In the grinding process of materials using ball mills, liners serve as one of the primary consumable components. The material requirements for these liners include high toughness and excellent wear resistance. For decades, high manganese steel casting has been the dominant material for ball mill liners due to its stable performance and reliability. Although medium- and low-alloy steel liners have seen limited application in smaller mills, their complex production processes and inconsistent quality have restricted their widespread use. High manganese steel casting, as an outstanding wear-resistant material, performs optimally under conditions involving substantial impact, such as strong冲击 and compression. Under such scenarios, the austenitic structure undergoes work hardening through deformation, rapidly increasing surface hardness from approximately HB170–230 to over HB500, thereby achieving high wear resistance. However, when employed in mill liners, the limited impact forces result in lower surface hardness and suboptimal wear performance, failing to fully utilize the potential of high manganese steel casting. To address these limitations, researchers have conducted extensive studies over the years, focusing on alloying standard high manganese steel with elements like chromium, vanadium, titanium, and rare earths, developing new dispersion strengthening techniques, and implementing surface treatments such as extrusion, explosive hardening, spraying, and wear-resistant alloy welding.
In our work, we aimed to enhance the service life of liners and reduce consumption by modifying the traditional high manganese steel casting. Based on GMn13, we introduced alloying elements and adjusted the water toughening process to develop a strong and tough high manganese steel casting designated as ZGMn13Cr2RE. This material demonstrated significant improvements in performance and economic benefits in practical applications. Below, we detail the chemical composition determination, heat treatment processes, experimental results, and industrial trials.
The chemical composition of high manganese steel casting plays a critical role in determining its mechanical properties and wear resistance. We systematically evaluated each element to optimize the alloy design. Carbon is a key factor influencing wear resistance; increasing carbon content enhances hardness and abrasion resistance but may reduce work hardening capacity by affecting the formation of stacking faults in the austenitic matrix. For liner applications subject to specific stresses, we set the carbon content at 1.25%–1.35%. Manganese ensures the stability of the austenitic structure, and reducing its content can lower the stacking fault energy, thereby improving work hardening ability. We selected a manganese range of 11%–13%. Chromium was added to form stable alloy carbides like (Fe,Cr)₃C, which resist dissolution and coarsening during heat treatment. These carbides act as hard dispersoids within the ductile austenitic matrix, enhancing wear resistance and work hardening. Chromium also promotes solid solution strengthening, increasing yield strength, tensile strength, and overall durability. The atomic radius of chromium (1.285 Å) is close to that of iron (1.27 Å), with a difference less than 8%, allowing it to form continuous substitutional solid solutions and induce lattice distortion, which improves mechanical properties. We determined the chromium content to be 1.5%–2.5%. Rare earth elements were incorporated to refine the microstructure, reduce impurities, and enhance toughness. Rare earths act as deoxidizers and desulfurizers, forming compounds that purify the steel melt. They also promote grain refinement, eliminate columnar crystals, and reduce hot cracking tendency by segregating at grain boundaries and inhibiting phosphorus embrittlement. Additionally, rare earths slow the precipitation and coarsening of secondary carbides during aging. The residual rare earth content was controlled at 0.08%–0.1%. Harmful elements like sulfur and phosphorus were strictly limited to S < 0.05% and P < 0.08%. The finalized chemical composition for the enhanced high manganese steel casting is summarized in Table 1.
| Element | Content Range |
|---|---|
| C | 1.25–1.35 |
| Si | 0.3–0.8 |
| Mn | 11–13 |
| Cr | 1.5–2.5 |
| RE | 0.08–0.1 |
| S | < 0.05 |
| P | < 0.08 |
The water toughening heat treatment is essential for achieving the desired microstructure and properties in high manganese steel casting. In the as-cast condition, the structure consists of austenite (A), carbides (K), and a small amount of pearlite (P), with carbides precipitating along austenite grain boundaries, leading to poor plasticity and high brittleness. Upon heating, transformations occur: below 400°C, no carbides precipitate; at 500°C, fine carbides begin to form; near the lower critical temperature Ac₁ (approximately 650–690°C for ZGMn13), numerous fine carbides and troostite appear; at 720°C, dissolution initiates; by 800°C, most coarse carbides dissolve, but residual particles remain; and at 900–1100°C, complete dissolution of carbides is achieved, except for some high-melting-point varieties. Heating above the upper critical temperature Ac₃ followed by rapid cooling (water quenching) yields a single-phase austenitic structure. For our enhanced high manganese steel casting containing chromium, the water toughening temperature was increased by 30–50°C compared to conventional practices to ensure dissolution of chromium carbides. We eliminated the 650–700°C preheating stage to avoid carbide precipitation and adopted a slow heating rate of ≤100°C/h directly to the toughening temperature, followed by sufficient holding and rapid quenching in flowing water not exceeding 48°C. This process minimizes thermal stresses and prevents crack formation. The relationship between holding time and carbide dissolution can be expressed by the equation: $$ t = \frac{k}{D^2} e^{Q/RT} $$ where \( t \) is the time, \( k \) is a constant, \( D \) is the carbide size, \( Q \) is the activation energy, \( R \) is the gas constant, and \( T \) is the temperature in Kelvin. This highlights the importance of temperature and time in microstructural control.
