JP3405468B2 - Manufacturing method of mechanical structural parts - Google Patents

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 a mechanical structural part used for obtaining a mechanical structural part having excellent mechanical strength such as surface pressure strength, bending fatigue strength, and torsional fatigue strength. .

[0002]

2. Description of the Related Art Conventionally, in order to improve mechanical strength such as surface pressure strength, bending fatigue strength and torsional fatigue strength of machine structural parts, it is often practiced to subject steel to surface hardening treatment. Surface hardening treatments such as carburizing, nitriding, and induction hardening are often adopted. (For surface hardening treatments for this type of steel, see, for example, "3rd Edition Iron and Steel Handbook, Volume VI Secondary Processing, Surface Treatment, and Heat Treatment."・ Welding ”Showa 5
May 31, 1995 Published by The Iron and Steel Institute of Japan, 56th edition
Pages 2 to 600, “14. Surface hardening ”for a detailed explanation. ).

In such a surface hardening treatment, for example, by using carburizing or carbonitriding treatment using a case-hardening steel having a C content as low as 0.13 to 0.23%, wear resistance and fatigue are improved. It is common to obtain mechanical structural parts with improved strength, but in addition to this, nitriding treatment (for example,
(Tufftride treatment, gas soft nitriding treatment, ion nitriding treatment)
Also induction hardening is often done.

[0004]

However, in the case of only the conventional nitriding treatment, the depth of the hardened layer is shallow, so that there is a limit to the improvement of rolling life and the improvement of bending fatigue strength and torsional fatigue strength still remains. There is a problem that it is not sufficient, there is a problem that the surface hardness is low and the rolling life is extremely short only by induction hardening, and the resistance to temper softening is also low, and it can be obtained by rapidly cooling austenite containing nitrogen and carbon. It was a subject to make it possible to further utilize the excellent tempering softening resistance and cracking resistance of martensite.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has excellent resistance to temper softening and cracking of martensite obtained by rapidly cooling austenite containing nitrogen and carbon. The purpose of the present invention is to obtain a mechanical structural component that can make better use of the generated resistance and is further excellent in mechanical strength such as surface pressure strength (pitting fatigue resistance), bending fatigue strength, and torsional fatigue strength.

[0006]

The method of manufacturing a mechanical structural component according to the present invention is, by weight%, C: 0.35 to 0.65.
%, Si: 0.03 to 1.50%, Mn: 0.3 to 1.
0:%, Cr: 0.1-3.0%, and in some cases, Al: 0.02-1.5%, V: 0.05-
One or more of 0.5% and Mo: 0.05 to 0.5%, Ni: 0.5 to 2.0%, and Ti: 0.005 to 0.05% , Nb: 0.01 to
0.10% of 1 type or 2 types, similarly, S: 0.02
0.40%, Pb: 0.01 to 0.50%, Ca: 0.
0003-0.010%, Te: 0.005-0.10
%, Bi: 0.01 to 0.50%, 1 or 2
After soft nitriding treatment is performed on the steel containing at least seeds and the balance Fe and impurities under the condition that the nitrided layer depth is 150 μm or more, the surface heating temperature is 900 to 1200 ° C., and the heating time is 1 to 10 sec. It is characterized in that induction hardening is performed under the condition that the nitrided layer becomes austenite.

Next, the reasons for limiting the chemical composition (% by weight) of steel applied in the method of manufacturing a mechanical structural part according to the present invention will be explained.

C is an element useful for securing the strength of mechanical structural parts, but if the content is too small, the strength cannot be secured sufficiently, so the content is made 0.35% or more.
However, if the C content is too large, the toughness may be deteriorated, so the content is made 0.65% or less.

Si is an element which is useful as a deoxidizing agent during the melting of steel, and is also useful for improving the resistance to temper softening and improving the rolling life. And 0.03% or more. But Si
If the content is too large, workability and toughness are deteriorated, so the content is made 1.50% or less.

Mn acts as a deoxidizing agent and a desulfurizing agent during the melting of steel, and is an element useful for improving the induction hardenability. To obtain such an action, Mn is set to 0.3% or more. However, if the Mn content is too high, the toughness is deteriorated, so the content is made 1.0% or less.

