JPH10219393A - Steel material for nitrocarburizing, nitrocarburizing component and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To provide a nitrocarburized component excellent in tensile strength, fatigue strength and bending properties even when a tempering treatment or the like is omitted, a method of manufacturing the same, and a nitrocarburized steel material as a base metal. SOLUTION: C: less than 0.20 to 0.38%, Si: 0.05 to 1.0
%, Mn: more than 1.0 to 1.5%, P ≦ 0.05%, S: 0.005 to 0.10
%, Cr ≦ 0.3%, Al ≦ 0.08%, Ti ≦ 0.03%, N: 0.008 ~
0.02%, Ca ≦ 0.005%, Pb ≦ 0.30%, Cu ≦ 0.3%, Ni ≦ 0.
3%, Mo ≦ 0.3%, V ≦ 0.2%, Nb ≦ 0.05%, fn1 ≧ 180, balance Fe and impurities, ferritic / pearlite structure, ferritic pearlitic steel with ferrite fraction of 10% or more. Furthermore, fn2 ≧
15 is better. A soft-nitrided part in which the above steel material is used as a base material and a nitride layer is formed on a surface portion thereof. The nitrocarburizing treatment may be performed without performing both normalizing and tempering treatment. However,
fn1 = 221C (%) + 99.5Mn (%) + 52.5Cr (%)-304Ti (%) + 577N (%) + 2
Five. fn2 = -192C (%)-32.8Mn (%)-25.1Cr (%) + 467Ti (%) + 726N
(%) + 122.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a steel material for nitrocarburizing, a nitrocarburized component, and a method for producing the same. For more information,
Even if nitrocarburizing treatment is performed without performing either tempering treatment or normalizing, nitrocarburized parts with high tensile strength and fatigue strength, and excellent bending characteristics, especially for automobiles, industrial machinery and construction machinery Nitrocarburized crankshaft and method of manufacturing the same,
And a steel material for nitrocarburizing as a base material thereof.

[0002]

2. Description of the Related Art As a method for manufacturing a crankshaft for an automobile, an industrial machine, a construction machine, or the like, a steel piece such as carbon steel for machine structure is hot-worked into a desired shape by a hot forging method or the like. a) a method of obtaining a desired strength by performing a tempering treatment (quenching / tempering treatment) or normalizing, and (b) a method of obtaining a desired strength by further soft-nitriding after the above-mentioned tempering treatment and normalizing. There is. The nitrocarburizing treatment of (b) is a treatment performed to impart higher fatigue strength to the crankshaft of (a). In any case, finish forming by machining may be performed after the tempering treatment or normalizing. In the case of (b), finish shaping by polishing or grinding may be performed after the nitrocarburizing treatment.

In recent years, so-called “non-tempering” or “non-normalizing” has been carried out on nitrocarburized parts such as nitrocarburized crankshafts in order to reduce cost. Are being considered.

However, when ordinary JIS carbon steel for machine structural use is used as a base material, a coarse crystal structure or a mixed grain structure at the time of hot working such as hot forging or the like, if the tempering treatment and normalizing are omitted. Is handed over to the final product, nitrocarburized parts. For this reason, the nitrocarburized parts have problems such as a decrease in fatigue strength and a decrease in bending characteristics. Therefore, the "non-tempering" and "non-normalizing" have not yet been implemented.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a nitrocarburized component having high tensile strength and fatigue strength (fatigue limit) and excellent bending characteristics without performing any heat treatment or normalizing. More specifically, a soft material having a tensile strength of 550 MPa or more, a fatigue strength of 400 MPa or more according to an Ono-type rotary bending fatigue test, and a bending characteristic with a crack generation limit stroke of 6 mm or more in a bending test using a specific test piece described later. It is an object of the present invention to provide a nitrided component, especially a nitrocarburized crankshaft for an automobile, an industrial machine, a construction machine, and the like, a method for producing the same, and a nitrocarburized steel material as a base material thereof.

[0006]

The gist of the present invention is to provide a steel material for nitrocarburizing shown in the following (1) and (2), a nitrocarburized component shown in (3), and a nitrocarburized component shown in (4). In the manufacturing method.

