Nichrome, Tophet A® Nickel 80 Chromium 20 Alloy,Ni20Cr Alloy,Nickel Chromium Alloy,E FORU

### **Nichrome 80/20 (Tophet A®) - Nickel-Chromium Resistance Heating Alloy** #### **Overview** **Nichrome 80/20** (commercially known as **Tophet A®**, NiCr 80/20, or Ni20Cr) is the most widely used nickel-chromium electrical resistance heating alloy. With a nominal composition of 80% nickel and 20% chromium, this alloy offers an optimal balance of high electrical resistivity, excellent oxidation resistance, and good high-temperature strength. The material forms a protective chromium oxide (Cr₂O₃) scale when heated, allowing continuous operation at temperatures up to 1200°C (2190°F) in air. Its stable resistance characteristics and long service life make it the industry standard for electrical heating elements. --- #### **Chemical Composition (Weight %)** | Element | Content (%) | Function | |---------|-------------|-----------| | **Nickel (Ni)** | **75.0-78.0%** | Provides oxidation resistance and ductility | | **Chromium (Cr)** | **19.0-21.0%** | Forms protective oxide scale; increases resistivity | | **Iron (Fe)** | **≤ 1.0%** | Controlled impurity | | **Manganese (Mn)** | **≤ 1.0%** | Deoxidizer during melting | | **Silicon (Si)** | **≤ 1.0%** | Enhances oxide scale adherence | | **Carbon (C)** | **≤ 0.08%** | Minimized to prevent carbide formation | | **Other Elements** | **≤ 0.5%** | Copper, aluminum, titanium | --- #### **Physical & Mechanical Properties** | Property | Value / Description | |----------|---------------------| | **Density** | **8.40 g/cm³** | | **Melting Point** | **1400°C** (2550°F) | | **Electrical Resistivity** | **108 μΩ·cm** (at 20°C) | | **Temperature Coefficient of Resistance** | **80 × 10⁻⁶/°C** (20-500°C) | | **Specific Heat** | **450 J/kg·K** | | **Thermal Conductivity** | **12.5 W/m·K** (at 20°C) | | **Coefficient of Thermal Expansion** | **14.0 × 10⁻⁶/°C** (20-1000°C) | | **Tensile Strength** | **780-850 MPa** (annealed condition) | | **Yield Strength** | **380-450 MPa** (annealed condition) | | **Elongation** | **30-40%** (annealed condition) | | **Hardness** | **70-85 HRB** (annealed condition) | --- #### **Key Characteristics & Applications** **Key Characteristics:** - **High Electrical Resistivity**: Enables compact heating element design - **Excellent Oxidation Resistance**: Protective Cr₂O₃ scale prevents further oxidation - **Good High-Temperature Strength**: Maintains structural integrity at operating temperatures - **Long Service Life**: Resists aging and resistance drift over time - **Good Formability**: Can be drawn into fine wires and rolled into thin strips **Maximum Operating Temperatures:** - **Continuous Service**: **1150°C** (2100°F) - **Intermittent Service**: **1200°C** (2190°F) - **Melting Point**: **1400°C** (2550°F) **Typical Applications:** - **Heating Elements**: Toasters, ovens, furnaces, industrial heaters - **Electrical Appliances**: Hair dryers, space heaters, electric blankets - **Industrial Equipment**: Heat treating furnaces, kilns, thermal processing systems - **Aerospace**: De-icing systems, environmental control systems - **Electronics**: Wirewound resistors, precision resistors - **Automotive**: Seat heaters, defroster elements --- #### **International Standards & Specifications** | Standard | Designation | Description | |----------|-------------|-------------| | **ASTM** | **B344** | Standard specification for nickel-chromium alloy strip/wire | | **IEC** | **60121** | International standard for resistance heating alloys | | **DIN** | **17470** | German standard for NiCr 8020 | | **JIS** | **C2520** | Japanese industrial standard | | **BS** | **BS 1116** | British standard for electrical heating alloys | | **UNS** | **N06008** | Unified Numbering System designation | --- #### **Manufacturing Forms & Processing** **Available Forms:** - **Wire**: 0.01 mm to 8.0 mm diameter - **Ribbon/Strip**: 0.05 mm to 3.0 mm thickness - **Rod**: 3 mm to 25 mm diameter - **Powder**: For thermal spray applications **Processing Considerations:** - **Annealing Temperature**: 850-950°C (1560-1740°F) - **Atmosphere Requirements**: Hydrogen or vacuum for bright annealing - **Forming**: Best done in annealed condition - **Welding**: Can be welded using TIG or resistance welding methods --- #### **Quality Control & Testing** - **Resistance Testing**: Per ASTM B63 - **Dimensional Tolerances**: Per ASTM B342 - **Surface Quality**: Free from scale and contamination - **Metallurgical Structure**: Austenitic grain structure verification - **High-Temperature Testing**: Life testing at elevated temperatures --- #### **Summary** **Nichrome 80/20 (Tophet A®)** represents the benchmark nickel-chromium electrical resistance alloy that has maintained its industry dominance for over a century. Its optimal combination of high electrical resistivity, exceptional oxidation resistance, and mechanical stability at elevated temperatures makes it the preferred choice for virtually all types of electrical heating applications. The well-established manufacturing processes, comprehensive international standards, and proven performance across diverse industries ensure its continued relevance in both conventional and emerging heating technologies. The alloy's reliability, predictable aging characteristics, and cost-effectiveness solidify its position as the fundamental material for electrical heating element design worldwide.

Packing of Standard Packing: Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and steel drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 3218 gallon liquid totes Special package is available on request.