JPH07102343A - Production of nitrided parts - Google Patents

Abstract

PURPOSE:To produce nitrided parts, having hard surface layer and also deep hardened layer and capable of minimizing the amount of machining, such as cutting, by subjecting a steel material of specific composition to heat treatment to control V precipitation, to cold working, and further to nitriding treatment. CONSTITUTION:A steel material, having a composition consisting of, by weight, 0.10-0.40% C, 0.10-0.70% Si, 0.20-1.50% Mn, 0.50-2.50% Cr, 0.05-0.60% V, and the balance essentially Fe, is used. The precipitation of V is controlled by holding this steel material, e.g., at 700-900 deg.C for 30min. Then, cold working is done, and further, nitriding treatment is applied. By this method, the nitrided parts, which has a hard and deep surface hardened layer as the result of the formation of VN in the surface layer part and where the amount of machining such as cutting is minimized, can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a nitriding component applicable to the production of mechanical structural components such as gears and rolling components.

[0002]

2. Description of the Related Art In the case of mechanical structural parts which are required to have surface fatigue strength, such as gears and rolling parts, they are usually surface-hardened by carburizing and hardening before use. By the way, in carburizing and quenching, the treated material is heated to a high temperature to be austenitized, and then C is invaded and diffused into the surface portion to increase carbonization, quenching by cooling, and further tempering treatment. Accompanied by metamorphosis. For this reason, there is a problem that the carburizing and quenching process causes relatively large dimensional changes and strain.

On the other hand, a nitriding treatment is also performed as a surface hardening treatment. In the case of this nitriding treatment, it is possible to perform the nitriding treatment at a low temperature below the transformation point of the material, no transformation is involved in the treatment, and therefore, there are advantages that the dimensional stability is good and the strain is small.

As a method of manufacturing a nitriding component using nitriding as a surface hardening means, for example, SACM64 containing Al, Cr, Mo having a strong affinity for N as a steel material.
It is customary to use 5 (Al-Cr-Mo steel), form it into a rough shape by hot forging, and then subject it to a final shape by machining such as cutting, and then perform nitriding treatment. .

[0005]

As a method of processing the final shape after hot forging, cold working such as cold forging may be considered. However, in the case of parts such as gears, this method is actually used. Is difficult to recruit.

In the case of a component such as a gear wheel which has a large load,
A certain core hardness is required, and in the case of the conventional method, it is necessary to set the material hardness in advance to a hardness that matches this, and in this case the material hardness is too hard and cold working is required. It is actually difficult to apply. Therefore, machining such as cutting is performed, but in this case, the amount of machining increases, the productivity deteriorates, and the manufacturing cost also increases.

When the SACM645 as the steel material is used for the nitriding treatment, AlN or the like is deposited on the surface layer to obtain a surface-hardened layer. However, the nitriding layer depth of AlN is shallow, and therefore this is a gear. When it is applied to the above, there is a problem that it is difficult to obtain a sufficient surface fatigue strength.

[0008]

The invention of the present application has been made in order to solve such a problem, and the gist thereof is C: 0.10-0.40%, Si: 0.
10 to 0.70%, Mn: 0.20 to 1.50%, C
r: 0.50 to 2.50%, V: 0.05 to 0.60
%, The balance of the steel material consisting essentially of Fe is subjected to a precipitation control heat treatment of V before the nitriding treatment, followed by cold working, and then further nitriding treatment (claim 1).

In another aspect of the present invention, the composition components of the steel material further include Al, Mo, Ti, Nb and T.
One or two or more of a and B, respectively, Al: 0.05
~ 1.00%, Mo: 3.00% or less, Ti: 1.50
% Or less, Nb: 0.02 to 1.50%, Ta: 0.02
˜1.50%, B: 0.05% or less can be contained in the steel material (claim 2).

In yet another embodiment, S, P
b, Te, Se, Ca, Bi, Sb, one or more of S, 0.01 to 0.40% and Pb: 0.4, respectively.
0% or less, Te: 0.40% or less, Se: 0.30% or less, Ca: 0.30% or less, Bi: 0.50% or less, S
b: 0.30% or less can be contained in the steel material (claim 3).

[0011]

ACTION AND EFFECT OF THE INVENTION In the present invention, in addition to Mn and Cr contained in the steel material, V having a large affinity with N is contained,
Prior to the nitriding treatment, a V precipitation control heat treatment is performed, followed by cold working and then nitriding treatment.

