JP6601359B2 - Carburized parts with excellent wear resistance and manufacturing method thereof - Google Patents

Description

    The present invention relates to a carburized part having high wear resistance used for automobiles and various industrial equipment and a method for manufacturing the same.

  In recent years, shafts and gears used in automobiles and the like are required to be reduced in size with a reduction in weight of the vehicle body for energy saving. On the other hand, since the load is increased due to the higher output of the engine, improvement in durability is required.

  Conventionally, parts have been formed using case-hardened steel such as JIS SCM420H, SNCM420H, etc., and surface treatment such as carburization has been performed and used for automobiles and the like. However, since it cannot withstand use under high stress, research and development has been advanced to improve wear resistance and fatigue strength by changing the steel material, changing the heat treatment method, and working hardening the surface.

For example, in Patent Document 1, carburization or carbonitriding treatment and quenching / tempering treatment are performed after forming a part shape with a steel material having a specific component, and carbide or carbonitride having an average particle size of 5 μm or less is deposited on the surface layer portion. Wear resistance is improved by using so-called high-concentration carburizing treatment.
In Patent Document 2, wear-resistant parts are defined by surface hardness and roughness, and as a material, chrome steel or chrome molybdenum steel specified in JIS G4053 or an alloy such as Mn or Mo is added. Is stipulated.

JP 2007-246941 A JP 2010-222673 A

  In Patent Document 1, the alloy cost is high because Cr is contained as a component and is a high alloy, and this heat treatment is a treatment at a high temperature for a long time, so that the heat treatment cost is also increased.

  In Patent Document 2, it is possible to improve the wearability by increasing the surface hardness or regulating the roughness, but it is possible with conventional steel, but the effect is not so great. If Mn and Mo are further increased, the cost will increase.

  An object of the present invention is to solve the above-described problems and to provide a carburized component having excellent wear resistance and a method for manufacturing the same.

In the present invention, in order to solve the above-mentioned problems, intensive research has been conducted and the following has been found.
1. A means for increasing the surface hardness with respect to the wear resistance is generally used, and therefore, carburizing, quenching and tempering, which is one of the surface hardening treatments, is performed. When carburizing, quenching and tempering are used, it is most effective to suppress the surface roughness to suppress friction and to suppress softening due to frictional heat generation.
2. When the surface roughness of the carburized material is viewed microscopically, the state of grain boundary oxidation at the time of carburizing affects the surface roughness. For this reason, it is not necessary when the surface is polished and used, but when used on the surface as it is carburized, quenched and tempered, the cost increases, so it is necessary to suppress grain boundary oxidation.
3. Addition of an alloy having temper softening resistance is effective for suppressing temper softening due to frictional heat generation. Among these, Si is a cheap and typical one.
4). Surface oxidation increases when Si is added to steel. However, the progress in the depth direction is delayed due to the progress of oxidation at the grain boundaries on the surface and the entire area within the grains. As a result, the surface roughness is smaller than the surface roughness when oxidation is performed with priority given to grain boundaries. Therefore, Si-added steel is indispensable for grain boundary oxidation control to suppress the surface roughness, but to control the surface oxidation state, control the carburizing conditions and control the grain boundary oxidation density of the surface layer. This is very important.
5). When Si is added, the transformation point of steel increases. By taking advantage of this point to control the internal structure and to control distortion due to heat treatment, it is possible to simplify and simplify distortion correction. At the same time, there is no need for polishing, and the surface hardness can be maintained at a low cost.

This invention is made | formed based on the above knowledge, and the characteristic is as follows.
[1] Component composition is C: 0.15-0.35 mass%, Si: 1.00-2.50 mass%, Mn: 0.40-0.70 mass%, Cr: 1.00-2.00 mass% , Mo: 0.3 mass% or less (including 0 mass%), Al: 0.010 to 0.080 mass%, N: 0.0040 to 0.0200 mass%, Cu: 0.50 mass% or less (including 0 mass%) Ni: 2.0 mass% or less (including 0 mass%), the remaining Fe and inevitable impurities, and a non-carburized portion satisfying the following formula (1), on the surface side from the non-carburized portion, The carburized part has a carburized part having a component composition with a high C content or even N content relative to the carburized part, and the carburized part has an oxidation density of 60% or more from the surface to a depth of 5 μm. Steel assembly Carburized parts having excellent wear resistance, wherein the 40% or less amount ferrite area ratio.
[Si] +3 [Cr] − [Mn] ≧ 4.0 (1)
However, [M] indicates the content (mass%) of the M element.
[2] As described in [1] above, the composition further contains one or more of Nb: 0.060 mass% or less, V: 0.20 mass% or less, and Ti: 0.200 mass% or less. Carburized parts with excellent wear resistance.
[3] The carburized part having excellent wear resistance according to any one of the above [1] or [2], further comprising B: 0.0050 mass% or less as a component composition.
[4] A component obtained by performing any one or more of machining, hot forging, cold forging, and warm forging using the steel material having the composition described in any one of [1] to [3] above. A method for producing a carburized part having excellent wear resistance, characterized by performing tempering after carburizing and quenching or carburizing and nitriding and quenching.