(1) By weight%, C: 0.20% or more and less than 0.38%, Si: 0.05 to 1.0%, Mn:
More than 1.0% and 1.5% or less, P: 0.05% or less,
S: 0.005 to 0.10%, Cr: 0.3% or less, A
l: 0.08% or less, Ti: 0.03% or less, N: 0.
008-0.02%, Ca: 0.005% or less, Pb:
0.30% or less, Cu: 0.3% or less, Ni: 0.3%
Hereinafter, Mo: 0.3% or less, V: 0.2% or less, Nb:
0.05% or less, and fn1 represented by the following formula is 18:
A steel material for nitrocarburizing characterized by being not less than 0, the balance being a chemical composition of Fe and unavoidable impurities, a structure comprising ferrite and pearlite, and a ferrite fraction of 10% or more.

Fn1 = 221C (%) + 99.5Mn (%) + 52.5Cr (%) − 304 Ti (%) + 577N (%) + 25 (2) In weight%, C: 0.20% Above, less than 0.38%, Si: 0.05-1.0%, Mn: more than 1.0% and 1.5% or less, P: 0.05% or less, S: 0.005-0.005%
0.10%, Cr: 0.3% or less, Al: 0.08% or less, Ti: 0.03% or less, N: 0.008 to 0.02
%, Ca: 0.005% or less, Pb: 0.30% or less,
Cu: 0.3% or less, Ni: 0.3% or less, Mo: 0.
3% or less, V: 0.2% or less, Nb: 0.05% or less,
And fn1 and fn2 represented by the above equation and the following equation are f
n1 ≧ 180 and fn2 ≧ 15 are satisfied, and the balance is the chemical composition of Fe and unavoidable impurities. The structure is composed of ferrite and pearlite, and the ferrite fraction is 10%.
A steel material for nitrocarburizing characterized by the above.

Fn2 = −192C (%) − 32.8Mn (%) − 25.1Cr (%) + 467Ti (%) + 726N (%) + 122 (3) The above (1) or (2) A nitrocarburized component comprising a steel material for nitrocarburizing having the chemical composition and structure described in 1) as a base material, and a nitrided layer provided on a surface layer portion.

(4) A nitrocarburizing treatment is performed on the nitrocarburizing steel material according to the above (1) or (2) without performing any of the tempering treatment and normalizing to form a nitrided layer on the surface layer portion. A method for producing a nitrocarburized component.

In the following, the inventions described in the above (1) to (4) are referred to as the inventions (1) to (4), respectively.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have conducted various studies to solve the above-mentioned problems. As a result, the following findings were obtained.

(A) When the C content is less than 0.38%,
In the case of a specific steel having a content of more than 1.0%, the fatigue strength is increased without deteriorating the bending properties, and the steel is preferably subjected to nitrocarburizing treatment without tempering or normalizing. Bending characteristics and large fatigue strength can be provided.

(B) The bending characteristics after nitrocarburizing are closely related to the matrix structure of the nitrocarburized component. That is, when bainite or martensite is mixed in a structure composed of ferrite and pearlite (hereinafter, referred to as “ferrite-pearlite structure”), the bending characteristics are significantly reduced. Therefore, the base metal structure needs to be a ferrite-pearlite structure. The base material refers to a portion that is not hardened by nitrocarburizing, and the base material structure is a structure before nitrocarburizing.

(C) In a ferrite-pearlite structure of steel having a specific chemical composition, when a ferrite fraction (area ratio when observed by an optical microscope) is 10% or more, a specific test piece described in the following example is used. In the bending test used, a desired crack generation limit stroke of 6 mm or more was obtained,
The bending due to the strain after nitrocarburizing can be easily corrected.

(D) In the ferrite-pearlite structure of a steel having a specific chemical composition, the fatigue strength can be arranged by fn1 in the above equation.

(E) In order to obtain a desired fatigue strength of 400 MPa or more in the Ono-type rotary bending fatigue test, fn1 ≧
180.

(F) A steel having a specific chemical composition has a ferrite fraction of 10% in a ferrite-pearlite structure.
In the above case, fn2 in the above equation has a correlation with bending characteristics (crack generation characteristics in a bending test using a specific test piece described later in the examples).

(G) When fn2 ≧ 15, the bending characteristics are very good.

The present invention has been completed based on the above findings.

Hereinafter, each requirement of the present invention will be described in detail. In addition, “%” of the component content means “% by weight”.

