Inherited from Middle Russian чюгунъ (čjugun) (att. no later than 1665), likely a back-formation from чюгунной (čjugunnoj) first appearing in the Pskov 3rd Chronicle in the context of a 1615 siege (even though iron shot was cast in Russia already in late 16th century).
A Turkic borrowing, the most closely fitting are Chuvash чугун (čugun) and Azerbaijani çuqun (“cast iron; iron pot”), but both may be Russian loans. Cf. also Tatar чуен (çuyen), Crimean Tatar çoyun, Ottoman Turkish جويكن (çöygen, “cast iron; teapot”), Kumyk чоюн (çoyun), Southern Altai чӧйгӧн (čöygön, “teapot”), Ukrainian чавун (čavun, “cast iron; iron pot”), Romanian ceaun (“cauldron”).
Mudrak notes that medieval Turkic cognates meant either 'bronze, copper' as with Karakhanid جُوذِن (čoδïn) or 'iron ore', that in Karluk-Yugur, Altay and Teleut they denote metallic vessels, and suggests that it was derived from Middle Chinese 鑄 (t͡ɕɨoH, “to cast”).
Räsänen notes that common turkic cognates (like to Southern Altai чой (čoy), Kumyk чоюн (çoyun), etc) were from Middle Chinese 鑄 (t͡ɕɨoH, “to cast”). Given that South Siberian Turkic has -y- (like to Shor шойун (šoyun), Tuvan шой (şoy), Khakas сойын (soyın), etc.), ultimately it was borrowed by 鑄 (t͡ɕɨoH, “to cast”).
Also, See also Bashkir ҡурғаш (qurğaş), Kyrgyz коргошун (korgoşun), Southern Altai коргожын (korgožïn).
чугу́н • (čugún) m inan (genitive чугуна́, nominative plural чугуны́, genitive plural чугуно́в, relational adjective чугу́нный, diminutive чугуно́к)