JP4822308B2 - Manufacturing method of hot forged non-tempered connecting rod - Google Patents

Description

【００２３】
このようにして得られたコンロッドから、引張試験片、硬さ試験片を切出し、弾性限、硬さを実測した。また、その測定値から実測弾性限感度を計算した。この結果を表２に示す。
【００２４】
【表２】

【００２５】
表２に示した結果から明らかなように、弾性限感度の推定値と実測値の間に良好な相関が認められることから、本発明に係わる熱間鍛造非調質コンロッドの製造方法において推定弾性限感度が１以上となるフェライト−パーライト組織が得られれば、現行コンロッドと同等以上の弾性限と、疲労強度を確保するに十分な硬さ（１８ＨＲＣ以上）が得られることが確認された。
【００２６】
【発明の効果】
以上説明したように、本発明に係わる熱間鍛造非調質コンロッドの製造方法においては、質量比で、Ｃ：０．３５〜０．５０％、Ｓｉ：０．１０〜０．７５％、Ｍｎ：０．１０〜１．４０％、Ｃｒ：１．００％以下、Ｃｕ：０．５０％以下、必要に応じてＳ：０．１２０％以下、Ｐｂ：０．３０％以下、Ｃａ：０．０１％以下、Ｂｉ：０．３０％以下のうちから選ばれる１種または２種以上を含み、残部Ｆｅ及び不可避不純物からなる成分組成の鋼に熱間鍛造を施したのち、その鍛造粗材に７００℃以上の温度でコイニングを施し、その後８００℃〜６００℃の間の冷却速度（コイニング後の温度が８００℃以下の場合には、その温度から６００℃までの冷却速度を１．５〜８℃／ｓに制御空冷することにより、ＨＲＣ硬さが１８〜３０であると共に、弾性限感度の推定式
（１／１００）（ｆａ／１００）^１／３（１５．８＋２６．１Ｍｎ％＋７．７５ｄ^−１／２）
＋（１／１００）（１−（ｆａ／１００）^１／３）（７９．６＋１．７２Ｓｏ^−１／２）
＋０．２８Ｓｉ％−０．７９≧１（ここで、ｆａ：平均フェライト面積率（％）、ｄ：平均フェライト粒径（ｍｍ）、Ｓｏ：平均パーライトラメラー間隔（ｍｍ））を満足するフェライト＋パーライト混合組織を得るようにしていることから、次のような優れた効果がもたらされる。
（１）成分組成や鍛造条件、さらに冷却条件を最適化したことによって、現行コンロッドと同等以上の弾性限となるフェライト−パーライト組織が得られ、Ｖなどの高価な添加元素の低減が可能となり、より安価に熱間鍛造非調質コンロッドを得ることができる。
（２）弾性限が向上するため、従来のコンロッドより低い硬さであっても必要十分な疲労強度を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a connecting rod for connecting a piston and a crankshaft in a reciprocating engine such as an automobile gasoline engine.
[0002]
[Prior art]
Conventionally, as hot forged non-tempered connecting rod steel, steel of about 22-30 is required by HRC, C: 0.37-0.43%, Si: 0.15-1.00%, 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 : 0.080 to 0.150%, Pb: 0.09% or less, and the balance was essentially steel made of Fe.
[0003]
[Problems to be solved by the invention]
However, the hot forged non-tempered connecting rod steel has a drawback of being expensive because it contains 0.080% or more of V in order to increase the hardness and elasticity limit. On the other hand, if the V content is simply reduced, the hardness and the elastic limit are lowered. Therefore, solving such a problem has been a problem in providing a connecting rod at a low cost.
[0004]
OBJECT OF THE INVENTION
The present invention has been made by paying attention to the above-mentioned problems in conventional connecting rods, and is capable of ensuring the necessary and sufficient hardness (18 HRC) and elastic limit even if the amount of V is reduced and the cost is low. It aims at providing the manufacturing method of a non-tempered connecting rod.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors have repeatedly evaluated and studied the connecting rod material and the manufacturing method thereof, and as a result, even after reducing the V amount, cooling between 800 ° C. and 600 ° C. after hot forging. (1/100) (fa / 100) ^1/3 (15.8 + 26.1 Mn% + 7.75 d ^−1/2 ) by controlling the cooling rate to 1.5-8 ° C./s.
+ (1/100) (1- (fa / 100) ^1/3 ) (79.6 + 1.72 So ^-1/2 )
+0.28 Si% + 3.38 V% −0.79 ≧ 1 (where fa: average ferrite area ratio (%), d: average ferrite particle size (mm), So: average pearlite lamellar spacing (mm)) Obtained the knowledge that the necessary elastic limit can be ensured by applying hot coining to the rough forged material as proposed in Japanese Patent Laid-Open No. 10-258335. The present invention has been completed. Also, with regard to hardness, conventionally, a hardness of 22 HRC or more was necessary to ensure 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 As a result, it was confirmed that sufficient fatigue strength was obtained with a hardness of 18 HRC or higher, and the present invention was achieved.
[0006]
