This guide covers 11 types of heat treatment. We explain how each process works, when to use it, and help you choose the best option for your CNC parts.

1. What is Heat Treatment? Why CNC Parts Need It

2. Bulk Heat Treatment (Types 1–4)

3. Surface Heat Treatment (Types 5–7)

4. Chemical Heat Treatment (Types 8–11)

5. Comparison Table: 11 Heat Treatment Types at a Glance

6. How to Choose the Right Heat Treatment

7. Expert Insight: Timing Heat Treatment Matters

8. Frequently Asked Questions (FAQ)

1. What is Heat Treatment? Why CNC Parts Need It

Heat treatment is a process. It heats the metal to a set temperature. It holds it there. Then it cools it at a set rate. This changes the microstructure inside the metal. Different microstructures give different properties.

How Heat Treatment Helps CNC Parts

A CNC machined part comes off the machine with raw properties. Heat treatment adds value.

• Hardness: The part resists wear and scratching.

• Strength: The part handles higher loads.

• Toughness: The part bends before it breaks.

• Wear resistance: The part lasts longer in moving applications.

• Stress relief: The part does not warp after machining.

2. Bulk Heat Treatment (Types 1–4)

Bulk treatment changes the whole part. From surface to center.

1. Annealing

Annealing softens the metal. The part is heated and cooled slowly.

• Why use it: Makes hard metals easier to machine. Removes internal stress.

• Best for: High-carbon steel, tool steel, castings.

• Result: Soft, ductile, easy to cut.

2. Normalizing

Normalizing refines the grain structure. The part is heated and cooled in air.

• Why use it: Creates a uniform structure. Improves machinability.

• Best for: Low-carbon steel, forgings.

• Result: Consistent grain size. No hard spots.

3. Quenching

Quenching is fast cooling. The part goes into water, oil, or polymer.

• Why use it: Creates martensite. This is a very hard structure.

• Best for: Tool steel, high-carbon steel, stainless.

• Result: Very high hardness. But the part can be brittle.

4. Tempering

Tempering follows quenching. The part is reheated to a lower temperature.

• Why use it: Removes quenching stress. Reduces brittleness.

• Best for: All quenched steels.

• Result: Good balance of hardness and toughness.

3. Surface Heat Treatment (Types 5–7)

Surface treatment hardens only the outside layer. The core stays soft and tough.

5. Induction Hardening

An electric coil creates a magnetic field. It heats the surface fast. Then a quench cools it.

• Why use it: Local hardening. Very fast. Good for shafts and gears.

• Best for: Medium-carbon steel.

• Result: Hard surface. Tough core.

6. Flame Hardening

A high-temperature flame heats the surface. Then a quench follows.

• Why use it: Flexible. Works on large parts. Low equipment cost.

• Best for: Large gears, rails, rolls.

• Result: Hard surface. Deeper case than induction.

7. Laser Hardening

A laser beam heats a small spot. The part self-quenches.

• Why use it: Very precise. Very low distortion.

• Best for: Small areas. Molds. Guide rails.

• Result: Hard line or pattern. Almost no warping.

4. Chemical Heat Treatment (Types 8–11)

These treatments add elements into the surface. They change the chemistry.

8. Carburizing

The part sits in a carbon-rich environment at high heat. Carbon diffuses into the surface.

• Why use it: Adds a high-carbon case to low-carbon steel.

• Best for: Gears, camshafts, pins.

• Result: Hard case (up to 60 HRC). Tough core.

9. Nitriding

Nitrogen diffuses into the surface. No quenching needed.

• Why use it: Very high surface hardness. Very low distortion.

• Best for: Dies, molds, crankshafts.

• Result: Extremely hard surface (over 1000 HV). Good fatigue life.

10. Carbonitriding

Carbon and nitrogen go into the surface together.

• Why use it: Faster than carburizing. Better hardenability.

• Best for: Small parts. Fasteners. Pins.

• Result: Thin, hard case. Good for high-volume parts.

11. Boriding

Boron diffuses into the surface. A very hard iron boride layer forms.

• Why use it: Extreme wear resistance. Higher than nitriding.

• Best for: Extrusion screws, dies, mining parts.

• Result: Very high hardness (up to 2000 HV). Brittle case.

5. Comparison Table: 11 Heat Treatment Types at a Glance

6. How to Choose the Right Heat Treatment

Use this guide to match your need to the process.

7. Expert Insight: Timing Heat Treatment Matters

“The biggest mistake is heat treating before machining. Hard steel is hard to cut. It wears out tools. It takes more time. We always tell clients: rough machine first, then heat treat, then finish grind. This way, the tool cuts soft steel. The final grind removes any warping. For parts with tight tolerances, this is the only way. For nitriding, we machine to final size. Nitriding does not change size. It is the safest process for precision parts.”
— Metallurgy Engineer, DongGuan YiTai Electronic Technologies

One-Stop Service: CNC Machining + Heat Treatment

At ‘DongGuan YiTai Electronic Technologies’ , we do both. We machine your part. We heat treat it. All in one place.

We offer annealing, quenching & tempering, induction, nitriding, and more. We help you pick the right process. We control the whole job. No shipping between shops. No lost parts.

Send us your drawing. Tell us the material. Tell us the hardness or strength you need. We will recommend the best heat treatment. We will give you a quote for machining and treatment together.

8. Frequently Asked Questions (FAQ)

Q: Can I heat treat after CNC machining?
A: Yes. This is the normal order. Rough machine. Then heat treat. Then finish grind. If you heat treat first, the part becomes hard. Machining becomes slow and expensive.

Q: Which heat treatment gives the least distortion?
A: Nitriding gives the least distortion. It uses low temperature. No quenching. The part stays stable. For precision parts like mold cores, nitriding is the best choice.

Q: What is the difference between case hardening and through hardening?
A: Case hardening hardens only the surface. The core stays soft. This is good for gears and shafts. Through hardening hardens the whole part. This is good for tools and wear parts.

Q: Can stainless steel be heat treated?
A: Yes. But not all stainless. Martensitic stainless (like 410, 420, 440C) responds to quenching and tempering. Austenitic stainless (like 304, 316) does not harden by heat treatment. It only work hardens.

Q: How do I specify heat treatment on my drawing?
A: Write the hardness value (e.g., 45–50 HRC) and the process name (e.g., Quench and Temper). For case hardening, write the case depth (e.g., 0.5mm min). We can also help you write the spec.

Q: Does DongGuan YiTai Electronic Technologies offer all 11 types?
A: We offer most of them. We do annealing, quench & temper, induction, nitriding, carburizing, and laser hardening. For flame hardening and boriding, we partner with certified specialists. We manage the whole process for you.

DongGuan YiTai Electronic Technologies Co.,Ltd

DongGuan YiTai Electronic Technologies Co.,Ltd is a manufacturing service provider located in Dongguan, China.

YiTai specialized in CNC turning machining and sheet metal fabrication mainly. As a member of Hung Mou Group, we focus on the overseas marketing development. And based on our parent company’s manufacturing capability and resources, YiTai also expended machining services such as die casting, injection molding, aluminum profile extrusion, 3D printing, which are committed to providing customers with one-stop purchasing services and experience.

 CNC MACHINING , CNC MILLING , CNC TURNING , SHEETMETAL , FASTENER , OTHERS