JPH10306317A - Production of connecting rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a connecting rod having high strength and high precision by previously subjecting steel having a specified compsn. as the stock to preform working using a bar stock as-rolled, once heating it to a specified temp. or above, subjecting it to forging into the shape of a connecting rod in a specified temp. range, subsequently executing quenching such as water cooling and transforming it into martensite. SOLUTION: A steel having a compsn. contg. C, Si and one or more kinds among Mn, Cr, Ni, Cu, Mo, W, Ta, V, Nb and B as hardenability improving elements so as to satisfy prescribed relation is used as the stock. This is subjected to preform working by cold plastic working such as forging, roll working or the like or machining using a bar stock as-rolled or as-subjected to softening heat treatment such as tempering or the like, is once heated to the Ac3 point or above as a blank for forging, is forged in the temp. range of 550 to 950 deg.C into the shape of a connecting rod, is thereafter subjected to quenching such as water cooling, oil cooling or the like and is transformed into martensite.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, high-precision connecting rod suitable for manufacturing a connecting rod used for connecting a piston and a crankshaft in a reciprocating engine as a high-strength, high-precision connecting rod. The present invention relates to a method for manufacturing a rod.

[0002]

2. Description of the Related Art Conventionally, in the production of connecting rods, generally, hot forging by a deburring method is employed.

[0003] However, it is difficult to ensure sufficient accuracy in the hot forging by such a deburring method.
Further, there is a disadvantage that the material yield is considerably poor.

In recent years, a closed forging method that does not generate burrs has been put to practical use in order to increase the precision of a connecting rod. However, this closed forging method has a disadvantage in that a forging load becomes considerably large. is there.

[0005] In order to further improve the accuracy, attempts have been made to use a high-precision blank by performing a cold preform before forging or to lower the forging temperature. .

In order to reduce the weight of such a connecting rod having high precision, the strength is set to 1100 MPa.
In the case of high strength exceeding that of conventional ferrite and pearlite steel, conventional ferrite and pearlite steel cannot sufficiently cope with it. There is a problem that it is difficult to secure high accuracy due to cracks and the like.

Therefore, in order to enable the production of a connecting rod having high strength and high precision, cold preformability (cold forgeability) is good and warm forgeability during closed forging is required. In addition, there is a problem that a material that can be quenched from a relatively low temperature after warm forging is required.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and has good cold preformability (cold plastic workability such as cold forging). It is possible to manufacture a high-strength and high-precision connecting rod using steel that is excellent in warm forgeability during closed forging and that can be quenched from a relatively low temperature after warm forging. It is intended to be.

[0009]

According to a first aspect of the present invention, there is provided a method for manufacturing a connecting rod, wherein: C: 0.04 to 0.15% by weight, Si:
0.08 to 0.50%, and as hardenability improving elements, Mn: 3.0% or less, Cr: 3.0% or less,
Ni: 4.0% or less, Cu: 1.0% or less, Mo: 3.
0% or less, W: 0.5% or less, Ta: 0.5% or less,
V: 0.3% or less, Nb: 0.08% or less, B: 0.0
One or more selected from 1% or less of manganese equivalent (Mn) having quenchability represented by the following formula:
eq) 3.4 ≦ Mneq ≦ 6.0 Mneq = Mn (%) + Cr (%) + Ni (%) / 2+
Cu (%) + Mo (%) + W (%) + Ta (%) + V
(%) + 10 (Nb (%) − 0.02) + XB (however, when B is contained in a range of 0.0005% or more and 0.01% or less, XB = 1.0), the balance being Fe and impurities Using steel consisting of, as it is, in a rolled state, or using a bar that has been subjected to softening heat treatment such as annealing, plastic working such as forging or roll working in advance,
Alternatively, a preform process is performed by a cutting process, and then, as a blank for forging, once heated to a temperature of ₃ points or more of Ac, forged into a connecting rod shape in a temperature range of 550 to 950 ° C., and thereafter, water-cooled, or It is characterized in that quenching such as oil cooling is performed to form martensite.

