JP3491612B2 - Crankshaft steel with excellent machinability and wear resistance - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a crankshaft steel which is capable of omitting induction hardening and has excellent machinability and wear resistance, and a crankshaft manufactured using the steel.

[Prior art]

A crankshaft of an automobile engine or the like has a crankpin which is a connecting portion with a connecting rod and a crank journal which is an attaching portion to a cylinder block, as shown in FIG. 1 described later.
The rotary motion of the crankshaft is supported by the sliding bearing made of a bearing alloy mainly containing Al, Cu, Sn, etc. at the connecting portion and the mounting portion. Also,
An oil film is usually formed between the shaft (crankshaft pin and journal) and the bearing to make a rotary motion.

The crank pin and the crank journal receive high surface pressure at high speed due to the explosive force or rotational inertia of the engine. Therefore, in crankshafts made from steel forging, conventionally, in order to improve wear resistance or seizure resistance, the sliding parts of the crankpin and crank journal with the bearings have been subjected to surface treatment such as induction hardening or nitrocarburizing. It has been subjected.

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, cast, and cut into a crankshaft shape. According to the casting method, since the cast product has good machinability, 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 of melting a steel material, rolling the ingot, forging in a hot state, and cutting at the final point to form a crankshaft shape.
In addition, induction hardening is required to improve wear resistance and seizure resistance. Therefore, this method is expensive.

However, when mounted on an engine and operated, the crankshaft produced by the casting method is noisier than the crankshaft produced by the steel forging method. The reason is,
This is because the cast crankshaft has lower rigidity than the steel forged one.

Therefore, the present inventors have taken advantage of the characteristics of the steel forged crankshaft having high rigidity,
We focused on the development of a low-cost crankshaft with excellent machinability, because induction hardening of the journal part can be omitted. For that purpose, a steel material having contradictory properties of wear resistance and machinability is required.

Prior arts relating to forged steel having excellent wear resistance are listed. Japanese Unexamined Patent Publication (Kokai) No. 6-128690 relates to a crankshaft steel for forging. The composition of this steel is C: 0.30 to 0.60% by weight, 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
To 0.0200%, Al: 0.005 to 0.018%, balance Fe and impurity elements, and A
l ₂ O ₃ : 0.005% or less, SiO ₂ : 0.001%
It is the following. And, in this steel, the ferrite-pearlite structure exhibits good wear resistance due to the precipitation hardening of V carbide. Further, it is not necessary to subject the crank pin and the crank journal of the crank shaft to induction hardening and softening. Further, the fatigue strength is high due to the precipitation hardening of V carbide. However, from the viewpoint of cost, it is desired that expensive alloy elements such as V are not contained as much as possible.

Further, in Japanese Patent Laid-Open No. 10-137888,
A method of manufacturing a hot forged part is disclosed. Explaining 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, wt%), balance: consisting of iron and unavoidable impurities, the following formula Ceq = C + Si / 7 + Mn / 5 + Cr / 9
The carbon equivalent (Ceq) represented by +1.5 V is 0.
Steel in the range of 80 to 1.10%, 1150 to 13
Hot forging into a desired part shape under a heating temperature in the range of 00 ° C. to prepare an as-forged part, and then the as-forged part thus prepared is carried out at 0.2 to 10 ° C.
Air-cooled at a cooling rate within the range of / sec, and has the following mechanical properties, 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 less than 15% and not more than 5% is prepared, and then a fitting portion of this rough part with another part is prepared. The surface roughness of the fitting portion is 5 to 25 μm
Finish processing is performed within the range of.

The hot forged parts obtained had a ferrite ratio of 5
%, It is possible to reduce fretting wear that occurs in fitting parts with other parts such as bearings, and it has excellent wear resistance. Further, it is not necessary to carry out surface hardening treatment after quenching / tempering and cutting, and it is possible to manufacture hot forged parts with excellent fretting wear resistance. However, in the forged component disclosed in Japanese Patent Laid-Open No. 10-137888, it is necessary to make the surface roughness of the shaft portion rough.
In an automobile engine or the like, even if the shaft (crankshaft) has good wear, there is a problem in that bearing damage, particularly abnormal wear, becomes significant. If operation is continued with abnormally worn bearings, there is a risk of shaft wear and seizure. Further, since the structure is mainly composed of pearlite, there is a problem that the machinability is poor and the manufacturing cost of parts is increased.

