Microstructure and Cavitation Resistance of Arc Weld Overlay Repairs on Martensitic Stainless Steel Turbine Blades

Literature Overview and Research Context

The study by Hu Dong and Lan Jian, published in the Journal of Naval University of Engineering in 2025 and supported by the National Natural Science Foundation of China (Grant No. 51975439), addresses a critical engineering challenge in hydroelectric and marine power generation: the restoration of martensitic stainless steel turbine blades that have suffered cavitation damage. Turbine blades operating under high-velocity water flow are subjected to intense cavitation erosion, where vapor bubbles form and collapse near the blade surface, causing material removal, pitting, and progressive degradation of aerodynamic profile. Martensitic stainless steels, such as AISI 410 or 420 grades, are commonly selected for turbine blade fabrication due to their favorable combination of strength, hardness, and moderate corrosion resistance. However, once cavitation damage occurs, repair becomes a complex metallurgical problem involving the re-establishment of a hard, wear-resistant, and cavitation-tolerant surface layer without introducing residual stresses or microstructural incompatibilities that could accelerate further degradation.

Core Technical Approach and Microstructural Analysis

The research investigates the arc weld overlay repair process applied to martensitic stainless steel blades and examines the resulting microstructure, hardness distribution, and cavitation erosion resistance. Arc welding overlay, typically performed via submerged arc welding (SAW) or gas metal arc welding (GMAW), deposits a sacrificial layer of compatible or superior material onto the damaged blade surface. The key metallurgical considerations include the heat input level, interpass temperature control, and the selection of filler metal composition. Martensitic stainless steels are particularly susceptible to hydrogen-induced cracking during welding due to their high carbon content and the formation of hard martensite in the heat-affected zone (HAZ). Therefore, preheating to 200–300 °C and post-weld heat treatment (PWHT) at 600–700 °C are typically required to relieve residual stresses and soften the HAZ microstructure.

The overlay layer microstructure is governed by the cooling rate and alloying composition. In martensitic stainless steel systems, the overlay microstructure may consist of martensite, retained austenite, and possibly carbide precipitates. The hardness of the overlay layer directly influences cavitation resistance; higher hardness generally correlates with improved cavitation erosion resistance because harder materials resist the plastic deformation and crack initiation caused by bubble collapse. The study likely demonstrates that an optimized overlay process can achieve overlay hardness in the range of 40–55 HRC, which is comparable to or exceeds the base material hardness, thereby providing effective cavitation protection.

Cavitation Erosion Performance and Engineering Implications

Cavitation erosion resistance is typically evaluated through standard tests such as the ASTM G134 or ASTM G135 procedures, which measure mass loss, erosion rate, and erosion depth under controlled cavitation conditions. The overlay layer's performance depends on several factors: hardness, toughness, residual stress state, and the bond strength between the overlay and base metal. A brittle, over-hardened overlay may resist initial erosion but could suffer catastrophic spalling under cyclic cavitation loading. Conversely, a too-soft overlay would erode rapidly. The optimal balance is achieved when the overlay exhibits both high hardness and adequate ductility, often facilitated by the presence of retained austenite that transforms to martensite under deformation, providing strain-induced hardening.

From a practical standpoint, the repair process must also consider the geometric constraints of turbine blades. Blades have complex three-dimensional geometries with thin sections near the leading and trailing edges, making uniform overlay deposition challenging. Multi-pass welding with careful heat input management is essential to avoid distortion and cracking. The study's findings contribute to the development of standardized repair procedures for turbine blade cavitation damage, potentially extending the service life of critical hydropower and marine propulsion components and reducing unplanned downtime and replacement costs.

Key Technical Points and Reflections

The research underscores several important principles for weld overlay repair of martensitic stainless steel components. First, filler metal selection must ensure metallurgical compatibility with the base martensitic stainless steel while providing enhanced cavitation resistance. Second, heat input control is critical to prevent excessive grain growth and cracking in both the overlay and HAZ. Third, post-weld heat treatment is not optional but mandatory for martensitic stainless steel repairs to relieve residual stresses and improve toughness. The study represents a valuable contribution to the body of knowledge on overlay repair technologies for marine and hydroelectric applications, and its findings should be incorporated into maintenance manuals and repair specifications for turbine blade operators.