JP2003055715A - Method for producing hot forged non-heat treated connecting rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a hot forged non-heat treated connecting rod which can secure sufficient hardness of >=18HRC and a sufficient elastic limit even when inexpensive stock steel having a reduced V content is used. SOLUTION: Steel having a composition containing 0.35 to 0.50% C, 0.10 to 0.75% Si, 0.10 to 1.40% Mn, <=1.00% Cr and <=0.50% Cu, and, if required, further containing one or more kinds selected from <=0.08% V, <=0.120% S, <=0.30% Pb, <=0.01% Ca and <=0.30% Bi is hot-forged, and is subjected to coining at >=700 deg.C. After that, the steel is subjected to controlled air cooling at a cooling rate of 1.5 to 8 deg.C/s in the range of 800 to 600 deg.C, so that the connecting rod having hardness of 18 to 30HRC, and provided with a ferrite + pearlite mixed structure satisfying a conditional equation calculated from Mn, Si and V, the average ferrite area ratio, the average ferrite grain size, the average pearlite lamellar intervals is obtained.

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 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, as a hot forged non-heat treated connecting rod steel, HRC of about 22 to 30 is required, and C:
0.37 to 0.43%, Si: 0.15 to 1.00%,
Mn: 0.60 to 1.10%, P: 0.030% or less,
S: 0.070% or less, Cr: 0.40% or less, Cu:
0.50% or less, Mo: 0.05% or less, V: 0.08
The steel used was 0 to 0.150%, Pb: 0.09% or less, and the balance being substantially Fe.

[0003]

However, since the above-mentioned hot forged non-heat treated connecting rod steel contains V in an amount of 0.080% or more in order to increase hardness and elastic limit,
It had the drawback of being expensive. On the other hand, simply reducing the V content lowers the hardness and elastic limit, and thus solving such a problem has been a problem in providing a connecting rod at low cost.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems in the conventional connecting rod, and it is necessary to secure a necessary and sufficient hardness (18HRC) and an elastic limit even if the amount of V is reduced and the cost is reduced. It is an object of the present invention to provide a method for manufacturing a hot forged non-heat treated connecting rod that can be manufactured.

[0005]

In order to achieve the above object, the present inventors repeated various evaluations and studies on a connecting rod material and a manufacturing method thereof, and as a result, after hot forging, even if the V content was reduced, By controlling the cooling rate between 800 ° C. and 600 ° C. to 1.5-8 ° C./s by air cooling, (1 /
100) (fa / 100) ^1/3 (15.8 + 26.1 Mn% +
7.75d ^-1/2 ) + (1/100) (1- (fa / 10
0) ^1/3 ) (79.6 + 1.72So ^-1/2 ) + 0.28Si
% + 3.38V% −0.79 ≧ 1 (where fa: average ferrite area ratio (%), d: average ferrite grain size (m
m), So: a ferrite + pearlite mixed structure satisfying the average pearlite lamellar spacing (mm)) is obtained, and the forged rough material is hot coined as proposed in JP-A-10-258335. As a result, the inventors have obtained the knowledge that the required elastic limit can be secured, and completed the present invention. Regarding hardness, conventionally, hardness of 22 HRC or more was required to secure fatigue strength, but from the above knowledge, the elastic limit was improved and the fatigue limit was increased, and shot peening was performed as necessary. 18H
It was confirmed that sufficient fatigue strength can be obtained with a hardness of RC or more, and the present invention has been completed.

