Why NADCAP Certification Matters for Aerospace Heat Treating
June 30, 2025
In the world of metal treatment, achieving the right balance between hardness, strength, and ductility is critical. Two of the most widely used heat treating processes—tempering and annealing—serve unique roles in achieving desired material properties. But despite their widespread use, these terms are often misunderstood or confused. At Southwest Metal Treating (SWMT), we’re experts in both techniques. Whether you’re working with steel, aluminum, or specialty alloys, understanding these treatments can greatly improve the performance, machinability, and lifespan of your components.
What Is Tempering?
Tempering is a heat treatment process typically performed after quenching, which rapidly cools a metal to lock in hardness. However, quenching also makes the metal brittle. Tempering addresses this issue by reheating the metal to a controlled temperature—usually between 300°F to 1,300°F (150°C to 700°C)—and then cooling it slowly.
Purpose of Tempering:
- Reduce brittleness
- Improve ductility
- Relieve internal stresses
- Maintain adequate hardness
How Tempering Works:
After a metal is quenched and hardened, its internal structure (specifically the martensite phase in steel) is very hard but prone to cracking. By tempering, the metal is reheated to allow structural rearrangement, which lowers hardness slightly but significantly increases toughness and stress resistance.
Common Applications:
- Tool steels
- Automotive parts
- Cutting tools
- Springs
- Gears
What Is Annealing?
Annealing is a more general-purpose heat treatment aimed at softening metal, improving its workability, and restoring ductility after hardening or cold working. Annealing typically involves heating the metal to a temperature above its recrystallization point, holding it at that temperature for a specific period, and then cooling it slowly, usually in a furnace.
Purpose of Annealing:
- Soften metal for machining or forming
- Improve electrical conductivity
- Relieve internal stresses
- Enhance ductility and toughness
- Refine grain structure
How Annealing Works:
When a metal is heated to its critical temperature and held there, new, strain-free grains form during the cooling phase. This process resets the metal’s internal structure, reducing hardness and enhancing its ability to deform without cracking.
Common Applications:
- Sheet metal fabrication
- Electrical wiring (copper, aluminum)
- Structural steel shaping
- Cold-worked metals (drawn wire, rolled sheets)
Key Differences Between Tempering and Annealing
| Feature | Tempering | Annealing |
| Objective | Reduce brittleness and maintain hardness | Soften metal and improve ductility |
| Temperature Range | 300°F – 1,300°F (150°C – 700°C) | Up to 1,650°F (900°C), depending on material |
| Cooling Method | Typically air cooled | Slow cooling, often in a furnace |
| Material State Before Treatment | Usually hardened (quenched) | Cold-worked, hardened, or stressed |
| End Result | Tough, less brittle, slightly softer metal | Soft, ductile, stress-relieved metal |
| Applications | Tools, mechanical parts, high-stress components | Fabricated parts, wiring, structural materials |
When to Use Tempering vs. Annealing
Use Tempering when:
- The metal has been quenched and hardened but is too brittle for practical use.
- You need to fine-tune the hardness vs. toughness tradeoff.
- The component will be subjected to mechanical stress or impact.
Example: A quenched steel gear may be extremely hard but prone to cracking under load. Tempering it allows the gear to absorb shocks without failing.
Use Annealing when:
- You need to machine, bend, or form the metal and it’s too hard or brittle to do so.
- The material has gone through multiple forming operations and has become work-hardened.
- You want to prepare metal for further heat treatment or electrical conductivity enhancement.
Example: Sheet metal used in automotive body panels is annealed to restore flexibility after cold rolling, allowing for easier stamping and forming.
Benefits of Tempering and Annealing
Benefits of Tempering:
- Improves mechanical performance under stress
- Reduces risk of cracking or failure
- Enhances toughness while retaining much of the original hardness
- Customizable based on desired final properties
Benefits of Annealing:
- Increases ductility and softness
- Restores machinability in hardened metals
- Removes internal stresses from cold work or welding
- Produces a uniform, fine-grained structure
Why the Right Heat Treatment Matters
Choosing between tempering and annealing isn’t just a technical decision—it directly impacts the safety, durability, and functionality of your finished parts. Improper heat treatment can result in premature failure, machining difficulties, or even hazardous working conditions. That’s why working with a trusted heat treating partner is critical.
Why Choose Southwest Metal Treating (SWMT)?
At Southwest Metal Treating, we bring over 30 years of experience in precision heat treating services. Whether your project calls for tempering, annealing, quenching, normalizing, or carburizing, we deliver consistent results tailored to your specifications.
What Sets SWMT Apart:
- Advanced heat treating equipment
- Experienced metallurgists and technicians
- Custom solutions for complex alloys and components
- Fast turnaround and competitive pricing
- ISO-certified quality assurance
- ITAR Registered
- NADCAP Accredited for Heat Treating
No matter the industry—aerospace, automotive, manufacturing, oil & gas, or tooling—we have the expertise and infrastructure to treat your metal right.
