JP5477248B2 - Nitriding steel and nitriding parts with excellent machinability - Google Patents

Description

  The present invention provides a steel for nitriding that is excellent in strength and machinability and from which a hard nitrided layer can be obtained by nitriding treatment such as gas nitriding, plasma nitriding, gas soft nitriding, salt bath soft nitriding, etc., and a hard nitrided layer on the surface layer The present invention relates to a nitriding component having

  In automobiles and various industrial machines, many parts whose surface is hardened are used to improve fatigue strength. Typical surface layer hardening methods include carburizing, nitriding, induction hardening, and the like. Unlike other methods, the nitriding treatment is performed at a low temperature below the transformation point, so that heat treatment distortion can be reduced.

  In addition, a method for strengthening the base material by precipitating Mo and V carbides using heating during nitriding has been proposed (for example, Patent Document 1).

  However, the nitriding process at a low processing temperature has a problem that the effective hardened layer becomes shallow. For example, the nitriding treatment performed in an ammonia atmosphere requires a long treatment time of 20 hours or more in order to obtain a high surface hardness due to slow diffusion of nitrogen.

  In addition, the soft nitriding treatment performed in a bath or atmosphere containing carbon together with nitrogen has a relatively high nitrogen diffusion rate, and an effective hardened layer depth of 100 μm or more can be obtained in several hours. However, in order to apply to parts having high fatigue strength, it is necessary to further increase the effective hardened layer depth.

  Further, in the nitriding treatment, since the steel part is heated to a temperature lower than the transformation point, strengthening by quenching cannot be used. Therefore, it is necessary to ensure the strength before the nitriding treatment, and it is necessary to increase the strength of the material before the nitriding treatment.

  For such problems, by reducing the Mn content, increasing the Cr content, and optimizing the Al and V contents, the effective hardened layer depth after the nitriding treatment is secured, and the metal structure of the base material is bainite. A nitriding component has been proposed (for example, Patent Document 2).

  Furthermore, in order to make a part into a predetermined shape, the material before nitriding is subjected to cutting, so that the nitriding steel is required to have strength and machinability.

  In order to solve such a problem, steel suitable for improvement of fatigue strength by nitriding treatment with improved broachability as a metal structure mainly composed of bainite has been proposed (for example, Patent Document 3).

  In addition, steel having a metal structure mainly composed of bainite by adding Mo and V in combination and adding an appropriate amount of Al has been proposed (for example, Patent Document 4).

JP-A-5-25538 JP 2006-22350 A JP 2006-249504 A JP-A-8-176732

  Compared to carburizing, which is currently the mainstream technology for improving fatigue strength, the effective hardened layer depth is insufficient in nitriding, and in order to obtain high fatigue strength, the strength of the material before nitriding is further increased. And excellent machinability is also required.

  The present invention provides a nitriding steel that secures the surface hardness and effective hardened layer depth after nitriding treatment for improving fatigue strength, and is excellent in strength and machinability before nitriding treatment, and the nitriding steel. An object of the present invention is to provide a nitriding part manufactured as a raw material.

  The inventors have examined the strength and machinability of nitriding steel containing Al and Cr, and further, after nitriding steel is cut into a predetermined shape, nitriding treatment is performed, and surface hardness and The effective hardened layer depth was measured.

  As a result, the product of the contents of Al and N (the product of the Al content (mass%) in steel and the N content (mass%) in steel. Hereinafter, it may be referred to as Al × N. ) Of 0.008 or less, it became clear that machinability can be secured.

  Moreover, about content of Al and Cr, in order to obtain favorable surface layer hardness and effective hardened layer depth, the knowledge that it is preferable to make 1.9Al + Cr into an appropriate range was acquired. In addition, 1.9Al + Cr is the sum of the value of 1.9 times the Al content (mass%) in steel and the value of Cr content (mass%) in steel.

The present invention has been made based on these findings, and the gist thereof is as follows.
(1) In mass%,
C: 0.03-0.3%,
Si: 0.5% or less (including 0%),
Mn: 0.1 to 4.0%,
S: 0.005 to 0.2%,
Cr: 0.1~ 0.99%,
Al: 0.02~ 0.44%,
N: 0.002 to 0.018% ,
V: 0.05 to 0.48%,
Mo: 0.05-0.5%
The content of Al and N satisfies Al × N ≦ 0.008, the content of Al and Cr satisfies 0.5% ≦ 1.9 Al + Cr ≦ 1.41%, and the balance A nitriding steel comprising Fe and inevitable impurities.

