JP2002256384A - Steel for crank shaft having excellent machinability and wear resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide low-cost steel for a crank shaft which has excellent machinability and wear resistance, attacks a bearing only to a small extent, and to provide a crank shaft produced by using the steel. SOLUTION: The steel for a crank shaft having excellent machinability and wear resistance has a composition containing, by weight, 0.55 to 0.61% C, <=0.60% Si, 1.00 to 2.00% Mn, 0.04 to 0.35% S, 0.05 to 0.50% Cr, <0.005% Al and <=0.0020% O and the balance Fe with inevitable impurities. After hot forging, the steel has a structure essentially consisting of pearlite having a pro-eutectoid ferrite fraction of <=3%, and containing sulfide inclusions with a thickness of <=20 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crankshaft steel which can eliminate induction hardening and is excellent in machinability and wear resistance, and a crankshaft manufactured using the same.

[Prior art]

2. Description of the Related Art A crankshaft of an automobile engine or the like has, as shown in FIG. 1 to be described later, a crankpin which is a connecting portion with a connecting rod and a crank journal which is a mounting portion to a cylinder block.
The rotational movement of the crankshaft is supported by a sliding bearing made of a bearing alloy mainly composed of Al, Cu, Sn or the like at the connecting portion and the mounting portion. In addition, an oil film is usually formed between a shaft (a pin or a journal of a crankshaft) and a bearing, and the shaft is rotated.

[0003] The crankpin and the crank journal receive a high surface pressure at a high speed due to the explosive force or rotational inertia force of the engine. For this reason, in the forged steel crankshaft, the surface of the conventional crankpin and crank journal that slides with the bearing is subjected to surface treatment such as induction hardening or soft nitriding in order to improve wear resistance or seizure resistance. Have been.

[0004] The crankshaft is manufactured by a casting method or a steel forging method. The former casting method is a method in which cast iron is melted and cast, and this is cut to form a crankshaft. According to the casting method, the casting has good machinability, so that it is easy to cut, and there is no need for induction hardening. Therefore, it can be manufactured at low cost. On the other hand, the latter steel forging method is a method in which a steel material is melted, its ingot is rolled, hot forged, and cut at the final point to form a crankshaft. In addition, it is necessary to perform induction hardening to improve wear resistance and seizure resistance. Therefore, this method is expensive.

However, when mounted on an engine and operated, the crankshaft of the casting method has a higher noise than the crankshaft of the steel forging method. The reason is,
This is because the crankshaft of the casting method has lower rigidity than that of the steel forged.

Accordingly, the present inventors have developed a pin, while taking advantage of the characteristics of a steel forged crankshaft having high rigidity.
We focused on the development of a low-cost crankshaft with excellent machinability, in which induction hardening of the journal part can be omitted. For that purpose, a steel material having contradictory characteristics of wear resistance and machinability is required.

Prior art relating to forged steel having excellent wear resistance is disclosed in JP-A-6-128690 and JP-A-10-1.
No. 37888 and JP-A-2000-265242. JP-A-6-128690 relates to a steel for crankshafts for forging. The composition of the steel is expressed as a weight ratio of C: 0.30 to 0.60%, Si: 0.05.
1.00%, Mn: 0.40 to 1.50%, S: 0.
04 to 0.12%, V: 0.10 to 0.40%, Cr:
0.05 to 0.50%, Ca: 0.0005 to 0.02
00%, Al: 0.005 to 0.018%, the balance being Fe and impurity elements, and Al ₂ O ₃ :
0.005% or less, SiO ₂ : 0.001% or less. In this steel, the ferrite-pearlite structure exhibits good wear resistance due to precipitation hardening of V carbide. Also, there is no need to perform induction hardening and softening on the crankpin and the crank journal of the crankshaft. In addition, fatigue strength is high due to precipitation hardening of V carbide.

However, Japanese Patent Application Laid-Open No. Hei 6-12869 discloses
Unless a relatively large amount of V is contained in the forged crankshaft steel disclosed in No. 0, the steel does not exhibit good inherent wear resistance, resulting in an increase in cost. From the viewpoint of cost, it is desired that expensive alloying elements such as V are not contained as much as possible.