In the manufacturing process of parts such as gears, generally, hot forging and subsequent cooling treatment are carried out. When V is contained in the steel material, V is combined with C in the steel material at that time to form V.
It becomes C and precipitates.

The deposited VC has a function of increasing the hardness of the material. On the other hand, if V in the material is deposited as VC, the production of VN is hindered during the nitriding treatment, so that a sufficient surface is obtained. I can't get the hardness. Further, when VC is finely dispersed and precipitated, the hardness of the entire material becomes so hard that it becomes difficult to carry out cold working.

Therefore, in the present invention, the precipitation control heat treatment of V is performed prior to the nitriding treatment, and the treatment for making V into a solid solution state in the matrix is performed before the nitriding treatment. That is, in the present invention, the V precipitation control heat treatment is a heat treatment for suppressing V precipitation, and specifically, this heat treatment can be carried out by holding at a temperature of 700 to 900 ° C. for 30 minutes or more. This precipitation control heat treatment may be carried out in the cooling process after hot forging, or may be carried out by cooling once to normal temperature and then reheating.

When such a precipitation control heat treatment is applied, most of the V contained in the material is in the state of solid solution in the matrix. Therefore, when the nitriding treatment is applied thereafter, the surface layer portion is good. VN is generated on the surface to obtain a hard surface-hardened layer. Moreover, the hardened layer made of VN is a hardened layer having a deeper depth than the hardened layer made of AlN, and greatly contributes to the improvement of the surface pressure fatigue strength.

Further, since the hardness of the material itself is not hard in the state where the precipitation of VC is suppressed, the final shape can be easily obtained by cold working in the subsequent steps.
Therefore, according to the present invention, even when machining such as cutting is performed, the machining amount can be reduced, the production efficiency can be increased, and the manufacturing cost can be reduced.

Moreover, cold working can cause work hardening to obtain a desired hardness. The degree of improvement in hardness at that time depends on the working degree. For example, in the case of the above gear, the desired core hardness can be obtained with a working degree of 10% or more, preferably 30% or more. . Of course, when it is desired to harden only the portion close to the surface layer, cold working can be performed at a working degree lower than this.

According to the method of claim 2, in addition to the above components, one or more of Al, Mo, Ti, Nb, Ta and B are further contained as steel components in the above predetermined amount ranges, respectively. Thereby, the surface hardness can be further increased or the matrix can be further strengthened.

The method of claim 3 further includes S, Pb, T
One, two or more of e, Se, Ca, Bi and Sb are contained, whereby machinability can be enhanced.

Next, the reasons for limiting each component in the present invention will be described in detail. C: 0.10 to 0.40% C is required to be 0.10% or more to obtain the required core hardness. However, if it exceeds 0.40%, the formation of nitrides is hindered during the nitriding treatment, and the hardened layer becomes shallow. Further, toughness and cold workability are deteriorated and machinability is deteriorated.
Therefore, in the present invention, the upper limit is set to 0.40%.

Si: 0.10 to 0.70% Si is required to be 0.10% or more for the deoxidizing action at the time of melting and refining. However, if it exceeds 0.70%, the toughness and cold workability deteriorate, so the upper limit is made 0.70%.

Mn: 0.20 to 1.50% Mn is required to be 0.20% or more for the deoxidizing action and for securing the basic strength. However, if it exceeds 1.50%, the toughness and cold workability deteriorate, so 1.50%
Below.

Cr: 0.50 to 2.50% Cr is an element that promotes the diffusion of N, and is required to be 0.50% or more in order to improve the nitriding characteristics (nitriding depth). However, the effect is saturated at 2.50%, so the upper limit is 2.50%.
And

V: 0.05 to 0.60% V is an element having a strong affinity with N, and is an element effective for surface hardening and increasing the depth of the hardened layer. For this purpose, V is contained in the present invention in an amount of 0.05% or more. However, the effect is saturated at 0.60%, so the upper limit is 0.60%.
And

Al: 0.05 to 1.00% Al is an element having a strong affinity with N as with V, and forms a harder surface layer that is harder than V (however, VN).
The depth of the hardened layer is shallower than that of. Therefore, in combination with V, A
It is desirable to add l. The required amount for that is 0.0
It is 5% or more. However, if the amount of Al increases, the generation of VN is hindered and the depth of the hardened layer becomes shallow, so the upper limit must be 1.00%.

