JP3081927B2 - Carburized and quenched parts for drive shaft coupling and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carburized and quenched component (e.g., CVJ) for a drive shaft constant velocity joint (hereinafter referred to as "CVJ") having excellent strength characteristics such as torsional fracture strength and rolling fatigue characteristics.
J ball cage) and a method of manufacturing the same.

[0002]

2. Description of the Related Art For example, shaft couplings for transmitting torque used for transmitting power from a driving axle of a vehicle or the like to a driven axle are roughly classified into "constant velocity joints" and "non-constant velocity joints". However, a barfield type joint is a typical example of the former. This is, as shown in FIG. 1, between an outer race (outer ring) 2 fixed to the drive shaft 1 and an inner race (inner ring) 4 fixed to the driven shaft 3. Multiple (for example, 6)
, And these balls are inserted into the ball cage 6.
It is a structure held by. Since the ball cage 6 and the inner race 4 are intended to transmit a very large rotational force mechanically, they need to have high strength and toughness, and have a contact surface with the ball 5. Has excellent wear resistance,
Rolling fatigue resistance is required.

[0003] Accordingly, such case CVJ parts are applied with "case hardened steel" which is imparted with high surface hardness and rolling fatigue by carburizing and quenching.
Cr such as SCM415, SNC415, SNCM415
Alloys for mechanical structures of Ni-Cr, Ni-Cr, and Ni-Cr-Mo series are used as case hardened steels, processed into the required part shapes, and then subjected to carburizing and quenching for use. Was offered.

However, in recent years, with the improvement of the performance of automobiles and the like, CVJ has also been required to have higher strength. Therefore, the above-mentioned steels specified in JIS require the strength desired for CVJ parts. The characteristics cannot be sufficiently satisfied.

[0005] On the other hand, price competition for products has continued to intensify, and there has been a strong demand for cost reduction of CVJ parts. Of course, great efforts have been made to reduce the cost of CVJ parts, but it has been recognized that it is absolutely necessary to reduce the “production cost by carburizing and quenching” in order to further reduce costs. ing. In order to reduce the cost of carburizing and quenching, it is most effective to shorten the carburizing time. Therefore, studies have been made to shorten the carburizing time by increasing the carburizing temperature as compared with the conventional case. However, if the carburizing temperature is increased, there is a problem that the strain generated in the quenching process after carburizing increases. Therefore, in CVJ parts that require high-precision dimensional control, increasing the carburizing temperature is a measure that must be avoided. ing. Moreover,
When the carburizing temperature is increased, the austenite crystal grains grow abnormally during the carburizing process, resulting in a "coarse-grained mixed grain structure in which coarse grains are scattered". There is also a problem that the strength is reduced.

[0006] In order to meet the requirements for carburized and quenched members from the viewpoint of the raw material, as a case hardening steel, an “improved steel made by adding B and devising a combination of alloy components such as Cr, Mo, and Ni” has been used. Some have been proposed (see, for example, JP-A-2-170944 and JP-A-5-117806), but none of them has been sufficiently satisfactory for CVJ parts.

That is, generally, in order to ensure high strength and abrasion resistance in a carburized part, toughness tends to be sacrificed, and therefore resistance to an impact load is poor and the carburized part is broken at a low load. In particular, in the case of a component having a stress concentration portion on the surface, the strength is significantly reduced after carburizing and quenching. The above-mentioned B-added steel (steel described in Japanese Patent Application Laid-Open No. 5-117806) is intended to improve this drawback and to improve the workability. In particular, the effect of the addition of B is remarkable. However, even when a CVJ part is manufactured from this B-added steel, the expected impact load strength, wear resistance and rolling fatigue cannot often be secured, and the problems relating to shortening of carburizing time are sufficiently solved. I couldn't do that either.

Accordingly, an object of the present invention is to provide a CVJ carburized and quenched component having high wear resistance, rolling fatigue characteristics, and excellent strength and toughness including impact load strength, at a stable and low cost. Was placed on offering.

