Heat treatment is a group of industrial processes used to alter the physical properties of materials by controlled heating and cooling. There are several common heat treatment methods including annealing, normalizing, hardening, and tempering. The goal of heat treatment is to achieve desired properties such as increased strength, hardness, ductility or corrosion resistance by changing the material's microstructure and relieving internal stresses.

1. Lora M. Labandero

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 is a group of industrial, thermal and metalworking
processes used to alter the physical, and sometimes
chemical, properties of a material.
 is the process of heating metal without letting it
reach its molten, or melting, stage, and then cooling
the metal in a controlled way to select desired
mechanical properties.
Heat treating

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 It can change a material’s physical (mechanical) properties and
it aids in other manufacturing steps.
 It relieves stresses, to machine or making the part easier weld.
 Increases strength, making the material ductile or more flexible.
 Introduces wear-resistant (hardness) characteristics, either just
to the surface or right through the part.
 Improves brittleness. Some metals can become weak or brittle
once exposed to a specific environment, so they need to be
treated in order to overcome this.
 Can improve the electrical and magnetic properties of a metal,
which will improve its compatibility with other materials.
Benefits of Heat Treating

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 Heat Treatment Steel: Annealing.
 Heat Treatment Steel: Normalizing.
 Heat Treatment Steel: Hardening.
 Heat Treatment Steel: Tempering.
The 4 Types of Heat Treatment Steel Undergoes

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 Annealing is a heat treatment method where a metal
such as aluminum, copper, steel, silver, or brass is
heated to a specific temperature, held at that
temperature for some time to allow transformation
to occur, and then air cooled. This process increases
the metal’s ductility and decreases hardness to make
the metal more workable.
ANNEALING

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 Normalizing is an annealing process for steel where
it is heated 150-200°F higher than in annealing and
held at the critical temperature long enough for the
transformation to occur.
NORMALIZING

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 In heat treating to harden a metal, the metal is heated
to a temperature where the elements in the metal
become a solution. Before doing this, defects in the
crystal lattice structure of metal are the primary
source of ‘give’ or plasticity.
HARDENING

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Tempering is a method of heat treating used to increase
the resilience of iron-based alloys like steel. Iron-based
metals are very hard, but they are often too brittle to be
useful for most purposes.
TEMPERING

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 Annealing. Heating and slowly cooling metal (usually steel) to
remove stress, make the metal softer, refine the structure, or
change its ductility.
 Carburizing. Adding carbon to the surface of iron-based alloys
by heating the metal to below its melting point (usually 1,560
and 1,740°F) and putting it in contact with carbon-rich solids,
liquids, or gasses.
 Case hardening. This hardens an iron alloy’s surface by first
carburizing and then quenching it to fix the process, so that the
center is relatively soft. Thus, the part consists of a hardened
case around a soft core.
 Cyanide hardening. This is a variant on case hardening that
brings the metal surface in contact with molten cyanide salt.
The part is then quenched.
HEAT TREATING PROCESSESS

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 Drawing (tempering). Metal is reheated after being hardened, then held at
a specific temperature, and finally quenched. This process reduces
hardness and increases toughness.
 Nitriding. This is a hardening process whereby nitrogen is added to the
metal surface through contact with ammonia gas. It produces case
hardening without quenching.
 Precipitation hardening. This is a hardening process (also known as age
hardening) in which certain metals are held at elevated temperatures
without quenching.
 Quenching. Steel is rapidly cooled by immersing it into oil or water, fixing
its structure in a hardened state.
 Sphereoidizing (anneal). This describes any process of heating and
cooling steel for the purpose of increasing the amount of rounded or
globular carbide in the metal.
 Cold working. While not a heat treating process, it is used to change a
metal’s characteristics.

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 In simple terms, heat treatment is the process of heating
the metal, holding it at that temperature, and then cooling
it back. During the process, the metal part will undergo
changes in its mechanical properties.
 The final outcome depends on many different factors.
These include the time of heating, time of keeping the
metal part at a certain temperature, rate of cooling,
surrounding conditions, etc. The parameters depend on
the heat treatment method, type of metal and part size.
 Over the course of this process, the metal’s properties will
change. Among those properties are electrical resistance,
magnetism, hardness, toughness, ductility, brittleness and
corrosion resistance.
Heat Treatment Process Steps

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HEATING
HOLDING
COOLING

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 Annealing
 Normalising
 Hardening
 Ageing
 Stress relieving
 Tempering
 Carburisation
Common Heat Treatment Methods

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Heat treatment EQUIPMENT
Facility name Model Heat treatment type Throughput
Electric resistance
furnace
250 kw pit type A, N, Q, T φ1000 × 4500L, 1900 kg,
1000°C
210 kw pit type A, T φ700 × 4500L, 1900kg,
800°C
Gas nitriding φ500 × 3800L, 1200kg
100 kw pit type A, N, Q, T φ850 × 2000L, 1900 kg,
1000°C
100 kw box type A, N, T 600W × 600H × 1500L,
1900 kg, 1000°C
60 kw box type A, T 700W × 400H × 1400L,
500 kg, 700°C
70 kw box type A, N, T 650W × 400H × 1200L,
500kg, 1000°C
24 kw box type A, N, Q, T 500W × 450H × 650L,
500 kg, 1000°C

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Facility name Model
Heat treatment
type
Throughput
Slip plane
hardening
equipment
Capacity of 250 kw Induction
hardening
2000W × 1000H ×
8000L
Vacuum furnace 150 kw pit type Vacuum hardening,
sintering
φ600 × 1200L, 500
kg, 1250°C
180 kw horizontal
type
Vacuum hardening,
sintering
650W × 500H ×
1000L, 450 kg,
1320°C
Cryostat -70°C Sub zero treatment 300W × 400H ×
2000L
Salt bath 24 kw Partial annealing φ250 × 500L, 500 kg,
900°C

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