[0010] In an embodiment of the method for manufacturing a connecting rod according to the present invention, as described in claim 2, A is contained in the steel as a nitride-forming element.
1: 0.1% or less, and Ti: 0.1% or less.

Similarly, in an embodiment of the method of manufacturing a connecting rod according to the present invention, as described in claim 3, S:
0.3% or less, Pb: 0.3% or less, Bi: 0.15%
Hereinafter, one or two or more selected from Te: 0.1% or less and Ca: 0.05% or less can be included.

Similarly, in the embodiment of the method for manufacturing a connecting rod according to the present invention, as described in claim 4, after quenching by water cooling or oil cooling, the temperature of 200 to 600 ° C. The aging treatment can be performed for one minute or more in the temperature range.

Similarly, in an embodiment of the method for manufacturing a connecting rod according to the present invention, a shot peening process is performed after quenching such as water cooling or oil cooling. You can also do so.

[0014]

Next, the reasons for limiting the chemical composition (% by weight) of the steel used in the method of manufacturing a connecting rod according to the present invention will be described.

C: Martensite hardness is determined by the content of C, and also has the effect of increasing the deformation resistance during metastable austenite. Therefore, C
By setting the content in the range of 0.04 to 0.15%, deformation resistance during metastable austenite is low, and a strength of about 1100 to 1600 MPa can be secured.

Si: Si is an element that enhances the hardenability of steel, but at the same time, increases the deformation resistance, especially the deformation resistance in the cold state.
The range was 0.50%.

Mn: Mn is an element that enhances the hardenability of steel, but also an element that increases deformation resistance, like Si. Therefore, the upper limit of the Mn content is determined and is set to 3.0% or less.

Cr: Cr is an element that enhances the hardenability of steel, and is an element that precipitates carbide during tempering to increase tempering softening resistance. However, Cr is set to 3.0% or less because Cr easily forms a primary carbide and reduces the deformability during forging.

Ni, Cu: Ni and Cu are elements that enhance the hardenability of steel without increasing deformation resistance.
Even if a large amount is contained, the effect is saturated, so that the content of Ni is set to 4.0% or less, and the content of Cu is set to 1.0% or less.

Mo, W, Ta: Mo, W, Ta is an element that enhances the hardenability of steel and also increases the tempering softening resistance. However, similarly to Cr, the effect of lowering the deformability at the time of forging works. Therefore, Mo was set to 3.0% or less, W was set to 0.5% or less, and Ta was set to 0.5% or less.

V: V is an element effective for improving the hardenability of steel by setting the content of V to 0.3% or less.
0.3% or less.

Nb: Nb is an element effective for improving the hardenability of steel, but its solid solubility is quite small, so its upper limit was made 0.08%.

B: When B is contained in a very small amount, it has an effect of remarkably enhancing the hardenability of steel, and more preferably 0.000.
5% or more. However, if the content is too large, the hardenability is rather reduced, so the content is set to 0.01% or less.

Al: Al combines with N to form a stable nitride to prevent coarsening of crystal grains, thereby ensuring good toughness. However, when the content increases, the forgeability is reduced, so that the content is set to 0.1% or less.

Ti: Ti, like Al, has the effect of forming a stable nitride and preventing coarsening of crystal grains, thereby ensuring good toughness. When B is added,
N has the effect of preventing it from becoming N. However, when the content increases, the forgeability is reduced, so that the content is set to 0.1% or less.

S, Pb, Bi, Te, Ca: S, Pb,
Bi, Te and Ca have the effect of enhancing the machinability of steel,
Since it is also an element that inhibits forgeability, even if it is contained, 0.3% or less for S and 0.3% for Pb.
%, Bi is 0.15% or less, Te is 0.1% or less, and Ca is 0.05% or less.

Fe: Fe is the balance of steel because it is a basic component of steel.

