JPH08291371A - Forged parts having high strength layer on surface and its production - Google Patents

Abstract

PURPOSE: To produce parts imparted with high precision after working by using a stock having low deformation resistance and high machinability while being incorporated with high carbon instead of many stages required for a carburizing stage and in which strains caused by heat treatment are suppressed as well and to provide a method for producing the same. CONSTITUTION: This forged parts having a high strength layer on the surface are the ones having a compsn. contg., by weight, 0.3 to 1.0% C, 0.6 to 1.3% Si, 0.3 to 1.5% Mn, <=0.02% P, <=0.1% S and 0.01 to 0.035% Al and contg., at need, one or more components among 0.05 to 5.0% Ni, 0.001 to 0.004% B, 0.002 to 0.008% N and 0.05 to 0.20% Mo, and in which the inside contains 0.2 to l.0% graphite and at least the surface layer part has a hardened structure, and furthermore, the method for producing the same is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing high-strength forged parts that transmit power by sliding, such as gears and joint parts. Machine parts are provided.

[0002]

2. Description of the Related Art High-strength mechanical parts such as gears and joint parts that transmit power by sliding may be subjected to surface carburization in order to reduce friction and wear. This process is widely used in automobiles, construction machinery, aircraft, etc. as a manufacturing technology for parts used in large quantities.

In the carburizing step, after forging or cutting using a low carbon steel material of 0.2 to 0.3% by weight at most, high carbon is contained only in the surface by carburizing to realize high strength by heat treatment. There is an aim in that. However, in the carburizing process, the components must be kept in the furnace at a high temperature of about 900 ° C. for a long time, which requires a great deal of processing cost, and thus the cost reduction of this process has been demanded. Especially when large parts or small parts are used in severe conditions, it is necessary to increase the carburizing depth, so the processing time increases dramatically.
It is a major obstacle to the process. Further, when carburizing for a long time in this way, oxygen penetrates into the crystal grain boundaries of the material to form an abnormal layer of material, which becomes a problem.

Since carburizing causes the amount of surface carbon to be about 0.8% by weight, carburizing should be unnecessary if a steel material having a carbon content equivalent to this is used for forming and quenching. However, when high carbon steel is subjected to forging and cutting, the high deformation resistance of the material causes early damage of the forging die and significantly shortens the life of the cutting tool, so that it cannot be established as a production process.

In order to solve this problem, it is most effective to reduce the deformation resistance of the material, but the material used for cold forging cannot be omitted even if the C content is about 0.22%. It is very difficult to cold forge a complicated shape with a steel material having a C content of 0.8% even if it is annealed.
Also, parts can be made by rough forming by hot forging, finish forming by cutting and heat treatment, but due to high deformation resistance and low machinability, dimensional accuracy at the time of processing decreases and heat treatment distortion increases. In addition, due to frequent occurrence of quench cracks, the application is limited to parts with extremely simple shapes.

[0006]

The present invention has been devised to solve many problems associated with the carburizing process.
A material with low deformation resistance and high machinability is used for high precision after processing, and distortion due to heat treatment is suppressed, and a deep high-strength quenching structure that is especially required for large parts etc. can be arbitrarily set. The object is to provide a forged component which can be provided and which realizes a significant cost reduction, and a manufacturing method thereof.

[0007]

The present invention has been made on the basis of the above findings, and the gist of the present invention is C: 0.3 to 1.0% by weight%, Si: 0.6 to
1.3%, Mn: 0.3 to 1.5%, P
: ≤ 0.02%, S: ≤ 0.1%,
Al: 0.01 to 0.035%, or further Ni: 0.05 to 5.0%, B: 0.00
1 to 0.004%, N: 0.002 to 0.008%,
Mo: 0.05 to 0.20%, one or more, and the balance Fe and inevitable impurities, and the graphite content is 0.2 to 1.0%, and the average grain size of the graphite. Contains graphite having a diameter of 4 μm or less and a particle number of 3,000 / mm ² or more, and further having a graphitization ratio of the carbon of 10% or more,
Furthermore, at least the surface layer part has a high strength layer on the surface characterized by having a quenched structure, and cold forging of rod-shaped steel material having the above chemical components, and after forming by appropriately combining the cutting steps, the surface In the method for manufacturing a forged component, the surface layer portion is subjected to a quenching treatment in order to impart high strength to the.

