Abstract
The pinning effect of cerium inclusions in the austenite grain growth of SS400 steel at 1300 °C is investigated by using a semi-empirical-simulation. Firstly, steel samples containing cerium inclusions are prepared; then the properties of inclusions are determined using SEM. In situ observation of austenite grain growth is performed by LSCM, to determine the fitting parameters of the model such as the grain mobility and the pinning parameter. These parameters are directly inserted into our phase field simulation. The time-dependent Ginzburg-Landau (TDGL) equation is implemented in our phase field model, where the effects of inclusion and grain boundary interaction are inserted as a potential term in the local free energy. The results proved that the optimal size of austenite grains can be achieved by changing the volume fraction of inclusions. In fact, by increasing the volume fraction of inclusions from 0 to 0.1, the austenite grain growth can be decreased where the boundary mobility reduces from 2.3×10−12 m4/Js to 1.0×10−12 m4/Js. The results also demonstrated that increasing the temperature can provide more energy for grain to overcome the inclusions’ pinning force. Moreover, it was shown that the classical Zener model, R c = 0.45 r p f i − 1 , describes the pinning effect of cerium inclusions.
Highlights
SS400 steel is a constructional grade ferritic-pearlitic steel [1]
One of the heat treatment processes of steel and other ferrous alloys is the austenitization process, where these materials are heated above their critical temperatures long enough for a ferrite to austenite transformation to take place [2,3]
The purpose of austenitizing steel and other ferrous alloys is to transform them into the required shape and provide proper strength and resistance to the material [2]
Summary
SS400 steel is a constructional grade ferritic-pearlitic steel [1]. This kind of steel has wide applications in land vehicles and structures. Different studies have been performed to investigate the controlling of the austenite grain size during the austenitizing process of the steels [5,6,7,8]. The reason of these numerous interests is the important impact of grain size on diffusive and diffusionless phase transformations, precipitation, and mechanical properties such as toughness, ductility, strength, and hardness [7]. During the cooling process from the austenitization temperature to the room temperature, the ferrite phase is homogenously nucleated on the grain boundaries, edges, and corners [5,11]. The grain boundary mobility, M, is obtained using the fitting parameter for experimental values of interface motion extracted from the in situ observation of austenite grain growth under confocal microscopy
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