Mneq: Manganese equivalent (Mneq) indicating the hardenability of steel is as follows: Mneq = Mn (%) + Cr (%) + Ni (%) / 2+
Cu (%) + Mo (%) + W (%) + Ta (%) + V
(%) + 10 (Nb (%) − 0.02) + XB (XB = 1.0 when B is contained in a range of 0.0005% or more and 0.01% or less).
When q is 3.4 or more, stable forging and quenching becomes possible, so Mneq was set to 3.4 or more. On the other hand,
When Mneq is 6.0 or less, excellent forgeability, especially excellent deformability is exhibited, and when Mneq is 6.0 or less, good cold preform workability can be obtained. Therefore, Mneq was set to 6.0 or less.

The steel to which the present invention having such a chemical component composition is applied has good cold preform workability (cold plastic workability such as cold forgeability), and also has the property at the time of closed forging. It has excellent warm forgeability and can be hardened at a relatively low temperature after warm forging.

In the method for manufacturing a connecting rod according to the present invention, a steel having the chemical composition as described above is used as a raw material, and a rod in a rolled state or in a state subjected to softening heat treatment such as annealing is used in advance. Plastic working such as forging or roll working in the cold, or preform processing by cutting, and then heated to a _three- point temperature or more once as a blank for forging, forming a connecting rod shape in the temperature range of 550 to 950 ° C Forging is performed, and thereafter, quenching such as water cooling or oil cooling is performed to form martensite. This will be described in more detail below. In the following description, steel having the chemical composition and the manganese equivalent (Mneq) shown in Tables 1, 2 and 3 will be used, and FIGS.
A description will be given based on the results of examining various characteristics shown in FIG.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

In the normal case, when quenching is performed from work-hardened unrecrystallized austenite including metastable (500 ° C. or more) austenite, the formation of ferrite, pearlite, and bainite, which are diffusion transformations, is remarkably promoted. However, the hardenability is greatly reduced.

Therefore, in order to perform forging and quenching from a low temperature as in the present invention, sufficient hardenability must be ensured.

Conversely, if sufficient hardenability is secured,
By quenching from work hardened austenite,
A considerably higher strength can be obtained.

When forging a metastable austenite, the deformation resistance increases mainly in proportion to the C content. This is because C forms a solid solution in austenite.

The deformation resistance at this time has a considerably larger value than the case where processing is performed immediately after heating directly to the forging temperature (in the case of a normal method), even at the same temperature. This is because in a normal method, forging is performed in a soft ferrite state.

The steel having the above-mentioned chemical composition to which the present invention is applied is a component system which is hardly softened by annealing or the like, but by reducing the C content, it is possible to reduce the deformation resistance. did. This is because forging can be performed in the austenite region where the amount of solid solution of C is small.

In order to improve the accuracy of the connecting rod, in the preform processing performed in advance,
(Eye) It depends on how thin the section (rod) is.

For the preform processing in this case, plastic processing such as forging, roll processing, and spinning processing, and cutting processing can be considered. However, in consideration of actual production, plastic processing is more preferable than cutting processing. Is more preferable. Then, in order to perform processing with higher accuracy, it is desirable to perform cold working.

Therefore, before the preform processing, it is required that the hardness is low and the deformability is sufficiently high.

For this purpose, it is desirable that the structure after rolling be a structure mainly composed of ferrite or bainite. However, since there is the problem of hardenability described above, it is sufficient to make the structure mainly composed of bainite. It can be said that.

By setting the upper limit of the manganese equivalent (Mneq) to 6.0, a structure mainly composed of ultra-low C bainite can be obtained, and good cold forgeability can be obtained. Incidentally, it is well known that extremely low C bainite has a very ductile structure.

Next, the hardenability after forging will be described.

As in the present invention, after the material is once heated to an Ac ₃ transformation point temperature or higher (for example, 850 ° C. or higher), plastic working such as forging is performed in a temperature range of 550 to 950 ° C., which is near the metastable austenite region. When quenching is performed continuously (in the case of process 1 shown in FIG. 1A),
As shown in FIG. 2, the nose of the ferrite that precipitates and transforms in a diffusive manner is largely shifted to the left.

