CuZn39Pb2 Brass: Properties, Applications, and Manufacturing for Precision Machined Parts

CuZn39Pb2 (European standard CW612N), commonly known as "Forging Brass" or "Hot Stamping Brass," is a prominent alloy celebrated for its exceptional balance between hot formability and machinability. Its unique properties make it the premier choice for the "precision hot forging followed by high-speed precision machining" to manufacture lots of precision parts.

This alloy is widely utilized in the manufacturing of industrial components such as gears, bushings, and high-precision mechanical parts due to its good machinability and cost-effectiveness; Its moderate electrical conductivity makes it sufficient for many electrical connector uses; But as the evolving environmental regulations in recent days, higher-cost lead-free alternatives are replacing CuZn39Pb2 (which contains approximately 2% lead) in applications involving potable water systems and plumbing fixtures.

This guide will provide a comprehensive understanding of CuZn39Pb2 brass, exploring its chemical composition, key characteristics and properties, applications and cost, environmental considerations, equivalents, and alternative materials.

 

 

 

 

 

What is CuZn39Pb2 Brass?

 

CuZn39Pb2 is a leaded brass alloy characterized by its duplex α+β structure. This heterogeneous biphasic microstructure(The internal structure of the metal is not uniform; instead, it is a blend of two different microstructures) is the reason behind its versatility: the α-phase ensures stability, toughness, and corrosion resistance, while the β-phase provides excellent plasticity at high temperatures for forging; the finely dispersed lead particles throughout the α+β structure serve as a lubricant to ensure excellent performance during secondary machining operations.

 

Here Highlighting Key Characteristics of CuZn39Pb2 Brass:

 

• Exceptional Machinability: Rated at 85-90% relative to the free-cutting benchmark (CW614N). In CNC machining, this minimizes the formation of built-up edge (BUE) on cutting tools, resulting in superior surface finishes and reducing the need for subsequent polishing. 
• Superior Hot Formability: High plasticity in the hot state makes it ideal for complex mold filling.
  
• Good Corrosion Resistance: Reliable performance against water, organic acids, and alkaline compounds.
  
• Aesthetic Quality: Features a typical deep golden-yellow color and accepts high-quality surface finishes like chrome or nickel plating, or nickel-chromium plating.
  
• Limited Environmental Uses: Contains 2% Lead which is not allowed to be used in drinking water systems in USA and European.
  
• Moderate Electrical Conductivity: But it is sufficient for many electrical connectors uses.
  
• Good Thermal Conductivity: Exhaust valve, temperature control valve body can apply this material.
  
• Thermal Processing: Non-heat-treatable alloy, and heat processing only release the brass internal stress to improve its stability.

 

 

 

 

 

Chemical Composition of CuZn39Pb2 Brass

 

CuZn39Pb2 brass composition is simple and primarily composed of copper, 39% zinc, approximately 2% lead as its name suggests. Below table shows CuZn39Pb2 brass chemical composition and each elements’ role:

 

Table 1: Chemical Composition of CuZn39Pb2 Brass

 

 

 

 

        

Physical Properties of CuZn39Pb2 Brass

 

CuZn39Pb2 has a typical dark yellow or golden yellow color with good thermal conductivity, moderate electrical conductivity, and a relatively high expansion coefficient (dimensional stability may be considered when designing the parts). You can find its specific physical properties in below table:

 

Table 2: Physical Properties of CuZn39Pb2 Brass

 

 

 

 

Mechanical Properties of CuZn39Pb2 Brass

 

 
The mechanical properties of CuZn39Pb2 brass primarily depend on its temper (delivery state), which is determined by whether the material has undergone extrusion, cold drawing, or forging. For CuZn39Pb2 brass’ mechanical properties, you can check in the following:

 

 

Strength and Ductility

The mechanical strength of CuZn39Pb2 is positioned at the medium-to-high level among brass alloys. Its performance varies according to the degree of work hardening, categorized by temper designations such as R360, R430, and R500. In procurement or design, the following suffixes are commonly specified: 

 

• M (As Manufactured): The standard production state where mechanical properties are not specified; only the chemical composition is guaranteed.
• R360 / H090 (Soft or Hot Forged): Tensile strength≥360 MPa with a hardness of approximately 90-125 HB. This state offers the highest toughness and is ideal for subsequent deformation.
  
• R430 / H110 (Half-Hard): Tensile strength ≥430 MPa with a hardness of approximately 110-140 HB. This is the most common temper, providing an optimal balance between strength and machinability.
  
• R500 / H130 (Hard): Tensile strength ≥500 MPa with a hardness ≥130 HB. It is primarily used for components requiring high wear resistance.
  

 

 

High-Temperature Mechanical Properties (Hot Forging Performance) 

The most outstanding mechanical characteristic of CuZn39Pb2 occurs within the 650°C to 750°C temperature range: 

• Hot Plasticity: At these temperatures, theβ-phase within the alloy becomes highly active, granting the metal a fluid-like filling capacity.
  