  According to the present invention, a carburized part having excellent wear resistance can be obtained. The carburized parts of the present invention can be suitably used for automobiles, industrial machinery gears, and the like. Moreover, according to the manufacturing method of the present invention, the carburized component of the present invention can be manufactured at low cost so as to be mass-produced. From the above, it is extremely useful industrially.

It is a figure explaining the carburizing quenching tempering process conditions used for the Example.

In this invention, the component composition of the steel material used as a raw material, the microstructure of the surface layer of a part, and the steel structure of a non-carburized part are prescribed | regulated. Each limitation reason is described below.
In the following description, the unit of the content of each element of the component composition is “mass%”, and is simply “%” unless otherwise specified.
Ingredient composition

C: 0.15-0.35 mass%
C is necessary for ensuring the strength, and determines the internal hardness after carburizing, quenching, and tempering. If it is less than 0.15 mass%, the internal hardness decreases, the bending stress decreases, and the strength cannot be ensured. On the other hand, when it exceeds 0.35 mass%, the retained austenite of the surface layer becomes excessive, the surface hardness is lowered, the internal toughness is deteriorated, and the fatigue characteristics are deteriorated. Therefore, it is set to 0.15 to 0.35 mass%.

Si: 1.00-2.50 mass%
Si is an element effective for increasing the temper softening resistance. When the softening resistance is low, softening due to frictional heat occurs and wear is accelerated. The suppression effect is effective at 1.00 mass% or more. Si also has the effect of raising the transformation point. After carburizing and tempering or carburizing and nitriding and quenching and tempering, Si needs to be 1.00 mass% or more so that ferrite is preferably present in an amount of 15% or more in the non-carburized part. On the other hand, when it contains 2.50 mass% or more, a ferrite exceeds 40%, internal hardness falls and fatigue strength falls. Therefore, it is set to 1.50 to 2.50 mass%.

Mn: 0.40 to 0.70 mass%
Mn is an element that enhances hardenability. In order to ensure hardenability, the content is set to 0.40 mass% or more. On the other hand, if the content exceeds 0.70 mass%, the transformation point is excessively lowered, the heat treatment deformation is increased, and the fatigue strength is lowered. Therefore, it is set to 0.40 to 0.70 mass%.

Cr: 1.00 to 2.00 mass%
Cr is an element improving the temper softening resistance as well as a hardenability improving element. In order to exhibit both performances, it is necessary to contain 1.00 mass% or more. On the other hand, if it exceeds 2.00 mass%, the effect of increasing the softening resistance is saturated. Further, since the hardenability becomes too high, the toughness inside the gear is deteriorated, the fatigue crack progresses quickly, and the bending fatigue strength decreases. Therefore, it is set to 1.00 to 2.00 mass%.

Mo: 0.3 mass% or less (including 0 mass%)
Although addition of Mo is not essential, since it is a hardenability improving element, it can be contained up to 0.3 mass%. If it exceeds 0.3 mass%, the hardenability is too high and cracking easily occurs, and since it is expensive, the economic efficiency is also deteriorated.

Al: 0.010-0.080 mass%
Al is an element effective for deoxidation, and the effect is exhibited by addition of 0.010 mass% or more. Further, when added up to 0.080 mass%, it combines with N to produce AlN, and has the function of suppressing the coarsening of crystal grains. If it exceeds 0.080 mass%, coarse grains are generated and fatigue cracks are easily developed, and the bending fatigue strength is lowered. Therefore, it is set to 0.010 to 0.080 mass%.

N: 0.0040-0.0200 mass%
N combines with Al to produce AlN, which suppresses coarsening of crystal grains and improves fatigue strength. To obtain the effect, 0.0040 mass% or more is necessary. On the other hand, if it exceeds 0.0200 mass%, the effect is not only saturated, but also defects such as blow holes are generated inside, leading to a decrease in bending fatigue strength. Therefore, it is set as 0.0040-0.0200 mass%.

