Acro News

Understanding Material Temper

Most of us are familiar with the old hardness call outs: Full Hard, Half Hard, Etc.  But some of the numbering systems can be confusing.  As the temper number goes up for steel the material get softer, but as the number goes up for copper it gets harder.  Many of these numeric or descriptive tempers overlap on the Rockwell Scale and only measure “Surface Hardness”.   The temper from the mill is mostly determined by chemical composition but can be altered through working or heat treating.  If it’s the “strength” of the finished part that is the important characteristic, chemical composition can be more important the temper call out.  The secret is to know what finished characteristic you need and work backwards.  Free consultation from a metallurgist is readily available.  See below for some of the number/descriptive temper call-out confusion.

STANDARD LOW CARBON STEEL TEMPERS
Temper indicates the mechanical properties of hardness, strength, stiffness and ductility. It is classified by degree of Rockwell Hardness

NO. 1 TEMPER = Full Hard: Sometimes Referred to as “Spring”.  Thickness 0.069 and thinner Rockwell B-90 minimum thickness 0.070″ and heavier Rockwell B-84 minimum. This temper is not intended for Cold Forming.

NO. 2 TEMPER = Half Hard: Rockwell B-7O minimum and B-85 maximum, approximately. This temper can be bent 90 degrees across the direction of rolling around a radius equal to its thickness.

NO. 3 TEMPER = Quarter Hard: Rockwell B-6O minimum and B-75 maximum, approximately. This temper can be bent 180 degrees across the direction of rolling over one thickness of the strip and 90 degrees in the direction of rolling around a radius equal to its thickness.

NO. 4 TEMPER = Soft: Sometimes Referred to as “Annealed”. Rockwell B-65 maximum, approximately. This temper can be bent flat upon itself in any direction.

NO. 5 TEMPER = Dead Soft:Rockwell B-55 maximum, approximately. This temper can be bent flat upon itself in any direction.

STANDARD COPPER TEMPERS
H00 TEMPER = 1/8 Hard
H01 TEMPER = 1/4 Hard
H02 TEMPER = 1/2 Hard
H03 TEMPER = 3/4 Hard
H04 TEMPER = Hard
H06 TEMPER = Extra Hard
H08 TEMPER = Spring

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