KR20200016008A - Lean duplex stainless steel for architecture and method for manufacturing thereof - Google Patents

Abstract

The present invention relates to lean duplex stainless steel used as an interior or exterior material of a building and, more specifically, to a method for manufacturing lean duplex stainless steel and lean duplex stainless steel manufactured therefrom, wherein the lean duplex stainless steel has a surface with minimized light reflection while having uniform luster. The lean duplex stainless steel comprises: 0.03 wt% or less (excluding 0 wt%) of C; 0.4-0.7 wt% of Si; 2.3-2.7 wt% of Mn; 0.15-0.19 wt% of N; 20.0-20.4 wt% of Cr; 2.3-2.7 wt% of Ni; 0.5 wt% or less of Cu; 1.3-1.5 wt% of Mo; 0.035 wt% or less of P; 0.003 wt% or less of S; and the remainder consisting of Fe and other unavoidable impurities.

Description

Lean duplex stainless steel for building interior and exterior and manufacturing method thereof {LEAN DUPLEX STAINLESS STEEL FOR ARCHITECTURE AND METHOD FOR MANUFACTURING THEREOF}

The present invention relates to a lean duplex stainless steel used for the interior or exterior of a building, and a method of manufacturing the same.

In general, the exterior of a building is made of glass, metal plates or tiles. Among them, the tiles are fixed, which takes a lot of time and money when replacing the exterior. Recently, the trend is to use glass or metal plate, but glass or metal plate has a problem of severe light reflection.

In particular, when the metal plate is applied as an exterior panel application, a material having excellent corrosion resistance, uniform gloss, and minimal light reflection is required, and it should be able to be manufactured at low cost in consideration of economic aspects.

As a suitable material for this, STS329LD steel, which is a lean duplex stainless steel, can be proposed. The STS3329LD steel has a low Ni content and high nitrogen, thereby providing economical and corrosion resistance at the same time.

On the other hand, when the production of the STS329LD steel in the playing process, because of the duplex structure has a limitation in using as an exterior material.

Therefore, in producing STS329LD steel suitable for interior and exterior panel applications, there is a need for a method of having a surface with minimal light reflection while having uniform glossiness as well as corrosion resistance.

One aspect of the present invention is a lean duplex stainless steel used for interior or exterior of a building, a method of manufacturing a lean duplex stainless steel having a uniform gloss and having a surface with minimal light reflection and a lean manufactured therefrom To provide a duplex stainless steel.

The subject of this invention is not limited to the above-mentioned matter. Additional objects of the present invention are described in the general description, and those skilled in the art will have no difficulty understanding the additional objects of the present invention from the contents described in the present specification.

One aspect of the present invention, in weight%, C: 0.03% or less (excluding 0%), Si: 0.4-0.7%, Mn: 2.3-2.7%, N: 0.15-0.19%, Cr: 20.0-20.4%, Ni: 2.3 ~ 2.7%, Cu: 0.5% or less, Mo: 1.3 ~ 1.5%, P: 0.035% or less, S: 0.003% or less, balance Fe and other unavoidable impurities Provides lean duplex stainless steel for interior and exterior.

Another aspect of the invention, the step of producing a steel strip having the alloy composition described above; Hot rolling the steel strip to produce a hot rolled material; Hot rolling and pickling the hot rolled material; Manufacturing a cold rolled material by cold rolling the hot rolled annealing treated hot rolled material; And annealing the cold rolled material;

Annealing the cold-rolled material annealing is a method of manufacturing a building interior and exterior lean duplex stainless steel comprising the step of projecting a shotball at a speed of 2000 ~ 2500rpm and a pickling treatment at a HF concentration of 15 ~ 20g / L to provide.

According to the present invention, it is possible to provide a lean duplex stainless steel having a uniform gloss and having a surface with minimal light reflection.

The lean duplex stainless steel of the present invention can be suitably applied for interior and exterior of buildings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a detailed view of a twin roll sheet casting machine.
FIG. 2 shows the surface a of STS329LD steel produced by the continuous casting process and the surface b of STS329LD steel produced by the strip casting process.

The inventors believe that STS329LD steel, a lean duplex stainless steel that is excellent in corrosion resistance and can be manufactured at low cost, is suitable as a material for building interior and exterior. It confirmed that it was unsuitable as a exterior material which is required.