That is, the method for producing a hot forged non-tempered connecting rod according to the present invention is based on the above knowledge, and in terms of mass ratio, C: 0.35 to 0.50%, Si: 0.10 to 0.0. 75%, Mn: 0.10 to 1.40%, Cr: 1.00% or less, Cu: 0.50% or less, if necessary, S: 0.120% or less, Pb: 0.30% or less, Ca: 0.01% or less, Bi: 0.3% or less selected from one or more selected from the following, after hot forging to steel consisting of the remainder Fe and inevitable impurities , the forged coarse material Is subjected to coining at a temperature of 700 ° C. or higher, and when the coarse material temperature after coining exceeds 800 ° C., the cooling rate between 800 ° C. and 600 ° C. , when the coarse material temperature is 700 ° C. or higher and 800 ° C. or lower. The cooling rate from that temperature to 600 ° C is 1.5-8 ° C respectively Controlled air cooling to / s, HRC hardness is 18-30,
(1/100) (fa / 100) ^1/3 (15.8 + 26.1 Mn% + 7.75 d ^−1/2 )
+ (1/100) (1- (fa / 100) ^1/3 ) (79.6 + 1.72 So ^−1/2 )
+0.28 Si% −0.79 ≧ 1 (where fa: average ferrite area ratio (%), d: average ferrite particle size (mm), So: average pearlite lamellar spacing (mm))) The structure is obtained, and the structure of the method for manufacturing the hot forged non-tempered connecting rod is used as a means for solving the above-described conventional problems.
[0007]
Moreover, as a suitable form of the said manufacturing method concerning this invention, it was set as the structure which performed shot peening in the state of controlled air cooling after hot forging. In addition, each component element in the present invention is an essential component except for selective components such as S, Pb, and Ca, and a component that defines only an upper limit such as Cr and Cu is included when the content is 0%. Absent.
[0008]
In the method for manufacturing a hot forged non-tempered connecting rod according to the present invention, since the material steel not containing the V amount is used, the manufacturing cost is low. In addition, in a predetermined chemical component, that is, by mass ratio, C: 0.35 to 0.50%, Si: 0.10 to 0.75%, Mn: 0.10 to 1.40%, Cr: 1.00 % Or less, Cu: 0.50% or less, if necessary, S: 0.120% or less, Pb: 0.30% or less, Ca: 0.01% or less, Bi: 0.30% or less After subjecting the steel of the component composition comprising the remaining Fe and unavoidable impurities to hot forging, the forged coarse material is subjected to coining at a temperature of 700 ° C. or higher, and then 800 ° C. to 600 ° C. By controlling air cooling to 1.5-8 ° C./s at a cooling rate between 0 ° C. (when the temperature after coining is 800 ° C. or lower, from that temperature to 600 ° C.) ,
(1/100) (fa / 100) ^1/3 (15.8 + 26.1 Mn% + 7.75 d ^−1/2 )
+ (1/100) (1- (fa / 100) ^1/3 ) (79.6 + 1.72 So ^−1/2 )
+0.28 Si% −0.79 ≧ 1 (fa: average ferrite area ratio (%), d: average ferrite particle size (mm), So: average pearlite lamellar spacing (mm)), hardness Since a ferrite + pearlite mixed structure of HRC18-30 is obtained, a necessary and sufficient elastic limit is ensured.
[0009]
Further, in the method for manufacturing a hot forged non-tempered connecting rod according to the present invention, shot peening can be performed in a controlled air-cooled state after hot forging, if necessary, and thereby, As the scale is removed, compressive residual stress is generated on the surface of the connecting rod, and the fatigue strength is improved.
[0010]
The reason why the composition of each component and the structure cooling rate are limited to the above ranges in the method for producing a hot forged non-tempered connecting rod according to the present invention will be described below.
[0011]
C: 0.35-0.50%
C is an element to be included for increasing the hardness and strength. If the content is less than 0.35%, the required hardness and strength cannot be obtained. Since the machinability is lowered, the content is set in the range of 0.35 to 0.50%.
[0012]
Si: 0.10 to 0.75%
