C26000 brass, also known as cartridge brass or 70/30 brass, has been the material of choice for ammunition cartridge cases since the mid-19th century. Its unique combination of mechanical strength, formability, and corrosion resistance makes it ideally suited for the demanding application of containing high-pressure propellant gases during firing. This alloy’s ability to undergo severe deep drawing operations without cracking, while maintaining dimensional stability under cyclic loading, has cemented its position as the gold standard in munitions manufacturing. Beyond ammunition, C26000 is widely used in electrical connectors, automotive heat exchangers, and precision CNC-machined components where reliability and performance are non-negotiable.
1. C26000 Basic Information
C26000 is a wrought alpha-beta brass alloy with a nominal composition of 70% copper and 30% zinc. It is classified under the Unified Numbering System (UNS) as C26000 and is also known as cartridge brass due to its historical and primary use in ammunition. The alloy exhibits excellent cold working properties, allowing it to be deep drawn into complex shapes like cartridge cases without cracking. Its high ductility and moderate strength provide the necessary resilience to withstand the cyclic loading of chambering, firing, and extraction. The alloy’s face-centered cubic (FCC) crystal structure in the alpha phase contributes to its exceptional formability, while the beta phase (present at higher zinc contents) is avoided in standard C26000 to maintain optimal cold workability. The material is typically supplied in annealed (O) or half-hard (H02) tempers, with the annealed condition preferred for initial forming operations and the half-hard temper used for final machining and finishing.
2. Chemical Composition
The precise chemical composition of C26000 is critical to its performance. The following table provides the standard composition ranges as specified by ASTM B36/B36M and other relevant standards. Tight control of impurities, particularly lead and iron, is essential to prevent hot shortness during casting and to maintain consistent mechanical properties across production batches.
| Element | Content (%) | Role |
|---|---|---|
| Copper (Cu) | 68.5 – 71.5 | Primary alloying element; provides strength, corrosion resistance, and workability. |
| Zinc (Zn) | Balance | Secondary alloying element; increases strength and hardness while reducing cost. |
| Lead (Pb) | ≤ 0.07 | Impurity; kept low to avoid hot shortness and cracking during forming. |
| Iron (Fe) | ≤ 0.05 | Impurity; can refine grain size but excessive amounts reduce ductility. |
| Tin (Sn) | ≤ 0.05 | Impurity; improves corrosion resistance but can reduce formability. |
| Nickel (Ni) | ≤ 0.05 | Impurity; can increase strength but is generally undesirable. |
| Other Elements (Total) | ≤ 0.15 | Includes antimony, bismuth, phosphorus, etc., kept to a minimum. |
The copper content is maintained between 68.5% and 71.5% to ensure a fully alpha-phase microstructure at room temperature, which provides maximum ductility. Zinc acts as a solid solution strengthener, with each 1% increase in zinc content raising tensile strength by approximately 10 MPa. The strict limits on lead (≤0.07%) are particularly important because lead forms low-melting-point eutectics at grain boundaries, which can cause intergranular cracking during hot working or high-speed machining. Iron, while beneficial for grain refinement up to 0.02%, must be controlled to avoid the formation of hard, brittle iron-zinc intermetallics that reduce formability.
3. Mechanical & Physical Properties
The mechanical and physical properties of C26000 brass are highly dependent on its temper condition. The following tables present typical values for the annealed (soft) and half-hard (H02) tempers, which are most relevant for CNC machining and forming operations. These properties are measured at room temperature (20°C) unless otherwise specified.
Mechanical Properties
| Property | Annealed (O) | Half-Hard (H02) | Unit |
|---|---|---|---|
| Tensile Strength | 330 – 380 | 430 – 520 | MPa |
| Yield Strength (0.2% offset) | 110 – 160 | 280 – 360 | MPa |
| Elongation (in 50 mm) | 45 – 55 | 20 – 30 | % |
| Hardness (Rockwell B) | 50 – 65 HRB | 75 – 85 HRB | – |
| Hardness (Vickers) | 90 – 120 HV | 140 – 170 HV | – |
| Modulus of Elasticity | 110 | 110 | GPa |
| Poisson’s Ratio | 0.34 | 0.34 | – |
| Fatigue Strength (10⁷ cycles) | 100 – 130 | 150 – 200 | MPa |
| Shear Strength | 220 – 260 | 300 – 360 | MPa |
Physical Properties
| Property | Value | Unit |
|---|---|---|
| Density | 8.53 | g/cm³ |
| Thermal Conductivity (at 20°C) | 120 | W/m·K |
| Electrical Conductivity (at 20°C) | 28 | %IACS |
| Specific Heat Capacity (at 20°C) | 0.375 | J/g·K |
| Melting Range (Liquidus) | 955 | °C |
| Melting Range (Solidus) | 910 | °C |
| Coefficient of Thermal Expansion (20-300°C) | 19.9 × 10⁻⁶ | /°C |
| Electrical Resistivity (at 20°C) | 6.2 × 10⁻⁸ | Ω·m |
| Magnetic Permeability | 1.0 (non-magnetic) | – |
The high thermal conductivity of 120 W/m·K is a key advantage in CNC machining, as it rapidly dissipates heat from the cutting zone, reducing tool tip temperatures by up to 30% compared to steels. This property also makes C26000 ideal for heat exchanger applications. The electrical conductivity of 28% IACS is moderate, suitable for electrical connectors where both conductivity and mechanical spring properties are required. The coefficient of thermal expansion (19.9 × 10⁻⁶ /°C) must be accounted for in precision machining, as a 100°C temperature rise can cause a 0.2% dimensional change in a 100 mm part.
