Hardfacing Welding of Wear-Resistant Alloy on Large Hot Rolling Slab Rolls

Literature Overview

This paper by Zhang Zhongtao of Ansteel North Mechanical Works, published in Ansteel Technology (1992, Vol. 4, pp. 28-32), reports on the development and industrial application of a dispersion-strengthened steel electrode wire designated H25Cr3Mo2MnVA for hardfacing large hot rolling slab rolls. The work represents a significant milestone in China's domestic development of wear-resistant hardfacing consumables for heavy-duty rolling mill applications, drawing upon international experience while achieving notable technical-economic benefits for rolling mills.

Core Technical Content

The fundamental challenge addressed in this paper is the severe wear experienced by hot rolling slab rolls, which operate under extreme conditions of high temperature, heavy contact pressure, and abrasive interaction with steel slabs at temperatures exceeding 900°C. The roll surface is subjected to a combination of adhesive wear, abrasive wear, and thermal fatigue cracking, leading to frequent roll replacement and significant production downtime.

The electrode wire H25Cr3Mo2MnVA is a dispersion-hardened steel electrode designed specifically for this application. Its chemical composition and microstructural design are critical to its performance:

The vanadium and molybdenum additions promote the formation of fine, stable carbide particles (VC and Mo₂C) that provide exceptional resistance to abrasive and adhesive wear at elevated temperatures. Chromium contributes to oxidation resistance and hardenability, while manganese assists in deoxidation and promotes austenite stabilization in the weld metal.

Process Analysis and Engineering Practice

The paper emphasizes that the success of hardfacing depends not only on consumable selection but also on the welding process parameters and preparation procedures. Key process considerations include:

• Pre-weld preparation: The roll surface must be thoroughly cleaned to remove scale, oil, and previous weld deposits. Any cracks or defects in the base metal must be addressed prior to hardfacing.
• Preheating: For large-diameter rolls, preheating to 200-300°C is recommended to reduce residual stresses and prevent cold cracking in the transition zone between base metal and hardfacing layer.
• Interpass temperature control: Maintaining interpass temperature between 150-250°C ensures adequate plasticity in the previous weld pass while preventing excessive grain growth.
• Layer design: Multiple thin layers are preferred over a single thick layer to minimize dilution with the base metal and ensure consistent hardfacing composition throughout the weld deposit.
• Post-weld treatment: Depending on the roll service requirements, post-weld heat treatment may include stress-relief annealing or controlled cooling to optimize the hardfacing microstructure.

From an engineering practice perspective, the economic benefits of this hardfacing system are substantial. A typical large hot rolling slab roll has a diameter of 800-1200 mm and a working length of 1500-2500 mm. Without hardfacing, roll life may be limited to 500-1000 hours of operation. With proper hardfacing, this can be extended to 3000-5000 hours, representing a 3-5 times improvement in service life and a corresponding reduction in roll replacement costs and production interruptions.

Key Questions and Reflections

Several important technical questions arise from this literature:

1. Dilution control: How effectively can the base metal dilution be controlled in multi-layer hardfacing of large rolls, given the substantial cross-section of the roll body? The paper does not provide quantitative dilution data, which limits our understanding of the actual hardfacing composition achieved in service.
2. Cracking resistance: The transition zone between the hardfacing layer and the low-carbon steel base metal is susceptible to cracking due to thermal expansion mismatch and residual stress concentration. The paper does not adequately address cracking prevention strategies beyond preheating.
3. Service life validation: While the paper claims "obvious technical-economic effects," detailed service life data comparing the H25Cr3Mo2MnVA hardfacing with conventional hardfacing materials would strengthen the case for widespread adoption.
4. Microstructural evolution during service: The hardfacing microstructure undergoes changes during rolling service due to thermal cycling, mechanical deformation, and chemical interaction with the rolled steel. Understanding these in-service microstructural changes is essential for predicting wear life and optimizing the hardfacing composition.

Study Insights and Implications

This paper represents an important step in China's development of domestically produced hardfacing consumables for critical industrial applications. The H25Cr3Mo2MnVA wire demonstrates that dispersion-strengthened steel electrodes can achieve competitive performance with imported alternatives at significantly lower cost. The key insight is that the combination of vanadium and molybdenum carbide particles provides superior high-temperature wear resistance compared to conventional high-carbon steel electrodes that rely solely on carbide volume fraction for hardness.

For engineers working in rolling mill maintenance, this paper provides a practical framework for hardfacing repair programs. The recommended approach of using multiple thin layers with controlled interpass temperatures, combined with proper base metal preparation, forms the foundation of a reliable hardfacing repair methodology that can be adapted to other heavy-duty wear applications including mill backup rolls, guide rolls, and work rolls in various rolling configurations.

The paper's publication in 1992 reflects the rapid pace of domestic technology development in China's metallurgical industry during that era. While some process details may have evolved with modern welding equipment and monitoring systems, the fundamental principles of hardfacing consumable selection and process control remain valid and continue to guide current engineering practice in roll maintenance worldwide.