3.7.1.1 Annealing Processes for Steel

Five basic annealing processes for steel are shown in Table 3-5.

Table 3-5 Basic Annealing Processes for Carbon and Alloy Steels

Material

Purpose Process Comments
0.30% to 0.60% Carbon Facilitate machining Full anneal: heat to 28 to 56°C (50 to 100°F) above the upper critical limit and cool slowly at a predetermined rate. Long cycle time, sometimes many hours.
Up to 0.25% Carbon Facilitate cold working Process anneal (sub-critical annealing or stress-relief annealing): heat to a point just below the lower critical point, hold for a prescribed time and cool.  
0.69% or higher Carbon Facilitate cold working or machining Spheroidizing: heat to just below the critical point or to just above and slow cool (5.5°C or 10°F per hour) through the critical point.  
All   Normalizing:1 heat to 55 to 85°C (100 to 150°F) above the upper critical point and slow cool. Ensures homogeneous austenitic grain size on reheating for hardening, and improves toughness.
Thin sections or small parts   Isothermal annealing (cycle annealing): heat to above the upper critical point, cool rapidly to predetermined level, hold, then cool to room temperature. Rapid cycle.

1Normalizing is often specified for parts that will be hardened and tempered. This annealing process refines the grain size and improves metal toughness.

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Five basic annealing processes for steel are shown in Table 3-5.

Table 3-5 Basic Annealing Processes for Carbon and Alloy Steels

Material

Purpose Process Comments
0.30% to 0.60% Carbon Facilitate machining Full anneal: heat to 28 to 56°C (50 to 100°F) above the upper critical limit and cool slowly at a predetermined rate. Long cycle time, sometimes many hours.
Up to 0.25% Carbon Facilitate cold working Process anneal (sub-critical annealing or stress-relief annealing): heat to a point just below the lower critical point, hold for a prescribed time and cool.  
0.69% or higher Carbon Facilitate cold working or machining Spheroidizing: heat to just below the critical point or to just above and slow cool (5.5°C or 10°F per hour) through the critical point.  
All   Normalizing:1 heat to 55 to 85°C (100 to 150°F) above the upper critical point and slow cool. Ensures homogeneous austenitic grain size on reheating for hardening, and improves toughness.
Thin sections or small parts   Isothermal annealing (cycle annealing): heat to above the upper critical point, cool rapidly to predetermined level, hold, then cool to room temperature. Rapid cycle.

1Normalizing is often specified for parts that will be hardened and tempered. This annealing process refines the grain size and improves metal toughness.

Return to Table of Contents

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Five basic annealing processes for steel are shown in Table 3-5.

Table 3-5 Basic Annealing Processes for Carbon and Alloy Steels

Material

Purpose Process Comments
0.30% to 0.60% Carbon Facilitate machining Full anneal: heat to 28 to 56°C (50 to 100°F) above the upper critical limit and cool slowly at a predetermined rate. Long cycle time, sometimes many hours.
Up to 0.25% Carbon Facilitate cold working Process anneal (sub-critical annealing or stress-relief annealing): heat to a point just below the lower critical point, hold for a prescribed time and cool.  
0.69% or higher Carbon Facilitate cold working or machining Spheroidizing: heat to just below the critical point or to just above and slow cool (5.5°C or 10°F per hour) through the critical point.  
All   Normalizing:1 heat to 55 to 85°C (100 to 150°F) above the upper critical point and slow cool. Ensures homogeneous austenitic grain size on reheating for hardening, and improves toughness.
Thin sections or small parts   Isothermal annealing (cycle annealing): heat to above the upper critical point, cool rapidly to predetermined level, hold, then cool to room temperature. Rapid cycle.

1Normalizing is often specified for parts that will be hardened and tempered. This annealing process refines the grain size and improves metal toughness.

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