Effects of Heat Treatment Parameters on the Microstructure and Properties of Bainitic Steel
- PDF / 3,360,390 Bytes
- 10 Pages / 593.972 x 792 pts Page_size
- 89 Downloads / 225 Views
JMEPEG https://doi.org/10.1007/s11665-019-04452-x
Effects of Heat Treatment Parameters on the Microstructure and Properties of Bainitic Steel Bogusława Adamczyk-Cies´lak, Milena Koralnik, Roman Kuziak, Michał Smaczny, Tomasz Zygmunt, and Jarosław Mizera (Submitted April 16, 2019; in revised form September 16, 2019) The results obtained in the present study demonstrate the effects of various types of heat treatment processes on the microstructure and hardness of new trip-assisted carbide-free bainitic steel. The steel was subjected to three variants of heat treatment processing with an isothermal bainitic transformation temperature in a range from 350 to 480 °C. Changes of temperature and time of isothermal holding caused changes in the values of retained austenite (RA) volume fraction and carbon content. Reduction in the isothermal holding temperature resulted in the increased concentration of carbon in austenite. Also, the investigations of the microstructure showed that size and morphology of the austenite evolved during heat treatment. The SEM observations revealed that the steel subjected to heat treatment is composed of the carbide-free bainite with ferrite plates and a high volume fraction of retained austenite in the form of thin layers or islands. With the lower isothermal holding temperature and the higher degree of bainitic transformation, the more the RA morphology changed from island to layer type. The application of the lowest isothermal temperature resulted in a significant refinement of the microstructure components: the bainitic ferrite plates and the RA layers. Also, the mechanical properties obtained from the tensile testing and hardness measurements were correlated to the microstructure of the investigated steel after different isothermal holdings. Keywords
bainitic steel, martensite, mechanical properties, retained austenite
1. Introduction Significant progress has been made in recent years in the field of transport, which includes railways. Due to the development of high-speed railways, the increase in axle load and the intensification of rail traffic, new materials are being sought which will ensure a longer lifetime of the elements used to build railway infrastructure. A particular example of this is the rails which are exposed to wear due to the friction generated by the rolling stock, as well as contact-fatigue defects (Ref 1). The material that has traditionally been used for the production of rails is pearlitic steel (manganese alloyed). It has been recently found that the limit of the improvement of the mechanical properties of this type of alloy has already been reached. Steels with a carbide-free bainitic structure are being considered as a good alternative, as they are characterized by a lower carbon content than pearlite steels while having a higher content of alloying elements. Bainite is a product of an austenite transformation that occurs at an intermediate temperature between the pearlite and martensitic transformation temperatures. The bainitic transformation displays features of b
Data Loading...
