JP7304415B2 - Method for producing high-manganese steel with excellent vibration isolation and formability, and high-manganese steel produced by this method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a steel material used for steel plates for automobiles or construction, and more particularly, it relates to anti-vibration and molding that can be used in places where anti-vibration for noise reduction is required. The present invention relates to a high manganese steel material with excellent toughness and a method for manufacturing the same.

Recently, in manufacturing automobiles or materials such as construction materials, noise reduction is a problem that manufacturers must solve. In the case of automobile manufacturers, parts that generate a lot of noise, such as engines and oil pans, are particularly required to have excellent mechanical properties as well as vibration damping properties. In the case of building materials, as regulations on noise between floors are tightened, the actual situation is that there is a demand for the development of steel materials with excellent anti-vibration properties as bottom plates of multi-story buildings including apartments.

On the other hand, high manganese (Mn) anti-vibration steel is a type of steel that has high anti-vibration properties and excellent mechanical properties by converting noise energy into heat energy by interfacial sliding of epsilon martensite upon external impact. Suitable for use for noise reduction purposes.

In general, high manganese anti-vibration steel is produced by a series of processes of steelmaking - continuous casting - hot rolling, or by adding a cold rolling process to this to produce a hot rolled or cold rolled steel sheet, and then post-heating the steel sheet. is applied to form an epsilon martensite and/or recrystallized structure to ensure vibration isolation.

By the way, the post-heat treatment process performed to ensure anti-vibration properties is a high-cost heat treatment that is usually applied at a temperature of 900° C. or higher for a time exceeding 10 minutes, preferably for a time of 60 minutes or longer. This is a factor that hinders the general use of manganese anti-vibration steel.

Currently, the demand for noise reduction is continuously increasing, and it is necessary to develop a steel material that can achieve both anti-vibration properties and excellent formability while omitting post-heat treatment, which is a high-cost heat treatment. is the actual situation.

Korea Registered Patent No. 10-1736636

One aspect of the present invention is that in providing a high manganese anti-vibration steel, it is possible to omit the post-heat treatment process that is essential for improving anti-vibration properties, and to reduce the cost of the anti-vibration steel compared to the conventional method. An object of the present invention is to provide a method for producing a high manganese steel product having excellent vibration properties and formability, and a high manganese steel product produced by this method.

The subject of the present invention is not limited to what has been described above. A further subject of the present invention is described in the general content of the specification, and a person having ordinary knowledge in the technical field to which the present invention belongs can understand from the content described in the specification of the present invention. There is no difficulty in understanding further objects of the invention.

One aspect of the present invention is, in weight %, carbon (C): 0.1% or less, manganese (Mn): 8 to 30%, silicon (Si): 3.0% or less, phosphorus (P): 0.1% or less. 1% or less, sulfur (S): 0.02% or less, nitrogen (N): 0.1% or less, titanium (Ti): 1.0% or less (excluding 0%), boron (B): 0. heating a steel slab containing 01% or less and the balance Fe and other inevitable impurities at a temperature of 1150 to 1350° C.; finish hot rolling the heated steel slab to produce a hot-rolled steel sheet; and It includes a step of cooling the hot-rolled steel sheet to 700 ° C. or less, and the finish hot rolling is performed at a temperature (FDT (° C.)) that satisfies the following relational expression 1. To provide a method for manufacturing high manganese steel.

[Relationship 1]
FDT (°C) ≥ 928 + (480 x C) + (450 x N) + (0.9 x Mn) + (65 x Ti)
(Here, each element means weight content.)

Another aspect of the present invention is a steel material manufactured by the above-described manufacturing method, which has the above-described alloy composition and contains epsilon martensite and the balance austenite phase with an area fraction of 90% or more as a microstructure. To provide a high manganese steel material with a completely recrystallized structure and excellent vibration damping and formability.

According to the present invention, it is possible to provide a high-manganese steel material with excellent anti-vibration properties and formability even if the post-heat treatment process, which has conventionally been required to improve the anti-vibration properties of manganese anti-vibration steel, is omitted. .

In addition, the present invention can provide a high-manganese anti-vibration steel at a relatively low cost by omitting the post-heat treatment process, so it has a technical effect in terms of economy and anti-vibration properties are required. There is an effect that it can be applied universally in the field where it is used.

