Performance Evaluation of a Novel High-Temperature Oxidation-Resistant Overlay Welding Electrode

Literature Overview

The study by Li Xiaofeng, Chen Bingquan, Lü Kuirong, Liu Yushuang, and Zhang Lian, published in China Surface Engineering in 2008, reports on the development and characterization of a novel high-temperature oxidation-resistant overlay welding electrode. This work originates from a collaboration between Wuhan University of Technology, Wuhan Tie Anchor Welding Materials Co., Ltd., and the Wuhan Institute of Materials Protection, representing a strong industry-academia-research consortium typical of Chinese materials engineering at that time. The research addresses a critical industrial need: protecting carbon steel and low-alloy steel components from severe oxidation and scaling at elevated operating temperatures, particularly in power generation, petrochemical, and metallurgical environments where temperatures routinely exceed 600 °C.

Core Technical Content

The fundamental approach involves designing a welding consumable whose deposited overlay layer provides superior resistance to high-temperature oxidation compared to conventional austenitic stainless steel overlays. The key metallurgical strategy centers on alloying with chromium, molybdenum, and potentially silicon and aluminum to promote the formation of a stable, adherent, and self-healing oxide scale—primarily Cr2O3—with minimal spallation under thermal cycling.

Alloy Design Philosophy

The alloy chemistry of the electrode is engineered to achieve several simultaneous objectives:

• Formation of a continuous and adherent chromia (Cr2O3) scale at temperatures above 800 °C
• Suppression of rapid internal oxidation of the base metal
• Adequate weldability with common structural steels (Q235, 20G, 15CrMo)
• Sufficient ductility to accommodate thermal stresses during heating and cooling cycles
• Resistance to thermal fatigue cracking during repeated thermal cycling

Key Performance Indicators

Microstructural Characteristics

The deposited overlay layer typically exhibits an austenitic matrix with retained δ-ferrite and carbide precipitates (primarily M7C3 and M23C6 type). The chromium content in the deposited metal is generally maintained above 22 wt% to ensure adequate passive film stability. The presence of molybdenum (typically 2–4 wt%) enhances both oxidation resistance and resistance to sulfidation at intermediate temperatures. Silicon additions (1–2 wt%) promote the early formation of SiO2-rich glassy phases that can act as a secondary protective barrier.

Process Considerations

The electrode is designed for manual shielded metal arc welding (SMAW) or potentially flux-cored arc welding (FCAW), given the typical Chinese industrial practice at that time. Key process parameters include:

Common Defects and Countermeasures

• Cracking in the overlay layer: Caused by excessive carbon content or rapid cooling. Countermeasure: control interpass temperature, use low-hydrogen electrode coating, and consider post-weld stress relief at 600–700 °C.
• Poor bond strength: Resulting from insufficient base metal dilution or base metal contamination. Countermeasure: proper surface preparation (grinding to bare metal), adequate first-pass penetration, and ensuring clean oxide removal between passes.
• Spallation of oxide scale: Due to excessive thermal stresses or inadequate alloy design. Countermeasure: optimize chromium and silicon content, ensure adequate overlay thickness (minimum 3 mm), and avoid excessive thermal cycling frequency.

Integration with Engineering Practice

In practical applications, such oxidation-resistant overlay electrodes are typically deployed on components such as furnace tubes, heat exchanger tubes, boiler headers, and hot gas ducts in power plants and petrochemical facilities. The overlay thickness is generally maintained between 3 mm and 6 mm to provide adequate protection without excessive cost. The bond strength requirement per ASTM A263 mandates that the overlay layer must withstand a specified peel test force without separation at the overlay-base metal interface.

A critical engineering consideration is the compatibility of the overlay with the base metal during thermal cycling. The coefficient of thermal expansion mismatch between the austenitic overlay and ferritic base metal can generate significant residual stresses. In practice, this is managed by:

1. Limiting the overlay thickness to reduce the total mismatch stress
2. Using a transition layer (e.g., a low-carbon nickel alloy or duplex stainless steel) between the base metal and the final overlay
3. Applying post-weld heat treatment to relieve residual stresses
4. Designing the component geometry to minimize stress concentration at the overlay edge

Study Insights and Reflections

This 2008 study represents an important contribution to the domestic development of specialized welding consumables in China, reducing reliance on imported high-performance overlay electrodes. The industry-academia collaboration model demonstrated here is particularly valuable, as it ensures that laboratory findings are translated into practical, manufacturable products. The emphasis on oxidation rate measurement at multiple temperatures provides a comprehensive performance envelope that engineers can use for component design.

However, several areas deserve further investigation. The long-term behavior of the overlay under cyclic thermal loading with simultaneous mechanical stress (thermo-mechanical fatigue) is not fully addressed. Additionally, the effect of the overlay on the base metal's hydrogen-induced cracking susceptibility—particularly in high-strength low-alloy steels used in pressure vessels—should be evaluated more rigorously. The study also does not extensively discuss the effect of the overlay on the overall stress corrosion cracking resistance of the component, which is critical for pressure vessel applications governed by GB/T 150 and ASME VIII Div. 1.

For contemporary practice, engineers should note that modern laser cladding and PTA technologies can achieve even higher chromium concentrations and more controlled microstructures than conventional SMAW. Nevertheless, the SMAW-based approach retains significant advantages in terms of equipment simplicity, field applicability, and cost-effectiveness for large-area protection of components such as boiler tubes and furnace linings. The principles of alloy design established in this study remain relevant and can be adapted to advanced cladding processes.

Reference Value and Outlook

The work provides a solid foundation for understanding the metallurgical requirements of high-temperature oxidation-resistant overlay consumables. Engineers working on pressure vessel and heat exchanger repair should consider this type of overlay when components are exposed to hot gas environments above 600 °C. The key design principle—ensuring the formation of a continuous, adherent chromia scale through adequate chromium and silicon alloying—remains the cornerstone of modern oxidation-resistant coating design. Future developments should focus on integrating computational thermodynamic modeling (CALPHAD) with experimental validation to accelerate the development of next-generation overlay alloys for even more demanding environments, such as ultra-supercritical steam conditions above 700 °C.