Development of Iron-Based High-Temperature Wear-Resistant Alloy Overlay Electrodes

Literature Overview

This 1996 paper published in the Journal of Shenyang University of Technology by Xu Guojian and colleagues from Shenyang University of Technology, in collaboration with Shenyang High Voltage Switch Co., Ltd., presents the development of a Cr-Mo-B alloy system overlay welding electrode designed for high-temperature wear resistance. The study includes both laboratory characterisation and field service evaluation, providing practical validation of the electrode's performance in a real industrial application on brick-making machinery.

Core Technical Findings

The developed overlay electrode belongs to the Cr-Mo-B alloy family and produces weld deposits with a microstructure consisting of martensite matrix containing eutectic colonies of borides and carbides. The key hard phases identified include borides (Fe2B, CrB) and carbides (Mo2C, Cr7C3), which provide both room temperature and elevated temperature hardness. The deposit demonstrates wear resistance 2 to 3 times that of the conventional "Dui 667" electrode at ambient temperature, with hardness reaching HV306.4 at 700 degrees Celsius. Field testing on brick-making machine dual-shaft mixer blades showed a service life improvement of more than 5 times compared to the original quenched 45 steel components.

Interpretation of Technical Points

The Cr-Mo-B system is a classic iron-based hardfacing alloy design that exploits the complementary contributions of chromium, molybdenum, and boron to achieve combined room temperature and elevated temperature wear resistance. Chromium promotes formation of hard and stable carbides and borides, molybdenum enhances tempering resistance of the martensitic matrix and forms its own hard carbide phase, and boron forms extremely hard boride compounds that are particularly effective against abrasive wear.

The martensitic matrix is significant because it provides the necessary toughness to support the hard phases without catastrophic brittle fracture. The eutectic microstructure, where borides and carbides are distributed throughout the martensite in a lamellar or network pattern, creates an efficient load-bearing architecture that distributes applied stresses across both hard and tough phases.

The red hardness (hot hardness) of HV306.4 at 700 degrees Celsius is particularly noteworthy. Many iron-based hardfacing alloys experience significant softening above 500 degrees Celsius due to martensite decomposition and carbide coarsening. The retention of substantial hardness at 700 degrees Celsius indicates that the specific combination of Cr, Mo, and B in this alloy creates phases with high thermal stability.

Connection to Engineering Practice

The field service evaluation on brick-making machine blades provides invaluable practical validation. Brick-making machinery operates under severe conditions involving continuous abrasion by clay and refractory materials, cyclic thermal loading, and mechanical impact. The 5-fold improvement in service life translates directly into reduced downtime, lower maintenance costs, and improved production throughput.

For engineers considering similar applications, the following factors should be evaluated:

1. Wear mechanism identification: Determine whether the dominant wear mechanism is abrasion, adhesion, erosion, or a combination thereof, as different hardfacing systems excel against different mechanisms.
2. Temperature profile: Establish the maximum and cyclic operating temperatures to ensure that the selected hardfacing alloy maintains adequate hardness and wear resistance throughout the thermal cycle.
3. Mechanical loading: Assess the magnitude and nature of mechanical stresses (impact, bending, cyclic) to ensure that the overlay has sufficient toughness to resist cracking and spalling.
4. Base metal compatibility: Verify that the hardfacing alloy can be deposited on the base metal without excessive cracking, porosity, or dilution-related property degradation.

Key Questions and Reflections

The paper prompts reflection on the role of boron in iron-based hardfacing alloys. Boron is known to be a carbide suppressor, promoting boride formation at the expense of carbide formation. The specific balance between boride and carbide phases in the Cr-Mo-B system appears to be critical for achieving the reported combination of hardness and toughness. Small variations in boron content could significantly alter the phase balance and consequently the wear performance.

Furthermore, the long-term stability of the boride and carbide phases under prolonged thermal exposure at 700 degrees Celsius warrants consideration. While the measured hardness at this temperature is satisfactory, extended exposure could lead to phase coarsening, decomposition, or transformation that would progressively reduce hardness and wear resistance over time. Understanding the time-temperature dependence of microstructural stability is essential for predicting long-term service performance.

Study Insights and Implications

This work from 1996 remains highly relevant to modern engineering practice, demonstrating the enduring value of iron-based hardfacing alloys for high-temperature wear applications. The integration of laboratory development with field validation provides a model for consumable development that bridges the gap between metallurgical research and industrial application. The Cr-Mo-B system offers an economical alternative to more expensive Ni-base or Co-base hardfacing alloys for many applications, and the demonstrated 5-fold life improvement makes the economic case compelling. Engineers should not overlook iron-based systems when specifying overlay welding consumables, as they often provide the best combination of performance and cost-effectiveness for moderate to severe wear conditions.