Accordingly, the present inventors have studied in depth how to form a surface with minimal gloss while having uniform gloss in manufacturing STS329LD steel. As a result, it was confirmed that when the STS329LD steel is manufactured through a strip casting process, there is no generation of streaks, thereby improving surface uniformity, thus completing the present invention.

In particular, in the present invention, in the production of STS329LD steel using a strip casting process, by optimizing the annealing and pickling process after cold rolling, a lean duplex stainless steel having a surface having uniform gloss and minimal light reflection There is a technical significance in providing this.

With reference to FIG. 1, the twin roll type thin-plate casting method is demonstrated. As shown in FIG. 1, the molten steel is accommodated in the ladle 2, the molten steel introduced into the tundish 3 along the nozzle is introduced into the casting roll 1, and the molten steel introduced into the tundish 3 is The solidification is started through the molten steel injection nozzle 4 between the edge dams 7 provided at both ends of the casting roll 1, that is, between the casting rolls 1. At this time, in the molten portion between the casting rolls to protect the molten surface with the meniscus shield (5) in order to prevent oxidation and inject the appropriate gas to properly control the atmosphere. The thin plate is manufactured and drawn while rolling out the roll nip where both casting rolls meet, and then rolled through the rolling mill 12 and then wound in the winding facility 11 through the cooling process 10.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

First, the lean duplex stainless steel for building interior and exterior according to an aspect of the present invention by weight, C: 0.03% or less (excluding 0%), Si: 0.4 ~ 0.7%, Mn: 2.3 ~ 2.7%, N: 0.15 ~ 0.19%, Cr: 20.0-20.4%, Ni: 2.3-2.7%, Cu: 0.5% or less, Mo: 1.3-1.5%, P: 0.035% or less, S: 0.003% or less, residual Fe and other unavoidable impurities can do.

The above-described composition reduces the content of Mo, Ni, which is an expensive component in the conventional system of duplex stainless steel, increases the mechanical properties by increasing the content of Mn and N, and improves the mechanical properties of the lean duplex stainless steel. It is an ingredient system.

Hereinafter, the reason for limiting the content of each component as described above will be described. At this time, unless otherwise specified, the content of each component means weight%.

Carbon (C): 0.03% or less (excluding 0%)

C is a forming element of the austenite phase and is an element effective for increasing the strength by solid solution strengthening. Excessive addition of C readily binds to carbide forming elements such as Cr, which are effective for corrosion resistance at the ferrite-austenite phase boundary, thereby lowering the Cr content around the grain boundary and reducing corrosion resistance. Therefore, in order to maximize corrosion resistance, it is preferable to add 0.03% or less, and 0% is excluded.

Silicon (Si): 0.4 ~ 0.7%

Si is added for the deoxidation effect. In addition, the Si is an element that is concentrated in the ferrite during the annealing heat treatment as a forming element on the ferrite phase. Therefore, it is preferable to add at least 0.4% in order to secure deoxidation and ferrite phase fraction. However, when the content exceeds 0.7%, the hardness of the ferrite phase is sharply increased to lower the elongation and the fraction of the austenite phase is decreased. In addition, in the steelmaking process, the slag fluidity is lowered and corrosion resistance is degraded by combining with oxygen to form inclusions. Therefore, the Si content is preferably limited to 0.4 to 0.7%.

Manganese (Mn): 2.3-2.7%

Mn is an element which increases the deoxidizer and nitrogen solubility, and is added in place of expensive Ni as an austenite forming element. As the content of Mn increases, nitrogen solubility is improved, but there is a disadvantage in that MnS is formed by combining with S in steel and inhibiting corrosion resistance. In addition, when the content of Mn decreases, it is difficult to secure an appropriate austenite phase fraction even by adjusting the austenite forming elements Ni, Cu, and N, and due to the low solubility of added N, nitrogen cannot be sufficiently employed at normal pressure. . Therefore, the content of Mn is preferably limited to 2.3 ~ 2.7%.

