KR20020051530A - method of deoxidation of nickel alloy to improve cleanness - Google Patents

Abstract

PURPOSE: A deoxidation method of an invar is provided to achieve the invar having good clearness by deoxidizing the invar with titanium only after a vacuum oxygen decarburization. CONSTITUTION: In the deoxidation method of an invar, namely a specific steel consisting of nickel of 36 percent by weight and iron, with improved clearness, after a decarbonization process in a vacuum oxygen decarburization line of an electric furnace is completed, molten steel is secondarily decarbonated and denitrated, and then the amount of titanium is adjusted in a range of 0.005 to 0.5 percent by weight.

Description

Method for deoxidation of nickel alloy to improve cleanness

In the present invention, various non-metallic inclusions (hereinafter referred to as inclusions) in Inva steel (36% Ni-Fe steel) or large inclusions (5 mm or more in size) exist to not only reduce the cleanliness of the steel, but also to improve the physical properties of the product. The method for deoxidation of Inva steel, which solves the problem of deterioration, is particularly excellent in cleanliness by performing deoxidation with only titanium and adjusting its concentration within the range of 0.005% to 0.5% after completion of Vacuum Oxygen Decarburization (VOD). It relates to a deoxidation method of Inba River.

In general, the distribution of inclusion size among Inba steel slabs and their cold rolled products by deoxidation method in the steelmaking process is shown in Table 1. As can be seen from Table 1, the deoxidation method is carried out to reduce the oxygen present in molten steel after decarburization. During deoxidation of silicon (Si), silica (SiO ₂ ) inclusions are present in the steel in the size of 10-50 μm and they are cold because they have good stretchability. Among the rolled products, it is extended to large inclusions up to 20-1200 μm, so that various surface defects and demands cause cracks during processing. In the steel deoxidized with Mn-Si, MnO-SiO ₂ containing much SiO ₂ as MnO-SiO _{2 type} , which is also excellent in elongation, is stretched during cold rolling and usually distributed to 5-300 μm so that cracks on the surface of cold rolled coils Various steelmaking defects such as In addition, Al deoxidation does not have extensible inclusions, but the inclusions are usually present in steel in the form of aggregated alumina clusters (Alumina Cluster, Al ₂ O ₃ , melting point: 2020 ℃), which are too hard to cause cracks when rolling. This can cause surface defects. Therefore, although deoxidation by Ca is effective to control the composition of the alumina cluster, it is effective to control the composition of all the alumina in the molten steel. Therefore, the remaining alumina inclusions and calcium aluminate (Calcium aluminate; CaO-n Al ₂₎ O ₃ : melting point> 1500-1900 ° C.), ie, calcium aluminate with high alumina content. These are also problematic because they are high melting point inclusions.

In addition, the CaO-Al ₂ O ₃ -MgO system, which is common in all deoxidation methods, tends to exist in steel. Because the origin of these inclusions are slag properties, they are mainly present in the steel by slag incorporation by gas bubbling, and the gas bubbling process is common to any deoxidation method, which causes problems in product cleanliness. .

Therefore, there are a lot of difficulties in the production of steel, which requires very good ultra-cleanness, the inclusion of only 5 μm or less in the Invar steel.

In order to solve this problem, a recently known Japanese patent (95-289775, Japanese metallurgical industry, Published Information 97-111329) describes the slag composition as CaO-SiO ₂ -Al ₂ O ₃ system and the Al ₂ O ₃ composition. It is a method of using artificial slag containing 4% or more. Although this method is effective, there is a limit to the removal of the deoxidation products already present in the molten steel since the absorption of these inclusions at the slag / molten steel interface is easy only when all of the deoxidation products by Al, Si, etc. have to rise.

In addition, Japanese Patent (95-268124) filed by Sumitomo Metal, Japan, is a method of deoxidizing Al after deoxidation of Si and Mn, and deoxidation using rare earth elements such as La and Ce. This technique is as effective as Al and Ca deoxidation, but there is a limit to the composition control of all alumina inclusions remaining in the molten steel. That is, even when treated with rare earth elements, alumina remains in the steel, and in the case of inclusions containing a large amount of Al ₂ O ₃ in the Ce (La) O—Al ₂ O ₃ —SiO ₂ system, it is also a cause of surface defects during cold rolling. The problem is that demand can be a source of dissatisfaction because of the inclusion of 5-20 μm of inclusions, which is the limit for the final product.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and the prior art, that is, various deoxidation products present in molten steel containing 36% nickel cause cracks in cold-rolled surface products, or the demand is included in product property requirements. In order to solve the problem caused by the VOD (Vacuum Oxygen Decarburization) after the vacuum Oxygen Decarburization (VOD) to provide a method for refining Inva steel with excellent cleanliness by deoxidizing with titanium (Ti) The purpose.

