Akademik Veri Yönetim Sistemi
Tezin Türü: Yüksek Lisans
Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Metalurji ve Malzeme Mühendisliği Bölümü, Türkiye
Tezin Onay Tarihi: 2017
Öğrenci: ZEREN ÖZGENECİ
Danışman: BİLGEHAN ÖGEL
Özet:This study aims to investigate the effect of the amount of retained austenite and undissolved carbides on the wear resistance of the heat treated bearing steels. As inner and outer ring material 100Cr6 steel grade was used. The specimens were austenitized in the range 800°C to 1000°C, and then, quenched to room temperature in oil to produce a hard martensitic phase. A composite microstructure of undissolved carbides, martensite and retained austenite were observed in hardened steel specimens. It was seen that the amount of undissolved carbides decreases but the amount of retained austenite increases with an increase in austenitization temperature. The amount of retained austenite in all the samples were in the range of 10% to 58% in as-quenched condition. Four different tempering stages were applied to as-quenched samples: The first group and second group specimens were tempered at 180°C and at 235°C, respectively. The third group was double tempered at 190°C, and then, at 170°C. In the fourth group, a subzero treatment at -120°C was applied to the as-quenched specimen before tempering at 170°C. In all tempering operations, the tempering time was 90 minutes. The selection of different combinations of tempering yielded specimens having a very large range of retained austenite content (0%-26%) and hardness values (58 HRC-67 HRC). The highest amount of retained austenite was obtained in the samples tempered at 180°C. On the other hand the lowest amount of retained austenite was obtained in the samples sub-zero treated (-120°C) and tempered at 170°C. For this reason, the wear tests of bearings under contaminated lubrication was prepared from these steel components. It was found that maximum bearing service life time under contaminated lubrication was obtained after an austenitization treatment at 900°C and tempering at 180°C having a hardness of 63 HRC and a retained austenite content of 12%.