JP2012036475A - Method for manufacturing rolling part and gear with long service life under hydrogen environment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing steel components such as a bearing part and a gear whose service life is long even under a hydrogen-intrusion environment, taking the workability of the steel and the part into account.SOLUTION: In the method for manufacturing a rolling part or a gear whose service life in a hydrogen environment is excellent, the rolling part or the gear produced from the steel composed of, by mass%, 0.10 to 0.45% C, 0.01 to 1.0% Si, 0.10 to 2.0% Mn, 0.030% or less P, 0.035% or less S, 1.30 to 3.50% Cr, 0.003 to 0.10% Al and 0.004 to 0.050% N, and the balance being Fe and inevitable impurities is subjected to being 0.50 to 0.75% to form the surface layer having an amount of (C+N) carburization or carbonitriding treatment in a pattern shown in Fig.2.

Description

  TECHNICAL FIELD The present invention relates to a rolling part typified by a bearing that requires a long life in an environment where hydrogen invades and a method for heat treating steel used for gears.

  In recent years, power transmission parts such as automobile parts are required to be reduced in size and weight in order to reduce the environmental load. Furthermore, these parts are also required to have characteristics that can cope with conflicting problems such as harsh use environments and maintenance-free. Under such circumstances, in rolling parts and gears represented by bearings, for example, when used in an environment where water penetrates into the lubricating oil, or when hydrogen is generated due to decomposition of the lubricating oil, etc. It is known that when hydrogen intrudes into a component, problems such as peeling and breakage occur in a short period of time. Therefore, extending the life of parts in a hydrogen intrusion environment is an important issue.

  As a conventional technique for solving this problem, a technique for preventing intrusion of hydrogen by forming an oxide film on a rolling surface with Cr has been proposed (see, for example, Patent Document 1). However, the Cr oxide film is not a fundamental solution and is not sufficient because the film may break during use.

  In addition, as a conventional technique, Ti carbide, carbonitride, or Al nitride is dispersed and deposited near the surface of a component by adding a large amount of Ti or Al to extend the rolling life under foreign matter lubrication and clean lubrication. Have been proposed (see, for example, Patent Document 2). In this technology, finely precipitated Ti or Al carbides and carbonitrides become hydrogen trap sites, and these carbides / carbonitrides reduce the austenite crystal grains and increase the hardness. Improved wear and long life. However, based on high-carbon steel, a large amount of Ti or Al carbides and carbonitrides that are effective in extending the service life are produced, resulting in a decrease in hot workability. Therefore, workability when rolling steel and forging parts. Adversely affect. Furthermore, there is a problem that the tool life when cutting parts is reduced.

  Furthermore, as conventional technologies, a structure change delay due to a large amount of Cr content, a pinning effect by Cr carbide and carbonitride, an improvement in grain boundary strength by refining the crystal grain size, and a delay in structure change propagation speed are proposed. (For example, see Patent Document 3). Further, as a conventional technique, a technique has been proposed in which Cr and N in the material are increased and the retained austenite is stabilized to suppress early peeling accompanied by a white structure change (see, for example, Patent Document 4). . However, in these inventions, the amounts of solute C and N are not specified, and thus cannot be said to be sufficient. Moreover, since a large amount of C is contained as a steel material, it is difficult to roll the steel material or forge it into parts, and there is also a problem that the tool life when cutting the parts is reduced.

Japanese Patent No. 3009254 Japanese Patent No. 3591236 JP 2005-147352 A JP 2007-262449 A

Sanyo Technical Report, 15 (2008), 43. Sanyo Technical Report, 16 (2009), 45.

  The problem to be solved by the present invention is to provide a method of manufacturing a part having a long life even under a hydrogen intrusion environment, for example, a bearing part or a gear, in consideration of the workability of the steel material and the part.