(A) Chemical composition C: 0.20% or more and less than 0.38% C is an element effective for imparting a desired tensile strength of 550 MPa or more to steel parts (products). Requires a content of 0.20% or more. But 0.3
If the content is 8% or more, the fatigue strength is reduced due to the relationship between toughness and fatigue strength, especially the Mn content described below.
Further, the bending characteristics may be deteriorated and cracks may be generated when correcting the bending due to the strain after the nitrocarburizing treatment. Therefore,
The content of C is set to 0.20% or more and less than 0.38%.
The preferred range of the C content is 0.30 to 0.35.
%.

Si: 0.05-1.0% Si is an effective element for deoxidizing steel. Further, it also has the effect of increasing the fatigue strength. However, the content is 0.05
%, The effect of addition is poor. On the other hand, when the content exceeds 1.0%, the bending characteristics are deteriorated. Therefore,
The Si content was 0.05 to 1.0%. Note that the Si content is desirably 0.05 to 0.3%.

Mn: more than 1.0% and not more than 1.5% Mn is an element effective for deoxidizing steel and also an element effective for enhancing hardenability. Further, it also has the function of improving the soft nitriding properties and increasing the fatigue strength. Among the functions described above, the function of improving the nitrocarburizing property and increasing the fatigue strength is as follows.
This is exhibited when the content of Mn exceeds 1.0% in relation to the content. On the other hand, if the content exceeds 1.5%, the bending characteristics may be deteriorated, and cracks may be generated when correcting the bending due to the strain after the nitrocarburizing treatment. Therefore, Mn
Was set to more than 1.0% and 1.5% or less. In addition,
The preferred content of Mn is 1.05 to 1.4%.

P: 0.05% or less P lowers fatigue strength and bending characteristics (correction characteristics). In particular, when the content exceeds 0.05%, the fatigue strength and bending properties are significantly reduced. Therefore,
The content of P was set to 0.05% or less. The P content is preferably set to 0.02% or less.

S: 0.005 to 0.10% S has an effect of improving the machinability. However, if the content is less than 0.005%, the effect of addition is poor. On the other hand, when the content exceeds 0.10%, the fatigue strength and the bending properties are significantly reduced. Therefore, the S content is set to 0.005 to 0.10%. In addition, from the viewpoint of greatly improving the machinability, the S content is preferably set to 0.02 to 0.10%.

Cr: 0.3% or less Cr need not be added. When added, it has the effect of improving the nitrocarburizing properties and increasing the fatigue strength. To ensure this effect, the content of Cr is preferably set to 0.03% or more. However, when Cr is contained in an amount exceeding 0.3%, the bending properties are significantly reduced. Therefore,
The content of Cr was set to 0.3% or less. In order to obtain extremely excellent bending characteristics, the Cr content is preferably set to 0.1% or less.

Al: 0.08% or less Al deteriorates bending characteristics. In particular, when the content exceeds 0.08%, the bending characteristics are significantly reduced. Therefore, the Al content is set to 0.08% or less.
The upper limit of the Al content is preferably set to 0.05%.

Ti: 0.03% or less Ti need not be added. If added, it has the effect of making the crystal grains finer and improving the nitrocarburizing properties.
To ensure these effects, it is preferable that the content of Ti is 0.003% or more. However, 0.03%
If the content exceeds the above range, the bending characteristics may be deteriorated, and cracks may be generated when the bending due to the strain after the nitrocarburizing treatment is corrected. Therefore, the content of Ti is set to 0.03% or less.

N: 0.008 to 0.02% N is an effective element for forming nitrides and refining crystal grains. However, if the content is less than 0.008%, the above effects cannot be sufficiently expected. On the other hand, 0.02%
However, the effect is saturated even if it is contained in excess of, and the economic efficiency is only lost. Therefore, the N content is 0.008 to
0.02%.

Ca: 0.005% or less Ca may not be added. If added, it has the effect of improving machinability. In order to surely obtain this effect, the content of Ca is preferably set to 0.0005% or more. However, if the content exceeds 0.005%, the fatigue strength and bending properties are significantly reduced. Therefore, the Ca content is set to 0.005% or less.

Pb: 0.30% or less Pb may not be added. If added, it has the effect of improving machinability. In order to surely obtain this effect, the content of Pb is preferably set to 0.05% or more. However, if the content exceeds 0.30%, the fatigue properties and bending properties are reduced. Therefore, the Pb content is set to 0.30% or less.

