Abstract
Steel bearings have plenty of usages in manufacturing different kinds of ball bearings, bearings and cold rolling rollers. Heat treatment has an important role in the properties of this group of steels. Therefore, in current research the effect of tempering temperature on the microstructure, hardness, impact energy and wear resistance in forged steel containing Chrome, Manganese and Molybdenum will be studied. For this purpose, the samples were tempered after austenitizing at 900ºC and quenching in the oil at 6 temperatures of 150, 250, 350, 450, 550 and 650 ºC for an hour. Then microstructural studies and mechanical properties of the samples including hardness, impact energy and wear resistance were surveyed on the samples. The results showed that the hardness was gradually decreased (impact energy gradually increased) at the temperature range of 150 - 250 ˚C and at temperature range of 350 -650ºC, the hardness would decrease and the impact energy would increase. Also, the wear resistance would decrease with an increase in the tempering temperature. The result should be justified considering the softening of the structure and the reduction in martensite tetragonality which stems from an increase in the tempering temperature. The study of the wear surface of the samples indicated that the dominant wear mechanism was adhesive wear in which with an increase the tempering temperature due to a reduction in the hardness of the samples, more sever adhesive wear was observed. DOI: http://dx.doi.org/10.5755/j01.mech.24.6.22478
Highlights
Bearing steels cover a wide range of wearresistance steels with high strength and they are widely used in variety of industries such as manufacturing of bearings, ball bearings, spare parts of vehicles and hot and cold rollers due to their unique properties such as formability, easy machining, fatigue resistance which stems from rolling and thermal stability
In a study done by Amini et al [7] on martensitic stainless steel (Grade1.4057), the impact energy was almost constant till 350oC and at the temperature range of 350550oC, the impact energy decreased owing to the secondary hardness and at temperatures above 550oC
The hardness was gradually decreased at the temperature range of 150 - 250oC but at 350 - 650oC, with an increase in the tempering temperature, the hardness decreased and the impact energy increased which it was as a result of the structure softening, a decrease in martensitic tetragonality and the formation of ferrite phase
Summary
Bearing steels cover a wide range of wearresistance steels with high strength and they are widely used in variety of industries such as manufacturing of bearings, ball bearings, spare parts of vehicles and hot and cold rollers due to their unique properties such as formability, easy machining, fatigue resistance which stems from rolling and thermal stability. Controlling heat treatment parameters like tempering temperature to obtain optimized microstructure and mechanical properties is of great importance [1]. The effect of heat treatment on microstructure and mechanical properties is very important owing to the high utilization of this steel in the manufacture of cold rolling rollers and bearings. In current study, the effect of tempering temperature on the microstructure, hardness, impact and wear resistance of the steels, have been examined using some testing methods such as impact test, hardness test and pin-on-disk wear test. For accurate examination of carbide, identifying the type of precipitated carbide in the martensitic base during the tempering process, EDS analysis was performed at 550oC This test was done by field emission scanning electron microscopy (TESCAN MIRA 3). The pin was made of 100Cr6 steel with the hardness of 64 HRC
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