Therefore, in order to realize stable hardenability, a large amount of hardenability improving elements such as Mn and Cr must be contained in order to delay ferrite transformation or pearlite or bainite transformation. Therefore, the total amount of these is represented by a manganese equivalent (Mneq), and is specified to be 3.4 or more in the present invention.

FIG. 3 shows the relationship between the manganese equivalent (Mneq) and the hardness after forging and quenching (HV).
Shows the relationship between forging temperature and tensile strength. As is apparent from FIG. 3, when the manganese equivalent (Mneq) is 3.4 or more, stable forging and quenching can be performed. Further, as is clear from FIG. 4, by performing plastic working such as forging in a temperature range of 550 to 950 ° C., a higher strength can be obtained than in the state of only quenching (in the case of process 2). . this is,
This is because the same process as ausforming, which is one of the thermomechanical treatments, is used.

FIG. 5 shows that the temperature is 100 to 700 ° C. after forging and quenching.
The relationship between the aging temperature and the strength when the aging treatment was performed in the temperature range of
７００700 ° C., more preferably 200-60 ° C.
By performing the aging treatment for 1 minute or more in the temperature range of 0 ° C., the strength, particularly the yield strength, is higher in the case of quenching-aging treatment without forging, and the superiority appears.

Next, the forgeability will be described.

FIG. 6 shows the deformation resistance during forging in Process 1 and Process 2 shown in FIGS. 1A and 1B, respectively.

As apparent from FIG. 6, process 1
Is lower than the deformation resistance in Process 2. And at extremely low C, and
In a material having a Mneq of 3.4 or more, austenite having a small amount of C solid solution is softer than ferrite + bainite + fine cementite, which is a structure after annealing, so that deformation resistance during forging in process 1 is soft. Is lower. In addition, the fact that the hardness is hardly reduced by a softening heat treatment such as annealing is also significantly related.

FIG. 7 shows the result of examining the relationship between the C content and the deformation resistance. The deformation resistance at low temperature γ is most affected by the C content, and FIG. 7 well reflects the result. ing. It is preferable that the material basically suitable for warm forging (γ region) is a low C-containing steel like the steel applied in the present invention.

FIG. 8 shows low-temperature annealing (680 ° C. × 2 h / A).
It is a figure which shows the result of having investigated the relationship between the manganese equivalent (Mneq) after C), the deformation resistance in cold, and the critical compressibility. At this time, if the structure after rolling is ferrite or bainite-based conditions, that is, if the manganese equivalent (Mneq) is 6.0 or less, excellent forgeability, particularly excellent deformability is exhibited.

Therefore, by setting the upper limit of the manganese equivalent (Mneq) to 6.0, excellent cold preform properties can be obtained. Conversely, when the manganese equivalent (Mneq) exceeds 6.0, it can be improved by performing a considerably long softening treatment, but this is not preferable in terms of cost.

FIG. 9 shows the results of a study on the relationship between the forging temperature and the tensile strength of the steel containing the free-cutting component, and FIG. 10 shows the results of examining the critical compression ratio of the steel containing the free-cutting component. The results show that, even when a free-cutting component is contained, good forging-quenching strength and excellent cold forgeability are ensured.

[0057]

EXAMPLE In this example, steel having a chemical composition shown in Table 4 was used as a raw material.

[0058]

[Table 4]

Then, by cutting the raw material in the rolled state, the bar material 11 as shown in FIG.
Is prepared, and then swaging (cold preform processing) is performed as plastic processing to obtain FIG. 11 (B).
A cold preform formed body 12 having a large end corresponding portion 12a, a rod portion corresponding portion 12b, and a small end corresponding portion 12c as shown in FIG.

Next, the cold preform-processed molded body 12 is heated as a forging blank once to 820 ° C. which is equal to or higher than the Ac _three- point temperature, and then subjected to warm (closed) forging at a temperature of 800 ° C., as shown in FIG. The large end 13a and the rod (I (eye) section) 13 as shown in FIG.
b and a small end portion 13c, plastic working is performed on the shape of the connecting rod molded body 13, and then quenching by oil cooling (the elapsed time from immediately after forging to quenching is about 20
Secondly, a connecting rod 14 having a large end portion 14a, a rod portion (I (eye) section portion) 14b, and a small end portion 14c as shown in FIG. 11D is obtained. The shapes after forging were remarkably good in both steel types.