1 is a graph showing loss rate values at a deformation rate of 900 (m 2 /(m×10 ⁻⁶ )) of invention steel and comparative steel in accordance with FDT (° C.) in an example of the present invention. 1 is a graph showing loss rate values at deformation rates of 200 to 900 (m 2 /(m×10 ⁻⁶ )) for invention steels and comparative steels in an example of the present invention. 1 shows a microstructure photograph of an invention steel according to an example of the present invention. 1 shows XRD measurement results of an invention steel according to an example of the present invention and a comparative steel. FIG. 4 illustrates a method of measuring a loss rate with respect to a deformation rate using a cantilever method.

The present inventors have found that, in the case of conventional high manganese anti-vibration steel, it is necessary to apply a costly heat treatment (also known as a post-heat treatment process) in order to improve anti-vibration properties, which ultimately increases the production cost. It was confirmed that there is a limit to generalization, as well as a significant increase.

Therefore, the present inventors have made intensive studies on a method that can achieve both anti-vibration properties and excellent formability without the high-cost heat treatment. As a result, by optimizing the manufacturing process as well as controlling the alloy composition, the fraction of the epsilon martensite phase in the steel can be maximized, resulting in vibration damping and formability even in a series of hot rolling processes alone. It was confirmed that it is possible to provide a steel material excellent in resistance, and the present invention was completed.

The present invention will be described in detail below.

According to one aspect of the present invention, a method for producing a high manganese steel material having excellent vibration damping properties and formability includes preparing a steel slab having an alloy composition described later, hot rolling and cooling the steel slab, thereby producing a high manganese steel material. can be manufactured.

First, the reason for restricting the alloy composition in obtaining the high manganese steel material aimed at in the present invention will be described in detail. At this time, unless otherwise specified, the content of each element means weight content (% by weight).

Carbon (C): 0.1% or less Carbon (C) is an element that stabilizes austenite in steel and is advantageous in ensuring strength. However, if the content exceeds 0.1%, the dissolved C fraction becomes excessively high, which may hinder hot workability and greatly reduce vibration damping properties.
Therefore, in the present invention, C can be contained in an amount of 0.1% or less.

Manganese (Mn): 8-30%
Manganese (Mn) is an essential element for stably securing austenite and epsilon-martensite structures. In the present invention, Mn should be contained in an amount of 8% or more in order to secure an epsilon martensite phase in a certain fraction or more without performing a separate heat treatment process. However, if the content exceeds 30%, the manufacturing cost rather increases, and the content of phosphorus (P) increases during the process of refining a large amount of Mn, which causes slab cracking. In addition, as the Mn content increases, internal grain boundary oxidation occurs excessively during slab heating, causing oxide defects on the surface of the steel and deteriorating surface properties during subsequent plating.
Therefore, in the present invention, the Mn content can be 8-30%, more preferably 14-20%.

Silicon (Si): 3.0% or Less Silicon (Si) is a solid-solution-strengthening element, and is advantageous in reducing grain size and improving yield strength due to its solid-solution effect. However, when the Si content increases, a silicon compound is formed on the surface of the steel sheet during hot rolling, degrading the pickling property and degrading the surface quality of the hot rolled steel sheet. Moreover, if it is added excessively, the weldability is greatly deteriorated.
Therefore, in the present invention, Si can be contained in an amount of 3.0% or less.

Phosphorus (P): 0.1% or less and Sulfur (S): 0.02% or less Lower amounts are advantageous. Of these, when the P content exceeds 0.1%, it causes segregation and reduces the workability of the steel, and when the S content exceeds 0.02%, coarse manganese sulfide ( MnS) is formed to cause defects such as flange cracks, which impairs the formability of the steel sheet, especially the hole expandability.
Therefore, in the present invention, P can be contained in an amount of 0.1% or less and S can be contained in an amount of 0.02% or less.

Nitrogen (N): 0.1% or less Nitrogen (N) is an element that forms nitrides. Impairs workability and elongation, and reduces vibration isolation.
Therefore, in the present invention, even if the content of N is 0.1% or less and the content is 0%, it is reasonable to secure the target physical properties.

