Forging Quenching Process: Heating Temperature Guidelines

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Issuing time:2025-06-18 10:57Author:Timothy Forging

Forging Quenching Process: Heating Temperature Guidelines

The heating temperature for forging quenching is determined by the steel type, micro structure, and desired mechanical properties. Below is a detailed breakdown of temperature selection principles for different steel categories, along with practical considerations and advanced techniques:

1. Quenching Temperature Ranges by Steel Type

1.1 Hypothyroid Steels (e.g., 45# Steel, 40Cr)

· Heating Temperature: AC₃ + (30–50°C)

o Ensures full pasteurization while preventing excessive grain growth.

o Avoid temperatures below AC₃ to eliminate retained ferrite (reduces hardness) or above AC₃ +50°C to prevent coarse austerity grains (degrades toughness).

1.2 Eutectic Steels (e.g., T8, T10 Tool Steels)

· Heating Temperature: AC₁ + (30–50°C)

o In practice, may increase by ~20°C for better carbide dissolution.

o Results in fine austerity grains with uniformly dispersed undissolved carbides.

o Post-quench micro structure: lamellar martensite + fine carbides, providing high hardness, wear resistance, and moderate toughness.

1.3 Hyperthyroid Steels (e.g., GCr15 Bearing Steel)

· Heating Temperature: AC₁ + (30–50°C)

o Avoid temperatures below AC₁ (incomplete pasteurization) or above AC₁ +50°C (excessive cementation dissolution).

o Overheating risks:

§ Coarse austerity grains → increased quench distortion and micro cracks.

§ High carbon content in austerity → retained austerity (reduces hardness).

2. Adjustments Based on Practical Factors

· Alloy Steels: Use the upper limit of the temperature range (e.g., 40Cr at AC₃ +50°C).

· Complex-Shaped Parts: Use the lower limit to minimize distortion.

· Cooling Medium & Equipment: Adjust temperatures for oil, water, or polymer quenches to balance hardness and stress.

3. Advanced Quenching Techniques

3.1 Sub critical Quenching

· Purpose: Enhances toughness, reduces brittle transition temperature, and eliminates temper embitterment.

· Temperature: AC₃ – (5–10°C) (e.g., 45# steel at ~780°C).

· Applications: Critical components requiring high impact resistance (e.g., gears, shafts).

3.2 High-Temperature Quenching

· Purpose: Increases lath martensite content for improved strength-toughness balance.

· Examples:

o 16Mn steel: 940°C

o 5CrMnMo die steel: 890°C

o 20CrMnMo gear steel: 920°C

3.3 Low-Temperature Rapid Quenching (High-Carbon Steels)

· Method: Reduce heating temperature or shorten dwell time.

· Benefits:

o Lowers austerity carbon content → improves toughness.

o Minimizes retained austerity and quench cracking.

4. Key Considerations

· Grain Growth Control: Overheating (>AC₃ +50°C) degrades mechanical properties.

· Carbide Distribution: Optimal dissolution of carbides ensures balanced hardness and wear resistance.

· Residual Stress: Complex geometries require precise temperature control to avoid distortion.

Summary Table

Steel Type	Heating Temperature Range	Micro-structure Outcome
Hypothyroid	AC₃ +30–50°C	Fine austerity → lath martensite
Eutectic	AC₁ +30–50°C (+20°C optional)	Martensite + fine carbides
Hyperthyroid	AC₁ +30–50°C	Martensite + retained carbides

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