[0008]

FIG. 1 (a) shows an example of a conventional gear section, where 1 is a carburized portion and 2 is a non-carburized portion, which usually has a low carbon quenching structure or non-quenching structure. FIG. 1 (b) is an example of one embodiment of the gear of the present invention, 3 is a high carbon quenched structure, 4 is a high carbon non-quenched structure containing 0.2 to 1.0% of graphite.

In order to manufacture a component having such a texture distribution, a material in which a part or all of carbon in the inside is graphite in advance is used, and it is formed by cold forging or cutting, and if it is subjected to high frequency heating, for example, the surface layer The graphite of No. 3 forms a solid solution, and a quenched structure such as 3 can be obtained by quenching. FIG. 2 shows an example of a process for manufacturing a part by conventional carburizing and quenching. Steel 5 is roughly forged by cold forging 6, and after finishing by cutting 7, carburizing and quenching 8 is applied to make part 9. . At this time, the carburizing and quenching 8 is usually heat-treated at 900 ° C. for about 10 hours.

On the other hand, FIG. 3 shows an example of one embodiment of a process for manufacturing a component according to the present invention, in which induction hardening 10 is used instead of carburizing and hardening. Induction hardening is 900 ° C
It is sufficient to heat for 2 to 3 minutes, which is a great energy saving compared to the case where a large amount of energy is input to the conventional carburizing and quenching of FIG. Since the material is a very soft material containing graphite, it is possible to omit 7 cutting and form parts by cold forging.

Further, in the step of the method of the present invention shown in FIG. 3, since a part or all of the carbon contained in the material at the time of cutting is graphite, the cutting property is extremely high, and high-speed cutting is possible and the cutting tool is also used. Life is improved and cutting cost is greatly reduced. Further, since the residual cutting stress is low and the inside of the gear has a soft structure containing graphite, distortion of the part shape due to quenching is relaxed.

Further, the hardening depth of the surface can be easily changed by the induction hardening conditions. This is
Carburizing and quenching is a great advantage compared to requiring a very long time to secure the depth. Therefore, this effect is increased especially in large parts. FIG. 4 shows another embodiment of the method of the present invention, which is a case of normal quenching instead of induction quenching, and when internal hardness is a problem, internal cutting is performed by cutting 11 and normalizing 11. The graphite is almost gone and hard.

FIG. 5 (a) is an example of a conventional shaft cross section, where 1 is a carburized portion and 2 is a non-carburized portion, which usually has a low carbon quenching structure or non-quenching structure. ) Is an example of one embodiment of the shaft of the present invention, 3 is a high carbon quenched structure, 4 is a high carbon non-quenched structure, and contains 0.2 to 1.0% of graphite.
Since the quenching structure of No. 3 is given by, for example, induction hardening, the quenching structure depth of No. 3 can be arbitrarily controlled depending on the hardening conditions, for example, the frequency of the high frequency and the heating time. This is a great advantage compared to the conventional case where it was extremely difficult to increase the carburizing depth.

By heating not only the surface but also the inside and then quenching, it is possible to make the inside considerably hard, and it is also possible to obtain the required characteristics according to the application. In addition, carbon content is 0.6% by utilizing the low deformation resistance of the material.
Since the above materials can be easily cold forged, it can be very effectively applied to tapping screws and constant velocity joint parts that have been conventionally carburized and quenched after cold forging using low carbon steel. Next, the reasons for limiting the chemical components of the rod-shaped steel material and the forged parts which are the objects of the present invention will be described.

The lower limit of C is 0.3% in order to secure the strength after quenching and to secure the amount of graphite necessary for obtaining sufficient machinability. The upper limit was 1.0% in order to prevent quench cracking due to heat treatment. Si has a small bonding force with carbon atoms in steel and is effective for graphitization, so at least 0.6% is necessary. If it exceeds 1.3%, the ferrite phase becomes hard and cold forgeability deteriorates, so the upper limit is set. The value was 1.3%.

