Microstructure and Tribological Properties of Tool Steel AISI O2 After Thorough Cryogenic Heat Treatment
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RESISTANCE UDC 620.186:620.178.16:669.14.018.25
MICROSTRUCTURE AND TRIBOLOGICAL PROPERTIES OF TOOL STEEL AISI O2 AFTER THOROUGH CRYOGENIC HEAT TREATMENT Esad Kaya,1 Koray Kýlýçay,1 and Mustafa Ulutan1 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 44 – 50, June, 2020.
Steel AISI O2 (type 9G2) for a cold-working tool after different quenching, tempering, and cryogenic treatment regimes is studied. It is established that after cryogenic treatment the amount of residual austenite decreases by a factor of 4.3 compared with a quenched condition. The highest hardness 69 HRC is achieved after quenching and cryogenic treatment, and in this case wear resistance is higher by a factor of 2.36 than after quenching and tempering. After cryogenic treatment there is also a reduction in friction coefficient.
Key words: steel AISI O2, microstructure, heat treatment, cryogenic treatment, wear resistance.
in cutter life by 10 – 40% has been observed in [1], and in [10] an increase in the hardness of steels Vanadis 4, AISI D2, an AISI H13 was observed with a reduction in cryogenic treatment temperature. Mechanical properties and phase transformations in steel AISI D2 after treatment at temperatures from –140°C to –196°C have been studied in [11]. An increase in hardness after cryogenic treatment is due to transformation of residual austenite into martensite, whereas an increase in ductility and wear resistance is due to particle refinement within tempered martensite and homogenization of carbide phase. An increase has been shown in [12] for high-temperature hardness after deep cryogenic treatment of high-speed steels AISI M2 and AISI T1, also an increase in bending strength (by 25%), and an increase in impact strength by 57 – 78% has been demonstrated. The effect of cryogenic treatment on tribological properties of steels AISI A2, D2, M2, and O1 for cold treatment has been studied in [13]. It has been demonstrated that wear resistance of these steels increased by 620, 380, 200, and 400% respectively. During a study of the dependence of wear rate for steel D3 on cryogenic treatment combined with repeated tempering it has been established that a very slow wear rate corresponded to treatment with single-stage tempering [14]. The best wear resistance for steel AISI D2 was observed with performance of cryogenic treatment between quenching and tempering [15]. The effect of mild and deep cryogenic treatment on tribological and mechanical properties of carbu-
INTRODUCTION Currently in order to improve surface properties and microstructure of tool steels for cold treatment of metals (below 200°C) there is use of various heat treatment versions [1, 2]. One version if cryogenic treatment that is classified in accordance with the minimum temperature achieved during cooling: cold treatment (–80°C), mild cryogenic (–140°C), and deep cryogenic (–160°C) treatment. Cryogenic treatment embraces the whole cross section of a workpiece. According to published data use of cryogenic treatment is most effective between quen
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