Cr is an element that is useful for improving the nitriding property, particularly for increasing the nitriding depth, and also for improving the induction hardenability.
% And above. However, even if the Cr content is increased, the effect of improving the nitriding characteristics is saturated, so the content is made 3.0% or less.

All of Al, V, and Mo are elements useful for improving nitriding characteristics, Al is an element particularly useful for improving surface hardness, and V is particularly useful for improving nitriding depth. Since it is an element that is also useful for improving the core hardness, and Mo is an element that is particularly useful for improving the nitriding depth and the induction hardenability, Al is 0.02% or more,
0.05% or more for V, 0.05 for Mo
One or two or more of% or more may be optionally contained. However, if the Al content is too large, the effect of improving the nitriding characteristics is saturated, so it is set to 1.5% or less, and if the V content is too large, the effect of improving the nitriding characteristics is saturated, so it is set to 0.5 or less. If the Mo content is too high, the effect of improving the hardenability is saturated and the machinability is deteriorated, so 0.5% or less is preferable.

Ni is an element that contributes to the improvement of the induction hardenability and the toughness, so 0.5% or more may be contained in some cases. However, Ni
If the content is too large, the effect of improving the hardenability is saturated and the machinability is deteriorated. Therefore, the content is preferably 2.0% or less.

Since Ti and Nb are elements useful for refining the crystal grains and improving the nitriding characteristics, the Ti content is 0.
Depending on the case, 005% or more and 0.01% or more of Nb may be contained. However, Ti, Nb
If the content is too large, the toughness will decrease, so
0.05% or less for Ti, 0.1 for Nb
It is better to be 0% or less.

Since S, Pb, Ca, Te, and Bi are all elements that contribute to the improvement of machinability, in the case of mechanical structural parts that are required to have excellent machinability, these 1 It is also possible to add seeds or two or more kinds. In this case,
0.02% or more for S, 0.01 for Pb
%, Ca may be 0.0003% or more, Te may be 0.005% or more, and Bi may be 0.01% or more. However, if these contents are too high, strength (especially roller pitting strength)
As well as decreasing the toughness in the longitudinal (rolling) direction, S is 0.40% or less, Pb is 0.50% or less, and Ca is 0.010%.
Hereinafter, Te is preferably 0.10% or less and Bi is preferably 0.50% or less.

In the present invention, the steel having the above composition is subjected to the soft nitriding treatment under the nitriding condition such that the nitriding layer depth becomes 150 μm or more. It is necessary to improve the surface pressure strength (pitting fatigue resistance) by carbon martensite. As shown in FIG. 3, when the depth of the nitrided layer is less than 150 μm, surface depression is likely to occur. For this reason, it may be damaged, resulting in a significantly short life, which is not preferable. In this case, the depth of the nitrided layer means the distance from the surface layer to the portion where the hardness is the same toward the core.

And, as such soft nitriding treatment,
Gas soft nitriding treatment can be used, and in addition, soft nitriding treatment such as tufting treatment or ion nitriding treatment can be used.

In the present invention, as described above, since the soft nitriding treatment is performed under the condition that the nitride layer depth is 150 μm or more, the induction hardening is performed under the condition that the nitride layer becomes austenite. Such induction hardening is carried out in order to improve the surface pressure strength due to nitrogen + carbon martensite, and to improve the bending fatigue strength or torsional fatigue strength due to the core martensite.

In this case, the heating conditions for induction hardening are that the surface heating temperature (T) is 900 ° C. or more and 1200 ° C. or less and the heating time (t) is 1 sec or more and 10 sec or less. Furthermore, it is desirable that the relationship between the average surface heating temperature and the heating time defined by Z in the following equation be in the range of 200 ≦ Z ≦ 1000.

