Microstructure control of AISI 4135 for optimization of fatigue and fracture performance

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Metalurji ve Malzeme Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2018

Öğrenci: BURAK ÖZCAN

Eş Danışman: CEMİL HAKAN GÜR, KORAY YURTIŞIK

Özet:

Avoiding early fatigue failure of the AISI 4135 steel shafts in trains is an important task. This study aims to improve the damage tolerance of AISI 4135 steel by modifying its microstructure via heat treatment. The overall effect of various heat treatment procedures on the damage tolerance was analyzed by considering the threshold stress intensity factor and fatigue strength. Detailed investigations on the mechanical properties were performed, and fracture surfaces were investigated. The resistance of the steel specimens having ferritic-pearlitic, bainitic and tempered-martensitic microstructure against initiation and propagation of the small flaws were demonstrated by constructing Kitagawa-Takahashi diagrams. The results showed that ferritic-pearlitic AISI 4135 axles that are being utilized in service is inappropriate, and the damage tolerance of these axles regarding the fatigue crack propagation threshold can be remarkably improved via isothermal or quench-temper applications.