Further, Japanese Unexamined Patent Publication No. 2000-265242 discloses a non-heat treated steel for hot forging. The composition of this steel is C: 0.40 to 0.70% by weight, 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: 0.005-0.025%,
Pb: 0.030% or less, S: 0.20% as required
Hereafter, it contains one or more selected from Te: 0.030% or less, Ca: 0.01% or less and Bi: 0.30% or less, and the balance is Fe and impurities, and after hot forging Is characterized by ferrite + pearlite, and the area of proeutectoid ferrite is 10% or less.

The above-mentioned non-heat treated steel for hot forging is a non-heat treated steel that does not require quenching and tempering after hot forging by properly selecting the alloy composition and limiting the area ratio of proeutectoid ferrite to a certain value or less. Even if high-quality steel is not subjected to surface treatment such as induction hardening or nitrocarburizing after forming by machining,
Shows excellent wear resistance. However, this JP-A-200
The non-heat treated steel for hot forging disclosed in No. 0-265242 contains a relatively large amount of Al and N.
There are many hard inclusions such as N and Al2O3 that exhibit opponent attacking properties. The crankshaft of an automobile engine or the like slides and rotates through an oil film between the crankshaft and the sliding bearing, and the presence of the hard inclusions under such conditions causes significant wear damage to the bearing. There is a problem that the shaft will be worn out.

In view of the above-mentioned conventional problems, the present invention is excellent in machinability and wear resistance, has low aggression to bearings, and is low in cost, and is manufactured by using the steel for crankshafts. It is intended to provide a crankshaft.

[0013]

According to the invention of claim 1, in% by weight, 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, balance Fe and inevitable impurities, the structure after hot forging is mainly pearlite with a pro-eutectoid ferrite content of 3% or less, and contains sulfide-based inclusions with a thickness of 20 μm or less The steel for crankshafts is excellent in machinability and wear resistance.

The inventors of the present invention have earnestly studied to achieve both of the contradictory characteristics of wear resistance and machinability in a steel forged crankshaft at a low cost while also considering the reduction of bearing damage. As a result, the present invention has been achieved. i) The structure of the crankshaft steel has a ferrite fraction of 3%
The following are mainly pearlite. Further, since the amount of Al in the crankshaft steel is restricted 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 0.04 to 0.3 in crankshaft steel
5% content, Al content less than 0.005%,
By restricting the amount of O (oxygen) to 0.0020% or less, the machinability of the crankshaft can be improved. iii) Sulfide-based inclusions such as MnS generated by containing S deteriorate the wear resistance of the crankshaft when the thickness is large, but ensure the wear resistance because the thickness is 20 μm or less. You can

As described above, the crankshaft steel of the present invention is excellent in machinability and wear resistance, has low aggression to bearings, and is low in cost. In addition, quenching and tempering after hot forging are not necessary, and induction hardening and soft nitriding for wear resistance are also unnecessary. It also has good machinability. The reasons for limiting the amount of each element (% by weight) of the crankshaft steel are shown 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 decrease, so the lower limit is 0.62%,
Preferably, it should be 0.67% or more. On the other hand, C
If it exceeds 0.80%, the strength increases more than necessary and the machinability decreases, so the upper limit must be 0.80%, preferably 0.76% or less.

Si: 0.60% or less, Si is an element effective as a deoxidizing auxiliary material during steel making, and is also an element effective in improving strength and wear resistance. However, when Si exceeds 0.60%, the machinability is deteriorated, 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 auxiliary material during steel making, and is an element necessary for securing the strength of steel. Mn is 0.30
If it is less than%, the strength decreases, so the lower limit is 0.3.
It should be 0%, preferably 0.40% or more. On the other hand, when 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 should be 50% 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.
The lower limit must be 0.04%, preferably 0.13% or more. On the other hand, if S exceeds 0.35%, the strength and hot workability of steel are impaired, so the upper limit is 0.35%.
%, Preferably 0.20% or less.