( 2 ) The nitriding steel as described in (1 ) above, further containing, in mass%, B: 0.0005 to 0.005%.

( 3 ) Furthermore, in mass%,
Ca: 0.0003 to 0.005%,
Mg: 0.0003 to 0.005%
The steel for nitriding as described in (1) or ( 2) above, wherein one or both of the above are contained.

( 4 ) Furthermore, in mass%,
Ti: 0.01~0.3%,
Nb: 0.01 to 0.3%
The steel for nitriding according to any one of the above (1) to ( 3 ), wherein one or both of the above are contained.

( 5 ) A nitriding component having a nitride layer on the surface layer, wherein the base material is mass%,
C: 0.03-0.3%,
Si: 0.5% or less (including 0%),
Mn: 0.1 to 4.0%,
S: 0.005 to 0.2%,
Cr: 0.1~ 0.99%,
Al: 0.02~ 0.44%,
N: 0.002 to 0.018% ,
V: 0.05 to 0.48%,
Mo: 0.05-0.5%
The content of Al and N satisfies Al × N ≦ 0.008, the content of Al and Cr satisfies 0.5% ≦ 1.9 Al + Cr ≦ 1.41%, and the balance A nitriding component comprising Fe and inevitable impurities, wherein the surface layer has a hardness of 700 HV or more.

( 6 ) The base material is further in mass%,
B: 0.0005 to 0.005%
The nitriding part as described in ( 5) above, which contains

( 7 ) The base material is further in mass%,
Ca: 0.0003 to 0.005%,
Mg: 0.0003 to 0.005%
The nitriding component according to ( 5 ) or ( 6 ) above, wherein one or both of the above are contained.

( 8 ) The base material is further in mass%,
Ti: 0.01 to 0.3%,
Nb: 0.01 to 0.3%
The nitriding part according to any one of the above ( 5 ) to ( 7 ), wherein one or both of the above are contained.

( 9 ) The nitriding according to any one of ( 5 ) to ( 8 ), wherein the metal structure of the base material is 50% or more in terms of the total area ratio of one or both of bainite and martensite. Processing parts.

  According to the present invention, it is possible to obtain a nitriding steel that has good strength and machinability before nitriding treatment and high surface hardness after nitriding treatment.

  In addition, according to the nitriding steel of the present invention, since machinability before nitriding treatment is good, it is possible to reduce the man-hour of cutting performed before manufacturing a nitrided part, Since the treatment is performed at a temperature lower than the austenite transformation point, it is possible to obtain a nitrided component having a very small heat treatment strain and a sufficient surface layer hardness.

  Furthermore, according to the nitriding steel of the present invention, since the strength of the steel material before nitriding is high, not only the surface hardness of the nitriding component after nitriding is improved, but also the fatigue strength of the nitriding component is improved. be able to.

It is the figure which expanded and showed one tooth | gear of the gear component which is one Embodiment of this invention.

  In the present invention, nitriding steel is steel used as a material for nitriding parts. The nitriding steel is manufactured by hot working a steel piece.

  The nitriding component of the present invention is a component that has been subjected to nitriding treatment by performing necessary cutting processing after hot working or cold working of the nitriding steel of the present invention. Moreover, although the components obtained by nitriding the nitriding steel of the present invention have extremely small heat treatment distortion, finishing may be performed as necessary.

  In the present invention, “nitriding treatment” means a treatment of diffusing nitrogen into the surface layer of a steel part that has been machined into a predetermined shape and hardening, and is a treatment of diffusing nitrogen and carbon into the surface layer of a steel material. Including “soft nitriding”.

  Typical examples of these nitriding treatments include gas nitriding, plasma nitriding, gas soft nitriding, salt bath soft nitriding, etc. Among them, gas soft nitriding and salt bath soft nitriding are classified as soft nitriding treatments. It is.

