KR100559496B1 - Copper mother alloys containing barium for the use of manufactureing stainless steels - Google Patents

Abstract

The present invention has a higher recovery rate than commercially available commercially available MM and Ca-Si, and exhibits a beneficial effect on their deoxidation, desulfurization and hot workability, as well as the formation of highly brittle intermetallic phases during casting. Stainless steel, consisting of 3.0 to 25% Ba and the remainder consisting of copper and inevitable impurities, in weight percent, to slow casting speed to prevent casting cracks and provide an environmentally friendly base alloy with low dust and gas generation Provided is a barium-based copper master alloy for steel production.

Description

Barium-containing copper master alloy for stainless steel production {COPPER MOTHER ALLOYS CONTAINING BARIUM FOR THE USE OF MANUFACTUREING STAINLESS STEELS}

Figures 1a to 1c shows the effect of the addition of the master alloy according to the invention on the edge crack (Edge Crack) generation of super duplex stainless steel during hot rolling, Figure 1a is a case where the master alloy according to the present invention is not added, 1b shows a case where the master alloy MM2 according to the present invention is added alone, and FIG. 1c shows a case where the master alloys MM2 and Ba2 according to the present invention are added together.

2 is a chart showing the effect of the addition of the master alloy according to the present invention on the high temperature ductility of the super duplex stainless steel hot rolled sheet during the Gleeble Test.

3 is a diagram showing the effect of the addition of the master alloy according to the present invention on the anodic polarization behavior (0.5N HCl + 1.0N NaCl solution at 50 ° C) of a super duplex stainless steel hot rolled sheet subjected to 10 minutes aging at 850 ° C. .

Figures 4a and 4b shows the effect of the addition of MM and Ba according to the present invention on the solidification structure of the super duplex stainless steel casting material, Figure 4a is a solidification structure of the steel is added MM1 + Ba1, Figure 4b is not added MM and Bark Show the solidification of the steel.

FIG. 5 is a chart showing the effect of MM and Ba addition on the corrosion resistance of super duplex stainless steel in the cast state (coin positive polarization test in 0.5N HCl + 1.0N NaCl solution at 50 ° C.).

6a and 6b show the effect of the addition of MM and Ba in accordance with the present invention on the microstructure of the super duplex stainless steel casting material aging heat treatment for 30 minutes at 850 ℃, Figure 6a shows the microstructure of the steel to which MM1 + Ba1 is added 6b shows the microstructure of steel without MM and Ba added, respectively.

7A and 7B are X-ray diffraction test results showing the effect of the addition of MM and Ba according to the present invention on the formation of brittle phases (α and χ phases) of super duplex stainless steel castings aged at 850 ° C. for 30 minutes. 7A shows the test results of the steel to which MM1 + Ba1 was added, and FIG. 7B shows the test results of the steel to which MM and Ba were not added.

8 is a diagram showing the effect of the addition of MM and Ba according to the present invention on the corrosion resistance of super duplex stainless steel castings aged aged at 850 ℃ for 30 minutes (coin in 0.5N HCl + 1.0N NaCl solution at 50 ℃ Anode polarization test).

The present invention has the effect of deoxidation and desulfurization when refining stainless steel, inhibits the sole production of Al ₂ O ₃ , MnS non-metallic inclusions that adversely affect the properties of the steel, reduce the occurrence of cracks during hot working, casting The present invention relates to a method for greatly increasing the content of rare earth and barium, which can improve corrosion resistance and toughness by delaying the precipitation of intermetallic phases such as sigma and kasang, which are highly brittle. The application of this method also greatly reduces dust and gas generation during dissolution.

Mischmetal is a mixture of rare earth metals in the form of atomic number 57 to 71, which is currently used by some manufacturers in the production of cast and hot rolled sheets, with a minimum of 50% Ce, certain La, Nd and Pr, Defined as Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Fe of less than 1%, for example, the main component is 51% Ce-26% La-15.5 % Nd-5.5% Pr with the remainder being MM consisting of Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc and Fe up to 1%, hereinafter referred to as "MM" Among the above-mentioned effects, it is effective in suppressing the occurrence of cracking during deoxidation, desulfurization and hot working, but it is pointed out that the content of stainless steel is also low due to the low recovery rate during charging.

In addition, the Ca mother alloy (commercialized commercially available commodity chemical composition: 31% Ca-60% Si-1.4Al%-remaining Fe) has the effect of deoxidation and desulfurization, and is also effective in suppressing crack formation during hot working. However, there is a lot of dust and gas generation causes environmental pollution, there is a low economic recovery due to a low recovery rate at the time of charging.