  As described above, it is known that when hydrogen intrudes into a component, a white texture change occurs and problems such as peeling and breakage occur in a short period of time. Therefore, the inventor has advanced the investigation of the generation mechanism of the structure change and the causal relationship between hydrogen and short-life exfoliation with the ultimate goal of creating countermeasures for exfoliation caused by hydrogen (for example, Non-Patent Document 1, Non-Patent Document). 2). As a result, early exfoliation due to hydrogen is caused by the plastic strain localization of hydrogen that has penetrated into the steel, and a needle-like structure is formed at the interface of the martensite block. It has been clarified that propagation or connection leads to large internal cracks that cause premature detachment, and that the white texture change is a secondary phenomenon caused by the geometric effect of the internal cracks. Moreover, as a countermeasure, it is important to suppress hydrogen concentration at the martensite block interface, and for that purpose, it has been found that reducing solute C and solute N in martensite is effective. It was. By reducing the amount of (C + N) on the surface by carburizing or carbonitriding, or by adding carbides and carbonitride-forming elements such as Cr, Mo, V, and adjusting the quenching temperature, solid solution C and solid solution N can be reduced. It becomes possible.

  That is, as a means for solving the problem, in the invention of claim 1, in mass%, C: 0.10 to 0.45%, Si: 0.01 to 1.0%, Mn: 0.10 2.0%, P: 0.030% or less, S: 0.035% or less, Cr: 1.30 to 3.50%, Al: 0.003 to 0.10%, N: 0.004 to 0 A rolling part or gear made of a steel material containing 0.050% and the balance being Fe and inevitable impurities is subjected to carburizing or carbonitriding treatment to reduce the (C + N) amount in the steel material surface of the rolling part or gear to 0.1. It is a manufacturing method of a rolling part or a gear excellent in life in a hydrogen environment characterized by being 50 to 0.75%.

  In the invention of claim 2, in mass%, C: 0.10 to 0.45%, Si: 0.01 to 1.0%, Mn: 0.10 to 2.0%, P: 0.030% S: 0.035% or less, Cr: 1.30 to 3.50%, Al: 0.003 to 0.10%, N: 0.004 to 0.050%, and Mo: 0 0.01 to 1.20%, V: 0.01 to 0.50%, Ni: 0.10 to 2.0%, Nb: 0.01 to 2.0%, Ti: 0.01 to 0.17 %, B: One or more of 0.0001 to 0.005%, and the remaining rolling parts or gears made of steel with Fe and inevitable impurities are subjected to carburizing or carbonitriding treatment. The life in a hydrogen environment characterized by the amount of (C + N) in the steel surface layer of moving parts or gears being 0.50 to 0.75% The is a manufacturing method of the rolling part or gear. When B is contained, carbonitriding is not performed.

In the invention of claim 3, by mass, C: 0.10 to 0.45%, Si: 0.01 to 1.0%, Mn: 0.10 to 2.0%, P: 0.030% S: 0.035% or less, Cr: 1.30 to 3.50%, Al: 0.003 to 0.10%, N: 0.004 to 0.050%, with the balance being Fe and When rolling parts or gears made of steel, which is an inevitable impurity, are carburized or carbonitrided, and the quenching temperature after carburizing or nitriding is T, the quenching temperature T satisfies the following formula (1). The rolling component or gear having a long life in a hydrogen environment, characterized in that the amount of (C + N) in the steel surface layer of the rolling component or gear is 0.50 to 2.0%. It is a manufacturing method.
800 ° C. ≦ quenching temperature T ≦ 750 ° C. + 39 × (Cr% + 0.8 × Mo% + 3 × V%) ° C. (1)

In the invention of claim 4, in mass%, C: 0.10 to 0.45%, Si: 0.01 to 1.0%, Mn: 0.10 to 2.0%, P: 0.030% S: 0.035% or less, Cr: 1.30 to 3.50%, Al: 0.003 to 0.10%, N: 0.004 to 0.050%, and Mo: 0 0.01 to 1.20%, V: 0.01 to 0.50%, Ni: 0.10 to 2.0%, Nb: 0.01 to 2.0%, Ti: 0.01 to 0.17 %, B: One or more of 0.0001 to 0.005%, and the remaining rolling parts or gears made of steel with Fe and inevitable impurities are carburized or carbonitrided, and these When the quenching temperature after carburizing or nitriding of T is T, the quenching temperature T satisfies the following formula (1), and the rolling parts Properly is rolling part or gear manufacturing method having excellent life under hydrogen environment, characterized in that a 0.50 to 2.0 percent of (C + N) content in the steel surface layer of the gear. When B is contained, carbonitriding is not performed.
800 ° C. ≦ quenching temperature T ≦ 750 ° C. + 39 × (Cr% + 0.8 × Mo% + 3 × V%) ° C. (1)

  The reasons for limiting the steel components in the present invention will be described below. Hereinafter, “%” represents “% by mass”.

