The Bottom Line: Which Should You Choose? Choose Monel when your environment involves seawater, hydrofluoric acid, or highly reducing conditions. Choose stainless steel when oxid...
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The core secret behind the ability of CR20NI80 high-purity NiCr and NiCrFe alloys to operate reliably at high temperatures for extended periods lies in the dense chromium oxide protective layer formed on their surface. The presence of nickel enhances the adhesion of the oxide film to the substrate, preventing the oxide film from peeling off during drastic temperature fluctuations. This oxide film is extremely thin but incredibly dense, effectively preventing external oxygen atoms from diffusing into the deeper layers of the substrate. When the surface is damaged, chromium in the substrate quickly migrates to the surface and reforms the protective layer. Although its linear expansion coefficient of 18 × 10⁻⁶/℃ is slightly higher than that of steel, its thermal expansion process exhibits highly linear characteristics. This means that precise physical modeling can be performed when designing the heating element support structures of large industrial electric furnaces, avoiding element distortion or short circuits caused by thermal stress.
| Property | Type | Cr20Ni80 | Cr30Ni70 | Cr15Ni60 | Cr20Ni35 | Cr20Ni30 |
| Main chemical (%) | Ni | Bal | REST | 55.0–61.0 | 34.0–37.0 | 30.0–34.0 |
| Cr | 20.0–23.0 | 28.0–31.0 | 15.0–18.0 | 18.0–21.0 | 18.0–21.0 | |
| Fe | ≤1.0 | ≤1.0 | Bal | Bal | REST | |
| Max continuous service temp. (℃) | 1200 | 1100 | 1000 | 1000 | 1000 | |
| Melting point (℃) | 1400 | 1380 | 1390 | 1390 | 1390 | |
| Density (g/cm³) | 8.4 | 8.1 | 8.2 | 7.9 | 7.9 | |
| Resistivity (μΩ·m 20℃) | 1.09±0.05 | 1.18±0.05 | 1.11±0.05 | 1.04±0.05 | 1.04±0.05 | |
| Elongation (%) | ≥20 | ≥20 | ≥20 | ≥20 | ≥20 | |
| Specific heat (J/g℃ at 20℃) | 0.44 | 0.461 | 0.494 | 0.5 | 0.5 | |
| Thermal conductivity (k J/m.h℃) | 60.3 | 45.2 | 45.2 | 43.8 | 43.8 | |
| Line expansion coefficient (α×10⁻⁶/℃(20–1000℃)) | 18 | 17 | 17 | 19 | 19 | |
| Micro structure | Austenite | Austenite | Austenite | Austenite | Austenite | |
| Magnetic properties | Non-magnetic | Non-magnetic | Non-magnetic | Weak magnetic | Weak magnetic | |
The Bottom Line: Which Should You Choose? Choose Monel when your environment involves seawater, hydrofluoric acid, or highly reducing conditions. Choose stainless steel when oxid...
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