Quenching&annealing and Tempering’s different
When the term “annealing” is applied to
ferrous alloys without qualification, full annealing is applied. Precision metal parts This is achieved by heating above the alloy’s transformation
temperature, then applying a cooling cycle which provides maximum softness.
This cycle may vary widely, depending on composition and characteristics of the
specific alloy.
Quenching is a rapid cooling of a steel or alloy from the austenitizing
temperature by immersing the workpiece in a liquid or gaseous medium. Quenching
medium commonly used include water, 5% brine, 5% caustic in an aqueous
solution, oil, polymer solutions, or gas (usually air or nitrogen).
Selection of a quenching medium depends largely on the hardenability of
material and the mass of the material being treating (principally section
thickness).
Precision metal parts The cooling capabilities of the above-listed quenching media vary
greatly. In selecting a quenching medium, it is best to avoid a solution that
has more cooling power than is needed to achieve the results, thus minimizing
the possibility of cracking and warp of the parts being treated. Modifications
of the term quenching include direct quenching, fog quenching, hot quenching,
interrupted quenching, selective quenching, spray quenching, and time quenching.
Tempering. Precision metal parts In heat treating of ferrous alloys,
tempering consists of reheating the austenitized and quench-hardened steel or
iron to some preselected temperature that is below the lower transformation
temperature (generally below 1300 ℃ or 705 ℃). Tempering
offers a means of obtaining various combinations of mechanical properties.
Tempering temperatures used for hardened steels are often no higher than 300 ℃(150 ℃). The term “tempering” should not be confused
with either process annealing or stress relieving. Even though time and
temperature cycles for the three processes may be the same, the conditions of
the materials being processed and the objectives may be different.
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