In each connecting rod, the portions (AA ′, BB ′, CC) shown in FIG.
When the hardness in ') was measured, the results were also shown in FIG.

As is clear from FIG. 12, the hardness after quenching is significantly different between steel type F and steel type B.
In steel type B, since the manganese equivalent (Mneq) was insufficient, the structure after quenching was almost all bainite, and the hardness was low.

On the other hand, the steel type F shows a stable hardness distribution, and the structure is all martensite, so that it is possible to manufacture a high-strength and high-precision connecting rod. Was.

[0064]

According to the method for manufacturing a connecting rod of the present invention, C: 0.04 to 0.15% by weight, S:
i: 0.08 to 0.50%, and as hardenability improving elements, Mn: 3.0% or less, Cr: 3.0% or less, Ni: 4.0% or less, Cu: 1.0 % Or less, Mo:
3.0% or less, W: 0.5% or less, Ta: 0.5% or less, V: 0.3% or less, Nb: 0.08% or less, B:
One or two or more selected from 0.01% or less are manganese equivalents (Mneq) exhibiting hardenability represented by the following formula: 3.4 ≦ Mneq ≦ 6.0 Mneq = Mn (%) + Cr ( %) + Ni (%) / 2+
Cu (%) + Mo (%) + W (%) + Ta (%) + V
(%) + 10 (Nb (%) − 0.02) + XB (however, when B is contained in a range of 0.0005% or more and 0.01% or less, XB = 1.0), the balance being Fe and impurities Using steel consisting of, as it is, in a rolled state, or using a bar that has been subjected to softening heat treatment such as annealing, plastic working such as forging or roll working in advance,
Alternatively, a preform process is performed by a cutting process, and then, as a blank for forging, once heated to a temperature of ₃ points or more of Ac, forged into a connecting rod shape in a temperature range of 550 to 950 ° C., and thereafter, water-cooled, or Since it is made to be martensite by quenching such as oil cooling, cold preformability (cold plastic workability)
Is good, and also has excellent warm forgeability during closed forging,
Moreover, it is possible to use steel that can be quenched from a relatively low temperature after warm forging as a material, and it is possible to manufacture a connecting rod with high strength and high accuracy. Effect is brought about.

Then, as described in claim 2,
In steel, as a nitride forming element, Al: 0.1% or less,
To produce a high-strength and high-precision connecting rod having one or two types selected from Ti: 0.1% or less and having further refined toughness in which crystal grains are refined. This is a great effect that is possible.

Further, as described in claim 3, as a machinability improving element in steel, S: 0.3% or less, P
b: 0.3% or less, Bi: 0.15% or less, Te: 0.
1% or less, Ca: 1% selected from among 0.05% or less
By including a seed or two or more kinds, a remarkable effect that the machinability of the material at the time of forging can be further improved is brought about.

Further, as described in claim 4, after quenching such as water cooling or oil cooling,
By performing the aging treatment for 1 minute or more in the temperature range of 00 to 600 ° C., a remarkable effect that it is possible to obtain a connecting rod with further improved strength, particularly yield strength, is obtained. .

Further, as described in claim 5, the shot peening process is performed after quenching such as water cooling or oil cooling.
A remarkable effect is obtained that it is possible to obtain a connecting rod having higher strength, especially fatigue strength.

[Brief description of the drawings]

FIG. 1 shows a basic process (process 1) (FIG. 1A) in a method for manufacturing a connecting rod according to the present invention and a basic process (process 2) (FIG. 1B) in a general method for manufacturing a connecting rod. FIG.

FIG. 2 is a diagram illustrating a nose of ferrite that precipitates and transforms diffusively when heated to 850 ° C. or higher and then forged in the range of 550 to 950 ° C. near the metastable austenite region and continuously quenched. It is explanatory drawing which shows a mode that it approaches the left side largely.