Cr: 0.05 to 0.50%, Cr is an element effective in improving the wear resistance of steel. When Cr is less than 0.05%, no improvement can be expected, so it is necessary to set the lower limit to 0.05%, preferably 0.10% or more. On the other hand, if Cr exceeds 0.50%, the machinability deteriorates, 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 machinability_TwoO_Threeand
Since AlN is generated, it is necessary to keep it as low as possible. A
When l is 0.005% or more, A1_TwoO _Threeand
Abrasion resistance and workability due to increase in AlN and coarsening
The upper limit is 0.005% because it deteriorates the property.
There is a need.

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

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

Sulfide inclusions are formed in the crankshaft steel. The thickness of the sulfide-based inclusions must be limited to 20 μm or less from the viewpoint of wear resistance. If the thickness of the sulfide-based inclusions exceeds 20 μm, the wear resistance will decrease.

The invention of claim 2 is such that, in% by weight, 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 unavoidable impurities, and the structure after hot forging is mainly pearlite with a pro-eutectoid ferrite content of 3% or less,
A crankshaft steel having excellent machinability and wear resistance, which is characterized by containing a sulfide-based inclusion having a thickness of 20 μm or less.

The crankshaft of the present invention has a V content of 0.01 to 0.0
Contains 9% by weight. V is an element effective for ensuring the wear resistance of steel. In order to obtain that effect, at least 0.01% is required, so the lower limit is 0.01%.
%, Preferably 0.03% or more. However, if the V content exceeds 0.09%, the cost increases, so the upper limit was made 0.09%. Other points of the present invention are the same as the invention of claim 1 above.

According to a third aspect of the present invention, the crankshaft steel further comprises Bi: 0.01 to 0.
30%, Pb: 0.01 to 0.30%, Ca: 0.00
03-0.020%, Mg: 0.0003-0.002
It is preferable to contain one kind or two kinds or more selected from the group of 0% and REM: 0.001 to 0.10%. This further improves the machinability of steel. The significance of each element will be explained below.

Bi: 0.01 to 0.30%, Bi is an element effective in improving machinability, and in order to exert its effect, it is 0.01% or more, preferably 0.02% or more. Need to be included. On the other hand, when Bi is contained in excess of 0.30%, the effect is saturated, the cost becomes high, and the hot workability is impaired, so the upper limit is 0.30%, preferably 0.15%. Must be:

Pb: 0.01 to 0.30%, Pb is an element having the same effect as Bi and effective for improving the machinability, and in order to exert the effect, 0.01% or more, preferably It is necessary to contain 0.04% or more. On the other hand, P
When b is included in excess of 0.30%, the effect is saturated and the hot workability is impaired, so the upper limit is 0.30%,
This is preferably 0.25% or less.

Ca: 0.0003 to 0.020%, Ca is an element effective in improving machinability, and in order to exert its effect, 0.0003% or more, preferably 0.0005% The above contents are required. On the other hand, 0.0
Even if the content exceeds 20%, the effect is saturated and the cost increases, so the upper limit was made 0.020%.

Mg: 0.0003 to 0.020% Mg exhibits the same effect as Ca, and when it is combined with Ca, a large machinability improving effect and mechanical property anisotropy improving effect are obtained. can get. In order to obtain the effect, at least Mg is 0.0003% or more, preferably 0.003%.
It is necessary to add 0.05% or more, but even if it is contained more than necessary, the effect is saturated and useless, so the upper limit of Mg is set to 0.
It was set to 020%.

REM: 0.001 to 0.10% REM is a rare earth element effective for improving machinability, and in order to exert its effect, 0.001% or more, preferably 0.1%.
It is necessary to contain 005% or more. On the other hand, REM is 0.
Even if the content exceeds 10%, the effect is saturated and the cost increases, so the upper limit was made 0.10%.

