Development of High-Hardness Wear-Resistant Fe-Cr-B-C Surfacing Electrodes

Literature Overview

The paper by Li Yasong et al. from Jiamusi University, published in Guangdong Chemical Industry (2024, Vol. 51, No. 15, pp. 29-31), presents a systematic investigation into the design and evaluation of manual surfacing electrodes based on the Fe-Cr-B-C alloy system. The authors aimed to develop an economical, high-hardness wear-resistant electrode by leveraging widely available and cost-effective raw materials such as high-carbon ferrochromium, boron carbide, and minor additions of ferrovanadium, ferromolybdenum, and ferрониobium alloy powders. This work is particularly relevant to engineers dealing with abrasive wear applications in mining, cement, and material handling equipment where surfacing repairs are routinely performed in the field.

Core Technical Approach

The electrode design philosophy centers on the flux composition rather than the electrode core alloying. The researchers selected H08A-class mild steel wire as the electrode core, relying entirely on the flux coating to deliver the required alloying elements to the weld metal. This approach offers significant economic advantages since the core wire is a commodity product, while the flux can be tailored with specific alloy powders. The multi-layer surfacing technique was employed to ensure adequate dilution control and to achieve the desired microstructural characteristics in the final surface layer.

Alloy Design and Flux Composition

The key alloying strategy involves:

• High-carbon ferrochromium: Provides chromium for carbide formation and enhances wear resistance through secondary hardening effects.
• Boron carbide (B4C): Introduces boron into the weld metal, promoting the formation of hard boride phases.
• Ferrovanadium, ferromolybdenum, ferрониobium: Added in small quantities to refine the microstructure, increase solid solution strengthening, and promote the formation of fine precipitates.

Microstructural Analysis

The microstructural investigation using optical microscopy (OM) and X-ray diffraction (XRD) revealed that the surfacing layer consists primarily of:

• Acicular (lath) martensite: The base matrix phase resulting from the high carbon and alloy content combined with rapid solidification.
• Eutectic structure of Fe and (Fe,Cr)3(B,C): Hard boride and borocarbide phases distributed along grain boundaries and interdendritic regions.

The average Rockwell hardness achieved was 61.8 HRC, which is competitive with many commercial wear-resistant surfacing alloys and significantly exceeds the hardness of unalloyed weld metal.

Key Technical Parameters

Engineering Practice Implications

From a practical standpoint, the achievement of 61.8 HRC hardness with good weldability and slag removal characteristics is notable. In field applications, high hardness without corresponding ductility often leads to cracking during service. The absence of internal cracks in the as-welded condition suggests that the alloy design maintains an acceptable balance between hardness and toughness. However, engineers should note that hardness above 60 HRC typically necessitates post-weld stress relief or controlled cooling to prevent delayed cracking in thick sections.

The use of boron carbide as a flux additive is particularly interesting because boron is a sensitive element that can be lost during welding due to its low boiling point. The multi-layer surfacing approach helps mitigate this issue by allowing the initial layers to serve as a reservoir for boron redistribution in subsequent passes.

Study Insights and Reflections

This work demonstrates that cost-effective wear-resistant surfacing solutions can be developed through rational flux design without resorting to expensive cobalt-based or nickel-based alloy systems. The Fe-Cr-B-C system offers a compelling alternative for moderate-severity abrasive wear applications where extreme temperature resistance is not required. For engineers specifying surfacing materials for mineral processing equipment or conveyor components, this electrode system warrants further evaluation under actual service conditions, particularly regarding hardness retention after thermal cycling and resistance to adhesive wear mechanisms.