JP2002194502A - Crank shaft steel superior in both machinability and abrasion resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide crank shaft steel that is produced inexpensively and is superior in machinability and abrasion resistance with weak aggression upon bearings, and crank shaft products made of the same. SOLUTION: This crank shaft steel is superior in machinability and abrasion resistance comprising, in terms of weight %, 0.62-0.80% C, 0.60% or less Si, 0.30-1.80% Mn, 0.04-0.35% S, 0.05-0.50% Cr, less than 0.005% Al, 0.0020% or less O, and the remainder being Fe and unavoidable impurities. The steel features that its post hot rolling texture is primarily made of perlite containing 3% or less of pro-eutectoid ferrite and also contains sulfide inclusions not greater than 20 micrometer in thickness.

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 omit 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. Also,
Normally, an oil film is formed between a shaft (a pin or a journal of a crankshaft) and a bearing, and the shaft rotates.

[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 case of steel forged crankshafts, conventionally, surface treatments such as induction hardening or soft nitriding have been applied to the sliding parts of the crankpin and the crank journal with the bearing to improve wear resistance or seizure resistance. It has been subjected.

[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 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.

The prior art relating to forged steel having excellent wear resistance is listed. JP-A-6-128690 relates to steel for crankshafts for forging. The composition of this steel is expressed as a weight ratio of C: 0.30 to 0.60%, Si:
0.05 to 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
0.0200%, Al: 0.005 to 0.018%, the balance being Fe and impurity elements;
l ₂ O ₃ : 0.005% or less, SiO ₂ : 0.001%
It is as follows. 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, from the viewpoint of cost, it is desirable not to contain expensive alloying elements such as V as much as possible.

Japanese Patent Application Laid-Open No. Hei 10-137888 discloses that
A method for manufacturing a hot forged part is disclosed. To explain this manufacturing method, 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%
(Above, weight%), balance: composed of iron and unavoidable impurities, the following formula: Ceq = C + Si / 7 + Mn / 5 + Cr / 9
The carbon equivalent (Ceq) represented by + 1.5V is 0.
Steel in the range of 80 to 1.10% was changed from 1150 to 13
Hot forging into the desired part shape at a heating temperature in the range of 00 ° C. to prepare the as-forged part, and then the as-forged part prepared in this way is heated to 0.2 to 10 ° C.
/ Sec, and has the following mechanical properties, and has a Brinell hardness (HB): 250 to 290,
Yield stress (YP): 600 N / mm2 or more, elongation (E
l): A rough part having a metal structure mainly composed of pearlite having a ferrite area ratio (fF) of not more than 15% and a ferrite area ratio (fF) of not more than 5% is prepared. The surface roughness of the fitting portion is 5 to 25 μm
Finishing is performed so as to be within the range.

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 Patent Application Laid-Open No. 2000-265242 discloses a non-heat treated steel for hot forging. 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.

[0011] The non-heat treated steel for hot forging can be prepared by appropriately selecting the alloy composition and regulating the area ratio of proeutectoid ferrite to a certain value or less, so that quenching and tempering after hot forging is unnecessary. Even if high-quality steel is not subjected to surface treatment such as induction hardening or soft nitriding after forming by machining,
Shows excellent wear resistance. However, Japanese Patent Application Laid-Open
The non-heat treated steel for hot forging disclosed in Japanese Patent Application No. 0-265242 contains a relatively large amount of Al and N.
There are many hard inclusions such as N and Al2O3 which show aggressiveness to the other party. 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 it is excellent in machinability and abrasion resistance, has low aggressiveness to bearings, and is manufactured at low cost. It is intended to provide a crankshaft.