Titanium (Ti): 1.0% or less (excluding 0%)
Titanium (Ti) is an element that combines with carbon to form carbides, and the formed carbides suppress grain growth and are advantageous for grain refinement. In addition, it has a scavenging effect by forming a compound with C and N, which is advantageous for improving vibration damping properties. When the Ti content exceeds 1.0%, excessive titanium segregates at grain boundaries to cause grain boundary embrittlement, and the formation of coarse precipitation phases hinders the effect of suppressing grain growth. There is something.
Therefore, in the present invention, 1.0% or less of Ti can be contained, but 0% is excluded.

Boron (B): 0.01% or less Boron (B), when added together with Ti, has the effect of forming a high-temperature compound at grain boundaries to prevent grain boundary cracks. However, if the content of B exceeds 0.01%, it is not preferable because it forms a boron compound and deteriorates the surface properties.
Therefore, in the present invention, B can be contained in an amount of 0.01% or less.

In the steel material of the present invention, in containing each element in the above composition, when C and N are added in combination, the sum of these contents (C + N, wt%) is preferably 0.1% or less.

C and N are interstitial solid-solution elements, and when combined with Ti and the like to form carbonitrides, they can improve anti-vibration performance. If it exceeds 1%, the proportion of dissolved C or dissolved N increases, deteriorating hot workability and elongation, and reducing vibration damping properties.
Therefore, when C and N are added in combination, the sum of their contents can be 0.1% or less.

On the other hand, the steel material of the present invention may further contain additional elements in addition to the above alloy composition in order to improve physical properties.

In one aspect, at least one of nickel (Ni): 0.005-2.0% and chromium (Cr): 0.005-5.0% may be further included.

Nickel (Ni): 0.005-2.0%
Nickel (Ni) is an element that effectively contributes to ensuring high-temperature ductility. In order to obtain the above effects, the content may be 0.005% or more, and the higher the content, the more effective the prevention of delayed fracture and slab cracking. However, Ni is an expensive element, and considering this, it can be contained in an amount of 2.0% or less.

Chromium (Cr): 0.005-5.0%
Chromium (Cr) reacts with external oxygen during the hot rolling or annealing process to preferentially form a Cr-based oxide film (Cr ₂ O ₃ ) with a thickness of 20 to 50 μm on the surface of the steel. It prevents Mn, Si, etc. contained in the steel from eluting to the surface layer. This has the effect of contributing to the stabilization of the steel surface structure and improving the surface properties of the plating. In order to obtain the above effect, 0.005% or more of Cr can be contained, but if the content exceeds 5.0%, chromium carbide is formed, which rather deteriorates workability and delayed fracture resistance. It is not preferable because it will decrease.
Therefore, when Cr is added in the present invention, it can be contained in an amount of 0.005 to 5.0%.

Furthermore, as one aspect, niobium (Nb): 0.005 to 0.5%, vanadium (V): 0.005 to 0.5%, and tungsten (W): 0.005 to 1.0% One or more can be further included.

Niobium (Nb): 0.005 to 0.5%
Niobium (Nb) is an element that combines with carbon in steel to form carbides, and can obtain the effect of increasing strength or refining the grain size. In general, Ti forms a precipitation phase at a temperature lower than that of Ti, so it is an element that has a large effect of refining the crystal grain size and precipitation strengthening by forming a precipitation phase. It also has the effect of lowering the fraction of dissolved C and improving vibration isolation.

In order to obtain the above effect, 0.005% or more of Nb can be contained. However, if the content exceeds 0.5%, an excessive amount of Nb segregates at the grain boundaries to cause grain boundary embrittlement, or the formation of coarse precipitation phases reduces the effect of suppressing grain growth. . Furthermore, there is a problem of delaying recrystallization during the hot rolling process and increasing the rolling load.
Therefore, when adding Nb in the present invention, it can be contained in an amount of 0.005 to 0.5%.

Vanadium (V): 0.005-0.5% and Tungsten (W): 0.005-1.0%
Vanadium (V) and tungsten (W) are elements that combine with C and N to form carbonitrides. is large. In addition, it has the effect of reducing the fractions of dissolved C and dissolved N to improve vibration damping properties.

In order to obtain the above effects, each content can be 0.005% or more, but if it exceeds 0.5% in the case of V or exceeds 1.0% in the case of W, the precipitation phase is excessively coarsened, the effect of suppressing grain growth is reduced, and causes hot shortness.
Therefore, in the present invention, V can be added in an amount of 0.005 to 0.5%, and W can be added in an amount of 0.005 to 1.0%.

