1. Basic Standards & Grades (GB/T 8263 Abrasion Resistant White Cast Iron)
Common corresponding grades for industrial liners:
Cr15 → KmTBCr15Mo (15% chromium molybdenum high chromium cast iron)
Cr20 → KmTBCr20Mo (20% chromium molybdenum high chromium cast iron)
Cr26 → KmTBCr26 (26% high chromium cast iron, low or zero molybdenum)
Standard Chemical Composition (Mass Fraction)
表格
| Material Grade | Cr | C | Mo | Si | Mn | Impurities P/S | Cr/C Ratio |
|---|---|---|---|---|---|---|---|
| Cr15 | 14.0~18.0% | 2.8~3.4% | 0.4~0.8% | 0.4~1.0% | 0.5~1.2% | ≤0.05% | 4.5~6 |
| Cr20 | 18.0~22.0% | 2.7~3.3% | 0.5~1.0% | 0.4~1.0% | 0.5~1.2% | ≤0.05% | 5~7 |
| Cr26 | 24.0~28.0% | 2.2~3.0% | 0.3~0.6% | 0.3~0.9% | 0.4~1.0% | ≤0.04% | 6~8 |
Core principle: Higher chromium content generates more M₇C₃ chromium carbide hard phases. A Cr/C ratio between 4 and 8 ensures uniform and continuous carbide distribution, balancing wear resistance and toughness.
2. Metallographic Structure & Mechanical Property Comparison
All three materials consist of tempered martensite, M₇C₃ hard carbides and minor retained austenite. The microhardness of carbides reaches HV1800~2200, serving as the core wear-resistant skeleton.
Performance Parameters After Standard Heat Treatment
表格
| Performance Index | Cr15 Liner | Cr20 Liner | Cr26 Liner |
|---|---|---|---|
| Rockwell Hardness HRC | 58~61 | 59~62 | 60~65 |
| Impact Toughness αk (J/cm²) | ≥7 | ≥8 | ≥8.5 |
| M₇C₃ Carbide Volume Fraction | 22%~28% | 28%~35% | 35%~45% |
| Relative Wear Service Life (Benchmark) | 100% (Reference) | 140%~180% | 220%~300% |
| Erosion & Corrosion Resistance | Average | Good | Excellent |
| Maximum Thermal Fatigue Operating Temp | ≤300℃ | ≤350℃ | ≤400℃ |
Differences in Performance Logic
Cr15: Lowest chromium content with the least carbides. Slightly lower toughness but the lowest raw material cost. Ideal for low-abrasion working conditions with cost priority.
Cr20: Balanced chromium level with optimized trade-off among wear resistance, toughness and cost. The mainstream liner material widely adopted in cement and mining industries.
Cr26: High chromium content greatly increases carbide proportion, delivering top-tier hardness, wear resistance, high-temperature resistance and acid-alkali erosion resistance. The only drawback is higher raw material cost.
3. Standard Heat Treatment Process (Critical to Service Life)
Complete quenching and tempering procedures are mandatory for high chromium liners. As-cast liners only reach HRC40~46, with wear resistance less than 60% of qualified heat-treated products.
Cr15 (KmTBCr15Mo) Quenching: Hold at 940~980℃ for 2~4 hours, cool with dedicated quenchant; Tempering: Low-temperature temper at 220~280℃ for 3~6 hours to relieve internal stress; Final hardness HRC≥59.
Cr20 (KmTBCr20Mo) Quenching: Hold at 980~1030℃ for 2~5 hours; Tempering: Low-temperature temper at 230~290℃; Optimal hardness HRC60~62.
Cr26 (KmTBCr26) Quenching: Hold at 1010~1060℃ for 3~6 hours to fully dissolve secondary carbides; Tempering: Hold at 250~300℃ for 4~8 hours; Stable hardness above HRC62. Tempering temperature can be slightly raised for high-temperature service scenarios to boost thermal stability.
Process Taboos: Natural air cooling quenching and tempering above 400℃ are strictly prohibited, which drastically reduce hardness and abrasion resistance.