[0009]

In order to achieve the above-mentioned object, the present inventors have, in particular, a) In general, carburized parts generally have a tempering temperature of 180 to 20 after carburizing.
It is about 0 ° C., so if the hardenability is excessive, the toughness of the core is impaired, and if the hardenability is insufficient, the strength is impaired. It is necessary to design the components. B) The elements that cause the embrittlement of the grain boundaries due to carburization are reduced as much as possible, and the impact load strength is reduced by directing the active addition of elements that improve the grain boundary strength. It is necessary to minimize the occurrence of intergranular fracture, which causes cracking. C) To reduce the carburizing cost of CVJ parts, shortening the carburizing time is the most effective, but increasing the carburizing temperature In the method of shortening the carburizing time by carrying out, the strain generated by the carburizing and quenching process becomes large, not only impairing the dimensional accuracy of extremely important products for CVJ parts, but also generating a mixed grain structure that causes a reduction in impact load strength. , Carburizing temperature It is necessary to design the components so that the carburizing time can be shortened without increasing the temperature. D) Since the dimensional accuracy of the product is extremely important for CVJ parts, it is necessary to minimize the occurrence of heat treatment distortion during carburizing and quenching. Even if the quenching cooling is moderated so that quenching distortion does not occur by changing the type of oil and the temperature, the imperfect quenching structure that causes deterioration of impact load strength, wear resistance and rolling fatigue characteristics is reduced. It was necessary to design the components to prevent this from occurring, and as a result of earnest research while repeating many experiments based on the basic idea that the following findings were obtained.

[0010] Conventionally, it is difficult to stably secure sufficient impact load strength, wear resistance, rolling fatigue, and the like for carburized and quenched steel materials because "an abnormal carburized layer is generated due to grain boundary oxidation occurring during carburization. As a result, the hardenability of the steel decreases near the grain boundaries, and this leads to the formation of an incompletely hardened structure. " However, the present inventors have found that the "precipitation of carbides on austenite grain boundaries generated when quenching a carburized material" has a greater adverse effect than the adverse effect due to the "grain boundary oxidation during carburization". It has been found that this phenomenon causes the formation of an incompletely quenched structure in the surface layer of the part during carburizing and quenching. In addition, this “carbide precipitation at grain boundaries during quenching of carburized material”
Has also been found to be able to be prevented by adding a predetermined amount of B.

[0011] The conventionally proposed B-added case hardening steel includes:
In order to prevent grain boundary oxidation during carburizing, the alloying elements are reduced, and the decrease in hardenability due to the reduction in alloying elements is reduced by B
Some have adopted the component design philosophy to be supplemented by addition.
Has a tendency to decrease as the C content in steel increases. Therefore, in such a B-added case hardening steel based on the idea that the hardenability is supplemented by B, if the C content in the surface layer is increased by carburization, the effect of improving the hardenability of B disappears in the surface layer. As a result, an incompletely quenched structure is apt to be formed in the carburized surface layer, and it has not been possible to sufficiently obtain impact load strength, wear resistance and rolling fatigue. In addition, it was considered that this tendency gradually became more prominent due to the "treatment for reducing carburizing and quenching distortion" described above.

On the other hand, it is possible to prevent the "precipitation of carbides at the grain boundaries occurring during the quenching treatment of the carburized material", thereby suppressing the formation of an incompletely quenched structure in the carburized and quenched surface layer. In case hardening steels to which B is added under the idea of よ う, it is not necessary to worry particularly about the problem of "disappearance of" the effect of improving the hardenability of B "in the portion where the amount of C is increased by carburization"
It is possible to stably improve the impact load strength, abrasion resistance and rolling fatigue resistance without being greatly influenced by the C content of the carburized portion.

However, the effect of preventing the precipitation of carbides at the grain boundaries during the quenching treatment of the carburized material by the addition of B is described.
It is essential to reduce the N content in the steel to a specific region in order to secure the content. That is, the present inventors have found that 0.0%
Even when N of about 07% by weight (usually about the lower limit of steel) is contained, the addition of B stably secures the "effect of preventing carbide precipitation at grain boundaries during quenching of carburized material". It is difficult to do so, but when the N content in the steel is reduced particularly to a region of less than 0.006% by weight, the above-mentioned effect by adding B becomes remarkable, and various strengths such as impact load strength characteristics and toughness are sufficiently improved. I was able to clarify that it would be.

It has also been found that when the N content in the steel is less than 0.006% by weight, the rolling fatigue characteristics are remarkably improved. That is, regarding the rolling fatigue characteristics, conventionally, Ti is always added at the same time in B-added steel, so Ti
It was thought that N deteriorated the rolling fatigue characteristics, but it was confirmed that N in the steel had an adverse effect on the rolling fatigue characteristics even in the steel without Ti added, and this adverse effect was caused by N-containing steel. It has been found that the amount can be substantially eliminated by controlling the amount to less than 0.006% by weight.

