicklime by improving the method of adding ferroalloy and Al deoxidizer. That is, in the present invention, a portion of Al deoxidizer is added in advance before the addition of Fe-Mn and the charcoal agent, and the rest is added before the addition of Fe-Si to reduce dissolved oxygen, thereby suppressing the formation of MnO and SiO ₂ . It is to reduce the slag oxidation degree and to maintain the basicity at least 5 at all times.

MnO in the slag is caused by the outflow of slag in the converter and is produced by oxidizing Mn in the Fe-Mn alloy iron added to the ladle. Further, in the ladle slag SiO ₂ is SiO contained in hyeongseokjung to commit to the SiO _2, and Fe-Si alloy cheoljung Si is oxidized produced SiO ₂ and the slag fluidity securing of the outlet slag of in a converter tapping ₂ (Usually around 15-20%). Therefore, in order without increasing the calcium oxide amount to lower the degree of oxidation of the ladle slag to increase the basicity lower the SiO ₂ W Bahia preferentially prevent the outflow of the converter slag, but this simhamyeo variation depending on the converter operating conditions of hyeongseokjung SiO ₂ Since the concentration is also unchanged, it is necessary to reduce the amount of MnO and SiO ₂ generated from Fe—Mn alloy iron and Fe—Si alloy iron.

Therefore, in the present invention, MnO and SiO ₂ by oxidation of Fe-Mn alloy iron and Fe-Si alloy iron by deoxidizing molten steel by first adding a part of Al deoxidizer to Fe-Mn alloy iron and Fe-Si alloy iron. Suppress the occurrence. Thermodynamically, Al has a greater affinity with oxygen than Si and Mn, making it a stronger deoxidizer.

However, an important fact obtained through the study of the present invention is that the total amount or too much of the Al deoxidizer should not be added from the beginning of tapping to completely deoxidize the molten steel. If this happens, the carbonaceous material added to adjust the carbon concentration of the steel is not dissolved due to lack of agitation and remains in the molten state in the molten steel, and the tapping is completed, resulting in a rapid reaction with the dissolved oxygen remaining in the subsequent process. There is a problem causing safety accidents by splashing molten steel. Therefore, in the present invention, the weak deoxidation is performed at 20-40% of the total amount of Al deoxidizer added to the initial tapping.

As described above, the Al deoxidizer is added at the beginning of the tapping, followed by the Fe-Mn alloy iron and the charcoal material for the ingredient adjustment in the usual manner. When the carbonaceous material is added, the molten steel is agitated by falling from the converter to the ladle and generating CO gas, so that the carbonaceous material is easily dissolved in the molten steel. Subsequently, the remaining Al deoxidizer of the estimated input amount is added to the Fe-Si alloy iron while deoxidizing molten steel. Therefore, the Si of the oxidation reaction of Fe-Si alloy is suppressed cheoljung can minimize the SiO ₂ amount. Later, when quicklime and fluorspar are added at the end of the class, it is possible to increase the basicity of the ladle slag. In the present invention, since the input order of the ferroalloy and the Al input amount are distributed to bring the basicity and oxidation degree to an appropriate level, the input amount of quicklime and fluorspar does not need to be increased compared to a normal level.

According to the present invention, the Al input order and the amount may be appropriately distributed in the existing method. In other words, the oxidation degree is kept below 1.3%. To the ladle slag to a low melting point and to manage the basicity CaO 5-7 is a 55-60% by weight, Al ₂ O ₃ may also be a 29-32% by weight.

Hereinafter, the present invention will be described in detail through examples.

Example 1

While casting 100 tons of molten steel in ladle, ferroalloy and subsidiary materials were added in the order as shown in FIG. 2. Here, the conditions were the same except for the change of the aluminum injection order and the change of the charged amount. That is, in the case of quicklime and fluorspar, both quickener: 500kg / Ch and fluorspar: 100kg / Ch were added to both the conventional example and the invention example. In addition, both conventional and inventive examples add a small amount of aluminum to finely adjust the Al concentration in the molten steel after tapping, and transfer the ladle after tapping to a bubbling process to blow inert gas to make the components uniform and to analyze the components. After the addition of fine alloy ferrous alloy, and then inert gas was blown again, calcium wire was added to promote floating separation of the deoxidation product Al ₂ O ₃ .

