What Is a Work Hardening Service?
Work hardening services refers to a phenomenon in which a metal becomes harder when a force is applied to it.
The phenomenon in which a wire becomes harder and more brittle and breaks when bent is an example of hardening services. As hardness increases, tenacity, such as elongation and drawing, will decrease.
As the degree of work hardening increases, the microstructure is disrupted, electrical resistance increases, and specific gravity decreases. When work-hardened materials are heated, the transitions increased by work hardening dissipate and soften. In hot work, heat softens the material, whereas in cold work, only hardening services occurs, making the material hard and brittle.
Uses of Work Hardening Services
Work hardening services are used to improve the strength of materials that cannot be quenched, such as aluminum and stainless steel. In the case of steel, it is sometimes used in combination with annealing after cold working, and is applied to gears and automotive springs.
Annealing removes internal strains and residual stresses that have increased due to hardening services, making the product less susceptible to cracking and more tough. When an item is cold worked, crystals are distorted and irregularly arranged, but when heated to the recrystallization temperature, the rearrangement of crystal grains can change the material into a hard and elastic material.
Principle of Work Hardening Services
When a load is first applied to a metal, the metal is deformed, but after the load is removed, the deformation may or may not return to its original state. The return to the original state is called elastic deformation, and the failure to return to the original state is called plastic deformation. Plastic deformation is a phenomenon in which atoms slide across a certain crystal plane. Plastic deformation is caused by the movement of transitions, which are linear lattice defects.
A material that is easy to move easily undergoes plastic deformation, while a material that is hard to move due to the accumulation of transitions becomes a hard material. The ease of hardening services depends on the material, and the hardening services index (n-value) is used as a guide. In the curve showing the relationship between stress on the vertical axis and strain on the horizontal axis, the relationship between stress and strain in the plastic region above the yield point is as follows:
σ = Cεn
The larger the n value, the easier hardening services will become. Work hardening services make the material harder, but also makes it more brittle. This is based on the principle of eliminating dislocations by heating to the recrystallization temperature, where the movement of atoms becomes active.