KR101410200B1 - Flux composition acquisition method for reducing oxygen content in weld pool of weld zone and flux composition thereof - Google Patents

Abstract

The present invention relates to a method for obtaining a flux composition for reducing the oxygen content in a molten metal of a welded portion, comprising the steps of: melting steel specimens constituted of the same metal composition, respectively, and a plurality of fluxes in which oxides and fluorides are mixed in different composition ratios The method includes the steps of preparing a material and reacting it with the molten steel sample, measuring the oxygen content in each steel sample reacted with the flux material for each set time interval, And obtaining a range of composition ratios of the oxides and fluorides for reducing the oxygen content in the molten metal by using the oxygen removal rate calculated for each of the steel samples , A flux composition for reducing the oxygen content in the molten metal of the weld zone Provides an acquisition method.
According to the flux composition obtaining method and the flux composition for reducing the oxygen content in the molten metal of the weld portion, a plurality of flux materials in which oxides and fluorides are mixed in different composition ratios are reacted with a steel sample, By analyzing the velocity, it is possible to obtain a composition ratio range of oxides and fluorides excellent in oxygen reduction ability, and there is an advantage that a flux composition useful for oxygen reduction can be constituted.

Description

Technical Field [0001] The present invention relates to a flux composition for reducing oxygen content in a molten metal of a welded joint, and a flux composition for reducing the oxygen content in the weld metal,

TECHNICAL FIELD The present invention relates to a flux composition obtaining method and a flux composition for reducing oxygen content in a molten metal of a weld portion, and more particularly, to a flux composition obtaining method for reducing oxygen content in a molten metal of a weld portion, To a flux composition obtaining method for reduction and a flux composition thereof.

In general, non-metallic oxides (hereinafter referred to as inclusions) in welds are one of the main factors affecting the mechanical strength of welds. The inclusions are formed by combining oxygen and oxygen with elements having high affinity to oxygen such as Cr, Si, Mn, Al, Ti, etc. in the welded portion. The nonmetallic inclusions formed act as cracking points at the fracture of the weld or serve as propagation paths of the cracks, thereby reducing the toughness of the weld.

Particularly, when the microstructure of the welded portion is composed of martensite and bainite, it has a great influence on the toughness of the welded portion, so that the inclusion is particularly required to be removed. In addition, it is very important to ensure a high oxygen removal rate because the welding is done in a very short time.

Japanese Patent Application No. 1997-226502 proposes a technique for improving the toughness of a weld metal by controlling the mass% of metal components such as Al, Mg, Mn, and Si. However, no method for determining the oxygen removal rate from the combination of oxides and fluorides constituting the flux and obtaining a flux composition for improving the toughness of the welded portion is disclosed.

In the present invention, a plurality of flux materials in which oxides and fluorides are mixed in different composition ratios are used to analyze oxygen removal rate in a steel sample, thereby obtaining a range of composition ratios of oxides and fluorides excellent in oxygen reduction ability, It is an object of the present invention to provide a flux composition obtaining method and flux composition for reducing the oxygen content in a molten metal of a welded portion which can provide a flux composition useful for abatement.

The present invention relates to a method for obtaining a flux composition for reducing the oxygen content in a molten metal of a welded portion, comprising the steps of: melting steel specimens constituted of the same metal composition, respectively, and a plurality of fluxes in which oxides and fluorides are mixed in different composition ratios The method includes the steps of preparing a material and reacting it with the molten steel sample, measuring the oxygen content in each steel sample reacted with the flux material for each set time interval, And obtaining a range of composition ratios of the oxides and fluorides for reducing the oxygen content in the molten metal by using the oxygen removal rate calculated for each of the steel samples , A flux composition for reducing the oxygen content in the molten metal of the weld zone Provides an acquisition method.

The step of acquiring the composition ratio range of the oxides and fluorides for reducing the oxygen content in the molten metal may include combining the composition ratio values of the flux material corresponding to the steel samples of the upper group having the fast oxygen removal rate, The composition ratio range of the oxide and the fluoride for reducing the oxygen content in the molten metal can be obtained, respectively.

The oxide includes a plurality of CaO, Al ₂ O ₃ , SiO ₂ , and MgO, and the fluoride may include at least one of CaF ₂ , MgF ₂ , Na ₃ AlF ₆ , and NaF.