That is, the method for manufacturing a hot forged non-heat treated connecting rod according to the present invention is based on the above-mentioned findings, and in a mass ratio, C: 0.35 to 0.50%, Si: 0.
10 to 0.75%, Mn: 0.10 to 1.40%, C
r: 1.00% or less, Cu: 0.50% or less, V: 0.08% or less, and / or S: 0.12 as required.
0% or less, Pb: 0.30% or less, Ca: 0.01% or less, Bi: 0.30% or less, a steel containing one or two or more kinds and the balance substantially Fe. After performing hot forging, the forging rough material is subjected to coining at a temperature of 700 ° C. or higher, and then air-cooled by controlling the cooling rate between 800 ° C. and 600 ° C. to 1.5-8 ° C./s, and then HRC. The hardness is 18-30 and (1/100) (fa / 10
0) ^1/3 (15.8 + 26.1 Mn% + 7.75d ^-1/2 ) +
(1/100) (1- (fa / 100) ^1/3 ) (79.6 + 1.
72So- ^{1 / 2} ) + 0.28Si% + 3.38V% -0.
79 ≧ 1 (however, fa: average ferrite area ratio (%),
d: average ferrite grain size (mm), So: average pearlite lamellar spacing (mm)), and a structure for obtaining a ferrite + pearlite mixed structure is obtained. It is characterized in that it is a means for solving the above-mentioned conventional problems.

A preferred embodiment of the manufacturing method according to the present invention is characterized in that after hot forging, shot peening is performed in a controlled air-cooled state. In addition, each component element in the present invention is V, S, P
All components other than the selective components such as b and Ca are essential components, and components having only an upper limit such as Cr and Cu whose content is 0% are not included.

[0008]

In the method for manufacturing a hot forged non-heat treated connecting rod according to the present invention, since the raw material steel containing no V amount or even containing V amount is reduced to 0.08% or less, Manufacturing cost is low. In addition, a predetermined chemical component, that is, a mass ratio of C: 0.35 to 0.5
0%, Si: 0.10 to 0.75%, Mn: 0.10
1.40%, Cr: 1.00% or less, Cu: 0.50%
Hereinafter, if necessary, V: 0.08% or less, and / or S: 0.120% or less, Pb: 0.30% or less, C
a: 0.01% or less, Bi: 0.30% or less, and 1 or 2 or more selected, and the balance substantially Fe.
After hot forging a steel having a composition of the following composition, the forging rough material is coined at a temperature of 700 ° C. or higher, and then a cooling rate between 800 ° C. and 600 ° C. is 1.5-8 ° C. /
By controlled air cooling to s, (1/100) (fa / 1
00) ^1/3 (15.8 + 26.1 Mn% + 7.75d ^-1/2 )
+ (1/100) (1- (fa / 100) ^1/3 ) (79.6+
1.72So ^-1/2 ) + 0.28Si% + 3.38V%-
0.79 ≧ 1 (where fa: average ferrite area ratio (%), d: average ferrite grain size (mm), So: average pearlite lamellar spacing (mm)), and hardness H
Since a ferrite + pearlite mixed structure of RC18 to 30 is obtained, a necessary and sufficient elastic limit is secured.

Further, in the method for manufacturing a hot forged non-heat treated connecting rod according to the present invention, shot peening can be performed after hot forging in a controlled air-cooled state, if necessary. As the scale on the material surface is removed, compressive residual stress is generated on the surface of the connecting rod, and the fatigue strength is improved.

In the following, in the method for producing a hot forged non-heat treated connecting rod according to the present invention, the reason why each component composition, the structure cooling rate, etc. are limited to the above range will be explained.

C: 0.35-0.50% C is an element to be contained in order to increase hardness and strength, and if less than 0.35%, necessary hardness and strength cannot be obtained. On the other hand, if the content is more than 0.50%, the toughness and machinability deteriorate, so the content is 0.35 to 0.
The range was 50%.

Si: 0.10 to 0.75% Si is an element to be contained as a deoxidizing agent and for improving the hardness, strength and elastic limit by solid solution strengthening ferrite. If it is less than 10%, the solid solution strengthening of ferrite will be insufficient, and if it is more than 0.75%, toughness and machinability will decrease. Therefore, the content is set to the range of 0.10 to 0.75%.