Si is an element to be added as a deoxidizer and further to strengthen the solid solution strengthening of ferrite to improve the hardness, strength, and elasticity limits. However, if it is less than 0.10%, the solid solution strengthening of ferrite is not possible. On the other hand, if it exceeds 0.75%, the toughness and machinability deteriorate. Therefore, the content was made into the range of 0.10 to 0.75%.
[0013]
Mn: 0.10 to 1.40%
Mn is an element to be contained in order to refine the lamella spacing of the pearlite and improve the toughness of the pearlite portion and to increase the hardness, strength and elasticity limit. At this time, if it is less than 0.10%, the required hardness and strength cannot be obtained, and conversely if it exceeds 1.40%, the machinability decreases, so the content is made 0.10 to 1. The range was 40%.
[0014]
Cr: 1.00% or less Cr is an effective element for increasing hardness and strength. However, since it will become expensive if it exceeds 1.00%, the content was made 1.00% or less. Note that Cr is an essential component as described above, and does not include 0%.
[0015]
Cu: 0.50% or less Cu is a component that is often mixed as an impurity, but if it is 0.50% or less, the material is not affected, so the upper limit of its content was made 0.50%. Note that Cu does not include the case of 0%.
[0017]
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 are elements to be included for improving the machinability of steel, and these can be added as necessary. However, if the addition amount of these elements is too large, the hot forgeability and fatigue strength are reduced, so even if added, S is 0.120% or less, Pb is 0.30% or less, and Ca is 0.01%. Hereinafter, Bi needs to be 0.30% or less.
[0018]
(1/100) (fa / 100) ^1/3 (15.8 + 26.1 Mn% + 7.75 d ^−1/2 )
+ (1/100) (1- (fa / 100) ^1/3 ) (79.6 + 1.72 So ^-1/2 )
+0.28 Si% + 3.38 V% −0.79 ≧ 1
In order to ensure an elastic limit equal to or greater than that of the current product required for the connecting rod, Mn amount, Si amount, V amount, fa: average ferrite area ratio (%), d, which satisfies the above elastic limit sensitivity estimation formula : The average ferrite particle size (mm), So: The above-mentioned estimation formula of elastic limit sensitivity calculated from the average pearlite lamellar spacing (mm) must be satisfied. In addition, the lower limit of the elastic limit sensitivity of the current connecting rod steel is 1.
[0019]
Cooling rate after hot forging: 1.5-8 ° C / s
By appropriately increasing the cooling rate between 800 ° C. and 600 ° C. after hot forging, the mixed structure of ferrite and pearlite is refined and mechanical properties are improved. At this time, if the cooling rate is too slow, the necessary elastic limit and hardness cannot be obtained, and conversely, if it is too fast, bainite is generated in the structure and machinability is lowered. It was set to 1.5 to 8 ° C./s. In addition, although coining is performed at a temperature of 700 ° C. or higher after hot forging, when the temperature after coining is 800 ° C. or lower, the cooling rate from that temperature to 600 ° C. is within the above range.
[0020]
【Example】
The present invention will be specifically described below based on examples. Needless to say, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
[0021]
First, steel having the components shown in Table 1 was melted. This steel was made into a 35 mm diameter steel bar by hot rolling, then heated to 1200 ° C and forged into a connecting rod, then subjected to controlled air cooling under the conditions of coining at a temperature of 700 ° C or higher and the cooling rate shown in Table 1. Thus, a connecting rod having a predetermined structure was obtained. Further, the estimated elastic limit based on the above formula from Mn amount, Si amount, V amount, fa: average ferrite area ratio (%), d: average ferrite particle size (mm), So: average pearlite lamellar spacing (mm) Sensitivity was calculated.
[0022]
[Table 1]