• Forging Pressure: Compared to other copper alloys, it exhibits lower deformation resistance during hot forging, which effectively extends tool and die life.
  

 

Fatigue and Impact Properties

 

• Impact Toughness (Charpy Impact Strength): Approximately 10 - 20 J/cm².
• Fatigue Strength: At 108 cycles, the fatigue limit is approximately 130 - 150 MPa. For components subjected to high-frequency vibrations, a larger safety factor should be incorporated into the design.
  

 

Shear Strength

The shear strength typically ranges from 60% to 70% of the tensile strength, roughly 220 - 320 MPa. This serves as a critical reference index for designing threads, fasteners, and shear pins.

 

 

 

Environmental Concerns about the 2% Lead of CuZn39Pb2

 

A critical point for CuZn39Pb2 uses in recent days is the restriction of lead in drinking water systems. Under US regulations (SDWA & NSF/ANSI 372), the weighted average lead content for pipes and fittings must be < 0.25% (In this range can be called lead-free).

 

• Since CuZn39Pb2 contains ~2% lead, it is strictly prohibited for potable water delivery systems in the US and high-standard EU projects.
• Its application has shifted to "non-potable" systems, including HVAC, industrial fluid power, automotive fuel systems, and electrical connectors.
  
• While it remains on the EU's "4MS Positive List" for very specific low-contact applications, it is being phased out of the residential plumbing sector.
  
• Lead-free brass (e.g. C27450, C46500 or silicon brass C87850) is typically controlled to contain less than 0.1% or 0.2% lead and can be the more safety and acceptable alternative materials.
  

 

 

 

CuZn39Pb2 Cost Analysis 

 

Cost of CuZn39Pb2 includes the material price and manufacturing cost. The price of CuZn39Pb2 fluctuates in real-time based on the market prices of its base metals, copper and zinc. It is also influenced by the supply form (rods, plates, etc.) and order volume. Generally, it is categorized as a medium-cost brass alloy.

 

 

Compared to Lead-Free Brass:

CuZn39Pb2 is typically more economical than lead-free alternatives (such as silicon brass CW724R). Furthermore, due to its lead content, CuZn39Pb2 offers superior machinability. When considering the total processing cost—which includes significantly reduced tool wear and shorter cycle times—CuZn39Pb2 holds a clear competitive advantage in high-volume production.

 

 

Compared to Pure Copper:

CuZn39Pb2 is considerably cheaper than pure copper. This is primarily because zinc is much less expensive than copper, and CuZn39Pb2 contains a substantial amount of zinc (approximately 39%).

 

 

Compared to Other Complex Brass Alloys:

The chemical composition of CuZn39Pb2 is relatively straightforward. Unlike specialized alloys, it does not contain expensive alloying elements (such as tin, nickel, or high amounts of silicon), making its market price more accessible and predictable.

 

 

 

CuZn39Pb2 Stress Relieving and Softening

 

While CuZn39Pb2 is a non-heat-treatable alloy—meaning its hardness cannot be increased through traditional "quenching and tempering"— but other specific thermal treatments are essential to manage material stability and formability. These processes are suggested for specific manufacturing stages:

 

 

Forging Preheat (650°C–750°C) for Pre-Forming Stage

This is required specifically before hot forging or hot stamping operations. At this temperature, the CuZn39Pb2 brass becomes highly plastic, which allows the material to flow into intricate mold cavities, achieving complex shapes without the risk of cracking. 

 

 

Soft Annealing (450°C–550°C) for Inter-Processing Stage 

This is used when the material has become too hard or brittle due to heavy cold working (such as deep drawing or severe bending). The process reduces the CuZn39Pb2 hardness and restores its ductility, allowing for further deformation without structural failure. 

 

 

Stress Relieving (250°C–350°C) for Post-Processing Stage

It belongs to a final step performed after machining or light cold forming. This is a safety measure to eliminate residual internal stresses. It is highly recommended for precision parts to prevent Stress Corrosion Cracking (SCC), which can occur unexpectedly when the brass is exposed to humid or ammonia-rich environments.

 

 

 

 

Machining and Forming for CuZn39Pb2 Brass

 

CNC Machining

 

 

 

• Tooling: Standard High-Speed Steel (HSS) or Carbide tools work perfectly. For high-volume CNC, use uncoated carbide (K-grade) with a polished rake face for a mirror finish.
  
• Chip Control: Expect short, brittle chips. This makes CW612N ideal for automated bar feeders.
  
• Dimensional Stability: Due to the relatively high thermal expansion coefficient of the brass, ensure the workpiece is cooled to room temperature before final precision measurement to avoid "undersized" errors.
  
• Post-Machining Caution: Always perform Stress Relieving (as mentioned in the Thermal Processing section) if the machined part has thin walls or will be used in high-stress environments.

 

 

Forming 

 

• Hot Forming: Excellent. It is the premier choice for hot stamping and forging for typical valve bodies.
• Cold Forming: Limited. Heavy cold deformation (like deep drawing) is not recommended. Minor bending or rolling is possible but may require intermediate annealing.
  