Japanese Patent Application Laid-Open No. Hei 10-137888 discloses that
For the purpose of improving wear resistance, a method for producing a hot forged part having excellent wear resistance is disclosed. This manufacturing method will be described. First, C: 0.40 to 0.60%, Si:
0.01 to 0.50%, Mn: 0.3 to 2.0%,
Cr: 0.01 to 2.00%, V: 0.03 to 0.
20%, N: 0.0050 to 0.0200% (or more,
% By weight), balance: composed of iron and inevitable impurities, Ceq = C + Si / 7 + Mn / 5 + Cr / 9 + 1.5
A steel having a carbon equivalent (Ceq) represented by V in the range of 0.80 to 1.10% is hot forged to a desired part shape under a heating temperature in the range of 1150 to 1300 ° C. Then, the as-forged part is prepared, and then the forged as-prepared part thus prepared is subjected to a temperature of 0.2 to 10 ° C./sec.
Air cooling at a cooling rate within the range of, and having the following mechanical properties, Brinell hardness (HB): 250 to 290, yield stress (YP): 600 N / mm ² or more, elongation (El): 1
A rough part having a metal structure mainly composed of pearlite having a ferrite area ratio (fF) of 5% or less and a ferrite area ratio (fF) of 5% or less is prepared. Finishing is performed so that the surface roughness of the part is in the range of 5 to 25 μm.

The obtained hot forged part has a ferrite ratio of 5
% Or less, it is possible to reduce fretting wear generated in a fitting portion with other parts such as a bearing, and to have excellent wear resistance. In addition, there is no need to perform surface hardening treatment after quenching / tempering and cutting, so that a hot forged part excellent in fretting resistance can be manufactured. However, in the forged part disclosed in Japanese Patent Application Laid-Open No. 10-137888, it is necessary to increase the surface roughness of the shaft.
In an automobile engine or the like, even if the shaft (crankshaft) has good wear, there is a problem that bearing damage, particularly abnormal wear, becomes remarkable. If the operation is continued with the abnormally worn bearing, there is a danger that the shaft may be worn and seizure may occur. In addition, since the structure is mainly composed of pearlite, there is a problem that the machinability is inferior and the cost of manufacturing parts increases.

Japanese Unexamined Patent Application Publication No. 2000-265242 discloses a non-heat treated steel for hot forging having excellent wear resistance for the purpose of improving wear resistance. The composition of this steel is as follows: C: 0.40 to 0.70%, Si:
0.50% or less, Mn: 0.90 to 1.80%, Cr:
0.05-1.00%, s-Al: 0.01-0.04
5%, and N: 0.005 to 0.025%,
If necessary, Pb: 0.030% or less, S: 0.20%
Hereinafter, one or more selected from the group consisting of Te: 0.030% or less, Ca: 0.01% or less and Bi: 0.30% or less, with the balance being Fe and impurities, after hot forging Has a structure of ferrite + pearlite, and has a proeutectoid ferrite area of 10% or less.

The non-heat treated steel for hot forging according to the above invention does not require quenching and tempering after hot forging by appropriately selecting the alloy composition and regulating the area ratio of proeutectoid ferrite to a certain value or less. Non-heat-treated steel shows excellent wear resistance even without surface treatment such as induction hardening or soft nitriding after forming by machining. However, the non-heat treated steel for hot forging disclosed in Japanese Patent Application Laid-Open No. 2000-265242 contains a relatively large amount of Al and N.
There are many hard inclusions such as AlN and Al ₂ O ₃ that exhibit aggressiveness. A crankshaft of an automobile engine or the like slides and rotates through an oil film between the bearing and a sliding bearing. Under such conditions, the presence of the hard inclusions causes the bearing to wear and damage significantly. As a result, there is a problem that the shaft is worn.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide a low-cost crankshaft which is excellent in machinability and wear resistance, has low aggression to bearings, and has low cost.