  Further, it can be confirmed that the part is a nitriding part by the fact that the surface layer is cured and the nitrogen concentration of the surface layer is increased. In particular, the soft nitriding component has a hardened surface layer of 100 μm or more and has a deep effective hardened layer.

  The present inventors have examined the strength and machinability of nitriding steel containing Al and Cr in order to harden the surface layer portion by nitriding treatment.

  As a result, the present inventors have found that when a large amount of N is contained in the nitriding steel containing Al, coarse AlN is generated and the machinability deteriorates.

  The inventors have also found that machinability is improved by controlling the relationship between the Al content and the N content. Specifically, it was found that the machinability can be secured by setting the product Al × N of the Al content (mass%) and the N content (mass%) in steel to 0.008 or less.

  And the present inventors are based on the knowledge that Al and Cr are effective in hardening the surface layer part, but on the other hand, if these are excessively contained in the steel, the effective hardened layer depth is reduced. Further investigations were made.

  As a result, in order to obtain good surface hardness and effective hardened layer depth, the relationship between Al content and Cr content is controlled, and 1.9Al + Cr is within the range of 0.5 to 1.8%. The knowledge that it was preferable was obtained.

  The reason why the coefficient of Al is set to 1.9 is that the effective hardened layer depth of the nitride layer has a correlation with the total atomic concentration of Al and Cr. That is, since the atomic weight of Cr is 52 and the atomic weight of Al is 27, the relationship between the effective hardened layer depth and the surface hardness of the nitrided layer can be arranged by 1.9 Al + Cr in mass%.

  The reason why the component composition of the base material of the nitriding steel and the nitriding component obtained by nitriding the nitriding steel in the present invention will be described. The base material refers to a portion other than the nitrided layer in the nitrided component after nitriding.

  C is an element that enhances hardenability and is effective for improving strength, and further contributes to precipitation strengthening of the nitrided layer by precipitating alloy carbides during nitriding. If C is less than 0.03%, the required strength of the cured layer and the core cannot be obtained, and if it exceeds 0.3%, the strength becomes too high and the workability is impaired. Accordingly, the C content has a lower limit of 0.03% and an upper limit of 0.3%. However, from the viewpoint of facilitating securing of strength before and after nitriding and obtaining better machinability, the C content is preferably 0.05% at the lower limit and 0.25% at the upper limit. .

  Mn is an element useful for enhancing the hardenability and ensuring the strength before and after the nitriding treatment. If Mn is less than 0.1%, sufficient strength cannot be secured, and if it exceeds 4%, the strength increases excessively and the workability decreases. Therefore, the Mn content has a lower limit of 0.1% and an upper limit of 4.0%. In addition, since an effective hardened layer depth may reduce by containing excessive Mn, it is preferable that the upper limit of Mn content shall be 2.5%.

  S combines with Mn and exists as MnS inclusions. MnS has an effect of improving machinability, but in order to make the effect remarkable, it is necessary to contain S in an amount of 0.005% or more. On the other hand, if the S content exceeds 0.2%, the effect of improving the machinability is saturated and the forgeability is significantly reduced. Therefore, the S content has a lower limit of 0.005% and an upper limit of 0.2%. The upper limit of the S content is preferably 0.1%, more preferably 0.06%.

Cr is an element that is extremely effective for forming a carbonitride between N entering during nitriding and C in the steel, and significantly increasing the hardness of the nitrided surface layer by precipitation strengthening. However, when Cr is excessively contained, the effective hardened layer depth may become shallow. If the Cr content is less than 0.1%, a sufficient effective hardened layer cannot be obtained. On the other hand, if the Cr content exceeds 2.0%, the effect of obtaining a sufficient effective hardened layer is saturated, and the effective hardened layer depth decreases. Therefore, the lower limit of the Cr content is 0.1% and the upper limit is 2.0%. The upper limit of the preferable Cr content is 0.8%. The upper limit of the Cr content is 0.99% based on the examples.

Al is an element effective to form a nitride with N that penetrates during nitriding, increase the hardness of the nitrided layer, and obtain a deeper effective hardened layer. If Al content is less than 0.02%, it can not be obtained sufficient surface hardness, whereas when the content exceeds 1.0%, the effect of table layer hardness improved saturation, more effective curing The layer depth also decreases. Accordingly, the Al content has a lower limit of 0.02% and an upper limit of 1.0%. A preferable upper limit of the Al content is 0.3%. The upper limit of the Al content is 0.44% based on the examples.

