Annealing vs Tempering [+Process Selection Tips]

This expert guide compares both heat treatments to help you choose the right one for better performance, less stress, and longer part life.

The Value of Heat Treatment

Heat treatment improves material performance by enhancing ductility, relieving stress, refining structure, and increasing part durability. Among the many methods, annealing and tempering are two core processes.

Which one fits your project best? This guide compares their principles, benefits, and applications to help you decide with confidence.

What Is Annealing?

Annealing is a heat treatment process where a metal is heated to its recrystallization temperature, held for a period, and then slowly cooled—typically inside the furnace. The goal is to alter the microstructure to increase ductility and reduce hardness, making the metal more workable.

Key Points:

● Process: Heat to recrystallization → Soak → Slow furnace cooling

● Common Materials: Low-carbon steel, aluminum alloys, austenitic stainless steel, copper alloys

● Primary Objectives:

• Increase ductility

• Reduce hardness

• Relieve internal stress

• Refine grain structure

• Improve machinability and electrical properties

Annealing is especially useful before or after forming operations to ensure materials are easier to machine or bend without cracking. It also helps reset the structure of cold-worked metals to their original form.

What Is Tempering?

Tempering is typically performed after quenching (rapid cooling) and involves reheating the metal to a lower temperature followed by controlled cooling. It is commonly used to reduce the brittleness caused by quenching and restore toughness to hardened metals.

Key Points:

● Process: Quenching → Reheat at 150–650 °C → Controlled cooling

● Purpose: Reduce brittleness while improving toughness, ductility, and dimensional stability

● Temperature Ranges & Effects:

• Low (150–250 °C): Slight hardness reduction, minimal toughness gain

• Medium (250–450 °C): Balanced hardness and toughness

• High (450–650 °C): Maximum toughness, lower hardness

Tempering is vital for parts that require strength and toughness, such as structural tools, die components, automotive shafts, and aerospace fasteners.Annealing vs. Tempering: Side-by-Side Comparison

Material Selection Considerations

Steel:

● High-carbon steel: Often tempered after quenching for tools, knives, and springs.

● Medium/low-carbon steel: Commonly annealed before cold forming or machining to improve formability.

Aluminum Alloys:

● Typically annealed to improve formability and relieve stress after welding.

● For CNC applications, annealing prior to finishing enhances dimensional stability and reduces tool wear.

Stainless Steel:

● Austenitic grades benefit from annealing to prevent intergranular corrosion and ensure maximum corrosion resistance.

● Martensitic grades may be tempered to improve toughness after hardening.

Copper and Brass:

● Annealed to restore softness after work hardening and improve electrical conductivity.

If you’re unsure whether your part needs full recrystallization or a more moderate refinement of grain structure, understanding normalizing could be the key.

To tell the differences beyween annealing vs. normalizing, check out our article: Annealing vs. Normalizing: Contrasts, Benefits, and Applications.

CNC Machining & 3D Printing Applications

CNC Machining:

Annealing before CNC machining reduces tool wear, improves chip removal, and ensures more consistent part geometry. Post-machining tempering can be used to reduce internal stress and improve service life.

3D Printing (SLM/DMLS):

Metal parts produced via Selective Laser Melting often undergo annealing to relieve residual stresses caused by rapid solidification and prevent warping. Post-annealing heat treatments can also enhance fatigue resistance.

Real-world examples:

● Tooling: Tempering significantly extends mold life in injection molding and die casting.

● Aerospace: Annealing of titanium parts ensures dimensional stability and stress relief for safety-critical components.

● Medical Devices: Stainless steel surgical instruments are annealed and/or tempered for precise balance between hardness and ductility.

Cost & Energy Efficiency

Annealing involves longer cycles and slow furnace cooling, resulting in higher energy use and longer lead times. However, it is essential for formability and dimensional accuracy.

Tempering, in contrast, is quicker and more energy-efficient, ideal for high-throughput workflows and operations.

Optimized Options:

● Use of vacuum furnaces and inert gas atmospheres (e.g., argon, nitrogen) helps avoid oxidation and contamination.

● Modern fast-cycle furnaces and induction heating systems shorten cycles and reduce electricity usage.

● Smart temperature control, automation, and batch optimization lower overall process costs and improve sustainability.

Quality Control & Industry Standards

Precise process control and testing are critical for achieving desired mechanical properties and meeting industry standards.

Testing Methods:

● Hardness testing (Rockwell, Vickers, Brinell)

● Charpy impact testing for toughness

● Metallographic examination of grain structure

● Residual stress analysis via X-ray diffraction or hole-drilling

Key Standards:

● AMS 2750E: Calibration and control of heat treatment equipment (aerospace standard)

● ISO 9001 & ISO 14001: Quality and environmental management systems

● ASTM A255: Standard test methods for determining hardenability of steels

● NADCAP Accreditation: Required for aerospace heat treating operations

Which Should You Choose?

Choose annealing if your priority is improving ductility, machinability, and stress relief—especially before forming or machining.

Choose tempering if your goal is to reduce brittleness and enhance toughness after hardening. In many cases, both treatments may be used in a complementary sequence to achieve precise material performance.

Still unsure? Let Unionfab help you determine the ideal heat treatment route for your components.

Heat Treatment as a Value-Added Service at Unionfab

At Unionfab, we provide professional heat treatment services as a value-added solution to support your 3D printing and CNC machining needs:

• Supported processes: Annealing, Tempering, Quenching, Normalizing, Aging

• Integrated service: Combine heat treatment seamlessly with our CNC and industrial 3D printing workflows

• Advanced capabilities: Vacuum/inert atmosphere furnaces, precise thermal profiling, rapid heating

• Quality assurance: Full traceability, inspection reports, and material certifications available

• Engineering support: Free consultation and tailored process optimization for every project

FAQs

Does tempering soften metal?

Yes, but selectively—it reduces brittleness while preserving adequate strength.

Can all metals be heat treated?

No. Some non-ferrous metals and precipitation-hardened alloys have specific heat treatment windows and require different approaches.

Is heat treatment alone sufficient for high-performance parts?

Not always. It is often used in conjunction with precision machining, surface finishing, and coating processes.

Will dimensions change after heat treatment?

Yes. Thermal expansion, phase transformation, and internal stress relief can cause dimensional shifts, especially in annealing. Design allowances and post-treatment machining are recommended.

How do I choose between annealing and tempering?

Consider your material, desired mechanical properties, manufacturing stage, and end-use requirements. Consult with engineers to ensure the correct sequence and conditions.