[0014]

According to the first aspect of the present invention, C:
0.55 to 0.61%, Si: 0.60% or less, M
n: 1.00-2.00%, S: 0.04-0.35
%, Cr: 0.05 to 0.50%, Al: 0.005
%, O: 0.0020% or less, the balance being Fe and unavoidable impurities, the structure after hot forging is mainly pearlite having a proeutectoid ferrite fraction of 3% or less, and has a thickness of 20%.
A crankshaft steel excellent in machinability and wear resistance characterized by containing a sulfide-based inclusion of not more than μm.

The inventors of the present invention have been eager to achieve a low cost of steel bearing forged crankshaft at the same time as achieving a balance between conflicting characteristics such as wear resistance and machinability while also reducing bearing damage. As a result of repeated studies, the present invention has been achieved. i) The structure of the crankshaft steel has a ferrite fraction of 3
% Of pearlite. Further, since the amount of Al in the steel for the crankshaft is regulated to less than 0.005%, the generation of hard inclusions is suppressed. Therefore, the wear resistance of the crankshaft is improved, and damage to the bearing can be prevented. ii) S in steel for crankshafts is 0.04 to
0.35% content and 0.005% Al content
By limiting the O (oxygen) amount to 0.0020% or less, the machinability of the crankshaft can be improved. iii) Sulfide-based inclusions such as MnS generated by the inclusion of S deteriorate the wear resistance of the crankshaft when its thickness is large, but the wear resistance is ensured by setting the thickness to 20 μm or less. Can be.

As described above, the steel for crankshafts of the present invention is excellent in machinability and wear resistance, less aggressive to bearings, and low in cost. Further, quenching and tempering after hot forging are not required, and induction hardening and nitrocarburizing for wear resistance are not required. Also, the machinability is good. The reasons for limiting the amounts (% by weight) of each element in the steel for crankshafts are described below.

C: 0.55 to 0.61%, C is an element necessary for securing strength and improving wear resistance. If C is less than 0.55%, the strength and wear resistance of the steel decrease, so C needs to be 0.55% or more, preferably 0.57% or more. On the other hand, C is 0.61
%, The strength unnecessarily increases and the machinability decreases. Therefore, C is 0.61% or less, preferably 0.1%.
It needs to be 59% or less.

Si: 0.60% or less Si is an element effective as a deoxidizing aid in steel making and an element effective in improving strength and wear resistance. However, if the Si content exceeds 0.60%, the machinability is reduced. Therefore, the Si content is 0.60% or less, preferably 0.35%.
% Or less.

Mn: 1.00 to 2.00%, Mn is an element effective as a deoxidizing aid in steel making and an element necessary for ensuring the strength of the steel and improving the wear resistance. If Mn is less than 1.00%, the strength and wear resistance are reduced. Therefore, Mn needs to be 1.00% or more, preferably 1.20% or more. On the other hand, when Mn is 2.
If it exceeds 00%, a low-temperature transformation structure such as bainite or martensite is generated, and the machinability is reduced. Therefore, Mn needs to be 2.00% or less, preferably 1.60% or less.

S: 0.04 to 0.35%, S is an essential element for improving the machinability of steel.
If S is less than 0.04%, the effect cannot be obtained.
S needs to be 0.04% or more, preferably 0.13% or more. On the other hand, when S exceeds 0.35%,
S is 0.35 to impair the strength and hot workability of steel.
% Or less, preferably 0.20% or less.

Cr: 0.05 to 0.50%, Cr is an element effective for improving the wear resistance of steel. If the Cr content is less than 0.05%, the improvement cannot be expected, so the Cr content needs to be 0.05% or more, preferably 0.10% or more. On the other hand, if the Cr content exceeds 0.50%, the machinability is reduced. Therefore, the Cr content needs to be 0.50% or less, preferably 0.35% or less.

Al: less than 0.005%, A1 generates Al ₂ O ₃ and AlN which are harmful to wear resistance and machinability, and therefore must be kept as low as possible. A
When l is 0.005% or more, Al ₂ O ₃ and A
Al is required to be less than 0.005% because it causes an increase and a coarsening of 1N, thereby deteriorating wear resistance and machinability.

