Heat treatment

The mechanical properties of metals are critical for any metallic product. It is very important to realize the necessary heat treatment of a product as to attain the desired properties. Heat treatment can change or treat properties such as hardness, toughness, malleability, ductility, micro-structure, and stress concentration. Different types of heat treatment addresses different types of properties change.

1- Quenching

It is the process of rapidly cooling heated workpiece. This process is done by dipping the heated metal piece in oil, water or air. The selection of a quenchant medium is determined by the carbon content. It is used to harden the metal.

2- Tempering

For most steels tempering involves heating to between 250 and 500 °C, holding that temperature for an appropriate amount of time, then cooling slowly over an appropriate length of time.

It’s the process of reheating quench-hardened to a temperature below the transformation range, and then cooling at any rate desired to control the hardness of quenched steels.

3- Annealing

Heat treatment wherein a material is altered causing changes in its properties such as strength and hardness. It consists of heating and holding to a suitable temperature followed by cooling at an appropriate rate. It is used primarily for softening of metallic materials.

- It is the process involving heating and cooling, usually applied to induce softening. It also refers to treatments intended to alter mechanical or physical properties, produce a definite microstructure, or remove gases.

- Nonferrous metals: A heat treatment designed to effect: (1) softening of a cold worked structure by recrystallization or grain growth or both; (2) softening of an age hardened alloy by causing a nearly complete precipitation of the second phase in relatively coarse form; (3) softening of certain age hardenable alloys by dissolving the second phase and cooling rapidly enough to obtain a supersaturated solution (this usage is generally applied to nickel-base and copper-base alloys; the treatment should be called more precisely a solution heat treatment); (4) relief of residual stress.

4- Normalizing

Normalizing of steel is a heat-treating process that includes the heating of the workpiece sufficiently high to relieve stress. The workpiece must be held at temperature long enough for stress relieving depending on the quality of steels. The workpiece is then cooled slowly. Normalization may increase or decrease the strength and hardness of a given steel, depending on the thermal and mechanical history of the product.

It’s the process in which a ferrous alloy is heated to a suitable temperature above the transformation range and is subsequently cooled in still air at room temperature.

5- Precipitation hardening (especially for non-ferrous metals)

It relies on changes in solid solubility with temperature to produce fine particles of an impurity phase.

6- Case (surface) hardening

It is the process of hardening the surface of a metal by including elements into the material's surface.