JP3329177B2 - Carburized parts with excellent bending strength and impact properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carburized part having excellent bending strength and impact characteristics, and more particularly to a carburized part such as a gear for a differential gear of an automobile, which is likely to be damaged by an impact bending stress. .

[0002]

2. Description of the Related Art Carburized steel is used as a base material (steel material) of gears (bevel gears) used in differentials of automobiles, but may be damaged by an impact bending stress. is there.
This stress is caused by a shock load generated when the vehicle suddenly starts or stops, or when the vehicle travels at high speed on an uneven road (bad road).

[0003] The strain rate when the above-mentioned impact load acts varies depending on the degree of sudden start or stop, and the degree of high-speed running on a rough road. For this reason, a differential gear having resistance to a shocking load in a wide range of strain rates has a differential gear excellent in bending strength under both high strain rates and low strain rates. There is a need for device gears.

Conventionally, bevel gears for differentials have been manufactured by processing a desired shape using a JIS standard steel such as SCr420 or SCM420 as a base material and then carburizing the same.

[0005] However, recent movements such as increasing the output of an engine and reducing the weight of parts require increasingly higher flexural strength. Sufficient life cannot be obtained under load.
Therefore, in order to increase the resistance to the above-mentioned shocking load, steel premised on carburizing treatment is disclosed in Japanese Patent Application Laid-Open No. 62-1843.
No. 1993. That is, in the publication, S
i and Mo are added in combination (Mo: 0.5 to 1.
0% and Mo + Si: 1 to 2%), and a steel having an increased impact strength is disclosed.

However, the addition of a large amount of Si and Mo not only increases the material cost, but also increases the deformation resistance during cold forging, which is a gear manufacturing process, and lowers the machinability during cutting. The adverse effect occurs. in addition,
According to the study of the present inventors, even when using a carburized gear made of steel as a base material proposed in the above-mentioned publication, even if the engine is made to have a high output or a light weight as described above, the impact load may cause. It has become clear that damage cannot be always dealt with and does not have a sufficient effect. That is, when the steel proposed in the above publication was used as a base material, among the bending strengths required for bevel gears for differential gears, the bending strength at a low strain rate was not particularly satisfactory. It is.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is not only to increase the production cost, but also to minimize the addition of Si or Mo, which adversely affects the cold forgeability and machinability during production, to a steel base material. , Carburized parts that have excellent resistance to damage due to shock loads in a wide strain rate range, which is a problem in bevel gears for automobile differentials, etc., in other words, high strain rates and low strain rates An object of the present invention is to provide a carburized part having excellent bending strength under both conditions.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have studied the chemical composition of the steel material as the base material of the carburized part, the structure of the carburized part, and the mode of damage of the carburized part. As a result, the following findings were obtained.

The hardness of the base material after carburization has a correlation with the bending strength. That is, the flexural strength of the carburized part is greatly reduced with the decrease of the base metal hardness. The “base material” is a portion that is not carburized and hardened, that is, a portion other than the carburized hardened layer, and refers to “material steel”.

[0010] B is known as an element that enhances the hardenability of steel. However, when the C content is high, such as in a carburized layer, the effect of improving the hardenability hardly occurs. Therefore, B
By carburizing and quenching the added steel, only the hardness of the base material can be increased.

If the amount of Mn and Cr and the amount of Mn + Cr (the total amount of Mn and Cr) are adjusted and the appropriate amount of B is added to the steel whose quenchability is controlled and then carburized and quenched, the entire region of the carburized hardened layer is obtained. In addition to martensite and retained austenite, troostite can be formed. In addition, it is relatively easy to control the amount of troostite produced (area fraction of troostite).

