Effects of chemical composition of brass alloy type LS59-1 on the quality of ball valves

The effect of the chemical composition of material of brass ball valves on the quality of the finished valve is studied. This type of ball valves is produced with listed below operations of manufacturing (smelting, continuous casting of cylindrical blocks, hot stamping, machining and subsequent surface nickel plating). The presence of cracks and microcracks is analyzed. The microstructure was studied by optical and scanning electron microscopy (JEOL JSM 7001F and Carl Zeiss Axio Observer D1m). The hardness of individual phases was measured on a Futur Tech FM-800 microhardness tester. It has been established that the zinc content in the studied alloys is in the range of 35-37 %. Fluctuations of the zinc content do not have a significant impact on the probability of the appearance of discontinuities in the material (pores, microcracks, cracks). So, in two alloys (nos. 1, 4) such defects are determined, and in brasses nos. 2, 3, 5 they are absent. The content of impurities of aluminum, silicon, iron, tin, nickel varies both in qualitative and quantitative composition, while reaching no more than 1 % of each one. These elements, dissolving in α- and β-phases, and, mainly in the latter, affect the structural composition of brass - a more solid β-phase appears, the hardness of the phases increases. Impurities tend to combine with each other, forming compounds that initiate microcracks. In alloy no. 1, which has a single-phase α-structure, low-melting lead particles are distributed both inside its grains and along its boundaries, which adversely affects the behavior of brass during hot deformation. In microcracks of material no. 1, in addition to lead, non-metallic formations based on Fe, Si are also noted. In two-phase (α + β) brass no. 4, where the content of Fe, Sn, Al, Ni, and Pb (2.86 %) is increased compared to other alloys, the tendency to cracking is also increased. Although, in general, the transition from a single-phase α-structure to a two-phase (α + β) promotes the redistribution of lead inclusions in the β-phase or in the α/β intergranular boundaries as a result of the α ↔ β transition during hot working and, as a result, weakens the negative effect of lead. The hardness of the studied alloys varies. Alloys no. 3 and no. 5, where no discontinuities were found, have almost the same quantitative ratio of α- and β-phases - 40 : 60, but the microhardness of both phases in brass no. 3 is higher.