Heat treatment and properties of a cast complex profile blade of a hydroturbine

Abstract

The mode of heat treatment of massive castings of the blades of the impeller of the hydroturbine "Dniester HPSP" from steel of the martensitic class CA-6NM has been worked out. Based on the determination of mechanical properties, measurements of stiffness over the entire surface of the blades and metallographic studies, the expediency of the proposed heat treatment mode using intensive cooling and high tempering after high-temperature austenitizing heating is shown. It is shown that this mode provides the necessary level of mechanical properties of blade castings, eliminates the negative effect of internal stresses arising during crystallization and rapid cooling during subsequent heat treatment. Determination of the chemical composition of castings and its compliance with the requirements of ASTM A743 / A743M-98a ensures that the required level of product properties is obtained. Metallographically established the absence of unwanted segregation and the uniformity of the structure, the uniformity of mechanical properties over the body of the blade, which leads to an increase in resistance to destruction due to cavitation. As a result of the research, the expediency of using the following heat treatment mode for massive complex-profile castings of blades made of corrosion-resistant steel of martensitic class CA-6NM, consisting of heating to a temperature of 1030-1040°C and tempering at 580-590°C using rapid cooling, was confirmed. Keywords: hydraulic turbine blades, heat treatment, structure, mechanical properties.