Resistance of steels of railroad wheels to corrosion-fatigue fracture
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RESISTANCE OF STEELS OF RAILROAD WHEELS TO CORROSION-FATIGUE FRACTURE I. M. Andreiko,1 V. V. Kulyk,1 and O. P. Ostash1,2
UDC 539.43:620.193:669.018.294
We have investigated the characteristics of cyclic crack resistance of medium- and high-strength wheel steels and their ability to form a protective film on a newly formed surface in distilled water and 3.5% NaCl aqueous solution. We have established that the negative influence of these corrosive environments on the cyclic crack resistance of both steels is insignificant and manifests itself most of all at the beginning of the medium-amplitude region of the cyclic crack resistance (fatigue-crack growth rate) diagrams, which is more noticeable for medium-strength steel. Keywords: steels of railroad wheels, corrosion, corrosion-cyclic crack resistance, microfractography.
The manufacture of railroad wheels does not include any kind of rust protection, and, hence, they can corrode under the influence of atmospheric environment. This concerns new wheels and those after long-term operation. As shown in [1], the corrosion rate, which is characterized by the parameter K , constitutes 0.3 to 0.32 g/(m 2 ⋅h) for wheel steel (0.61% С) in the rim of a new wheel. For steel with lowered carbon content (0.46%) but additionally microalloyed with 0.1% V and having an increased content of manganese (up to 1.0%) and silicon (up to 0.47%), the parameter K is greater: 0.33 to 0.4 g/(m 2 ⋅h) . For wheels after operation, with decrease in the carbon content in steel from 0.65 to 0.59%, the corrosion rate grows on the rolling surface [ K = 0.36 and 0.41 g/(m 2 ⋅h) , respectively], but, on the contrary, decreases in the middle part of the rim [ K = 0.29 and 0.22 g/(m 2 ⋅h) ] [1]. These results seem ambiguous, only a trend toward a decrease in the corrosion rate of steel on the rolling surface of new wheels and those after operation with increase in the carbon content in it [1] is observed. The cracks on the rolling surface of wheels, arising under the action of working cyclic loads in the wheel– rail contact zone, can decrease their service life, especially in the presence of corrosive environments. As established in [2], the fatigue-crack growth rate in 65G steel for low load amplitudes in distilled water is higher as compared with tests in air. However, the results of detailed investigations of the corrosion and stress corrosion fracture of wheel steels are practically absent in the literature. The aim of the present work is to study the corrosion resistance and characteristics of the cyclic crack resistance (CCR) of wheel steels under the influence of a corrosive environment depending on their strength. Material and Procedure of Experiments We tested specimens of steels, cut out of a high-strength experimental-industrial KP-type wheel and a medium-strength KP-2-type wheel of mass production. The chemical composition and mechanical characteristics of these steels after tests under static and cyclic loads in air were presented in [3]. 1 2
Karpenko Physicomechanical Institute, Ukrainian N
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