In addition, the composition ratio range of the oxide and a fluoride for the oxygen content is reduced in the molten metal of the weld, from 40 to 50% by weight of CaO, 0.1 - 5 mass% of Al ₂ O _3, 20 ~ 25 mass% SiO _2, 10 to 25% by mass of fluoride, and 0.1 to 15% by mass of other oxides.

Here, the fluoride is CaF ₂ And the other oxide is MgO, and the basicity index defined by the following equation may have a value of 2.7 to 3.4.

Incidentally, the present invention is 40-50% by weight of CaO, 0.1 - 5 mass% of Al ₂ O _3, 20 - 25 mass% of SiO _2, and other oxides of 10 to 25% by weight of fluoride, and 0.1 to 15% by weight To provide a flux composition for reducing the oxygen content in the molten metal of the welded portion.

In the flux composition, the fluoride may include at least one of CaF ₂ , MgF ₂ , Na ₃ AlF ₆ , and NaF.

Further, in the flux composition, the fluoride may be CaF ₂ And the other oxide is MgO, and the basicity index may have a value of 2.7 to 3.4.

According to the flux composition obtaining method and the flux composition for reducing the oxygen content in the molten metal of the weld portion according to the present invention, a plurality of flux materials in which oxides and fluorides are mixed in different composition ratios are reacted with a steel sample, It is possible to obtain a composition ratio range of oxides and fluorides excellent in oxygen reduction ability.

In addition, the present invention can constitute a flux composition useful for oxygen reduction having the above-mentioned composition ratio range. When such a flux composition is used for welding, it is possible not only to secure a low oxygen concentration in a welded portion in a short time, There is an advantage that it can be improved.

1 is a flow chart of a flux composition acquisition method for reducing oxygen content in a molten metal of a weld according to an embodiment of the present invention.
2 is a graph showing a change in oxygen concentration according to step S130 of FIG.
FIG. 3 is a conceptual diagram illustrating an oxygen removal rate calculation process according to step S140 of FIG.
4 is a graph showing the result of step S140 of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention.

The present invention provides a ratio of various oxides and fluorides constituting a basic flux-cored wire (hereinafter referred to as flux) capable of securing a low oxygen concentration in a welded portion in a short time, as one of the methods for improving the toughness of a weld portion of an ultra high strength steel .

To this end, a flux material composed of a ratio of various oxides and fluorides is reacted with a molten steel material to analyze the oxygen removal rate according to the flux composition, and then the ratio of oxides and fluorides excellent in oxygen reduction ability can be obtained. A flux composition useful for abatement can be made.

Hereinafter, a method for obtaining a flux composition for reducing oxygen content in a molten metal of a welded portion according to an embodiment of the present invention will be described in detail. 1 is a flow chart of a flux composition acquisition method for reducing oxygen content in a molten metal of a weld according to an embodiment of the present invention.

First, steel samples made of the same metal composition are respectively melted (S110). In this step S110, a steel material sample having a metal composition shown in Table 1 is melted at 1600 DEG C using a melting means such as a high frequency induction furnace.

element Si Cr Mn Fe Content (% by mass) 0.5 0.5 2.0 balance

In this embodiment, a steel material having the composition shown in Table 1 is used as an example. However, the present invention is not necessarily limited to this and can be applied to various steel material samples.

Next, a plurality of flux materials in which oxides and fluorides are mixed in different composition ratios are prepared and respectively reacted with the molten steel samples (S120).

Here, the flux materials used refer to Examples 1 to 12 of Table 2. The comparative example in Table 2 shows a composition ratio close to that of the conventional flux material.

CaO
(mass%) CaF2
(mass%) Al2O3
(mass%) MgO
(mass%) SiO2
(mass%) basicity index Oxygen Removal Rate (%) Example 1 23.3 20 5 5 46.6 0.98 90 Example 2 35 20 5 5 35 1.60 130 Example 3 42 20 5 5 28 2.20 160 Example 4 46.6 20 5 5 23.3 2.78 250 Example 5 50 20 0.1 5 25 2.99 170 Example 6 43.3 20 10 5 21.6 2.57 80 Example 7 40 20 15 5 20 2.36 80 Example 8 50 20 5 0.1 25 2.55 180 Example 9 43.3 20 5 10 21.6 3.04 140 Example 10 40 20 5 15 20 3.33 220 Example 11 53.3 10 5 5 26.6 2.35 120 Example 12 40 30 5 5 20 3.33 170 Comparative Example 33.3 40 5 5 16.6 4.10 100

Of the flux materials in Table 2, CaO, Al ₂ O ₃ , SiO ₂ , and MgO are oxides, and CaF ₂ is fluoride.