C: 0.10 to 0.45%
C is an element necessary for imparting strength, but if it is less than 0.10%, it cannot ensure carburization and core strength after carbonitriding, and if it exceeds 0.45% As the toughness decreases, the hardness of the material increases and the workability decreases. Therefore, C is set to 0.10 to 0.45%, preferably 0.14 to 0.28%.

Si: 0.01 to 1.0%
Si is an element effective for deoxidation of steel, and is added to impart hardenability necessary for steel and increase strength. In addition, it is an element effective for rolling life in a poorly lubricated state in order to improve temper softening resistance. However, if it exceeds 1.0%, carburizing and carbonitriding properties deteriorate and the material hardness increases. Processability is reduced. Therefore, Si is set to 0.01 to 1.0%, preferably 0.10 to 0.70%.

Mn: 0.10 to 2.0%
Mn is an element that improves the hardenability of the steel, but if it is less than 0.10%, the improvement of hardenability cannot be ensured, and deoxidation is insufficient, exceeding 2.0%. And the hardness of the material increases and the workability decreases. Therefore, Mn is set to 0.10 to 2.0%, preferably 0.20 to 1.60%.

P: 0.030% or less P is an element that segregates at grain boundaries to lower toughness and fatigue strength and lower part strength, so is 0.030% or less.

S: 0.035% or less When added, S forms MnS effective for machinability, but MnS is an element that deteriorates rolling fatigue life, cold workability, and toughness. Therefore, S is set to 0.035% or less.

Cr: 1.30 to 3.50%
Cr gives hardenability and strength improvement to steel, and further reduces C and N by forming a compound with C and N, and is effective in suppressing hydrogen concentration at the block interface of martensite. It is. Further, this carbide or carbonitride serves as a hydrogen trap site and is also effective in detoxifying hydrogen. If Cr is less than 1.30%, these effects cannot be sufficiently obtained. If it exceeds 3.50%, the hardness is increased and the workability is lowered. Therefore, Cr is set to 1.30 to 3.50%.

Al: 0.003-0.10%
Al has the effect of deoxidizing steel, and at the same time combines with nitrogen to produce AlN and suppresses the coarsening of crystal grains, but the deoxidation effect is insufficient at less than 0.003%. If it exceeds 0.10%, oxides increase, fatigue strength decreases, and workability further decreases. Therefore, Al is made 0.003 to 0.10%.

N: 0.004 to 0.050%
N forms a compound with Al and Nb in steel and has an effect of preventing coarsening of austenite crystal grains at the time of carburizing. Effect of preventing coarsening of grains when N is less than 0.004% Is too small, and if it is more than 0.050%, nitrides increase and fatigue strength and workability deteriorate. Therefore, N is set to 0.004 to 0.050%. However, in the case of adding B, which will be described later, if N is present, BN is generated and the effect of adding B is lost, so N is made 0.015% or less.

Mo: 0.01 to 1.20%
Mo is an element that improves the hardenability, strength, and toughness of steel. Further, by forming a compound with C and N, solid solution C and solid solution N are reduced, and hydrogen is introduced into the martensite block interface. It is effective in suppressing concentration. Further, this carbide or carbonitride serves as a hydrogen trap site and is also effective in detoxifying hydrogen. However, when there is too much Mo, workability will fall and the steel material cost will rise, so Mo is made 0.01 to 1.20%.

V: 0.01 to 0.50%
V is an element that improves the hardenability and strength of steel. Further, by forming a compound with C and N, solid solution C and solid solution N are reduced, and hydrogen is concentrated at the block interface of martensite. It is effective to suppress. Further, this carbide or carbonitride serves as a hydrogen trap site and is also effective in detoxifying hydrogen. However, if V is too much, workability is reduced and the steel material cost is increased, so V is set to 0.01 to 0.50%.

Ni: 0.10 to 2.0%
Ni is an element effective for improving the hardenability and toughness of steel. However, if it is less than 0.10%, its effect is small, and if it exceeds 2.0%, the hardness of the material increases so much that the workability decreases. And the steel material cost increases. Therefore, Ni is made 0.1 to 2.0%.

