UNS C54400, widely known in the industry as "Free-Cutting Phosphor Bronze" or "Alloy B-2," represents the apex of machinability within the highly resilient phosphor bronze family. While standard phosphor bronzes offer legendary fatigue life and spring memory, they are notoriously difficult to machine. C54400 solves this by precisely alloying Copper, Tin, Zinc, and approximately 4% Lead (Pb). The lead is insoluble in the solid matrix, dispersing as microscopic globules that act as built-in chip breakers and dry lubricants during CNC turning.
The result is an alloy boasting an impressive 80% Machinability Rating (compared to standard C51000 at 20%), while retaining the exceptional wear resistance, anti-galling properties, and high-cycle fatigue thresholds expected of a phosphor bronze. C54400 is the premier choice for complex, custom-threaded electromechanical fasteners, intricate thrust washers, and high-friction rotating hardware that must be mass-produced via high-speed automated screw machines.
| Material Classification | Free-Machining Phosphor Bronze (Alloy B-2) |
|---|---|
| UNS Designation | C54400 |
| Microstructure | Alpha Solid Solution with Dispersed Lead Particles |
| Magnetic State | Completely Non-Magnetic |
| Density | 8.89 g/cm³ (0.321 lb/in³) |
| Size Range | Metric: M1.6 to M24 | Imperial: #0 to 1" |
| Primary Attribute | 80% Machinability Rating combined with High Fatigue Life |
Contains detailed high-speed CNC turning feed rates, tooling tool-wear parameters, threading tolerances, and high-cycle friction resistance limits for complex turned components.
⬇ DOWNLOAD DATASHEETIn automated fastener manufacturing, inconsistent lead dispersion leads to tool chatter, torn threads, and component rejection. Ananka ensures that every lot of C54400 solid bar stock is backed by stringent, verifiable mill documentation for absolute metallurgical uniformity.
C54400 is heavily alloyed compared to standard bronzes. The 4% Tin provides the core strength and wear resistance, while the 4% Lead ensures the metal cuts crisply. A 4% Zinc addition acts as a secondary solid-solution strengthener and aids in deoxidation, alongside the trace Phosphorus.
| Copper (Cu) | Tin (Sn) | Lead (Pb) | Zinc (Zn) | Phosphorus (P) | Iron (Fe) |
|---|---|---|---|---|---|
| Balance (~88.0) | 3.50 – 4.50 | 3.50 – 4.50 | 1.50 – 4.50 | 0.01 – 0.50 | 0.10 Max |
| Mechanical Property | Typical Limits (Half-Hard to Hard Temper) |
|---|---|
| Tensile Strength | 60,000 - 85,000 psi (415 - 585 MPa) |
| Yield Strength | 50,000 - 70,000 psi (345 - 480 MPa) |
| Machinability Rating | 80% (Relative to Free-Cutting Brass at 100%) |
| Hardness (Rockwell B) | 75 - 85 HRB |
| Standard / System | Designation |
|---|---|
| ASTM Specifications | ASTM B139 (Rod, Bar, and Shapes) |
| Common Trade Names | Free-Cutting Phosphor Bronze, Alloy B-2, Alloy 544 |
| European Equivalent | EN CW456K / CuSn4Pb4Zn4 (DIN 2.1028) |
| British Standard (BS) | PB104 |
| Mating Bolts/Machine Screws | Internal Threads (Nuts) | Washers |
|---|---|---|
| C54400 CNC Turned Screws & Studs | C54400 Custom Machined Nuts | C51000 or C54400 Thrust/Flat Washers |
While C54400 possesses excellent strength and fatigue resistance for a bronze, the significant lead content slightly reduces its ultimate tensile threshold compared to pure C51000. Care must be taken not to over-torque smaller diameter precision machine screws to avoid head shearing.
| Nominal Diameter | Threads Per Inch (UNC) | Max Target Torque (in-lbs) | Max Target Torque (ft-lbs) |
|---|---|---|---|
| #10 | 24 | 35 - 40 | ~ 3 |
| 1/4" | 20 | 70 - 80 | ~ 6.5 |
| 3/8" | 16 | 180 - 210 | ~ 16 |
| 1/2" | 13 | 400 - 450 | ~ 35 |
It is a deliberate metallurgical trade-off. By adding 4% Lead, C54400 sacrifices a small amount of absolute ductility and tensile strength to gain a massive boost in manufacturing speed. Standard C51000 has a terrible machinability rating of just 20%, generating long, tangled chips that ruin tools. C54400 cuts beautifully at an 80% rating, making complex geometries economically feasible.
No. Just like Free-Cutting Brass (C36000), the heavy 4% Lead content makes the alloy highly susceptible to cracking under extreme deformation. If you attempt to cold-head a bolt from C54400, the lead particles act as fracture points and the head will shatter. C54400 fasteners are strictly manufactured via CNC subtractive machining from solid rod or bar stock.
In C54400, the ~4% Zinc addition acts primarily as an advanced deoxidizer during the initial smelting process, assisting the Phosphorus. Furthermore, Zinc greatly improves the fluidity of the molten bronze before casting, which is critical for ensuring the 4% Lead content is dispersed evenly and uniformly throughout the ingot before it is drawn into rod stock.
