Development of Hot Rolling Roll Wear-Resistant Overlay Welding Electrodes - Literature Study Notes

Context and Application Requirements

Hot rolling mill rolls operate under uniquely demanding conditions that distinguish them from other industrial applications. The roll surface is in direct contact with hot metal strips at temperatures ranging from 800 °C to 1200 °C, subject to high contact pressures, sliding friction, and repeated thermal cycling. The resulting wear mechanisms include abrasive wear from oxide scale removal, adhesive wear from metal-to-metal contact, and thermal fatigue from cyclic heating and cooling. The overlay electrode developed in this study is specifically designed to withstand these combined degradation mechanisms.

The performance requirements for a hot rolling roll overlay electrode are stringent and multifaceted:

Electrode Chemistry and Microstructural Design

The electrode chemistry is the foundation of overlay performance. For hot rolling roll applications, the filler metal must incorporate elements that form stable, heat-resistant carbides and oxides while maintaining sufficient toughness to resist cracking.

The primary alloying elements and their functions are as follows:

The microstructural target is a composite of hard carbide particles (Cr7C3, Mo2C, VC) dispersed in a ductile matrix of martensite and retained austenite. The retained austenite fraction, typically 10-25% by volume, serves a dual purpose: it provides transformation-induced plasticity (TRIP) that absorbs thermal and mechanical stresses, and it undergoes martensitic transformation during quenching, generating additional compressive residual stresses that inhibit crack propagation.

The electrode coating composition is designed to provide adequate slag coverage, deoxidation, and alloying. A typical coating composition includes CaO, SiO2, Al2O3, TiO2, and iron oxide, with a basicity ratio (CaO/SiO2) of 2.0-3.0. The coating also contains alloying powders of chromium, molybdenum, and vanadium to supplement the wire core composition and ensure the final weld metal meets the target chemistry.

Performance Evaluation Methodology

The evaluation of hot rolling roll overlay electrodes requires accelerated testing that simulates actual rolling conditions. The following test protocol is recommended:

The literature reports that the developed electrode achieves a room-temperature hardness of 55-58 HRC, with hardness retention of approximately 85% after exposure to 600 °C for 100 hours. The abrasive wear rate is reduced by a factor of 2.5-3.0 compared to the uncoated roll substrate. Thermal fatigue testing shows no visible cracking after 500 cycles between 25 °C and 900 °C, indicating excellent resistance to thermal stress cycling.

Process Parameters and Welding Procedure

The welding procedure for hot rolling roll overlay must balance high heat input (to promote full alloying and reduce cracking) with controlled cooling (to achieve the target microstructure). The following parameters are typical:

The preheat of 200-300 °C is recommended to reduce the risk of cracking in the substrate, particularly for high-carbon roll materials such as W12Cr4V4 or high-speed steel. However, the electrode is designed to be tolerant of reduced preheat conditions, with acceptable results achievable even at 100 °C preheat for lower-carbon substrates.

Engineering Practice and Field Performance

Field trials of the developed electrode on actual hot rolling mill rolls have demonstrated significant improvements in roll life. A typical case study involves a 650 mm finish mill roll in a strip mill processing hot-rolled coil. The original roll life was approximately 800-1000 tons of steel processed before requiring regrinding or replacement. After overlay welding with the developed electrode, the roll life extended to 2200-2800 tons, representing a 2.5-3.0× improvement.

The overlay layer thickness of 3-5 mm provides sufficient material for multiple regrinding cycles during the roll's extended service life. After the overlay layer is ground away during normal operation, the remaining overlay provides continued protection until the substrate is exposed, at which point the roll requires re-overlay.

Study Insights and Reflections

The development of a purpose-designed hot rolling roll overlay electrode, as opposed to adapting general-purpose hardfacing electrodes, yields substantial performance benefits. The key insight from this research is that the microstructural design must be tailored to the specific degradation mechanisms of the application. For hot rolling, the combination of thermal stability, thermal fatigue resistance, and abrasive wear resistance requires a carefully balanced alloy system that no single element can provide alone.

The practical challenge lies in maintaining consistency of electrode performance from batch to batch, which requires strict control of the coating composition, drying conditions, and storage environment. The electrode must be stored at controlled humidity below 60% RH and dried at 300 °C for 2 hours before use to prevent hydrogen-induced cracking. Future research should focus on extending the service life further through the incorporation of nano-scale carbide reinforcements and on developing automated overlay welding procedures that ensure consistent bead geometry and chemistry across large roll surfaces.

This work exemplifies the principle that overlay welding is not merely a surface treatment but a metallurgical engineering discipline that requires deep understanding of the interaction between filler metal chemistry, thermal cycle, and service environment.