According to a fourth aspect of the present invention, in a crankshaft having a pin portion and a journal portion, the crankshaft has a weight% of C: 0.62 to 0.80% and Si:
0.60% or less, Mn: 0.30 to 1.80%, S:
0.04 to 0.35%, Cr: 0.05 to 0.50%,
A hot forged product obtained by hot forging a crankshaft steel consisting of Al: less than 0.005%, O: 0.0020% or less, the balance Fe and unavoidable impurities, and the structure of the hot forged product is , Mainly composed of pearlite with a pro-eutectoid ferrite content of 3% or less and containing sulfide-based inclusions with a thickness of 20 μm or less. The sliding surface of the pin portion and the journal portion with the slide bearing has a surface roughness Rz. Is 1 μm or less, and the crankshaft has excellent machinability and wear resistance.

The crankshaft of the invention of claim 4 is manufactured by using the steel for crankshaft of the invention of claim 1.

The surface roughness Rz of the sliding cylindrical surface of the pin portion and the journal portion with respect to the slide bearing is 1 μm or less. If 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 aggression with respect to plain bearings, and is low in cost. Also, quenching after hot forging
No tempering is required, and neither induction hardening nor soft nitriding for wear resistance is required. It also has good machinability. The crankshaft of the present invention, for example, slides and rotates through the oil film between the sliding surface of the pin portion and the sliding bearing and the sliding bearing. The crankshaft of the present invention is
After hot forging the crankshaft steel according to the invention of claim 1 into a crankshaft shape, the surface roughness Rz is 1 μm.
It can be manufactured by subjecting it to finishing processing so that the thickness becomes m or less.

According to a fifth aspect of the present invention, in a crankshaft having a pin portion and a journal portion, the crankshaft has a weight% of C: 0.62 to 0.80% and 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, a hot forged product obtained by hot forging a crankshaft steel consisting of the balance 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
Machinability and wear resistance, characterized in that the sliding surface of the pin portion and the journal portion with the slide bearing has a surface roughness Rz of 1 μm or less, and contains sulfide-based inclusions of m or less. It is an excellent crankshaft.

The crankshaft of the present invention is excellent in machinability and wear resistance, has little attack on the slide bearing, and is low in cost. The crankshaft of the present invention can be manufactured using the steel for crankshafts of the second aspect of the present invention.

According to the sixth aspect of the present invention, the steel for crankshafts described above further has a Bi content of 0.01 to 0.
30%, Pb: 0.01 to 0.30%, Ca: 0.00
03-0.020%, Mg: 0.0003-0.002
It is preferable to contain one kind or two kinds or more selected from the group of 0% and REM: 0.001 to 0.10%. This further improves the machinability of steel. The crankshaft of the present invention can be manufactured using the steel for crankshafts of the third aspect of the present invention.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1 A crankshaft steel according to an embodiment of the present invention was prepared and the following performances were evaluated. As crankshaft steels, Samples A to I of the present invention, Comparative Samples J to Q, Sample R of non-heat treated steel (conventional steel) conventionally used for crankshafts, and Sample S of conventional cast iron were used. Got ready. Among Samples A to I of the present invention, Samples A to C (first invention product) are in weight%, 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: less than 0.005%, O: 0.0020% or less, balance Fe and unavoidable impurities (P, Cu, Ni, Mo, N)
It is made of steel. Samples D and E (second invention products) are steels containing V0.01 to 0.09% in addition to these components. Samples F to I (third invention product), in addition to the above components, were Bi: 0.01 to 0.30%, Pb: 0.01 to
0.30%, Ca: 0.0003 to 0.020%, M
g: 0.0003 to 0.0020%, and REM: 0.
It is a steel containing one kind or two or more kinds selected from the group of 001 to 0.10%. The components are shown in Table 1.

Each of the crankshaft steels was melted in a vacuum melting furnace, hot rolled, and then forged to a diameter of 60 mm. afterwards,
After heating at 1200 ° C. for 30 minutes, air-cooled heat treatment was performed to obtain a test material. This treatment imitates the actual crankshaft forging process, and the hardness and structure obtained are almost the same as those of the actual crankshaft for automobile engines. A hardness test piece, a tensile test piece, a cutting test piece, and a hot working test piece were cut out from the obtained test material and used for the test.