4. CNC Machining Characteristics
C26000 brass is classified as having excellent machinability, with a machinability rating of approximately 80% relative to free-cutting brass (C36000, rated at 100%). Its high thermal conductivity (120 W/m·K) rapidly dissipates heat from the cutting zone, reducing tool wear and thermal distortion. The alloy produces short, broken chips that are easily evacuated, minimizing chip packing and surface scratching. For CNC machining of cartridge cases and other precision components, the following parameters are recommended:
- Cutting Speed: 150 – 250 m/min for carbide tools; 80 – 120 m/min for high-speed steel (HSS) tools.
- Feed Rate: 0.05 – 0.15 mm/rev for finishing; 0.15 – 0.30 mm/rev for roughing.
- Depth of Cut: 0.5 – 2.0 mm for roughing; 0.1 – 0.5 mm for finishing.
- Tool Material: Carbide (ISO K10-K20) or polycrystalline diamond (PCD) for high-volume production.
- Coolant: Water-soluble coolant at 5-10% concentration; flood application recommended to control chip evacuation.
- Surface Finish: Achievable Ra 0.4 – 0.8 µm with proper parameters; mirror finishes possible with polishing.
- Chip Control: Use chip breakers on inserts to produce 6-9 chips; avoid long stringy chips that can wrap around the tool.
- Tool Life: Carbide tools typically achieve 30-60 minutes of cutting time per edge at recommended speeds; PCD tools can exceed 200 minutes.
The alloy’s low cutting forces (approximately 60% of those for mild steel) allow for higher spindle speeds and feed rates without compromising accuracy. However, care must be taken to avoid work hardening, which can occur if feed rates are too low (below 0.02 mm/rev). For thread turning operations on cartridge cases, single-point threading with carbide inserts at 80-120 m/min and 0.1-0.2 mm depth per pass is recommended. The material’s excellent chip evacuation properties make it suitable for Swiss-type CNC lathes, where continuous chip flow is critical for long, slender parts.
5. Applications
Beyond its iconic use in cartridge cases, C26000 brass is employed in a wide range of applications requiring a balance of strength, formability, and corrosion resistance. Key applications include:
- Ammunition: Cartridge cases for rifles, pistols, and shotguns (e.g., 5.56mm NATO, .308 Winchester, 12-gauge). The alloy’s ability to withstand internal pressures up to 400 MPa during firing is critical.
- Electrical Components: Connectors, terminals, and switch parts where moderate conductivity (28% IACS) and spring properties are needed. Used in automotive fuse holders and relay contacts.
- Automotive: Radiator cores, heat exchanger tubes, and oil cooler components. The high thermal conductivity (120 W/m·K) ensures efficient heat transfer.
- Plumbing: Valve bodies, fittings, and decorative trim due to its corrosion resistance in fresh water and dezincification resistance when properly alloyed.
- Musical Instruments: Brass instruments (trumpets, trombones) where acoustic properties and formability are critical. The alloy’s damping capacity (0.5-1.0% at 100 Hz) contributes to tonal quality.
- CNC Machined Parts: Precision gears, bushings, and decorative hardware requiring tight tolerances (±0.01 mm). Used in aerospace instrumentation and medical device housings.
- Marine Hardware: Propellers, pump impellers, and fittings for fresh water applications, though not recommended for saltwater due to susceptibility to stress corrosion cracking.
6. Why Choose Dongguan Stirling Metal Products Co., Ltd.
Dongguan Stirling Metal Products Co., Ltd. is a premier provider of C26000 brass materials and CNC machining services. Our expertise in handling this alloy ensures that every component meets the highest standards of quality and performance. We offer a comprehensive one-stop solution from material procurement to finished parts, backed by rigorous quality control and fast turnaround times.
- ✅ Material Sourcing: We supply C26000 brass in sheet, bar, and tube forms with full Mill Test Certificates (MTC) ensuring traceability and compliance with ASTM B36/B36M standards. Our inventory includes annealed (O), half-hard (H02), and full-hard (H04) tempers in thicknesses from 0.5 mm to 100 mm.
- ✅ CNC Machining: Our 5-axis CNC centers achieve tolerances of ±0.01 mm and surface finishes down to Ra 0.4 µm, ideal for cartridge case components and precision parts. We utilize high-pressure coolant systems (70 bar) for optimal chip evacuation in deep-hole drilling operations.
- ✅ Sample Making: Rapid prototyping in 3-5 days, allowing for design validation before mass production. We offer free DFM (Design for Manufacturing) analysis to optimize your part geometry for cost-effective machining.
- ✅ Batch Production: Efficient production runs with delivery in 7-15 days, depending on complexity and volume. Our automated production lines can handle quantities from 100 to 100,000+ parts per month.
- ✅ Surface Treatment: In-house capabilities for polishing (to Ra 0.1 µm), electroplating (nickel, chrome, gold), and passivation to enhance corrosion resistance and aesthetics. We also offer chemical brightening for decorative applications.
- ✅ Quality Assurance: ISO 9001:2015 certified facility with in-house tensile testing (Instron 5960), hardness testing (Rockwell and Vickers), and dimensional inspection using CMM (Zeiss Contura G2) with accuracy of ±0.002 mm.
- ✅ Secondary Operations: We provide heat treatment (annealing, stress relieving), laser marking, and assembly services to deliver fully finished components.
For a Free Quote, please Contact Us! Our engineering team is ready to discuss your C26000 brass requirements and provide a competitive solution. We offer volume discounts for orders exceeding 10,000 parts and can provide material certifications for all supplied alloys.