When O (oxygen): 0.0020% or less, and when O exceeds 0.0020%, there is a problem that the thickness of the sulfide-based inclusion becomes large and the wear resistance is reduced. Needs to be 0.0020% or less.

The structure of the steel for crankshafts after hot forging must be mainly pearlite having a pro-eutectoid ferrite fraction of 3% or less from the viewpoint of wear resistance. If the fraction of pro-eutectoid ferrite exceeds 3%, the problem of reduced wear resistance occurs.

It is necessary to regulate the thickness of the sulfide inclusions formed in the steel for crankshaft to 20 μm or less from the viewpoint of abrasion resistance. The thickness of sulfide inclusions is 20
If it exceeds μm, the wear resistance will decrease.

According to a second aspect of the present invention, in addition to the crankshaft steel, Bi: 0.0
1 to 0.30%, Pb: 0.01 to 0.30%, C
a: 0.0003-0.020%, Mg: 0.0003
To 0.020%, and REM: 0.001 to 0.10%
It is preferable to contain one or more selected from the group consisting of This further improves the machinability of the steel. Hereinafter, the significance of each element will be described.

Bi: 0.01 to 0.30%, Bi is an element effective for improving the machinability, and in order to exhibit the effect, 0.01% or more, preferably 0.02% or more. Must be included. On the other hand, when Bi is contained in excess of 0.30%, the effect is saturated, the cost is increased, and hot workability is impaired. Therefore, Bi is 0.30% or less, preferably 0.15% or less. It is necessary to

Pb: 0.01 to 0.30%, Pb is an element which is effective for improving machinability and exhibits the same effect as Bi. To exhibit the effect, 0.01% or more, preferably 0.04% or more is required. On the other hand, P
If b is contained in excess of 0.30%, the effect is saturated and the hot workability is impaired. Therefore, Pb must be 0.30% or less, preferably 0.25% or less.

Ca: 0.0003-0.020%, Ca is an element effective in improving machinability, and in order to exhibit the effect, 0.0003% or more, preferably 0.0005%. The above content is necessary. On the other hand, 0.0
If the content exceeds 20%, the effect is saturated and the cost increases, so Ca was set to 0.020% or less.

Mg: 0.0003% to 0.020% Mg exhibits the same effect as Ca, and when it is present as a composite with Ca, a large effect of improving machinability and an effect of improving anisotropy of mechanical properties are obtained. can get. In order to obtain the effect, at least Mg is 0.0003% or more, preferably 0.0003% or more.
Although the content is required to be 0.05% or more, even if it is contained more than necessary, the effect becomes saturated and is useless, so that Mg is 0.02% or more.
0% or less.

REM: 0.001 to 0.10% REM is a rare earth element effective for improving machinability. In order to exhibit its effect, REM is 0.001% or more, preferably 0.1% or more.
005% or more is required. On the other hand, REM was set to 0.
If the content exceeds 10%, the effect is saturated and the cost is increased. Therefore, the REM is set to 0.10% or less.

According to a third aspect of the present invention, there is provided a crankshaft having a pin portion and a journal portion, wherein the crankshaft is 0.55 to 0.61% by weight, Si:
0.60% or less, Mn: 1.00-2.00%, S:
0.04 to 0.35%, Cr: 0.05 to 0.50%,
Al: less than 0.005%, O: 0.0020% or less, a hot forged product obtained by hot forging a crankshaft steel comprising the balance of Fe and inevitable impurities, and the structure of the hot forged product is as follows. , Mainly composed of pearlite having a pro-eutectoid ferrite fraction of 3% or less and containing sulfide-based inclusions having a thickness of 20 μm or less. A crankshaft excellent in machinability and wear resistance characterized in that Rz is 1 μm or less.

The third aspect of the present invention is a crankshaft.
It is manufactured using the steel for crankshafts according to the invention.

The surface roughness Rz of the sliding cylindrical surface of the pin portion and the journal portion with the sliding bearing is 1 μm or less. When Rz exceeds 1 μm, the wear resistance of the crankshaft and the slide bearing deteriorates.

