In the field of engineering materials, improving the toughness of white cast iron, particularly high-chromium variants, has long been a focal point for researchers. The inherent brittleness of white cast iron often limits its use in applications involving impact or dynamic loading. Traditional approaches have focused on altering carbide morphology—such as spheroidization, nodularization, or plate-like formation—to enhance mechanical properties. However, these methods have shown limited success due to process constraints or insufficient improvements in toughness. In this study, we propose that modifying carbide morphology is a necessary but not sufficient condition for toughness enhancement. We hypothesize that simultaneously refining the matrix microstructure, improving grain boundary conditions, and controlling carbide distribution can lead to significant gains in toughness for high-chromium white cast iron. Based on this premise, we conducted a series of experiments using specific modifiers to treat the white cast iron, followed by heat treatments to optimize the matrix composition. Our results demonstrate that this integrated approach not only improves carbide morphology but also enhances impact toughness, fracture toughness, and multi-impact resistance, thereby expanding the application range of high-chromium white cast iron to components subjected to moderate impact loads.
The core objective of this research is to develop a high-chromium white cast iron with balanced toughness and wear resistance. We aimed to achieve this by: (1) investigating pathways to modify carbide morphology and distribution, (2) determining the optimal matrix composition and phase proportions, (3) exploring methods to refine grain boundaries and improve their metallurgical state, and (4) validating the material’s performance through field trials on impact-prone wear parts. This article details our experimental methodology, presents quantitative results using tables and formulas, and discusses the implications for industrial applications.
To ensure consistency and comparability across experiments, we controlled all process variables rigorously. The base high-chromium white cast iron was melted in medium-frequency induction furnaces, with compositions maintained within the following ranges: Carbon (C) 2.6–3.2%, Silicon (Si) 0.8–1.5%, Manganese (Mn) 0.5–1.0%, Chromium (Cr) 14–18%, Molybdenum (Mo) 0.5–1.5%, Copper (Cu) 0.5–1.0%, and trace elements like Sulfur (S) and Phosphorus (P) kept below 0.05%. The melting temperature was set at 1550±10°C, after which deoxidation was performed. The molten white cast iron was then treated with modifiers—specifically, two types referred to as Modifier A and Modifier B—using a ladle inoculation method. These modifiers contain surface-active elements designed to influence solidification behavior. After treatment, the white cast iron was poured at 1380±10°C into green sand molds to produce standard test specimens, including impact samples (20×20×110 mm), small-energy multi-impact samples (φ10×100 mm), thermal analysis samples, and bending test samples.
We performed thermal analysis to understand the effects of modification on liquidus and eutectic temperatures, which reflect primary crystallization characteristics. Key mechanical properties were evaluated: impact toughness (αk) was measured using Charpy tests, fracture toughness (KIC) was determined via standard methods, and small-energy multi-impact resistance was tested under a load of 1.5 J. Additionally, bending strength and deflection were assessed. Microstructural analysis was conducted on samples from each batch, with quantitative metallography using image analysis to measure parameters such as the nominal diameter of primary austenite dendrites (Dγ), carbide area fraction (Ac), and carbide shape factor (Fc). The shape factor Fc is defined to quantify carbide isolation; for spherical carbides, Fc approaches unity, while for interconnected networks, it decreases. We also used electron probe microanalysis (EPMA) to examine elemental distribution and scanning electron microscopy (SEM) to observe fracture surfaces and wear morphologies.
The modifiers were selected through screening tests from several candidates. Modifier A and Modifier B showed the most promising results in preliminary trials. Their addition led to notable changes in the as-cast white cast iron: carbide morphology shifted from continuous blocks to isolated spheroids, vermicular forms, or plate-like structures, and the matrix grain size was refined. To further optimize properties, we applied various heat treatment cycles, designated as HT1, HT2, and HT3, involving austenitizing, quenching, and tempering processes. The effects on toughness and hardness were systematically recorded.
Our findings are summarized in the following tables and formulas. First, the influence of chemical composition on as-cast carbide morphology is critical. For high-chromium white cast iron, the volume fraction of carbides (Vc) can be estimated using the equation:
$$ V_c = \frac{C – 0.06 \cdot Cr}{6.69} \times 100\% $$
where C and Cr are weight percentages. This formula highlights that increasing chromium content reduces carbide volume, but morphology control requires additional interventions. Table 1 shows the effect of Modifier A and Modifier B on oxygen and sulfur content, as well as on liquidus and eutectic temperatures.
| Modifier | Addition (wt%) | Residual Oxygen (ppm) | Residual Sulfur (wt%) | ΔTliquidus (°C) | ΔTeutectic (°C) |
|---|---|---|---|---|---|
| None | 0 | 120 | 0.04 | 0 | 0 |
| Modifier A | 0.3 | 40 | 0.02 | -15 | +4 |
| Modifier B | 0.4 | 50 | 0.03 | -12 | +3 |
The data indicate that modification reduces oxygen and sulfur levels, lowers the liquidus temperature by 12–15°C, and raises the eutectic temperature by 3–4°C. These changes promote finer solidification structures and cleaner grain boundaries in the white cast iron. The reduction in oxygen is particularly important, as excessive oxygen (>80 ppm) can hinder modifier effectiveness.