[0012] The "troostite" here is different from the "incompletely quenched layer" found on the surface of a steel material when ordinary gas carburizing is performed. That is, in the so-called "incompletely quenched layer", alloying elements such as Cr, Mn, and Si on the surface of the steel material are oxidized during carburizing and quenching, and the alloying elements (Cr, Mn, Si, and the like) are deficient in the peripheral portion. This is a structure caused by insufficient hardenability. This structure appears as a layer on the surface of the steel material or in a shape along the oxide at the grain boundary. On the other hand, the above-mentioned “troostite” is observed in the form of particles in martensite and retained austenite, and has a structure clearly different from the above-mentioned “incompletely quenched layer”. Both of them can be easily distinguished by observing with an optical microscope at a magnification of about 500 times.

When the troostite is formed in the carburized hardened layer, both the static bending strength and the Charpy impact value (impact characteristics) are improved. However, if the area fraction of the troostite is too large, the bending strength deteriorates.

From the above and the above, the problem of the occurrence of damage due to an impact load in a wide range of strain rates in carburized parts, in other words, the occurrence of damage due to bending under both high strain rates and low strain rates. In order to solve the problem, regarding the structure after carburizing and quenching, the structure of the carburized hardened layer may be a mixed structure of martensite, retained austenite, and troostite having excellent static bending strength and impact properties. on the other hand,
The structure of the base material may be anything as long as it has hardness enough to secure a desired bending strength.

[0015] The surface C content of the carburized hardened layer affects the wear resistance, bending strength and toughness (impact properties) of the carburized part. That is, the surface C amount of the carburized hardened layer is 0.6% by weight.
%, Wear resistance deteriorates. On the other hand, if the content exceeds 1.1% by weight, the carburized hardened layer becomes significantly embrittled,
Flexural strength and impact properties are greatly reduced.

Here, the “surface C amount” is “0.1 from the surface.
means the C concentration (% by weight) of the matrix in a region up to mm, and "the surface C amount is less than 0.6%" means that the C concentration distribution in the region is 0.6% even if part thereof. % ". Similarly, “the surface C amount exceeds 1.1%” means that “the C concentration distribution in the above-mentioned region partially exceeds 1.1%”.

The surface C amount (surface C concentration distribution) may be measured by a calibration curve using an apparatus such as a wavelength dispersion type EPMA.

On the extreme surface, there is a case where it is difficult to perform an accurate analysis due to a problem of a characteristic X-ray generation region due to a mount of a sample or the like. In such a case, the influence of the mount is closest to the surface. The surface C amount may be read by extrapolating from the points that do not exist.

The gist of the present invention based on the above findings is as follows.
(1) - Ru carburized parts near excellent in flexural strength and impact properties shown in (3).

(1) The base material is C: 0.1 to 100% by weight.
0.3%, Mn: 0.5 to 1.3%, Cr: 0.1 to
1.1%, and Mn + Cr: 0.9 to 1.9%,
B: 0.001-0.005%, Al: 0.01-0.
1%, Mo: 0.01 to 0.15% , N : 0.003 to
0.015%, Si: 0.3% or less, P: 0.03% or less, S: 0.03% or less, steel having a chemical composition of the balance Fe and unavoidable impurities, and the surface carbon content of the carburized hardened layer Is weight%
A carburized part having excellent bending strength and impact characteristics, characterized in that the carburized hardened layer has an area fraction of troostite of 5 to 50%. (2) The base material is, by weight%, C: 0.1 to 0.3%, M
n: 0.5 to 1.3%, Cr: 0.1 to 1.1%, and
Mn + Cr: 0.9-1.9%, B: 0.001-
0.005%, Al: 0.01 to 0.1%, Nb: 0.
001-0.05% and Ti: 0.002-0.05%
One or more of the following, N: 0.003 to 0.015%, S
i: 0.3% or less, P: 0.03% or less, S: 0.03
% Or less, and the chemical composition of the balance of Fe and unavoidable impurities
Thus, the surface C amount of the carburized hardened layer is 0.6 to 1.1 in weight%.
% And the surface of troostite in the carburized hardened layer
A bending strength characterized in that the integral ratio is 5 to 50%;
Carburized parts with excellent impact characteristics. (3) The base material is, by weight%, C: 0.1 to 0.3%, M
n: 0.5 to 1.3%, Cr: 0.1 to 1.1%, and
Mn + Cr: 0.9-1.9%, B: 0.001-
0.005%, Al: 0.01 to 0.1%, Mo: 0.
01-0.15%, Nb: 0.001-0.05% and
Ti: one or more of 0.002 to 0.05%, N:
0.003 to 0.015%, Si: 0.3% or less, P:
0.03% or less, S: 0.03% or less, balance Fe and
Steel with chemical composition of unavoidable impurities, the surface of carburized hardened layer
C content is 0.6-1.1% by weight and its carburizing hardening
The area fraction of troostite in the layer is 5 to 50%.
Carburized section with excellent bending strength and impact characteristics
Goods. In addition, the above-mentioned "area fraction of troostite" refers to "average area fraction of troostite over the entire region of the carburized hardened layer".

