热处理含英文

Heat treatment

Heat treatment is a method used to alter the physical, and sometimes chemical, properties of a

material.

The

most

common

application

is

metallurgical.

Heat

treatments

are

also

used

in

the

manufacture of many other materials, such as glass. Heat treatment involves the use of heating or

chilling,

normally

to

extreme

temperatures,

to

achieve

a

desired

result

such

as

hardening

or

softening of a material. Heat treatment techniques include annealing, case hardening, precipitation

strengthening,

tempering

and

quenching.

It

is

noteworthy

that

while

the

term

heat

treatment

applies only to processes where the heating and cooling are done for the specific purpose of altering

properties

intentionally,

heating

and

cooling

often

occur

incidentally

during

other

manufacturing

processes such as hot forming or welding.

Heat treatment of metals and alloys

Metallic materials consist of a microstructure of small crystals called

nature of the grains (i.e. grain size and composition) is one of the most effective factors that can

determine the overall mechanical behavior of the metal. Heat treatment provides an efficient way

to manipulate the properties of the metal by controlling rate of diffusion, and the rate of cooling

within the microstructure.

Complex

heat

treating

schedules

are

often

devised

by

metallurgists

to

optimize

an

alloy's

mechanical properties. In the aerospace industry, a superalloy may undergo five or more different

heat

treating

operations

to

develop

the

desired

properties.

This

can

lead

to

quality

problems

depending on the accuracy of the furnace's temperature controls and timer.

Annealing

退火

Annealing

is

a

technique

used

to

recover

cold

work

and

relax

stresses

within

a

metal.

Annealing

typically results in a soft, ductile metal. When an annealed part is allowed to cool in the furnace, it is

called

a

anneal

heat

treatment.

When

an

annealed

part

is

removed

from

the

furnace

and

allowed

to

cool

in

air,

it

is

called

a

heat

treatment.

During

annealing,

small

grains

recrystallize to form larger grains. In precipitation hardening alloys, precipitates dissolve into the

matrix,

Typical annealing processes include,

and full annealing.

Hardening and tempering (quenching and tempering)

调质处理（淬火

+

回火）

To

harden

by

quenching,

a

metal

(usually

steel

or

cast

iron)

must

be

heated

into

the

austenitic

crystal

phase

and

then

quickly

cooled.

Depending

on

the

alloy

and

other

considerations

(such

as

concern for maximum hardness vs. cracking and distortion), cooling may be done with forced air or

other gas (such as nitrogen), oil, polymer dissolved in water, or brine. Upon being rapidly cooled, a

portion of austentite (dependent on alloy composition) will transform to martensite, a hard brittle

crystalline structure. The quenched hardness of a metal depends upon its chemical composition and

quenching

method.

Cooling

speeds,

from

fastest

to

slowest,

go

from

polymer

(n),

brine,

fresh water, oil, and forced air. However, quenching a certain steel too fast can result in cracking,

which is why High-tensile steels like AISI 4140 should be quenched in oil, tool steels such as 2767

or H13 hot work tool steel should be quenched in forced air, and low alloy or medium- tensile steels