Another component of the invention is Fe. However, unintentional contamination from raw materials or the surrounding environment may inevitably occur during normal manufacturing processes and cannot be ruled out. These impurities are known to anyone skilled in the normal manufacturing process, so the full content thereof is not specifically mentioned herein.

After preparing the steel slab having the alloy composition as described above, it can be heated, which can go through a heating step in the temperature range of 1150-1350°C.

When the steel slab is heated, if the temperature is too low, an excessive rolling load may be applied during subsequent hot rolling.

On the other hand, in the present invention, the larger the austenite grain size, the higher the fraction of the epsilon martensite phase in the final fine structure, so the higher the heating temperature, the better. Also, the higher the heating temperature, the more advantageous the subsequent hot rolling process can be. However, since the present invention contains a large amount of Mn, when heating at an excessively high temperature, there is a problem that internal oxidation occurs violently and the surface quality deteriorates. ° C. or less, and more advantageously, it can be carried out at 1300° C. or less.

A steel slab heated as described above can be hot rolled to produce a hot rolled steel sheet. At this time, it is preferable to perform finish hot rolling at a temperature (FDT (° C.)) that satisfies the following relational expression 1.

[Relationship 1]
FDT (°C) ≥ 928 + (480 x C) + (450 x N) + (0.9 x Mn) + (65 x Ti)
(Here, each element means weight content.)

The above relational expression 1 is derived through a number of experiments, and is an important factor for producing a high manganese steel material with excellent vibration damping properties and formability, which is the object of the present invention.

Specifically, the present invention can induce the growth and recrystallization of austenite grains with sufficient size by performing finish hot rolling at a temperature above the temperature at which complete recrystallization occurs, thereby: The epsilon martensite phase can be stably ensured in subsequent cooling and/or winding steps.

If the temperature during the finish hot rolling is lower than the temperature derived from the above relational expression 1, it becomes difficult to induce the growth and recrystallization of austenite grains, and the epsilon martensite phase is sufficiently formed as the final microstructure. Therefore, a non-recrystallized structure may be formed and the vibration damping property may be deteriorated.

Further, the finish hot rolling can be carried out at a total rolling reduction of 80% or more, more preferably 90% or more. When the total rolling reduction is 80% or more during the finish hot rolling, a sufficient driving force for recrystallization can be secured.

The hot-rolled steel sheet manufactured as described above can be cooled, and at this time, it is preferable to cool to 700° C. or lower.

If the final temperature exceeds 700° C. during the cooling, excessive scale is generated and an excessive process is required to remove the scale. It is not preferable because it becomes

In the present invention, cooling to room temperature may be performed, and in this case, there is an effect of ensuring more excellent anti-vibration properties compared to high manganese anti-vibration steel manufactured by the existing post-heat treatment process (Table 3 below). ).

Therefore, in the present invention, it is preferable that the cooling be completed in the temperature range of 700°C or less, more preferably 500°C or less, still more preferably normal temperature to 300°C. Thus, the lower the cooling end temperature, the smaller the amount of remaining austenite, which is more advantageous from the viewpoint of securing the epsilon martensite phase in the final microstructure.

On the other hand, the cooling can be performed by normal water cooling (for example, a cooling rate of 10° C./s or more), and when the cooling end temperature is normal temperature to 300° C., rapid cooling can be used to secure the cooling end temperature. can. The cooling rate during the rapid cooling is not particularly limited, but as an example, it can be performed at a cooling rate of 50 ° C./s or more, but in consideration of the equipment specifications, it can be performed at 200 ° C./s or less. .
Here, normal temperature means about 20 to 35° C., although it is not particularly limited.

In the present invention, after the cooling is completed, the winding process can be further performed at that temperature. This can be done selectively in consideration of the thickness of the steel material.

The high manganese steel material of the present invention obtained by completing the above-described cooling process contains an epsilon martensite phase with an area fraction of 90% or more, and does not contain a completely recrystallized structure, that is, a non-recrystallized structure. High anti-vibration properties and formability can be ensured.

Hereinafter, a high manganese steel material having excellent vibration damping properties and formability according to another aspect of the present invention will be described in detail.