4. Applicable Working Conditions, Equipment & Materials for Each Liner Grade
4.1 Cr15 High Chromium Liner (Economical Grade)
Applicable Scenarios: Low abrasion, small-diameter ball mills, soft raw materials, intermittent production Equipment: Small ball mills Φ≤2.4m, coal mills, small fine sand crushers, low-erosion chutes Raw Materials: Coal, limestone, shale, clay and other medium-low hardness ores Advantages: Lowest procurement cost, lightweight, low replacement expense Disadvantages: Short service life under high-hardness ore and continuous full-load operation; Not suitable for wet grinding with acidic slurry Expected Service Life: 3~5 years, equivalent to only 60%~70% service life of Cr20 liners under identical conditions
4.2 Cr20 High Chromium Liner (Universal Mainstream Grade, Highest Market Share)
Applicable Scenarios: Medium abrasion, dry & wet dual-purpose, standard cement/mining working conditions, balanced wear resistance & cost Equipment: Φ2.4~3.6m cement raw meal mills, slag mills, metal ore ball mills, impact crusher inner liners, medium-sized silo chutes Raw Materials: Granite, iron ore, quartz sand, cement clinker, aggregate sandstone Advantages: Balanced wear resistance and toughness, resistant to medium impact, compatible with dry & wet grinding, optimal cost performance Disadvantages: Inferior to Cr26 liners under ultra-hard ores (basalt, emery sand) and continuous high-temperature erosion Expected Service Life: 5~8 years, 1.5~1.8 times longer than Cr15 liners
4.3 Cr26 High Chromium Liner (High-End Wear Resistant Grade for Heavy Abrasion)
Applicable Scenarios: Severe abrasive wear, high temperature, acidic slurry, large-diameter mills, continuous production with high-hardness raw materials Equipment: Large mineral processing ball mills Φ≥3.6m, vertical mill liners, high-temperature clinker mills, metallurgical sinter chutes, high-corrosion wet grinding equipment Raw Materials: Basalt, high-silicon quartz, hard metal ores, high-temperature clinker, sulfur-containing acidic slurry Advantages: Top wear resistance, superior high-temperature oxidation resistance, acid & alkali erosion resistance, excellent thermal fatigue performance, free from rapid groove wear Disadvantages: High upfront purchasing cost; Inferior to thick-wall high manganese steel under heavy impact from oversized bulk materials Expected Service Life: 7~10 years, 2~3 times longer than Cr15 and 1.4~1.7 times longer than Cr20 under the same operating environment
5. Liner Structure & Key Casting Technology
Molding Process: Lost foam precision casting or resin sand casting for integrated forming of wave liners, stepped lifting liners, flat liners and end cover liners. Cr26 material has larger shrinkage rate, so molds require extra shrinkage allowance.
Anti-Cracking Design: Liners thicker than 60mm are alloyed with molybdenum and vanadium to refine grain structure. Internal chills are installed on large liners to avoid carbide segregation and brittleness.
Installation Matching: Pre-reserved bolt holes for single-piece replacement. Compared with high manganese steel liners, high chromium liners can be 15%~25% thinner under equal wear resistance standards, reducing mill load and power consumption.
6. Quick Material Selection Reference Table
表格
| Working Condition | Preferred Grade | Alternative Grade | Not Recommended |
|---|---|---|---|
| Small coal mill, intermittent limestone grinding | Cr15 | Cr20 | Cr26 (Unnecessary high cost) |
| Standard cement mill, iron ore & aggregate production line | Cr20 | Cr26 (Long-term full-capacity production) | Cr15 (Frequent replacement required) |
| Large mineral processing mill, high-temp clinker, acidic wet grinding, high-silicon hard rock | Cr26 | Thickened Cr20 | Cr15 |
| Coarse grinding bin with large ore bulk & heavy impact | High Manganese Steel Liner | Bimetallic Composite High Chromium Liner | Pure Cr15/Cr20/Cr26 (Prone to corner cracking) |
| Normal-temperature dry grinding, limited budget production line | Cr15 | Cr20 | - |
7. Operation & Maintenance Notes
Impact Limitation: All three grades are medium-low impact wear-resistant materials. For coarse grinding bins with feed bulk size over 100mm, high manganese steel or bimetallic composite liners are prioritized to prevent cracking of high chromium liners.
Corrosive Environment: Cr26 is mandatory for sulfur-containing and acidic slurry; Cr15 suffers pitting corrosion which accelerates abrasion.
Temperature Limitation: Only Cr26 maintains stable performance under long-term working temperature over 350℃. Long-term high-temperature service softens Cr15 via tempering, doubling wear loss.
Installation & Maintenance: Welding and cutting of high chromium liners are forbidden, as high-temperature welding generates cracks. Fill gaps between liners with wear-resistant castable during installation to avoid material erosion on bolts.
8. Cost & Comprehensive Benefit Summary
Cr15: Lowest upfront investment but frequent shutdown for replacement. Suitable for small-capacity factories with low downtime loss.
Cr20: Optimal overall comprehensive cost, standard configuration for 80% cement plants and medium-small mines.
Cr26: Higher one-time procurement price yet doubled replacement cycle. Minimal overall operation and maintenance cost for large continuous production lines, drastically cutting economic losses caused by production downtime.