Therefore, C, Si,
Combining Mn, Cr, Mo, Al, and S, adjusting the content ratio, and limiting the N content to less than 0.006% by weight and adding an appropriate amount of B, carburization at low temperature and short time It was also found that a high-strength steel material having excellent impact load strength, abrasion resistance and rolling fatigue resistance can be stably obtained even when slow cooling is performed in the subsequent quenching treatment.

Moreover, in the carburized and quenched steel material whose chemical composition has been adjusted as described above, the hardness profile (hardness distribution) of the cross section is particularly surface hardness: Hv 650 to 800, core hardness: Hv 250 to 450, It was also confirmed that when the condition of surface layer hardening depth: 0.2 to 1.2 mm was satisfied, the above-mentioned properties required for recent carburized and quenched parts for CVJ were sufficiently satisfied.

The present invention has been completed on the basis of the above-mentioned findings and the like.
The chemical composition of the substrate is C: 0.1 to 0.25% (hereinafter, the percentage representing the component ratio is referred to as% by weight), Si: 0.2 to 0.4%, Mn:
0.3 to 0.9%, P: 0.02% or less, S: 0.001 to 0.15
%, Cr: 0.5 to 0.9%, Mo: 0.15 to 1%, Al: 0.
01 to 0.1%, B: 0.0005 to 0.009%, N: 0.006
% Or more: Ni: 0.3-4.0%,
Ti: 0.01 to 0.3%, Nb: 0.01 to 0.3%, V: 0.01 to
0.3%, Zr: 0.01 to 0.3%, including at least one type, and the balance being substantially Fe, and surface hardness: Hv 650 to 800, core hardness: Hv 250 to 450, hardening depth : By having a cross-sectional hardness distribution of 0.2 to 1.2 mm, excellent wear resistance, rolling fatigue characteristics and dimensional accuracy can be ensured, and the cost has been reduced. "
It has a great feature in "C: 0.1 to 0.25%,
Si: 0.2 to 0.4%, Mn: 0.3 to 0.9%, P: 0.02%
Below, S: 0.001 to 0.15%, Cr: 0.5 to 0.9
%, Mo: 0.15 to 1%, Al: 0.01 to 0.1%, B:
0.0005 to 0.009%, N: contains less than 0.006%, or Ni: 0.3 to 4.0%, Ti: 0.01 to 0.3%,
Nb: 0.01 to 0.3%, V: 0.01 to 0.3%, Zr: 0.01 to
A case hardened steel member having a chemical composition containing at least one or more of 0.3% and having substantially the remainder of Fe is obtained by carburizing temperature: 880 to 930 ° C, carburizing time: 1 to 3 hours, and quenching temperature: Excellent wear resistance by carburizing and quenching under the condition of 800-870 ° C., surface hardness: Hv 650-800, core hardness: Hv 250-450, hardening depth: 0.2-1.2 mm sex,
The point is that carburized and quenched parts for CVJ with rolling fatigue characteristics can be manufactured stably at low cost with high dimensional accuracy. "
Is also characterized.

[0018]

The reasons for limiting the chemical composition of the member, the manufacturing conditions, and the like in the present invention as described above will now be described. (A) Chemical composition a) C C is a basic component that secures the hardness and strength of steel. The steel must have a hardness of Hv250 or more to secure enough strength not to be deformed during use as a carburized / quenched part. To secure the required hardness, the C content is set to 0.1% or more. There is a need. On the other hand, if the content of C exceeds 0.25%, the core toughness of the steel deteriorates. Therefore, the C content is 0.1
0.20.25%.

B) Si Conventionally, in case-hardened steel, the amount of Si is often suppressed because Si is an element that contributes to grain boundary embrittlement due to grain boundary oxidation during carburization. However, in the product of the present invention, the effect of improving the hardenability of Si is positively used in order to secure the hardenability of the carburized layer and achieve a high impact fracture strength. If the Si content is less than 0.2%, the desired hardenability of the carburized layer cannot be ensured. On the other hand, if the Si content exceeds 0.4%, the Since the "vulnerability" becomes remarkable, the Si content is set to 0.2 to 0.4%.