In the present invention, to the CaO for the flux composition change 23.3 53.3% by mass, CaF ₂ from 10 to 40% by weight, Al ₂ O ₃ and 0.1 to 15 mass%, the MgO from 0.1 to 15 mass%, SiO ₂ of 16.6 to 46.6 By mass%. At this time, the value of the ratio of (CaO mass%) / (SiO2 mass%) should be in the range of 0.5 to 2.0.

In Table 2, the Basicity Index is defined by Equation 1 below.

CaF _{2, which} is a fluoride other than oxides in the flux, is a component added mainly because it improves the bead appearance as a slag forming agent. For the effect of the bead appearance, a certain amount of CaF ₂ should be added, but if the addition amount exceeds a certain range, the amount of fume and spatter is increased and the viscosity of the fused metal is lowered, resulting in bead failure do. Therefore, it is important to specify the proper CaF ₂ content.

After the step S120, the oxygen content in each of the steel samples reacted with the flux material is measured for each set time interval (S130). As the measuring means for measuring the oxygen content, various well-known means can be used.

Here, the measurement time period is divided into 1 minute, 3 minutes, 5 minutes, 10 minutes, 30 minutes and 60 minutes. Of course, such a time interval unit is only an embodiment, and the present invention is not necessarily limited thereto.

In step S130, molten steel samples are sampled at each time interval to analyze the oxygen content. The method of analyzing the oxygen content from the sample is well known in the prior art, so a detailed description thereof will be omitted.

As the time elapses after the reaction of the flux material, the oxygen content on the sample will be reduced, but the speed at which it is reduced will depend on the composition ratio of the flux material. When the elements having a large affinity with oxygen in the welded portion are bonded with oxygen, nonmetal oxides (inclusions) are formed, and the formed inclusions have a great influence on the toughness of the welded portion. Therefore, it is necessary to find a flux composition having a high initial oxygen removal rate.

When the measurement of the oxygen content over time is completed, the initial oxygen removal rate for each steel sample is calculated from the oxygen content according to the time interval at step S140. Such a calculation process can be performed by a separate calculation processing unit such as a computer.

The step S140 corresponds to a process of measuring the initial oxygen removal rate in the molten metal according to various flux compositions in order to confirm the effect of reducing the oxygen content in the molten metal due to the ratio of various oxides and fluorides in the basic flux cored wires. Accordingly, the initial oxygen removal rate due to the chemical reaction between the molten steel sample and the flux material can be measured.

2 is a graph showing a change in oxygen concentration according to step S130 of FIG. Here, only the comparative example, the fourth embodiment and the seventh embodiment are shown for convenience of explanation.

In FIG. 2, the descent rate of the initial oxygen concentration is faster than that of the example 7 and the comparative example in the case of Example 4 (1), which is also visually confirmed. It can also be seen that the initial oxygen concentration decline rate of Example 7 () is slower than that of the comparative example. Here, 'initial' may mean an arbitrary time range (1 minute to 10 minutes (or 5 minutes)) corresponding to the initial stage of the reaction.

The descending rate of the initial oxygen concentration means the initial oxygen removal rate. Therefore, the faster the descent rate of the initial oxygen concentration, the faster the initial oxygen removal rate.

However, the decrease in the initial oxygen concentration in FIG. 2 is a nonlinear curve shape, and it is difficult to linearly detect the descending slope of the initial oxygen concentration. In this embodiment, the nonlinear curve is converted into a linear linear shape through a regression linear method, and the slope value of the converted linear straight line is immediately determined as an initial oxygen removal rate. If the slope value of the straight line is large, the initial oxygen removal rate is fast, and if the slope value is small, the initial oxygen removal rate is slow.

The relationship between two variables can be expressed as a linear equation like the form y = ax + b, and a is the slope to be obtained immediately. Lt; / RTI > Regression analysis is used to determine various reaction rates or to determine the removal rate of impurities.