Nb: 0.01-0.20%
Nb forms fine Nb carbides and carbonitrides to suppress coarsening of austenite crystal grains during carburization. Further, this carbide or carbonitride serves as a hydrogen trap site and is effective for detoxification of hydrogen. However, if it is less than 0.01%, the effect is small, and if it exceeds 0.20%, Nb carbide or carbonitride. A thing coarsens and the crystal grain coarsening inhibitory effect falls. Therefore, Nb is set to 0.01 to 0.20%.

Ti: 0.01 to 0.17%
Ti is an element which precipitates finely in steel as TiC, disperses and strengthens the steel, and suppresses the generation and propagation of fatigue cracks. Further, Ti carbide or carbonitride serves as a hydrogen trap site and is effective for detoxification of hydrogen. However, the effect is small at 0.01% or less, and the workability decreases when it exceeds 0.17%. . Therefore, Ti is set to 0.01 to 0.17%.

B: 0.0001 to 0.005%
B is an element that remarkably improves the hardenability of steel by addition of a very small amount, and segregates at the grain boundary and suppresses grain boundary fracture, thereby improving fatigue strength and impact strength after carburization. If it is less than%, the effect is not sufficient, and if it exceeds 0.005%, the effect is saturated. Therefore, B is set to 0.0001 to 0.005%. In addition, when adding B, nitriding is not performed but only carburizing is performed.

(C + N) content on the surface layer by carburizing or carbonitriding: 0.50 to 0.75%
As described above, the early breakage due to hydrogen intrusion is caused by the concentration of hydrogen at the martensite block interface, which is prolonged by reducing the solid solution (C + N) amount in martensite to 0.75% or less. Life can be extended. However, since an amount of (C + N) of 0.50% or more is necessary to ensure the hardness necessary for the rolling fatigue life, the amount of (C + N) on the outermost surface after carburizing or carbonitriding is set to 0.50. By setting it as 0.75%, early breakage due to hydrogen intrusion can be suppressed.

Quenching temperature after carburizing or carbonitriding T: 800 ° C. ≦ T ≦ 750 ° C. + 39 × (Cr% + 0.8 × Mo% + 3 × V%) ° C. and (C + N) amount on the surface layer: 0.50-2. 0%
By adding Cr, Mo, and V that generate carbide or carbonitride and quenching at a temperature that satisfies the above formula, the amount of solid solution (C + N) in martensite is reduced, as described above. It is possible to suppress early damage caused by hydrogen. However, when the quenching temperature T is less than 800 ° C., a large amount of reticulated carbide is generated, and therefore 800 ° C. ≦ T ≦ 750 ° C. + 39 × (Cr% + 0.8 × Mo% + 3 × V%) ° C. Further, even if the amount of (C + N) on the surface layer exceeds 2.0%, a large amount of network carbide is generated, so the amount of (C + N) on the surface layer is set to 0.50 to 2.0%.

  By adopting the means described above, even in a hydrogen environment in which hydrogen may invade a conventional steel part and cause problems such as early breakage, the part according to the present invention, for example, a bearing part, has hydrogen penetrating into the steel part. However, the steel material in the present invention has good machinability without causing peeling, so the wear amount of the carbide tool is small, and the workability is excellent. Produces an unprecedented effect.

The shape of a thrust type | mold rolling fatigue test piece is shown, (a) is a front view, (b) is a side view. It is a figure which shows the heat processing pattern, (a) shows carburizing and hardening, (b) shows carbonitriding and hardening.

  Embodiments of the present invention will be described below. A steel (hereinafter referred to as “Example Steel”) and a comparative steel (hereinafter referred to as “Comparative Example Steel”) according to an embodiment of the present invention containing each component having the chemical composition shown in Table 1 are vacuumed at 100 kg. It was made into steel by melting in a melting furnace. Subsequently, these steels were hot-forged at 1200 ° C. to produce 65 mm diameter steel bars, held at 900 ° C. for 90 minutes, and then air-cooled and normalized. Then, after maintaining at 600 ° C. for 4 hours, it was air-cooled and subjected to a low-temperature annealing treatment. In addition, it has shown that the shaded part of the comparative example steel of Table 1 remove | deviates from the component range of the Example steel of this invention. Furthermore, in description of each component element of Example steel of Table 1, the value of the range which is less than the composition range of the component element of steel in this invention is contained as an unavoidable impurity on actual operation.