FIG. 3 is a graph illustrating a result of examining a relationship between a manganese equivalent (Mneq) and hardness after forging and quenching.

FIG. 4 is a graph illustrating the result of examining the relationship between forging temperature and tensile strength.

FIG. 5 is a graph illustrating the result of examining the relationship between aging temperature and strength when aging is performed in a temperature range of 100 to 700 ° C. after forging and quenching.

FIG. 6 is a graph illustrating the result of examining the relationship between forging temperature and deformation resistance.

FIG. 7 is a graph illustrating the result of examining the relationship between the C content and the deformation resistance.

FIG. 8 Manganese equivalent after low-temperature annealing (Mneq)
6 is a graph illustrating the result of examining the relationship between the deformation resistance and the critical compression ratio.

FIG. 9 is a graph illustrating the result of examining the relationship between forging temperature and tensile strength for steel containing a free-cutting component.

FIG. 10 is a graph illustrating a result of examining a critical compression ratio of steel containing a free-cutting component.

FIG. 11 is an explanatory view showing a manufacturing process of the connecting rod in the embodiment of the present invention.

FIG. 12 is an explanatory view showing a measurement site and a measurement result of the hardness of the connecting rod obtained in Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Raw material (bar material) 12 Cold preform processed molded object 13 Connecting rod molded object 14 Connecting rod 14a Large end 14b Rod (I (eye) section) 14c Small end

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI C22C 38/54 C22C 38/54 38/60 38/60 F16C 7/02 F16C 7/02 (72) Inventor Takaki Mizuno Saitama 1-4-1 Chuo, Wako-shi, Japan Inside Honda R & D Co., Ltd.

Claims (5)

[Claims] C .: 0.04 to 0.15% by weight,
Si: 0.08 to 0.50%, and as hardenability improving elements, Mn: 3.0% or less, Cr: 3.0% or less, Ni: 4.0% or less, Cu:
1.0% or less, Mo: 3.0% or less, W: 0.5% or less, Ta: 0.5% or less, V: 0.3% or less, Nb:
One or more selected from 0.08% or less, B: 0.01% or less, manganese equivalent (Mneq) having quenchability represented by the following formula: 3.4 ≦ Mneq ≦ 6.0 Mneq = Mn (%) + Cr (%) + Ni (%) / 2+
Cu (%) + Mo (%) + W (%) + Ta (%) + V
(%) + 10 (Nb (%) − 0.02) + XB (however, when B is contained in a range of 0.0005% or more and 0.01% or less, XB = 1.0), the balance being Fe and impurities Using steel consisting of, as it is, in a rolled state, or using a bar that has been subjected to softening heat treatment such as annealing, plastic working such as forging or roll working in advance,
Alternatively, a preform process is performed by a cutting process, and then, as a blank for forging, once heated to a temperature of ₃ points or more of Ac, forged into a connecting rod shape in a temperature range of 550 to 950 ° C., and thereafter, water-cooled, or A method for producing a high-strength and high-precision connecting rod, which comprises quenching by oil cooling or the like to form martensite. 2. In steel, as a nitride-forming element, Al:
2. The method for manufacturing a high-strength and high-precision connecting rod according to claim 1, comprising one or two kinds selected from 0.1% or less and Ti: 0.1% or less. 3. In a steel, as a machinability improving element, S:
0.3% or less, Pb: 0.3% or less, Bi: 0.15%
The high-strength and high-precision connecting rod according to claim 1 or 2, wherein one or more kinds selected from the group consisting of Te: 0.1% or less and Ca: 0.05% or less are included. Manufacturing method. 4. The aging treatment for one minute or more in a temperature range of 200 to 600 ° C. after quenching such as water cooling or oil cooling. Manufacturing method of high strength and high precision connecting rod. 5. The method for manufacturing a high-strength and high-precision connecting rod according to claim 1, wherein shot peening is performed after quenching such as water cooling or oil cooling. .