JP2520124B2 - Re-Melted Chilcum Shaft - Google Patents

Description

Detailed Description of the Invention [Object of the invention]

(Field of industrial application) The present invention relates to a remelting chill cam shaft used as a component of an internal combustion engine. (Prior Art) A camshaft used as a component of an internal combustion engine is required to have excellent wear resistance on its sliding surface with the cam. Therefore, as a method of obtaining a camshaft with excellent surface wear resistance, a chill is set in a part of the camshaft casting mold, and the portion corresponding to this chill is supercooled to form a chill hardened layer. was there. However, this method has a drawback that the step of setting the chill is troublesome and the flashing is often generated, so that the removal man-hour is increased. As a method of surface hardening without using such a chill, there has been a method of forming a chill hardened layer by self-cooling after remelting the surface of the camshaft by TIG arc or the like, in addition to induction hardening. As a conventional remelted chill cam shaft, C: 3.0-3.6
%, Si: 1.5 to 2.4%, P: 0.1% or less, Mn: 0.5 to 2.0%, S:
A chill hardened layer is formed by remelting and self-cooling the surface of a camshaft made of gray cast iron with a composition of 0.08 to 0.2% and the balance Fe by plasma arc or the like (Japanese Patent Laid-Open No. 60-184694) and , A chill-hardened layer containing remelted and self-cooled cementite as the main phase over the entire circumference of the cam sliding surface (JP-A-60-234167), and a chill containing cementite as the main phase A hardened layer and a quench-hardened layer formed on the entire circumference of the cam sliding surface (Japanese Patent Laid-Open No. Sho 61-96)
No. 60-234169), or a chill-hardened part with a cementite structure as the main phase in 10 to 75 area% of the sliding surface of the cam, and the rest as a quench-hardened part (JP-A-60-258426). was there. (Problems to be Solved by the Invention) However, in the conventional remelted chill cam shaft illustrated above, the structure of the heat-affected zone due to remelting is not particularly controlled, and the heat-affected zone is not affected. The structure of is not controlled by selecting the component composition of the camshaft or adjusting the cooling rate after remelting, but even if it is simply made of gray cast iron or a chill hardened part and a quench hardened part are formed, Since it is formed by cooling, there is a problem that the pitting resistance is low and fatigue peel wear may occur especially under sliding conditions under high surface pressure, and the aggression to the cam that is the other material is great. It was (Object of the Invention) The present invention has been made by paying attention to the above-mentioned conventional problems, and by adjusting the composition of components of the camshaft or adjusting the cooling rate after remelting, It has a re-melted chill hardened layer, and the structure of the heat-affected zone due to re-melting is made appropriate, and the pitting resistance is good even under sliding conditions under high surface pressure, and the re-melting is low against the mating material. It is intended to provide a chill cam shaft.