Hereinafter, an example applied to the present invention will be described. It can be confirmed that the initial oxygen removal rate decreases non-linearly with time as shown in FIG. 2. Therefore, in this embodiment, it is assumed that the decrease in oxygen concentration is proportional to the square of the oxygen concentration. From this, Equation (2) below can be deduced.

Here, K _o The value is an apparent oxygen removal rate constant, which represents a value corresponding to the slope value to be obtained, that is, the initial oxygen removal rate. This K _o is used as a measure to compare the relative initial oxygen removal rate between the flux materials of each example in Table 2 and the comparative example.

In the last equation of Equation 2, the left side corresponds to the y variable in the first order equation, the t (time) on the right side corresponds to the x variable, and K _o corresponds to the slope value a of the straight line.

3 is a conceptual diagram illustrating an initial oxygen removal rate calculation process according to step S140 of FIG. The left graph of FIG. 3 corresponds to the oxygen concentration change with time as raw data corresponding to FIG. Since the left graph has non-linearity as shown in FIG. 2, it can be transformed into a linear graph as shown in the right side through Equation (2).

That is, in the right graph, the nonlinear curve is linearized by constructing the left side as the y-axis and the right side as the time axis in the last equation of Equation (2). For reference, the last point in the theoretical interpretation is excluded from the regression process. In the right graph, the dotted line portion corresponds to a straight line between two points corresponding to 1 minute and 10 minutes, and the reliability of the straight line according to the present invention obtained by regression of four points is lower than that of the present invention.

The slope of the straight line K _o Values can be calculated for each of Examples 1 to 12 and Comparative Examples. The initial oxygen removal rate (%) in Table 2 shows how the K _o value of the comparative example is set to 100 (%) and the K _o value of each embodiment is based on 100 (%) based on 100 . The example in which the initial oxygen removal rate is 100% or more corresponds to a flux material having a better oxygen reducing ability than the comparative example, and the embodiment with less than 100% corresponds to a flux material having an oxygen reducing ability lower than that of the comparative example.

4 is a graph showing the result of step S140 of FIG. FIG. 4 shows the initial oxygen removal rate for each comparative example and corresponds to the data in Table 2.

Here, Examples 1, 6, and 7 show initial oxygen removal rate characteristics lower than the initial oxygen removal rate of 100% (dotted line) in the comparative example. As a result, excellent initial oxygen removal rate compared to the comparative example was secured in nine of the twelve examples. Especially, in the two examples (Examples 4 and 10), the initial oxygen removal rate .

Referring to the results of Table 2 and FIG. 4, When the CaO concentration is less than 40 mass%, the thermodynamically equilibrium oxygen content increases and the oxygen removal rate decreases. When the CaO concentration exceeds 50 mass% (Example 11), the flux has a relatively high viscosity, The removal rate is lowered.

When the Al ₂ O ₃ concentration is 5% by mass or more, the melting point of the flux rises and it is difficult to secure proper fluidity. Therefore, it is required to be 5% by mass or less.

When the SiO ₂ concentration is 20 mass% or less, the basicity of the flux excessively increases, the viscosity of the flux increases, the fluidity deteriorates, and when the SiO ₂ concentration is 25 mass% or more, the thermodynamic equilibrium oxygen content increases.

When the CaF ₂ concentration is 10 mass% or less, it is difficult to secure the fluidity of the flux, so that the oxygen removal rate is lowered. When the CaF ₂ concentration is 25 mass% or more, the flux fluidity is too low to make the bead shape bad, .

The optimal composition ratio range can be extracted from the composition ratio satisfying all of the above conditions. That is, the composition ratio range of the oxides and fluorides for reducing the oxygen content in the molten metal can be obtained from the initial oxygen removal rate calculated for each steel sample (S150). The step S150 may be performed in the operation processing unit.

For example, the optimal composition ratio range of oxides and fluorides for reducing the oxygen content can be determined by combining the composition ratios of the flux materials corresponding to the steel samples of the upper-group of which the initial oxygen removal rate is fast.

The optimum composition ratio of the oxides and fluorides for reducing the oxygen content in the molten metal of the welded part is preferably 40 to 50 mass% of CaO, 0.1 to 5 mass% of Al ₂ O ₃ , 20 to 25 mass% of SiO ₂ , 10 to 25 mass% fluoride, and 0.1 to 15 mass% other oxides. In this embodiment, the fluoride is CaF ₂ and the other oxide is MgO.

