Structure and wear characteristics of cast iron after laser surface modification

Abstract

The paper presents the results of studies of macro- and microstructure of alloyed chromium-vanadium cast iron after laser treatment (LT) in air using a continuous laser source with a variation in its power from 60 to 100 W and scanning speed of the laser beam varying from 5 to 17 mm/s. Metallography and durometry methods were used to determine composition and structure of the laser exposure zones (LEZ). It is shown that LT with a slight melting of the surface leads to a significant increase in microhardness in LEZ. In this case, martensite is the main structure in the near-surface layer of LEZ in the melting zone, and ledeburite structure prevails in the quenching zone. For the studied LT modes, LEZ depth is 220 – 310 μm. At the same time, microhardness is more than 2.5 – 4.2 times higher than microhardness of the base metal and reaches 820 HV0.1, that is a significant factor in increasing the wear resistance of the material. On the contrary, no significant structural changes were found in the case of LT without melting the surface. In order to identify the role of LT in wear of cast iron, sliding friction tests were carried out according to the “disk – finger” scheme at a pressure in the contact zone of 12.5 MPa and indenter rotation speed of 580 rpm. According to the test data, a significant decrease in linear wear and the wear intensity after the surface melting was found. The wear intensity is reduced by more than 100 times, and linear wear – by more than 50 times. The characteristics of LEZ surface cause a decrease in the friction coefficient by 30 % relative to the untreated surface.