Effect of Pretreatment on Microstructure and Properties of Y-Containing Austenitic Surfacing Electrode A Technical Study Note

Literature Overview

The paper by Feng Anhua, Hong Yongchang, Qing Hua, and Huang Ming, published in Metal Heat Treatment (Vol. 23, No. 1, 1998, pp. 23-25), investigates the influence of substrate pretreatment on the microstructure and properties of surfacing deposits produced with yttrium-containing austenitic electrodes. The research was conducted jointly by the Metallurgical Department of East China Institute of Metallurgy and the Jiangdong Electric Welding Rod Factory of Maanshan Steel Company. The work addresses the practical challenge of surface repair of components that have failed under combined high-temperature and wear service conditions.

Technical Background and Design Rationale

The surfacing electrode was developed as an austenitic precipitation-strengthened consumable with yttrium (Y) addition. The design philosophy incorporates three synergistic strengthening mechanisms:

• Solid solution strengthening: Chromium, nickel, and cobalt dissolved in the austenitic matrix provide baseline strength and corrosion resistance.
• Precipitation strengthening: Fine carbide and intermetallic precipitates (Cr₇C₃, Ni₃Mo, Co₃W) provide age-hardening response and wear resistance.
• Rare earth modification: Yttrium addition refines grain structure, modifies inclusion morphology, and improves high-temperature creep resistance through grain boundary segregation control.

The pretreatment study examined three substrate preparation methods:

Microstructure Evolution Analysis

The authors conducted systematic metallographic examination of surfacing deposits produced on each pretreatment condition. The key microstructural observations include:

1. As-welded condition: All deposits exhibited a predominantly austenitic matrix with 5–15% retained ferrite, fine carbide particles (1–5 μm), and occasional δ-ferrite stringers. The yttrium addition resulted in approximately 30% grain refinement compared to conventional austenitic electrodes, with average grain size reduced from 80–100 μm to 55–70 μm.
2. Effect of pretreatment on dilution: The machining and grinding pretreatments produced lower dilution rates (8–12%) compared to shot blasting (15–20%), due to the smoother surface geometry providing more consistent arc stability. However, the shot-blasted surface exhibited superior mechanical interlocking between the base metal and the surfacing deposit.
3. Interface characterization: SEM examination revealed that the machined surface produced a relatively clean interface with minimal interfacial defects, while the shot-blasted surface showed excellent mechanical bonding with micro-anchoring of the deposit into the peened surface profile. The ground surface, despite its smoothness, showed occasional micro-porosity at the interface due to trapped grinding debris.

Mechanical Property Results

The following table summarizes the mechanical properties achieved under different pretreatment conditions:

The shot-blasted pretreatment consistently provided the best overall performance, particularly in terms of adhesion strength and crack resistance. This result is attributed to the compressive residual stress field introduced by shot peening, which counteracts the tensile thermal stresses developed during surfacing.

Engineering Practice Guidelines

For engineers performing surface repair of high-temperature wear components, the following recommendations emerge from this research:

1. Preferred pretreatment: Shot blasting (Sa 2.5 grade, Al₂O₃ media, 0.5–1.0 mm diameter) provides the optimal combination of surface cleanliness, mechanical anchoring, and compressive residual stress for subsequent surfacing.
2. Surface preparation sequence: For heavily corroded or scaled surfaces, a two-step approach is recommended—first remove heavy scale by grinding or machining, then apply shot blasting to create the optimal surface profile.
3. Electrode storage and handling: Yttrium-containing electrodes are moisture-sensitive and should be stored in dry conditions (relative humidity < 60%) and baked at 300 °C for 1 hour before use to ensure low hydrogen content.
4. Interpass temperature control: Maintain interpass temperature between 150–200 °C to prevent excessive grain growth while ensuring adequate fusion between passes.
5. Post-weld considerations: For components requiring immediate high-temperature service, solution treatment at 1100–1150 °C for 1–2 hours followed by water quenching restores full austenitic character and precipitation-hardening response.

Study Insights and Reflections

This research highlights a frequently overlooked aspect of surfacing quality—the substrate pretreatment method significantly influences the achieved deposit properties, sometimes more than variations in welding parameters themselves. The finding that shot blasting provides superior adhesion and crack resistance compared to conventional machining or grinding is particularly relevant for field repair applications where maximum reliability is required.

From a metallurgical perspective, the synergistic effect of yttrium addition and compressive surface stress in reducing crack sensitivity demonstrates the principle that multiple strengthening and toughening mechanisms can be combined to achieve performance levels unattainable by any single approach. Engineers should consider the entire process chain—from substrate preparation through electrode selection to post-weld treatment—as an integrated system rather than addressing each step independently.