Understanding Copper Tube Temper and Work Hardening
Copper tube is available in multiple temper conditions — from fully soft (annealed) to extra-hard (drawn) — each suited to different applications. Understanding the relationship between work hardening, annealing, and mechanical properties is essential for selecting the right copper tube and ensuring proper fabrication. This guide covers the complete science and engineering of copper tube temper management for 2026 projects.
The Science of Work Hardening in Copper
What Is Work Hardening?
Work hardening (strain hardening) occurs when copper is plastically deformed — drawn through dies, bent, or formed — at temperatures below its recrystallization temperature. The deformation increases dislocation density in the crystal structure, which increases strength and hardness but reduces ductility.
The Stress-Strain Relationship
- Elastic region: Copper deforms elastically up to its proportional limit, returning to original shape when stress is removed
- Yield point: Beyond this point, permanent (plastic) deformation begins
- Work hardening region: As deformation continues, increasing stress is required for further strain
- Ultimate tensile strength: Maximum stress before necking begins
- Fracture: Material fails when ductility is exhausted
How Drawing Creates Different Tempers
Copper tube is manufactured by extrusion followed by cold drawing through progressively smaller dies. The amount of cold work (reduction in cross-section) determines the final temper:
- Light drawing (5-15% reduction): Light drawn temper
- Moderate drawing (15-30%): Half-hard temper
- Heavy drawing (30-50%+): Hard drawn temper
- Extra heavy drawing: Extra-hard (spring) temper
Copper Tube Temper Designations
| Temper | Designation | Typical Tensile Strength | Typical Hardness (HV) | Elongation | Common Use |
|---|---|---|---|---|---|
| Soft (Annealed) | O60 / H55 | 200-250 MPa | 40-50 | 50%+ min | Bent tubing, refrigeration |
| Light Drawn | H55 | 250-300 MPa | 60-75 | 30-40% | General plumbing |
| Half-Hard | H58 | 300-340 MPa | 75-90 | 20-25% | Plumbing, water service |
| Hard Drawn | H80 | 350-400 MPa | 100-120 | 10-15% | Rigid tubing, structural |
| Extra-Hard (Spring) | H06 | 400+ MPa | 120+ | 5-10% | Special applications |
Annealing: Restoring Ductility
Why Anneal Copper?
- Restore ductility after work hardening for further forming or bending
- Relieve residual stresses from cold working
- Achieve uniform grain structure
- Improve electrical conductivity (which decreases with cold work)
- Prepare material for end-use where flexibility is required
Annealing Process Parameters
| Parameter | Range | Notes |
|---|---|---|
| Temperature | 400-700°C | Recrystallization starts at ~400°C; full anneal at 650-700°C |
| Time at temperature | 30-120 minutes | Depends on wall thickness and load size |
| Cooling | Furnace cool or air cool | Both produce equivalent results for copper (no quench requirement) |
| Atmosphere | Protective (N₂, H₂, or vacuum) | Prevents oxidation and maintains bright surface |
Annealing Methods
- Bright annealing: In protective atmosphere (N₂ or dissociated ammonia). Maintains bright, clean surface without post-anneal cleaning.
- Batch annealing: In bell furnaces with protective atmosphere. Used for coils of tube.
- Continuous annealing: In-line with the drawing process. For high-volume production.
- Flame/induction annealing: Local annealing of specific areas. Requires careful temperature control.
Mechanical Properties After Annealing
After full annealing (650°C, 1 hour), copper tube properties return to approximately:
- Tensile strength: 200-250 MPa (Type C12200 / DHP copper)
- Yield strength (0.5% extension): 60-100 MPa
- Elongation in 50mm: 50% minimum
- Hardness: 40-50 HV
- Grain size: 0.040-0.060mm (ASTM E112 grain size 5-7)
Work Hardening After Annealing
Annealed copper can be work hardened again by bending, drawing, or other cold working. However:
- Each cycle of work hardening → annealing → work hardening produces progressively larger grain size
- Excessive grain growth (from repeated cycles) reduces strength and surface quality
- Maximum recommended annealing cycles: 3-5 for most applications
- Final anneal grain size should be verified per specification
Bending Hardened Copper Tube
When bending hard-drawn copper tube:
- Bend radius: Minimum 3-5x tube OD for hard temper; 1-3x for soft temper
- Springback: Hard temper has more springback — compensate by overbending
- Wrinkling: Use mandrel bending for thin-wall hard tube to prevent collapse
- If bend radius is too tight for hard temper: Anneal the tube first, then bend
Quality Testing
Hardness Testing
- Vickers hardness (HV) per ASTM E92 on tube cross-section
- Rockwell superficial (15T, 30T) per ASTM E18
- Verify temper matches specification
Tensile Testing
- Per ASTM B42 or ASTM B88 requirements
- Verify tensile strength, yield strength, and elongation
Grain Size Measurement
- Per ASTM E112 using comparison or intercept methods
- Critical for verifying annealing quality
- Typical requirement: Grain size 5-7 (0.035-0.053mm)
Bend Testing
- Per ASTM B280 or application-specific requirements
- Verify tube can be bent to specified radius without cracking
CoreMetal Steel: Copper Tube Supplier
CoreMetal Steel supplies copper tube in all tempers (soft, half-hard, hard) in Types K, L, M, and ACR per ASTM B88, B75, and B280. Available in straight lengths and coils, with full certification.
Contact: Tracy | tracy@coremetalsteel.com | +86 18291910632
Conclusion
Understanding copper tube work hardening and annealing is essential for proper material selection and fabrication. The right temper ensures optimal performance in bending, forming, and end-use applications. Visit CoreMetal Steel Blog for more technical resources.