[0013]

According to the first aspect of the present invention, C:
0.62-0.80%, Si: 0.60% or less, Mn:
0.30 to 1.80%, S: 0.04 to 0.35%, C
r: 0.05 to 0.50%, Al: less than 0.005%,
O: 0.0020% or less, the balance being Fe and unavoidable impurities, the structure after hot forging is mainly pearlite having a pro-eutectoid ferrite fraction of 3% or less, and contains sulfide-based inclusions having a thickness of 20 µm or less. A steel for crankshafts having excellent machinability and wear resistance.

The present inventors have intensively studied to achieve a balance between the contradictory characteristics of wear resistance and machinability in a steel forged crankshaft at a low cost while taking into account the reduction of bearing damage. As a result, the present invention has been achieved. i) The structure of the steel for crankshaft has a ferrite fraction of 3%
The following are mainly 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 the steel for crankshafts is 0.04-0.3
5%, Al content is less than 0.005%,
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 must be ensured because the thickness is set 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, has low aggression to bearings, and is 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: 0.62 to 0.80%, C is an element necessary for securing strength and improving wear resistance. If C is less than 0.62%, the strength and wear resistance of the steel are reduced.
Preferably, it must be 0.67% or more. On the other hand, C
Exceeds 0.80%, the strength increases more than necessary and the machinability decreases, so the upper limit must be set to 0.80%, preferably 0.76% or less.

Si: 0.60% or less Si is an element effective as a deoxidizing aid at the time of steel making and is also an element effective for improving strength and wear resistance. However, if Si exceeds 0.60%, the machinability is reduced, so the upper limit must be 0.60%, preferably 0.35% or less.

Mn: 0.30 to 1.80%, Mn is an element effective as a deoxidizing aid in steel making and an element necessary for ensuring the strength of steel. Mn is 0.30
%, The lower limit is 0.3.
0%, preferably 0.40% or more. On the other hand, if Mn exceeds 1.80%, a low-temperature transformation structure such as bainite or martensite is formed, which causes a decrease in machinability. Therefore, the upper limit is 1.80%, preferably 1.80%.
It must be 50% or less.

S: 0.04 to 0.35%, S is an element indispensable for improving the machinability of steel.
If S is less than 0.04%, the effect cannot be obtained.
The lower limit needs to be 0.04%, preferably 0.13% or more. On the other hand, when S exceeds 0.35%, the strength and hot workability of steel are impaired, so the upper limit is set to 0.35%.
%, Preferably 0.20% or less.

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

Al: less than 0.005%, A1 is Al harmful to wear resistance and machinability₂O₃and
In order to generate AlN, it is necessary to keep it as low as possible. A
If l is 0.005% or more, A1₂O ₃and
AlN increase and coarsening cause wear resistance and
The upper limit is set to 0.005%, as this will deteriorate the performance.
There is a need.

If O (oxygen) is 0.0020% or less, and if O exceeds 0.0020%, there is a problem that the thickness of the sulfide-based inclusions becomes large and the wear resistance is reduced. Must be set to 0.0020%.

The structure of the steel for crankshaft after hot forging has a pro-eutectoid ferrite fraction of 3 from the viewpoint of wear resistance.
% Or less of pearlite. If the fraction of pro-eutectoid ferrite exceeds 3%, the problem of reduced wear resistance occurs.

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

According to a second aspect of the present invention, in the weight percent, C: 0.6%
2 to 0.80%, Si: 0.60% or less, Mn: 0.3
0 to 1.80%, S: 0.04 to 0.35%, Cr:
0.05 to 0.50%, V: 0.01 to 0.09%, A
l: less than 0.005%, O: 0.0020% or less, balance Fe and inevitable impurities, the structure after hot forging is mainly pearlite with a fraction of proeutectoid ferrite of 3% or less,
A crankshaft steel excellent in machinability and wear resistance, characterized by containing a sulfide inclusion having a thickness of 20 μm or less.

In the crankshaft of the present invention, in addition to the steel component of the first aspect of the present invention, V is set to 0.01 to 0.0.
Contains 9% by weight. V is an element effective for securing the wear resistance of steel. In order to obtain the effect, it is necessary to contain at least 0.01%.
%, Preferably 0.03% or more. However, if the V content exceeds 0.09%, the cost increases, so the upper limit is set to 0.09%. Other aspects of the present invention are the same as those of the first aspect.