The amount of Mn is required to be the sum of the amounts necessary for fixing and dispersing sulfur in steel as MnS, and the lower limit value is 0.3%. On the other hand, if the amount of Mn becomes large, it is difficult to graphitize, so the upper limit was made 1.5%. P impairs hot workability, so the upper limit was made 0.02%. S improves the machinability but impairs the cold forgeability, so S was made 0.1% or less.

Since Al serves as a deoxidizing material for molten steel and adjusts the grain size, it is necessary to add Al in an amount of 0.01% or more. If the addition is too large, the cold forgeability is impaired, so 0.035% was made the upper limit. B forms BN in steel and accelerates graphitization, so it is desirable to add B. The lower limit for obtaining the effect is 0.001%, and the effect is saturated at 0.004.
%.

N is at least 0.002% for converting to BN
Is necessary, but 0.008% was made the upper limit because problems such as aging occur when it is large. Ni is effective to secure the strength, and is preferably added in an amount of 0.05% or more. However, if the strength during cold forging is too high, it becomes difficult to process, so 5.0% was made the upper limit.

Mo is effective in precipitating graphite in ferrite grains, and is preferably added in an amount of 0.05% or more.
If the addition amount is large, the hardness of the ferrite base increases, so the upper limit was made 0.20%. The weight content of graphite in the steel material and the forged parts is set to 0.2% or more. If it is less than this, the forging die and cutting tool life cannot be increased in the processing before heat treatment, and the processing accuracy decreases. This is because the strain after heat treatment becomes high. on the other hand,
If the internal graphite content exceeds 1.0%, the machinability improving effect is saturated, so it is desirable to keep the content within these ranges.

The average particle size is 4 μm or less and the number of particles is 30.
When the graphite contains 00 pieces / mm ² or more, the toughness of the inside is high, and not only is it effective in preventing breakage, but such a material has high quenchability due to rapid diffusion of carbon during heat treatment. Does not cause problems such as incomplete quenching. On the other hand, in the production of the above-mentioned parts, it is effective to use a rod-shaped material having a graphitization rate of carbon content of 10% or more and perform cold forging and cutting in an appropriate combination to form the rod. Graphitization rate is 10%
The above is because the material is not sufficiently softened and the machinability is not high below this range.

Next, in the present invention, a rod-shaped steel material containing the above chemical components is formed by appropriately combining cold forging and cutting steps, and then, at least the surface layer portion is subjected to a quenching treatment to impart surface strength, preferably. The induction hardening process imparts an induction hardening structure. The induction hardening conditions must not only ensure the surface hardness required for forged parts, but also take into consideration the economical cost.

As for the induction hardening treatment conditions satisfying the above various conditions, the frequency used is usually adopted in the heat treatment.
kHz is optimum, and quenching temperature range is 800-90
It shall be in the range of 0 ° C. If the temperature is 800 ° C. or lower, an incompletely quenched state cannot be obtained and a sufficiently hardened structure cannot be obtained. On the other hand, if it exceeds 900 ° C, quenching becomes excessive, the hardness becomes too high, and it becomes brittle, cutting time and cost increase, and it is not economical. Although the range of application of the induction-hardened structure varies depending on the intended shape of the part, it is at least a part or the whole of the surface layer part of the part, but normally it is desirable to apply it to a sliding part that is heavily worn.

If necessary, tempering can be performed after quenching.

[0024]

EXAMPLES Table 1 shows examples of chemical components used in the method of the present invention, examples of chemical components of conventionally used steel materials, and respective graphitization ratios. Here, Steel types 1 to 3 are examples of chemical components used in the method of the present invention, and Steel type 4 is an example of SCM420 for JIS structure as a conventionally used steel material.

[0025]

[Table 1]

Next, a gear was prototyped by the method of the present invention and the conventional method. In the conventional method, steel type 4 shown in Table 1 was used, a gear blank was manufactured by cold forging through the steps shown in FIG. 2, and the bevel gear of module 9 was cut with a hobbing machine, followed by gas carburizing at 935 ° C. for 9 hours and diffusion for 4 hours. Hardened. On the other hand, in the method of the present invention, Table 1
After rolling each of the steel types 1 to 3 after quenching and annealing, carbon 6
In the process of FIG. 3, the present invention 1 and 2 use cold forged gear blanks to produce a gear blank, using 0 to 95% of graphitized material.
After cutting a similar gear with a hobbing machine, a gear is manufactured by induction hardening at 3kHz and 870 ° C, and the present invention 3 is carried out by cold forging all at once to a tooth forming shape, and then induction hardening at 3kHz and 830 ° C. Gears were manufactured by entering.