C) Mn Mn, like Si, is often reduced in amount to suppress grain boundary embrittlement due to grain boundary oxidation during carburization. However, when Mn is reduced, the hardenability of the carburized layer decreases. It has been found that the action is increased and it is difficult to secure the high impact fracture strength aimed at by the present invention. That is, in the product of the present invention, if the Mn content is less than 0.3%, the desired hardenability of the carburized layer cannot be secured. It was found that "weakening of Mn near the grain boundary during carburization due to oxidation" causes no practical problem even if the Mn content exceeds 0.9%. Punching workability and grindstone grindability deteriorate remarkably. Therefore, Mn
The content was determined to be 0.3-0.9%.

D) PP is a very harmful impurity element in case hardening steel since it significantly promotes "weakening of grain boundaries due to precipitation of cementite on austenite grain boundaries during carburizing and quenching". Therefore, it is preferable to reduce the P content as much as possible. However,
Since reducing P results in an increase in the cost of the raw materials and the refining process, an allowable value is designed from the balance between the target performance and the cost. In the present invention, the allowable upper limit is set to 0.02% in consideration of the effect of B described later.

D) SS S is a component that is desired to be positively added in terms of improving machinability (machinability and punching properties) while deteriorating the toughness of steel. And, when the S content is less than 0.001%, the effect of improving machinability does not become remarkable, while, on the other hand, 0.15%
If the content of S exceeds that, the toughness of the steel deteriorates remarkably. Therefore, in the present invention, the S content is set to 0.001 to 0.15%. However, it is advisable to keep the S content low if it is used in such a way that less machinability is required.

E) Cr Cr is an indispensable component for securing the hardenability of the steel base and for securing the carbon concentration of the carburized layer in a short time. For that purpose, a content of 0.5% or more is required. It is. However,
At the same time, Cr significantly promotes "weakening of grain boundaries due to precipitation of cementite on austenite grain boundaries during carburizing and quenching", so it is necessary to limit the content to at most 0.9% or less. . However, if the Cr content is limited to 0.9% or less, the hardenability of the steel, particularly the hardenability of the carburized portion having a high C content, becomes insufficient, so that the present invention does not cause the grain boundary to become brittle. , Mo, and Ni were added to compensate for this.
For this reason, the Cr content is set to 0.5 to 0.9%, but is preferably adjusted to 0.5 to 0.65%.

F) Mo Mo is an essential component for improving the strength and toughness of the steel base and the carburized portion and ensuring the carbon concentration of the carburized layer in a short time. In particular, since the effect of improving the hardenability of Mo is hardly affected by the amount of carbon in the steel base, the effect of improving the hardenability is stably exhibited even in a carburized portion having a high carbon content. In addition, in steels in which the Cr content is reduced and the hardenability is replenished with B in order to suppress the brittleness of the grain boundaries due to carburization, the hardenability is remarkably reduced even at high carbon. The hardenability compensation of the carburized part is very important. In this case, when the Mo content is less than 0.15%, not only sufficient hardenability compensation cannot be performed, but also the amount of C that enters by short-time carburizing treatment decreases. From the viewpoint of imparting the above effects, it is preferable that the Mo content is large, but 1%
Since sufficient effects can be obtained with the addition up to, addition beyond this is considered to be uneconomical. Therefore, the Mo content is 0.
It was determined to be 15 to 1%.

G) Al Al is an effective component for deoxidizing steel and refining crystal grains. If its content is less than 0.01%, its effect is not sufficient. On the other hand, it is contained in excess of 0.1%. The Al content was determined to be 0.01 to 0.1% because the inclusions harmful to the toughness increased.

H) BB B suppresses "precipitation of carbides (Cr carbides and the like) on the austenite grain boundaries generated when quenching the carburized material", whereby the incomplete quenching structure of the carburized portion, It is an indispensable component for preventing grain boundary embrittlement and ensuring sufficient impact load strength, wear resistance, rolling fatigue characteristics, etc. for carburized and hardened materials. Also,
In the present invention, the Cr content is limited in order to prevent "the harmful effect of Cr that carbides are precipitated on the grain boundaries during carburizing and quenching to greatly promote the brittleness of the grain boundaries".
The steel also plays a role in ensuring the hardenability of the steel core by compensating for the "reduced hardenability of the steel matrix" resulting from the reduction of the Cr content. However, if the B content is less than 0.0005%, the desired effect due to the above effect cannot be obtained.
If B is contained in excess of B, the grain boundary embrittlement due to B will occur conversely, so the B content is set to 0.0005 to 0.009%. Even if the steel contains B to suppress "precipitation of carbides at the grain boundaries during carburizing and quenching", the above-mentioned effect of B can be obtained if the N content in the steel is about 0.007% of normal steel. It cannot be secured enough.