Cu: 0.50 mass% or less (including 0 mass%)
The content of Cu is not necessarily essential, but may be contained up to 0.50 mass% because it is an element that dissolves in steel and increases the strength of the steel material. However, if it exceeds 0.50 mass%, surface flaws occur during steel production, and surface defects are likely to occur during parts production. If parts are produced after surface grinding, etc., the cost increases. Profit. Therefore, Cu is used at 0.50 mass% or less. In order to effectively develop the solid solution strengthening by Cu, it is preferable to contain 0.02 mass% or more. Furthermore, when it contains Cu, it is preferable to contain Ni with the high effect which suppresses generation | occurrence | production of surface flaws simultaneously.

Ni: 2.0 mass% or less (including 0 mass%)
Ni is not necessarily required to contain Ni. However, it can be contained because it has a function of increasing the strength by solid solution in steel and increasing the hardenability of the surface by increasing the hardenability. When Ni is contained, the upper limit is set to 2.0 mass% because Ni is expensive as an alloy. In addition, in order to effectively express the effect of enhancing solid solution strengthening and hardenability by Ni, it is preferable to contain 0.02 mass% or more.

  The above is the basic component composition of the present invention, but in the case of further improving the characteristics, one or more of Nb, V, Ti and B can be contained.

Nb: 0.060 mass% or less Nb refines crystal grains by forming carbonitride and improves fatigue characteristics. Since the effect of refining crystal grains increases at 0.010 mass% or more, it is preferable to contain 0.010 mass% or more. On the other hand, even if the content exceeds 0.060 mass%, the effect is saturated, so 0.060 mass% is made the upper limit.

V: 0.20 mass% or less V improves the hardenability and increases the temper softening resistance like Si and Cr. In addition, carbonitride is formed to suppress coarsening of crystal grains. In order to exert such an effect, the content is preferably 0.030 mass% or more. On the other hand, even if it contains exceeding 0.20 mass%, it will saturate and sufficient effect will not be acquired, but only a manufacturing cost will rise, Therefore When it contains, 0.20 mass% is made an upper limit.

Ti: 0.200 mass% or less Ti generates a fine Ti compound to reduce crystal grains after forging and increase the strength. Since the effect increases at 0.005 mass% or more, it is preferable to contain 0.005 mass% or more. On the other hand, if the content exceeds 0.200 mass%, the Ti precipitate becomes coarse, and the life becomes a starting point of fatigue fracture, so that the life is reduced. Therefore, if contained, the upper limit is 0.200 mass%.

B: 0.0050 mass% or less B is effective in increasing the hardenability. Since the effect is obtained at 0.0005 mass% or more, it is preferably contained at 0.0005 mass% or more. On the other hand, if it exceeds 0.0050 mass%, the above-mentioned effect becomes saturated. Therefore, when it is contained, the upper limit is set to 0.0050 mass%.

  The balance other than the elements described above is Fe and inevitable impurities. Inevitable impurities include P and S. P can be contained up to 0.030 mass%, and S can be contained up to 0.030 mass%.

Furthermore, it is necessary to satisfy the following expression (1) as a parameter for improving wear resistance.
[Si] +3 [Cr] − [Mn] ≧ 4.0 (1)
However, [M] indicates the content (mass%) of the M element.
The above equation (1) is necessary to control the three factors of suppressing temper softening, improving the grain boundary oxidation state, and ensuring the amount of ferrite in the non-carburized part. When this value is smaller than 4.0, temper softening resistance Either the surface oxidation state or the deformation amount due to the insufficient amount of ferrite in the non-carburized part is not satisfied, and the wear resistance is not improved.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carburized part that is carburized and has a carburized portion from a surface to a predetermined depth. Carburizing treatment is performed on steel having the above component composition in the shape of a part, but the carburized region (carburized portion) is formed on the surface layer, and the deeper part is the non-carburized portion consisting of the above-described component composition. It becomes. That is, the carburized portion is formed on the surface side of the non-carburized portion. Naturally, the C content of the carburized portion is higher than the C content of the non-carburized portion. Further, a nitriding treatment may be performed simultaneously with the carburizing treatment or after the carburizing treatment. In this case, the N content of the carburized portion is higher than the N content of the non-carburized portion. When carburizing or carburizing and nitriding is performed, the vicinity of the surface layer is oxidized, but the oxidation density is an important requirement in the present invention. When the surface layer oxidation density from the surface to a depth of 5 μm is less than 60%, the surface oxidation extends mainly inside the grain boundary, and it is used as a part. Local wear tends to extend and fatigue characteristics are degraded. Therefore, 60% or more is necessary. As for the surface layer oxidation density, a part having a concentration of 4 times or more compared with the alloy content of the non-carburized part is obtained by mapping Si with high oxygen affinity using EPMA from the surface to a depth of 5 μm. The sum of the areas was divided by the entire observation area. The observation area was 3000 times and 200 fields were observed.