According to the fourth aspect of the present invention, in addition to the steel for a crankshaft used in the crankshaft, Bi: 0.01 to 0.30% by weight%,
Pb: 0.01-0.30%, Ca: 0.0003-
It preferably contains one or more selected from the group consisting of 0.020%, Mg: 0.0003 to 0.020%, and REM: 0.001 to 0.10%. This further improves the machinability of the steel for crankshafts. The crankshaft of the present invention is characterized in that:
Using the steel for crankshafts.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 First, steel for a crankshaft according to an embodiment of the present invention was prepared, and the following performance was evaluated. Samples A to I of the present invention and samples J to P for comparison, a sample Q of non-heat treated steel (conventional steel) conventionally used for a crankshaft, and a sample R of conventional cast iron were used as the crankshaft steel. Got ready. Samples A to C of samples A to I of the present invention
(1st invention product) is C: 0.55 to 0.61 by weight%.
%, Si: 0.60% or less, Mn: 1.00 to 2.00
%, S: 0.04 to 0.35%, Cr: 0.05 to
0.50%, Al: less than 0.005%, O: 0.00
The steel is composed of 20% or less, with the balance being Fe and inevitable impurities. Samples D to I were further expressed by weight: Bi: 0.01
~ 0.30%, Pb: 0.01 ~ 0.30%, Ca:
0.0003-0.020%, Mg: 0.0003-
It is a steel containing one or more selected from the group of 0.020% and REM: 0.001 to 0.10%. These components are shown in Table 1.

Each crankshaft steel was melted in a vacuum melting furnace, hot rolled, and forged to φ60 mm. afterwards,
After heating at 1200 ° C. for 30 minutes, air-cooled heat treatment was performed to obtain a test material. This process simulates an actual crankshaft forging process, and the obtained hardness and structure almost match those of an actual crankshaft for an automobile engine. From the obtained test materials, hardness test pieces, tensile test pieces, cut test pieces, and hot-worked test pieces were cut out and subjected to a test.

(Hardness, Microstructure) The hardness was measured using a Vickers hardness meter under a load of 30 kgf. After the hardness test, the polished specimen was examined with an optical microscope at a magnification of ×
Observation was made at 50 fields at 400, and the thickness of the sulfide-based inclusions was measured. As the thickness of the sulfide inclusions, the maximum value of the measured values was adopted as data. Then, 3%
It was corroded with nital, and the microstructure was observed with an optical microscope at a magnification of × 400, and the microstructure was determined and the fraction of ferrite was measured by a point counting method in 50 visual fields.

(Tensile Test) In the tensile test, tensile strength, 0.2% proof stress, elongation, and drawing were measured using a JIS 14A tensile test piece.

(Cutting Test) The cutting test was performed on the wear of a carbide tool, chip processing, and drill life, assuming a crankshaft processing step. Table 2 shows the conditions of these tests.

(Hot Working Test) In the hot working test, a high-temperature tensile test was performed at 1200 ° C. using a grease tester, and the aperture value after the test was measured.

The test results are shown in Tables 3 and 4.

[0043]

[Table 1]

[0044]

[Table 2]

[0045]

[Table 3]

[0046]

[Table 4]

From the above test results, the steels A to I of the present invention are mainly composed of pearlite having a sulfide inclusion thickness of 20 μm or less and a pro-eutectoid ferrite fraction of 3% or less.
Both properties are almost the same as conventional steel, and are suitable for use as crankshafts in terms of strength and machinability. In particular, the second invention steel (samples D to I) shows very excellent machinability. On the other hand, Comparative Steel J has a lower C content than the range of the present invention, a higher ferrite fraction, and is inferior in strength. For comparative steel K, Si
The amount is higher than the range of the present invention and the machinability is inferior. The comparative steel L was inferior in strength because the Mn content and the Cr content were lower than the range of the present invention, and the comparative steel M was conversely higher in the Mn content and the Cr content than the range of the present invention. , Bainite structure is mixed, and the machinability is poor. For the comparative steel N, the S content is lower than the range of the present invention and the machinability is inferior. For the comparative steel O, on the contrary, the S content is higher than the range of the present invention, and O (oxygen) Since the amount is also higher than the range of the present invention, the thickness of the sulfide-based inclusion is large,
Poor hot workability. About comparative steel P, Al content is higher than the range of the present invention, and is inferior in machinability.