I) N As described above, the amount of N in steel is very important to make the effect of B effective. That is, the amount of N in steel is 0.006%
For the first time, the effect of preventing the precipitation of carbides at the grain boundaries at the time of quenching of the carburized material becomes remarkable when B is reduced to a range of less than not only, and sufficient impact load strength is secured, Rolling fatigue properties are also significantly improved. It is desirable that the N content in steel be as small as possible. However, in industrial production in the atmosphere, the N content is 0.001% with current steelmaking technology.
% Is extremely difficult to achieve.

J) When more severe use is expected as Ni CVJ parts, Ni or Ti, Nb, V or
It is effective to contain one or more of Zr.
Ni is an effective component for improving the strength and toughness of the steel base, and also greatly contributes to improving the strength and toughness of the carburized portion in cooperation with Mo. However, if the Ni content is less than 0.3%, the effect is insufficient. On the other hand, if the Ni content exceeds 4.0%, the effect is saturated. 4.0%.

K) Ti, Nb, V and Zr These elements have the effect of refining the crystal grains of steel and improving the toughness.
It is preferred to include one or more species. However, if the content of each of these components is less than 0.01%, the above effect is insufficient. On the other hand, if the content exceeds 0.3%, on the contrary, the toughness and rolling fatigue characteristics of the steel are deteriorated. The content of Ti, Nb, V or Zr is 0.01 to 0.3 respectively.
%.

(B) Hardness distribution of the cross section of parts Of the CVJ parts, those manufactured by carburizing and quenching are mainly inner races and ball cages.
When a shocking rotational force is applied to the CVJ, the surface layer that is slightly brittle due to carburization often lacks. When such a deficiency trouble occurs, the CVJ does not operate smoothly, and the deficiency of the carburized layer is a matter which must be avoided by all means. As a result of the study by the present inventors, it has been found that in the case of a component having the chemical composition according to the present invention, when the surface hardness after carburizing and quenching exceeds Hv 800, the above-described chipping troubles frequently occur. It has also been found that, when the surface hardness of the window frame provided on the ball cage exceeds Hv 800, the impact tensile strength decreases, and the column cannot have the necessary breaking strength as a CVJ part. On the other hand, the surface hardness of the carburized and quenched part for CVJ having the chemical composition according to the present invention is Hv6.
If it is less than 50, the rolling fatigue characteristics deteriorate, and the rolling fatigue life of a high-strength CVJ component used at a higher surface pressure than before is insufficient. Therefore, the surface hardness of carburized and quenched parts for CVJ was limited to Hv 650 to 800.

The hardening depth after carburizing and quenching is 0.2 mm.
When the hardening depth exceeds 1.2 mm, the CVJ having the chemical composition according to the present invention is insufficient when the hardening depth exceeds 1.2 mm.
The impact tensile strength of a carburized and quenched part for use is reduced, and it is no longer possible to have the impact fracture strength required for a high-strength CVJ part. Therefore, the hardening depth after carburizing and quenching is
Limited to 0.2 to 1.2 mm.

When the hardness of the core portion of the carburized and quenched part is out of the range of Hv 250 to 450, the chemical composition according to the present invention also has the impact fracture strength required for the recent high strength CVJ. It will not be stable.

It is needless to say that the hardness distribution of the cross section of the carburized and quenched part for CVJ can be adjusted by fine adjustment of the chemical composition and control of the carburized and quenched and tempered conditions.