  When N is excessively contained in steel, the hardness is increased, and N and Al are combined to form coarse nitrides, resulting in deterioration of machinability. Therefore, N is limited to 0.018% or less. There is a need. On the other hand, the limit at which N can be industrially reduced at low cost is 0.002%. Therefore, the lower limit of N content is 0.002% and the upper limit is 0.018%. The upper limit of the preferable N content is 0.010%, and the more preferable upper limit of the N content is 0.006%.

  When the product of the contents of Al and N [Al × N] exceeds 0.008, coarse AlN is generated and machinability deteriorates. Therefore, the upper limit of [Al × N] is set to 0.008. Moreover, the preferable upper limit of [Al × N] is 0.003, and the more preferable upper limit is 0.0015.

Moreover, although Al and Cr are effective for hardening the nitrided layer, on the other hand, if they are excessively contained in the steel, the effective hardened layer depth is reduced. The relationship between the effective hardened layer depth and the surface hardness of the nitrided layer can be controlled by the value of 1.9 Al + Cr in mass%. In order to make the effective hardened layer deeper, it is preferable to set the lower limit of 1.9Al + Cr to 0.5% and the upper limit to 1.8%. The upper limit of 1.9Al + Cr is 1.41% based on the examples.

  Si is an element useful as a deoxidizer, but does not contribute to the improvement of surface hardness in the nitriding treatment, and makes the effective hardened layer depth shallow. Therefore, it is necessary to limit the upper limit of Si content to 0.5%. In order to obtain a deeper effective hardened layer depth, the preferable upper limit of the Si content is 0.1%. The lower limit of the Si content is preferably as low as possible, and is most preferably 0%.

  P is an element that has the effect of segregating at grain boundaries and reducing toughness. Therefore, it is preferable to reduce as much as possible, and it is preferable to make the upper limit 0.03%. The lower limit is preferably 0.0001% of the industrial limit.

  V and Mo are elements effective for ensuring hardenability and obtaining a bainite structure, and form carbonitrides with N and C in the steel that enter during nitriding, or Cr and composite carbonitrides. By forming, it is an element effective for obtaining surface hardness and effective hardened layer depth. When the lower limit of the V and Mo contents is 0.05%, respectively, the above effect cannot be obtained sufficiently. On the other hand, when the upper limit of the V and Mo contents exceeds 1.0%, the cost is met. The effect is not obtained.

Therefore, when one or both of V and Mo are contained, it is preferable that the lower limit of the content of V and Mo is 0.05% and the upper limit is 1.0%. More preferable upper limits of the V and Mo contents are 0.5%. The upper limit of the V content is 0.48% based on the example.

  B is an element that improves the hardenability and is effective in improving the machinability when precipitated as BN. When the B content is less than 0.0005%, the effect of improving the machinability cannot be sufficiently obtained. On the other hand, when the B content exceeds 0.005%, BN is excessively precipitated, resulting in deterioration of casting characteristics and hot deformation characteristics. As a result, wrinkles are likely to occur during production. Therefore, it is preferable that the lower limit of the B content is 0.0005% and the upper limit is 0.0050%. A more preferable upper limit of the B content is 0.003%.

  Ca and Mg are deoxidizing elements and generate oxides in steel. These elements form a composite oxide with Al, and the machinability is improved by softening the Al oxide. If the Ca and Mg contents are each less than 0.0003%, the above effect cannot be obtained sufficiently, and if it exceeds 0.005%, CaS and MgS are generated, and the machinability is lowered.

  Therefore, when one or both of Ca and Mg are contained, it is preferable that the lower limit of the content of Ca and Mg is 0.0003% and the upper limit is 0.005%, respectively. More preferably, the lower limit of Ca and Mg is 0.0003%, and the upper limit is 0.003%.

  Ti and Nb are elements that form carbonitrides with N and C in steel that penetrate during nitriding, and are effective elements for obtaining surface hardness and effective hardened layer depth. In order to increase the hardness of the nitrided layer and increase the effective hardened layer depth, it is preferable to contain 0.01% or more of Ti and Nb, respectively. On the other hand, the above effect is saturated even if Ti and Nb are added in excess of 0.3%.