According to a third aspect of the present invention, the steel for a crankshaft further includes Bi: 0.01 to 0.
30%, Pb: 0.01 to 0.30%, Ca: 0.00
03-0.020%, Mg: 0.0003-0.002
0% and one or more selected from the group of REM: 0.001 to 0.10%. 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 its 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 saturates, the cost increases, and the hot workability is impaired. Therefore, the upper limit is set to 0.30%, preferably 0.15%. It is necessary to:

Pb: 0.01 to 0.30%, Pb is an element effective for improving machinability and has the same effect as Bi. To exhibit the effect, 0.01% or more, preferably, Pb is used. 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.
Preferably, it is required to be 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
Even if the content exceeds 20%, the effect is saturated and the cost increases, so the upper limit is made 0.020%.

Mg: 0.0003% to 0.020% Mg exhibits the same effect as Ca, and when present in a composite with Ca, has a large effect of improving machinability and an effect of improving anisotropy of mechanical properties. 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.
020%.

REM: 0.001 to 0.10% REM is a rare earth element effective for improving machinability. 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 upper limit is set to 0.10%.

According to a fourth aspect of the present invention, there is provided a crankshaft having a pin portion and a journal portion, wherein the crankshaft is 0.62 to 0.80% by weight, Si:
0.60% or less, Mn: 0.30 to 1.80%, 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. And a sulfide-based inclusion having a thickness of 20 μm or less, which is mainly composed of pearlite having a pro-eutectoid ferrite fraction of 3% or less, and a sliding surface of the pin portion and the journal portion with a sliding bearing has a surface roughness Rz. Is not more than 1 μm, and is excellent in machinability and wear resistance.

A fourth aspect of the present invention is a crankshaft manufactured using the steel for a crankshaft according to the first aspect of the present invention.

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

The crankshaft of the present invention is excellent in machinability and wear resistance, has low aggressiveness against a sliding bearing, and is low in cost. In addition, quenching after hot forging
No tempering is required, and no induction hardening or soft nitriding for wear resistance is required. Also, the machinability is good. The crankshaft according to the present invention is slidably rotated via an oil film between, for example, a pin portion and a sliding surface of the sliding bearing and the sliding bearing. The crankshaft of the present invention
After the crankshaft steel according to the first aspect of the present invention is hot forged into a crankshaft shape, the surface roughness Rz is 1 μm.
m can be manufactured by performing a finishing process so as to be not more than m.

According to a fifth aspect of the present invention, there is provided a crankshaft having a pin portion and a journal portion, wherein the crankshaft is 0.62 to 0.80% by weight, Si:
0.60% or less, Mn: 0.30 to 1.80%, S:
0.04 to 0.35%, Cr: 0.05 to 0.50%,
V: 0.01 to 0.09%, Al: less than 0.005%,
O: a hot forged product obtained by hot forging a crankshaft steel comprising 0.0020% or less and the balance of Fe and unavoidable impurities, and the structure of the hot forged product has a pro-eutectoid ferrite fraction of 3%. The following are mainly pearlite and have a thickness of 20μ
m and sulphide inclusions of less than 1 m, and the sliding surface of the pin and the journal with the sliding bearing has a surface roughness Rz of 1 μm or less. An excellent crankshaft.

The crankshaft of the present invention is excellent in machinability and wear resistance, has low aggressiveness against a sliding bearing, and is low in cost. The crankshaft of the present invention can be manufactured using the steel for a crankshaft according to the second aspect of the present invention.