Nitrogen (N): 0.15-0.19%

N is an element that contributes to stabilization of the austenite phase together with Ni in duplex stainless steel, and is one of the elements concentrated on the austenite phase during annealing heat treatment. Therefore, it is possible to improve the corrosion resistance and strength by incidentally increasing the N content, but it is necessary to control the content because the solid solubility of N changes according to the content of Mn added. In the Mn range of the present invention, if the N content exceeds 0.19%, blow holes and pin holes may occur during casting due to excess nitrogen solubility to cause surface defects of the product. On the other hand, if the N content is too low, it is difficult to secure an appropriate percentage of lean duplex stainless steel with the decrease in strength. Therefore, the content of N is preferably limited to 0.15 ~ 0.19%.

Chromium (Cr): 20.0-20.4%

Cr is an element which stabilizes ferrite together with Si, and plays a major role in securing the ferrite phase of duplex stainless steel and is an essential element for securing corrosion resistance. As the Cr content increases, the corrosion resistance of the steel is improved, but since the ferrite phase is excessively stabilized, there is a disadvantage in that the content of expensive Ni or other austenite stabilizing elements must be increased in order to maintain an appropriate fraction of the austenite phase. Therefore, in order to secure sufficient corrosion resistance while maintaining the phase fraction of ferrite-austenite, it is preferable to limit the content of Cr to 20.0 to 20.4%.

Nickel (Ni): 2.3 ~ 2.7%

Ni is an element which stabilizes an austenite phase together with Mn, Cu, and N, and plays an important role in securing the austenite phase of duplex stainless steel and is one of the elements effective in securing an elongation during cold working. Such Ni is preferably added in an amount of 2.3% or more to prevent a phenomenon in which workability is rapidly hardened due to the generation of excessive calcined organic martensite and the workability is lowered to secure the austenite phase stability. On the other hand, excessive addition of Ni increases the austenite phase fraction, making it difficult to secure an appropriate ferrite phase fraction, as well as stabilizing the austenite phase so that generation of the calcined organic martensite phase during cold working is suppressed, thereby ensuring sufficient work hardenability. It is difficult to secure a competitive edge by increasing the manufacturing cost of products due to difficult and expensive Ni. Therefore, in order to reduce the cost, it is desirable to reduce the expensive Ni content as much as possible, and to increase the Mn and N to replace it to maintain the austenite phase fraction. More preferably, the content of Ni is preferably limited to 2.3 to 2.7%.

Copper (Cu): 0.5% or less (except 0%)

Cu, which plays a role similar to that of Ni, is preferably lowered to a minimum in order to reduce cost. When the content of Cu exceeds 0.5%, product processing becomes difficult due to hot brittleness. Therefore, the Cu content is preferably limited to 0.5% or less. However, 0% is excluded considering the level inevitably added in the steel manufacturing process.

Molybdenum (Mo): 1.3-1.5%

Mo is an element added in order to further improve corrosion resistance. By adding such Mo, the corrosion resistance of 329LD steel grade can be ensured at 316L or more, and from this, favorable corrosion resistance can be ensured in moisture or a chlorine atmosphere.

In order to obtain sufficient corrosion resistance, it is preferable to add Mo to 1.3% or more. However, since it is an expensive element, it is preferable to limit it to 1.5% or less in consideration of manufacturing cost.

Phosphorus (P): 0.035% or less (excluding 0%), Sulfur (S): 0.003% or less (excluding 0%)

P and S are unavoidable impurities, and it is preferable to remove them as much as possible, but in order to lower the content, it is preferable to limit the P: 0.035% or less and S: 0.003% or less.

On the other hand, the remaining components of the present invention is iron (Fe). However, in the ordinary steel manufacturing process, impurities that are not intended from raw materials or the surrounding environment may be inevitably mixed, and thus cannot be excluded. Since these impurities are known to those skilled in the art of ordinary steel manufacturing, not all of them are specifically mentioned in the present specification.

Lean duplex stainless steel of the present invention having the above-described alloy composition is that the glossiness satisfies 13 to 15, as described above, the present invention can provide a steel with a low surface gloss and a uniform gloss, thereby minimizing light reflection. have.

Meanwhile, the glossiness may be measured by using a gloss meter using a gloss meter, for example, by illuminating a light source at a predetermined angle (for example, 20 degrees and 60 degrees), and the ratio of the amount of light received from the receiver to the amount of incident light. Is calculated and shown. The angle of the light source can be set differently depending on the surface of the material.