Cu: 0.3% or less Cu need not be added. If added, it has the effect of increasing the static strength (tensile strength). To ensure this effect, it is preferable that the content of Cu be 0.01% or more. A more preferable Cu content is 0.05% or more. However, when the content exceeds 0.3%, the hot workability is reduced. Therefore, the content of Cu is set to 0.3% or less.

Ni: 0.3% or less Ni may not be added. If added, it has the effect of improving toughness. To ensure this effect, the content of Ni is preferably set to 0.01% or more. A more preferred Ni content is 0.05% or more. However, even if Ni is contained in an amount exceeding 0.3%, the above-described effect is saturated and economic efficiency is impaired. Further, the machinability is reduced. Therefore, the content of Ni is reduced to 0.3%.
It was as follows.

Mo: 0.3% or less Mo need not be added. If added, it has the effect of increasing hardenability and improving toughness. To ensure these effects, it is preferable that the content of Mo be 0.01% or more. More preferred Mo content is
0.03% or more. However, even if the content exceeds 0.3%, the effect is saturated, and the economic efficiency is only lost. Therefore, the content of Mo is set to 0.3% or less.

V: 0.2% or less V may not be added. If added, it has the effect of generating V carbonitride, improving nitrocarburizing properties and increasing fatigue strength. To ensure this effect, it is preferable that the content of V be 0.01% or more. However, if the content exceeds 0.2%, the bending characteristics may be degraded, and cracks may be generated when the bending due to the strain after the nitrocarburizing treatment is corrected. Therefore, the V content is set to 0.2% or less.
In order to secure extremely excellent bending characteristics, the V content is preferably set to 0.1% or less.

Nb: 0.05% or less Nb may not be added. If added, it has the effect of generating NbN and improving the nitrocarburizing properties. In order to surely obtain this effect, the content of Nb is preferably set to 0.003% or more. However, when the content exceeds 0.05%, the bending characteristics are deteriorated, and cracks may occur when the bending due to the strain after the nitrocarburizing treatment is corrected. Therefore, the content of Nb is set to 0.05% or less. In addition,
In order to ensure extremely excellent bending characteristics, the Nb content is preferably set to 0.02% or less.

Fn1: In the ferrite-pearlite structure in which the chemical composition of the steel is in the above-mentioned range of the content from C to Nb, the fatigue strength can be represented by fn1 as represented by the above equation. When the value of fn1 is 180 or more, a desired large fatigue strength of 400 MPa or more can be obtained. Therefore, fn1 ≧ 180. Note that if the value of fn1 exceeds 260, the machinability may deteriorate, so the value of fn1 is preferably set to 260 or less.

Fn2: In the ferrite-pearlite structure in which the chemical composition of the steel is in the above-mentioned range of the content from C to Nb, the bending characteristic is represented by f.
n2. When the value of fn2 is 15 or more, extremely good bending characteristics (a crack generation limit stroke far exceeding 6 mm) can be obtained.
Therefore, fn2 ≧ 15 is set for a case where extremely good bending characteristics are required. If the value of fn2 exceeds 65, the static strength (tensile strength) may decrease, so the value of fn2 is desirably 65 or less.
As described above, only when the ferrite fraction in the ferrite-pearlite structure is 10% or more, f
n2 has a correlation with bending characteristics.

(B) Structure The bending characteristics after nitrocarburizing have a close relationship with the matrix structure of the nitrocarburized component. If bainite or martensite is mixed in the ferrite / pearlite structure, the bending characteristics are significantly reduced. Therefore, the base metal structure needs to be a ferrite-pearlite structure. As described above, the base material refers to a portion that has not been hardened by nitrocarburizing, and the base material structure refers to a structure before nitrocarburizing.

When the structure of the base material is ferrite. Even if it has a pearlite structure, if the ferrite fraction (area ratio when observed with an optical microscope) is less than 10%, the desired 6 m
A crack generation limit stroke of m or more cannot be obtained. Therefore, the ferrite fraction in the ferrite-pearlite structure was set to 10% or more. If the ferrite fraction in the ferrite-pearlite structure exceeds 70%, the fatigue strength may decrease, so the ferrite fraction is preferably set to 70% or less.

The steel having the chemical composition shown in the above (A) is heated, hot-worked, formed into a desired nitrocarburized component, and then cooled at a cooling rate of air cooling or lower. If so, a ferrite-pearlite structure having a ferrite fraction of 10% or more can be easily obtained. Here, “air cooling” refers to one that complies with JIS classifications such as “air cooling”, “furnace cooling”, and “water cooling”. The above-mentioned heating may be performed by a usual method in a temperature range of 1200 to 1300 ° C. There is no particular limitation on the hot working, and a normal working method such as hot forging may be used.
After the hot working, machining such as cutting may be performed as necessary.

