Microstructure and Wear Resistance of FeCr15B2MnTi Open-Arc Surfacing Alloy

Literature Overview

This research by Gong Jianxun, Yao Huiwen, and Cheng Shiyao, published in Ordnance Materials and Science in 2019 (Volume 42, Issue 4, pages 82-86), investigates the microstructure and wear resistance of a high-boron FeCr15B2MnTi surfacing alloy deposited using self-shielded flux-cored wire in an open-arc surfacing process. The work was supported by the Hunan Provincial Natural Science Foundation (Grant 2015JJ5031). This study represents an evolution of the research program initiated in the earlier work on chromium effects in Fe-C-V-B alloys, extending the investigation to include titanium as an additional alloying element and employing a different deposition process.

Core Technical Findings

The principal findings of this study reveal a complex microstructural evolution driven by the interaction of high boron content, chromium, and titanium in the surfacing alloy:

• The high-boron open-arc surfacing alloy precipitates a large quantity of white primary phases with microhardness ranging from 927.3 HV₀.₁ to 1739 HV₀.₁
• The volume fraction of these primary phases exceeds 80% of the microstructure
• As TiC primary phase quantity increases, the volume fraction of the white primary phases decreases
• Embedded within the light gray M₂B phase is M₂₃(C,B)₆, classified as a carbon-boron type hard phase
• Increasing titanium content significantly reduces the brittle transformation eutectic (α-Fe + M₃(C,B)), causing weld cracks to disappear
• The wear mechanism involves both micro-cutting and micro-flaking, with micro-cutting being the dominant mechanism

Microstructural Analysis

The microstructure of this alloy can be understood through the lens of solidification sequence and phase transformation:

1. Primary crystallization of high-hardness carbide/boride phases (TiC, VB, CrB)
2. Formation of the M₂B iron boride matrix with embedded M₂₃(C,B)₆ particles
3. Eutectic solidification of remaining liquid into (α-Fe + M₃(C,B)) transformation eutectic

The critical insight is the role of titanium as a microstructure refiner and crack suppressor. Titanium preferentially forms TiC particles that act as nucleation sites and consume boron from the melt, thereby modifying the eutectic reaction. The reduction in brittle transformation eutectic is particularly significant because this phase is responsible for crack initiation and propagation in high-boron surfacing alloys.

Technical Parameters and Phase Analysis

Wear Mechanism Analysis

The identification of micro-cutting as the dominant wear mechanism is consistent with the high volume fraction of hard phases in a relatively softer matrix. In this mechanism, the hard carbide and boride particles act as cutting edges that remove material from the counterface. Micro-flaking occurs when clusters of hard phases are pulled out from the matrix, leaving depressions that accelerate subsequent wear. The transition from crack-prone to crack-free welds with increasing titanium is directly related to the reduction of the brittle eutectic that would otherwise provide crack initiation sites.

Process Analysis and Standards Context

The use of open-arc (self-shielded) surfacing with flux-cored wire represents a practical approach for field applications where shielding gas equipment is not available. This process is particularly relevant for:

• Field repair of mining and construction equipment
• Large-scale surfacing operations in outdoor environments
• Applications requiring high deposition rates with minimal equipment complexity

From a standards perspective, surfacing alloys of this type would typically be evaluated according to relevant Chinese national standards (GB/T) for surfacing materials and their performance requirements. The classification TG455 indicates conformance with surfacing welding technology standards. The mechanical testing protocols implied by the study (microhardness mapping, wear testing) align with standard practices for surfacing alloy characterization.

Engineering Practice Applications

This alloy system is particularly suited for applications requiring extreme abrasion resistance in environments where the component is subject to severe sliding or rolling contact with abrasive materials. Typical applications include:

• Mining equipment components (shovel teeth, bucket liners)
• Cement industry equipment (grinding mill liners, chutes)
• Agricultural machinery (plowshares, harrow teeth)
• Power generation equipment (furnace wear plates)

Critical Process Parameters

The successful deposition of this high-boron alloy requires careful attention to several process parameters:

• Preheating temperature: adequate preheating (typically 150-250°C) is essential to reduce thermal gradients and prevent hot cracking
• Interpass temperature: must be maintained to prevent excessive cooling rates that could promote brittle phase formation
• Wire feed speed and travel speed: must be optimized to achieve proper dilution control and bead profile
• Flux composition: the self-shielded flux must provide adequate deoxidation and slag protection

Key Reflections and Study Insights

The most significant contribution of this paper is the demonstration that titanium addition can simultaneously improve both the microstructure quality and the wear performance of high-boron surfacing alloys. The mechanism by which titanium reduces the brittle eutectic fraction while maintaining or even increasing the volume of hard primary phases represents an elegant solution to the classic toughness-wear resistance trade-off in boron-containing alloys.

From a practical standpoint, the elimination of weld cracks through titanium addition is perhaps the most immediately valuable finding. Cracking in surfacing welds is one of the most common quality issues encountered in production, and the ability to prevent cracking through alloy design rather than solely through process control represents a significant advance in surfacing technology.

The micro-cutting wear mechanism identified in this study has important implications for matching surfacing alloys to specific wear conditions. In applications where the counterface material is relatively soft, the micro-cutting mechanism is most effective, but in applications involving hard counterface materials, the alloy may require additional toughness to resist micro-flaking and spalling. Engineers should carefully consider the counterface material properties when specifying this type of surfacing alloy.

This research contributes to the systematic understanding of how multiple alloying elements interact in complex surfacing systems, providing a foundation for rational alloy design rather than empirical trial-and-error approaches.