Mn: 0.10 to 1.40% Mn is an element contained to refine the lamellar spacing of pearlite, improve the toughness of the pearlite portion, and increase the hardness, strength and elastic limit. is there. At this time,
If it is less than 0.10%, the required hardness and strength cannot be obtained, and conversely if it is more than 1.40%, the machinability decreases, so its content should be 0.10 to 1.40%. The range was set.

Cr: 1.00% or less Cr is an effective element for increasing hardness and strength. However, if the content exceeds 1.00%, it becomes expensive, so the content is set to 1.00% or less. In addition,
Cr is an essential component as described above and does not include the case of 0%.

Cu: 0.50% or less Cu is a component often mixed as an impurity, but if it is 0.50% or less, it does not affect the material, so the upper limit of its content is 0.50%. And It should be noted that Cu does not include the case of 0%.

V: 0.08 or less V is an element effective for precipitation strengthening ferrite and increasing hardness, strength and elastic limit. Further, since V carbonitride becomes a nucleus of ferrite generation, it is an effective element for refining ferrite. Therefore, it can be added if necessary, but if added in excess of 0.08%, it becomes very expensive, so V was made 0.08% or less.

S: 0.120% or less, Pb: 0.30% or less, Ca: 0.01% or less, Bi: 0.30% or less S, Pb, Ca and Bi improve the machinability of steel. It is an element to be contained in order to add, and these can be added if necessary. However, if the addition amount of these elements is too large, the hot forgeability and the fatigue strength are deteriorated. Therefore, even if added, S is 0.120% or less, Pb is 0.30% or less, and Ca is 0.01% or less. Hereinafter, Bi needs to be 0.30% or less.

(1/100) (fa / 100) ^1/3 (15.8)
+26.1 Mn% + 7.75d ^-1/2 ) + (1/100) (1
-(Fa / 100) ^1/3 ) (79.6 + 1.72So ^-1/2 ) +
0.28Si% + 3.38V% −0.79 ≧ 1 In order to secure an elastic limit equal to or higher than that of the current product required for the connecting rod, M satisfying the above equation for elastic limit sensitivity is satisfied.
n amount, Si amount, V amount, fa: average ferrite area ratio (%), d: average ferrite grain size (mm), So: average pearlite lamellar interval (mm) Need to be satisfied. The lower limit of the elastic limit sensitivity of the current connecting rod steel is 1.

Cooling rate after hot forging: 1.5 to 8 ° C./s By appropriately increasing the cooling rate between 800 ° C. and 600 ° C. after hot forging, a mixed structure of ferrite and pearlite can be obtained. It becomes finer and the mechanical properties are improved.
At this time, if the cooling rate is too slow, the required elastic limit, hardness cannot be obtained, and conversely, if it is too fast, bainite is generated in the structure and machinability deteriorates. It was set to 1.5 to 8 ° C / s.

[0020]

EXAMPLES The present invention will be specifically described below based on examples. It is needless to say that the present invention is not limited to the above-described embodiments and can be implemented in various modified forms without departing from the spirit of the present invention.

First, steels having the components shown in Table 1 were melted. This steel is hot-rolled into φ35 mm steel bar, heated to 1200 ° C to forge a connecting rod, then coined at a temperature of 700 ° C or higher, and controlled air cooling is performed under the cooling rate conditions shown in Table 1. Then, a connecting rod having a predetermined tissue was obtained. Also, Mn amount, Si amount, V
From the amount, fa: average ferrite area ratio (%), d: average ferrite grain size (mm), So: average pearlite lamellar spacing (mm), the estimated elastic limit sensitivity was calculated based on the above formula.

[0022]

[Table 1]

From the connecting rod thus obtained,
Tensile test pieces and hardness test pieces were cut out and the elastic limit and hardness were measured. The measured elastic limit sensitivity was calculated from the measured values. The results are shown in Table 2.