(C) Manufacturing conditions of carburized and quenched parts for shaft joints a) Carburizing temperature As described above, CVJ parts require extremely high dimensional accuracy, so that deformation strain can be generated by carburizing and quenching. It must be prevented as much as possible. The deformation occurring in the carburized and quenched parts for CVJ is greatly affected by the temperature of the carburizing treatment, and when the carburizing temperature is lowered, the heat treatment distortion is greatly improved. In the case of the steel having the chemical composition according to the present invention, a deep hardening depth can be obtained in a short time even if carburizing is performed at a temperature lower than the “region exceeding 930 ° C.” which has been conventionally performed, and the desired characteristics can be obtained. It is possible to secure it stably. However, when the carburizing temperature is lower than 880 ° C., even if the chemical composition according to the present invention is used, it takes a long time to achieve a desired carburizing depth and the cost is increased. There is a possibility that the curing depth of 0.2 mm or more may not be realized. Therefore, the carburizing temperature was set at 880-930 ° C.

B) Carburizing time If carburizing treatment is carried out for as long as about 4 hours as in the prior art, the amount of carbide on the austenite grain boundaries precipitated during carburizing and quenching increases, and the fracture strength of CVJ parts increases. Decrease. This tendency is remarkable especially in the case of a ball cage window frame. In the case of the steel having the chemical composition according to the present invention, a desired carburized depth can be achieved at a low temperature even with a carburizing treatment of 3 hours or less, and the desired characteristics of the carburized and quenched part for CVJ can be secured. It is possible. In addition, by performing the processing at a low temperature for a short time, the manufacturing cost can be reduced. However, if the carburizing time is less than 1 hour, even with the steel having the chemical composition according to the present invention, the carburized hardening depth required for CVJ parts of 0.2 mm or more cannot be realized. Therefore, the carburizing time was determined to be 1 to 3 hours.

C) Quenching temperature If the temperature at the time of quenching and quenching after carburizing exceeds 870 ° C., heat treatment distortion which causes deterioration of dimensional accuracy, which is the most important for CVJ parts, increases. The upper limit of the heat retention temperature (quenching temperature) was set to 870 ° C. On the other hand, when the temperature is lower than 800 ° C., ferrite is generated at the core of the CVJ part to be carburized and quenched, and the strength of the part is reduced.
The lower limit of the heat retention temperature (quenching temperature) before quenching was 800 ° C.

As described above, dimensional accuracy is extremely important in CVJ parts. In particular, it is a major technical problem to minimize the occurrence of deformation strain during carburizing heat treatment. Carburizing temperature 8
The temperature is 80 to 930 ° C, and the carburizing time is also 1 to 3 hours. However, when CVJ parts are manufactured under such carburizing conditions, the hardening depth of the carburized layer is 0.2 to 1.2 m, which is necessary to maintain the life of the CVJ, even though the problem of deformation strain can be solved.
There is a greater concern that it will be less than 0.2 mm without entering the range of m.
In order to prevent this situation, there is a method of increasing the carbon potential during carburization. However, if this method is adopted, the hardness of the outermost surface exceeds Hv800, and the above-described deficiency trouble frequently occurs.

Therefore, as a result of intensive studies, it was confirmed that realizing the hardness distribution of the cross section of the component as described above within the range of the carburizing conditions described above is the best means for manufacturing a high-strength CVJ. is there. Such high strength CV
In order to achieve more stable J parts,
It is largely due to the improvement of carburizing technology such as "Stable and strict control of the carbon potential" and "Uniform temperature control of parts during carburizing in the carburizing furnace". Improving composition is also important.

Next, the present invention will be described with reference to examples.

【Example】

Example 1 First, a 150 kg ingot having the chemical composition shown in Tables 1 and 2 was obtained by vacuum smelting and casting, and then subjected to hot forging and normalizing treatment. “Smooth round bar tensile test specimen with parallel part diameter: 8.0mmφ” by processing
And "notched tensile test piece test piece" shown in FIG.

[0040]

[Table 1]

[0041]

[Table 2]

Next, a tensile test was carried out on each of the above test pieces, which were subjected to a low-temperature, short-time carburizing, quenching and tempering treatment under the conditions shown in FIG. 3, and the smooth tensile strength and the notch tensile strength were measured. Was evaluated for toughness. Further, for the tensile test pieces subjected to the same carburizing treatment, the hardness distribution in the cross section of the parallel portion was measured, and the surface hardness, hardening depth and core hardness were obtained. The “hardening depth” is “hardness of the surface hardened layer is Hv5
The distance from the surface at the position “13” was obtained. The results are shown in Tables 1 and 2.