Embodiment 2 In this embodiment, a prototype of an actual crankshaft was mounted on an engine and its wear resistance was measured. The steels to be measured are the samples A to I according to the present invention, the samples J to P for comparison, and the non-heat treated steel (conventional steel) conventionally used for crankshafts, as shown in Table 1. Q and conventional cast iron R. Of these, samples A to Q were melted in a vacuum melting furnace, hot rolled, and then hot rolled into a crankshaft 1 having a journal 11 and a pin 12 as shown in FIG. After forging, it was air-cooled. These forged crankshafts were finished by machining and subjected to a test. Sample Q was also prepared by subjecting the pin portion and the journal portion to an induction hardening treatment in which the hardened layer had a depth of 3 mm. Sample R is J
Cast iron specified by IS: FCD700-2,
After casting into a crankshaft shape by casting, it was finished by machining and used as a test sample. In this example, the mechanical finish of the pin portion and the journal portion was wrapped so that the surface roughness Rz was 0.8 μm or less in each of the test samples.

Prior to the abrasion test, each specimen was measured on the sliding surface of each pin and each journal by using a surface roughness meter to measure the average roughness Rz and straightness at 10 points in the longitudinal direction of the crankshaft. Was done. As the surface roughness Rz, the maximum value measured in each pin portion and each journal portion was adopted, and is shown in Table 5.

In the wear test, the crankshaft sample was mounted on an engine together with a sliding bearing for an automobile engine, and the engine was operated. Lubricating oil is supplied to the cylindrical sliding surface 10 of the journal portion 11 and the pin portion 12 with the slide bearing during operation.
In addition, various test conditions, such as an engine operating condition, an operating pattern, and an operating time, were set identically between the specimens.

After the abrasion test, the change in straightness of each pin and each journal of the test sample was measured again, and the amount of shaft wear was calculated from the change in straightness before and after the test. That is, as shown in FIG. 2, the shaft surface shape 31 of the crankshaft before the test and the shaft surface shape 32 after the test are measured, and the amount of change in both the portion corresponding to the width B of the slide bearing is calculated. The shaft wear amount 33 was determined. As reference data, the weight change of each slide bearing before and after the wear test was measured, and the bearing wear was calculated. The results of the shaft wear and bearing wear are the index values when the maximum value of the values measured in each pin portion and each journal portion is adopted and the result of sample R is set to 100. Indicated.

FIG. 3 shows an example of the results of the wear test. In Fig. 3, in order from the left, the induction steel is not subjected to induction hardening, the conventional steel (sample Q) is not induction hardened, the conventional steel (sample Q) is induction hardened, and the casting (sample R) shows the wear amount of the shaft and the bearing in the case of R). These values are shown as relative values when the casting material S is set to 100.

After the abrasion measurement, each pin portion and each journal portion of the sample were cut and polished, and the surface hardness and the internal hardness were measured by a Vickers hardness meter. After that, it was polished again and observed with an optical microscope at a magnification of × 400, the thickness of sulfide inclusions was measured, the structure of the surface layer was determined by microstructure observation corroded with 3% nital, and the ferrite content was determined by the point counting method. The rate was measured.
For the surface hardness, internal hardness, and ferrite fraction, the average of the values measured in each pin and each journal is used. For the sulfide thickness, the average value of each pin and each journal is used. Table 5 shows the maximum value measured in the above.

