Influence of High Mn-Cu-Mo on Microstructure and Fatigue characteristics of Austempered Ductile Iron

International Conference on Recent Advances in Materials, Mechanical and Civil Engineering

材料科学;机械制造;土木建筑工程

Banavasi Shashidhar, M.^1 ; Ravishankar, K.S.^1 ; Naik Padmayya, S.^2

Dept of MME, NITK Surathkal, India^1

Dept of Mechanical Engg, AITM Bhatkal, India^2

关键词: Austempered ductile irons;    Bainite transformations;    Fatigue characteristics;    Fatigue striations;    Fractured surfaces;    Initiation and propagation;    Intercellular regions;    Retained austenite;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/330/1/012020/pdf
DOI  :  10.1088/1757-899X/330/1/012020

来源: IOP

【 摘 要 】

The impacts of high Mn content on microstructure and fatigue characteristics of ADI at 300, 350 and 400 °C for 120 min have been examined. Optical microscopy images reveals bainite morphology only at 300°C. Higher Mn contents hinders bainite transformation in the locales of Mn and Mo segregation, where in stage II reaction initiates near the graphite nodules before stage I reaction ends away from the nodules which creates more unreacted austenite volume after cooling forming martensite around the periphery creating austenite-martensite zone at 350 °C and tremendously articulated at 400°C. Feathery ferrite laths, stable retained austenite and uniform density hardness in the matrix, promotes higher toughness and fatigue properties (250 MPa @ 106cycles) at 300 °C. Presence of stage II carbides in the eutectic cell and austenite-martensite zone in the intercellular regions, due to their embrittlement in the matrix, makes easy crack path for initiation and propagation deteriorating properties at 350°C and above. SEM images of fatigue fractured surface revealed that at 300°C, showed a regular crack interconnecting graphite nodule, fatigue striation and quazi-cleavage fracture mode, and at 350 & 400°C reveals the carbide, austenite-martensite and porosity/defect final fracture region.