Experimental studies were conducted to evaluate the effects of water toughening on the enhanced high manganese steel casting. Melting was performed in a 0.5-ton medium-frequency furnace, with rare earth addition for modification. The chemical composition of the rare earth alloy and the trial steel are provided in Tables 2 and 3, respectively. Mechanical properties and microstructure were assessed according to standard specifications, with results detailed in Table 4. The microstructure examination revealed non-metallic inclusions below level 2A and no overheated carbides across various toughening temperatures (1000–1100°C). The data indicate significant improvements in tensile strength (σ_b), yield strength (σ_s), elongation (δ₅), impact toughness (α_k), and hardness (HB) compared to conventional high manganese steel casting. These enhancements are attributed to the combined effects of chromium and rare earths, which introduce hard, dispersed phases and refine the grain structure. The optimal water toughening temperature was identified as 1050–1100°C, ensuring a balance between carbide dissolution and avoidance of grain growth.
| Parameter | Value |
|---|---|
| RE Content (%) | 29–32 |
| Si Content (%) | ≤40 |
| Ca Content (%) | ≤4 |
| Mn Content (%) | ≤4 |
| Ti Content (%) | ≤3.5 |
| Fe Content (%) | Balance |
| Density (g/mm³) | 4.5–5 |
| Melting Point (°C) | 1080–1250 |
| Element | Content |
|---|---|
| C | 1.28 |
| Si | 0.67 |
| Mn | 12.28 |
| Cr | 2.01 |
| S | 0.015 |
| P | 0.046 |
| RE Residual | 0.085 |
| Toughening Parameters | σ_b (MPa) | σ_s (MPa) | δ₅ (%) | α_k (J/cm²) | HB | Microstructural Observations |
|---|---|---|---|---|---|---|
| As-cast | — | — | — | — | — | Numerous carbides in grains and continuous networks at boundaries |
| 1000°C × 2h, water quench | 794 | 643 | 56 | 220 | 398 | Austenite with dispersed undissolved carbides (W4) and precipitated carbides (X2) |
| 1050°C × 2h, water quench | 817 | 689 | 56 | 241 | 295 | Austenite with minimal undissolved carbides (W1) and precipitated carbides (X2) |
| 1100°C × 2h, water quench | 807 | 687 | 55 | 230 | 291 | Austenite with minimal undissolved carbides (W1) and precipitated carbides (X2) |
Industrial production of liners was carried out for a large-scale ball mill (e.g., Ø2600 mm × 13000 mm) using a 500 kg medium-frequency furnace. The melting process mirrored the experimental setup, with rare earth added at 0.2% in the ladle after preheating to 200–300°C and granulated to 5–10 mm. The pouring temperature was controlled at 1380–1400°C, and molds were made with CO₂-hardened sodium silicate sand coated with magnesite-based alcohol paint. Castings were cooled below 200°C before shakeout, and defect-free liners underwent heat treatment with the optimized water toughening curve: slow heating at ≤100°C/h to 1050°C, holding for 4.5 hours, followed by water quenching. This high manganese steel casting process ensured consistent quality and performance.
The industrial trial involved installing the enhanced high manganese steel casting liners in the first compartment of a ball mill processing bauxite ore with low-chromium alloy grinding balls. Over nearly one year of operation, totaling approximately 5500 hours, the liners demonstrated a service life increase of over 50% compared to the historical average of 3600 hours. This extension not only reduced material costs but also decreased the frequency of liner replacements, yielding substantial economic benefits. The success of this trial underscores the practicality of the modified high manganese steel casting for heavy-duty applications.
In conclusion, the incorporation of chromium and rare earth elements into high manganese steel casting effectively refines the microstructure, enhances initial hardness, and improves wear resistance and yield strength. This allows the high manganese steel casting to perform optimally under various stress conditions, fully leveraging its耐磨 potential. The adjusted water toughening process, which excludes the 650–700°C holding stage and emphasizes slow heating, adequate soaking, high toughening temperatures, and rapid cooling, is crucial for achieving superior properties. The application of this strong and tough high manganese steel casting in ball mill liners results in a 1.5-fold increase in service life, offering reliability and significant technical-economic advantages. Future work could explore further alloying and process optimizations to expand the capabilities of high manganese steel casting in diverse industrial settings.