Kam mili üretiminde kullanýlan gri dökme demir ve sfero dökme demirlerde çil oluþumunun mekanik özelliklere etkisi

Otomobillerde kullanýlan kam milleri dökme demirden (gri dökme demir, küresel dökme demir) veya çelikten üretilmektedir. Bu çalýþmada gri ve küresel grafitli dökme demirin yüzeylerinde çil oluþumunun sertlik, aþýnma, darbe tokluðu ve mikro yapý üzerine etkisi incelenmiþtir. Bu amaçla, gri ve küresel dökme demirlerden çilli ve çilsiz olmak üzere dört farklý kam mili hazýrlanmýþtýr. Kam milleri döküm yöntemiyle üretildikten sonra mekanik testler yapýlmýþtýr. Yüzeyde oluþan çilin dökme demirin sertliðini ve aþýnma direncini artýrdýðý, gri çil ve küresel çil dökme demirin aþýnma miktarýnýn hemen hemen ayný olduðu tespit edilmiþtir. Maksimum sertlik gri çil dökme demirde elde edilmiþtir. Gerçekleþtirilen darbe tokluðu testi sonucunda darbe tokluðunun çil oluþumu ile azaldýðý tespit edilmiþtir. Maksimum darbe tokluðu Küresel dökme demirde elde edilmiþtir. Dökme demirlere ait mikro yapý optik mikroskopta incelendi ve aþýnma yüzeyleri ise taramalý elektron mikroskobu ile incelenerek aþýnma mekanizmalarý deðerlendirildi.

Effect of chill formation on the mechanical properties and microstructure of grey and nodular cast irons used in automotive industry

Cam shafts used in automobiles are produced by cast iron (grey cast iron, nodular cast iron) or steel. In this study, effect of chill formation on the surface of grey and nodular cast irons is investigated on the wear behavior, hardness, impact toughness and microstructure of grey and nodular cast irons. For this purpose, four types cam shaft made of grey cast iron with and without chill on the surfaces and nodular cast iron with and without chill on the surfaces, were casted. Mechanical tests were conducted after the camshafts have been produced by casting method. Surface hardness and wear resistance of grey and nodular cast irons have been improved by chill formation on the surfaces and it is concluded that the amount of wear on the surfaces of grey cast iron with chill and nodular cast iron with chill is almost the same. Maximum hardness value was obtained on the surface of grey cast iron with chill. The impact toughness has been found to decrease by chill formation. Maximum impact toughness value was obtained on nodular cast iron. Microstructures of grey cast iron with and without chill and nodular cast iron with and without chill were examined under optical microscope and worn surfaces of cast irons were examined by scanning electron microscopy (SEM). Wear mechanisms of the four types of cast iron were evaluated by SEM examination.