The amount of ferrite in the non-carburized part When a certain amount of ferrite is present in the structure of the non-carburized part after carburizing and quenching tempering or carburizing and nitriding quenching and tempering, it is possible to reduce deformation of parts. Therefore, the ferrite content is preferably 15% or more in terms of area ratio. On the other hand, if it is present in excess of 40%, the internal hardness is too low and the fatigue strength is reduced. Therefore, the amount of ferrite in the non-carburized portion is limited to 40% or less in terms of area ratio. In addition, for the measurement of the ferrite content, cut and polished carburized parts etched with nital are observed in 100 visual fields with an optical microscope at a magnification of 400 times, and binarized by image processing to obtain an area of a white portion. Is determined as a percentage of the total area.

Manufacturing method of carburized part The carburized part which concerns on this invention is manufactured as follows. The steel material having the above component composition is formed into a desired part shape such as a gear by one or more of machining, hot forging, warm forging, and cold forging. Alternatively, a desired part shape such as a gear may be formed by machining after hot forging, cold forging, or warm forging. These processes may be combined in any way. The temperature conditions for hot forging and warm forging may be the conventional methods. For example, hot forging is performed at 1000 to 1300 ° C, and warm forging is performed at 400 to 950 ° C.

Carburizing quenching or carburizing and nitriding quenching is performed on a member processed into a part shape such as a gear, and then tempering is performed. About carburizing quenching, carburizing nitrocarburizing quenching, and tempering treatment, what is necessary is just to follow a conventional method, and there is no particular condition. After that, hold for 0 to 3 hours, then put into oil at 60 to 130 ° C, or cool and quench with inert gas such as nitrogen gas or helium gas, then reheat to 150 to 220 ° C and temper The process of performing The carburizing process includes a case involving a diffusion process. Further, the nitriding treatment may be performed simultaneously with any one or more of the above carburizing treatment, diffusion treatment, furnace cooling and holding.
The carbon potential is controlled for the atmosphere control during the carburizing treatment, but the equilibrium carbon concentration and oxidation state differ depending on the component composition of the steel, so carburize under the same steel material in advance, and adjust accordingly depending on the result There is a need. In addition, the final oxidation state of the steel surface layer is determined by adjusting the atmosphere control. In order to control the oxidation state of the steel surface layer as well as obtaining the required carburized hardened layer depth, the component composition is limited and the atmosphere is controlled. Both controls are required.

  In addition, by performing such carburizing treatment or carburizing and nitriding treatment, quenching, and tempering treatment, the ferrite content in the non-carburized portion is 40% or less within the range of the component composition of the present invention described above. In addition, the surface layer oxidation density from the surface to a depth of 5 μm is 60% or more.

  Steels having chemical components shown in Table 1 were melted. Steel No. shown in the table. Nos. 1-26 are compatible steels that satisfy the composition of the present invention. Reference numerals 40 to 57 are comparative steels that are outside the component range of the present invention. Steel No. Nos. 56 and 57 are conventional steels. 56 is JIS SCM420H, Steel No. 57 is an SCM822H standard material and is outside the scope of the present invention. In Table 1, P and S are contents mixed as inevitable impurities. Moreover, about Cu and i, when it is less than 0.02 mass%, it is described as content of Cu and i which are not added positively but are inevitably mixed.

  The ingots of the above-described compatible steel, comparative steel, and conventional steel were prepared into a round bar steel having a diameter of 70 mm by hot rolling, and the obtained round bar steel was subjected to normalization treatment.

  Roller pitting fatigue test pieces were produced from these round steel bars. As shown in FIG. 1, the roller pitching test piece is heated to 950 ° C., carburized and diffused, cooled in the furnace, soaked at 850 ° C. for 30 minutes, and then heated to 70 ° C. oil. And quenching. Thereafter, it was reheated to 180 ° C., soaked for 2 hours, and then air-cooled. For steel No. 26 and No. 55 (No. 27 and No. 56 in Table 2), ammonia gas was introduced into the furnace during the cooling process after carburizing treatment, and carburizing nitrocarburizing and tempering treatments were performed to prepare test pieces.