From the results shown in Tables 1 and 2 above,
All steel materials after low-temperature short-time carburizing, quenching and tempering satisfying the conditions specified in the present invention show a smooth tensile strength of 120 kgf / mm ² or more, and the notch tensile strength is 130 kgf / mm ² or more. It turns out that it has excellent breaking strength.

Separately from these, for each of the steel materials after the low-temperature short-time carburizing, quenching and tempering treatments, a mirror-polished finish having an average surface roughness (Ra) of 0.05 μm is applied to # 60 spindle oil. A thrust rolling fatigue test at room temperature with lubrication was performed. At this time, the evaluation of rolling fatigue characteristics
A test was conducted by changing the surface pressure to determine the number of repetitions of the stress load until the peeling life, and a method of comparing and obtaining the surface pressure of the rolling fatigue limit from the SN diagram was adopted. Tables 1 and 2 also summarize these results. From these results, it can be confirmed that all of the steel materials after the low-temperature, short-time carburizing, quenching and tempering treatment satisfying the conditions specified in the present invention exhibit excellent rolling fatigue characteristics.

Example 2 Table 3 was obtained by vacuum melting and casting.
After obtaining 150kg steel ingots of each chemical composition shown in the following table, they were subjected to hot forging and normalizing, and further processed by machining to obtain a window of a ball cage which is one of important CVJ parts. “6.0” as shown in Fig. 4 where the “pillar of the frame” is simulated.
A square prism tensile test piece having a parallel section of mm × 5.0 mm was prepared.

Next, FIG. 5 and Tables 4 and 5
Were subjected to carburizing, quenching and tempering treatments under various conditions, and the hardness distribution in the cross section of the parallel portion was measured to determine the surface hardness, the hardening depth and the core hardness. The “curing depth” was determined in Example 1.
In the same manner as in the above case, the distance from the surface at the “position where the hardness of the surface hardened layer becomes Hv513” was used. Further, a tensile test was performed on a tensile test piece subjected to the same carburizing, quenching and tempering treatment, and the breaking load was also measured.

[0047]

[Table 4]

[0048]

[Table 5]

Further, the strain generated in the column portion of the ball cage by the carburizing and quenching treatment was simulated using test pieces having the shape and dimensions shown in FIG. In this test, using a high-precision dial gauge, the thickness at five positions on each side of the column was measured before and after carburizing and quenching as shown in FIG. And The difference between the maximum value of each deformation amount at the five positions and the minimum value was calculated as the maximum deformation amount and used for evaluation. The results are shown in Tables 4 and 5.

From the results shown in Tables 4 and 5, it is first confirmed that the carburized and quenched member satisfying the conditions specified in the present invention exhibits excellent breaking strength. Also, regarding the heat treatment distortion, it can be seen that the carburized and quenched member satisfying the conditions specified in the present invention has a small amount of distortion as a whole. Furthermore, looking at the effects of carburizing conditions in Tables 4 and 5, there is almost no difference in the hardening distribution in the cross section of the carburized and quenched member even at a low temperature and a short period of carburizing treatment. It is clear that a reduction in cost can be achieved.

Example 5 Table 6 was obtained by vacuum casting.
After obtaining 1-ton steel ingots of each chemical composition shown in Table 1, these were hot forged into round steel pieces and further hot-formed by a mandrel mill pipe-making method, and then "cold drawing → stress relief annealing" To give
Obtained a mules steel pipe. Some slabs are hot forged to 30
It was forged into a steel rod of mmφ.

[0052]

[Table 6]

Next, two types of CVJ parts were prototyped using the steel pipe and the steel rod. A ball cage was produced from the seamless steel pipe, and an inner race was produced from the steel rod on an actual mass production machine. The ball cage and the inner race were heat-treated under the conditions of carburizing and quenching described in Table 7, and then assembled together with other parts into a CVJ.

[0054]

[Table 7]

The prototype CVJ was slowly loaded with a rotational force using a torsion tester, and the quasi-static torsional fracture strength was determined. These results were compared with the results of each ball case studied separately.
Table 7 summarizes the hardness distributions of the inner and inner race sections.

From the results shown in Table 7, it can be seen that the CVJs of both sizes incorporate the parts of the present invention manufactured according to the conditions specified in the present invention, and that of the comparative product (to which the conventional conditions are applied). It can be seen that it has a quasi-static torsional fracture strength as high as 13 to 14%.

