1. What is Material Grade C360?
Material grade C360, commonly known as C360 brass or "free-cutting brass," is a widely used copper-zinc-lead alloy classified under the ASTM International standard (specifically ASTM B16/B16M, which covers free-cutting brass rod, bar, and wire for machined parts). It is part of the "300 series" brass alloys, where the numerical designation ("360") indicates its specific composition and performance profile.
C360 brass is renowned for its exceptional machinability-the best among common brass grades-earning it the industry benchmark status (with a machinability rating of 100%, against which other free-cutting metals are measured). This property makes it ideal for high-volume production of precision machined parts that require tight tolerances and smooth surface finishes.
Beyond machinability, C360 brass balances moderate strength, good ductility, and acceptable corrosion resistance in mild environments (e.g., air, freshwater). It is widely used in industries such as automotive, electronics, plumbing, and hardware for components like nuts, bolts, screws, fittings, electrical terminals, and decorative fasteners. Notably, "C360" is often a shorthand for the formal ASTM designation C36000 (the trailing "00" indicates standard purity and is frequently omitted in casual industry reference).
2. What is the Chemical Composition of C360?
The chemical composition of C360 brass (conforming to ASTM B16/B16M) is tightly regulated to ensure its signature free-cutting performance and consistent mechanical properties. The key elements and their weight percentage ranges are as follows:
| Element | Weight Percentage Range | Role and Significance |
|---|---|---|
| Copper (Cu) | 60.0–63.0% | The base metal; provides ductility, moderate corrosion resistance, and structural integrity. |
| Zinc (Zn) | Remainder (~35.0–38.0%) | The primary alloying element; boosts strength and hardness while reducing material cost. |
| Lead (Pb) | 2.5–3.7% | The critical "free-cutting" additive; reduces friction during machining, prevents tool galling, and produces small, brittle chips that are easy to clear-this is what makes C360 brass ideal for high-speed machining. |
| Iron (Fe) | Maximum 0.35% | A controlled impurity; limited to avoid brittleness and minimize tool wear (excess iron can form hard particles that scratch cutting tools). |
| Nickel (Ni) | Maximum 0.50% | A minor impurity; no intentional addition (trace amounts may come from raw material sources, but do not significantly affect performance). |
| Other Impurities | Maximum 0.50% (total) | Includes elements like tin (Sn) or aluminum (Al); strictly limited to maintain composition consistency and prevent degradation of machinability or ductility. |
This composition is critical to C360 brass's performance: the copper-zinc matrix provides the alloy's base properties, while lead enables its superior machinability-striking a balance that no other common brass grade matches for precision machining applications.
3. What is the Hardness of C360?
The hardness of C360 brass depends primarily on its processing state (annealed, cold-worked, or as-cast), as cold working increases hardness by straining the metal's crystal structure (at the cost of ductility). Below are the typical hardness values for C360 brass in its most common states, measured using the Brinell Hardness Test (HB)-the standard for brass alloys:
| Processing State | Typical Brinell Hardness (HB) | Key Context |
|---|---|---|
| Annealed | ~80–90 HB | The most common state for C360 brass. Annealing (heating to ~600–700°C, then slow cooling) relieves internal stress, maximizes ductility, and ensures consistent, moderate hardness-ideal for machining parts that may require post-machining forming (e.g., bending small fittings). |
| Cold-Worked (Light) | ~100–110 HB | Achieved via minor cold working (e.g., light rolling or drawing). Hardness increases slightly, improving wear resistance while retaining sufficient ductility for most applications (e.g., electrical terminals). |
| Cold-Worked (Heavy) | ~120–140 HB | Result of significant cold working (e.g., heavy drawing or stamping). Maximizes hardness and strength for parts that require high wear resistance (e.g., fasteners for heavy-duty hardware), though ductility is reduced. |
For reference, C360 brass's annealed hardness (~80–90 HB) is softer than many stainless steels (e.g., 316 SS: ~150–180 HB) but harder than pure copper (~30–40 HB)-a balance that allows for easy machining while ensuring the finished part can withstand typical service loads without deformation. When specifying C360 brass for a project, hardness is often tied to the processing state, with annealed material being the default choice for most machining needs.