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The requirements of the present invention will be described below in detail. In addition, "%" of the component content is "wt%".
Means

(A) Chemical Composition of Base Material (Material Steel) C: C has the effect of increasing the hardness of the base material (base steel) after carburizing and quenching to improve the bending strength of the carburized part. However, if the C content is less than 0.1%, the effect of addition is poor. On the other hand, if it exceeds 0.3%, the toughness is reduced, and the Charpy impact characteristics are deteriorated. Therefore, the content of C is set to 0.1 to 0.3%. Note that C
The content is preferably set to 0.15 to 0.25%.

Mn: Mn has the effect of increasing the hardness of the base material after carburizing and quenching to increase the bending strength. But,
If the content is less than 0.5%, the effect of addition is poor. On the other hand, if Mn is excessively added, the austenite grain boundary is embrittled, so that the bending strength is rather deteriorated. In particular,
When the Mn content exceeds 1.3%, the bending strength is significantly reduced. Therefore, the content of Mn is set to 0.5 to 1.3%.
And Note that the Mn content is desirably 0.6 to 1.2%.

Cr: Cr also has the effect of increasing the hardness of the base material after carburizing and quenching to increase the bending strength. However, if the content is less than 0.1%, the above effects cannot be expected. On the other hand, excessive addition of Cr causes embrittlement of austenite grain boundaries, so that bending strength is rather deteriorated.
In particular, when the Cr content exceeds 1.1%, the bending strength is significantly reduced. Therefore, the content of Cr is 0.1 to
1.1%. The preferred content of Cr is 0.2
~ 1.0%.

Mn + Cr: The amount of Mn + Cr greatly affects the amount of troostite generated in the carburized hardened layer, thereby affecting the characteristics of the carburized part. That is, this value is 0.9%
If it is less than 50%, the average area fraction of the troostite over the entire area of the carburized hardened layer exceeds 50%, so that the bending strength of the carburized part is deteriorated. On the other hand, if it exceeds 1.9%, it becomes difficult to form troostite in the carburized hardened layer, and the troostite area fraction becomes less than 5%, so that the static bending strength and the Charpy impact of the carburized part are reduced. Both values (impact characteristics) deteriorate. Therefore, the amount of Mn + Cr, which is the sum of the contents of Mn and Cr, is set to 0.9 to 1.
9%. In addition, it is preferable that the amount of Mn + Cr is 1.0 to 1.8%.

B: B is an important element in the present invention. B has the effect of increasing only the hardenability of the base material without increasing the hardenability of the carburized layer quenched after carburization. For this reason, it has the effect of increasing the bending strength of the carburized part by increasing the base metal hardness. However, when the content of B is 0.
If the content is less than 001%, the effect of addition is poor. If the content exceeds 0.005%, the effect is saturated and the cost is increased, and the hot workability is deteriorated. Therefore, the content of B is set to 0.001 to 0.005%. Note that the content of B is preferably set to 0.0015 to 0.003%.