1 is a graph showing the Inva river cleanliness index by deoxidation method.

Figure 2 is a graph showing the size of inclusions in Invar steel cold rolled material for each deoxidation method.

3 is a graph showing the inclusion index of the Inba steel cold rolled material according to the deoxidation method.

Hereinafter, the present invention will be described in more detail with reference to the drawings.

In the present invention, after decarburization is completed in an AOD refining furnace in one electric furnace, the molten steel is pulled out and subjected to decarburization and denitrification treatment in a VOD refining furnace for the second time, and the titanium is adjusted to 0.005-0.5% by weight% to perform deoxidation. Provided is a deoxidation method of nickel-containing steel with improved cleanliness. In the present invention, in the case of Si: 0.2% Al: 0.003% of the basic component of Fe-36Ni, at least about 0.005% of TiO2 oxide should be formed in order to generate fine TiO2 oxide as Ti addition, wherein the amount of TiO2 oxide in the steel is too small in the total inclusions. For most inclusion compositions to be present as TiO2, it should be at least about 0.5%, preferably 0.2%.

Table 2 shows the results of evaluating the size and cleanliness of the inclusions in the solidified ingot and the cleanliness index of the cold rolled material after cold rolling after melting using 100kg vacuum induction furnace.

The cleanliness index of the Inba steel cast steels by deoxidation method is shown in Table 1, and the cleanliness index of the cast iron by deoxidation method is shown in FIG. 1 using this data. The steel deoxidation of steel Nos. 17 and 18, that is, titanium, was superior to steel Nos. 10 and 11 (Si deoxidation), steels 12 and 13 (Mn-Si deoxidation) and steels 15 and 16 (Al deoxidation). Able to know.

2 shows the maximum size distribution of inclusions in the cold rolled material according to the deoxidation method. As can be seen from the diagram, Si deoxidation (Gal 10,11) exists up to 220μm, and Mn-Si deoxygenation (Gal 13,14) is also distributed up to 150 μm, Al deoxidation (Gal 15,16) In this case, it exists as a cluster and distributes up to 220 μm, which shows that there is a limit to controlling the inclusion distribution below 5 μm, which is the limit of Invar steel.

However, in the case of deoxidation (thickness 17,18) with titanium, the inclusions show very good cleanliness level with distribution of 5μm or less.

Figure 3 is a comparison of the defect grade index of Inba steel cold rolled material by deoxidation method, titanium deoxidizers (Gang 17, 18) is the lowest grade 1 compared to Si, Mn-Si, Al deoxidizers, very excellent deoxidized with Ti It can be seen that the product shows the level of cleanliness.

As such, for the production of clean steel of Inva steel containing 36% Ni, the addition of titanium is the best in terms of cleanliness index of cast steel, inclusion size distribution of cast steel and defect occurrence grade of cold rolled products. Showed.

Table 1 shows the general size distribution of inclusions in cast steel and cold rolled products, and Table 2 shows the cleanliness index in cast steel and cold rolled products according to the deoxidation method.

Deoxidation Method Inclusion Composition Large inclusion size in cast steel Product mediation size after cold rolling Maximum allowable size of product defect Si -SiO2-CaO-Al2O3-MgO 10-50 20-1200 5 Mn-Si -MnO--SiO2CaO-Al2O3-MgO 5-30 5 to 300 Al -Al2O3CaO-Al2O3-MgO-CaO-Al2O3-MgO 5 ~ 200 20-300

division River times Large inclusion size in cast steel (μm) Cast Cleanliness Index (mm2 / 5 × 10cm2) Cold Rolled Product Cleanliness Index Si deoxidation 10 10-160 0.022 7 Si deoxidation 11 17-220 0.038 9 Si deoxidation 12 10-120 0.008 6 Mn-Si Deoxidation 13 20-150 0.024 7 Mn-Si Deoxidation 14 15-70 0.011 6 Al deoxidation 15 5 to 180 0.009 5 Al deoxidation 16 5 ~ 220 0.015 6 Ti deoxidation 17 <5 0.0024 One Ti deoxidation 18 <5 0.0027 One

As described above, according to the present invention, molten steel containing 36% nickel can be deoxidized to titanium (Ti) after vacuum refining (VOD; Vacuum Oxygen Decarburization) to obtain inva steel having excellent cleanliness.

Claims (1)

After decarburization is completed in the AOD refining furnace of the electric furnace, the molten steel is pulled out and subjected to decarburization and denitrification treatment in the VOD refining furnace for the second time, and the titanium is adjusted to 0.005-0.5% by weight to perform deoxidation treatment. Deoxidation method of nickel-containing steel with improved cleanliness.