(Hardness, Microstructure) Hardness was measured with a Vickers hardness meter under a load of 30 kgf. After the hardness test, the polished test piece was magnified with an optical microscope.
The thickness of sulfide inclusions was measured by observing 50 fields of view at 400. For the thickness of sulfide inclusions, the maximum measured value was used as data. After that, the test piece was corroded with 3% nital, the microstructure was observed with an optical microscope at a magnification of × 400, and the structure was determined and the ferrite fraction was measured by the point counting method in 50 fields of view.

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

(Cutting Test) The cutting test was carried out on the assumption of the machining process of the crankshaft, and was carried out on wear of the cemented carbide tools, chip disposability, and drill life. The conditions of these tests are shown in Table 2.

(Hot Working Test) In the hot working test, a high temperature tensile test at 1200 ° C. was carried out by a greeble tester, and the reduction 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 were mainly composed of pearlite having a thickness of sulfide inclusions of 20 μm or less and a structure of proeutectoid ferrite fraction of 3% or less.
All properties are almost the same as conventional steel, and in terms of strength and machinability, they are suitable for use as crankshafts. In particular, Samples F to I (third invention) exhibit extremely excellent machinability. In contrast, Comparative Steel J has a C content lower than the range of the present invention, has a high ferrite fraction, and is inferior in strength. Comparative steel K, on the contrary, has a C content higher than the range of the present invention and is inferior in machinability. In Comparative Steel L, the amount of Si is higher than the range of the present invention, and the machinability is poor. 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 the Mn content and the Cr content are higher than the range of the present invention. , Mixed with bainite structure and poor machinability. The comparative steel O has an S content lower than the range of the present invention and is inferior in machinability, and the comparative steel P has an S content 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 inclusions is large and the hot workability is poor. In Comparative Steel Q, the amount of Al is higher than the range of the present invention, and the machinability is poor.

Embodiment 2 In this example, a prototype crankshaft was assembled in an engine and the wear resistance was measured. The steels to be used for the measurement are shown in Table 1, 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. 2 is a sample R and a conventional cast iron sample S. Of these, Samples A to R were melted in a vacuum melting furnace, hot rolled, and then hot forged into a crankshaft shape 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 used for testing.

As for the sample R, a sample was also prepared in which the pin portion and the journal portion were subjected to the induction hardening treatment under the condition that the quench hardened layer depth was 3 mm. Sample S was cast iron: FCD700-2 specified by JIS, and was cast into a crankshaft shape by casting, and then finished by machining to obtain a test piece. In addition, in the present embodiment, the machining finish of the pin portion and the journal portion of any of the test pieces was lapping so that the surface roughness Rz was 0.8 μm or less.

Prior to the abrasion test, each sample had a 10-point average roughness: R on the sliding surface of each pin portion and each journal portion in the longitudinal direction of the crankshaft using a surface roughness meter.
z and straightness measurements were taken. The surface roughness Rz adopts the maximum value measured in each pin and journal,
The results are shown in Table 5.

The wear test was carried out by assembling the above crankshaft specimen with the sliding bearing for an automobile engine into the engine and operating the engine. 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.
Various test conditions such as engine operating conditions, operating patterns, operating time, etc. were set to be the same among the test items.

After the abrasion test, the straightness change of each pin portion and each journal portion of the sample was measured again, and the shaft wear amount was calculated from the straightness change amount 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 of the crankshaft after the test are measured, and the change amount of both of the portions corresponding to the width B of the slide bearing is calculated. The shaft wear amount 33 was obtained. As reference data, the amount of weight change of each slide bearing before and after the wear test was measured and the amount of bearing wear was calculated. The shaft wear amount and the bearing wear amount are shown in Table 5 in the form of an index when the maximum value of the values measured in each pin portion and journal portion is adopted and the result of sample S is 100. It was

An example of the results of the abrasion test is shown in FIG. In FIG. 3, in order from the left side, when the developed steel (Sample G) is not induction hardened, the conventional steel (Sample R) is not induction hardened, and the conventional steel (Sample R) is induction hardened, the casting The amount of wear of the shaft and bearing in the case of (Sample S) is shown. These values are shown as relative values when the cast sample S is set to 100.