Al: Al has an effect of suppressing coarsening of austenite grains at the time of carburizing treatment and miniaturizing crystal grains of a hardened layer and a base material after carburizing and quenching. However, if the content is less than 0.01%, the above-mentioned effect is not exhibited, and both the bending strength and the impact characteristics of the carburized component are reduced due to the coarsening of the crystal grains. On the other hand, when the content exceeds 0.1%, the above-mentioned effect is saturated. Therefore, the content of Al is 0.01 to
0.1%. The preferable content of Al is 0.0
2 to 0.05%.

N: N forms nitride and forms austenite during carburizing.
Hardening layer and base metal after carburizing and quenching, suppressing coarsening of crystal grains
Has the effect of refining the crystal grains in the part.
Content of at least 0.003%. However,
When the amount exceeds 0.015%, the above-mentioned action is saturated, and
The effect of the addition of B described above is lost. Accordingly
Thus, the content of N was set to 0.003 to 0.015%. What
The upper limit of the N content is preferably set to 0.012%.
No.

The base material of the carburized part of the present invention has the above-mentioned amount
In addition to C, Mn, Cr, Mn + Cr, B, Al and N
Further, Mo or / and one or more of Ti and Nb
Is contained in the following range.

Mo: Mo has an effect of improving the hardenability of steel. In particular, fine
The addition of an amount of quenching improves the hardenability of the carburized layer for the base metal.
Has the effect of increasing the torque in the carburized hardened layer.
It is an element suitable for adjusting the amount of statite formation. Previous
The described action of Mo is obtained at a content of 0.01% or more.
However, to ensure the effect, Mo should be more than 0.05%
Is preferable. However, its content
If it exceeds 0.15%, the trousers in the case hardened
Makes it difficult to generate troostite and impregnate it.
Static bending strength and Charpy impact value (impact characteristics) of charcoal parts
Cannot achieve the object of the present invention, which is to increase both. I
Therefore, the content of Mo is set to 0.01 to 0.15%.
Was.

Nb, Ti: one or more of Nb and Ti, that is, Nb and Ti
Carburizing by adding or containing one or both of them
Suppression of coarsening of austenite grains during processing
The hardened layer after carburizing and quenching,
Can be thinned. The above-mentioned action is the content of Nb in the case of Nb
Is 0.001% or more, and in the case of Ti, its content
Can be obtained at 0.002% or more,
In order to obtain, the content of Nb should be 0.005% or more.
It is preferable that the content of Ti is 0.005% or more.
Is preferred. However, Nb and Ti are each 0.05%.
%, The effect is saturated and the cost increases.
It's just Therefore, one of Nb and Ti
When adding the above, the contents of Nb and Ti
0.001-0.05%, 0.002-0.05%
Was.

Si: Si forms a grain boundary oxide layer at austenite grain boundaries on the surface of a carburized component when gas carburized. For this reason, the bending strength and impact characteristics of the carburized part are reduced. In particular, when the content exceeds 0.3%, the grain boundary oxide layer is formed to a deep position below the surface, and the bending strength and impact characteristics of the carburized part are significantly reduced. Therefore, the upper limit of the content of Si is set to 0.3%. In addition,
It is desirable that the Si content be 0.15% or less.

P: P deteriorates the strength and toughness (impact characteristics) of the carburized hardened layer, and particularly when the content exceeds 0.03%, the bending strength and toughness of the carburized part are significantly deteriorated. Therefore, the upper limit of the P content is set to 0.03%. Note that the content of P is preferably set to 0.025% or less.

S: S also degrades the strength and toughness of the carburized hardened layer. In particular, when the content exceeds 0.03%, the bending strength and toughness of the carburized part are significantly deteriorated. Therefore,
The upper limit of the content of S was set to 0.03%. Note that the content of S is preferably set to 0.025% or less.