The high manganese steel material of the present invention can be obtained by the manufacturing process described above. Also, since it has the alloy composition described above, the alloy composition of the steel material is replaced with the items already mentioned.

The high manganese steel material of the present invention is preferably composed of epsilon martensite and the balance austenite phase with an area fraction of 90% or more (including 100%) as a microstructure. In particular, the present invention has a completely recrystallized structure that does not contain any unrecrystallized structure, and can ensure excellent vibration damping properties. More preferably, it can contain 95% or more of the epsilon martensite phase. .

Thus, the high manganese steel material of the present invention contains a high fraction of the epsilon martensite phase and effectively removes residual dislocations through complete recrystallization, so that external impact is applied. In some cases, the epsilon martensite phase contributes to the improvement of damping performance by increasing the rate of converting impact energy into thermal energy.

On the other hand, the high manganese steel material of the present invention does not contain any phase other than the above phases as a microstructure, for example, it does not contain alpha '(α')-martensite phase at all. Let me clarify.

In particular, the present invention can form an epsilon martensite phase in a sufficient fraction, even though it omits the high-cost heat treatment that is performed in the production of conventional high-manganese anti-vibration steel. Moldability can also be ensured. Therefore, it can be said that the high manganese steel material of the present invention has economical and advantageous technical effects as compared with the conventional high manganese anti-vibration steel.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples. However, it should be noted that the following examples are merely to illustrate and explain the present invention in more detail, and are not intended to limit the scope of rights of the present invention. This is because the scope of rights of the present invention is determined by the matters described in the claims and matters that can be reasonably inferred therefrom.

(Example)
A steel slab having an alloy composition shown in Table 1 below was heated-hot-rolled-cooled under the conditions shown in Table 2 to produce each hot-rolled steel sheet. At this time, for comparison, a specific steel type was post-heat treated, and the post-heat treatment was performed at 1000° C. for 30 minutes and then air-cooled.

After that, the mechanical properties and microstructure of each hot-rolled steel sheet were measured, and the results are shown in Table 3 below.

At this time, in order to measure mechanical properties, a JIS No. 5 tensile test piece was prepared, and then yield strength (YS), tensile strength (TS) and elongation (T-El and U-El) were measured. Also, the microstructure was measured using XRD (X-ray diffraction), and the fraction of each phase was derived from the peak intensity of each phase.

Then, as shown in FIG. 5, a cantilever method was used to measure the loss ratio for deformation ratios of 200 to 900 (m/(m×10 ⁻⁶ )). At this time, the loss rate value (X _n =(1/π)ln(X _n /X _n+1 )) at a deformation ratio of 900 (m/(m×10 ⁻⁶ )) is shown in Table 3 below.

（表３において、α’－Ｍはアルファ’－マルテンサイト、γはオーステナイト、ε－Ｍはイプシロンマルテンサイト相を意味する。）

(In Table 3, α'-M means alpha'-martensite, γ means austenite, and ε-M means epsilon martensite phase.)

As shown in Tables 1 to 3 above, the invention steels 1 to 6 were subjected to finish hot rolling at a temperature that satisfies the alloy composition and manufacturing conditions, particularly at a temperature that satisfies the relational expression 1 proposed by the present invention, and finished cooling at 700 ° C. or less. , the epsilon martensite phase is formed in an amount of 95% or more, so that excellent vibration damping properties can be ensured.

Further, all of the invention steels 1 to 6 have a total elongation of more than 40%, which confirms their excellent formability.

It can be seen that this has equal or better vibration damping properties and formability than the high manganese vibration damping steel (see Comparative Steel 5) subjected to conventional post-heat treatment.

On the other hand, in the case of comparative steels 1 to 4 and 6 to 9, which do not satisfy the production conditions of the present invention (relational expression 1, etc.), the alpha'(α')-martensite phase is formed, Not only was the vibration damping property inferior, but also the total elongation was less than 40%, and the formability was also inferior.

FIG. 1 is a graph showing the value of the loss rate of each test piece at a loss rate of 900 (m 2 /(m×10 ⁻⁶ )) according to FDT (° C.).
As shown in FIG. 1, only the invention steels 1 to 6 subjected to finish hot rolling at a temperature that satisfies the relational expression 1 of the present invention have a loss rate of 0.05 or more. It can be seen that it has an effect equal to or greater than that of 5.