  Then, it processed into the shape of the thrust type | mold rolling fatigue test piece 1 which is outer diameter: (phi) 60mm, inner diameter: (phi) 20mm, and thickness D: 8.3mm from the steel bar manufactured above.

  The thrust type rolling fatigue test piece 1 of this machined shape is heated to 930 ° C. as shown in the carburization + quenching pattern of FIG. 2A, soaking at the same temperature for 0.5 hours and 3.0 hours. Carburizing and Carburizing Conditions for Carburizing and Diffusion for 2.5 Hours, Lowering to Arbitrary Temperature T ° C, Holding at that Temperature for 0.5 Hours, and Quenching in Oil (OQ) to 60 ° C Thus, carburizing and quenching aiming at various surface carbon concentrations was performed, and a thrust type rolling fatigue test piece 1 was prepared.

  Further, the thrust type rolling fatigue test piece 1 is heated to 930 ° C. shown in the carbonitriding + quenching pattern of FIG. 2B, and soaking at the same temperature for 0.5 hours and carburizing for 3.0 hours. Depending on the carbonitriding quenching conditions in which diffusion is performed for 2.5 hours, the temperature is lowered to an arbitrary temperature T ° C., nitriding treatment is performed at the same temperature for 1.5 hours, and then further quenched in oil at 60 ° C. Carbonitriding and quenching aimed at carbon concentration and nitrogen concentration was performed, and a thrust type rolling fatigue test piece 1 was prepared.

  Thereafter, all the prepared thrust type rolling fatigue test pieces 1 were subjected to a tempering treatment that was held at 180 ° C. for 1.5 hours, and the surface was polished as a finishing process to a thickness D of 8.0 mm. A thrust type rolling fatigue test piece 1 was finished.

  In order to simulate the hydrogen intrusion environment, the thrust type rolling fatigue test piece 1 before the rolling test was charged with hydrogen. The hydrogen charging condition was that the thrust type rolling fatigue test piece 1 was held for 48 hours in an ammonium thiocyanate solution having a concentration of 20% at a specific solution of 250 ml / sheet and 50 ° C. Immediately after hydrogen charging, the thrust type rolling fatigue test piece 1 is washed and the corrosion products on the test surface are removed by buffing, and then the thrust type rolling fatigue test is performed at a maximum contact surface pressure of 5.3 GPa. The number of cycles of the rolling fatigue test from the surface of the test piece to peeling was determined by a machine.

Calculated value of 750 ° C. + 39 × (Cr% + 0.8 × Mo% + 3 × V%) ° C. for each steel type (described as calculation temperature T0 in Table 2), quenching temperature T of thrust type rolling fatigue test piece 1, heat treatment Method, surface (C + N) amount analyzed by EPMA, L ₅₀ life by rolling fatigue test, and tool after cutting for 10 minutes in low temperature annealing state before carburizing or carbonitriding: Carbide JIS P20, Table 2 shows the amount of wear of the turning tool under the conditions of cutting edge R: 0.4 mm, peripheral speed: 150 m / min, cutting depth: 0.5 mm, feed: 0.25 mm / rev, and cutting oil: none. It was shown to. In Table 2, the shaded portion has a surface (C + N) amount outside 0.50 to 0.75% and a quenching temperature T: 800 ° C. ≦ T ≦ 750 ° C. + 39 × (Cr % + 0.8 × Mo% + 3 × V%) Quenching temperature when not satisfying ° C, surface (C + N) amount less than 0.5% or more than 2.0%, hydrogen type thrust type rolling The L ₅₀ life of rolling fatigue of the fatigue test piece 1 is less than 15 × 10 ⁶ cycles, and the wear amount of the carbide tool exceeds 10 mm for 10 minutes.

Therefore, from Table 2, No. of the example steel. A to E have a long life because the L ₅₀ life is 15 × 10 ⁶ cycles or more by adjusting the quenching temperature and the surface (C + N) amount, and the wear amount of the carbide tool is 0.10 mm or less. And machinability. In addition, even if the composition range of the example steel of the present invention has a component, the quenching temperature in Table 2 or the surface (C + N) amount deviates from the solid solution (C + N) amount, Alternatively, since a large amount of reticulated carbide is generated, the L ₅₀ life is less than 15 × 10 ⁶ cycles, and as shown by the netting, the above-mentioned long life effect is not obtained. Because it is out of scope, it was marked as out of scope in the remarks.