[Effective hardened layer depth, structure observation, surface hardness, internal hardness]
For the pre-test material of the roller pitching specimen subjected to carburizing, quenching and tempering, the transfer surface was cut, and the hardness distribution of the cross section was measured to determine the effective hardened layer depth.
Moreover, hardness measurement and structure observation were performed in the internal non-carburized part, and the area ratio of ferrite was also measured for the structure. The area ratio of ferrite is measured by taking a sample from the core (diameter center) of the test piece, observing 100 views of the surface etched with nital after polishing with an optical microscope at a magnification of 400 times, and imaging them. It binarized by processing, and the area of the white portion was obtained, and the ratio to the total area was obtained.
Regarding the internal hardness, a sample was taken from the core part (diameter center) of the test piece, and the Vickers hardness (micro Vickers 2.94N) was measured at five points, and the average value thereof was obtained.
Further, the surface hardness and the prior austenite grain size (old γ grain size) of the carburized portion were also investigated for the pre-test material of the roller pitching test piece that had been carburized and quenched and tempered. For the surface hardness, five points of Vickers hardness (micro Vickers 2.94N) were measured at a position 0.03 mm deep from the surface, and the average value thereof was determined. The prior austenite grain size was obtained by observing the same spot with the surface hardness measured at 100 times with an optical microscope to obtain the austenite grain size number.

[Amount of retained austenite]
About the material before the test of the roller pitching test piece which implemented carburizing quenching tempering, the amount of retained austenite of the surface layer part was investigated by X-ray diffraction.

[Surface layer oxidation density, grain boundary oxide layer depth]
Regarding the roller pitching test piece subjected to the above carburizing quenching and tempering, the concentration of Si up to a position of 5 μm below the surface was investigated by EPMA. The area ratio which is a ratio with the whole area was measured about the part concentrated 4 times or more with respect to the density | concentration of the non-carburizing part (cross-sectional center position of the roller pitching test piece which performed carburizing quenching tempering). Before the analysis, the state of grain boundary oxidation on the surface layer was observed in all fields of view, and the portion where oxidation proceeded to the deepest was defined as the grain boundary oxide layer depth.

[Abrasion measurement]
The amount of wear was investigated by a roller pitching test. The crowning amount on the large roller side was set to 150 mmR, and the surface pressure was rotated to 100,000 times at a surface pressure of 3200 MPa, and the wear curve of the cross section of the contact surface of the test piece was collected to determine the maximum wear depth with respect to the pre-test surface.

[Gear fatigue test]
Further, a round bar steel having a diameter of 100 mm was prepared by hot rolling from the ingots of the above-described compatible steel, comparative steel, and conventional steel, and the obtained round bar steel was subjected to normalization treatment. Gears with tooth width 10mm, module 2.5, pitch circle 100mm, rotating speed 3000rpm, lubricating oil with transmission oil at 80 ° C, changing torque and examining the number of repetition until breakage, with 10 million repetitions The maximum torque that did not break was evaluated as fatigue strength.

表２中の鋼No.は表１中の鋼No.と同じものを指す。表２から下記事項が明らかである。 Table 2 shows the test results.

Steel No. in Table 2 refers to the same steel No. in Table 1. From Table 2, the following matters are clear.

  Invented steel No. About 1-27, abrasion resistance was favorable and high fatigue strength was obtained.

In contrast, no. For 40, C% is lower than the scope of the invention. Therefore, the internal hardness after carburizing, quenching and tempering was low, and the surface layer hardness was also lower than the range of the present invention. As a result, wear resistance was reduced, tooth root breakage and tooth surface pitching were likely to occur, and the gear fatigue strength was reduced.
No. No. 41 has a higher C content than the scope of the invention. For this reason, the amount of residual γ after carburizing is too large, and a high surface hardness is not obtained, so that the wear resistance is reduced. In addition, the internal toughness was insufficient, and the destruction at the root portion was likely to occur. Therefore, the gear fatigue strength decreased.

  No. No. 42 had a Si amount less than the range of the present invention, and therefore the grain boundary oxide layer was deepened. Moreover, since the temper softening resistance was too low, the wear resistance was lowered, pitching was likely to occur, and the gear fatigue strength was also lowered.

  No. No. 43 has more Si than the scope of the present invention. As a result, too much soft ferrite was generated inside, and bending fatigue failure at the tooth root was likely to occur, and the gear fatigue strength was reduced.

