Mechanical properties and structure of deposited wear-resistant metal

Abstract

620.17:621.791.92 Wear-resistant hard-alloy coatings (facings) of high-carbon iron-based alloys, with a composition close to that of tool steels, are used to increase the abrasive-wear resistance of working friction surfaces of products. Our aim here is to study the mechanical properties of the deposited metal after different technological conditions of coating deposition.Metal was deposited on steel 40 by means of 5-ram-diameter UONI 13/N7 electrodes, with a coating containing various alloying elements such as C, Cr, Nb, Mo, Mn, V, Si, and B. During deposition all the alloying elements with different transition factors entered the deposited metal, thus determining its phase and chemical composition, structure, and properties. Standard specimens with various contents of alloying elements were prepared for abrasion tests from the deposited metals obtained (Table 1). The number of cycles of abrasive sliding over the specimen until the thickness of the specimen decreased by 3 inn1 was the criterion for evaluating the wear resistance. The wear resistance (N) was compared with the hardness (H, HRC) and grain size (Fig. I). Metals were deposited in the order of increasing wear resistance (N, cycle/ram). The wear resistance of specimens of deposits 1, 4, 3, 7 (stage I), 2, 6, 5 (stage II), 8 (stage III) increased nonmonotonically and discontinuously. The wear resistance of the deposited metal varied over the wide interval from 2500 to 75,000 cycles per mm of wear of the surface of the specimen. No correlation between the hardness (H, HRC), grain size (Dg), and wear resistance was observed for the deposited metals studied,The average grain size in the deposited metals differs: Dg = 10-60/xm (Fig. 1). The transitional segment from one stage to the next on the wear-resistance curve correlated with an abrupt reduction of grain size (deposited metals 1, 2, 8). In our opinion the stepped nature of the wear resistance curve can be explained by both quantitative structural-phase changes (reduction of grain size, increase in the number of second phases) and qualitative changes (appearance of new structural-phase components).Indeed, as the wear resistance of the deposited metals increases the number of second phases increases in the grain body and especially along the boundaries, the become larger, and the configuration becomes more complicated (Fig. 2a-g). Characteristically, a qualitatively new structure consisting of grains with a continuous, distinct edging of the second-phase component appears in specimens of deposited metals 2, 6, 5, which correspond to the second stage of increase in wear resistance (Fig. 2d-t'). A martensitic acicular structure forms inside the grains (Fig. 2h, i), as indicated by the high microhardness values, 350-1300 H (see Fig. 1).The phase components of the deposited metals were identified by an x-ray structure analysis on a Rotafiex diffractometer, using the JGPDS files and a Diamond personal computer. The results of the analysis are given in Table 2. Martensite and residual austenite were the phas...

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