Abstract
In the present investigation, the influence of austempering temperature and time on the microstructure and dry sliding wear behavior of high silicon steel was studied. The test specimens were initially austenitised at 900°C for 30 minutes, thereafter austempered at various temperatures 280°C, 360°C and 400°C, for varying duration from 30 to 120 minutes. These samples after austempering heat treatment were subsequently air cooled to room temperature, to generate typical ausferritic microstructures and then correlated with the wear property. The test outcomes demonstrate the slight increase in specific wear rate with increase in both austempering temperature and time. Specific wear rate was found to be minimum at an austempering temperature of 280°C, that exhibits lower bainite microstructure with high hardness, on the other hand specific wear rate was found to be slightly high at increased austempering temperatures at 360°C and 400°C, due to the upper bainite structure that offered lower hardness to the matrix. The sample austempered at 280°C for 30 minutes offered superior wear resistance when compared to other austempering conditions, mainly due to the presence of fine acicular bainitic ferrite along with stabilized retained austenite and also some martensite in the microstructure.
Highlights
Steels with an ausferritic structure have a few points of interest including high strength, great toughness, superior wear resistance relying on the transformation temperature and time [1]
The present investigation was focused to evaluate the effect of varying austempering heat treatment parameters on the microstructure and wear behavior of AISI 9260 high silicon steel
At elevated austempering temperature i.e., at 360°C adequate availability of time for growth of bainitic ferrite laths and at 400°C, isothermal holding for longer duration actuates the second stage response of bainitic transformation, where carbides get precipitated in retained austenite (Fig. 1(f)), which reduces the retained austenite content and were confirmed from X-ray diffractometer (XRD) analysis displayed in the figure 2(c)
Summary
Steels with an ausferritic structure (i.e., a blend of ferrite and carbon rich austenite) have a few points of interest including high strength, great toughness, superior wear resistance relying on the transformation temperature and time [1]. The extraordinary blend of these properties with that of the low expenses of the raw material and heat treatment contrasted with customary steels discover their utilization in various fields like automotive, railway components and cutting tools applications [2]. The deleterious effect of cementite is overcome by smothering their precipitation by adding adequate quantity of silicon %) [4], due to insolubility of silicon in cementite. The present investigation was focused to evaluate the effect of varying austempering heat treatment parameters on the microstructure and wear behavior of AISI 9260 high silicon steel
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