  Therefore, when one or both of Ti and Nb are contained, the upper limit of the content of Ti and Nb is preferably 0.3%.

  In the present invention, in order to increase the strength of the nitrided component after the nitriding treatment in the entire nitrided layer and the base material, it is preferable that the metal structure of the base material is one or both of bainite and martensite.

  And since bainite and martensite have a large amount of alloy elements that precipitate during soft nitriding, the bainite and martensite are made effective by precipitation strengthening of soft nitriding by making the metal structure of nitriding steel bainite and martensite. In addition, the hardness of the nitride layer can be increased.

  In particular, in order to sufficiently obtain the effect of precipitation strengthening, it is preferable to set the total area ratio of one or both of the base material bainite and martensite to 50% or more in the nitrided component. In order to strengthen precipitation more effectively, it is preferable to set the total area ratio of one or both of the base material bainite and martensite in the nitrided component to 70% or more.

  The area ratio of the metal structure of the base material in the nitriding component can be evaluated by mirror polishing, etching with a nital solution, and observing with an optical microscope. For example, with respect to the position where the hardness of the base material in the nitriding part is measured, the optical field is used to observe five fields of view at 500 times and a photograph is taken, and the bainite and martensite portions are determined visually, The area ratio of each of bainite and martensite may be obtained by image analysis.

  Next, the surface hardness of the nitriding component of the present invention will be described.

  The nitriding part of the present invention is subjected to nitriding such as gas nitriding, plasma nitriding, gas soft nitriding, salt bath soft nitriding, etc., so that the effective hardened layer depth is 300 μm or more, and the surface hardness is 700 HV or more. It has excellent characteristics.

  Further, according to the soft nitriding treatment, excellent properties such as an effective hardened layer depth of 300 μm or more and a surface hardness of 700 HV or more can be obtained in a treatment time of 10 hours or less.

  The surface hardness is evaluated by Vickers hardness and measured according to JIS Z 2244.

  Next, the manufacturing method of the nitriding steel and nitriding component of the present invention will be described.

  Since the main manufacturing process of nitriding steel is hot rolling, and the main manufacturing process of nitriding parts is hot forging, the conditions and methods in hot rolling and hot forging will be described below.

  When the heating temperature of the steel material before hot rolling or hot forging is less than 1000 ° C., the deformation resistance at the time of hot rolling or hot forging increases, and the manufacturing cost required for hot rolling or hot forging is high. There is a possibility. Moreover, if the alloying element contained in the steel material is not sufficiently solutionized, the hardenability is lowered and there is a concern that the bainite fraction is lowered. Therefore, it is preferable to set the heating temperature before hot rolling or hot forging to 1000 ° C. or higher.

  On the other hand, when the heating temperature before hot rolling or before hot forging exceeds 1300 ° C., the austenite grain boundary becomes coarse, so the heating temperature is preferably 1300 ° C. or less.

  Also, in order to prevent the reduction of the area ratio of bainite and martensite and to suppress the formation of ferrite and pearlite structures, the cooling rate until the steel becomes 500 ° C. or less after hot rolling or hot forging is controlled. It is preferable to do.

  If the cooling rate until the steel material reaches 500 ° C. or less is less than 0.1 ° C./s, the fraction of bainite and martensite may decrease, and there is a possibility that a ferrite / pearlite structure is formed.

  On the other hand, the upper limit of the cooling rate to 500 ° C. or lower is preferably faster in order to increase the martensite area ratio. However, from the viewpoint of workability, when suppressing the formation of martensite, the upper limit of the cooling rate is preferably 10 ° C./s.

  Therefore, after the hot rolling or hot forging, the cooling rate until the steel becomes 500 ° C. or less is preferably in the range of 0.1 to 10 ° C.

  Further, using the nitriding steel of the present invention manufactured by hot rolling, a nitriding treatment is applied to a part, for example, a gear, which is manufactured by cold working (for example, cold forging, cutting) on a part having a predetermined shape. By doing so, the fatigue strength of the nitrided component can be improved while suppressing heat treatment strain.

  Examples of the nitriding treatment include gas nitriding, plasma nitriding, gas soft nitriding, and salt bath soft nitriding.