Table 2 shows the cutting cost ratio and the heat treatment use ratio in the case of the method of the present invention and the conventional method, respectively.

[0028]

[Table 2]

The cutting cost ratio of the present invention 1 and 2 is 1 in the conventional method.
0.7, 0.2 in the present invention 3, and the heat treatment cost ratio was 0.2 in all cases. Moreover, these gears are equal to or better than the conventional products in dimensional accuracy and durability.

[0030]

As described above, the parts which have been processed by a great number of man-hours can be manufactured much easier and with high accuracy, which makes a great contribution to the industry.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a gear, FIG. 1A is a view showing a cross-section of a conventional gear, and FIG. 1B is a view showing a cross-section of a gear manufactured according to an embodiment of the present invention. Is.

FIG. 2 is a diagram showing a conventional manufacturing process.

FIG. 3 is a diagram showing a manufacturing process of the present invention.

FIG. 4 is a diagram showing a manufacturing process of another embodiment of the present invention.

5A and 5B are sectional views of a shaft, FIG. 5A is a sectional view of a conventional shaft, and FIG. 5B is a sectional view of a shaft manufactured according to an embodiment of the present invention. .

[Explanation of Codes] 1 ... Carburized part 2 ... Non-carburized part 3 ... High carbon quenching structure 4 ... High carbon non-quenching structure 5 ... Steel material 6 ... Cold forging 7 ... Cutting 8 ... Carburizing quenching 9 ... Parts 10 ... Induction hardening 11 ... Normalizing 12 ... Hardening

Claims (7)

[Claims] 1. C: 0.3-1.0% by weight%, Si:
0.6 to 1.3%, Mn: 0.3 to 1.5%, P ≦ 0.
02%, S ≦ 0.1%, Al: 0.01 to 0.035%
Containing 0.2 to 1.0% as graphite inside, with the balance consisting of iron and unavoidable impurities, and at least the surface layer portion having a hardened structure to form a high strength layer on the surface. Forged parts that have. 2. In weight%, further Ni: 0.05-5.
0%, B: 0.001 to 0.004%, N: 0.002
~ 0.008%, Mo: 0.05 ~ 0.20%, 1
2. A forged part having a high-strength layer on the surface according to claim 1, characterized in that the forged part contains two or more kinds. 3. The graphite content of the inside is 0.2 to 1.
0%, the average particle size of the graphite is 4 μm or less, and the number of particles is 300.
3. The forged part having a high-strength layer on the surface according to claim 1, wherein the number is 0 pieces / mm ² or more. 4. C: 0.3-1.0% by weight%, Si:
0.6 to 1.3%, Mn: 0.3 to 1.5%, P ≦ 0.
02%, S ≦ 0.1%, Al: 0.01 to 0.035
%, The balance contains iron and unavoidable impurities, and a rod-shaped steel material having a graphitization ratio of the carbon of 10% or more is formed by appropriately combining cold forging and cutting, and then at least the surface layer is quenched. A method for producing a forged component having a high-strength layer on the surface, which is characterized by imparting surface strength. 5. Further, Ni: 0.05 to 5.0 in weight%.
%, B: 0.001 to 0.004%, N: 0.002
The method for producing a forged component having a high-strength layer on the surface according to claim 4, wherein one or more of 0.008% and Mo: 0.05 to 0.20% are included. 6. The average particle size is 4 μm or less, and the number of particles is 3000.
The method for producing a forged component having a high-strength layer on the surface according to claim 4 or 5, characterized in that a rod-shaped steel material containing graphite / mm ² or more is used. 7. The method according to claim 5, wherein after the forming such as cold forging and cutting, normalizing is performed and then quenching is performed.
6. A method for manufacturing a forged component having a high-strength layer on the surface according to any one of 6 and 7.