Next, we evaluated the impact of modifiers on mechanical properties. Table 2 compares the impact toughness (αk) and small-energy multi-impact resistance (Nf at 1.5 J) for different modifier treatments in the as-cast and heat-treated states.
| Condition | Modifier | αk (J/cm²) | Nf (cycles, 1.5 J) | Fracture Toughness KIC (MPa·m¹ᐧ²) | Hardness (HRC) |
|---|---|---|---|---|---|
| As-cast | None | 4.5 | 8,000 | 18.5 | 58 |
| As-cast | Modifier A | 6.8 | 15,000 | 22.0 | 56 |
| As-cast | Modifier B | 6.2 | 13,500 | 20.5 | 57 |
| HT1 Treated | Modifier A | 9.5 | 22,000 | 25.0 | 60 |
| HT2 Treated | Modifier A | 10.2 | 25,000 | 26.5 | 59 |
| HT3 Treated | Modifier A | 8.8 | 20,000 | 24.0 | 61 |
Modifier A consistently outperformed Modifier B, with impact toughness stabilizing above 9.5 J/cm² after heat treatment. The small-energy multi-impact life exceeded 20,000 cycles, and fracture toughness reached over 25 MPa·m¹ᐧ². These improvements are attributed to microstructural changes quantified in Table 3, which presents quantitative metallography data for the white cast iron samples.
| Sample | Dγ (μm) | Ac (%) | Fc | Carbide Perimeter (mm/mm²) |
|---|---|---|---|---|
| Unmodified | 45.2 | 28.5 | 0.35 | 120 |
| Modifier A | 28.7 | 25.8 | 0.62 | 185 |
| Modifier B | 32.4 | 26.5 | 0.55 | 160 |
| Modifier A + HT2 | 25.3 | 24.0 | 0.70 | 210 |
Here, Dγ is the nominal diameter of primary austenite, Ac is the carbide area fraction, and Fc is the shape factor calculated as:
$$ F_c = \frac{4\pi A_c}{P_c^2} $$
where Pc is the carbide perimeter per unit area. Higher Fc values indicate more spherical, isolated carbides. The modified white cast iron shows reduced Dγ (refined grains), decreased Ac (lower carbide volume), and increased Fc and perimeter (improved distribution). These changes contribute to toughness enhancement by reducing stress concentrations and crack initiation sites.
The heat treatment cycles were designed to optimize the matrix phase composition. We found that a matrix comprising approximately 60% austenite and 40% martensite, with dispersed secondary carbides, offers the best balance of toughness and hardness. The transformation behavior can be described using the Koistinen-Marburger equation for martensite formation:
$$ f_m = 1 – \exp[-k(M_s – T)] $$
where fm is the martensite fraction, k is a constant, Ms is the martensite start temperature, and T is the quenching temperature. For our white cast iron, Ms is around 180°C, and heat treatment HT2 (austenitizing at 980°C, oil quenching, and tempering at 250°C) yielded the desired phase mix. This treatment further spheroidizes carbides and relieves internal stresses.
Field trials were conducted on three types of wear parts: fan mill beaters, impact crusher hammers, and ball mill liners. These components were manufactured from the modified high-chromium white cast iron and compared with traditional high-manganese steel parts under identical operating conditions. The results, shown in Table 4, demonstrate significant life extensions.
| Component | Material | Weight Loss (%) | Service Life (days) | Life Increase (vs. High-Mn Steel) |
|---|---|---|---|---|
| Fan Mill Beater | High-Mn Steel | 15.2 | 30 | 1× (base) |
| Fan Mill Beater | Modified White Cast Iron | 4.8 | 150 | 5× |
| Impact Crusher Hammer | High-Mn Steel | 22.5 | 45 | 1× |
| Impact Crusher Hammer | Modified White Cast Iron | 7.3 | 180 | 4× |
| Ball Mill Liner | High-Mn Steel | 18.9 | 120 | 1× |
| Ball Mill Liner | Modified White Cast Iron | 5.1 | 480 | 4× |
The modified white cast iron parts showed no fractures or catastrophic failures during operation, confirming their reliability under impact loads. The wear resistance improvement is attributed to the optimized microstructure, where hard carbides are well-dispersed in a tough matrix. Economic analysis reveals substantial cost savings: for example, in cement plants, switching to white cast iron liners can reduce annual expenses by over 30%, considering reduced part replacement, downtime, and maintenance. On a larger scale, widespread adoption could save thousands of tons of steel annually, with corresponding energy and environmental benefits.
In conclusion, our research demonstrates that improving the toughness of high-chromium white cast iron requires a holistic approach. Simply altering carbide morphology is insufficient; one must also refine the matrix grains, purify grain boundaries, and control phase proportions through modification and heat treatment. The use of Modifier A and Modifier B effectively transforms carbide morphology to spheroidal or plate-like forms, reduces grain size, and enhances mechanical properties. After optimal heat treatment, this white cast iron achieves impact toughness above 10 J/cm², multi-impact resistance over 20,000 cycles, and fracture toughness exceeding 25 MPa·m¹ᐧ². Field validations confirm that components made from this material outperform high-manganese steel in impact-wear applications, with life increases of 4–5 times. This work expands the applicability of white cast iron to dynamic loading conditions, offering a cost-effective and durable alternative for industrial wear parts. Future studies could explore the precise mechanisms of modifier action and further optimize compositions for specific service environments.