Influence of residual stresses on the contact durability of surface-hardened 20KhN3A steel
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INFLUENCE OF RESIDUAL STRESSES ON THE CONTACT DURABILITY OF SURFACE-HARDENED 20KhN3A STEEL R. A. Khrunyk, M. P. Berezhnyts’ka, and S. O. Hrebenyuk
UDC 541.183:539.4.014
The change in residual stresses on a cemented surface after surface-plastic deformation under rolling friction in a weakly active oil medium was determined and its influence on contact durability was estimated in [1]. It was established that residual tensile stresses decrease the contact durability of steel [2]. In the present work, we investigate the influence of residual stresses on the contact durability of specimens made of improved and 20KhN3A cemented chisel steels after surface plastic deformation with rolls and ball in aqueous and oil media of different adsorption activity. Materials and Experimental Procedure Specimens with a diameter of 10 – 20 mm and a length of 70 and 150 mm were subjected to thermal (hardening at 1153 K in oil and high tempering at 673 K (improvement)) and chemicothermal (cementation at 1203 K for 24 h, cooling to 1153 K, hardening in oil, and tempering at 443 K with cooling in air) treatments. Then the specimens were ground and polished. Some specimens were spun in a three-roll device by carrying an “Industrial’na-50” oil, this oil with 2% of a compound of tars, and water with 1% of a DS-10 “Sintanol” spirit to the contact zone. The radius of the profile of a roll is equal to 5 mm and its diameter is equal to 40 mm. The number of revolutions of a detail v = 4.1 rev / sec, the feed S = 0.11 mm / rev, and one passage is used. Loads applied to the roll are equal to 1.96 and 2.45 kN, which corresponds to the contact stresses σmax = 6.3 and 6.7 GPa calculated in the elastic range. Other specimens were spun with a ball 16 mm in diameter that freely rotates in the device. We use the following modes of spinning: v = 3.1 rev / sec, S = 0.1 mm / rev, and P = 1.96 and 2.45 kN (the corresponding contact stresses σmax = 6.0 and 6.46 GPa). The “Industrial’na-50” oil is carried to the contact zone. After spinning with rolls, which leads to deformation of the metal according to the contact-shear procedure, in the surface layer appear residual stresses τ in the axial and circumferential directions [3], and the principal stresses σ act at the angle α to the axis. Only in the case of spinning with a freely rotating ball were they absent [4]. We determine the normal and tangential residual stresses in surface layers of bars by the known methods given in [5, 6]. We investigate contact durability with a UKVS installation in the rolling mode by carrying a drilling washing clay solution and the “Industrial’na-50” oil to the contact zone [7]. The contact stresses σmax belong to the range 1.5 – 9.8 GPa and the number of revolutions of the specimen varies from 125 to 375 rev / sec. Results of Testing In improved and cemented steels subjected to spinning with roll and ball, there appear compression residual stresses that have qualitatively similar distributions across the thickness of the surface layer. Near the surface, they are smaller than u
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