JP3963684B2 - Method for producing cast iron member - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a cast iron member, and more particularly, to a method for manufacturing a cast iron member having excellent wear resistance and high strength because the surface layer portion has high hardness.
[0002]
[Prior art]
FIG. 3 shows a cast iron camshaft A for an internal combustion engine mounted on an automobile. For example, the camshaft A is manufactured as follows. That is, first, the raw material is melted to form a molten metal. As raw materials, steel scraps, return materials (design parts such as gates or scraps of hot water, cast iron members produced as defective products, etc.), pig iron and the like are used.
[0003]
Next, the molten metal is poured into a mold such as a sand mold or a mold and then cooled and solidified. By this cooling and solidification, a molded product having a shape substantially corresponding to the camshaft A is obtained. The cooling rate at this time is generally about 240 ° C./min for the sand mold and about 1000 ° C./min for the mold, although it depends on the type of mold.
[0004]
That is, the cooling rate of the molten metal can be remarkably increased by using the mold. In other words, the use of the mold has the advantage that the camshaft A, which is a molded product, and thus a finished product, can be efficiently manufactured.
[0005]
By the way, when the molten metal is cooled and solidified in such a high cooling rate, a chill structure made of cementite (Fe ₃ C) is formed on the surface layer portion of the molded product. Further, when free N is present in the molded product in an amount of about 55 ppm or more, a fine layered structure (hereinafter referred to as fine pearlite) is formed in the portion where the chill structure was present by performing a heat treatment on the molded product. Generate. This fine pearlite has a high hardness, and therefore the wear resistance of the surface layer portion of the camshaft A is remarkably improved.
[0006]
As described above, the camshaft A having excellent wear resistance hardly wears when the journal portion slides with respect to the journal receiver, for example. That is, by forming fine pearlite after forming a chill structure, a camshaft having a long life can be configured.
[0007]
In addition, in this case, the strength of the camshaft A is increased. In other words, the cross-sectional area can be reduced as long as it has substantially the same strength and wear resistance as compared with a camshaft in which fine pearlite is not generated. Therefore, since the weight can be reduced, the fuel consumption of an automobile or the like equipped with the internal combustion engine in which the camshaft A is incorporated can be improved.
[0008]
[Problems to be solved by the invention]
By the way, as described above, steel scrap, return material, pig iron and the like are used as the raw material of the camshaft A, and these contain a large amount of Ti, V, Zr, Nb, Al and the like. Such a metal element quickly combines with free N present in the molten metal to form a nitride. In other words, they function as nitrogen capture elements that capture free N.
[0009]
When the ratio of free N in the molten metal is less than 55 ppm due to trapping of free N, decomposition of the chill structure is promoted when the molded product is heat-treated. That is, the chill structure (cementite) disappears by being decomposed into austenite (γ-Fe) and graphite. Therefore, in this case, fine pearlite cannot be obtained, and eventually, there is a problem that a camshaft having good wear resistance and high strength cannot be obtained.
[0010]
The present invention has been made in order to solve the above-mentioned problems, and it is possible to make the free N in the molten metal a ratio such that fine pearlite can be obtained with certainty. For this reason, cast iron having a high hardness surface layer portion. It aims at providing the manufacturing method of the member made from cast iron which can obtain a member made.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is a method for producing a cast iron member having a pearlite structure in the surface layer portion,
A first step of obtaining a molten metal by melting a raw material containing at least one element of Ti, V, Zr, Nb, and Al ;
A second step in which the molten metal is cooled and solidified under a condition that a chill structure is formed in a surface layer portion in a mold to form a molded product;
A third step of transforming the chill structure generated in the surface layer portion of the molded product in the second step into a pearlite structure by subjecting the molded product to heat treatment;
Have
After the free N in solution water and more than 55ppm by adjusting the ratio of the element to 0.5 wt% or less in total in the melt in the first step, and characterized in that said second step To do. In the following, the element is referred to as a nitrogen trap element.
[0012]
When the ratio of the nitrogen trapping element in the molten metal is 0.5% by weight or less, if the free N is 55 ppm or more, particularly 70 ppm or more, a part of the free N is not trapped by the nitrogen trapping element. If it does, it will remain in the melt without combining with the nitrogen-trapping element and forming a nitride. For this reason, since decomposition of the chill structure when the heat treatment is applied to the molded product is suppressed, the chill structure causes transformation of the fine pearlite structure. That is, since the finished product has a fine pearlite structure with high hardness on the surface layer, the wear resistance is remarkably good.
[0013]
In addition, in this cast iron member, a small amount of nitride generated by capturing N is dispersed. For this reason, this cast iron member exhibits a behavior similar to that of a particle dispersion strengthened composite material, and has the advantage of improved toughness and strength as compared with a general cast iron member.
