Malleable cast iron

Japanese: 可鍛鋳鉄 - かたんちゅうてつ（英語表記）malleable cast iron

Also called malleable castings. White cast iron that has been specially treated to give it malleability. There are two types. (1) White core malleable cast iron. White cast iron is wrapped in iron oxide powder and mill scale (surface oxides of steel formed during hot rolling), packed into an iron box, slowly heated to 900-1000°C in a furnace, and left for several days before being slowly cooled in the furnace. During this time, the inside of the cast iron is decarburized, becoming a ferrite or pearlite matrix, making it malleable. It is called white core because the white cementite remains in the center. It is suitable for processing small thin-walled items, and is used for bicycles and spinning machines. (2) Black core malleable cast iron. White cast iron is held at 850-950°C for 40 hours, and then held at 680-720°C for several tens of hours. During this process, the carbides in the cast iron become graphite particles and are dispersed and precipitated between the crystal grains, increasing the ferrite in the matrix, making it malleable. If the heating and holding time in the latter stage is short, the pearlite will not decompose sufficiently and will remain, resulting in slightly harder and stronger pearlitic malleable cast iron, so the holding time is adjusted depending on the purpose. The name blackheart comes from the fact that the cross section appears black due to the precipitated graphite (called tempered graphite). It has a wide range of uses, including pipe fittings, automobile frames, gears, building hardware, household goods, and tools. The tensile strength of malleable cast iron is about the same for both whiteheart and blackheart, at around 30 to 40 kg/ ^mm2 , for ordinary products, but for blackheart pearlitic cast iron it is 40 to 60 kg/ ^mm2 .

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

マリアブル鋳物ともいう。白鋳鉄に特殊な処理を施して可鍛性をもたせたもので，2種ある。 (1) 白心可鍛鋳鉄　白鋳鉄を酸化鉄粉，ミルスケール (熱間圧延時にできる鋼材表面酸化物) で包んで鉄箱に詰め，炉中で 900～1000℃にゆっくり加熱し，数日そのままおいたあと炉中で徐冷する。その間に鋳鉄内部は脱炭され，フェライトまたはパーライト地になって可鍛性となる。中心部にセメンタイトが白く残るので白心といわれる。薄肉の小物の処理に適し，自転車や紡織機の部品に使われる。 (2) 黒心可鍛鋳鉄　白鋳鉄を 850～950℃で 40時間保持後，さらに 680～720℃で数十時間保つ。この処理で鋳鉄内の炭化物は黒鉛粒となって結晶粒間に分散析出し，地のフェライトが増して可鍛性が得られる。後段の加熱保持時間が短いとパーライトが十分分解せずに残って，少し硬く強いパーライト可鍛鋳鉄になるので，目的により保持時間を調整する。析出する黒鉛 (焼戻し黒鉛という) のため断面が黒く見えるので黒心の名がある。パイプ継手，自動車のフレーム，歯車，建築金物，家庭用品，工具などに用途が広い。可鍛鋳鉄の引張り強さは，普通品では白心も黒心もほぼ同じで 30～40 kg/mm² 程度であるが，黒心パーライト鋳鉄では 40～60 kg/mm² である。

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