Wear resistance of steel obtained by surfacing a flux-cored wire 30N8Kh6M3STYu

The wear resistance of steel 30N8Kh6M3STYu as a result of surfacing by flux-cored wire was investigated. It was found that the average value of the relative mass wear of such a metal is 0.0002818 g/m, and the average value of the linear wear is 0.0006194 mm/m. The average value of the coefficient of friction after running in increased from 0.192 to 0.211, and the average value for the test was 0.207. The microhardness of the matrix of such a metal as a result of aging is in the range of 639–683 HV, the microhardness of the eutectic is 650–786 HV and the hardening phase is in the range of 783–882 HV. It has been shown that the steel hardening mechanism of such a system is determined by the compounds of carbides, for the most part, TiMo0.707C0.5, Cr3C2, and a small amount of TiC, SiC, intermetallic compounds, mostly Cr0.92Mo3.08, Fe0.875Mo0.125, Fe2Ti, and a small amount of Mo0984Ni0.016, Ti3Al, Ni3Ti, and Fe24N10 nitride formed as a result of aging. The established complex of dispersed phases precipitated after aging determines the wear resistance of such steel. The flux-cored wire created on the basis of 30N8Kh6M3STYu steel can be used for surfacing parts working under friction of metal on metal.


Introduction
The competitiveness of industrial enterprises is largely determined by the duration of the production equipment. The effectiveness of using such equipment depends on technological interruptions, and scheduled and emergency repairs. Parts subject to wear usually have a short period of operation, which is determined the total life of the equipment. These parts include shafts for various purposes, working in conditions of friction of metal on metal.
A promising way to increase the service life of such parts is to apply wear-resistant coatings of maraging steel on their working surfaces, including those deposited by flux-cored wire [1][2][3][4]. They have high strength, ductility and good adaptability, which makes them a promising structural material for the technology of the present and the future [5][6][7][8].
Currently, the most widely used are economically alloyed steels with the effect of secondary hardening related to precipitation hardening alloys. The main alloying system for such steels is Fe -Ni -Cr [9,10]. With a content of 5-14% Ni and 5-9% Cr in such steels, a pure martensitic structure is obtained. To reduce the critical temperatures of the onset of martensitic transformation in steels with a Ni and Cr content at a lower level, as well as to increase the strength of martensite after quenching, it is advisable to use C [11,12]. At a concentration of C in the range of 0.25-0.3%, it is possible to apply  [5,6,9,11,12]. At the same time, such steels have a low degree of hardening and, as a result, low indicators of wear resistance [9]. Therefore, they can find application mainly for the manufacture of parts and assemblies operating in conditions of moderate wear.
A higher hardening effect of steels can be achieved by creating various dispersed intermediate phases. The effectiveness of hardening by such phases is determined by the composition and structure of the released particles, size, nature of distribution in the matrix, interaction with it, and the effect of precipitates on the structure [11,12]. These factors determine the higher service properties of steel. The effective phases causing significant hardening include carbides, titanium and aluminum nitrides, and complex compounds based on them [5-7, 9, 11].
At the same time, it is known that to increase the wear resistance of such steel by increasing the hardening effect, it is possible with the additional introduction of Si in its composition. Silicon can significantly reduce the solubility in martensite of Ti, Mo and Al, forming ultrafine reinforcing particles. Strengthening the effect of secondary hardening of steel can be achieved with the introduction of Si in its composition up to 2.0% [13].

Results of the experiments and discussion
The results of chemical analysis of the studied metal 30N8Kh6M3STYu obtained by surfacing an experimental flux-cored wire are shown in Table 1. The average mass wear of the samples for the friction path of 113 m (after 300 revolutions) is 0,0020 g. For the friction path of 1130 m (after 3000 revolutions) the mass wear is already 0,3182 g, while the wear along the length reaches 0,698 mm. The average value mass wear per test was 0,0002818 g/m. The average value linear wear per test was 0,0006194 mm/m ( Table 2). Figure 1 shows the dependence of the friction moment on the friction path.   The results of the X-ray phase analysis of this metal after aging are shown in Figure 4. The results of the interpretation of the metal diffractogram are summarized in Table 3.   The basis of the matrix of the coating metal after heat treatment is martensite. This structure consists of 14 main kinds of compounds of phase components. In it, carbide particles are present, for the most part, TiMo 0,707 C 0.5 , as well as a small amount of Cr 3 C 2 , and a very small amount of SiC, TiC. Another group of compounds are intermetallic compounds. This is mostly Cr 0.92 Mo 3.08 , Fe 0,875 Mo 0,125 , Fe 2 Ti, as well as a small amount of Mo 0,984 Ni 0,016 , Ti 3 Al, Ni 3 Ti, and a very small amount of FeCr, FeAl, NiTi 2 . A small amount of Fe 24 N 10 nitride is observed in the structure.
The results obtained show that a feature of the transformation of the structure of the metal of the 30N8Kh6M3STYu coating as a result of heat treatment is the appearance in the structure of four carbides with the participation of Fe, Cr, Mo, Si, Ti, Ni, nine intermetallic phases with the participation of Fe, Cr, Ni, Ti, Mo, Al, and iron nitride Fe 24 N 10 , instead of iron carbide Fe 5 C 2 and five intermetallic phases with the participation of Fe, Ni, Ti, Si, Mo in the metal structure after surfacing.
A typical micro-region of the fine metal structure obtained by transmission electron microscopy is shown in Figure 5. As can be seen, the predominant precipitates in the martensitic matrix are FeCr compounds (Fig. 6, a) of considerable length, surrounded on all sides by Ti 3 Al intermetallic particles (Fig. 6, b). In addition, large particles of complex carbide TiMo 0,707 C 0.5 (Fig. 6, c) (Fig. 6, d) are observed. The established complex of these phases that precipitated as a result of aging determines to a greater extent the wear resistance of such steel.