Configuration of the Invention

(Means for Solving the Problems) The remelted chill cam shaft according to the present invention has a remelted chill hardened layer on the surface, and a structure control hardened layer based on a bainite phase in a heat-affected zone due to remelting. It is characterized by having. As described above, the remelted chill cam shaft according to the present invention is characterized in that the heat-affected zone due to remelting is a microstructure-controlled hardened layer based on the bainite phase. When forming the tissue control hardened layer, it is preferable to adopt one or both of adjusting the component composition of the camshaft and adjusting the cooling rate after the excessive melting. Of these, when adjusting the component composition, the camshaft shall be made of an alloy cast iron composition, and in% by weight, C:
3.0-3.5%, Si: 1.5-2.5%, Mn: 0.3-1.0%, Cr: 0.5-
1.0%, M ₀ : 0.3 to 1.0%, P: 0.1% or less, S: 0.1% or less, and the balance Fe is particularly desirable. That is, in order to obtain a structure-controlled hardened layer based on the bainite phase in the heat-affected zone due to remelting more easily than the conventional gray cast iron, it is particularly preferable to use an alloy cast iron in which the amounts of Cr and M ₀ are controlled. preferable. On the other hand, when adjusting the cooling rate after re-melting, the heat-affected zone after re-melting is 10 in the temperature range of 150 ℃ ~ 350 ℃.
It is particularly preferable to control the cooling rate so that the cooling may pass within 30 minutes or longer. In this way, the structure of the heat-affected zone is controlled. In this case, it is particularly desirable to form a hardened layer (acicular cast iron structure) based on a bainite transformation phase of 0.5 to 2.0 mm. Further, as a means for remelting, it is preferable to use a high-density energy heat source such as TIG arc, plasma arc, laser beam, electron beam or the like, and it is particularly preferable to carry out preheat treatment before remelting. FIG. 1 is a sectional view of a remelting chill cam shaft according to an embodiment of the present invention in a direction perpendicular to the cam axis, and FIG. 2 is a sectional view of a cam portion in the cam axis direction. It has a remelted chill hardened layer 3 on the surface, a structure control hardened layer (acicular cast iron structure) 4 based on bainite phase in the heat-affected zone due to remelting, and a hollow oil hole 5 in the central part. In addition, the hollow oil hole 5 has a cam oil hole 6. When manufacturing a camshaft having such a structure, for example, a TIG arc is used as a high-density energy heat source, and as shown in FIG. 3, the tungsten electrode 12 of the torch 11 for TIG arc and the surface of the cam portion 2 are separated. An arc 13 is generated between them, and a part of the surface of the cam portion 2 (an arc locus of a solid line) or the entire circumference (an arc locus 14 including an imaginary line) is remelted with an arc locus 14 which partially overlaps or is close to, The cast iron composition of the cam portion 2 is adjusted in advance so that the remelted chill hardened layer 3 is formed on the surface and the bainite phase-based microstructure-controlled hardened layer 4 is formed in the heat-affected zone due to remelting. Or adjust the cooling rate after remelting. (Examples 1 to 7) Alloy cast iron having the composition shown in No. 1 to 7 of Table 1 was cooled and cast without using gold to produce a camshaft rough material.
In this state, the hollow oil hole (5) and the cam oil hole (6) are processed, the black skin of the cam part (2) and the journal part are cut, and machined to a predetermined size and remelted. A rough camshaft material was obtained. Next, each of the camshaft rough materials is preheated by resistance heating or furnace heating so as to reach the set temperature shown in Table 1, and the conditions shown in Table 2 are obtained by using the torch (11) for TIG arc. The surface of the cam sliding surface is heated and re-melted by irradiating high-density energy with, and then carried into a temperature-retaining tank at room temperature, and the holding time in the temperature range of 150 ° C to 350 ° C is as shown in Table 1. Thus, the chill hardened layer (3) and the hardened layer (4) based on the bainite transformation phase were formed on the surface of the cam portion (2). Subsequently, the cam portion (2) of the remelted and chilled camshaft rough material was polished to obtain a product camshaft. FIG. 5 is a photomicrograph showing the metal structure of the heat-affected zone of the camshaft according to this example, showing that the white portion is cementate and the acicular base is bainite (Hv450-550). (Comparative Examples 8 to 14) Alloy cast iron (excluding No. 13) having the composition shown in Nos. 8 to 14 in Table 1 was cast as it is without using a cold metal to produce a rough camshaft material. Then, in this state, the hollow oil hole (5) and the cam oil hole (6) are processed, and the black skin of the cam part (2) and the journal part are cut and machined to have a predetermined size. A camshaft rough material for remelting was obtained. Next, each of the camshaft rough materials is preheated by resistance heating or heating in a furnace so as to reach the set temperature shown in Table 1 (except No. 12 and 13), and the torch for TIG arc ( 11) was used to heat and re-melt the cam sliding surface by irradiating it with high-density energy under the conditions shown in Table 2, and then for Nos. 8 to 11 and 14, the cam sliding surface was brought into a room temperature insulation tank, No. 12 and 13 are left to cool in the atmosphere and are 150 ℃ to 350 ℃.
The chill-hardened layer (3) is cooled on the surface of the cam part (2) by cooling so that the holding time in the temperature range of is as shown in Table 1.
And the tissue layers shown in Table 1 were formed. Subsequently, the cam portion (2) of the remelted and chilled camshaft rough material was polished to obtain a product camshaft. FIG. 4 is a photomicrograph showing the metallographic structure of the heat-affected zone of the camshaft according to Comparative Examples Nos. 8-11, 13 and 14, where the white part is cementite and the lamellar matrix is pearlite (Hv200-350). Is shown. (Comparative Example 15) A cast shaft raw material was manufactured by casting cast iron having a composition shown in No. 15 of Table 1 in a mold using a cold metal.
The hollow oil hole (5) and the cam oil hole (6) are processed, and the black skin of the cam portion (2) and the journal portion is cut,
A camshaft rough material was obtained by performing mechanical processing so as to have a predetermined size. (Durability Test) Next, camshaft Nos. 1 to 7 of the examples shown in Table 1
And the camshaft Nos. 8 to 15 of the comparative example, the following third
A durability test was conducted under the durability conditions shown in the table. Then, the maximum wear depth of each cam and rocker arm tip after the durability test and the presence / absence of pitching in the cam nose portion were examined. The results are also summarized in Table 1. As is clear from the results shown in Table 1, the cam of Comparative Example No. 8 has a Cr content of 0.3%, which is as low as less than 0.5%, so that the tendency of white pig iron (chilling) is suppressed and As the structure becomes thinner, the hardenability of the rough material deteriorates, and the heat-affected zone catches on the pearlite nose of the TTT curve (constant temperature transformation curve) during heating and cooling, resulting in pearlite as shown in Fig. 4. It will be the base of the organization. In addition, in the cam having the soft pearlite bases around and just below the chill, not only the wear amount after the durability test is large, but also pitching occurs. Further, the cam of Comparative Example No. 9 has a low M ₀ content of 0.1% and less than 0.3%, so that the wear resistance is insufficient for the same reason as the No. 8 cam, Since the cams of Comparative Example No. 10 have low Cr and M ₀ contents, the wear resistance of the cams of Comparative Examples No. 8 and No. 9 is further deteriorated. On the other hand, in the cam of Comparative Example No. 11, since the C content is 2.8% and less than 3.0%, an incomplete chill structure is likely to occur, and therefore the wear resistance is somewhat deteriorated. On the other hand, since the cam of Comparative Example No. 12 was remelted without preheating and allowed to cool in the atmosphere, the cooling rate was large and the heat affected zone became a martensite base. Therefore, this No. 12
This cam is not preferable because it not only slightly attacks the opponent chip, but also easily cracks and pitches during the durability test. In addition, in the cam of Comparative Example No. 13, since it has a composition without addition of Cr, M ₀ and is rapidly cooled after remelting, since the heat-affected zone becomes a pearlite base, it is the same as the No. 8 cam. Therefore, the wear resistance is poor. Further, in the cam of Comparative Example No. 14, since the preheating temperature is too high, the cooling rate is slow and pearlite is generated, so that the wear resistance is inferior for the same reason as No. 8. Furthermore, in the conventional chill cam of Comparative Example No. 15, since the chill structure is coarse, the scuffing resistance is poor and the amount of wear is large. Compared to the above No. 8 to 15 cams, the No. 1 to 5 cams of the embodiment preheated the alloy cast iron camshaft rough material containing Cr: 0.5 to 1.0% and M ₀ : 0.3 to 1.0%. Re-melt the rear cam surface layer,
At the time of cooling, each cam heat affected zone was passed in the range of 150 ° C to 350 ° C for 10 minutes to 30 minutes to form an acicular structure based on the bainite phase, so that it has very excellent wear resistance. At the same time, it has become a cam with extremely low aggression against the opponent. In addition, the cams of Examples No. 6 and 7 have the same wear resistance as the No. 1 to No. 5 cams because the structure of the heat-affected zone is based on the bainite phase. Although become a aggression is relatively small, since the No.6 cam are increasingly 0.2 percent P content, brittle steadite phase into chilled structure _{(Fe-Fe 3 C-Fe} 3 P) Is deposited, and cracks are likely to form along this, so the pitch resistance is slightly inferior. Therefore, it is desirable that the P content be 0.1% or less. Amount is 1.2%,
Since the M ₀ content is as large as 1.2%, the margin for improving wear resistance is small, the attacking property on the mating tip material tends to increase, and chilling occurs when the cam rough material is cast. Since it is easy to get into the core, it is difficult to process hollow oil holes etc., so the Cr content is 1.0% or less, M ₀
It was confirmed that the content should be 1.0% or less.