According to the above-described manufacturing method, the "steel material for nitrocarburizing" according to the inventions (1) and (2) is obtained. This steel material is subjected to the following nitrocarburizing treatment, and becomes the “nitrocarburized component” according to the invention of (3).

(C) Nitriding treatment A part (steel material for nitrocarburizing) having the chemical composition of (A) and the structure of (B) and having a desired shape is subjected to nitrocarburizing treatment to obtain hard and deep nitriding. A layer is formed on the surface. Thus, a nitrocarburized component having high tensile strength and fatigue strength (fatigue limit) and excellent bending characteristics can be obtained. In addition,
The method of this soft nitriding treatment is not limited at all,
It can be done in the usual way.

The component (steel material for nitrocarburizing) having the desired shape as described above is subjected to only the nitrocarburizing treatment without performing either the tempering treatment or the normalizing treatment (the invention of (4)). , High tensile strength and fatigue strength, and excellent bending properties.

The surface hardness (referred to as Hv hardness at a position of 0.025 mm from the surface) and the effective hardening depth (referred to as a distance from the surface to the base material hardness) after the nitrocarburizing treatment are particularly limited. You don't have to. However, the surface hardness is preferably 600 to 900 in terms of Hv from the viewpoint of bending characteristics, and the effective hardening depth is preferably 0.1 mm or more from the viewpoint of securing fatigue strength. In addition, a more preferable effective hardening depth is 0.3 mm or more.

The nitrocarburized component according to the invention (3) may be further subjected to grinding or polishing as required after the nitrocarburizing treatment.

[0048]

EXAMPLE A steel having the chemical composition shown in Tables 1 and 2 was melted by a conventional method in a 50 kg test furnace. Steels 1 to 16 in Table 1 are steels whose components are in the ranges specified in the present invention. On the other hand, steels 17 to 33 in Table 2 are steels in which one of the components is out of the range specified in the present invention.
This steel is equivalent to IS S50C.

[0049]

[Table 1]

[0050]

[Table 2]

Next, these steels were formed into billets by a usual method, and then heated to 1250 ° C.
Hot forging was performed at ~ 1000 ° C to obtain a round bar having a diameter of 30 mm. The cooling after the hot forging at 1000 ° C. was air-cooled.

As for the steels 1 to 32, a test piece having a shape shown in FIG. 1, a tensile test piece of JIS No. 4 and a microscopic observation of a 25 mm diameter and a 20 mm thickness were obtained from the round bar having a diameter of 30 mm obtained as described above. A test piece was cut out. on the other hand,
For steel 33, the diameter 30 m obtained as described above
After a round bar of m was heated at 900 ° C. for 30 minutes and air-cooled, a test piece having the shape shown in FIG. 1 and a tensile test piece of IS4 were cut out.

Next, a test piece of steel 1-33 having the shape shown in FIG. 1 and a tensile test piece of JIS No. 4 were placed in a gas at a temperature of 570 ° C., in which ammonia gas was added to nitrogen gas at a ratio of 1: 1. The nitrocarburizing treatment was performed by holding for 3 hours, and then cooled into oil.

The tensile strength at room temperature (room temperature) was measured using a JIS No. 4 tensile test piece subjected to soft nitriding.

Ono type rotary bending fatigue test and bending test were performed using the test piece having the shape shown in FIG. 1 subjected to the nitrocarburizing treatment, and the fatigue characteristics and bending characteristics were investigated.

That is, at room temperature, in the air, at a rotation speed of 3000
An Ono-type rotary bending fatigue test was performed under the condition of rpm to determine bending fatigue strength (fatigue limit).

Further, a crack gauge was attached to the test piece having the shape shown in FIG.
A three-point bending test was performed under the conditions of m and a crosshead speed of 20 mm / min, and the limit stroke at which cracks occurred (crack occurrence limit stroke) was determined.

Further, steel 1 to 32 having a diameter of 25 mm and a thickness of 2
Using a test specimen for micro observation of 0 mm, the structure after hot working corresponding to the base metal structure was observed with an optical microscope (magnification: 200
Times) and the ferrite fraction was determined. All of steels 1 to 32 had a ferrite-pearlite structure.