[0024]

[Table 2]

As is clear from the results shown in Table 2, since there is a good correlation between the estimated value and the measured value of the elastic limit sensitivity, the method for producing the hot forged non-heat treated connecting rod according to the present invention. It was confirmed that if a ferrite-pearlite structure with an estimated elastic limit sensitivity of 1 or more is obtained, an elastic limit equal to or higher than that of the current connecting rod and hardness (18 HRC or more) sufficient to secure fatigue strength can be obtained. It was

[0026]

As described above, in the method for manufacturing a hot forged non-heat treated connecting rod according to the present invention, C: 0.35 to 0.50% and Si: 0.10 to 0 by mass ratio. ．
75%, Mn: 0.10 to 1.40%, Cr: 1.00
% Or less, Cu: 0.50% or less, V: 0.
08% or less, and / or S: 0.120% or less, P
b: 0.30% or less, Ca: 0.01% or less, Bi:
After hot forging a steel containing one or two or more kinds selected from 0.30% or less, and the balance consisting essentially of Fe, the forged raw material is heated at a temperature of 700 ° C. or more. Coining is performed, and then the cooling rate between 800 ° C. and 600 ° C. is controlled by air cooling at 1.5 to 8 ° C./s, whereby the HRC hardness is 18 to 30 and the elastic limit sensitivity estimation formula (1 / 100) (fa / 100) ^1/3 (15.8 + 2
6.1 Mn% + 7.75d ^-1/2 ) + (1/100) (1-
(fa / 100) ^1/3 ) (79.6 + 1.72So ^-1/2 ) +
0.28 Si% + 3.38 V% −0.79 ≧ 1 (however,
fa: average ferrite area ratio (%), d: average ferrite grain size (mm), So: average pearlite lamellar spacing (mm)). The excellent effect is brought about. (1) By optimizing the component composition, forging conditions, and cooling conditions, a ferrite-pearlite structure having an elastic limit equal to or higher than that of the current connecting rod can be obtained, and it becomes possible to reduce expensive additive elements such as V, A hot forged non-heat treated connecting rod can be obtained at a lower cost. (2) Since the elastic limit is improved, necessary and sufficient fatigue strength can be obtained even if the hardness is lower than that of the conventional connecting rod.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI Theme Coat (reference) C22C 38/20 C22C 38/20 38/60 38/60 (72) Inventor Hiroshi Idojiri Nada Kobe City Hyogo Prefecture 2 Nadahama Higashi-cho, Ku Within the Kado Steel Works (72) Inventor Tomonori Miyazawa 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Yoshio Okada 2 Takara-cho, Kanagawa, Yokohama, Japan Nissan Motor Co., Ltd. In-house (72) Inventor Koji Itakura 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Kai Naito 2 Takara-cho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd. (72) Inventor, Shiogase Kinoyuki 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (72) Inventor Jun Yoshida Kanagawa-ku, Yokohama-shi, Kanagawa 2 Takaramachi F-term in Nissan Motor Co., Ltd. (reference) 3J033 AA04 AB03 AC01 4E087 BA02 CA11 CA17 CB01 DB01 DB17 HA34 4K032 AA03 AA05 AA08 AA11 AA14 AA16 AA28 AA29 AA31 AA36 BA00 CD02

Claims (5)