  No. No. 44 has a Mn content lower than the range of the present invention. For this reason, the hardenability is too low, and the effective hardened layer depth is too shallow, so that bending fatigue failure at the root tends to occur, and the gear fatigue strength is reduced.

  No. No. 45 has a Mn content higher than the range of the present invention. For this reason, internal toughness was lowered, and many bending breaks occurred due to gear fatigue. In addition, the amount of ferrite inside was too small, the expression (1) was not satisfied, the amount of wear increased, pitching was likely to occur, and the gear fatigue strength was reduced.

  No. No. 46 has a small amount of Cr, and the hardenability is too low. For this reason, the hardened layer depth becomes too shallow and breakage at the tooth base is likely to occur, and pitching is also likely to occur, resulting in a reduction in gear fatigue strength.

  No. 47 has an excessively high internal hardness because the amount of Cr is too high. As a result, the toughness of the tooth root deteriorates and the bending breakage easily occurs, and the fatigue strength decreases.

  No. 48 has a high Mo content. Therefore, the hardenability was too high, and cracking occurred during carburizing and quenching, so that a fatigue test could not be performed.

  No. In No. 49, since the Al amount was too low, destruction at the root and tooth surface due to inclusion starting points was likely to occur, and the gear fatigue strength was reduced.

  No. In No. 50, since the amount of Al was too high, the austenite grains in the carburized portion were coarsened, and the fracture at the tooth root and the tooth surface was likely to occur, and the gear fatigue strength was reduced.

  No. 51 has too much Ti amount. Therefore, destruction at the Ti-based inclusion starting point occurred frequently. For this reason, bending breakage at the tooth root and pitching at the tooth surface are likely to occur, and the gear fatigue strength is reduced.

  No. 52 is too low in N content. As a result, coarsening of the crystal grains occurred, bending breakage at the tooth roots easily occurred, and the gear fatigue strength decreased.

  No. 53 has too much N content. Therefore, many fractures occurred at the starting point of internal cracks, and the gear fatigue strength decreased.

  No. 54, 55, and 56 were too low in the value of the formula (1), so the wear amount was large and the fatigue strength was also reduced.

  No. Since 57 and 58 are Si amounts and the value of Formula (1) is lower than the range of the present invention, the wear amount is large. Also, pitting was likely to occur due to the softening of the surface layer. Further, since the surface oxidation proceeded deeply along the grain boundary, it was easy to break due to the root bending stress, and the gear fatigue strength decreased.

  ADVANTAGE OF THE INVENTION According to this invention, the carburized component excellent in abrasion resistance and durability, and its manufacturing method which can be mass-produced can be provided.

Claims (5)

Component composition is C: 0.15-0.35 mass%, Si: 1.00-2.50 mass%, Mn: 0.40-0.70 mass%, Cr: 1.00-2.00 mass%, Mo: less not more than 0.3 mass% (including 0mass%), Al: 0.010~0.080mass% , N: 0.0040~0.0200mass%, a residual portion Fe and unavoidable impurities,
And a non-carburized portion that satisfies the following formula (1), and a carburized portion that is on the surface side of the non-carburized portion and has a component composition having a higher C content or higher N content than the non-carburized portion. ,
The carburized portion has an oxidation density of 60% or more from the surface to a depth of 5 μm,
A carburized part having excellent wear resistance, wherein the steel structure of the non-carburized part has a ferrite content in an area ratio of 15% to 40%.
[Si] +3 [Cr] − [Mn] ≧ 4.0 (1)
However, [M] indicates the content (mass%) of the M element.   The wear resistance according to claim 1, further comprising at least one of Nb: 0.060 mass% or less, V: 0.20 mass% or less, and Ti: 0.200 mass% or less as a component composition. Excellent carburized parts.   The carburized part having excellent wear resistance according to claim 1, further comprising B: 0.0050 mass% or less as a component composition. The component composition further includes at least one of Cu: 0.50 mass% or less and Ni: 2.0 mass% or less, in wear resistance according to any one of claims 1 to 3. Excellent carburized parts. A method for manufacturing a carburized part according to any one of claims 1 to 4 , wherein the steel material having the component composition according to any one of claims 1 to 4 is used for machining, hot forging, and cooling. Manufacture of carburized parts with excellent wear resistance, characterized by performing one or more of hot forging and warm forging to form parts, followed by tempering after carburizing quenching or carburizing and nitriding quenching Method.

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