Plasma Surfacing of Stellite Alloy on 1Cr12Ni2W1Mo1V Stainless Steel for Enhanced Erosion Corrosion Resistance

Literature Overview

This study by Zhang Youyi, Sun Xuejie, and Ran Chuanhai from Sichuan Vocational and Technical College of Engineering investigates the application of plasma arc surfacing to deposit a Stellite alloy overlay on 1Cr12Ni2W1Mo1V martensitic stainless steel. The work was published in Materials Protection (Volume 52, Issue 1, 2019, pages 88-91) and addresses a practical engineering need: improving the erosion-corrosion resistance of martensitic stainless steels used in severe aqueous environments. The base material 1Cr12Ni2W1Mo1V is a precipitation-hardening martensitic stainless steel with good mechanical strength and moderate corrosion resistance, commonly employed in pump impellers, valve components, and water-service piping. However, in applications involving high-velocity water flow with suspended solid particles, the base material suffers significant material loss. The authors systematically characterized the microstructure, hardness distribution, particle erosion behavior, and water erosion resistance of the Stellite overlay, providing valuable data for engineering design decisions.

Core Technical Findings

The study reveals several critical technical parameters and metallurgical observations that are directly relevant to engineering practice.

Microstructure Analysis

The Stellite overlay achieves good metallurgical bonding with the 1Cr12Ni2W1Mo1V substrate. The microstructure of the overlay consists of a dendritic Co-Cr solid solution matrix with uniformly distributed black carbide particles in the interdendritic regions. The predominant carbide phases are M7C3 (chromium-rich carbides) with a minor fraction of WC (tungsten carbide) particles. This microstructural configuration is characteristic of Co-Cr-W based Stellite alloys and is responsible for the excellent combined properties of hardness, toughness, and corrosion resistance. The dendritic morphology indicates a moderately rapid solidification rate typical of plasma arc surfacing, which produces a dilution ratio significantly lower than conventional arc welding methods.

Hardness Characteristics

The overlay hardness is approximately 1.96 times that of the base material, representing a nearly doubling of surface hardness. Notably, the second surfacing pass exhibited significantly higher hardness than the first pass. This observation is consistent with the dilution effect: the first pass experiences greater substrate dilution, reducing the effective Co-Cr-W content in the melt pool, while the second pass deposits onto the already-formed Stellite layer with minimal dilution, producing a more alloy-rich composition and consequently higher hardness. This layer-by-layer hardness gradient has important implications for multi-pass surfacing procedures and quality control.

Erosion Corrosion Performance

The Stellite overlay demonstrates superior particle erosion resistance compared to the base material. The water erosion rate of the overlay is substantially lower than that of the substrate, confirming that plasma surfacing with Stellite alloy effectively enhances the erosion-corrosion resistance of 1Cr12Ni2W1Mo1V stainless steel. The mechanism involves the synergistic effect of the hard Co-Cr solid solution matrix and the dispersed M7C3 and WC carbide particles, which collectively resist both mechanical abrasion and chemical attack.

Engineering Practice Implications

From a practical standpoint, several considerations emerge from this research that warrant attention in engineering applications.

Process Selection and Dilution Control

Plasma arc surfacing offers a significant advantage over conventional arc welding for overlay applications due to its focused, high-energy-density arc, which produces minimal substrate dilution. The dilution rate in plasma surfacing typically ranges from 5% to 15%, compared to 20% to 40% for submerged arc or gas metal arc surfacing. This low dilution is critical for maintaining the alloy composition and, consequently, the performance properties of the overlay. The observed hardness difference between the first and second passes underscores the importance of dilution control in multi-pass procedures. Engineers should consider whether a single-pass or multi-pass approach is appropriate for a given application, recognizing that the first pass will have somewhat lower hardness due to substrate dilution.

Application Scope

The combination of 1Cr12Ni2W1Mo1V base material and Stellite overlay is particularly well-suited for components subjected to combined erosion and corrosion in water or aqueous environments. Typical applications include pump impellers, turbine blades, valve trim, and pipe fittings in water treatment systems, hydropower installations, and marine engineering. The overlay provides a hard, erosion-resistant surface while the substrate retains its structural strength and moderate corrosion resistance. For applications requiring even higher corrosion resistance, alternative overlay alloys or multi-layer approaches may be considered.

Quality Control Considerations

The hardness gradient between passes should be monitored during production. A hardness profile across the overlay thickness should be measured and documented, with acceptance criteria established based on the minimum required hardness at the surface. The metallurgical bond between the overlay and substrate should be verified through macrographic examination after sectioning, ensuring no lack of fusion or cracking at the interface. For critical applications, the erosion-corrosion performance should be validated through coupon testing under conditions representative of the service environment.

Study Insights and Reflections

This study provides a clear demonstration of how plasma surfacing can effectively upgrade the surface performance of existing materials without replacing the entire component. The nearly twofold increase in hardness and the demonstrated improvement in erosion-corrosion resistance make this a practical and economical solution for extending component life in severe service conditions. The observation that the second pass is harder than the first is a useful practical insight that should be incorporated into process design. Engineers should also consider the thermal effects of multi-pass surfacing on the substrate, particularly for thinner components where heat accumulation may lead to undesirable microstructural changes in the heat-affected zone. The combination of microstructural characterization and performance testing provides a solid foundation for rational material selection and process optimization in erosion-corrosion service applications.