[Claims] 1. A mass ratio of C: 0.35 to 0.50%,
Si: 0.10 to 0.75%, Mn: 0.10 to 1.4
After hot forging a steel containing 0%, Cr: 1.00% or less, Cu: 0.50% or less and the balance substantially consisting of Fe, coining the forged raw material at a temperature of 700 ° C. or more. After that, the cooling rate between 800 ° C. and 600 ° C. is controlled by air cooling at 1.5-8 ° C./s, and the HRC hardness is 18-
30 and (1/100) (fa / 100) ^1/3 (1
5.8 + 26.1 Mn% + 7.75d ^−1/2 ) + (1/10
0) (1- (fa / 100) ^1/3 ) (79.6 + 1.72So
^-1/2 ) + 0.28Si% -0.79 ≧ 1 (however, fa:
Average ferrite area ratio (%), d: average ferrite grain size (mm), So: average pearlite lamellar spacing (m
A method for producing a hot forged non-heat treated connecting rod, characterized in that a ferrite + pearlite mixed structure satisfying m)) is obtained. 2. A mass ratio of C: 0.35 to 0.50%,
Si: 0.10 to 0.75%, Mn: 0.10 to 1.4
0%, Cr: 1.00% or less, Cu: 0.50% or less,
V: 0.08% or less, the balance is steel which consists essentially of Fe, after hot forging is performed, the forging raw material is subjected to coining at a temperature of 700 ° C or higher, and then 800 ° C to 600 ° C.
Controlling the cooling rate between 1.5 ° C and 1.5-8 ° C / s by air cooling,
HRC hardness is 18-30 and (1/100)
(fa / 100) ^1/3 (15.8 + 26.1 Mn% + 7.7
5d ^-1/2 ) + (1/100) (1- (fa / 100) ^1/3 ) (7
9.6 + 1.72So ^-1/2 ) + 0.28Si% + 3.3
8V% -0.79 ≧ 1 (however, fa: average ferrite area ratio (%), d: average ferrite grain size (mm), So:
A method for producing a hot forged non-heat treated connecting rod, characterized by obtaining a ferrite + pearlite mixed structure satisfying an average pearlite lamellar spacing (mm). 3. A mass ratio of C: 0.35 to 0.50%,
Si: 0.10 to 0.75%, Mn: 0.10 to 1.4
0%, Cr: 1.00% or less, Cu: 0.50% or less,
And S: 0.120% or less, Pb: 0.30% or less,
Ca: 0.01% or less, Bi: 0.30% or less, and one or more selected from the rest, and the balance substantially F
After hot forging the steel consisting of e, coining the forged raw material at a temperature of 700 ° C or higher, and then 800
The cooling rate between ℃ and 600 ℃ is controlled by air cooling at 1.5-8 ℃ / s, the HRC hardness is 18-30, and (1
/ 100) (fa / 100) ^1/3 (15.8 + 26.1 Mn%
+ 7.75d ^-1/2 ) + (1/100) (1- (fa / 100)
^1/3 ) (79.6 + 1.72So ^-1/2 ) + 0.28Si%-
0.79 ≧ 1 (however, fa: average ferrite area ratio (%), d: average ferrite grain size (mm), So: average pearlite lamellar spacing (mm)) to obtain a ferrite + pearlite mixed structure. A method for manufacturing a hot forged non-heat treated connecting rod. 4. A mass ratio of C: 0.35 to 0.50%,
Si: 0.10 to 0.75%, Mn: 0.10 to 1.4
0%, Cr: 1.00% or less, Cu: 0.50% or less,
V: 0.08% or less, S: 0.120% or less, P
b: 0.30% or less, Ca: 0.01% or less, Bi:
Steel containing at least one selected from 0.30% or less and the balance consisting essentially of Fe is subjected to hot forging, and then the forged raw material is subjected to coining at a temperature of 700 ° C. or more. Then, the cooling rate between 800 ° C. and 600 ° C. is controlled by air cooling at 1.5-8 ° C./s, and the HRC hardness is 18-
30 and (1/100) (fa / 100) ^1/3 (1
5.8 + 26.1 Mn% + 7.75d ^−1/2 ) + (1/10
0) (1- (fa / 100) ^1/3 ) (79.6 + 1.72So
^-1/2 ) + 0.28Si% + 3.38V% -0.79 ≧ 1
(However, fa: average ferrite area ratio (%), d: average ferrite grain size (mm), So: average pearlite lamellar spacing (mm)) to obtain a ferrite + pearlite mixed structure hot Manufacturing method of forged non-heat treated connecting rod. 5. The method for producing a hot-forged non-heat treated connecting rod according to claim 1, wherein shot peening is performed in a controlled air-cooled state after the hot forging.