[0057]

[Summary of effects] As described above, according to the present invention, CVJ carburizing with high strength, high toughness, and high dimensional accuracy having high fracture strength, abrasion resistance and rolling fatigue resistance and little heat treatment deformation. Industrial parts can be provided at low cost by using carburizing and quenching treatment in a shorter time than before, and the application of these parts can significantly improve the performance of CVJ (such as torsional fracture strength). A more useful effect is brought about.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an example of a bar-field type joint having a ball cage and an inner race.

FIG. 2 is an explanatory view of a notched tensile test piece.

FIG. 3 is a graph showing conditions of carburizing, quenching and tempering treatments employed in Examples.

FIG. 4 is an explanatory view of a square pillar tensile test piece prepared in an example.

FIG. 5 is a graph showing carburizing, quenching, and tempering treatment conditions adopted in another embodiment.

FIG. 6 is an explanatory view of a heat treatment deformation strain measurement test piece prepared in an example.

FIG. 7 is an explanatory diagram illustrating a method for measuring a heat-treated deformation strain measurement test piece.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Drive shaft 2 Driven shaft 3 Outer race 4 Inner race 5 Ball 6 Ball cage

[Table 3]

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuhiko Yoshida 1905-37, Hirooka, Fukuroi-shi, Shizuoka (72) Inventor Tatsuhiro Goto, 1031 Senden, Iwata-shi, Shizuoka (72) Inventor Akira Wakita 1039, Kamiokada, Iwata-shi, Shizuoka -1 (56) References JP-A-7-179990 (JP, A) (58) Fields studied (Int. Cl. ⁷ , DB name) C23C 8/22 C21D 6/00, 9/40 C22C 38/00 301 F16D 3/244

Claims (6)

(57) [Claims] 1. The method according to claim 1, wherein the chemical composition of the substrate is C:
0.1 to 0.25%, Si: 0.2 to 0.4%, Mn: 0.3 to
0.9%, P: 0.02% or less, S: 0.001 to 0.15%,
Cr: 0.5 to 0.9%, Mo: 0.15 to 1%, Al: 0.01
0.1%, B: 0.0005-0.009%, N: Less than 0.006%, and the balance is substantially Fe, and the surface hardness is Hv 650-800, the core hardness is Hv 250-450, and the surface layer is hardened. Depth: A high-strength carburized part for a driveshaft constant velocity joint characterized by having a sectional hardness distribution of 0.2 to 1.2 mm. 2. The method according to claim 1, wherein the base material further comprises:
The high-strength carburized and quenched part for a driveshaft constant velocity joint according to claim 1, characterized in that the part has a chemical composition containing 4.0%. 3. The method according to claim 1, wherein the substrate further comprises Ti: 0.01 to
0.3%, Nb: 0.01 to 0.3%, V: 0.01 to 0.3
%, Zr: high strength carburized quenching for a driveshaft constant velocity joint according to claim 1 or 2, characterized by having a chemical composition containing one or more of 0.01% to 0.3% of Zr. parts. 4. C: 0.1 to 0.25% by weight, S
i: 0.2 to 0.4%, Mn: 0.3 to 0.9%, P: 0.02%
Below, S: 0.001 to 0.15%, Cr: 0.5 to 0.9
%, Mo: 0.15 to 1%, Al: 0.01 to 0.1%,
B: 0.0005% to 0.009%, N: Less than 0.006%, case hardened steel member of chemical composition consisting essentially of Fe, carburizing temperature: 880 to 930 ° C, carburizing time: 1 to 3 hours, quenching Carburizing and quenching at a temperature of 800 to 870 ° C, surface hardness: Hv 650 to 800, core hardness: Hv 250 to 450, surface hardening depth: 0.2 to 1.2 mm. A method for manufacturing a high-strength carburized and quenched part for a drive shaft constant velocity joint. 5. The case hardening steel member further comprises Ni:
The method for producing a high-strength carburized and quenched part for a driveshaft constant velocity joint according to claim 4, characterized in that a part having a chemical composition containing 0.3 to 4.0% is used. 6. The case hardening steel member further includes Ti:
0.01 to 0.3%, Nb: 0.01 to 0.3%, V: 0.01 to
0.3%, Zr: characterized by using a chemical composition having a chemical composition containing one or more of 0.01 to 0.3%.
A method for manufacturing a high-strength carburized and quenched part for a drive shaft constant velocity joint according to claim 4 or 5.