(B) Surface C Content of Carburized Hardened Layer The surface C content of the carburized hardened layer has a great influence on the wear resistance, bending strength and impact characteristics of carburized parts. If the surface C content of the carburized hardened layer is less than 0.6%, the surface hardness of the carburized component will be low and sufficient wear resistance cannot be imparted. On the other hand, if it exceeds 1.1%, the carburized hardened layer is embrittled, and both the bending strength and the impact properties of the carburized component are reduced. Therefore, the amount of surface C after carburization is 0.6 to 1.1.
%. In addition, the amount of surface C after carburizing is 0.7 to 1.0%.
It is preferable that

(C) Structure of the carburized hardened layer The troostite generated in the carburized hardened layer has an effect of improving the bending strength and impact value of the carburized part. For this reason, in order to obtain a carburized component having excellent resistance to damage due to an impact load in a wide range of strain rates, it is important to control the structure of the carburized hardened layer of the carburized component. Therefore, in the present invention, the structure of the carburized hardened layer after carburizing and quenching is defined.

Generally, the main structure in the carburized hardened layer of a carburized and quenched part is composed of martensite and retained austenite. However, in the case of a component in which the target steel of the present invention is used as a base material (material steel) in which an appropriate amount of B is added while the amounts of Mn, Cr and Mn + Cr are strictly controlled, the above-described carburization is performed. Troostite is formed in the hardened layer in addition to martensite and retained austenite.

When the area fraction of troostite in the carburized hardened layer is less than 5%, the effect of improving the bending strength and impact value of the carburized component cannot be expected. On the other hand, when the area fraction of troostite exceeds 50%, the bending strength is reduced. Therefore, the area fraction of troostite in the carburized hardened layer was set to 5 to 50%. The preferred range of the area fraction of troostite in the carburized hardened layer is 10 to 40%.

The structure of the base material after carburization does not need to be particularly limited. That is, as long as the base material has a hardness enough to secure a desired bending strength, any structure may be used.

In the case of a component using the steel subject to the present invention as a base material, the structure in the carburized hardened layer can be obtained only by performing normal carburizing and quenching.

However, the above-mentioned area fraction of troostite is small in a portion where the cooling rate during carburizing and quenching is large, and is large in a portion where the cooling rate is slow. Therefore, when performing normal carburizing and quenching, considering the mass effect at the time of carburizing and quenching, the size of the target component is the outer diameter (for example, when the target component is a "gear", it corresponds to the diameter of the addendum circle) And preferably from about 25 mm to about 200 mm. On the other hand, regardless of the size of the target part,
In order to easily obtain a desired structure, the cooling rate during carburizing and quenching may be adjusted. For this purpose, water, oil, salt (salt) or the like may be appropriately selected as a cooling medium (quenching agent) and used at an appropriate temperature.

The carburized part according to the present invention is obtained by melting a base material (base steel) having the above-mentioned chemical composition by, for example, a usual method, hot rolling or forging, and further performing a heat treatment if necessary. Then, after forming into a desired part shape by cutting, forging, or the like, carburizing and quenching are performed, and tempering, grinding, and polishing are performed at a low temperature as necessary.

[0043]

EXAMPLE 150 kg of steel having the chemical composition shown in Tables 1 and 2 was vacuum-melted by an ordinary method. Steels A to M in Table 1
Is a steel to be subjected to the present invention (hereinafter referred to as the present invention steel), and steels N to W in Table 2 are comparative steels in which one of the components is out of the range specified in the present invention. Among the comparative steels, steels U and V correspond to JIS standard SCr420 and SCM420, respectively. Steel W is a high Si-Mo steel known as a carburizing steel having excellent impact characteristics.

[0044]

[Table 1]

[0045]

[Table 2]

Next, these steels were formed into billets by a usual method, and then heated to 1200 ° C.
A round bar having a diameter of 20 mm was formed by hot forging at a temperature of １０００1000 ° C., and was further normalized at 925 ° C.

From the round bar after normalization obtained in this way, FIG.
And a JIS No. 3 Charpy impact test piece were cut out.

