WC roll rings are critical components in high-speed wire rod rolling systems, determining production efficiency, product quality, and operational costs. Operating under extreme service conditions, their durability is predominantly governed by high-temperature oxidation resistance—a key failure mechanism in elevated-temperature environments.
This study elaborates on high-temperature oxidation principles, clarifies protective oxide film formation criteria, and applies these insights to the composition optimization of WC-Co-Ni cemented carbide roll rings, aiming to synergistically improve oxidation resistance, mechanical strength, and thermal fatigue performance.
Significance of High-Temperature Oxidation Resistance for WC Roll Rings
High-speed wire rod mills operate at 95–112 m/s, subjecting roll rings to harsh service environments: ambient temperatures approaching 1000℃, cyclic thermal shock, high rolling stress, and intense high-temperature oxidation/corrosion.
Among these factors, high-temperature oxidation is a primary cause of degradation—metallic constituents react with oxygen to form oxides that compromise structural integrity. Thus, understanding oxidation mechanisms is indispensable for designing WC roll rings with prolonged service life.
Schematic of the Metal Oxidation Process (Oxygen Adsorption – Dissociation – Ion Diffusion – Oxide Film Growth
Fundamental Principles of High-Temperature Oxidation
Mechanisms of Metal Oxidation at Elevated Temperatures
High-temperature oxidation is a heterogeneous reaction involving oxygen adsorption, dissociation, diffusion into the metal lattice, and oxide formation upon solubility saturation. Metals form either unstable liquid/gaseous oxides (e.g., V₂O₅, MoO₃) that accelerate oxidation, or dense, continuous, thermally stable solid oxides (e.g., Cr₂O₃, Al₂O₃, SiO₂) that inhibit oxygen penetration—critical for safeguarding WC roll ring integrity.
Critical Characteristics of Protective Oxide Films
Reliable protective oxide films for WC roll rings must satisfy four criteria:
(1) Pilling-Bedworth (P-B) ratio > 1 for complete surface coverage; (2) high thermodynamic stability (low decomposition pressure, high melting point);
(3) dense microstructure and high resistivity to suppress ion diffusion;
(4) strong interfacial bonding and matched thermal expansion with the substrate. For roll rings, a continuous, dense Cr₂O₃ film is the optimal protective mechanism due to its exceptional stability and barrier properties.
Selection Criteria for Oxidation-Resistant Alloying Elements
Alloying elements for enhancing WC roll ring oxidation resistance must:
(1) form protective oxide films (e.g., Cr→Cr₂O₃);
(2) exhibit higher oxide thermodynamic stability than the substrate;
(3) possess sufficient solid solubility in the matrix for continuous film formation. Cr is the core antioxidant element, while Al, Si, and rare earth metals also contribute—Cr remains primary for optimizing roll ring high-temperature performance.
Composition Design of WC Roll Rings Guided by Oxidation Theory
Design Rationale for Binder Phase Composition
WC-Co-Ni cemented carbide is widely used for WC roll rings due to balanced mechanical properties and corrosion resistance. Its oxidation resistance is determined by the binder phase, optimized herein based on oxidation principles:
(1) incorporate Cr to form a continuous Cr₂O₃ protective film;
(2) partially substitute Co with Ni to improve corrosion resistance and high-temperature stability;
(3) restrict Mo addition (enhances acidic corrosion resistance but forms volatile oxides that undermine protective films).
Binder Phase Compositions and Experimental Design
Five binder phase formulations were designed to investigate alloying element effects on roll ring performance (Table 1).
Table 1 Binder phase compositions of roll rings (mass fraction, %)
Alloy
Co
Ni
Cr
Mo
A
100
—
—
—
B
55
45.0
—
—
C
55
42.5
2.5
—
D
55
40.0
2.5
2.5
E
55
40.0
5.0
—
Experimental Results and Discussion
Physical and Mechanical Properties
Table 2 summarizes the physical and mechanical properties of roll ring samples. All formulations exhibit density (14.43–14.49 g·cm⁻³), hardness (86.6–88.1 HRA), and flexural strength (1841–2751 MPa) meeting high-speed rolling requirements. Partial Co substitution with Ni and appropriate Cr addition does not significantly compromise mechanical performance.
Table 2 Physical and mechanical properties of WC roll ring samples
Alloy
Density (g·cm⁻³)
Hardness (HRA)
Flexural Strength (MPa)
A
14.49
88.1
2744
B
14.47
86.6
2751
C
14.49
86.7
2406
D
14.45
86.9
2309
E
14.43
86.9
1841
High-Temperature Oxidation Resistance
Oxidation weight gain data (Table 3) demonstrate:
(1) Alloy E (5% Cr) exhibits the lowest oxidation weight gain (0.19% at 850℃, 1.56% at 1000℃) due to continuous Cr₂O₃ film formation;
(2) Alloy D (with Mo) shows no oxidation resistance improvement, as Mo oxides are volatile;
(3) all Cr-containing alloys outperform non-Cr formulations, confirming Cr’s indispensable role in enhancing WC roll ring oxidation resistance.
Table 3 Oxidation weight gain of roll ring samples (mass fraction, %)
Alloy
850℃
900℃
950℃
1000℃
A
0.35
1.16
1.55
2.57
B
0.74
1.36
1.99
2.59
C
0.45
0.99
1.66
2.37
D
0.74
1.18
1.73
2.60
E
0.19
0.47
0.94
1.56
Conclusions
High-temperature oxidation resistance for WC roll rings relies on forming a continuous, dense, thermally stable solid oxide film—Cr₂O₃ is the most effective protective oxide, providing the theoretical foundation for antioxidant design.
Adding ~5% Cr (in the binder phase) to roll rings facilitates Cr₂O₃ film formation, significantly improving 1000℃ oxidation resistance, with experimental results consistent with theoretical predictions.
Ni can partially replace Co to enhance roll ring corrosion resistance without compromising mechanics. Mo improves acidic corrosion resistance but offers limited oxidation protection, requiring strict content control.
WC roll ring composition design must integrate oxidation mechanisms with mechanical requirements to achieve synergistic optimization of performance. This study provides a scientific basis for rational design and performance improvement of WC roll rings in high-speed wire rod rolling.
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