 

 

 

 

Typical Applications of CuZn39Pb2 Brass

 

 

Thanks to its good corrosion resistance, thermal conductivity, surface finish, excellent machinability and hot forming ablity, CuZn39Pb2 brass is widely used across many applications such as:

 

 

 

 

 

Electrical & Electronics

 

Terminals, high-current connectors, and AC motor components.

Switchgear components and electrical bracketry where non-magnetism and moderate conductivity are required.

 

 

Automotive Industry

 

Fuel system sensors, fuel injection rails, and air conditioning manifold blocks.

Brake system hose endings and pneumatic connectors for commercial vehicles.

 

 

 

Precision Instruments

 

Clock and watch internal gears, lock cylinders, and high-quality hardware.

 

 

 

Industrial & Fluid Control

 

• Compressor valves, hydraulic connectors, and high-pressure manifold blocks.
  
• Heavy-duty gears, bushings, and wear-resistant bearings.
  
• Industrial pump housings and precision flow meters.
  

 

 

HVAC & Refrigeration 

 

• Thermostatic expansion valve (TXV) bodies and radiator valves.
  
• Refrigeration fittings and heat exchanger connectors (utilizing its excellent thermal conductivity and forging density).

 

 

 

 

Equivalents of CuZn39Pb2 Brass

 

 

Depending on your regions , you may find the following equivalents of CuZn39Pb2 brass:

 

 

Table 3: Equivalents of CuZn39Pb2 Brass

 

 

 

 

 

Conclusion

 

While environmental regulations of CuZn39Pb2 brass have narrowed its use in the drinking water sector, its outstanding forging plasticity and high-speed machining efficiency make it irreplaceable for industrial, automotive, and electrical engineering. By applying proper stress-relief annealing, you can ensure the long-term reliability of these high-performance brass components.

 

 

 

 

 

 

 

Case Study: Production Optimization at VMT CNC Machining Factory

 

 

A client approached VMT CNC Machining Factory with a high-precision hydraulic manifold project that was originally designed using 316 Stainless Steel. The production faced two major bottlenecks: extremely slow cycle times and frequent tool failures due to the material's toughness. These factors led to high unit costs.

 

 

 

 

The VMT Solution:

 

• Material Substitution: VMT engineering team switched the specification to CuZn39Pb2 (CW612N), which offered the necessary corrosion resistance and strength for hydraulic pressure.
  
• Process Optimization: Instead of machining the entire part from solid bar stock, VMT utilized hot-forged blanks. This reduced the volume of material to be removed and leveraged the alloy's superior forging density to ensure zero porosity in the manifold.
  
• High-Speed CNC Strategy: Employed uncoated K-grade carbide tools with optimized rake angles specifically for leaded brass.
  

 

 

The Result:

 

• 65% Reduction in Machining Time: The high machinability allowed for significantly higher spindle speeds and feed rates.
  
• 40% Decrease in Tooling Costs: The lubricating effect of the lead content dramatically extended tool life compared to stainless steel.
  
• Superior Surface Quality: VMT maintained a consistent surface roughness of Ra 0.8, eliminating the need for secondary polishing.
  

 

 

 

 

FAQs

 

 

What is the difference between CuZn39Pb2 and CuZn39Pb3?

 

The primary difference lies in lead content and processing focus: CuZn39Pb3 (CW614N) has higher lead for peak high-speed machining efficiency, while CuZn39Pb2 (CW612N) has slightly less lead to provide superior hot-forging and stamping properties. CW612N is the preferred choice when complex shapes must be forged before machining.

 

 

Is CuZn39Pb2 magnetic?

 

No, CuZn39Pb2 is essentially non-magnetic.This makes it an ideal material for electrical connectors and precision instruments that must operate without magnetic interference.

 

 

Can I weld this CuZn39Pb2 alloy?

 

Welding is generally not recommended for CuZn39Pb2 due to its high lead and zinc content, which can cause porosity and toxic fumes. If joining is required, brazing or soldering are the preferred methods as they operate at lower temperatures and maintain the structural integrity of the brass.

 

 

Does CuZn39Pb2 brass meet RoHS requirements?

 

CuZn39Pb2 contains approximately 2% lead, which exceeds the general 0.1% limit. However, it currently falls under specific RoHS exemptions (such as Exemption 6c for copper alloys containing up to 4% lead), though you must monitor ongoing regulatory updates as these exemptions are periodically reviewed.

 

 

How do I prevent my CuZn39Pb2 brass parts from cracking over time?

 

To prevent Stress Corrosion Cracking (SCC), parts should undergo a stress-relieving heat treatment (250°C - 350°C) after machining or cold forming. This process eliminates residual internal stresses that would otherwise lead to spontaneous cracking when exposed to moisture or ammonia.

 

 

What is its machinability rating?

 

CuZn39Pb2 has an excellent machinability rating of approximately 85% to 90% relative to the industry-standard Free-Cutting Brass (CW614N). The lead content acts as a chip-breaker, ensuring short, brittle chips and a high-quality surface finish with minimal tool wear.