  In order to obtain a nitrided layer having a surface hardness of 700 HV or more and an effective hardened layer depth of 300 μm or more, when performing gas nitriding, for example, it is held in an ammonia atmosphere at 540 ° C. for 20 hours or more.

In particular, as the nitriding treatment, for example, if a general gas soft nitriding treatment is performed with a mixed gas of N ₂ + NH ₃ + CO _{2 at} 570 ° C., the above-described nitride layer can be obtained in a processing time of about 10 hours.

  In other words, parts made of the nitriding steel of the present invention or parts obtained by hot working a steel slab having components in the same range as the nitriding steel of the present invention are softened in a practical and practical time. By performing the nitriding treatment, a deeper effective hardened layer can be obtained as compared with a sufficient surface hardness and a conventional soft nitriding treatment.

  The present invention will be further described in the examples. The conditions in the examples are one example of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. It is not something. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

  Steels having chemical components shown in Tables 1 and 2 were melted. The numerical values underlined in Tables 1 and 2 indicate that they are outside the scope of the present invention.

  Some of these steels were hot-rolled to obtain round bars with a diameter of 30 mm. Then, after heating to 1200-1250 degreeC and hot forging, it cooled at the cooling rate of 1-10 degreeC / s, and manufactured the hot forging goods which have a gear shape of thickness 10mm and diameter 35mm.

  FIG. 1 is an enlarged view showing one tooth of a gear part according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes one tooth in the gear part.

  The total area ratio of bainite and martensite of hot forged parts (in Tables 1 and 2, the area ratio of bainite + martensite) is mirror-polished and then etched with a nital solution, and the optical microscope shown in FIG. At the position indicated by reference numeral 2, five fields of view were observed at a magnification of 500, and a photograph was taken. A part consisting of bainite and martensite was visually determined, and the part was subjected to image analysis to determine the area ratio.

Further, the hot forged product was subjected to gas nitriding treatment by cutting to clean the gear-shaped surface. The conditions of the gas soft nitriding treatment were a mixed gas of NH ₃ : N ₂ : CO ₂ = 50: 45: 5 in terms of volume fraction, a temperature of 560 ° C., and a holding time of 10 hours.

  After the soft nitriding treatment, the surface hardness was measured. The surface layer hardness was measured in accordance with JIS Z 2244 by HV0.3 (2.9N) at a position inside 50 μm from the surface of the gear component after the soft nitriding treatment. The surface hardness before soft nitriding was measured in the same manner as a representative value of the strength of the base material of the nitriding component.

  Moreover, the effective hardened layer depth was made into the distance from the surface of the gear components after soft nitriding processing to the position where HV becomes 550 based on JISG0557.

  For machinability, steel pieces having the chemical components shown in Table 1 and Table 2 were hot forged to produce a test piece having a diameter of 45 mm and a length of 190 mm, and the test piece (before nitriding treatment) was tested. A lathe test was performed on a carbide-coated carbide tool on one side with a depth of cut of 2 mm, a feed rate of 0.3 mm / rev, and a circumferential cutting speed of 150 m / min. It evaluated by measuring the cutting time until it became 0.05 mm.

  The results are shown in Tables 3 and 4. The numbers underlined in Tables 3 and 4 indicate that they are outside the scope of the present invention. In Table 3, the effective hardened layer depth is a result measured after nitriding treatment.

In Table 3 and Table 4, No. which is an example of the present invention. 1 to 8 , 12 , 13 , 18 to 30 have a tool life of 7 minutes or more and good machinability, and the surface hardness after nitriding is sufficiently hard at HV700 or more, and a sufficient effective hardened layer of 300 μm or more The depth is obtained.

  Moreover, since the hardness of the example of the present invention was high before the nitriding treatment, it was confirmed that the fatigue strength after the nitriding treatment was sufficient.

  In contrast, no. Since 101 and 103 each have a C content and a Mn content lower than the lower limit of the present invention, sufficient strength cannot be obtained, and the surface layer hardness and the effective hardened layer depth are also inferior.

  No. Since 102 and 104 have C content and Mn content exceeding the upper limit of the present invention, respectively, the machinability is lowered and the tool life is shorter than 6 minutes.

