Heat treatment:

Heat treatment is used to control heating and cooling of the metals to change the properties and also to improve the performance or to enable processing.

For example:

Heat treatment is the method of hardening of a piece of hydrocarbon steel rod. After heating the rod when it turns to red heat, and later rushed into the cold water it undergoes the process rapidly. Later, it becomes hard and brittle. The material is again heated to dull red, but it allows the rod to cold very slowly, which then becomes very softer and less brittle. This process is known as the annealed. After the heat treatment done to the material, it is considered to be in its best condition for flow forming process. During the time of flow forming the grains are deformed, which results in most metals flattering work hardened if flow formed at room temperature. This is to remove the stress from the forming operations and prepare the material for machining process, and then material is made to normalize.

Processing:

Hot and cold working process is applied to the metals. The shape of the metal is obtained based upon the cold working process or hot working process. The temperature is not easy to explain. Hot works are done at the room temperatures and can be compressed into difficult shapes. The steel is not made to do hot work until it is red hot. When the metal is tested under the microscope then it contains very small grains. When the metals are worked or bend at the room temperature, at that instance the grains deform, later the metal becomes very hard and brittle. Hot process is applied to the metals at that instance crystals are also distorted. They reform is done instantly into the standard crystals, because the developed temperature is directly above the temperature of recrystallization for the metal being used. The cold working process is the flow forming of metals below the temperature where the recrystallization, on the other hand the hot working process is the flow forming metals above the temperature of recrystallization.

Environmental reactions:

The properties of the materials can also be affected by reaction with surroundings in which they are used.

Some examples are:

Resting of steel

Dezincification

Degradation of plastic

General properties of engineering materials:

Properties of materials play a key role. The properties are classified into several types they are:

Physical properties of materials:

The physical properties of the materials deals with some of the properties like temperature, melting, electrical conductivity, density, thermal conductivity, magnetic properties, corrosion resistance etc.

In the following properties some of them are considered to be more important, they are:

Density:

• For material density is known as mass per unit volume. The units are 
• At  the density of the material compared with the density of water is known as relative density.

  and

Electrical Conductivity:

Copper wire must be selected for the electrode or core of the cable; this is because the Copper acts as a very good electrical conductivity. The wire conductor material is provided by the insulation, for which a plastic material like polymerized has been chosen. This material has been select as it is a bad conductor of electricity; very few electrons can pass through it. Insulators are very bad conductors of electricity. When pure metals compare with alloys they are stronger. At room temperatures the pure metals have better conductivity than alloys. The temperature fall is improved with the conductivity of metals and metal alloys. Equally non – metallic materials used for insulators, as they offer a lower resistance to pass the electrons, and become poor insulators, as the temperature rises. For example glass is an excellent insulator.

Melting temperature of material:

The recrystallization temperature and melting temperature have a great effect on the materials and the properties of the alloy material.

Semi-Conductors:

Semi-conductor materials lie between the conductors and isolators materials. Depending upon the temperature, Semi-conductors are classified as good conductors are bad conductors. If there is increase in the temperature in small level, then one can observe the rapidly increase of conductivity of semiconductor materials. The electronic thermometer and the semi-conductors are used as temperature sensors. Semi-conductors have the capabilities, for which during the process of manufacturing the conductor’s properties are to be changed. Silicon and germanium are the examples of semi – conductors. In electronic industry, the conductors are extensively used in the manufacturing of solid devices such as integrated circuits, transistors, diodes and thermistors.

Thermal conductivity:

Thermal conductivity is the ability of the material to transmit heat energy by conduction.

For example tie up a soldering rod to the tip, which is attached to a wooden base.

The tip is made up of copper, as it is a good conductor of heat. It allows storing the heat energy and easily moves down to the tip, and to the work piece being soldered. Due to the low thermal conductivity the wooden handle remains cool and resists the flow of the heat energy.

Fusibility:

By applying the fusibility the metals are melted. In the figure it shows that by applying the heat the metals are melted automatically, and it has high fusibility. The materials that melt at high temperature are called as refractory materials. Polystyrene must acts as a thermal insulator and they considered to have low melting point.

Reluctance:

Some materials are good or bad conductors of electricity, and some materials are good or bad conductors of magnetism. The resistance offered by the magnetic circuit is known as the reluctance. The conductors which have good magnetic nature are low reluctance. Ferromagnetic materials are made up of steel and iron, which are also associated with the alloying elements like nickel and cobalt. The remaining materials are non – magnetic, as they offer a high reluctance to the magnetic flux field.

Temperature Stability:

Temperature change scan results in a high amount and it shows the effects on the structure and the properties of the material. If there is a change in the temperature then several can take place such as creep. Creep is defined as the gradual extension of a material over a long period of time while the applied load is kept constant. When we consider the plastic materials creep, which is an important factor, and they are considered when the metals works continuously at high temperatures. In gas turbine blades if the creep rate increases then automatically the temperature is to be increased and is vice versa as the temperature lowers.