FIG. 2 is a graph showing loss rate values of some test pieces at loss rates of 200 to 900 (m 2 /(m×10 ⁻⁶ )).
As shown in FIG. 2, in the case of the invention steel, it can be confirmed that the higher the deformation ratio, the higher the loss rate. I understand. On the other hand, in the case of the comparative steel, it can be confirmed that the loss rate does not exceed 0.020 even if the deformation rate increases.

FIG. 3 shows a photograph of the microstructure of Inventive Steel 4, and it can be confirmed that the microstructure is mostly formed of the epsilon martensite phase.

FIG. 4 shows the XRD measurement results of Inventive Steel 6 and Comparative Steel 6. As shown in FIG.
As shown in FIG. 4, in Comparative Steel 6, an alpha'(α')-martensite phase peak is observed, whereas in Invention Steel 6, only the epsilon martensite phase and austenite phase peaks are observed. is observed, and it can be confirmed that the intensity of the epsilon martensite phase is even greater.

Claims (9)

% by weight, carbon (C): 0.1% or less, manganese (Mn): 8 to 30%, silicon (Si): 3.0% or less, phosphorus (P): 0.1% or less, sulfur (S ): 0.02% or less, nitrogen (N): 0.1% or less, titanium (Ti): 1.0% or less (excluding 0%), boron (B): 0.01% or less, balance Fe and heating a steel slab consisting of other unavoidable impurities at a temperature of 1150-1350° C.;
finishing hot rolling the heated steel slab to produce a hot-rolled steel sheet; and cooling the hot-rolled steel sheet to 700° C. or less,
The finish hot rolling is characterized in that it is performed at a temperature (FDT, ° C.) that satisfies the following relational expression 1, and after the cooling, from the epsilon martensite with an area fraction of 90% or more (including 100%) and the remaining austenite phase A method for producing a high-manganese steel sheet having a completely recrystallized structure and excellent vibration damping properties and formability.
[Relationship 1]
FDT (°C) ≥ 928 + (480 x C) + (450 x N) + (0.9 x Mn) + (65 x Ti)
(Here, each element means weight content.)
2. The method for producing a high manganese steel sheet excellent in vibration damping properties and formability according to claim 1, wherein the finish hot rolling is performed at a total rolling reduction of 80% or more. The method for producing a high manganese steel sheet excellent in vibration damping properties and formability according to claim 1, wherein the cooling is completed at room temperature to 300°C. [Claim 2] The method of claim 1, further comprising winding after the cooling, the high manganese steel sheet having excellent anti-vibration properties and formability. 2. The steel slab according to claim 1, further comprising one or more of nickel (Ni): 0.005-2.0% and chromium (Cr): 0.005-5.0% by weight. A method for producing a high-manganese steel sheet with excellent anti-vibration properties and formability. Said steel slab, in weight percent, niobium (Nb): 0.005-0.5%, vanadium (V): 0.005-0.5% and tungsten (W): 0.005-1.0% The method for producing a high manganese steel sheet having excellent vibration damping properties and formability according to claim 1, further comprising at least one of % by weight, carbon (C): 0.1% or less, manganese (Mn): 8 to 30%, silicon (Si): 3.0% or less, phosphorus (P): 0.1% or less, sulfur (S ): 0.02% or less, nitrogen (N): 0.1% or less, titanium (Ti): 1.0% or less (excluding 0%), boron (B): 0.01% or less, balance Fe and Consists of other unavoidable impurities,
A high-manganese steel sheet with excellent anti-vibration properties and formability, having a fine structure consisting of epsilon martensite and the rest austenite phase with an area fraction of 90% or more (including 100%) , and having a completely recrystallized structure.
8. The steel plate according to claim 7 , wherein the steel plate further contains at least one of nickel (Ni): 0.005 to 2.0% and chromium (Cr): 0.005 to 5.0% by weight. High-manganese steel sheet with excellent anti-vibration properties and formability. The steel sheet contains niobium (Nb): 0.005 to 0.5%, vanadium (V): 0.005 to 0.5%, and tungsten (W): 0.005 to 1.0% by weight. The high manganese steel sheet having excellent vibration damping properties and formability according to claim 7 , further comprising one or more of them.

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