On the other hand, the inventors of the present application in PCT / KR03 / 00568 international application No. PCT / KR03 / 00568 using the MM and barium pure metal to suppress the formation rate of brittle intermetallic phase, high mechanical properties, high corrosion resistance, improved embrittlement resistance and hot It has been found that the processability can be improved and the characteristics can be expected to be improved if the recovery rate of these MM and barium pure metal is higher.

Accordingly, the present invention has a higher recovery rate than conventionally applied MM and Ca-Si, and exhibits a beneficial effect on their deoxidation, desulfurization and hot workability, as well as the formation of highly brittle intermetallic phases during casting. It aims at slowing down the speed of preventing casting cracks and providing environmentally friendly rare earth and barium mother alloys with low dust and gas generation.

In addition, the present invention provides a method for producing stainless steel having the above-described excellent properties using these master alloys.

The present invention provides, in weight percent, a barium-containing copper master alloy for the production of stainless steel consisting of 3.0-25% Ba and the remainder consisting of copper and inevitable impurities.

The role of each component in the rare earth nickel master alloy and barium copper master alloy according to the present invention is as follows.

Rare Earth Nickel Master Alloy

MM: 10 to 54%

MM (Ce, La, Nd, Pr, etc.) rare earth metal elements with a large atomic radius have an effect of decreasing the precipitation rate of the brittle intermetallic phases during casting, and spheroidize sulfides or combine with sulfur or oxygen to form rare earth oxides. Or it is an important element to improve the hot workability and machinability by forming Oxysulfide (Oxysulfide). Sulfur is fixed as a high melting point (melting point: 2100 ℃) compound in the initial process of solidification during welding, and it is effective in improving the weld cracking susceptibility. There is an effect of reducing the deformation resistance.

Ni: 46% to 90%

Rare earth metals of MM (Ce, La, Nd, Pr, etc.) form a solid solution with nickel base metals up to 54% (Ref. Equilibrium diagrams pp. 340). Nickel is an austenite stabilizing element which is an essential addition to stainless steels. Basic element.

Barium-based copper master alloy

Ba: 3-25%

Barium having a large atomic radius is effective in reducing the deposition rate of brittle intermetallic phases. In addition, it is possible to slow down the deposition rate of the intermetallic phases α and χ by combining with oxygen to form an oxide.

Cu: 75-97%

Ba forms a solid solution with copper base metals up to 25% (Ref. Equilibrium diagrams pp. 112), and copper acts as a useful element added to stainless steel to improve the corrosion resistance. In addition, copper induces a substitution-type solid solution strengthening effect to increase the tensile strength and yield strength.

It is possible to suppress the formation of the unwanted precipitate phase only by forming a solid solution with the above-described component composition. In addition, in order to obtain a target composition when comparing the recovery rate with respect to the addition amount in the production of super duplex stainless steel, it was confirmed through the experiments of the examples described below that producing the master alloy with the above-described ingredient composition shows the optimal characteristics.

Example

Example 1 Preparation of the Master Alloy According to the Invention

The mother alloy manufacturing method which concerns on this invention is as follows.

To produce a rare earth-based nickel master alloy, pure commercial grade nickel (purity 99.9%) was charged to a magnesia crucible mounted in a vacuum induction furnace, and then dissolved about 70% in a vacuum atmosphere of about 10 ^-2 torr, followed by Ar gas. After purging at about 50 torr, the remaining amount of Ni was dissolved. Then, MM (53% Ce-26% La-17% Nd -4% Pr) was added through the Hopper to complete dissolution, and then molten metal was injected into a fully preheated square steel mold to ingots weighing 25 kg (80 mm horizontally). x rare earth base alloys of 80 mm x height 300 mm) were prepared. The chemical compositions of these master alloy names REM 1, 2, 3 are shown in Table 1.

In order to manufacture a barium-based copper master alloy, pure commercial grade copper (purity 99.9%) was first dissolved under the above conditions, and then pure metal barium (purity 99.9%) was added to complete the dissolution. The molten metal was injected into the mold to prepare four types of master alloys having a 25 kg weight of ingot (80 mm x 80 mm x 300 mm in height). The chemical compositions of these master alloys Ba 1, 2, 3, 4 are shown in Table 1.

[Table 1] Comparison of chemical composition (unit: wt.%)

division MM Ni Ba Cu Inventive Alloy Rare Earth Master Alloy MM 1 10.39 89.35 - - MM 2 13.16 85.64 - - MM 3 14.69 60.79 - - Barium Base Alloy Ba 1 - - 7.06 92.86 Ba 2 - - 8.92 90.95 Ba 3 - - 13.47 78.08 Ba 4 - - 4.76 95.11 Comparison Mish Metal MM 100 - - - Barium pure metal Ba - - Over 99 -

Example 2 Comparison of Recovery of the Master Alloy, Mischmetal and Pure Metal Barium According to the Present Invention

Steel grades used to compare the recovery rate of the mother alloy, MM, and barium metal according to the present invention are formulated with the official resistance equivalent index [PREW =% Cr + 3.3 (% Mo + 0.5% W) + 30% N 50 grade super duplex stainless steel. The main chemical composition is 27% Cr-7% Ni-2.5% Mo-3.2% W-0.35% N-2% Mn-0.3% Si-0.02% C.

