抄録
Recently, the metal mold process for iron castings is employed on a considerable scale because of its economic and technical advantages. But the process is limited by the service life of the metal mold.
The authors have confirmed that the siliconized cast iron containing 6-11% Si in the thickness range of 30-80μ has high oxidation resistance and is substantially superior as a metal mold material. In addition to the problem of the service life of the mold, surface coatings on the mold which prevents errosion by molten cast iron detaches easily due to oxides formed in its use on the boundary between the coatings and the mold. From the above mentioned reason, durability of the surface coatings is related to oxidation resistance of the mold. Therefore, not only the service life of the mold but also the durability of the coatings can be extended by a good oxidation resistant mold. The authors applied the flame-sprayed (Ni-Al) alloy coating as a surface coating instead of air-spraying the mixture of water glass and refractory powder ordinarily used.
In this report, thermal shock and oxidation resistances of the flame-sprayed coatings on siliconized cast iron were investigated. Also the siliconizing and the service life of the mold in their real use were studied. The results are as follows.
(1) Under thermal shock test, the test articles were heated to 1,000°C for 15 min and was cooled in 22°C water. The flame-sprayed coatings on the siliconized cast iron withstood 8 cycles, but coatings on the untreated cast iron easily failed after only 1 or 2 cycles.
(2) In oxidation test heating the test articles at 900°C for 50 hr in air, oxide was not formed on the boundary between the coatings and the siliconized cast iron on the flame-spray coated siliconized cast iron, while thick oxide layers were formed on the boundary between the cast iron and the coatings causing detatchment of the coatings on the untreated cast iron. The coatings on the siliconized cast iron had good adherence.
(3) In the siliconizing of the mold, duration of the treatment should be decided in consideration of the maximum thickness of the mold as in the heat treatment of metals.
(4) Durability of the coatings and dimentional changes of the boss parts in the mold were improved fairly by siliconizing.