In addition, the lean duplex stainless steel is preferably an average surface roughness (Ra) of 2.0 ~ 2.5㎛.

On the other hand, according to another aspect of the present invention, it will be described in detail for the manufacturing method of lean duplex stainless steel for building interior and exterior.

As described above, the lean duplex stainless steel of the present invention having a low surface gloss and a uniform gloss can be prepared by [manufacturing a steel strip using a twin roll sheet continuous casting-producing a hot rolled material-hot rolling annealing and pickling treatment of the hot rolled material- Cold rolled material production-annealing treatment of the cold rolled material] may include the process.

First, the steel strip is a weight percent through a twin roll continuous casting process, C: 0.03% or less (excluding 0%), Si: 0.4 ~ 0.7%, Mn: 2.3 ~ 2.7%, N: 0.15 ~ 0.19%, Manufactured with Cr: 20.0-20.4%, Ni: 2.3-2.7%, Cu: 0.5% or less, Mo: 1.3-1.5%, P: 0.035% or less, S: 0.003% or less, balance Fe and other unavoidable impurities It is preferable.

The steel strip having the above-described alloy composition can be produced by using a twin roll thin sheet casting apparatus of molten steel controlled by the above-described alloy composition.

Specifically, the molten steel is supplied between a pair of casting rolls rotating in opposite directions, and the molten steel is solidified in contact with the casting roll surface to form a thin plate.

Thereafter, the steel strip manufactured as described above may be hot rolled to produce a hot rolled material.

The hot rolling may be performed immediately after casting, using an inline roller continuously disposed with a casting roll, and at this time, it is preferable to carry out at a reduction ratio of 20 to 40% at a temperature of 1000 to 1200 ° C.

If the temperature during the hot rolling is less than 1000 ℃ high strength should increase the reduction force In that case, rolling is impossible because it exceeds the facility limit. Also, no dynamic recrystallization occurs, resulting in poor quality. On the other hand, when the temperature exceeds 1200 ° C, defects due to scale occur due to high temperature oxidation, and surface quality deteriorates.

In addition, if the reduction ratio during hot rolling in the above-described temperature range is less than 20%, pores are formed in the central segregation, which may cause deterioration of quality, whereas when it exceeds 40%, rolling loads occur and sticking is performed. ), Resulting in poor surface quality.

The hot rolled material produced by the above can be hot annealed and pickled. At this time, the hot-rolling annealing is preferably carried out for 0.5 to 3 minutes at 1000 ~ 1150 ℃.

According to one embodiment of the present invention, the hot combustion annealing and pickling treatment may be performed in a hot combustion annealing furnace.

If the heat treatment temperature during the hot-rolling annealing is less than 1000 ℃ the two-phase ferrite and austenite defects during rolling, there is a tendency to reduce the elongation due to the lack of recovery and recrystallization of the heat treatment ferrite and austenite. On the other hand, when the heat treatment temperature exceeds 1150 ° C., the crystal grains of ferrite and austenite are too coarse, making it difficult to secure desired physical properties.

In addition, when the heat treatment time during the hot combustion annealing is less than 0.5 minutes, the diffusion causing the distribution of alloying elements is not sufficient. For this reason, the thickening of alloying elements does not generate | occur | produce sufficiently on austenite, and it is difficult to control the rate of transformation organic martensite formation at the time of cold working. On the other hand, when the heat treatment time exceeds 3 minutes, sagging of the plate occurs during heat treatment by the two-phase structure of ferrite and austenite, leading to a decrease in productivity and loss of heat source units.

As described above, the cold rolled material may be manufactured by cold rolling the hot rolled annealing and pickling treated hot rolled material. At this time, it is preferable to perform the cold rolling at a reduction ratio of 50 to 70%.

If the cold rolling rate is less than 50%, there is a possibility that the shape is poor, and if it exceeds 70%, rolling may be difficult due to the rolling load.

Through the cold rolling described above it can be produced a cold rolled material having a thickness of 1 ~ 2mm.

Usually, the surface roughness (Ra) of the cold rolled material manufactured through the cold rolling as described above is low as 0.1 ~ 0.2㎛. When the illuminance is low, light reflection is severe. Therefore, illuminance is increased by performing shotball projection in the annealing process.