After commercial melting of Fe, Cr, Mo, Ni, W, Cu, Si, Mn, Fe-Cr-N, etc., which have pure commercial grades, using a vacuum induction furnace, it is a conventional method by Al or Ca or Al + Ca complex deoxidation. After preliminary deoxidation, three rare earth nickel base alloys and four barium copper base alloys shown in Table 1 were added alone or in combination to prepare stainless steel. Table 2 shows a comparison of the recovery rates of the rare earth-based and barium-based master alloys according to the present invention when loading MM and barium metal.

As a result of wet analysis of the chemical composition of MM and Ba contained in the cast material by ICP Mass Spectroscopy, as shown in Table 2, MM is up to 4 times and Ba is 18 times as shown in Table 2. It can be seen that the degree of recovery is increased.

[Table 2] Comparison of recovery rate at charging (unit: wt.%)

division MM Ba adding analysis Recovery rate (Unit:%) adding analysis Recovery rate (Unit:%) Inventive Alloy MM 1 (3-2) 0.165 0.033 20 - - - MM 2 (3-3) 0.083 0.022 26.5 - - - MM1 + Ba1 (3-4) 0.165 0.07 42.4 0.022 0.002 9.1 MM2 + Ba2 (3-5) 0.083 0.034 41 0.011 0.0022 20.0 MM3 + Ba3 (2-1) 0.22 0.083 37.7 0.07 0.008 11.4 Ba4 (4-3) - - - 0.067 0.008 11.9 Comparison MM 0.304 0.032 10.5 - - - Ba - - - 0.092 0.001 1.1

Example 3 Effect of the Master Alloy Addition According to the Invention on Edge Crack Generation of Super Duplex Stainless Steel During Hot Rolling

After injecting molten metal melted under the conditions of Example 2 into a fully preheated square steel mold to examine the hot workability of the master alloy according to the present invention, after soaking at 1,250 ° C., a 30 kg ingot was produced. Hot rolling was performed to a thickness of 6 mm.

Considering the effects of rare earth and barium metal in the master alloy on the occurrence of edge cracks in the hot rolled sheet fabricated as described above (FIGS. 1A to 1C), rare earth nickel base alloys are added alone or barium copper In the case where the master alloy is added in combination, the length of the edge cracks is smaller than that in the case where the master alloy is not added, so that the hot workability is excellent.

On the other hand, after fabricating a hot tensile specimen of diameter 10mm, 120mm in length from a 12mm thick hot rolled sheet, the gobble test was performed to examine the effect of the master alloy addition on the high temperature ductility. From the measurement results of the reduction of the cross-sectional area (Fig. 2), when the rare earth nickel master alloy and the barium copper master alloy were added, the high temperature ductility was much higher than that of the non-added comparative alloy, and the composite addition content of these master alloys increased. It can be seen that the higher the hot ductility is increased. Combined effect of the master alloy according to the present invention is comparable edge crack reduction, high temperature as compared with the invention steel 10 (0.09% MM + 0.01% Ba) described by the inventors PCT / KR03 / 00568 An increase in ductility and high recoveries of rare earth metals and barium metals were obtained.

Example 4: Effect of the master alloy according to the invention on the corrosion resistance of aging heat-treated super duplex stainless steel hot rolled sheet

The hot rolled sheet was subjected to solid solution heat treatment in the range of 1,050 to 1,150 ° C, followed by aging heat treatment at 850 ° C for 10 minutes, and then anodic polarization at 1 mV / sec scanning rate in a degassed 50 ° C 0.5N HCl + 1.0N NaCl solution The results of the test (ASTM G5) are shown in FIG. 3.

FIG. 3 shows the addition of MM 2 alone, MM 3+ Ba3 complex, unadded BASE and commercial hot rolled plates (French USINOR INDUSTEEL, UR52N +), the mother alloys according to the present invention which were heat treated at 850 ° C. for 10 minutes. Anode polarization resistance is shown. In the polarization curve, the higher the formal potential and the lower the passivation current density, the better the formal resistance. Therefore, the formula resistance and the passivation current density can be compared to show the formula resistance.

The formal resistance of the master alloy MM3 + Ba3 composite steel and MM2 alone steel of the present invention is the precipitation of α and χ phases between metals of BASE and commercially available UR52N + (second generation duplex plate without rare earth elements and Ba added). It can be seen that the formal resistance is improved by the delay.