[0014]
Adjustment of the ratio of the nitrogen-trapping element is performed by using a raw material whose content of the nitrogen-trapping element is measured in advance, adjusting the ratio of the nitrogen-trapping element in the raw material to 0.5% by weight or less, and then melting to make a molten metal. Can be accomplished. That is, for example, the content of each nitrogen-trapping element in the raw material is adjusted to 0.5% by weight or less by combining various materials having different contents of the nitrogen-trapping element. Of course, only the nitrogen trapping element content of 0.5% by weight or less may be used as the raw material.
[0015]
Or you may make it adjust the ratio of the nitrogen capture element in the said molten metal to 0.5 weight% or less by blowing nitrogen gas with respect to the molten metal in which the ratio of a nitrogen capture element exceeds 0.5 weight%.
[0016]
In addition, Ti, V, Zr, Nb, Al, etc. are illustrated as a main thing of the nitrogen capture element which combines with N rapidly and forms nitride. Of course, these are adjusted so that the total content in the molten metal is 0.5% by weight or less.
[0017]
As a suitable example of the cast iron member manufactured in this manner, a member having a sliding surface can be exemplified. Since the sliding surface is excellent in wear resistance, the life of these members can be extended.
[0018]
As a specific example of a member having a sliding surface, a member having a journal portion such as a camshaft, a connecting rod, a balancer shaft, or the like, which is a vehicle member, can be cited.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the method for producing a cast iron member according to the present invention will be described and described in detail with reference to the accompanying drawings.
[0020]
FIG. 1 shows a flowchart of a method for manufacturing a cast iron member according to the present embodiment. This manufacturing method includes a first step S1 in which raw materials are melted to form a molten metal, and the molten metal is cooled and solidified in a mold (cavity) under the condition that a chill structure is generated in the surface layer portion to form a molded product. Step S2 and a third step of transforming the chill structure into a pearlite structure by subjecting the molded product to heat treatment.
[0021]
This manufacturing method will be specifically described by exemplifying a case where the camshaft A (see FIG. 3) is manufactured as a cast iron member in relation to a casting apparatus that performs the manufacturing method.
[0022]
As shown in FIG. 2, the casting apparatus 10 includes a pouring station 12, a mold forming apparatus 18 having a fixed mold 14 and a movable mold 16, a correction / cutting apparatus 20, and a heat treatment furnace 22. The movable mold 16 can be moved toward or away from the fixed mold 14 under the action of the cylinder 23 constituting the mold forming apparatus 18.
[0023]
A blow smoke device 28 is provided above the mold forming device 18 so as to be freely displaceable in the vertical direction. In addition, a workpiece picking robot 30 is provided in the upper part on the downstream side of the mold forming apparatus 18 so as to be movable in the horizontal direction. The blow smoke device 28 and the workpiece picking robot 30 are supported by a support base 31.
[0024]
The pouring station 12 includes a melting furnace 32, a pressurized pouring furnace 34, and a ladle 24 that receives the molten metal derived from the pressurized pouring furnace 34 and introduces the molten metal into the cavity of the mold molding apparatus 18. Among these, the melting furnace 32 is installed on the mount 36.
[0025]
When performing the manufacturing method according to the present embodiment, first, steel scraps, return materials, pig iron and the like are housed in the melting furnace 32 as raw materials.
[0026]
Here, each of these raw materials has a nitrogen trapping element contained therein, that is, a content of Ti, V, Zr, Nb, Al, etc. that forms a nitride by combining with free N present in the molten metal. It is measured in advance. The raw materials are selected in such a combination that the ratio of these elements in the raw materials is 0.5% by weight or less in total. For example, when a steel material containing 1% by weight of Ti is used as one of the raw materials, a steel material having a low Ti content is also added as a raw material, and finally the proportion of Ti in the raw material is 0.5% by weight. % Is adjusted to be below. Of course, when other nitrogen capture elements are included, the raw materials are selected so that the total amount of nitrogen capture elements is 0.5% by weight or less.
[0027]
In short, in the present embodiment, the content of nitrogen trapping elements in the raw material is adjusted to 0.5% by weight or less in total by combining various materials having different nitrogen trapping element contents.
[0028]
And in 1st process S1, the said raw material is melted by heating the melting furnace 32 from the periphery, and it is set as a molten metal.
[0029]
The melting furnace 32 can be tilted. That is, the rod 42 of the cylinder 40 is connected to the lower end portion of the gate 38 that is formed to protrude above the melting furnace 32. A support shaft 44 is connected to the bottom of the melting furnace 32 so as to be unevenly distributed from the center of the bottom toward the gate portion 38. For this reason, the melting furnace 32 tilts with the connecting portion with the support shaft 44 as a fulcrum, following the vertical movement of the rod 42. When pouring the molten metal into the transport ladle 46, the pouring gate 38 may be tilted toward the transport ladle 46 by moving the rod 42 downward.