Comparative Example Steel No. For F to I, no. F to H are excellent in L ₅₀ life, but have a large amount of carbide tool wear. That is, since machinability is poor, a problem occurs in the part machining process, so it is out of the scope of the present invention. , Indicated in the remarks as out of scope. Furthermore, No. of comparative example steel. Since I has less amount of Cr necessary for the present invention, since the L ₅₀ life has reached the release of low-cycle of less than 15 × 10 ⁶ cycles, because it is outside the scope of the present invention, shown covered Remarks .

  1 Thrust rolling fatigue test piece

Claims (4)

  In mass%, C: 0.10 to 0.45%, Si: 0.01 to 1.0%, Mn: 0.10 to 2.0%, P: 0.030% or less, S: 0.035 %: Cr: 1.30 to 3.50%, Al: 0.003 to 0.10%, N: 0.004 to 0.050%, the balance being Fe and inevitable impurities. Rolling parts or gears are subjected to carburizing or carbonitriding to reduce the (C + N) amount in the steel surface of the rolling parts or gears to 0.50 to 0.75% in a hydrogen environment. A method of manufacturing rolling parts or gears with excellent service life.   In mass%, C: 0.10 to 0.45%, Si: 0.01 to 1.0%, Mn: 0.10 to 2.0%, P: 0.030% or less, S: 0.035 %: Cr: 1.30 to 3.50%, Al: 0.003 to 0.10%, N: 0.004 to 0.050%, and Mo: 0.01 to 1.20% , V: 0.01 to 0.50%, Ni: 0.10 to 2.0%, Nb: 0.01 to 2.0%, Ti: 0.01 to 0.17%, B: 0.0001 Rolling parts or gears made of steel containing one or more of ~ 0.005%, the balance being Fe and inevitable impurities, carburized or carbonitrided by rolling steel or carbonitriding treatment Rolling parts with excellent life in a hydrogen environment characterized by the amount of (C + N) in the layer surface being 0.50 to 0.75% Method of manufacturing a gear. When B is contained in the steel material, carbonitriding is not performed. In mass%, C: 0.10 to 0.45%, Si: 0.01 to 1.0%, Mn: 0.10 to 2.0%, P: 0.030% or less, S: 0.035 %: Cr: 1.30 to 3.50%, Al: 0.003 to 0.10%, N: 0.004 to 0.050%, the balance being Fe and inevitable impurities. When rolling parts or gears are carburized or carbonitrided and the quenching temperature after carburizing or nitriding is T, the quenching temperature T satisfies the following formula (1). Or the manufacturing method of the rolling component or gear excellent in the lifetime in the hydrogen environment characterized by making the amount of (C + N) in the steel surface layer of a gear into 0.50 to 2.0%.
800 ° C. ≦ quenching temperature T ≦ 750 ° C. + 39 × (Cr% + 0.8 × Mo% + 3 × V%) ° C. (1) In mass%, C: 0.10 to 0.45%, Si: 0.01 to 1.0%, Mn: 0.10 to 2.0%, P: 0.030% or less, S: 0.035 %: Cr: 1.30 to 3.50%, Al: 0.003 to 0.10%, N: 0.004 to 0.050%, and Mo: 0.01 to 1.20% , V: 0.01 to 0.50%, Ni: 0.10 to 2.0%, Nb: 0.01 to 2.0%, Ti: 0.01 to 0.17%, B: 0.0001 Rolling parts or gears comprising steel material containing one or more of ~ 0.005%, the balance being Fe and inevitable impurities, carburized or carbonitrided, and after these carburized or nitrided When the quenching temperature is T, the quenching temperature T satisfies the following formula (1), and the steel material table of the rolling part or gear (C + N) amount from 0.50 to 2.0% and rolling part or production process of a gear having excellent life under hydrogen environment, characterized in that in the surface. When B is contained in the steel material, carbonitriding is not performed.
800 ° C. ≦ quenching temperature T ≦ 750 ° C. + 39 × (Cr% + 0.8 × Mo% + 3 × V%) ° C. (1)

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