Metal treatment – Stock – Ferrous
Patent
1998-11-09
2000-10-24
Yee, Deborah
Metal treatment
Stock
Ferrous
148320, 148543, 148545, 148540, 148579, 148659, C22C 3802, C22B 3808, C22B 3804
Patent
active
061361011
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a thixocast casting material, a process for preparing a thixocast semi-molten casting material, a thixocasting process, an Fe-based cast product, and a process for thermally treating an Fe-based cast product.
BACKGROUND ART
In carrying out a thixocasting process, a procedure is employed which comprises heating a casting 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, filling the semi-molten casting material under a pressure into a cavity in a casting mold, and solidifying the semi-molten casting material under the pressure.
An Fe--C--Si based alloy having a eutectic crystal amount Ec set in a range of 50% by weight .ltoreq.Ec.ltoreq.70% by weight is conventionally known as such type of casting material (see Japanese Patent Application Laid-open No.5-43978). However, if the eutectic crystal amount Ec is set in a range of Ec.ltoreq.50% by weight, an increased amount of graphite is precipitated in such alloy and hence, the mechanical properties of a cast product is substantially equivalent to those of a cast product made by a usual casting process, namely, by a melt producing process. Therefore, there is a problem that if the conventional material is used, an intrinsic purpose to enhance the mechanical properties of the cast product made by the thixocasting process cannot be achieved.
If a thixocast casting material made by utilizing a common continuous-casting process can be used, it is economically advantageous. However, a large amount of dendrite exists in the casting material made by the continuous-casting process. The dendrite phases cause a problem that the pressure of filling of the semi-molten casting material into the cavity is raised to impede the complete filling of the semi-molten casting material into the cavity. Thus, it is impossible to use such casting material in the thixocasting. Therefore, a relatively expensive casting material made by a stirred continuous-casting process is conventionally used as the casting material. However, a small amount of dendrite phases exist even in the casting material made by the stirred continuous-casting process and hence, a measure for removing the dendrite phases is essential.
In carrying out the thixocasting process, a semi-molten casting material prepared in a heating device must be transported to a pressure casting apparatus and placed in an injection sleeve of the pressure casting apparatus. To carry out the transportation of a semi-molten casting material, for example, a semi-molten Fe-based casting material, a measure is conventionally employed for forming an oxide coating layer on a surface of the material prior to the semi-melting of the Fe-based casting material, so that the oxide coating layer functions as a transporting container for the main portion of the semi-molten material (see Japanese Patent Application Laid-open No.5-44010). However, the conventional process suffers from a problem that the Fe-based casting material must be heated for a predetermined time at a high temperature in order to form the oxide coating layer and hence, a large amount of heat energy is required, resulting in a poor economy. Another problem is that even if a disadvantage may not be produced, when the oxide coating layer is pulverized during passing through a gate of the mold to remain as fine particles in the Fe-based cast product, and if the oxide coating layer is sufficiently not pulverized to remain as coalesced particles in the Fe-based casting material, the mechanical properties of the Fe-based cast product are impeded, for example, the Fe-based cast product is broken starting from the coalesced particles.
The present inventors have previously developed a technique in which the mechanical strength of an Fe-based cast product can be enhanced to the same level as of a carbon steel for a mechanical structure by finely spheroidizing carbide existing in the Fe-based cast product of an Fe--C--Si b
REFERENCES:
patent: 5037489 (1991-08-01), Kirkwood et al.
patent: 5133811 (1992-07-01), Kirkwood
patent: 5925199 (1999-07-01), Shiina et al.
Kikawa Kazuo
Shiina Haruo
Sugawara Takeshi
Takagi Isamu
Tsuchiya Masayuki
Honda Giken Kogyo Kabushiki Kaisha
Yee Deborah
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