【The invention's effect】

As described above, the remelted chill cam shaft according to the present invention has the remelted chill hardened layer on the surface and the bainite phase-based microstructure-controlled hardened layer in the heat-affected zone due to remelting. Therefore, even if it is a sliding condition under high surface pressure, the pitting resistance is good, the risk of fatigue peeling wear is extremely low, and the aggression against the mating material is also extremely low. It has excellent characteristics that it can be used over a wide range.

[Brief description of drawings]

FIG. 1 and FIG. 2 are sectional views of a remelting chill cam shaft according to an embodiment of the present invention in a direction perpendicular to each axis and a cam portion in the cam axis direction, and FIG. 3 shows a remelting chilling process procedure. FIG. 4 is a perspective view, FIG. 4 is a micrograph showing a metal structure of a heat-affected zone of a camshaft according to a comparative example, and FIG. 5 is a micrograph showing a metal structure of a heat-affected zone of a camshaft according to an example. 1 ... Re-melting chill cam shaft, 2 ... Cam part, 3 ... Re-melting chill hardened layer, 4 ... Bainite phase-based structure control hardened layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isao Doi 2 Takaracho, Kanagawa-ku, Yokohama-shi Nissan Motor Co., Ltd. (72) Inventor Akira Fujiki 2 Takara-cho, Kanagawa-ku, Yokohama-shi Nissan Motor Co., Ltd. (72) Inventor Tokusho Kanekane, 2 Takaracho, Kanagawa-ku, Yokohama City, Nissan Motor Co., Ltd. (72) Inventor, Ryoji Makino, 2 Takaracho, Kanagawa-ku, Yokohama City, Nissan Motor Co., Ltd. (56) Reference JP-A-59-23156 (JP, A)

Claims (1)

(57) [Claims] 1. A remelted chill cam shaft having a remelted chill hardened layer on its surface and a structure control hardened layer based on a bainite phase in a heat-affected zone due to remelting.