Z = (T + 273) × log (t)

If the surface heating temperature is lower than 900 ° C., it is not preferable because the nitride hardly forms a solid solution during induction hardening, and even if the surface heating temperature is 900 ° C. or higher, nitride is formed on the surface layer. Therefore, the crystal grains are difficult to coarsen due to the pinning effect, but if the surface heating temperature is higher than 1200 ° C., the crystal grains become coarse, which is not preferable. Therefore, it is desirable that the surface heating temperature during induction hardening be 900 to 1200 ° C.

If the value of Z is less than 200, it is not preferable because the nitride is less likely to form a solid solution during induction hardening, and if the value of Z is more than 1000, the surface skin tends to be rough, which is not preferable. .

[0023]

In the method of manufacturing a mechanical structural part according to the present invention, C: 0.35 to 0.65% by weight and Si:
0.03 to 1.50%, Mn: 0.3 to 1.0%, C
r: 0.1 to 3.0%, depending on the case,
Al: 0.02-1.5%, V: 0.05-0.5%,
One or more of Mo: 0.05 to 0.5%, similarly Ni: 0.5 to 2.0%, and similarly Ti:
0.005-0.05%, Nb: 0.01-0.10%
1 or 2 of the same, similarly, S: 0.02 to 0.
40%, Pb: 0.01 to 0.50%, Ca: 0.00
03-0.010%, Te: 0.005-0.10%,
Bi: after soft nitriding is performed on steel containing one or two or more of 0.01 to 0.50% and the balance Fe and impurities under the condition that the nitriding layer depth is 150 μm or more. Since induction heating is performed under the conditions that the surface heating temperature is 900 to 1200 ° C. and the heating time is 1 to 10 seconds and the nitride layer is austenitized, nitrogen + carbon obtained by quenching austenite containing nitrogen and carbon is obtained in the surface layer portion.
It becomes a machine structural part in which carbon martensite is formed, and its tempering softening resistance and crack initiation resistance are even better. It becomes a mechanical structural component that is more excellent due to mechanical properties such as.

[0024]

EXAMPLES Steels having the chemical compositions shown in Tables 1 and 2 were melted, forged to a diameter of 32 mm, and after normalizing,
As shown in FIG. 1, D ₁ = 26 mm, D ₂ = 22 mm,
A roller pitching test piece 1 having L ₁ = 28 mm, L ₂ = 51 mm, L ₃ = 130 mm was prepared, and as shown in FIG. 2, D ₅ = 8 mm, D ₆ = 15 mm, L ₅ = 5.
0 mm, L ₆ = 80 mm, L ₇ = 210 mm, R = 30
An Ono-type rotary bending test piece 2 having a size of mm was produced and used as a test material.

Then, each of the test materials except Comparative Example d-2 was subjected to a gas nitrocarburizing treatment under the conditions shown in Table 7, whereby the roller pitching test piece 1 was subjected to Tables 3 and 4 and Ono-type rotation. With respect to the bending test piece 2, a nitride layer having the values shown in the columns of "surface hardness after nitriding" and "nitride layer depth" in Tables 5 and 6 was obtained.

Subsequently, among the test materials after the nitriding treatment, for each test material except Comparative Example d-1, Table 8 (high frequency was used for the roller pitting test piece 1 and the Ono-type rotary bending test piece 2). The quenching conditions are different), and further, Table 3 and Table 4 for the roller pitching test piece 1 and Table 5 and Table 6 for the Ono type rotary bending test piece 2 show the "maximum surface heating temperature" and "heating time", respectively. , “Average surface temperature × time [Z = (T + 273) × log (t)] by induction hardening under the conditions shown in the columns, and also for the roller pitching test piece 1, Tables 3 and 4 and Ono formula For the rotary bending test piece 2, Table 5 and Table 6 show "surface hardness after induction hardening", respectively.
Hardened layers having the values shown in the columns of "nitriding depth after induction hardening" and "hardened layer depth after induction hardening" were obtained.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

[0031]

[Table 5]

[0032]

[Table 6]

[0033]

[Table 7]

[0034]

[Table 8]

Next, for each roller pitching test piece 1, a roller pitching test was conducted under the conditions of small roller (test piece): diameter 26 mm, large roller (counterpart material): diameter 130 mm, slip ratio: 40%, rotation speed: 1580 rpm. When carried out, similarly, the results shown in the columns of "pitching life" in Tables 3 and 4 were obtained.