(Example 1) Table 3 shows the carburizing conditions for the above two types of test specimens using steel A of the present invention as a base material.
In place of a to d, carburizing and quenching were performed according to the heat pattern shown in FIG. 2, and then tempering was performed at 180 ° C. for 2 hours. Note that, under all of the carburizing conditions a to d, the test pieces after carburizing were quenched in a 220 ° C. salt bath.

[0049]

[Table 3]

Thereafter, using the test piece subjected to the above treatment, a Charpy impact test at room temperature (room temperature) and a three-point bending test at room temperature (span 45 mm, strain rate of notch bottom 0.0
2 / sec). In the three-point bending test, the maximum load before the test piece was broken was evaluated, and this was defined as a three-point bending strength. Further, the surface C amount of the carburized hardened layer was measured by EPMA. Further, the hardness distribution from the surface was measured to specify the carburized hardened layer, and the structure of the carburized hardened layer was observed using an optical microscope.

Table 4 shows the test results. Table 4 shows the effect of the amount of surface C of the carburized hardened layer on the three-point bending strength and the Charpy impact value (impact characteristics). Table 4
With respect to the structure of the carburized hardened layer, the portion other than troostite (area fraction) means martensite and retained austenite.

From Table 4, in the case of the comparative example under carburizing condition d in which the surface C amount of the carburized hardened layer is higher than the value specified in the present invention,
It is apparent that both the bending strength and the Charpy impact value are lower than those of the carburizing conditions a to c of the examples of the present invention. In other words, under the carburizing condition d, the carburized hardened layer, particularly the carburized hardened layer on the surface, is embrittled because the surface C amount is too high at 1.15%, and troostite is generated in the carburized hardened layer. , Bending strength and impact value are both low.

[0053]

[Table 4]

(Example 2) Steels A to M of the present invention,
The above two types of test specimens, which are steels N to W as comparative steels, were subjected to carburizing and quenching according to the heat pattern shown in FIG. Tempered for hours. In this example, all the test pieces after carburization were quenched in a 220 ° C. salt bath.

Then, a Charpy impact test and a three-point bending test were performed on the test piece subjected to the above-mentioned carburizing, quenching and tempering under the same conditions as in Example 1. In the same manner as in Example 1, measurement of the surface C amount of the carburized hardened layer by EPMA, identification of the carburized hardened layer by hardness distribution measurement, and observation of the structure of the carburized hardened layer using an optical microscope were performed.

Table 5 shows the test results. In the test piece using the steel of the present invention as a base material, both the amount of surface C and the structure in the carburized hardened layer within the range specified by the present invention were obtained by carburizing and quenching under the carburizing conditions in Table 3a. When any steel is used as a base material, a three-point bending strength exceeding 2000 kgf and a Charpy impact value of 12.5 kgfmm / cm ² or more are obtained. As described above, when the steel of the present invention is used as a base material, JIS standard steel (steel U, V) or high Si-high M
It is clear that both the bending strength and the impact value are higher than the case where the conventional steel (steel W) of Example o is used as the base material, and the bending strength and the impact properties are excellent.

On the other hand, when the comparative steels N to T are used as the base metal, one or both of the three-point bending strength and the Charpy impact value are low.

In steel N, the amount of Mn + Cr is higher than the value specified in the present invention. Therefore, when steel N is used as a base material, no troostite is formed in the carburized hardened layer, and both the bending strength and the Charpy impact value are low.

In steel O, the amount of Mn + Cr is lower than the value specified in the present invention. For this reason, when steel O is used as a base material, troostite is excessively generated in the carburized hardened layer, and the bending strength is low.

The steel P has a higher Cr content than the value specified in the present invention. For this reason, the area fraction of troostite in the carburized hardened layer is within the range specified in the present invention, but the bending strength is low.

The steel Q has a higher Mn content than the value specified in the present invention. For this reason, the area fraction of troostite in the carburized hardened layer is within the range specified in the present invention, but the bending strength is low.