According to a sixth aspect of the present invention, the steel for a crankshaft further contains Bi: 0.01 to 0.
30%, Pb: 0.01 to 0.30%, Ca: 0.00
03-0.020%, Mg: 0.0003-0.002
0% and one or more selected from the group of REM: 0.001 to 0.10%. This further improves the machinability of the steel. The crankshaft of the present invention can be manufactured using the steel for a crankshaft according to the third aspect of the present invention.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1 A 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 Q for comparison, a sample R of non-heat treated steel (conventional steel) and a sample S of conventional cast iron conventionally used for crankshafts were used as crankshaft steel. Got ready. Among the samples A to I of the present invention, the samples A to C (first invention products) are C: 0.62 to 0.80% by weight, and Si:
0.60% or less, Mn: 0.30 to 1.80%, S:
0.04 to 0.35%, Cr: 0.05 to 0.50%,
Al: less than 0.005%, O: 0.0020% or less, balance Fe and unavoidable impurities (P, Cu, Ni, Mo, N)
Steel. Samples D and E (the second invention) are steels containing 0.01 to 0.09% V in addition to these components. Samples F to I (third invention product) were, in addition to the above components, Bi: 0.01 to 0.30%, Pb: 0.01 to
0.30%, Ca: 0.0003 to 0.020%, M
g: 0.0003-0.0020%, and REM: 0.
Steel containing one or more selected from the group of 001 to 0.10%. The components are shown in Table 1.

Each crankshaft steel was smelted in a vacuum melting furnace, hot rolled, and then 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. Thereafter, the test piece was corroded with 3% nital, and the microstructure was observed with an optical microscope at a magnification of × 400 to determine the structure and measure the ferrite fraction by the 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 No. 14A tensile test piece.

(Cutting Test) The cutting test was conducted on the carbide tool wear, 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.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

[Table 3]

[0050]

[Table 4]

From the above test results, the steels A to I of the present invention have a sulfide-based inclusion thickness of 20 μm or less and a structure mainly composed of pearlite having a proeutectoid 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, Samples F to I (third invention) exhibit extremely 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. Conversely, the comparative steel K has a higher C content than the range of the present invention and is inferior in machinability. The comparative steel L has a higher Si content than the range of the present invention and is inferior in machinability. The comparative steel M is inferior in strength because the Mn content and the Cr content are lower than the range of the present invention, and the comparative steel N is 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 O, the S content is lower than the range of the present invention and the machinability is inferior. For the comparative steel P, 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 inclusions is large and the hot workability is poor. The comparative steel Q has an Al content 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 shown in Table 1 as samples A to I according to the present invention, samples J to Q for comparison, and non-heat treated steels (conventional steels) conventionally used for crankshafts. And sample S of conventional cast iron. Of these, samples A to R were melted in a vacuum melting furnace, hot-rolled, and then hot-forged into a crankshaft having a journal portion 11 and a pin portion 12 as shown in FIG. After that, it was air-cooled.
These forged crankshafts were finished by machining and subjected to a test.

Sample R was prepared by subjecting the pin portion and the journal portion to induction hardening under the condition that the hardened layer had a depth of 3 mm. Sample S is cast iron: FCD700-2 specified by JIS. After casting into a crankshaft shape by casting, it was finished by machining to obtain 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 of the specimens was prepared by measuring the sliding surface of each pin portion and each journal portion in the longitudinal direction of the crankshaft by using a surface roughness meter with a 10-point average roughness: R
Measurements of z and straightness were made. As the surface roughness Rz, the maximum value measured in each pin and journal is adopted.
The results are 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 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. 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 amount of shaft abrasion 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 the bearing wear are shown in Table 5 using the maximum value of the values measured in each pin portion and journal portion, with the result of sample S taken as 100. Was.

FIG. 3 shows an example of the wear test results. In FIG. 3, in order from the left side, the developed steel (sample G) is not subjected to induction hardening, the conventional steel (sample R) is not subjected to induction hardening, the conventional steel (sample R) is induction hardened, The abrasion amount of the shaft and the bearing in the case of (Sample S) is shown. These values are shown as relative values when the sample S of the casting 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 surface hardness, internal hardness, and ferrite fraction, use the average of the values measured in each pin and journal.
Table 5 shows the maximum thickness of sulfide inclusions measured in each pin and journal.