The effect of the master alloy MM3 + Ba3 composite additive steel according to the present invention was comparable to the inventive steel 10 (0.09% MM + 0.01% Ba) to which the present inventors compositely added the MM and barium metal described above. The effect of the master alloy MM2 alone-added steel was comparable to the inventive steel 24 (0.025% MM) described in the inventors' previous application.

Example 5 Effect of the Master Alloy According to the Present Invention on the Solidification Structure of Super Duplex Stainless Steel Castings

Fe, Cr, Mo, Ni, W, Cu, Si, Mn, Fe-Cr-N, etc., which have pure commercial quality, are dissolved in the air using a high frequency induction furnace and then converted by Al or Ca or Al + Ca complex deoxidation After the preliminary deoxidation by a conventional method, a rare earth nickel master alloy MM1 and a barium copper master alloy Ba1 were added to prepare a super duplex stainless steel.

As can be seen from the effect of the addition of the MM and Ba composite of Figs. 4a and 4b on the coagulation structure, the MM and Ba composite addition steel (Fig. 4a) compared to the no additive steel (Fig. 4b) in the molten steel RE ₂ O ₃ + (RE, It is possible to prevent the formation of molten steel of Al ₂ O ₃ and MnS which adversely affects the characteristics of duplex stainless steel by the rare earth-based compound compound of 3 μm or less composed of Al) ₂ O ₂ S + RES and barium oxide. It acts as a heterogeneous nucleation site for normal growth, miniaturizing coagulation structure, and at the same time, MM (Ce, La, Nd, Pr, etc.) having a complex compound, oxide, and atomic radius of 20% or more than Cr, Mo, and W; and The deposition rate of the brittle intermetallic phase (α, χ, etc.) in which solute elements such as Cr, Mo, W, and Si are bonded and precipitated by Ba atoms can be delayed.

Example 6 Effect of the Master Alloy According to the Invention on the Corrosion Resistance of Super Duplex Stainless Steel Castings

Figure 5 shows the effect of the addition of MM and Ba composite on the corrosion resistance of the duplex stainless steel in the casting state, it is found that the MM and Ba addition steel is measured about 50 times less passivating current density than the additive-free steel, which is very excellent corrosion resistance Can be. This may be because the amount of precipitation of the intermetallic phase inhibiting corrosion resistance by the addition of MM and Ba is much smaller than that of the additive-free steel, as described in the solidification structure of FIG. 4. The mother alloy MM1 + Ba1 composite addition effect according to the present invention was comparable to invention steel 3 (0.05% MM + 0.01% Ba) in which the MM and barium metals of the inventors described above were added.

Example 7: Effect of the master alloy according to the invention on the aging characteristics of super duplex stainless steel castings

6A and 6B show the effect of the addition of MM and Ba composite to the microstructure of super duplex stainless steel castings that were aged heat-treated at 850 ° C. for 30 minutes after solid solution heat treatment at 1,130 ° C. It can be seen that the precipitation of the intermetallic phase (α, χ, etc.), which is more brittle than 6a) is not added to the steel (Fig. 6b).

7A and 7B show the effect of the addition of MM and Ba on the phase stability of super duplex stainless steel castings aged at 850 ° C. for 30 minutes by X-ray diffraction test. It can be seen that the precipitation of the intermetallic phases (α, χ etc.) having a stronger brittleness than this steel (Fig. 7B) is relatively small.

Figure 8 shows the effect of the addition of MM and Ba on the corrosion resistance of the super duplex stainless steel castings aging heat treatment for 30 minutes at 850 ℃, the MM and Ba composite steels (α) , χ, etc.) are relatively small, indicating that the official potential is measured high.

The above-described master alloy MM1 + Ba1 composite addition effects according to the present invention were comparable to the inventive steel 3 (0.05% MM + 0.01% Ba), which was a composite addition of MM and barium metal described in the above-mentioned applicants.

In the case of steelmaking, when the rare earth metal and barium are added using the master alloys according to the present invention, their recovery may be greatly increased, and their content in stainless steel may be greatly increased. Therefore, it reduces the occurrence of cracks during hot working, delays the precipitation of intermetallic phases such as sigma and carbure, which are brittle during casting, and improves corrosion resistance and toughness, reduces dust and gas generation, deoxidation and desulfurization. Increasing the efficiency of, can further suppress the formation of harmful non-metallic inclusions such as Al ₂ O ₃ , MnS.

Claims (1)

A barium-containing copper master alloy for the production of stainless steel, comprising, by weight, 3.0 to 25% Ba and the remainder consisting of copper and inevitable impurities.

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