In steel R, the content of Mn and Cr is lower than the value specified in the present invention, and the amount of Mn + Cr is much lower than the value specified in the present invention. For this reason, when steel R is used as the base material, a large amount of troostite is generated in the carburized hardened layer and the bending strength is low.

In the steel S, the amounts of Mn, Cr and Mn + Cr are higher than the values specified in the present invention. When steel S is used as a base material, the fact that no troostite is formed in the carburized hardened layer and the excessive amounts of Mn and Cr overlap, and both the bending strength and the impact value are low.

In the steel T, the B content is lower than the value specified in the present invention. For this reason, the hardness of the base material is extremely low and the bending strength is low in the test piece using steel T as the base material. Incidentally, the base material hardness of steel T was Hv280. On the other hand, in the case of the steel H of the present invention, in which the contents of the other component elements except for B, N and Ti are almost the same as the steel T, the base metal hardness was Hv350.

[0065]

[Table 5]

[0066]

The carburized part of the present invention is made of inexpensive steel and has excellent bending strength and impact characteristics. Therefore, a differential gear of an automobile in which damage due to an impact load in a wide range of strain rate becomes a problem. It can be used as carburized parts such as gears for vehicles.

[Brief description of the drawings]

FIG. 1 is a view showing the shape of a three-point bending test piece used in an example.

FIG. 2 is a diagram showing a heat pattern of carburizing and quenching performed in an example.

Continuation of the front page (56) References JP-A-9-241821 (JP, A) JP-A-9-67644 (JP, A) JP-A-8-311607 (JP, A) JP-A-8-302447 (JP) JP-A-8-3629 (JP, A) JP-A-5-263183 (JP, A) JP-A-1-19164 (JP, A) JP-B-47-44855 (JP, B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (3)

(57) [Claims] (1) The base material is, by weight%, C: 0.1 to 0.3.
%, Mn: 0.5 to 1.3%, Cr: 0.1 to 1.1%
And Mn + Cr: 0.9-1.9%, B: 0.0
01-0.005%, Al: 0.01-0.1%, M
o: 0.01 to 0.15% , N : 0.003 to 0.01
5%, Si: 0.3% or less, P: 0.03% or less, S:
A steel having a chemical composition of not more than 0.03% and the balance of Fe and unavoidable impurities, wherein the surface C amount of the carburized hardened layer is 0.6% by weight.
A carburized part excellent in bending strength and impact characteristics, characterized in that the carburized hardened layer has an area fraction of troostite of 5 to 50%. (2) The base material is C: 0.1 to 0.3 by weight%.
%, Mn: 0.5 to 1.3%, Cr: 0.1 to 1.1%
And Mn + Cr: 0.9-1.9%, B: 0.0
01-0.005%, Al: 0.01-0.1%, N
b: 0.001-0.05% and Ti: 0.002-
One or more of 0.05%, N: 0.003 to 0.0
15%, Si: 0.3% or less, P: 0.03% or less,
S: 0.03% or less, balance Fe and unavoidable impurity chemistry
A steel having a composition in which the carburized hard layer has a surface C content of
0.6 to 1.1% and the tor in the carburized hardened layer
Characterized in that the area fraction of the ostite is 5 to 50%.
Carburized parts with excellent bending strength and impact characteristics. (3) The base material is C: 0.1 to 0.3 by weight%.
%, Mn: 0.5 to 1.3%, Cr: 0.1 to 1.1%
And Mn + Cr: 0.9-1.9%, B: 0.0
01-0.005%, Al: 0.01-0.1%, M
o: 0.01 to 0.15%, Nb: 0.001 to 0.0
5% and Ti: at least one of 0.002 to 0.05%
Above, N: 0.003 to 0.015%, Si: 0.3% or less
Bottom, P: 0.03% or less, S: 0.03% or less, balance F
steel with chemical composition of e and unavoidable impurities, carburized
The surface C content of the layer is 0.6 to 1.1% by weight and
The area fraction of troostite in the carburized hardened layer is 5-5
Excellent bending strength and impact characteristics characterized by 0%
Carburized parts.