[0059]

[Table 5]

From the above results, the steels A to I of the present invention have a sulfide-based inclusion thickness of 20 μm or less, a pearlite-based microstructure with a pro-eutectoid ferrite fraction of 3% or less, and a shaft wear, The amount of bearing wear is almost the same as that of the conventional induction hardened steel R, and is superior to that of the conventional cast iron. 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 both shaft wear and bearing wear. Comparative Steel K has C content and Si wear, respectively. Although the amount is higher than the range of the present invention, the amount of shaft wear and the amount of bearing wear are comparable, but as shown in the first embodiment, the machinability is inferior. Since the comparative steel L contains more Si and has a higher ferrite fraction than the range of the present invention, the shaft wear and the bearing wear are large, and the machinability is poor. As for the comparative steel M, 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 N, 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. Comparative steel O has a lower S content than the range of the present invention and is comparable in shaft wear and bearing wear. However, as shown in Example 1, the machinability is inferior. Conversely, for steel P, the S content is higher than the range of the present invention, and O
Since the (oxygen) amount is also higher than the range of the present invention, the thickness of the sulfide-based inclusion is large, and both the shaft wear amount and the bearing wear amount are inferior.
In Comparative Steel Q, 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. Also,
Conventional steel R 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 of pins and journals, and the wear resistance was measured. The effect is further clarified. The steel subjected to the measurement is the sample A according to the present invention shown in Table 1,
Melted in a vacuum melting furnace, hot-rolled, hot-forged into a crankshaft shape as shown in Fig. 1, air-cooled (sample 1), and immediately heated to 900 ° C after hot forging A forged product was inserted into the heated heat treatment furnace, held for 10 minutes, and then gradually cooled at a rate of 0.5 ° C. per minute (sample 2). These forged crankshafts were finished by machining and subjected to a test.

In the present embodiment, the crankshaft of the specimen 2 was machine-finished in the pin portion and the journal portion, and lapped so that the surface roughness Rz was 0.8 μm or less. Regarding the crankshaft of sample 1, the pin portion and the journal were machined to finish with a surface roughness Rz: 0.8 μm or less (sample 1-1) and a surface roughness Rz: 2.0 to 3.0. Various changes were made so that 0 μm (sample 1-2) and surface roughness Rz: 4.0 to 5.0 μm (sample 1-3).

Prior to the abrasion test, each of the specimens was tested by measuring the cylindrical sliding surface of each pin and each journal in the longitudinal direction of the crankshaft using a surface roughness meter in the longitudinal direction of the crankshaft: Rz ( (Shaft roughness before the test) and straightness were measured. As Rz, the maximum value measured in each pin portion and each 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. Lubricating oil is supplied to the sliding surface 10 between the journal portion 11 and the slide bearing of the pin portion 12 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 amount of shaft wear and the amount of bearing wear are determined according to the second embodiment.
It was measured in the same manner as in That is, after the wear test, the straightness change of each pin and each journal of the test sample was measured again, and the shaft wear amount was calculated from the straightness change amount before and after the test (see FIG. 2). Also, as reference data,
The weight change of each bearing before and after the wear test was measured, and from this weight change, the bearing wear was calculated from the weight change. 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 S in the second embodiment is set to 100. And shown in Table 6.

After the 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. Then, it is polished again and observed with an optical microscope at a magnification of × 400, the thickness of sulfide inclusions is measured, the structure of the surface layer is determined by observing the microstructure corroded with 3% nital, and the ferrite content is determined by the point counting method. The rate was measured.
For surface hardness, internal hardness, and ferrite fraction, use the average of the values measured in each pin and each journal, and for the thickness of sulfide inclusions, use each pin and each journal. Table 6 shows the maximum value measured in each part.

