JPH09196044A - Manufacture of connecting rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connecting rod excellent in both buckling strength and fatigue strength by hot-forging low carbon boron steel into a connecting rod shape, then quenching it, and applying coining and shot peening to forged material. SOLUTION: Raw material formed of low carbon boron steel is hot-forged into a connecting rod shape and then quenched, and coining and shot peening is applied to obtained forged material without tempering it. Since coining is applied in the quenched state with high dislocation density, the forged material 1 is positively hardened, and buckling strength as a connecting rod is improved. Since the raw material steel contains low carbon, over-hardening is not generated even in the quenched state, and the dispersion of quenching ability caused by low carbonization is dissolved at a low cost by adding boron. Residual tensile stress generated by coining is made disappear by shot peening, and residual compressive stress is generated so as to improve the fatigue strength of the connecting rod.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a connecting rod (hereinafter referred to as "connecting rod") for connecting a piston and a crankshaft in a reciprocating engine such as an automobile gasoline engine.

[0002]

2. Description of the Related Art Conventionally, the above connecting rod is hot-forged and then tempered after medium forging of medium carbon steel such as S40C specified in JIS G 4051 (carbon steel for machine structure). It was manufactured by subjecting the forged raw material thus obtained to a slight cold forging (coining), and further machining the large end and the small end of the raw material, the cap mating surface and the like.

Alternatively, a forging raw material obtained by hot forging vanadium-added medium carbon steel obtained by adding vanadium to the above-mentioned medium carbon steel and then air-cooling without quenching / tempering is similarly subjected to coining. And were manufactured by machining.

[0004]

However, in the above-described conventional method for manufacturing the connecting rod, even in the case of the method of quenching and tempering the hot forged medium carbon steel, the medium carbon steel containing vanadium is hardened and quenched. Even in the method of hot-forging and air-cooling without tempering, although it is work-hardened by coining, the yield strength of the rough forged material is rather reduced, and the buckling strength, which is one of the most important performance requirements for connecting rods, In addition to the problem that it is not obtained, there is a problem that fatigue strength is reduced because tensile stress is generated by coining, and solving these problems has been a problem in the conventional connecting rod manufacturing method.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above problems in the conventional method of manufacturing a connecting rod, and provides a method of manufacturing a connecting rod capable of obtaining a connecting rod excellent in both buckling strength and fatigue strength. The purpose is to do.

[0006]

In order to achieve the above-mentioned object, the present inventor has made earnest studies on the constituent steel composition of the connecting rod, the heat treatment method, the cold working, etc. Since the low carbon steel left as it is does not excessively harden and has a high dislocation density, it can be easily work-hardened by the subsequent cold working to improve the yield strength and buckling strength. I came to find what I could do.

The present invention is based on the above findings, and the method for producing a connecting rod according to claim 1 of the present invention is a forging obtained by hot forging low carbon boron steel into a connecting rod shape, followed by quenching. In the method for producing a connecting rod according to claim 2 as an embodiment of the method for producing a connecting rod according to the present invention, the plastic deformation margin in the coining is the forged roughening. The carbon content of the low carbon boron steel is 0.03 to 0.03 in the method for producing a connecting rod according to claim 3, which is also characterized in that the thickness is 0.2 mm or more in the thickness direction of the material. 0.10 weight percent and boron content of 0.0010 to 0.0040 weight percent And which further claims 4
In the method for producing a connecting rod according to (1), the low carbon boron steel has a manganese content of 1.0 to 2.0% by weight, and the configuration of the method for producing such a connecting rod has been described above. This is a means for solving the conventional problems.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a connecting rod according to the present invention, low carbon boron steel is used as a raw material steel,
After forming into a connecting rod shape by hot forging, quenching is performed, and the obtained forged rough material is subjected to work hardening by being coined, and further subjected to shot peening to improve fatigue strength.

Generally, coining is a mild cold forging which is carried out for the purpose of correcting the thickness of a hot forged product. However, in the method of the present invention, at the same time as the thickness correction, the connecting rod, especially the rod portion, is processed. The buckling strength is improved by hardening, and for that purpose, the plastic deformation margin is set to 0.2 mm or more in the thickness direction of the forged rough material, as described in claim 2. Is desirable, depending on the size of the connecting rod and the required performance, 0.2 mm to 2.0 m
m can be selected.

Low carbon boron steel is used as the raw material steel. Particularly, as described in claim 3, carbon and boron contents are 0.03 to 0.10 weight percent and 0.1%, respectively. It is desirable to use low carbon boron steel at 0010 to 0.0040 weight percent,
As components other than carbon and boron, those containing 1.0 to 2.0 weight percent manganese can be used as described in claim 4. further,
Along with the above boron and manganese, a small amount of chromium, molybdenum or the like may be added as an auxiliary component for ensuring the hardenability of the low carbon steel and eliminating the variation in hardness.