Typical cold rolled plate (CR_2B) material has a high degree of gloss and reflects light very much. Even if the cold rolled sheet is subjected to bead blasting or vibration treatment, the glossiness remains similar and the light reflection is still severe. On the other hand, in the case of the hot rolled material HR_1D which increases the roughness by projecting the shotball, the glossiness is lowered to 50 or less, but the gloss uniformity is inferior.

Accordingly, the present invention proposes a method for annealing the cold rolled material.

Specifically, it is preferable to charge the cold rolled material into the annealing acid furnace to perform annealing-free pickling treatment, and the annealing-free pickling treatment step of the cold rolled material may include projecting a shot on the surface of the cold rolled material and performing a mild pickling treatment. It may include.

The annealing pickling treatment may be performed in an annealing pickling treatment process equipped with a shotball treatment facility, but according to one embodiment of the present invention, the annealing pickling treatment of the cold rolled material is used for hot rolling annealing and pickling treatment of the hot rolled material. It can be performed in a hot-rolled annealing furnace. When the annealing pickling treatment is performed in the hot combustion annealing furnace, it is easy to manage the surface roughness through the shotball treatment, and is also advantageous in improving the corrosion resistance through shape correction and weak pickling.

Projecting the shotball on the surface of the cold rolled material is to reduce the surface glossiness by increasing the surface roughness (Ra) of the surface of the cold rolled material. Preferably, the shotball is projected at a speed of 2000 to 2500 rpm to average 1.0 to 1.5 μm. It is preferable to have surface roughness Ra.

If the shot speed of the shotball is less than 2000 rpm, the average surface roughness is difficult to obtain an average surface roughness of 1.0 μm or more, whereas if the shot speed exceeds 2500 rpm, the roughness becomes too excessively large, resulting in a decrease in surface uniformity. If the roughness is too large, there is a problem that the corrosion resistance at the uneven portion is reduced, it would be desirable to manage the surface roughness by controlling the projection speed appropriately.

It is preferable to project the shotball so that the cold rolled material surface has a target average surface roughness, and then pickled at an HF concentration of 15 to 20 g / L.

If the HF concentration is less than 15g / L at the time of pickling, there is a fear that the acid pickling occurs, whereas if it exceeds 20g / L there is a risk that the cold rolled material damage occurs.

It is preferable to charge the cold rolled material into the annealing furnace in the same condition as described above and move the cold rolling material at a line speed of 30 to 40 rpm during the annealing.

If the line speed is less than 30rpm, the shot projection amount of the same area is increased and the illuminance becomes too large. On the other hand, if the line speed exceeds 40rpm, the shot projection amount of the same area is excessively reduced, so that illuminance of a desired size cannot be obtained.

Thus, by performing an annealing pickling in the annealing process of the produced cold rolled material, the cold rolled material which has low surface glossiness and uniform glossiness and low light reflection can be obtained.

The cold rolled material is a lean duplex stainless steel, can be suitably used for interior and exterior of the building, in particular, having a surface with minimal light reflection, there will be an effect that can be applied without restrictions in the downtown.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, it is necessary to note that the following examples are only for illustrating the present invention in more detail, and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.

( Example )

Manufactured STS329LD cold rolled material (0.02% C-0.41% Si-2.54% Mn-0.177% N-20.09% Cr-2.54% Ni-0.08% Cu-1.38% Mo-0.0267% P-0.0016% S) with a thickness of 1.5 mm Thereafter, annealing was performed under the conditions shown in Table 1 below to prepare respective stainless steels. The annealing-free pickling treatment was performed in a hot-burning annealing furnace.

Then, the surface gloss and average surface roughness (Ra) of each manufactured stainless steel were measured. In this case, the surface glossiness was measured at an incident angle of 60 ° and 20 ° using a gloss meter (PICOGLOSS 562 MC (ERICHSEN)). In addition, the surface roughness (Ra) was measured using a surface roughness tester (Surface Roughness Tester (SJ-400, Mitutoyo)).

division Shortball
Projection Speed (rpm) Acid concentration
(g / l) Week
(mpm) Glossiness Average roughness
(Ra) 60 degrees 20 degrees One 2300 15 30 14 2 2.1 2 2300 15 40 15 3 2.1 3 2300 20 30 13 2 2.2

On the other hand, Table 2 shows the gloss of the existing materials. In Table 2, BA (bright annealing) is subjected to bright annealing heat treatment and temper rolling after cold rolling, and 2B means annealing and temper rolling after cold rolling.