  No. Nos. 105 and 106 have a Cr content of No. 105. Since 107 and 108 have an Al content outside the range of the present invention, the effective hardened layer is shallow and less than 300 μm.

  No. Nos. 109 and 111 have S and N contents below the lower limit of the present invention. No. 109 did not produce sufficient MnS. Since 111 is a coarse nitride, machinability is reduced and the tool life is short.

  No. 110 was not evaluated because the S content exceeded the upper limit of the present invention and cracking occurred during forging.

  No. Since 112 [Al × N] exceeds the upper limit of the present invention, coarse AlN is generated, machinability is reduced, and the tool life is short.

  No. No. 113 has a Si content exceeding the upper limit of the present invention, so that the cured layer characteristics are lowered, and the surface layer hardness and the effective cured layer depth are small.

  As described above, No. which is a comparative example. In 101 to 113, it was confirmed that at least one of tool life, surface hardness before nitriding treatment, surface layer hardness after nitriding treatment, and effective hardened layer hardness was inferior.

  In addition, the place mentioned above is only what illustrated embodiment of this invention, and this invention can add a various change within the description range of a claim.

  As described above, according to the present invention, it is possible to obtain a nitriding steel having good strength and machinability before nitriding treatment and high surface hardness after nitriding treatment, which is industrially remarkable. Play.

  In addition, according to the nitriding steel of the present invention, since machinability before nitriding treatment is good, it is possible to reduce the man-hour of cutting performed before manufacturing a nitrided part, Since the treatment is performed at a temperature lower than the austenite transformation point, since the heat treatment strain is extremely small, a nitriding part can be obtained at a low cost. The present invention has high utility value industrially.

1 One tooth in gear part 2 Metal structure observation position after hot forging

Claims (9)

% By mass
C: 0.03-0.3%,
Si: 0.5% or less (including 0%),
Mn: 0.1 to 4.0%,
S: 0.005 to 0.2%,
Cr: 0.1~ 0.99%,
Al: 0.02~ 0.44%,
N: 0.002 to 0.018% ,
V: 0.05 to 0.48%,
Mo: 0.05-0.5%
The content of Al and N satisfies Al × N ≦ 0.008, the content of Al and Cr satisfies 0.5% ≦ 1.9 Al + Cr ≦ 1.41%, and the balance A nitriding steel comprising Fe and inevitable impurities. The steel for nitriding according to claim 1, further comprising, in mass%, B: 0.0005 to 0.005%. Furthermore, in mass%,
Ca: 0.0003 to 0.005%,
Mg: 0.0003 to 0.005%
One or both of these are contained, Steel for nitriding of Claim 1 or 2 characterized by the above-mentioned. Furthermore, in mass%,
Ti: 0.01~0.3%,
Nb: 0.01 to 0.3%
One or both of these are contained, The steel for nitriding of any one of Claims 1-3 characterized by the above-mentioned. A nitriding component having a nitride layer on the surface layer, wherein the base material is mass%,
C: 0.03-0.3%,
Si: 0.5% or less (including 0%),
Mn: 0.1 to 4.0%,
S: 0.005 to 0.2%,
Cr: 0.1~ 0.99%,
Al: 0.02~ 0.44%,
N: 0.002 to 0.018% ,
V: 0.05 to 0.48%,
Mo: 0.05-0.5%
The content of Al and N satisfies Al × N ≦ 0.008, the content of Al and Cr satisfies 0.5% ≦ 1.9 Al + Cr ≦ 1.41%, and the balance A nitriding component comprising Fe and inevitable impurities, wherein the surface layer has a hardness of 700 HV or more. The base material is further in mass%,
B: 0.0005 to 0.005%
The nitriding component according to claim 5 , further comprising: The base material is further in mass%,
Ca: 0.0003 to 0.005%,
Mg: 0.0003 to 0.005%
One or both of these are contained, The nitriding process part of Claim 5 or 6 characterized by the above-mentioned. The base material is further in mass%,
Ti: 0.01 to 0.3%,
Nb: 0.01 to 0.3%
One or nitrided component according to any one of claims 5-7, characterized in that it contains both. The metal structure of the base material, bainite and one or both total nitrided component according to any one of claims 5-8, characterized in that an area ratio of 50% or more of martensite.

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