[0023]
From the connecting rod thus obtained, tensile test pieces and hardness test pieces were cut out, and the elastic limit and hardness were measured. In addition, the measured elastic limit sensitivity was calculated from the measured value. The results are shown in Table 2.
[0024]
[Table 2]

[0025]
As is clear from the results shown in Table 2, since there is a good correlation between the estimated value of the elastic limit sensitivity and the actually measured value, the estimated elasticity is determined in the method for manufacturing a hot forged non-tempered connecting rod according to the present invention. It was confirmed that if a ferrite-pearlite structure having a limit sensitivity of 1 or more is obtained, an elasticity limit equal to or higher than that of the current connecting rod and a hardness sufficient for ensuring fatigue strength (18 HRC or more) can be obtained.
[0026]
【The invention's effect】
As described above, in the method for producing a hot forged non-tempered connecting rod according to the present invention, C: 0.35 to 0.50%, Si: 0.10 to 0.75%, Mn : 0.10 to 1.40%, Cr: 1.00% or less, Cu: 0.50% or less, if necessary, S: 0.120% or less, Pb: 0.30% or less, Ca: 0.0. 01% or less, Bi: including one or more selected from 0.30% or less, and after hot forging to the steel of the component composition comprising the balance Fe and inevitable impurities , Coining is performed at a temperature of 700 ° C. or higher, and then a cooling rate between 800 ° C. and 600 ° C. (if the temperature after coining is 800 ° C. or lower, the cooling rate from that temperature to 600 ° C. is 1.5 to 8 ° C. HRC hardness is 18-30 by controlled air cooling to ° C / s With the estimated ^equation of the elastic limit sensitivity (1/100) (fa / 100) 1/3 (15.8 + 26.1Mn% + 7.75d -1/2)
+ (1/100) (1- (fa / 100) ^1/3 ) (79.6 + 1.72 So ^−1/2 )
+ 0.28Si% −0.79 ≧ 1 (where, fa: average ferrite area ratio (%), d: average ferrite particle size (mm), So: average pearlite lamellar spacing (mm)) + ferrite + pearlite Since the mixed tissue is obtained, the following excellent effects are brought about.
(1) By optimizing the component composition, forging conditions, and further 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 is possible to reduce expensive additive elements such as V. A hot forged non-tempered connecting rod can be obtained at a lower cost.
(2) Since the elastic limit is improved, a necessary and sufficient fatigue strength can be obtained even if the hardness is lower than that of a conventional connecting rod.

Claims (3)

By mass ratio, C: 0.35 to 0.50%, Si: 0.10 to 0.75%, Mn: 0.10 to 1.40%, Cr: 1.00% or less, Cu: 0.50 When the forging rough material is subjected to coining at a temperature of 700 ° C. or higher after the steel containing the remaining Fe and the inevitable impurities is subjected to hot forging, and the coarse material temperature after coining exceeds 800 ° C. Is a cooling rate between 800 ° C. and 600 ° C. , and when the coarse material temperature is 700 ° C. or more and 800 ° C. or less, the cooling rate from that temperature to 600 ° C. is controlled to 1.5 to 8 ° C./s , respectively. And the HRC hardness is 18-30,
(1/100) (fa / 100) ^1/3 (15.8 + 26.1 Mn% + 7.75 d ^−1/2 )
+ (1/100) (1- (fa / 100) ^1/3 ) (79.6 + 1.72 So ^−1/2 )
+0.28 Si% −0.79 ≧ 1 (where fa: average ferrite area ratio (%), d: average ferrite particle size (mm), So: average pearlite lamellar spacing (mm))) A method for producing a hot forged non-tempered connecting rod characterized by obtaining a structure. By mass ratio, C: 0.35 to 0.50%, Si: 0.10 to 0.75%, Mn: 0.10 to 1.40%, Cr: 1.00% or less, Cu: 0.50 %, And S: 0.120% or less, Pb: 0.30% or less, Ca: 0.01% or less, Bi: 0.30% or less. After hot forging a steel composed of Fe and inevitable impurities , the forged rough material is coined at a temperature of 700 ° C. or higher, and when the coarse material temperature after coining exceeds 800 ° C. , 800 ° C. to 600 ° C. When the cooling rate is between 700 ° C. and 800 ° C. or less, the cooling rate from that temperature to 600 ° C. is controlled to 1.5-8 ° C./s , respectively , and the HRC hardness Is 18-30,
(1/100) (fa / 100) ^1/3 (15.8 + 26.1 Mn% + 7.75 d ^−1/2 )
+ (1/100) (1- (fa / 100) ^1/3 ) (79.6 + 1.72 So ^−1/2 )
+0.28 Si% −0.79 ≧ 1 (where fa: average ferrite area ratio (%), d: average ferrite particle size (mm), So: average pearlite lamellar spacing (mm))) A method for producing a hot forged non-tempered connecting rod characterized by obtaining a structure. 3. The method for producing a hot forged non-tempered connecting rod according to claim 1, wherein shot peening is performed after hot forging in a controlled air cooling state.