I. Introduction to Medium-Chromium Alloy Liners

The Medium Chromium Alloy Liner is a wear-resistant material developed specifically for medium-impact, medium-to-high abrasion conditions. By optimizing the chromium content (7–12%) and carefully balancing its multi-element alloy composition, it achieves an outstanding equilibrium between wear resistance, toughness, and cost-effectiveness—making it the ideal choice for lining plates in grinding equipment such as ball mills and vertical mills.

Performance Positioning

High-chromium cast iron vs. medium-chromium alloy vs. low-alloy steel

II. Performance Characteristics and Advantages of Medium-Chromium Alloy Liners

High hardness: The macroscopic hardness typically ranges from HRC 55 to 65 (in the quenched and tempered condition). The combination of a highly hard martensitic matrix and hard chromium carbides delivers exceptional resistance to abrasive wear.

Excellent wear resistance: Under abrasive wear conditions—particularly low-stress abrasive wear and moderate-stress erosive wear—the wear resistance significantly outperforms high-manganese steel (ZGMn13), typically achieving 1.5 to 3 times, or even more, its level. While the wear resistance is comparable to, or slightly lower than, that of premium high-chromium cast irons (such as Cr20 and Cr26), it offers a clear cost advantage.

Moderate toughness: It outperforms high-chromium cast iron (especially high-carbon, high-chromium cast iron) but falls short of high-manganese steel and premium alloy steels. This material can withstand moderate impact loads without easily undergoing brittle fracture or extensive spalling. It is well-suited for applications such as ball mill shell plates, grid plates, and lifting bars where the impact forces are not particularly severe.

A certain level of corrosion resistance: The addition of chromium gives it notable resistance to water and mineral slurry corrosion, surpassing that of ordinary carbon steel and low-alloy steel.

Good hardenability: Thanks to elements such as chromium, molybdenum, and nickel, the medium-chromium alloy exhibits excellent hardenability, ensuring uniform hardness across the cross-section of thick liners—such as those exceeding 100 mm—and enabling the core to develop a microstructure dominated by martensite.

III. Material Classification and Application Scenarios of Medium-Chromium Alloy Liners

Main material types

Medium-carbon, medium-chromium Type I: Suitable for crushing applications with high demands on impact toughness, this material enhances crushing efficiency by optimizing the motion state of the grinding media.

Type II medium-carbon, medium-chromium: Slightly higher carbon content results in a more uniform distribution of carbides, enhancing wear resistance and making it ideal for high-intensity wear applications.

High-carbon, medium-chromium alloy steel: containing 0.65%–0.7% carbon and 4.0%–4.5% chromium, combined with synergistic effects from elements such as Cu and Nb. It achieves a hardness of HRC50–55 and exhibits wear resistance 7.8 times greater than that of high-manganese steel²³.

Typical application areas

Mining ball mill: Protects the cylinder from direct impact by grinding media, suitable for dry-wet mixed grinding processes, and reduces equipment vibration by 1%.

Cement Industry: Utilizing alternative high-manganese steel liners to address deformation issues, reduce maintenance costs, and contribute to energy conservation and consumption reduction.

Crusher accessories: Used as a protective layer filling material, they cushion the impact of ore and reinforce the cylinder structure.

The Preparation Process and Technological Innovation of Medium-Chromium Alloy Liners

Key Production Processes

Component Design: By optimizing the formulation through multi-alloying—such as adding 0.2%–0.3% Re to high-carbon, medium-chromium liners—we achieve grain refinement and enhance the cleanliness of the molten steel. This approach also helps avoid the use of expensive elements like Mo and Ni, thereby reducing costs by 23%.

Heat treatment process: Utilizing a dual-medium quenching medium to achieve precise control of the austenitizing temperature, resulting in a composite microstructure of martensite + bainite + retained austenite, which balances hardness and toughness at level 14.

Casting and Melting: Melting in a 1550℃ medium-frequency induction furnace, followed by top-pour casting at 1450℃, ensuring uniform composition of the castings. Subsequently, the castings undergo cleaning and isothermal quenching to relieve internal stresses and optimize the microstructure.

IV. Important Notes

1. Operating Condition Matching: Avoid High Impact—In high-impact areas of large autogenous/mill semi-autogenous mills (such as the top of tall lifting bars), where toughness may be insufficient, prioritize the use of high-toughness alloy steel.

Pay attention to abrasive properties: For extremely hard, sharp abrasives (such as quartz sand), wear resistance may not be as good as that of high-chromium cast iron.

2. Heat Treatment Quality: Heat treatment is key to unlocking the full potential of medium-chromium alloys. Poor-quality heat treatment can lead to undesirable matrix structures (such as the formation of pearlite), uneven hardness, and poor toughness, significantly reducing service life.

3. Casting Quality: Internal defects (shrinkage porosity, slag inclusions) are common causes of early failure. Choose suppliers with a proven reputation and stable manufacturing processes.

4. Installation and Maintenance: Install strictly according to specifications, ensuring bolts are securely tightened. Regularly inspect the tightness and wear levels to prevent liner loosening or excessive wear that could lead to damage of the cylinder body.