[0011]

In the method of manufacturing the connecting rod according to the first aspect of the present invention, the raw material made of low carbon boron steel is hot forged into the connecting rod shape and then quenched, and the obtained forged rough material is tempered. Instead, coining and shot peening are performed, and since coining is performed while quenching with a high dislocation density, the forged rough material is surely work hardened, and the buckling strength as a connecting rod is improved. Also, since the material steel is low carbon,
Even if it is hardened as it is, it will not be excessively hardened, and the variation in hardenability due to low carbon content will be eliminated at low cost by adding boron. Then, by performing shot peening, the tensile residual stress caused by coining disappears and the compressive residual stress occurs, so that the fatigue strength of the connecting rod is improved.

As an embodiment of the connecting rod manufacturing method according to the present invention, in the connecting rod manufacturing method according to claim 2, a plastic deformation of 0.2 mm or more is applied in the thickness direction of the forged raw material during coining. Therefore, the buckling strength is surely improved by work hardening.

Similarly, in the method for producing a connecting rod according to claim 3 as an embodiment, the carbon content is 0.03 to
0.10 weight percent, boron content 0.0010
Since 0.0040 weight percent of low carbon boron steel is used, the buckling strength will be further improved by coining, and the hardness of the forged rough material will be moderate, and it will be performed after shot peening. It is easy to machine.

That is, when the carbon content of the low carbon boron steel is less than 0.03 weight percent, it is difficult to obtain the strength required for the connecting rod, and conversely 0.10.
If it exceeds the weight percentage, the hardness of the rough material becomes too high due to quenching, which makes machining difficult.

Boron is added to secure the hardenability which has become unstable due to the low carbon content as described above, and when the content is less than 0.0010% by weight, the above effect is obtained. Is not exhibited, and uneven baking is likely to occur, and when it exceeds 0.0040 weight percent, inclusions are formed with other alloy elements, and the strength as a connecting rod is rather lowered.

As an embodiment, in the method for producing a connecting rod according to claim 4, the manganese content is 1.0 to
Since 2.0% by weight of low carbon boron steel is used, variations in hardenability due to low carbon are effectively eliminated, and the strength required as a connecting rod is secured. That is, manganese, like boron, has the effect of stabilizing the hardenability that has become unstable due to low carbonization, and when the content is less than 1.0 weight percent, Such an effect cannot be obtained, and conversely 2.
If it exceeds 0 weight percent, the hardness after quenching becomes too high, which makes machining difficult and increases the processing cost.

[0017]

EXAMPLES Hereinafter, the method for producing a connecting rod according to the present invention will be described more specifically based on examples.

Embodiment 1 FIG. 1 is a process chart showing the procedure of a method for manufacturing a connecting rod according to the present invention.

First, as the raw material steel, C: 0.05 wt%,
Si: 0.20 wt%, Mn: 1.5 wt%, Cr:
A low carbon boron steel having a composition of 0.20 wt% and B: 0.002 wt% is heated to about 1200 ° C., hot forged into a connecting rod shape, and quenched in water at a temperature of about 1050 ° C. with strong stirring. Thus, a forged rough material was obtained.

Next, the forged raw material obtained as described above is
As shown in FIG. 2, after the plastic deformation margin d = 1.0 mm was coined, a 0.8 mm diameter steel ball having a hardness of 47 HRC was shot at a shot speed of 35 m / sec on the rod portion of the forged rough material. By projecting, arc height 0.30
Shot peening corresponding to mmA was performed.

Then, the rough material after shot peening was subjected to a predetermined machining process to finish a connecting rod having a predetermined size.

One of the two connecting rods thus obtained was subjected to a compression tester to measure the buckling strength, and the other connecting rod was subjected to a bending fatigue tester to investigate the fatigue strength. Table 1 shows the results.

In addition, the effect of buckling strength on the coining amount of the above material steel was investigated, and the manganese level was set to 3 without significantly changing the composition of the material steel.
The hardness after quenching was measured when using the material of the component system changed in stages, and the influence of manganese on the quenching hardness was investigated. These results are shown in FIG. 3 and Table 2, respectively.