After the above-mentioned wear measurement, each pin portion and each journal portion of the sample was cut and polished, and the surface hardness and the internal hardness were measured with a Vickers hardness meter. Then, re-polishing and observing with an optical microscope at a magnification of × 400, thickness measurement of sulfide inclusions, microstructure observation of the microstructure corroded by 3% Nital, microstructure observation, and ferrite counting 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,
Regarding the thickness of sulfide inclusions, Table 5 shows the maximum value measured in each pin and journal.

[0059]

[Table 5]

From the above results, in Steels A to I of the present invention, the thickness of sulfide inclusions is 20 μm or less, the structure is mainly pearlite with a pro-eutectoid ferrite fraction of 3% or less, and the axial wear amount, Both the amount of bearing wear is almost the same as that of the conventional steel R induction hardened, which is superior to conventional cast iron. In contrast, Comparative Steel J has a C content lower than the range of the present invention, has a high ferrite fraction, and is inferior in both shaft wear amount and bearing wear amount, and Comparative Steel K has C content and Si content, respectively. The amount is higher than the range of the present invention and is comparable to the amount of shaft wear and the amount of bearing wear, but as shown in Embodiment 1, the machinability is poor. The comparative steel L has a large amount of Si and a high ferrite content compared with the range of the present invention, so that the shaft wear amount and the bearing wear amount are large and the machinability is poor. Since the Mn amount and the Cr amount of the comparative steel M are lower than the range of the present invention, the hardness is low and the shaft wear amount is inferior. On the contrary, in Comparative Steel N, since the Mn content and the Cr content are higher than the range of the present invention, the bainite structure is mixed and the shaft wear amount and the bearing wear amount are inferior. Regarding the comparative steel O, the amount of S is lower than the range of the present invention, and although the amount of shaft wear and the amount of bearing wear are not inferior, the machinability is inferior as shown in the first embodiment. For steel P, on the contrary, the S content is higher than the range of the present invention, and
Since the amount of (oxygen) is also higher than the range of the present invention, the thickness of the sulfide-based inclusions is large, and both the shaft wear amount and the bearing wear amount are inferior.
In Comparative Steel Q, the amount of Al is higher than the range of the present invention, and the shaft wear amount and the bearing wear amount are inferior. Also,
The conventional steel R has a high ferrite fraction and is inferior in both shaft wear amount and bearing wear amount when induction hardening is not performed.

Embodiment 3 In this embodiment, a prototype crankshaft was mounted on an engine while varying the ferrite fraction and the surface roughness of the pins and journals, and the abrasion resistance of the present invention was measured. Further clarify the effect. 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, hot forging into a crankshaft shape as shown in Fig. 1 and air cooling (test sample 1) and immediately after hot forging to 900 ° C 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./min (sample 2). These forged crankshafts were finished by machining and used for testing.

In this example, the crankshaft of the sample 2 was machined to finish the pin portion and the journal portion so that the surface roughness Rz was 0.8 μm or less. Regarding the crankshaft of the sample 1, the machine finish of the pin portion and the journal part was such that the surface roughness Rz: 0.8 μm or less (sample 1-1), the surface roughness Rz: 2.0 to 3. Various changes were made such that the surface roughness Rz was 0 μm (sample 1-2) and the surface roughness Rz was 4.0 to 5.0 μm (sample 1-3).

Prior to the wear test, each sample had a 10-point average roughness in the longitudinal direction of the crankshaft: Rz ( The axial roughness before the test) and the straightness were measured. In addition, as Rz, the maximum value of the values measured in each pin portion and each journal portion is adopted and shown in Table 6.

The wear test was carried out by assembling the above crankshaft specimen with the sliding bearing for an automobile engine into the engine and operating the engine. Lubricating oil is supplied to the sliding surface 10 between the journal portion 11 and the sliding bearing of the pin portion 12 during operation. Various test conditions such as engine operating conditions, operating patterns, operating time, etc. were set to be the same among the test items.

The shaft wear amount and the bearing wear amount are the same as those in the second embodiment.
It measured by the method similar to. That is, after the wear test, the straightness change of each pin and each journal of the 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 amount of weight change of each bearing was measured before and after the wear test, and the amount of bearing wear was calculated from this amount of weight change. The results of the shaft wear amount and the bearing wear amount are indexed when the maximum value of the values measured in each pin portion and each journal portion is adopted and the result of the sample S in Embodiment 2 is 100. The results are shown in Table 6.

After the above-mentioned wear measurement, each pin portion and each journal portion of the sample was cut and polished, and the surface hardness and the internal hardness were measured with a Vickers hardness meter. Then, re-polishing and observing with an optical microscope at a magnification of × 400, thickness measurement of sulfide inclusions, microstructure observation of the microstructure corroded by 3% Nital, microstructure observation, and ferrite counting by the point counting method. The rate was measured.
For the surface hardness, internal hardness, and ferrite fraction, the average value of the values measured in each pin and each journal is adopted, and the thickness of the sulfide inclusions is each pin and each journal. The maximum of the values measured in the section is adopted and shown in Table 6.

[0067]

[Table 6]

From the above results, even if the steel of the present invention is used,
The surface roughness Rz of the shaft is 1 as in the samples 1-2 and 1-3.
It is clear that the shaft wear amount and the bearing wear amount increase when the ferrite content exceeds 3 μm or when the ferrite fraction exceeds 3% as in the sample 2. 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 composition range of the steel, the ferrite fraction, the thickness of the sulfide-based inclusions, and the surface roughness Rz of the crankshaft are within the scope of the claims of the present invention, excellent machinability and durability It exhibits wear resistance.

[0069]

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

[Brief description of drawings]

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

FIG. 2 is a schematic diagram of a method of measuring the amount of shaft wear in the second and third embodiments.

FIG. 3 is an explanatory diagram showing an example of a wear test result in the second embodiment.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ichie Nomura 1 Wano Wari, Arao-cho, Tokai-shi, Aichi Aichi Steel Co., Ltd. (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00- 38/60

Claims (6)

(57) [Claims] 1. By weight%, 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: less than 0.005%, O: 0.0020% or less, balance Fe and unavoidable impurities, and the structure after hot forging is mainly pearlite with proeutectoid ferrite fraction of 3% or less and thickness of 20 μm. A crankshaft steel having excellent machinability and wear resistance, which is characterized by containing the following sulfide-based 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, balance Fe and unavoidable impurities, and the structure after hot forging is a proeutectoid ferrite fraction 3 % Pearlite-based and a sulfide-based inclusion having a thickness of 20 μm or less, and a steel for crankshafts excellent in machinability and wear resistance. 3. The crankshaft steel according to claim 1 or 2, further comprising Bi: 0.01-wt%.
0.30%, Pb: 0.01 to 0.30%, Ca: 0.
0003 to 0.020%, Mg: 0.0003 to 0.0
020%, and REM: 0.001-0.10%, 1 type or 2 types or more selected from the group are contained, The crankshaft steel characterized by the above-mentioned. 4. A crankshaft having a pin portion and a journal portion, wherein the crankshaft has a weight%.
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
A hot forged product obtained by hot forging a crankshaft steel containing less than 5%, O: 0.0020% or less, the balance Fe and unavoidable impurities. 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. The sliding surface of the pin portion and the journal portion with the slide bearing has a surface roughness Rz of 1 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%.
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
A hot forged product obtained by hot forging a crankshaft steel containing 0% or less of balance Fe and inevitable impurities,
The structure of the hot forged product is mainly composed of pearlite with a pro-eutectoid ferrite content of 3% or less, contains sulfide inclusions with a thickness of 20 μm or less, and slides with the slide bearing in the pin portion and the journal portion. The moving surface has a surface roughness Rz of 1μ.
A crankshaft with excellent machinability and wear resistance, which is characterized by being m or less. 6. The steel for crankshafts according to claim 4 or 5, further comprising Bi: 0.01-wt%.
0.30%, Pb: 0.01 to 0.30%, Ca: 0.
0003 to 0.020%, Mg: 0.0003 to 0.0
A crankshaft containing one kind or two or more kinds selected from the group of 020% and REM: 0.001 to 0.10%.