[0054]

[Table 5]

From the above results, it is clear that the steels A to I of the present invention have a sulfide-based inclusion thickness of 20 μm or less, a pearlite-based microstructure having a pro-eutectoid ferrite fraction of 3% or less, and a shaft abrasion loss. The bearing wear is almost the same as that of the conventional induction hardened steel Q, and is superior to the conventional cast iron R. On the other hand, Comparative Steel J had a lower C content than the range of the present invention, a higher ferrite fraction, and was inferior in both shaft wear and bearing wear. Comparative Steel K had a Si content lower than that of the present invention. And the shaft wear amount and bearing wear amount are comparable, but as shown in the first embodiment, the machinability is inferior. Comparative steel L
With regard to (1), since the Mn content and the Cr content are lower than the ranges of the present invention, the hardness is low and the shaft wear is inferior. On the other hand, in the comparative steel M, since the Mn content and the Cr content are higher than the range of the present invention, a bainite structure is mixed, and both the shaft wear amount and the bearing wear amount are inferior. The comparative steel N has an S amount lower than the range of the present invention and is comparable to the shaft wear amount and the bearing wear amount. However, as shown in the first embodiment, the machinability is inferior. Conversely, for steel O, the amount of S is higher than the range of the present invention, and the amount of O (oxygen) is higher than the range of the present invention. Inferior in quantity. As for the comparative steel P, the Al content was higher than the range of the present invention, and both the shaft wear amount and the bearing wear amount were inferior. Further, the conventional steel Q has a high ferrite fraction and is inferior in both shaft wear and bearing wear when induction hardening is not performed.

Embodiment 3 In this embodiment, a prototype crankshaft was mounted on an engine by changing the ferrite fraction and the surface roughness Rz of the pin portion and the journal portion, and the wear resistance was measured. The effects of the invention will be further clarified. The steel used for the measurement is the sample A according to the present invention shown in Table 1.
After melting in a vacuum melting furnace and hot rolling,
After hot forging into a crankshaft shape as shown in (1) and air-cooled (sample 1), immediately after hot forging, 900 ° C
The forged product is inserted into a heat treatment furnace heated to a temperature, held for 10 minutes, and then slowly cooled at a rate of 0.5 ° C. per minute (sample 2)
Was prepared. These forged crankshafts were finished by machining and subjected to a test.

In the present embodiment, the crankshaft of the specimen 2 was machined and finished by lapping the pin portion and the journal portion so that the surface roughness Rz was 0.8 μm or less. Regarding the crankshaft of Sample 1, the pin and journal were machined to finish with a surface roughness Rz: 0.8 μm or less (Sample 1).
-1), surface roughness Rz: 2.0 to 3.0 μm (sample 1
-2), surface roughness Rz: 4.0 to 5.0 μm (sample 1
-3).

Prior to the abrasion test, each sample was tested by using a surface roughness meter to measure the sliding surface of each pin and each journal in the longitudinal direction of the crankshaft at 10 points of average roughness: R
z (axial roughness before test) and straightness were measured. As Rz, the maximum value measured in each pin portion and journal portion was adopted, and is shown in Table 6.

In the wear test, the crankshaft sample was mounted on an engine together with a sliding bearing for an automobile engine, and the engine was operated. On the sliding surface 10 of the journal part 11 and the pin part 12 with the sliding bearing,
Lubricating oil was supplied during operation. In addition, various test conditions, such as an engine operating condition, an operating pattern, and an operating time, were set identically between the specimens.

The shaft wear amount and the bearing wear amount are determined according to the second embodiment.
It was measured by the same method as described above. That is, after the wear test, the change in straightness of each pin portion and each journal portion of the test sample was measured again, and the amount of shaft wear was calculated from the change in straightness before and after the test (see FIG. 2). As reference data, the weight change of each bearing before and after the wear test was measured.
A bearing wear amount was calculated from the weight change amount. For the results of the shaft wear amount and the bearing wear amount, the maximum value of the values measured in each pin portion and each journal portion is adopted, and an index display when the result of the sample R in the second embodiment is set to 100. And shown in Table 6.

After the above wear measurement, each pin portion and each journal portion of the sample were cut and polished, and the surface hardness and the internal hardness were measured with a Vickers hardness meter. After that, it was polished again and observed with an optical microscope at a magnification of × 400, the thickness of sulfide inclusions was measured, the structure of the surface layer was determined by microstructure observation corroded with 3% nital, and the ferrite content was determined by the point counting method. The rate was measured.
For the surface hardness, internal hardness, and ferrite fraction, the average of the values measured in each pin and each journal is used. For the sulfide thickness, the average value of each pin and each journal is used. Table 6 shows the maximum value measured in the above.

