Microstructure and Wear Resistance of FeCr15B2MnTi Open-Arc Cladding Alloy

Literature Overview

Published in Ordnance Materials and Engineering in 2019 by Gong Jianxun, Yao Huiwen, and Cheng Shiyao from Xiangtan University, this study examines the microstructure and abrasive wear behavior of an FeCr15B2MnTi open-arc cladding alloy. The research, supported by the Hunan Natural Science Foundation Joint Fund, focuses on a high-chromium, boron-containing alloy system deposited using open-arc (gas shielded) welding methods. The alloy composition represents a deliberate design choice to maximize carbide formation and optimize the balance between hardness and toughness for severe abrasive wear applications.

Alloy Composition and Design Rationale

The FeCr15B2MnTi composition is engineered to produce a microstructure dominated by hard carbide phases with a supporting matrix that provides sufficient toughness to prevent catastrophic failure. Each alloying element serves a specific purpose in the overall design.

The high chromium content (15%) ensures the formation of extensive Cr₇C₃ and Cr₂₃C₆ carbide networks, while boron addition promotes the formation of ultra-hard B₄C and iron borides. Titanium contributes TiC and TiB₂ phases that are among the hardest known carbide and boride compounds. Manganese serves to stabilize retained austenite, providing transformation toughening without significantly reducing hardness.

Microstructural Characterization

Phase Distribution and Morphology

Optical microscopy and SEM examination reveal a complex microstructure consisting of multiple carbide and boride phases distributed within a mixed martensitic-austenitic matrix. The carbide network forms a continuous or semi-continuous structure that provides the primary wear resistance mechanism.

The primary phases identified include:

• Cr₇C₃: Network-forming carbides along grain boundaries
• Cr₂₃C₆: Blocky carbides in the interdendritic regions
• B₄C: Tetragonal boride particles, often associated with Cr carbides
• TiC: Cubic carbide particles, typically 1-5 μm in size
• TiB₂: Hexagonal boride particles, extremely hard (HV 3000+)
• Retained austenite: Matrix phase providing toughness

The morphology of these phases is critical for wear performance. Network-forming Cr₇C₃ carbides provide continuous hard paths that resist abrasive material removal, while discrete TiC and TiB₂ particles act as individual wear-resistant units that can be exposed as the softer matrix is removed.

Matrix Microstructure

The matrix consists primarily of martensite with varying amounts of retained austenite, depending on the cooling rate during welding. The high carbon and alloy content promotes martensite formation even at moderate cooling rates, ensuring high hardness throughout the deposit. The manganese addition stabilizes austenite that would otherwise transform completely to martensite, providing a toughening mechanism through stress-induced martensitic transformation during wear.

Wear Performance and Mechanism Analysis

Abrasive Wear Testing Results

The wear testing conducted in this study demonstrates that the FeCr15B2MnTi alloy achieves exceptional abrasive wear resistance, with specific wear rates significantly lower than conventional hardfacing alloys. The wear resistance index (ratio of baseline wear rate to alloy wear rate) typically exceeds 5-8 times that of standard 300-series stainless steel overlays.

Wear Mechanism Interpretation

The superior wear resistance of this alloy system is attributed to several synergistic mechanisms:

1. Hard carbide and boride phases resist microcutting and plowing by abrasive particles
2. The continuous carbide network prevents crack initiation and propagation
3. Retained austenite provides transformation toughening under impact loading
4. Chromium oxide films form in corrosive environments, providing additional protection
5. The multi-phase microstructure distributes stress and prevents localized damage

Open-Arc Cladding Process Considerations

The use of open-arc (gas shielded) welding for this alloy composition presents specific challenges and advantages compared to submerged arc welding. Open-arc methods provide better visual monitoring of the weld pool and allow more precise control of deposition geometry, but they are more susceptible to atmospheric contamination and spatter.

Process Parameters for Optimal Results

The gas shielded approach requires careful attention to gas coverage, particularly at the trailing edge of the weld pool where the solidifying metal is most vulnerable to oxidation. Incomplete shielding can lead to surface oxidation, porosity, and reduced hardness in the near-surface region.

Engineering Applications and Quality Control

This alloy system is particularly suited for applications involving severe abrasive wear, including:

• Mining equipment components (shovel buckets, conveyor chutes)
• Cement industry wear parts (mill liners, hoppers)
• Coal handling equipment (chutes,溜槽)
• Hydraulic cylinder liners
• Pump impellers and wear rings
• Pressure vessel internals in slurry service

Quality control procedures should include:

1. Hardness testing at multiple depths to verify consistent microstructure
2. Metallographic examination to confirm proper carbide distribution
3. Bond strength testing to ensure adequate substrate adhesion
4. Wear testing on coupons to validate performance before full-scale application
5. Non-destructive testing (MT or PT) to detect surface defects

Study Insights and Reflections

This research demonstrates the effectiveness of multi-element alloy design in achieving exceptional wear resistance through synergistic phase interactions. The FeCr15B2MnTi composition represents a carefully optimized balance between hardness-providing carbides and toughness-providing matrix phases, achieving performance levels that exceed many conventional hardfacing alloys.

For engineers in the bimetallic pressure vessel industry, this alloy system offers a promising option for protecting critical internals in abrasive slurry service. The open-arc deposition method provides flexibility for field application and repair work, while the alloy's resistance to both abrasive and corrosive wear mechanisms makes it suitable for harsh chemical processing environments. However, the high alloy content and resulting cost must be weighed against the service life extension benefits, and proper process control is essential to achieve the designed microstructure and performance.