The Effect of Austenization and Isothermal Soaking Temperatures on the Wear of Perlite Steel
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THE EFFECT OF AUSTENIZATION AND ISOTHERMAL SOAKING TEMPERATURES ON THE WEAR OF PERLITE STEEL S. Kalaman,1, 2 H. Baycýk,1 and O. Aycan1 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 5, pp. 46 – 49, May, 2020.
The authors have studied grade R260 rail steel after austenization in the temperature range from 800 to 930°C and isothermal soaking at 500, 550, and 600°C followed by quenching in water. The steel structure and abrasive wear resistance were characterized. Recommendations concerning an increase in steel wear resistance were provided.
Key words: perlite steel, isothermal transformation, interlamellar spacing; wear resistance.
tal technique to evaluate abrasive wear resistance of the rails is ball-on-disk testing. The abrasive material represents synthetic ruby composed of 99% of Al2O3 and 1% of Cr2O3 (hardness: 1570 – 1800 HV ), which practically does not wear out during testing. The normal load applied during wear tests should be comparable with the rail operating load. A load of 10 N results in the Hertz contact pressure of 2.5 GPa, which is greater than the contact pressure in the rail-wheel system, measuring about 1.8 GPa [33, 34]. If the contact pressure exceeds 1 GPa, the sample surface starts developing microcracks, and the sample microstructure changes [35]. The objective of this work is to study the effect of austenization and isothermal soaking temperatures during quenching on the structure and properties of grade R260 rail steel to evaluate the possibility of increasing mechanical characteristics of rails used in Turkey.
INTRODUCTION Rail steels have perlitic or bainitic structure. The type of rails depends on the load and train speeds. To obtain the desired microstructure and mechanical properties, rails are subjected to heat treatment [1 – 4]. Pearlitic rail steels are the most common. According to numerous studies [5 – 20], a decrease in the temperatures of austenization and isothermal soaking causes a decrease in the interlamellar spacing in pearlite, which contributes to an increase in hardness and wear resistance of these steels. Rails are made by hot rolling of blanks at various finishing temperatures (900 – 960°C) depending on the manufacturing conditions and purposes [3, 7, 8, 21 – 23]. Therefore, it is important to evaluate the effect of the austenization temperature during heat treatment on the mechanical properties of the rails. In addition, the surface quality is an important operating characteristic of the rails. An increased surface roughness causes noise and vibrations, which lead to high contact pressure, plastic deformation, and increase in the wear rate of the rails [24 – 30]. It was shown that when the asperity height (microroughness) of the rail surface increases from 2.5 – 3.0 to 0.5 – 1.0 mm, the rail wear resistance almost doubles [31]. According to the European railway standards, the maximum asperity height is 10 mm [32]. One of the common types of rail wear is abrasive wear. According to the data published in [33], the best
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