[0024]

[Table 1]

[0025]

[Table 2]

Comparative Example 1 As a raw material steel, C: 0.48 wt%, Si: 0.20 wt
%, Mn: 0.75 wt% medium carbon steel is heated to about 1200 ° C. and hot forged into a connecting rod shape,
After quenching in oil which was weakly stirred at a temperature of about 1050 ° C., it was tempered to a temperature of 600 ° C., and the obtained forged rough material was subjected to coining with a plastic deformation margin d = 1.0 mm. Next, the obtained rough material was subjected to the same machining to finish the connecting rod having the same size as that of the above-mentioned embodiment.

Then, using the two connecting rods thus obtained, the same compression test and bending fatigue test as those in the above-mentioned examples were carried out to obtain the buckling strength and the fatigue strength, respectively. The results are shown in Table 1.

Comparative Example 2 As a raw material steel, C: 0.40 wt%, Si: 0.21 wt
%, Mn: 0.80 wt%, V: 0.10 wt% Vanadium-added medium carbon steel was heated to about 1200 ° C., hot forged into a connecting rod shape, and then air-cooled as it was. Plastic deformation to forged rough material d =
A 1.0 mm coining was applied.

Then, the obtained rough material was subjected to the same machining to finish the connecting rod having the same size as that of the above-mentioned embodiment.

Then, using the two connecting rods thus obtained, the same compression test and bending fatigue test as those in the above-mentioned examples were carried out to obtain the buckling strength and the fatigue strength, respectively. The results are shown in Table 1.

As is clear from these results, Comparative Example 1 in which medium carbon steel was quenched and tempered and then coined, and vanadium-added medium carbon steel was coined without quenching and tempering. In the case of the applied Comparative Example 2, the buckling strength and the fatigue strength are low, whereas
It was confirmed that in the case of the examples of the present invention in which low carbon boron steel was quenched, and subjected to coining and shot peening without tempering, both buckling strength and fatigue strength were excellent, and excellent performance as a connecting rod was satisfied. It was

In the low carbon boron steel of the present invention, the hardness after quenching can be secured by setting the manganese content to 1.0% or more, and the coining amount is 0.2 mm or more. It was confirmed that the buckling strength was significantly improved by applying the plastic deformation of.

[0033]

As described above, according to the first aspect of the present invention.
In the method of manufacturing the connecting rod related to, the low carbon boron steel material is hot forged and then quenched, and the obtained forged rough material is subjected to coining and shot peening without tempering, so that plasticity by coining The work hardening based on the deformation increases the yield strength and enables the improvement of the buckling strength, and the shot peening causes the compressive residual stress, which has an extremely excellent effect of improving the fatigue strength of the connecting rod.

In the connecting rod manufacturing method according to claim 2 as an embodiment of the connecting rod manufacturing method according to the present invention, a plastic deformation of 0.2 mm or more is applied in the thickness direction of the forged raw material during coining. Therefore, the buckling strength can be surely improved, and in the method for producing a connecting rod according to claim 3 as an embodiment, the carbon content is 0.03 to 0.10 weight percent and the boron content is 0. Since 0.0010 to 0.0040 weight percent of low carbon boron steel is used, the buckling strength can be more reliably improved and the hardness of the rough material after quenching becomes appropriate. , The burden of machining is reduced, and the processing cost can be reduced.
Furthermore, in the method for producing a connecting rod according to claim 4, since the low carbon boron steel having a manganese content of 1.0 to 2.0 weight percent is used, the hardenability of the rough material is further stable. As a result, the excellent effect that the strength as a connecting rod can be secured is brought about.

[Brief description of the drawings]

FIG. 1 is a process drawing showing a procedure of a method for manufacturing a connecting rod according to the present invention.

FIG. 2 is a schematic view showing the outline of coining in the method for manufacturing a connecting rod according to the present invention.

FIG. 3 is a graph showing the relationship between the amount of coining and buckling strength in the method for manufacturing a connecting rod according to the present invention.

[Explanation of symbols]

 1 Forged rough material d Plastic deformation margin

Claims (4)

[Claims] 1. A method for producing a connecting rod, which comprises hot forging low carbon boron steel into a connecting rod shape, quenching, and then coining and shot peening the obtained forged rough material. 2. The method for producing a connecting rod according to claim 1, wherein the plastic deformation margin in the coining is 0.2 mm or more in the thickness direction of the forged rough material. 3. The carbon content of low carbon boron steel is 0.03.
~ 0.10 weight percent, boron content 0.001
It is 0-0.0040 weight%, The manufacturing method of the connecting rod of Claim 1 or Claim 2 characterized by the above-mentioned. 4. The manganese content of low carbon boron steel is 1.
It is 0 to 2.0 weight%, The manufacturing method of the connecting rod in any one of Claim 1 thru | or 3 characterized by the above-mentioned.