Metal founding – Process – Shaping liquid metal against a forming surface
Patent
1996-06-18
1998-09-08
Hail, III, Joseph J.
Metal founding
Process
Shaping liquid metal against a forming surface
164 97, 164122, 164 551, 148548, 148668, B22D 2700, B22D 1914, C21D 500, C22F 118
Patent
active
058031529
DESCRIPTION:
BRIEF SUMMARY
This is a continuation of International Application No. PCT/AU94/00264, with an international filing date of May 20, 1994, now abandoned.
TECHNICAL FIELD
The present invention relates to multiphase castings, and is particularly concerned with a casting method by which it is possible to refine a primary phase which forms out of a melt in a two phase region of a eutectic system. The invention is applicable to all metal systems whose solidification characteristics and final microstructures can be described by a eutectic phase diagram. Examples of such systems are aluminium/silicon, lead/tin, lead/antimony, copper/silver and iron alloys, especially white irons.
BACKGROUND OF THE INVENTION
In eutectic systems, solidification of alloys with hypereutectic and hypoeutectic compositions occurs over the temperature range defined by the liquidus and solidus temperatures for each alloy composition.
During solidification a primary phase forms by a nucleation and growth process. The size and distribution of the primary phase is determined, inter alia, by the cooling rate in the temperature interval between the liquidus and solidus. In general, the faster the cooling rate the finer the grain size and distribution of the primary solid phase.
There are several procedures described in the literature to increase the cooling rate through the solidification range: liquidus temperature. sand based moulds, e.g. zircon sand, chromite sand and various metal moulds. composition.
These procedures have certain limitations and are not applicable to every casting material or do not go far enough in the grain refinement process to substantially enhance desired material properties.
Some of these procedures, and some limitations, are discussed at length in Australian Patent Application AU-A-28865/84 in relation to white cast irons, both with hypoeutectic and hypereutectic compositions. AU-A-28865/84 sought to alleviate problems which had been identified in producing relatively thick section castings of high chromium hypereutectic white iron, by paying closer attention to the manufacturing variables in order to decrease the primary carbide size and to make the microstructure substantially constant throughout the casting section.
The wear resistant properties of white irons, including high chromium hypereutectic white irons, have been known for many years, and the latter alloys are used in the formation of wear resistant parts for lining pumps, pipes, nozzles, mixers and similar devices which are used to convey fluids containing abrasive particles, for example in mineral processing plants. The hypereutectic material consists of acicular M.sub.7 C.sub.3 (wherein M=Cr,Fe,Mo,Mn) primary carbides in a matrix, and, in a paper by K. Dolman : Alloy Development : Shredder Hammer Tips, Proceeding of Australian Society of Sugar Cane Technology, April 1983, pp 81-87, it was outlined how the wear resistant properties of these materials increase directly with the volume fraction of primary carbide that is present in sugar mill hammer tip castings 25 mm thick. However a corresponding decrease in fracture toughness was also noted and in order to give the hammer tips sufficient toughness they were bonded to mild steel backing plates. The difficulty in producing thick section castings because of the tendency to crack was also noted.
AU-U-28865/84 aimed to overcome the disadvantages of low fracture toughness and cracking by providing, in a high chromium hypereutectic white iron casting having a volume fraction of primary carbides in excess of 20% substantially throughout the alloy, a primary carbide mean cross-sectional dimension not greater than 75 .mu.m.
Apart from controlling the degree of superheat on pouring of the melt, it was proposed to achieve this aim by cooling the metal at a sufficient rate to restrict the growth of primary carbides. As an example of this procedure, a 25 mm thick hammer tip wear component cast in a zircon bearing shell mould was able to achieve a mean primary carbide diameter of 40 .mu.m, with a super chilled zone about 0.5
REFERENCES:
Derwent Abstracts Accession No. 83-739050/33,Class P53., RO, A, 80-621; Inst. Politehn. Bucur.; 30 Nov. 1982.
Derwent Abstracts Accession No. 93-062000/08, Class P53, JP, A, 05-9632; Sekisui. Chem. Ind. Co. Ltd.; 19 Jan. 1993.
Patent Abstract of Japan, C100, p. 20, JPA, 57-5813, Sumitomo Kinzoku Kogyo K.K.; 12 Jan. 1982.
Derwent Abstract Accession No. 22633B/12, Class M22, JP, A, 54-18426; Kawasaki Steel K.K.; 10 Feb. 1979.
Derwent Abstract Accession No. 53468B/29, Class M22, JP, A, 54-71726; Kawasaki Steel K.K.; 8 Jun. 1979.
International Search Report; PCT/AU94/00264; 22 Aug. 1994; R. Howe.
Dolman Kevin Francis
Harris Charles Philip
Thomson Andrew William
Walker Craig Ian
Hail III Joseph J.
Lin I.-H.
Warman International Limited
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