Restoration of a Steam Turbine Blade by Arc Welding With Orientation of Zones of Increased Hardness

Abstract

Turbine blades are characterized by abrasive wear and erosion by solid particles. Features of wear of these elements are its rapid development and unevenness. The consequences of this are a decrease in spalling, a decrease in its cost-effectiveness, and a shortening of the inter-repair period. As a way to avoid uneven wear of the blade surface, it looks like the deposition of metal layers with the orientation of zones of increased hardness. From the literature data and the experience of previous studies, it is known about the positive effect of carbides on the wear resistance of the deposited metal. Taking into account the fact that the turbine blades are made of steels 30ХГСА, 20Х2, 10ХСНД, it was decided to investigate the effect of local preliminary application of carbides on surfacing with materials corresponding to these steels in composition. Surfacing was performed with Veltek-450 HG and Veltek H-50 wires with a diameter of 2 mm, as well as with Plan T-201 tape with a width of 10 mm and a thickness of 3.2 mm, using a UD-249 device in an argon environment. Titanium and boron carbide powders mixed with GF-021 primer were used as strengtheners. Through metallographic research, it was established that the most striking signs of dissolution of carbides are observed when surfacing with Veltek H-460G wire. From the point of view of the properties of the deposited layers, the combination of Veltek H-460G wire with B4C can be considered the most effective of those considered. This is due to the fact that the lower layer deposited with B4C application is more ductile (398 HB), and the upper one is harder (464 HB), which has a favorable effect on the occurrence of tensile stresses. Layers with the orientation of zones of increased hardness should be placed transversely to the movement of abrasive particles and the direction of crack development. It is expected that the arrangement of zones of greater hardness in this way will contribute to a decrease in the intensity of cracking. And zones of lower hardness, in turn, will restrain the development of cracks due to their greater plasticity.