Table 3 summarizes the results of various tests.

From the results shown in Table 3, the steels 1 to 16 of the present invention having the chemical composition specified by the present invention and having the structure specified by the present invention have a desired tensile strength of 550 MPa or more. , A fatigue strength of 400 MPa or more and a crack generation limit stroke of 6 mm or more. This is JI
The performance is equal to or higher than the performance when soft nitriding treatment is performed after normalizing using steel 33 which is S50C equivalent steel of S. In the examples of the present invention, in the steels 1 to 15 satisfying fn2 ≧ 15, a large crack generation stroke far exceeding 6 mm is obtained.

On the other hand, in the steels 17 to 32 of Comparative Examples whose chemical composition and / or structure deviated from the conditions specified in the present invention,
At least one of the tensile strength, fatigue strength, and crack generation limit stroke has not reached the target value.

[0062]

[Table 3]

[0063]

The nitrocarburized component of the present invention has high tensile strength, fatigue strength and excellent bending properties, and can be used as a crankshaft for automobiles, industrial machines and construction machines. The steel material for nitrocarburizing, which is the base material of the nitrocarburized parts, can have desired characteristics as the final nitrocarburized parts, even if it is subjected to nitrocarburizing treatment without performing either tempering treatment or normalizing. Cost reduction is possible. As described above, the industrial effect of the present invention is extremely large.

[Brief description of the drawings]

FIG. 1 is a view showing the shape of a test piece used in an Ono-type rotary bending fatigue test and a bending test of an example.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Harunori Kakimi 5-1-1109 Shimaya, Konohana-ku, Osaka-shi, Osaka Inside the steelworks of the Kansai Works, Sumitomo Metal Industries, Ltd. (72) Inventor Masato Kurita Osaka, Osaka 4-5-33, Kitahama, Chuo-ku, Sumitomo Metal Industries, Ltd.

Claims (4)

[Claims] (1) By weight%, C: 0.38 at 0.20% or more.
%, Si: 0.05 to 1.0%, Mn: more than 1.0% and 1.5% or less, P: 0.05% or less, S: 0.00
5 to 0.10%, Cr: 0.3% or less, Al: 0.08
%, Ti: 0.03% or less, N: 0.008-0.
02%, Ca: 0.005% or less, Pb: 0.30% or less, Cu: 0.3% or less, Ni: 0.3% or less, Mo:
0.3% or less, V: 0.2% or less, Nb: 0.05% or less, fn1 represented by the following formula is 180 or more, and the balance is the chemical composition of Fe and unavoidable impurities. A steel material for nitrocarburizing, comprising: ferrite, pearlite, and a ferrite fraction of 10% or more. fn1 = 221C (%) + 99.5Mn (%) + 52.5Cr (%)-304Ti (%) + 577N (%) + 25 ... 2. In% by weight, C: 0.38 at 0.20% or more.
%, Si: 0.05 to 1.0%, Mn: more than 1.0% and 1.5% or less, P: 0.05% or less, S: 0.00
5 to 0.10%, Cr: 0.3% or less, Al: 0.08
%, Ti: 0.03% or less, N: 0.008-0.
02%, Ca: 0.005% or less, Pb: 0.30% or less, Cu: 0.3% or less, Ni: 0.3% or less, Mo:
0.3% or less, V: 0.2% or less, Nb: 0.05% or less, and fn1 and fn2 represented by the following equations and f
n1 ≧ 180 and fn2 ≧ 15 are satisfied, and the balance is the chemical composition of Fe and unavoidable impurities. The structure is composed of ferrite and pearlite, and the ferrite fraction is 10%.
A steel material for nitrocarburizing characterized by the above. fn1 = 221C (%) + 99.5Mn (%) + 52.5Cr (%)-304Ti (%) + 577N (%) + 25 ... fn2 = -192C (%)-32.8Mn (%)-25 .1Cr (%) + 467 Ti (%) + 726N (%) + 122 3. A nitrocarburized component comprising a steel for nitrocarburizing having the chemical composition and structure according to claim 1 or 2 as a base material, and a nitride layer provided on a surface layer. 4. A nitrocarburizing treatment is applied to the steel material for nitrocarburizing according to claim 1 or 2 without performing any tempering treatment and normalizing to form a nitrided layer on a surface layer portion. A method for producing a nitrocarburized component, comprising: