JP2001003117A - Production of crank shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a crank shaft having high precision and high strength, to eliminate the trouble of machining in the after-working and to improve the yield. SOLUTION: A carbon steel having compositional components of 0.46-0.48 wt.% C, <=0.14 wt.% Si, 0.55-0.65 wt.% Mn, <=0.015 wt.% P, <=0.015 wt.% S, <=0.15 wt.% Cu, <= 0.20 wt.% Ni, 0.35 wt.% Cr and the balance Fe with impurities, is continuously cold-forged to form the crank shaft and, thereafter, the crank shaft is held at 250-350 deg.C for 1-2.5 hr and an aging treatment for air- cooling to a room temp., is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for manufacturing a split crankshaft for an engine of a motorcycle or the like.

[0002]

2. Description of the Related Art A crankshaft to be incorporated in an engine of a motorcycle or the like is formed by shaping a disk-shaped split crankshaft with left and right shafts, and fitting pins into pin holes formed in respective disk-shaped weight portions. To connect the left and right split crankshafts. As a method of manufacturing the left and right split crankshafts, the mainstream is manufacturing by hot forging as disclosed in JP-A-59-4936.

[0003] Materials for hot forging include tempered steel and non-tempered steel. The tempered steel is heated (about 1200 ° C.) and then quenched and tempered to improve strength and toughness. Carbon steel used as a material for a crankshaft is tempered. In particular, in the case of hot forging, the strength of a forged product after hot forging can be enhanced by tempering utilizing the temperature of the forged product itself. The non-heat treated steel is obtained by heating (about 1200 ° C.) a material to which vanadium or the like has been added in advance and then cooling it by air to improve strength and toughness.

[0004] Incidentally, the crankshaft is provided with a worm and a tapered part in a part thereof, and the worm and the tapered part are required to have higher hardness than other parts. In order to partially harden these parts later by induction hardening or the like, the material must contain C (carbon). Therefore, as a material for hot forging for crankshafts, JISS is used.
Carbon steel such as 48C (hereinafter simply referred to as S48C) is used.

[0005] Incidentally, the component ratio of S48C is such that C is 0.1%.
45 to 0.51 wt%, Si is 0.15 to 0.35 wt% or less, Mn is 0.6 to 0.9 wt%, P is 0.03 wt% or less, S is 0.035 wt% or less, and Cu is 0.1 to 0.3 wt%. 3 wt% or less,
The standard is such that Ni is 0.2 wt% or less and Cr is 0.2 wt% or less.

[0006]

In the forming by hot forging, the mold surface is liable to wear, as a result, the accuracy of the forged product is deteriorated, the machining allowance after forging is increased, and the working efficiency is reduced. . Since the cost of lace processing is large, the number of machines increases, and the initial investment becomes enormous. In the case of hot forging, scale is generated due to forging after heating, and it is necessary to apply a release agent or the like. Therefore, it is difficult to keep the working environment optimal.

[0007] According to cold forging, the problems of molding accuracy, working environment and initial investment can be solved, but the biggest problem is that the deformability is small and cracks occur. Especially in the case of a split crankshaft, the difference in shape between the shaft and the disk-shaped weight is large and cold forging (upsetting)
Cracks are likely to occur at the time.

[0008]

In order to solve the above-mentioned problems, the present invention provides a method according to the present invention, wherein C is 0.46 to 0.48 wt% and Si is 0.1%.
4 wt% or less, Mn is 0.55 to 0.65 wt%, and P is 0.
015 wt% or less, S is 0.015 wt% or less, Cu is 0.
15 wt% or less, Ni is 0.20 wt% or less, Cr is 0.3
A continuous cold forging is performed using carbon steel containing 5 wt% or less and the balance being Fe and impurities to form a crankshaft, and then aging treatment (for example, at a temperature of 250 to 350 ° C and a temperature of 1 to 2.5 Time hold).

Here, the component ratio of the carbon steel is determined by JIS S48C (hereinafter simply referred to as S) used as a hot forging material.
48C), the content of C is almost the same as that of S48C from the viewpoint of ensuring hardenability, and Si, P, S and Cu are elements that adversely affect the deformability.
Is a component ratio in which the content of is reduced.

The reasons for setting the component composition ratio in the above range will be described below. First, C is an element having the greatest effect on the cold forgeability per unit%, and has a mechanical property, especially a material strength,
It is important in terms of hardenability. That is, the crankshaft needs a predetermined mechanical strength as a whole,
High hardness is locally required such as a worm and a tapered portion. In order to increase the hardness by quenching after forging a portion where high hardness is required locally, the proportion of C is set to 0.46.
０．４0.48 wt%.

[0011] Further, Si is present in pig iron as a raw material and is almost removed during the steel making process, but may be added as a deoxidizing agent at the end of the steel making process.
Although 35 wt% is contained and part enters steel and forms a solid solution with ferrite, it is preferably as little as possible and preferably 0.14 wt% or less as a cold forging material because it inhibits forgeability.

Although Mn remains to some extent in the steelmaking process, it is added as a deoxidizing agent.
0.90 wt% is contained. This Mn combines with S and is dispersed in the steel as manganese sulfide, and a part of the Mn is dissolved in ferrite. However, Mn that easily bonds to S becomes MnS, and this MnS tends to be a starting point of a crack during forging. Therefore, it is desirable to reduce it, but M which forms a solid solution in ferrite
n facilitates baking and suppresses the growth of crystal grains. For this reason, the amount of Mn is set to 0.55 to 0.65 wt%.

P is dissolved in ferrite in a solid solution. When P is contained in a large amount, it is combined with a part of iron to form iron phosphide.
When a solid solution forms in ferrite, elongation of the ferrite is reduced, the impact value at room temperature is also reduced, and cracks are easily generated during processing. And this P is allowed to 0.03 wt% in S48C, and this allowable value is too high for a cold forging material. Therefore, the ratio of P is set to 0.
015 wt% or less.

S combines with a part of Mn to form MnS, and this MnS becomes a starting point of a surface crack generated at the time of cold forging, and is allowed to be up to 0.035 wt% in S48C. Is too high. Therefore, the ratio of S is set to 0.015 wt% or less.

Since Cu is less oxidized than Fe when heated at high temperature, it enriches the surface and causes red-hot embrittlement. Therefore, approximately equivalent amount of Ni is added to prevent red-hot embrittlement. On the other hand, Cu, like P, may increase ferrite hardness by a small amount and impair the cold forgeability, so that Cu is set to 0.15 wt% or less.

In addition to the above-mentioned effects, Ni also has an effect of increasing hardenability, preventing low-temperature brittleness, and improving corrosion resistance.
Add the same amount as 48C. Further, Cr increases the hardenability and tempering resistance, increases the corrosion resistance, and easily forms a stable carbide. Therefore, Cr is contained in the same amount as S48C.

In cold forging the material of the above-mentioned components, first, a first spheroidizing annealing treatment is performed to spheroidize the internal carbides, and thereafter, drawing is performed at a predetermined cross-sectional reduction rate to obtain a desired size. If the spheroidizing treatment is further promoted by increasing the spheroidizing rate by promoting the dispersion of the internal carbides by the second spheroidizing annealing treatment, the hardness is reduced and the formability is improved, and the elongation rate of the surface layer portion is improved. Is also preferred.

Crankshafts are formed by cold forging using carbon steel having the composition shown in (Table 1) below, and are subjected to aging treatment for various heating and holding times as shown in (Table 2).
The surface hardness (HRC) before the aging treatment, the surface hardness (HRC) after the aging treatment, and the internal hardness (HRC) were measured, and the lattice constant of the metal crystal was analyzed by X-ray diffraction. Here, the temperature of the aging treatment was 300 ° C. A is without aging treatment.

[0019]

[Table 1]

[0020]

[Table 2]

The correlation between the hardness (HRC) before and after the aging treatment and the average lattice constant was compared and analyzed (Table 3).
It was found that the larger the average lattice constant (d value), the higher the hardness (HRC).

[0022]

[Table 3]

This means that the greater the number of lattice defects between atoms, that is, the greater the average lattice constant (d value), the higher the hardness. This is presumed to be due to the fact that subsequent cooling to the ambient temperature to the atmosphere causes precipitation between crystals and that many dislocations can be fixed.

FIG. 5 is a TEM photograph (100,000 times) showing the metal structure before the aging treatment, and FIG. 6 is a TEM photograph (100,000 times) showing the metal structure after the aging treatment. From this, it is confirmed that the number of precipitates existing between the crystals is increased after the aging treatment compared to before the aging treatment. It is considered that the hardness is improved due to the increase in the number of the precipitates, the fixation of dislocations, or the synergistic effect thereof.

The aging conditions are 250 to 35.
By maintaining the temperature at 0 ° C. for 1 to 2.5 hours and then allowing it to cool to room temperature, the improvement in hardness and mechanical strength can be maximized. This is clear from the analysis results shown in (Table 1) to (Table 3). No. of (Table 3). When the aging time is less than C (age time: 1.0H), the increase in hardness is small. D ~
No. No. F (aging time 1.5 to 2.5 H) was peaked. At G (aging time 4H), overaging has occurred and the hardness has decreased.

[0026]

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is an assembly drawing of a split crankshaft, FIG. 2 is an explanatory diagram for explaining the timing and measurement points of a hardness measurement test of the crankshaft before and after aging treatment,
FIG. 3 is a diagram showing a result of a mechanical strength test of the crankshaft according to the present invention, and FIG. 4 is a process diagram showing an example of a continuous cold forging process.

The crankshaft 1 shown in FIG. 1 includes left and right divided crankshafts 1a and 1b each having a disk shape with a shaft, and a connecting pin 1c which is connected to a pin hole p of a weight portion of the crankshafts 1a and 1b. Left and right crankshaft 1
After each of a and 1b is separately formed by continuous cold forging, each is subjected to an aging treatment according to the present invention, and then integrated by the connecting pin 1c.

First, before explaining the aging treatment after forming, an outline of a step of forming a split crankshaft by continuous cold forging from a billet will be described.

First, the composition of the billet is such that C is 0.4
6 to 0.48 wt%, Si is 0.14 wt% or less, Mn is 0.55 to 0.65 wt%, P is 0.015 wt% or less, S
Is 0.015 wt% or less, Cu is 0.15 wt% or less, Ni
0.20 wt% or less, Cr 0.35 wt% or less,
The balance is carbon steel composed of Fe and impurities.

The method for producing a billet from a rod having the above-mentioned composition is as follows: after pickling, a first spheroidizing annealing is performed to spheroidize cementite to improve the workability of the entire material, and to improve the inside of the material. Distortion can be given, and pearlite is miniaturized. Next, pickling and bonding are performed and a drawing process is performed to improve the limit upsetting rate. Next, the bar is cut into a desired size, pickled, and then subjected to a second spheroidizing annealing to disperse carbides and increase the spheroidizing rate.
When the second spheroidizing annealing is completed, the surface is adjusted by performing shot blasting and bonding to obtain a billet for cold forging.

When the billet manufactured in the above manner is prepared, as shown in FIG. 4, a multi-stage intermediate material is formed as a first step, and then the large-diameter portion is set up in a second step to expand the diameter. In the third step, the thickness of the large-diameter portion is formed in rough land asymmetrically in the left and right direction to finish the approximate shape as the weight portion.
In the fourth step, the large-diameter portion is finish-formed into a left-right asymmetrical shape, and a spline portion, a center hole, and the like are formed at necessary portions as necessary. In the fifth step, a pin hole p is punched in a part of the large-diameter portion, and at the same time, burrs on the outer periphery of the large-diameter portion are punched out simultaneously. Without molding.

The aging treatment according to the present invention is applied to the crankshaft formed in the above-described procedure, and
After holding at a temperature of 50 ° C. for 1 to 2.5 hours, it is performed by allowing to cool to room temperature.

FIG. 2 shows the procedure of a hardness measurement test of a crankshaft heated at a temperature of 300 ° C. for 2 hours, and FIG. 2A shows the timing of hardness measurement.
FIG. 2B is an explanatory diagram of hardness measurement points before aging, and FIG. 2C is an explanatory diagram of hardness measurement points after aging. Before the aging, as shown in FIG.
The surface hardness (HRC) of each part was measured, and three crankshafts No. 1 to No. 3 were used as test pieces. The results are as shown in (Table 4).

[0034]

[Table 4]

As shown in FIG. 2 (c), the hardness measurement points after the aging treatment were the surface hardness and the internal hardness at 7 points on the crankshaft. The results are as shown in (Table 5).

[0036]

[Table 5]

As a result, in the case of the No. 1 crankshaft, the average surface hardness (HRC) before aging was 23.6, whereas the average surface hardness (HRC) after aging was 23.9.
The average internal hardness (HRC) has increased to 25.8, and the average surface hardness (HRC) of the No. 2 crankshaft before aging was 23.3, whereas the average internal hardness (HRC) before aging was 23.3. Has an average surface hardness (HRC) of 24.2 and an average internal hardness (HRC) of 24.7. In the case of the No. 3 crankshaft, the average surface hardness (HRC) before aging is 2
The average surface hardness after aging (H
RC) is 24.4 and the average internal hardness (HRC) is 24.
In each case, it is confirmed that the hardness (HRC) is increased by the aging treatment.

FIG. 3 shows the results of measuring the slip torque of the crankshaft and the fatigue strength of a single unit. That is, in the crankshaft as shown in FIG. 3A, it was confirmed that the torque around the pin hole p of the left crankshaft at which the slip started satisfies the predetermined torque value.

Further, as shown in FIG. 3 (b), the SN diagram of the rotating bending fatigue test shows that the aging treatment material of the present invention (white outline) is compared with the conventional hot forged material (black solid). ) Are almost equivalent. That is, the rotary bending strength has substantially the same characteristics as the conventional hot forging material.

As shown in FIG. 3 (c), the SN diagram of the actual bending fatigue test shows that the aging treatment material (open area) of the present invention is compared with the conventional hot forging material (solid black). It shows that they are almost equivalent. That is, it can be seen that the actual bending strength has substantially the same characteristics as those of the conventional hot forging material.

[0041]

As described above, according to the method of manufacturing a crankshaft according to the present invention, a crankshaft continuously formed from a carbon steel having a predetermined component ratio is subjected to an aging treatment as a low-temperature heat treatment to provide hardness and mechanical strength. As a result, machining for surface treatment, such as using a hot forged material, and machining for assurance of accuracy can be eliminated, producing a crankshaft with excellent machining efficiency and excellent accuracy. can do. In addition, the yield is improved, and significant cost reduction is possible.

[Brief description of the drawings]

FIG. 1 is an assembled view of a split crankshaft.

FIG. 2 is an explanatory diagram illustrating timing and measurement points of a hardness measurement test of a crankshaft before and after aging treatment.

FIG. 3 is a diagram showing a result of a mechanical strength test of a crankshaft according to the present invention.

FIG. 4 is a process diagram showing an example of a continuous cold forging process.

FIG. 5 is a TEM photograph (10) showing a metal structure before aging treatment.
(0000 times)

FIG. 6 is a TEM photograph (10) showing the metal structure after the aging treatment.
(0000 times)

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[Procedure amendment]

[Submission date] April 19, 2000 (2004.1.
9)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

[0005] Incidentally, the component ratio of S48C is such that C is 0.1%.
45-0.51 wt%, Si is 0.15-0.35 wt% ,
Mn is 0.6 to 0.9 wt%, P is 0.03 wt% or less, S
Is 0.035 wt% or less, Cu is 0.3 wt% or less, Ni is 0.2 wt% or less, and Cr is 0.2 wt% or less.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tadashi Kobayashi 1-10-1 Shinsayama, Sayama City, Saitama Prefecture Honda Engineering Co., Ltd. (72) Inventor Mitsuru Kamikawa 1-10-1, Shinsayama, Sayama City, Saitama Prefecture Hong Inside Da Engineering Co., Ltd. (72) Inventor Fumio Fukuda 1500, Hirakawa, Otsu-cho, Kikuchi-gun, Kumamoto Honda Motor Co., Ltd.Kumamoto Factory (72) Inventor Hideki Matsuura 1500, Hirakawa, Otsu-cho, Kikuchi-gun, Kumamoto Honda Motor Co., Ltd F term in Kumamoto Factory (reference) 4E087 AA10 BA01 BA02 BA14 CA13 CA22 CA33 CB03 CB12 DA05 DB11 DB14 DB24 EC02 EC22 HA32 HA83 4K042 AA16 BA03 BA05 BA13 CA05 CA06 CA10 DA03 DA05 DC02 DC03 DE03

Claims (3)

[Claims] (1) C (carbon) is 0.46 to 0.48 wt%,
0.14 wt% or less of Si (silicon), 0.55 to 0.65 wt% of Mn (manganese), 0.015 wt% of P (phosphorus)
Hereinafter, S (sulfur) contains 0.015 wt% or less, Cu (copper) contains 0.15 wt% or less, Ni (nickel) contains 0.20 wt% or less, Cr (chromium) contains 0.35 wt% or less, and the balance is A method for manufacturing a crankshaft, comprising: performing continuous cold forging using a carbon steel containing Fe (iron) and impurities as a raw material to form a crankshaft; and then performing aging treatment. 2. C (carbon) is 0.46 to 0.48 wt%,
0.14 wt% or less of Si (silicon), 0.55 to 0.65 wt% of Mn (manganese), 0.015 wt% of P (phosphorus)
Hereinafter, S (sulfur) contains 0.015 wt% or less, Cu (copper) contains 0.15 wt% or less, Ni (nickel) contains 0.20 wt% or less, Cr (chromium) contains 0.35 wt% or less, and the balance is A carbon steel made of Fe (iron) and impurities is used as a raw material, and a first spheroidizing annealing step is performed on the raw material, and after the first spheroidizing annealing step, a drawing step of drawing at a predetermined cross-sectional reduction rate is performed. After the drawing step, a billet is formed by performing a second spheroidizing annealing step performed to promote the dispersion of carbides inside and increase the spheroidization rate, and to perform continuous cold forging using the billet. A method for manufacturing a crankshaft, comprising forming a crankshaft and then subjecting it to aging treatment. 3. The method for manufacturing a crankshaft according to claim 1, wherein the aging treatment is performed in a range from 250 to 3 times.
A method for manufacturing a crankshaft, wherein the method is held at a temperature of 50 ° C. for 1 to 2.5 hours, and then cooled to room temperature.