[0067]

[Table 6]

From the above results, even if 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 apparent that when the diameter exceeds μm or when the ferrite fraction exceeds 3% as in the sample 2, the shaft wear and the bearing wear increase. If the thickness of the sulfide inclusions is less than 20 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 crankshaft are within the claims of the present invention, excellent machinability and resistance to stiffness are obtained. It shows abrasion.

[0069]

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.

 ──────────────────────────────────────────────────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 F term in reference (reference) 3J033 AA02 AB03 AC01 BA20

Claims (6)

[Claims] C. 0.62 to 0.80% by weight,
Si: 0.60% or less, Mn: 0.30 to 1.80%,
S: 0.04 to 0.35%, Cr: 0.05 to 0.50
%, Al: less than 0.005%, O: 0.0020% or less, balance Fe and inevitable impurities, the structure after hot forging is mainly pearlite having a proeutectoid ferrite fraction of 3% or less, and has a thickness of 20 μm. A crankshaft steel excellent in machinability and wear resistance, characterized by containing the following sulfide inclusions. 2. C .: 0.62 to 0.80% by weight,
Si: 0.60% or less, Mn: 0.30 to 1.80%,
S: 0.04 to 0.35%, Cr: 0.05 to 0.50
%, V: 0.01 to 0.09%, Al: less than 0.005%, O: 0.0020% or less, the balance being Fe and unavoidable impurities, and the structure after hot forging has a proeutectoid ferrite fraction of 3 % Of a pearlite-based material having a thickness of not more than 20 μm and a sulfide-based inclusion having a thickness of not more than 20 μm. 3. The steel for crankshafts according to claim 1, wherein the steel for crankshafts further has a Bi: 0.01% by weight.
0.30%, Pb: 0.01 to 0.30%, Ca: 0.
0003-0.020%, Mg: 0.0003-0.0
020% and REM: steel for crankshafts, characterized by containing one or more selected from the group of 0.001 to 0.10%. 4. A crankshaft having a pin portion and a journal portion, wherein the crankshaft has a weight percentage of
, C: 0.62 to 0.80%, Si: 0.60% or less, Mn: 0.30 to 1.80%, S: 0.04 to 0.
35%, Cr: 0.05 to 0.50%, Al: 0.00
Less than 5%, O: 0.0020% or less, A hot forged product obtained by hot forging a crankshaft steel comprising the balance of Fe and unavoidable impurities, and the structure of the hot forged product is proeutectoid ferrite. The sliding surface of the pin and the journal with the sliding bearing has a surface roughness Rz of 1 μm or less, which is mainly composed of pearlite having a fraction of 3% or less and containing a sulfide inclusion having a thickness of 20 μm or less. A crankshaft with excellent machinability and wear resistance. 5. A crankshaft having a pin portion and a journal portion, wherein the crankshaft has a weight percent
, C: 0.62 to 0.80%, Si: 0.60% or less, Mn: 0.30 to 1.80%, S: 0.04 to 0.
35%, Cr: 0.05 to 0.50%, V: 0.01 to
0.09%, Al: less than 0.005%, O: 0.002
0% or less, a hot forged product obtained by hot forging a steel for a crankshaft comprising the balance of Fe and unavoidable impurities,
The structure of the hot forged product is mainly composed of pearlite having a pro-eutectoid ferrite fraction of 3% or less and contains sulfide-based inclusions having a thickness of 20 μm or less, and slides with the sliding bearing in the pin portion and the journal portion. The moving surface has a surface roughness Rz of 1μ.
m and a crankshaft excellent in machinability and wear resistance. 6. The crankshaft steel according to claim 4, wherein the steel for crankshafts further contains Bi: 0.01 to
0.30%, Pb: 0.01 to 0.30%, Ca: 0.
0003-0.020%, Mg: 0.0003-0.0
020% and REM: 0.001 to 0.10%. A crankshaft containing one or more kinds selected from the group.