When the optimum compositional ratio range is satisfied, it corresponds to Examples 4, 5, 9, 10 and 12, and the basicity thereof has a value of 2.7 to 3.4.

If the composition ratio obtained according to the present invention is used, it is preferable to use a composition ratio of 40 to 50 mass% CaO, 0.1 to 5 mass% Al ₂ O ₃ , 20 to 25 mass% SiO ₂ , 10 to 25 mass% And 0.1 to 15 mass% of other oxides. It is also possible to adjust the values within the range to adjust the basicity to a value of 2.7 to 3.4.

Here, the fluoride is not necessarily limited to CaF ₂ but may be CaF ₂ (fluorspar or fluorite), MgF ₂ (sellaite), Na ₃ AlF ₆ (cryolite), NaF (villiaumite) ). ≪ / RTI > Of course, the fluoride may be collectively referred to as various minerals containing fluorine (F).

INDUSTRIAL APPLICABILITY According to the present invention as described above, it is possible to secure a lower oxygen concentration in a welded portion in a short time by obtaining a suitable oxide and fluoride ratio of a basic flux cored wire useful for reducing oxygen in a welded portion.

That is, according to the present invention, a plurality of flux materials in which oxides and fluorides are mixed in different composition ratios are reacted with a steel material sample, and then the oxygen removal rate in the steel material sample is analyzed to determine the composition ratio range of oxides and fluorides Can be obtained. In addition, it is possible to constitute a flux composition useful for oxygen reduction having the composition ratio range described above. When such a flux composition is used for welding, it is possible not only to secure a low oxygen concentration in a welding portion in a short time, .

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (8)

A method for obtaining a flux composition for reducing oxygen content in molten metal in a weld zone,
Melting respective steel samples made of the same metal composition;
Preparing a plurality of flux materials in which oxides and fluorides are mixed in different composition ratios and reacting with the molten steel samples;
Measuring oxygen content in each of the steel samples reacted with the flux material for each set time interval;
Calculating an oxygen removal rate for each of the steel samples from the oxygen content according to the time interval; And
Wherein the oxygen removal rate of each of the steel samples is used to obtain a range of composition ratios of the oxides and fluorides for reducing the oxygen content in the molten metal, And combining the composition ratio values of the material to obtain a range of composition ratios of the oxides and fluorides for reducing the oxygen content in the molten metal, respectively, in order to reduce the content of oxygen in the molten metal. delete The method according to claim 1,
The oxide is CaO, Al ₂ O _3, SiO _2, including MgO, and the fluoride is CaF _2, MgF _2, Na ₃ AlF _6, NaF in the weld zone, comprising at least one molten metal in the oxygen content for the reduction ≪ / RTI > The method of claim 3,
The composition ratio of the oxides and the fluorides for reducing the oxygen content in the molten metal of the welded portion is not particularly limited,
40 and consisting of 50% by weight of CaO, 0.1 - 5 mass% of Al ₂ O _3, 20 to 25% by weight of SiO _2, 10 to 25 mass% of fluoride, and 0.1 to 15% by mass of MgO, the melt of a weld A method for obtaining a flux composition for reducing oxygen content in a metal. The method of claim 4,
The fluoride is CaF ₂ ,
A method for obtaining a flux composition for reducing oxygen content in a molten metal of a welded portion having a basicity index defined by the following formula and having a value of 2.7 to 3.4

. 40 to 50% by weight of CaO, 0.1 to 5 mass% of Al ₂ O _3, 20 ~ 25 mass% SiO _2, 10 ~ 25% by weight of fluoride, and consisting of other oxides of 0.1 to 15% by weight, of a weld A flux composition for reducing oxygen content in molten metal. The method of claim 6,
Wherein the fluoride comprises at least one of CaF ₂ , MgF ₂ , Na ₃ AlF ₆ , and NaF. The method of claim 6,
Wherein the fluoride is CaF ₂ and the other oxide is MgO,
Wherein a basicity index defined by the following formula is 2.7 to 3.4, and a flux composition for reducing the oxygen content in the molten metal of the welded portion

.

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