As a result, the invention examples A to L all had a pitting life of more than 10 ⁷ times and had excellent surface pressure fatigue strength (pitting fatigue strength).

On the other hand, in the case of Comparative Example d-1 in which only the nitriding treatment is performed and the induction hardening treatment is not performed, in the case of Comparative Example d-2 in which the nitriding treatment is not performed and only the induction hardening treatment is performed,
Comparative Example d- where the nitriding time is short and the nitriding layer depth is small
In the case of 3, Comparative Example d in which the heating time during induction hardening is short
In all cases of -4, the pitting life was short and the contact pressure fatigue strength was low.

On the other hand, when an Ono-type rotary bending fatigue test was conducted on each Ono-type rotary bending test piece 2 under the condition of the number of rotations: 3500 rpm, the same results were obtained in the "Fatigue limit" column of Tables 5 and 6. The results shown were obtained.

As a result, in each of Examples A to L of the present invention, the fatigue limit exceeded 600 N / mm ² and had excellent bending fatigue strength.

On the other hand, in each of Comparative Examples d-1 to d-4, the fatigue strength was low and the bending fatigue strength was poor.

[0041]

In the method for manufacturing a mechanical structural part according to the present invention, the surface heating temperature is set to 9 after the soft nitriding treatment is performed on the steel of the specific component under the condition that the nitriding layer depth is 150 μm or more.
Since induction hardening was carried out under conditions where the nitrided layer was austenitized at a heating temperature of 0 to 1200 ° C. for 1 to 10 sec, the excellent tempering of martensite obtained by quenching austenite containing nitrogen and carbon was achieved. It is possible to further utilize softening resistance and crack initiation resistance, and to provide a mechanical structural component having excellent mechanical properties such as surface pressure strength (pitting fatigue strength), bending fatigue strength, and torsional fatigue strength. It is possible to obtain a remarkably excellent effect.

[Brief description of drawings]

FIG. 1 is an explanatory view showing the shape of a roller pitching test piece.

FIG. 2 is an explanatory view showing the shape of an Ono-type rotary bending test piece.

FIG. 3 is a graph illustrating the influence of the depth of the nitride layer on the life.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C22C 38/60 C22C 38/60 (72) Inventor Shun Umegaki No. 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (56) References JP-A-2-232353 (JP, A) JP-A-59-50158 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C21D 1 / 06,6 / 00 C23C 8/26 C22C 38/00-38/60

Claims (5)

(57) [Claims] 1. C: 0.35 to 0.65% by weight,
Si: 0.03 to 1.50%, Mn: 0.3 to 1.0
%, Cr: 0.1 to 3.0%, the balance Fe and impurities to the steel, after the nitriding treatment is performed under the condition that the nitriding layer depth is 150 μm or more, the surface heating temperature is 900 to 1
A method for producing a mechanical structural component excellent in mechanical strength, which comprises performing induction hardening under conditions of 200 ° C. and a heating time of 1 to 10 seconds so that a nitride layer is austenitized. 2. In the steel, Al: 0.02 to 1.5%,
The production of a mechanical structural component excellent in mechanical strength according to claim 1, which contains one or more of V: 0.05 to 0.5% and Mo: 0.05 to 0.5%. Method. 3. The method for producing a mechanical structural component excellent in mechanical strength according to claim 1, wherein the steel contains Ni: 0.5 to 2.0%. 4. Ti: 0.005 to 0.05 in steel
%, Nb: 1 to 2 out of 0.01 to 0.10% or 2
The method for producing a mechanical structural component having excellent mechanical strength according to claim 1, further comprising a seed. 5. S: 0.02 to 0.40%, P in steel
b: 0.01 to 0.50%, Ca: 0.0003 to 0.
010%, Te: 0.005 to 0.10%, Bi: 0.
The method for producing a mechanical structural component excellent in mechanical strength according to any one of claims 1 to 4, containing one or more of 01 to 0.50%.