The Fatigue Crack Growth Rate Due to Single-Step Austempered Heat Treatment in Nodular Cast Iron

Mechanical Engineering Department, Engineering Faculty, Universitas Negeri Malang, Indonesia

^* Corresponding author: andoko.ft@um.ac.id

Abstract

Nodular cast iron comes to be the most used material in manufacturing industry. Recently, a number of engineering to enhance the mechanical properties of nodular cast iron have been being given including through the heat treatment called single-step austempered. In general, the process of single-step heat treatment is conducted through austenization at the temperature of 900°C with the holding time of 60 minutes and quenched at various austempered temperatures of 280, 310, and 340°C in the holding time of 60 and 120 minutes. The observation on fatigue crack behaviour was performed in comparison of stress R=0 and at 11-Hz frequency. From the result of the research, a graphic about relationship of crack length (a) and the number of cycles (N), and the graphic of the fatigue crack growth rate (da/dN) with the stress intensity factor of (Δk). In addition, it is found that the single-step austempered heat treatment at the austempered temperature at 340°C with the holding time of 120 minutes showed a slower fatigue crack growth rate in comparison to the temperature and time below. The slowness of the fatigue crack growth rate was caused by the higher percentage of the pearlite matrix phase in comparison to the ferrite matrix, nodular distance, and the relatively even nodule distribution.