Metal treatment – Stock – Ferrous
Reexamination Certificate
2000-03-10
2003-09-09
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
Ferrous
C148S320000
Reexamination Certificate
active
06616777
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thixocast Fe-based alloy material, and a process for heating the same.
BACKGROUND ART
In carrying out a thixocasting process, a procedure is employed which comprises heating an Fe-based alloy material into a semi-molten state in which a solid phase (a substantially solid phase and this term will also be applied hereinafter) and a liquid phase coexist, pouring the semi-molten Fe-based alloy material under a pressure into a cavity in a casting mold, and solidifying the semi-molten Fe-based alloy material under a pressure.
There is such a known Fe-based alloy material having a eutectic crystal amount Ec set in a range of 50% by weight≦Ec≦70% by weight (see Japanese Patent Application Laid-open No.5-43978).
However, if the eutectic crystal amount Ec is set to be equal to or larger than 50% by weight, the amount of graphite precipitated is increased in such an Fe-based alloy material, and hence, the mechanical properties of a cast product are substantially equivalent to those of a cast product made by casting. Therefore, with the conventional material, it is impossible to achieve an intrinsic purpose of enhancing the mechanical properties of the cast product made by the thixocasting process.
In a quenched area such as a thinner portion in the cast structure of the cast product, a portion which has been a spherical solid phase is transformed into a mixed structure of austenite and martensite. On the other hand, in a slowly cooled area such as a thicker portion, a portion which has been a spherical solid phase is transformed into a pearlite structure. Portions which have been liquid phases in both the areas are transformed into a ledeburite structure (a chilled structure).
If such a cast product is subjected to a thermal treatment, the following problem also arises: Graphite is finely precipitated in the quenched area, while it is precipitated in a coalesced manner in the slowly cooled area. As a result, the mechanical properties of both the areas are different from each other. For this reason, it is impossible to produce a cast product having mechanical properties uniform over the whole thereof.
Further, in the thixocasting process, the temperature of the semi-molten Fe-based alloy material, namely, the casting temperature is low as compared with the temperature of a molten metal. Therefore, when a cast product having a smaller thickness or having a complicated shape is produced by casting, the semi-molten Fe-based alloy material is cooled rapidly by the casting mold, and as a result, a portion which has been a liquid phase has a chilled structure having a low toughness. The chilled structure is liable to become a starting point for cracking on the solidification and shrinkage of the material, which is undesirable. Therefore, a measure to form an inner wall of a casting mold from a carbon material such as graphite is employed to moderate the quenching of the material. However, the following problem is encountered by utilizing the thixocasting process: The carbon material is worn violently and for this reason, the replacement of the casting mold must be performed frequently, which is uneconomic, and moreover, which results in a reduced productivity.
On the other hand, if the stability and productivity of components and metallographic structure and the like of the Fe-based alloy material are taken into consideration, it is optimal to produce such material by a continuous casting process. In the continuous casting process, however, the cooling rate of the Fe-based alloy material is high, and for this reason, a chilled structure may be produced in the material in some cases. When such an Fe-based alloy material is heated, the following problem arises: The temperature gradient of the inside of the material is increased depending on heating conditions, whereby cracks are produced in the material, and the material cannot be heated to a target temperature during induction-heating.
DISCLOSURE OF THE INVENTION
Accordingly, it is an object of the present invention to provide a thixocast Fe-based alloy material of the above-described type, from which a cast product having mechanical properties which are more excellent than those of a cast product made by casting, and which are uniform over the whole of the cast product, can be produced.
To achieve the above object, according to the present invention, there is provided a thixocast Fe-based alloy material comprising
1.8% by weight≦C≦2.5% by weight,
1.0% by weight≦Si≦3.0% by weight,
0.1% by weight≦Mn≦1.5% by weight,
0.5% by weight>Ni≦3.0% by weight, and
as the balance, iron (Fe) including inevitable impurities, and wherein a eutectic crystal amount Ec is in a range of 10% by weight<Ec<50% by weight.
A semi-molten Fe-based alloy material having liquid and solid phases coexisting therein is prepared by subjecting the Fe-based alloy material having the above composition to a heating treatment. In this semi-molten Fe-based alloy material, the liquid phase produced by a eutectic melting has a large latent heat. As a result, in the course of solidification of the semi-molten Fe-based alloy material, the liquid phase is supplied in a sufficient amount around the solid phase in response to the solidification and shrinkage of the solid phase, and is then solidified. Therefore, the generation of voids of a micron order in the cast product is prevented. In addition, the amount of graphite precipitated can be reduced by setting the eutectic crystal amount Ec in the above-described range. Thus, it is possible to enhance the mechanical properties, i.e., the tensile strength, the Young's modulus, the fatigue strength and the like of the cast product. In the Fe-based alloy material with the eutectic crystal amount Ec in the above-described range, it is possible to lower the casting temperature of the Fe-based alloy material, thereby providing the prolongation of the life of a casting mold.
However, if the eutectic crystal amount Ec is equal to or smaller than 10% by weight, the casting temperature of the Fe-based alloy material approximates to a liquidus temperature due to the small eutectic crystal amount Ec. Therefore, a heat load of a material transporting equipment to a pressure casting apparatus is high, thereby making it impossible to carry out the thixocasting. On the other hand, a disadvantage raised when Ec≧50% by weight is as described above.
In the above-described composition, manganese (Mn) is a cementite and austenite producing element, and nickel (Ni) is an austenite producing element. Therefore, Mn and Ni inhibit the slowly cooled area from being transformed into a pearlite structure. Thus, the cast structure of the entire cast product is such that a portion which has been a solid phase is transformed into a mixed structure of austenite and martensite, and a portion which has been a liquid phase is transformed into a ledeburite structure.
By subjecting such a cast product into a predetermined thermal treatment, a cast product having a uniformly thermally treated structure with fine graphite dispersed in a mixed structure of ferrite and pearlite is produced. This cast product has mechanical properties uniform over the whole thereof.
In the above-described composition, carbon (C) and silicon (Si) participate in the eutectic crystal amount, and the C content and the Si content are set in the above-described ranges to control the eutectic crystal amount in the above-described range. However, if the C content is smaller than 1.8% by weight, the casting temperature must be high, even if the Si content is increased to increase the eutectic crystal amount. Therefore, the advantage of the thixocasting is degraded. On the other hand, if C>2.5% by weight, the amount of graphite is increased. For this reason, the mechanical properties of the cast product is degraded, and the eutectic crystal amount is increased and hence, the handlability of the semi-molten Fe-based alloy material is deteriorated. If the Si content is smaller than 1.0% by weight, the casti
Tsuchiya Masayuki
Ueno Hiroaki
Armstrong Westerman & Hattori, LLP
Honda Giken Kogyo Kabushiki Kaisha
Ip Sikyin
LandOfFree
Fe alloy material for thixocasting and method for heating... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fe alloy material for thixocasting and method for heating..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fe alloy material for thixocasting and method for heating... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3060193