Microstructure and Properties of Fe-Cr-B-C Wear-Resistant Cladding Alloys

Literature Overview

This study provides a comprehensive investigation of the microstructure evolution and mechanical properties of Fe-Cr-B-C system wear-resistant cladding alloys, a material family widely employed in industrial applications such as mining equipment, cement grinding mills, power generation components, and material handling systems. The research systematically examines how chromium content, boron addition, carbon levels, and heat treatment conditions influence the formation of hard phases, microhardness distribution, wear resistance, and fracture toughness in the cladding layer. The findings are directly applicable to the selection and optimization of hardfacing consumables for severe abrasion service conditions.

Compositional Design and Phase Formation

The Fe-Cr-B-C system is characterized by the formation of multiple hard phases including Cr₇C₃, CrB, Cr₂B, and Fe₂B, whose relative proportions and distributions are governed by the alloy composition and solidification conditions. The study identifies four compositional regimes that produce distinct microstructural architectures.

Composition Range	Dominant Phases	Microstructure Type	Hardness (HV)
Low Cr (3–5%), Low B (0.5–1.0%), C (2.0–2.5%)	Cr₇C₃, Fe₃C	Martensite + carbides	800–1000
Medium Cr (8–12%), Medium B (1.5–2.5%), C (2.5–3.0%)	Cr₇C₃, CrB, Fe₂B	Martensite + borides + carbides	1200–1500
High Cr (15–20%), High B (3.0–4.0%), C (3.0–3.5%)	CrB, Cr₂B, Cr₇C₃	Boride network + carbides	1500–1800
Very High Cr (20–25%), Very High B (4.0–5.0%), C (3.5–4.0%)	Cr₂B, Cr₃B₄	Dense boride network	1800–2200

Heat Treatment Effects

The study demonstrates that heat treatment is a critical variable in optimizing the performance of Fe-Cr-B-C cladding alloys. The as-deposited microstructure typically contains retained austenite and coarse primary phases that can be refined through appropriate thermal processing.

Heat Treatment Condition	Hardness Change	Phase Transformation	Fracture Toughness Change
As-deposited	Baseline	Retained austenite + coarse carbides/borides	Baseline
750°C × 2 h air cool	+5–10%	Partial austenite decomposition, carbide spheroidization	+15–20%
800°C × 1 h oil quench	+10–15%	Full martensitic transformation, fine carbide dispersion	-5–10%
800°C × 1 h oil quench + 200°C × 2 h temper	+5–8%	Tempered martensite, reduced residual stress	+25–35%
900°C × 1 h water quench	+15–20%	Fine martensite, dissolved coarse borides	-10–15%

Wear Resistance and Fracture Toughness Trade-off

A central theme of the study is the inherent trade-off between wear resistance and fracture toughness in Fe-Cr-B-C cladding alloys. As boron and chromium content increase, the volume fraction of hard boride phases increases, driving hardness up to 2200 HV but simultaneously reducing fracture toughness from 15–20 MPa·m^½ in low-alloy compositions to 5–8 MPa·m^½ in high-alloy compositions.

The wear resistance was evaluated through dry sliding wear testing against SiC abrasive paper (P80 grit) at normal loads of 5, 10, and 20 N over sliding distances of 500 m. The wear volume loss decreased from 45–55 mm³ at 10 N load for the low-alloy composition to 8–12 mm³ for the high-alloy composition, representing a 4–5 fold improvement. However, the high-alloy compositions exhibited catastrophic spalling under impact loading conditions, with failure occurring at impact energies below 5 J compared to 15–20 J for the low-alloy compositions.

Process Parameters and Cladding Quality

The quality of the Fe-Cr-B-C cladding layer is significantly influenced by the welding process parameters. The study compares submerged arc welding (SAW), flux-cored arc welding (FCAW), and gas metal arc welding (GMAW) for depositing these alloys.

Process	Dilution (%)	Layer Thickness (mm)	Hardness Uniformity	Inclusion Content
SAW (single pass)	8–15	3.0–5.0	Good (±5%)	Low (<0.5%)
FCAW (multi-pass)	5–12	1.5–3.0	Moderate (±10%)	Moderate (0.5–1.5%)
GMAW (multi-pass)	3–8	0.5–2.0	Poor (±15%)	Low (<0.5%)
PTA (multi-pass)	2–5	0.3–1.5	Excellent (±3%)	Very low (<0.2%)

Engineering Application Guidance

The study provides clear guidance for matching Fe-Cr-B-C cladding compositions to specific service conditions. For sliding abrasion against hard, angular particles (such as in cement grinding or ore processing), the medium Cr–medium B composition with 800°C oil quench heat treatment offers the optimal balance of wear resistance (1200–1500 HV) and acceptable toughness. For impact-abrasion environments (such as in mining shovels or crusher jaws), the low Cr–low B composition with 750°C air cool treatment is preferred due to its superior fracture toughness.

A practical consideration highlighted by the study is the effect of cladding layer thickness on performance. Layers thinner than 1.0 mm are susceptible to substrate cracking under severe abrasion because the high hardness of the cladding creates a brittle substrate overlay interface. Layers thicker than 5.0 mm develop internal residual stresses that can cause spalling. The recommended thickness range is 2.0–4.0 mm, with a gradient in hardness from 800 HV at the surface to 600 HV at the interface to minimize interfacial stress.

Key Questions and Study Insights

The study raises an important question about the role of microstructure refinement in overcoming the hardness-toughness trade-off. While conventional approaches increase hardness by increasing boride volume fraction, alternative strategies such as nanostructured boride networks or composite cladding with a tough base layer and a hard surface layer could potentially decouple these properties.

Another insight is the importance of interpass temperature control in multi-pass cladding. Maintaining interpass temperatures below 200°C is essential to prevent the coarsening of primary boride phases, which would reduce hardness by 100–200 HV. In practice, this requires careful monitoring of the substrate temperature during multi-pass operations, particularly for thick cladding builds.

The Fe-Cr-B-C system remains one of the most versatile and widely used wear-resistant cladding material families, and the systematic compositional-structural-property relationships established in this study provide a reliable foundation for material selection and process optimization in industrial hardfacing applications.