[0062]

[Table 6]

From the above results, even when the steel of the present invention is used,
Like the specimens 1-2 and 1-3, the shaft surface roughness Rz is 1
It is clear that when the size exceeds μm or when the ferrite fraction exceeds 3% as in the sample 2, the shaft wear and the bearing wear are deteriorated. Sulfide inclusion thickness is 2
If it is less than 0 μm, the wear resistance of the shaft does not decrease. That is, in the present invention, when the steel composition range, the ferrite fraction, the thickness of the sulfide-based inclusions, and the surface roughness Rz of the shaft are within the claims of the present invention, excellent wear resistance and wear resistance are obtained. It shows the machinability.

[0064]

According to the present invention, there is provided a low-cost crankshaft steel which is excellent in machinability and wear resistance, has low aggression against bearings, and a crankshaft manufactured using the same. Can be provided.

[Brief description of the drawings]

FIG. 1 is a front view of a crankshaft according to Embodiments 2 and 3.

FIG. 2 is a schematic diagram of a method of measuring a shaft wear amount in Embodiments 2 and 3.

FIG. 3 is an explanatory diagram showing an example of a wear test result in Embodiment 2.

[Explanation of symbols]

 10: sliding surface, 11: journal, 12: pin, 31: shaft surface shape, 32: shaft surface shape after test, 33: shaft wear amount,

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naoki Iwama 1 Wanowari, Arao-cho, Tokai City, Aichi Prefecture Inside Aichi Steel Co., Ltd. (72) Inventor Kazue Nomura 1-Wanowari Arao-cho, Tokai City, Aichi Prefecture Steel, Aichi Steel Co., Ltd. F-term (reference) 3J033 AA02 AB03 AB10 AC01 BA01

Claims (4)

[Claims] C .: 0.55 to 0.61% by weight,
Si: 0.60% or less, Mn: 1.00 to 2.00
%, S: 0.04 to 0.35%, Cr: 0.05 to
0.50%, Al: less than 0.005%, O: 0.00
20% or less, the balance being Fe and unavoidable impurities, the structure after hot forging is mainly pearlite with a fraction of proeutectoid ferrite of 3% or less, and contains sulfide inclusions with a thickness of 20μm or less. Steel for crankshafts with excellent machinability and wear resistance. 2. In addition to the steel for crankshafts according to claim 1, Bi: 0.01 to 0.30% by weight.
Pb: 0.01-0.30%, Ca: 0.0003-
A crankshaft containing one or more selected from the group consisting of 0.020%, Mg: 0.0003 to 0.020%, and REM: 0.001 to 0.10%. For steel. 3. A crankshaft having a pin portion and a journal portion, wherein the crankshaft has a weight percentage of
, C: 0.55 to 0.61%, Si: 0.60% or less, Mn: 1.00 to 2.00%, S: 0.04 to 0.
35%, Cr: 0.05 to 0.50%, Al: 0.00
A hot forged product obtained by hot forging a crankshaft steel containing less than 5%, O: 0.0020% or less, balance Fe and unavoidable impurities, and the structure of the hot forged product is proeutectoid ferrite. It is mainly composed of pearlite with a fraction of 3% or less and contains sulfide-based inclusions with a thickness of 20 μm or less, and the sliding surface of the pin and the journal with the sliding bearing has a surface roughness Rz of 1 μm or less. A crankshaft having excellent machinability and wear resistance. 4. In addition to the crankshaft steel used in the crankshaft according to claim 3, further comprising:
Bi: 0.01 to 0.30%, Pb: 0.01 to
0.30%, Ca: 0.0003 to 0.020%, M
g: 0.0003-0.020%, and REM: 0.0
One or two selected from the group of 01 to 0.10%
A crankshaft characterized by containing at least one species.