[0030]
A transport ladle 46 supported by a hook 48 of a crane (not shown) is transported toward the pressurized pouring furnace 34 under the action of the crane. The transport ladle 46 is tilted by a first tilting mechanism (not shown), so that the molten metal in the transport ladle 46 is poured and stored in the inner chamber 52 of the pressurized pouring furnace 34 through the funnel 50. .
[0031]
A gas supply pipe 54 for introducing a gas for increasing the pressure of the inner chamber 52 is connected to the pressurized pouring furnace 34. That is, as the inert gas such as Ar is supplied from the gas supply pipe 54, the pressure in the inner chamber 52 increases, and as a result, the molten metal stored in the inner chamber 52 becomes pressurized molten metal. It is introduced into a hot water passage 58 provided in a hot water discharge section 56 of the furnace 34 and finally led out from a hot water outlet 59 of the hot water discharge section 56. As described above, the derived molten metal is poured into the ladle 24.
[0032]
The ladle 24 is placed on the load cell 60, and the amount of molten metal in the ladle 24 is controlled to a predetermined amount under the action of the load cell 60. That is, when the measured value of the weight of the molten metal poured into the ladle 24 matches a preset value set in the load cell 60, a control signal from a control unit (not shown) electrically connected to the load cell 60 is obtained. As a result, a valve (not shown) interposed in the gas supply pipe 54 is closed. Accordingly, the supply of gas to the inner chamber 52 of the pressurized pouring furnace 34 is stopped, and as a result, the derivation of the molten metal from the hot water outlet 59 of the pressurized pouring furnace 34 is stopped.
[0033]
The ladle 24 can be tilted by a second tilting mechanism (not shown). Along with this tilting operation, a predetermined amount of molten metal introduced into the ladle 24 is poured into the cavity of the mold forming apparatus 18 through the gate 64 constituting the mold forming apparatus 18, and the second step S2 is performed. Be started. In addition, before the fixed mold 14 and the movable mold 16 of the mold forming apparatus 18 are clamped, a release agent is applied in advance to the cavity surface by the blow smoke apparatus 28.
[0034]
Here, melting of raw materials in the melting furnace 32, conveyance of the molten metal from the melting furnace 32 through the conveyance ladle 46, introduction of the molten metal from the tapping part 56 of the pressurized pouring furnace 34 to the ladle 24, All done in the atmosphere. For this reason, when going through these processes, nitrogen dissolves into the molten metal from the atmosphere and becomes free N. In addition, since a very small amount of N is contained in the raw material, free N derived from this N is also present in the molten metal. A part of these free N is trapped by the nitrogen trapping element as described above and forms, for example, a nitride such as TiN. However, since the free N is present in excess as compared with the nitrogen trapping element, There is still about 70 to 80 ppm of free N.
[0035]
In other words, in the second step S2, the molded article B is produced by cooling and solidifying the molten metal containing about 70 to 80 ppm of free N.
[0036]
The molten metal introduced into the cavity of the mold forming apparatus 18 is cooled at a cooling rate of about 1000 ° C./min, and finally solidifies into a molded product B. A chill structure made of cementite (Fe ₃ C) is formed on the surface layer portion of the molded product B.
[0037]
The obtained molded product B is gripped by the workpiece picking robot 30 after the movable mold 16 is separated from the fixed mold 14 and the mold is opened. As the workpiece take-out robot 30 moves in the horizontal direction, the molded product B is conveyed to the correction / cutting device 20. In the correction / cutting device 20, trimming or the like is performed on the molded product B.
[0038]
Thereafter, the molded product B is conveyed under the action of the transfer robot 66 and introduced into the heat treatment furnace 22. In the heat treatment furnace 22, the third step S3, that is, heat treatment is performed on the molded product B, and a camshaft A (cast iron member) as a finished product is obtained.
[0039]
This heat treatment is for transforming the chill structure (Fe ₃ C) generated in the surface layer portion of the molded product B into a pearlite structure. That is, when heat is applied to the chill structure existing in the surface layer portion of the cast iron molded product B containing N of 55 ppm or more, decomposition of the chill structure into austenite (γ-Fe) and graphite does not proceed sufficiently. For this reason, fine pearlite is generated. The temperature and time of the heat treatment may be set to conditions such that the chill structure transforms into a pearlite structure.
[0040]
This fine pearlite has a high hardness, and therefore the wear resistance of the surface layer portion of the camshaft A is remarkably improved. That is, by adjusting the content of nitrogen trapping elements such as Ti, V, Zr, Nb, Al, etc. in the molten metal to 0.5% by weight or less, a pearlite structure can be reliably generated, resulting in wear resistance. An excellent camshaft A can be obtained with certainty.