The results are shown in Table 1.

division End point temperature (℃) End point oxygen (ppm) Ladle Slag Composition (%) Nozzle clogging Al input amount T.Fe MnO CaO SiO ₂ Al ₂ O ₃ basicity Primary Secondary Conventional Example 1 1683 647 0.44 0.6 52.07 10.54 24.14 4.74 ○ 0 85 Conventional Example 2 1643 949 1.24 0.69 44.90 19.33 22.05 2.32 ○ 0 125 Conventional Example 3 1666 811 1.07 0.85 43.96 20.57 20.56 2.13 ○ 0 105 Conventional Example 4 1715 932 1.28 0.58 46.20 14.45 25.46 3.19 ○ 0 120 Conventional Example 5 1698 877 1.87 0.74 49.04 15.06 24.78 3.25 ○ 0 115 Inventive Example 1 1653 610 0.37 0.43 58.12 9.01 24.66 6.40 × 30 50 Inventive Example 2 1676 870 0.61 0.31 56.34 8.76 26.31 6.43 × 40 75 Comparative Example 1 1673 480 0.56 0.10 54.78 12.30 27.11 4.45 ○ 10 50 Inventive Example 3 1705 481 0.94 0.32 55.92 9.85 26.31 5.68 × 20 40 Inventive Example 4 1710 631 0.31 0.21 53.94 10.47 25.04 5.15 × 30 55 Inventive Example 5 1706 910 0.53 0.15 56.22 8.85 26.85 6.35 × 50 70 Inventive Example 6 1695 908 0.72 0.31 57.45 9.50 25.91 6.05 × 40 80 Inventive Example 7 1680 850 0.58 0.41 55.30 9.12 26.62 6.06 × 30 80 Comparative Example 2 1712 934 0.42 0.62 54.34 13.23 25.96 4.11 ○ 20 100 Inventive Example 8 1710 712 0.51 0.72 53.18 14.50 24.93 3.67 ○ 10 85

As shown in Table 1, the conventional example (1) is a case where the temperature rise treatment in the LF after the converter is pulled down, the basicity of the ladle slag shows a significantly higher value than the other conventional examples, the target base is less than 5.0 . Conventional Example (2-5) shows that the MnO concentration of the ladle slag is in the range of 0.6-0.85% by adding Fe-Mn alloy iron and Fe-Si alloy iron before the Al deoxidizer, and the SiO ₂ concentration is 14.45% -20.57. The slag basicity was lowered up to%, resulting in lower slag basicity, which resulted in clogging of the nozzle during the casting process, resulting in failure to complete casting normally.

The invention example and the comparative example are a case in which aluminum is input in the initial stage of tapping, a Fe-Si alloy iron, a briquette material is added, and the rest is added. In the case of the invention example and the comparative example, the addition of Al before Fe-Mn, Fe-Si, the production of MnO, SiO ₂ is suppressed, which is generally lower than the conventional example. In particular, in the case of Inventive Example (1-8) in which Al was initially added at 27-38% of the total loading amount, nozzle clogging did not occur because the basicity of the slag was 5% or more.

Figure 3 shows the case of deoxidation by the conventional method and ladle slag composition when the deoxidation by the method of the present invention, _{CaO-SiO 2 -Al 2 O 3} 3 binary state phases. In the case of the conventional example, it can be seen that the nozzle clogging is a direct cause during the continuous casting operation because the low melting point slag composition cannot be generated on the CaO-SiO ₂ -Al ₂ O ₃ ternary state diagram. On the other hand, when the invention example is to satisfy the low-melting-point slag composition range of inclusions improves the absorption capacity on the _{CaO-SiO 2 -Al 2 O 3} 3 ternary phase diagram with the control of the ferroalloy during tapping input method tundish nozzle during the continuous casting operation Normal casting was possible by preventing clogging.

As described above, the present invention improves the deoxidation method during the conversion of the converter, thereby stably obtaining a low melting point slag composition, preventing nozzle clogging during continuous casting, and preventing interference between processes, thereby eliminating the burden on the worker, Improvement can be aimed at. In addition, there is a useful effect that contributes to environmental improvement by reducing the amount of slag generated.

Claims (1)

In the method for producing C: 0.5-0.8 wt% hard steel wire by pouring molten steel of converter into ladle and adding Fe-Mn alloy, peat material, Fe-Si alloy, Al deoxidizer, quicklime and fluorspar in order. During the tapping of the molten steel, 20 to 40% of the total amount of the Al deoxidizer is first introduced, followed by the Fe-Mn alloy iron and a briquette material, followed by the addition of the remaining Al deoxidizer, and then the quicklime and fluorspar. A slag deoxidation method during converter runout of molten steel of a high carbon light steel wire, comprising adjusting the basicity of the slag to 5 to 7 and adjusting the oxidation degree of the ladle slag to 1.3 wt% or less.