Material
Surface mapping Glossiness 60 degrees 20 degrees CR BA 862 573 CR 2B 114 49 CR 2B 132 63 CR Bead 158 39 CR Vib 104 40 HR 1D-soft brushing 5 One HR 1D-hard brushing 34 10

As shown in Table 2, the general cold rolled material (CR) has high glossiness of 100 or more and severely reflects light.

However, in the case of hot rolled material (HR) whose roughness is increased by shotball projection, glossiness is lowered to 50 or less, but gloss uniformity is inferior. As HR material undergoes hot rolling annealing, non-uniform surface scale is generated due to temperature non-uniformity in high temperature state, so the gloss uniformity is inevitably deteriorated. In addition, the gloss uniformity decreases while undergoing strong pickling to remove the scale.

However, as shown in Table 1, the cold rolled material produced through the process proposed in the present invention can be confirmed that not only the light reflection is minimized as well as the gloss uniformity is low as the gloss level to 13 to 15 levels.

1 ... casting roll 2 ... ladle
3 ... Tundish 4 ... Immersion nozzle
5 ... meniscus shield 6 ... brush roll
7 ... edge dam 8 ... casting
9 ... punch roll 10 ... water cooling system
Winding coil 12 Hot rolling mill

Claims (8)

By weight, C: 0.03% or less (excluding 0%), Si: 0.4-0.7%, Mn: 2.3-2.7%, N: 0.15-0.19%, Cr: 20.0-20.4%, Ni: 2.3-2.7%, Cu: 0.5% or less, Mo: 1.3-1.5%, P: 0.035% or less, S: 0.003% or less, balance Fe and other unavoidable impurities,
Lean duplex stainless steel for building interior and exterior with 13 ~ 15 gloss.
The method of claim 1,
The stainless steel is a lean duplex stainless steel for building interior and exterior with an average surface roughness (Ra) of 2.0 ~ 2.5㎛.
Weight% using twin roll continuous casting, C: 0.03% or less (excluding 0%), Si: 0.4 ~ 0.7%, Mn: 2.3 ~ 2.7%, N: 0.15 ~ 0.19%, Cr: 20.0 ~ 20.4% Preparing a steel strip comprising Ni: 2.3-2.7%, Cu: 0.5% or less, Mo: 1.3-1.5%, P: 0.035% or less, S: 0.003% or less, balance Fe and other unavoidable impurities; Hot rolling the steel strip to produce a hot rolled material; Hot rolling and pickling the hot rolled material; Manufacturing a cold rolled material by cold rolling the hot rolled annealing treated hot rolled material; And annealing the cold rolled material;
The annealing of the cold rolled material is an annealing process for manufacturing interior and exterior lean duplex stainless steel comprising the step of projecting a shotball at a speed of 2000 ~ 2500rpm and a pickling treatment at a HF concentration of 15 ~ 20g / L.
The method of claim 3, wherein
Method for producing a building interior and exterior lean duplex stainless steel for moving the cold rolled material annealing treatment at a line speed of 30 ~ 40rpm.
The method of claim 3, wherein
The annealing treatment of the cold rolled material is an annealing method for manufacturing interior and exterior lean duplex stainless steel that is performed in a hot combustion annealing furnace.
The method of claim 3, wherein
The hot rolling is a manufacturing method of lean duplex stainless steel for building interior and exterior construction is to be carried out at a reduction ratio of 20 to 40% in the temperature range of 1000 ~ 1200 ℃.
The method of claim 3, wherein
Hot-rolled annealing of the hot rolled material is a manufacturing method of lean duplex stainless steel for interior and exterior building construction that is performed for 0.5 to 3 minutes in the temperature range of 1000 ~ 1150 ℃.
The method of claim 3, wherein
The cold rolling is a manufacturing method of lean duplex stainless steel for interior and exterior building construction that is carried out at a reduction ratio of 50 ~ 70%.

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