[0041]
In addition, a small amount of nitride such as TiN is dispersed in the camshaft A. For this reason, since the camshaft A exhibits a behavior similar to that of the particle dispersion strengthened composite material, there is an advantage that the toughness and strength are higher than those of a camshaft formed of a general cast iron member.
[0042]
In addition, you may make it perform machining, such as turning, with respect to the camshaft A in which the pearlite structure | tissue was formed in the surface layer part in this way.
[0043]
In this embodiment, the content of nitrogen trapping elements was adjusted to 0.5 wt% or less by selecting various combinations of raw materials. However, the content of nitrogen trapping elements such as Ti, V, Zr, Nb, Al, etc. It goes without saying that only those having a content of 0.5% by weight or less can be used as raw materials. In the present invention, the latter case is included in adjusting the content of the nitrogen-trapping element to 0.5% by weight or less.
[0044]
Further, the content of the nitrogen trap element may be adjusted at any time point before the molten metal is cooled and solidified. That is, for example, nitrogen gas is blown into a molten metal in which a raw material containing a nitrogen trapping element exceeding 0.5 wt% is dissolved, and the nitrogen trapping element is contained by nitriding the nitrogen trapping element with this nitrogen gas. You may make it adjust the quantity to 0.5 weight% or less.
[0045]
Furthermore, in the above-described embodiment, the camshaft A has been described as an example of a cast iron member, but it goes without saying that it may be other than that.
[0046]
Furthermore, in the manufacturing method according to the present embodiment, a mold is used at the time of casting. However, the casting is particularly limited as long as casting is performed under conditions where a chill structure is generated in the molded product. It is not a thing.
[0047]
【The invention's effect】
As described above, according to the method for producing a cast iron member according to the present invention, the ratio of the nitrogen trapping element that traps free N present in the molten metal is adjusted to 0.5% by weight or less. Thereafter, the molten metal is cooled and solidified to cast a molded product. For this reason, when the molded product is heat-treated, the chill structure can be easily transformed into fine pearlite, so that a finished product with extremely high surface layer hardness, excellent wear resistance, and high strength can be obtained. The effect that it can be easily obtained is achieved.
[0048]
In addition, this makes it possible to reduce the weight of the cast iron member. Therefore, if the cast iron member is a member for a vehicle, the fuel efficiency of the automobile can be improved.
[Brief description of the drawings]
FIG. 1 is a flowchart of a method for manufacturing a cast iron member according to the present embodiment.
FIG. 2 is a schematic overall configuration diagram of a casting apparatus that performs the method for producing a cast iron member according to the present embodiment.
FIG. 3 is a schematic overall perspective view of a camshaft.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Casting apparatus 12 ... Pouring station 14 ... Fixed mold 16 ... Movable mold 18 ... Mold forming apparatus 20 ... Correction / cutting apparatus 22 ... Heat treatment furnace 24 ... Ladle 32 ... Melting furnace 34 ... Pressurizing pouring furnace 46 ... Transfer ladle 52 ... Inner chamber 54 ... Gas supply pipe 60 ... Load cell A ... Camshaft

Claims (5)

A method for producing a cast iron member having a pearlite structure in a surface layer part,
A first step of obtaining a molten metal by melting a raw material containing at least one element of Ti, V, Zr, Nb, and Al ;
A second step in which the molten metal is cooled and solidified under a condition that a chill structure is formed in a surface layer portion in a mold to form a molded product;
A third step of transforming the chill structure generated in the surface layer portion of the molded product in the second step into a pearlite structure by subjecting the molded product to heat treatment;
Have
After the free N in solution water and more than 55ppm by adjusting the ratio of the element to 0.5 wt% or less in total in the melt in the first step, and characterized in that said second step A method for manufacturing a cast iron member. The manufacturing method of claim 1, wherein, the previous use of a raw material content of Kimoto element is measured in advance, and molten metal by dissolving proportion of the element in the raw materials was adjusted to 0.5 wt% or less A method for producing a cast iron member characterized by the above. The manufacturing method of claim 1, wherein after adjusting the ratio of the element to 0.5 wt% or less in the melt by the ratio of the element is blown with nitrogen gas to the melt of more than 0.5 wt% A method for producing a cast iron member, wherein the second step is performed. The method for manufacturing a cast iron member according to any one of claims 1 to 3 , wherein a member having a sliding surface is manufactured as the cast iron member. The cast iron member according to claim 4 , wherein any one of a camshaft, a connecting rod, and a balancer shaft is manufactured as the member having a sliding surface, and a journal portion is formed as the sliding surface. Manufacturing method.

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