Work Hardening

strain hardening involves creating surface compressive stresses that contribute to permanent plastic deformation of the material performed below the recrystallization temperature.

Work Hardening of a Material

The term strain hardening is used to describe an operation that transforms the mechanical properties of metal (rolling, drawing, collar forming and forging). As soon as the stress exceeds the elastic limit, the metal will undergo plastic deformation that will be permanent.

Following a strain hardening operation, we can observe an increase in the elastic limit of the same metal and also its hardness. However, it also becomes more brittle. In the case of highly alloyed steels, we can see an increase in strength until reaching the breaking point.

The opposite phenomenon occurs in low-alloy steels. Some austenitic steels undergo a martensitic transformation during strain hardening, particularly Hadfield steels (manganese steels or mangalloys, e.g., X120Mn12), which results in an even greater surface hardness.

strain hardening transformations are of “metallurgical order because we” modify the metallic structure on the surface to make it harder without introducing “atoms into the” iron lattice.

Work Hardening of Brass

Brass is an alloy of copper and zinc. The addition of zinc to copper up to 42% allows for a reduction in base price while increasing characteristics. Depending on the percentage of zinc, we obtain different properties of brass. The most malleable alloys for stamping are from CuZn30 to CuZn36, with a possible elongation of A% = 60% with 31% Zn. The mechanical properties are improved by a mechanical action of strain hardening ranging from quarter-hard to extra-hard or even spring. These different states of strain hardening allow for considerable improvement in tensile strength.

Work Hardening of Stainless Steels

Stainless steel is perfectly suited to undergo strong deformations while maintaining very good mechanical characteristics. Thanks to a high ratio of the material and its unique characteristics in elongation and strain hardening, it can respond to many complex shapes without welding.

Moreover, the operations of deformation and/or hardening of metals by strain hardening do not modify the chemical composition of these steels, we maintain their resistance to corrosion and oxidation, as well as aesthetic properties.

Stainless steel is often a material of choice for products intended for both industries and consumers. The strain hardening of austenitic stainless steels of type 1.4310 C1000 annealed is interesting for technical parts intended for springs or clips because the yield strength of this work-hardened stainless steel is high.

We use it for manufacturing products requiring good resistance to mechanical fatigue. These steels having a good formability allow us to achieve weight savings (springs, connection parts, switch blades, watchmaking parts, certain knives, etc.).

Work Hardening of Aluminum Alloys

The metallurgical states of alloys hardened by strain hardening are identified by a nomenclature starting with the letter H, followed by a number from 1 to 4 allowing to map the types of metal processing that the material will undergo after strain hardening. The second digit indicates the hardness of the strain hardening from the softest (1) to the hardest (9).

Work-hardened only means that this state applies to products that are only work-hardened without metal processing, corresponding to alloys of the 1000 series (Aluminum alloys with more than 99%), which, even with maximum strain hardening, retain good malleability.

H2 Work-hardened and partially annealed means that this state applies to products that are hardened by strain hardening above the final value and brought back to the desired value by partial annealing, corresponding to alloys of the 3000 series (Aluminum-manganese alloys).

H3 Work-hardened and stabilized means that this state applies to products that are work-hardened and whose mechanical properties are stabilized by a low-temperature metal processing applied to alloys of the 5000 series (Aluminum-magnesium alloys), some of which soften (lose mechanical properties) at room temperature. This stabilization process increases the elongation of the material during a stamping operation.

H4 Work-hardened and painted or lacquered means that this state applies to products that are work-hardened and subjected to a certain thermal metal processing during the baking of paints or lacquers. It is possible to restore the deformation capacity of the alloy by subjecting it to a thermal metal processing called recovery annealing, which is performed at temperatures above 300°C.

The number following the designation H1, H2, H3 or H4 indicates the degree of strain hardening undergone by this product. The higher the second digit between 1 and 9, the more significant the strain hardening, thus the harder the product compared to the fully annealed state (state 0).