Application of Nickel-Based Superalloy Surfacing Electrode on Sizing Press Module

Literature Overview

This paper by Wang Guanghuan, Jiang Guangbiao, and Jiang Guangjian, published in the journal Welding (2009, Vol. 6, pp. 40-43), reports on the application of a self-developed Ni-Cr-Mo-W nickel-based superalloy surfacing electrode on the working surface of sizing press modules in a hot rolling mill. The authors conducted a systematic evaluation encompassing mechanical property testing, high-temperature hardness measurement, metallographic examination, and cold-hot fatigue cycling tests. The study further compared the surface morphology of domestically produced surfacing modules against imported modules after processing 200,000 tonnes of steel, as well as after turning off 5 mm of the working surface. The results demonstrate that the nickel-based surfacing electrode effectively enhances the working surface performance and extends module service life, achieving full replacement of imported modules and realizing domestic production and manufacturing.

Core Technical Points

The sizing press module operates under extremely demanding conditions in a hot strip mill. The working surface is subjected to alternating thermal cycles from red-hot strip steel, mechanical impact loads, and abrasive wear simultaneously. The base material of the module is typically a medium-carbon alloy steel, which lacks sufficient red hardness and thermal fatigue resistance at elevated operating temperatures. The Ni-Cr-Mo-W superalloy system was selected because of its exceptional combination of high-temperature strength, thermal fatigue resistance, and oxidation resistance. The Ni-Cr phase provides the primary strengthening mechanism through solid solution strengthening and carbide precipitation, while Mo and W contribute secondary hardening through refractory carbide formation.

Surfacing Process Parameters and Metallurgical Analysis

The surfacing process employed manual arc welding with the proprietary nickel-based electrode. The key process considerations included maintaining interpass temperature below 200 °C to minimize dilution of the base metal into the weld overlay, controlling the welding current within the recommended range to ensure adequate penetration without excessive heat input, and implementing a multi-pass welding strategy to build up the overlay layer to the required thickness. The metallographic examination revealed a columnar-to-equiaxed transition in the grain structure from the fusion boundary toward the weld cap, with fine carbide precipitates distributed throughout the matrix. The high-temperature hardness tests confirmed that the surfacing layer retained hardness above 350 HV at 800 °C, significantly outperforming the base material which dropped below 200 HV under the same conditions.

Cold-Hot Fatigue Analysis

The cold-hot fatigue test subjected specimens to rapid thermal cycling between room temperature and 800 °C, simulating the actual thermal shock experienced by the module during hot strip rolling. The macroscopic examination of the cracked surfaces revealed that cracks initiated at the surface and propagated inward in a semi-elliptical pattern. Microscopic analysis of the crack surfaces showed intergranular cracking characteristics, indicating that grain boundary embrittlement was the dominant failure mechanism under thermal cycling. The Ni-Cr-Mo-W alloy's superior thermal fatigue resistance was attributed to its low coefficient of thermal expansion relative to the base steel, which reduces thermal strain accumulation at the fusion boundary.

Integration with Engineering Practice

This work carries significant practical implications for domestic steel mill operations. The sizing press module is a critical consumable component in the hot strip finishing mill, and its replacement frequency directly impacts production continuity and operating costs. The successful substitution of imported modules with domestically produced surfacing modules represents a major advancement in localization of hot rolling equipment components. The 200,000-tonne throughput comparison provides compelling field evidence that the domestic solution matches imported performance, thereby reducing dependency on foreign suppliers and cutting procurement costs substantially.

From a process engineering perspective, several practical lessons emerge. First, the surfacing layer thickness must be sufficient to accommodate both the expected wear during service life and the subsequent machining allowance. The 5 mm turning test after 200,000 tonnes of processing confirms that the overlay layer provides adequate material reserve. Second, the interpass temperature control is critical; excessive interpass heating leads to increased dilution and degradation of the overlay's high-temperature properties. Third, the welding sequence should be planned to minimize residual stress buildup, potentially incorporating post-weld stress relief treatment.

Key Questions and Reflections

A notable question arising from this study concerns the long-term stability of the surfacing layer under extended service conditions beyond 200,000 tonnes. While the current data demonstrates equivalence with imported modules, it would be valuable to investigate whether the domestic surfacing layer exhibits any progressive degradation mechanisms such as progressive carbide coarsening or progressive grain boundary sliding under prolonged thermal cycling. Additionally, the study does not address the dilution ratio quantitatively, which is a critical parameter affecting the final composition and properties of the surfacing layer. Future work should incorporate chemical analysis of the weld cross-section to determine the actual Ni-Cr-Mo-W composition gradient from the fusion boundary to the weld cap.

The study also raises the question of whether alternative surfacing techniques, such as plasma arc surfacing or cold spray, could offer improved dilution control and potentially better metallurgical outcomes. However, the manual arc welding approach has the advantage of being readily applicable in field maintenance conditions, which is a significant practical consideration for equipment maintenance operations.

Study Insights and Implications

This literature represents a well-executed engineering study that bridges fundamental metallurgical understanding with practical industrial application. The systematic evaluation methodology—combining mechanical testing, thermal fatigue simulation, metallographic analysis, and field performance comparison—provides a comprehensive validation framework that can be adopted for similar surfacing applications in other heavy industry sectors. The successful localization of this critical component demonstrates the principle that systematic metallurgical research combined with rigorous field validation can achieve import substitution even for demanding high-temperature applications. The work underscores the importance of understanding the specific failure mechanisms of industrial components before selecting appropriate repair or enhancement strategies, and it serves as a valuable reference for engineers working on similar surfacing problems in hot rolling equipment.