Ti: 1.50% or less Nb: 0.02 to 1.50% Ta: 0.02 to 1.50% These elements are effective for increasing the surface hardness by nitriding treatment. The required amount for both Nb and Ta is 0.02% or more. However, the effect is saturated at 1.50%, so the upper limits are made 1.50%.

Mo: 3.00% or less B: 0.05% or less These elements are effective elements for strengthening the matrix, but if they exceed 3.00% and 0.05%, respectively, the depth of the hardened layer decreases. Let Therefore, the upper limit values are 3.00%, 0.
05%.

S: 0.01 to 0.40% Pb: 0.40% or less Te: 0.40% or less Se: 0.30% or less Ca: 0.30% or less Bi: 0.50% or less Sb: 0.30% or less These elements are effective in improving machinability. However, if it is contained more than necessary, the hot workability and toughness are deteriorated, so the content is set within the above range.

[0029]

EXAMPLES In order to further clarify the characteristics of the present invention, examples thereof will be described in detail below. After melting each steel type having the composition shown in Table 1, hot working, cooling and reheating, performing VC precipitation control heat treatment at each temperature shown in Table 2, and then manufacturing the gear by cold working. Then, a nitriding treatment was performed. The cold working was performed at a working rate of 50%.

Surface hardness, nitriding depth and core hardness of the obtained gears were measured and a power circulation type gear fatigue test was conducted. The results are also shown in Table 2. However, the result of the power circulation type gear fatigue test is that the cumulative damage establishment is 10
It is shown as the number of repetitions in%.

The power circulation type gear fatigue test and the nitriding treatment were carried out under the following conditions. <Power circulation type gear fatigue test conditions> Specimen: Module 2.3 Spur gear speed: 2000 rpm Lubricating oil: Yes

<Nitriding treatment conditions> Treatment temperature and time: 570 ° C. × 4 hr Atmosphere: NH ₃ : N ₂ : CO ₂ = 5.5: 2.0: 2.5 Quenching: Oil cooling (80 ° C.)

[0033]

[Table 1]

[0034]

[Table 2]

Next, a power circulation type gear fatigue test was carried out for steel type A while changing the cold working rate, and the results shown in FIG. 1 were obtained.

From the results shown in Table 2, in the case of the present invention example, the core hardness is equal to or higher than that of the comparative example and the nitriding depth is deep,
It can be seen that the fatigue resistance is good.

From the results shown in FIG. 1, the cold working rate was 30%.
It can be seen that particularly excellent fatigue resistance is obtained in the above cases.

Although the embodiment of the present invention has been described in detail above, this is merely an example. For example, in the present invention, as the nitriding treatment, it is possible to use a method such as tufftride or ion nitriding instead of the gas nitriding in the above example. It can be carried out in other modes.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a cold working rate and a fatigue life when a gear is manufactured according to an embodiment of the present invention and the cold working rate is changed.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshimi Aoyama 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor Makoto Sumitomo, 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd.

Claims (3)

[Claims] 1. C: 0.10 to 0.40% Si: 0.10 to 0.7 on a weight basis.
0% Mn: 0.20 to 1.50% Cr: 0.50 to 2.
50% V: 0.05-0.60% The balance of the steel material consisting essentially of Fe is subjected to V precipitation control heat treatment before nitriding treatment, and then subjected to cold working, followed by nitriding treatment. A method for manufacturing a nitriding component, which comprises applying 2. The method for manufacturing a nitriding component according to claim 1, further comprising one or more of Al, Mo, Ti, Nb, Ta and B Al: 0.05-1.00% Mo: 3.00% or less Ti: 1.50% or less Nb: 0.02-1.
50% Ta: 0.02 to 1.50% B: 0.05% or less It is made to contain as a composition component of a steel material, The manufacturing method of the nitriding process part characterized by the above-mentioned. 3. The method for manufacturing a nitriding component according to claim 1, further comprising S, Pb, Te, Se, Ca, Bi,
One or two or more types of Sb are respectively S: 0.01-0.40% Pb: 0.40% or less Te: 0.40% or less Se: 0.30% or less Ca: 0.30% or less Bi: 0.50% or less Sb: 0.30% or less Sb: 0.30% or less is contained as a composition component of the steel material, a method for producing a nitriding component.