Editing Leaf spring (section)

===Heat treatment===

# '''Heating for hardening:''' Any metal, or alloy which can be hard drawn, or rolled to fairly high strength and retains sufficient ductility to form, may be used for springs, or any alloy which can be heat treated to high strength and good ductility before, or after forming may be used. For special spring properties such as good fatigue life, non-magnetic characteristics, resistance to corrosion, elevated temperatures and drift require special considerations. leaves are heated to critical temperature in an Oil-fired hardening furnace. Usually temperature maintained is between 850°C and 950°C.
# '''Cambering:''' The top leaf is known as the master leaf. The eye is provided for attaching the spring with another machine member. The amount of bend that is given to the spring from the central line, passing through the eyes, is known as camber. The camber is provided so that even at the maximum load the deflected spring should not touch the machine member to which it is attached. The camber shown in the figure is known as positive camber. The central clamp is required to hold the leaves of the spring. Machine used for this operation is Hydraulic press. Leaves are bent to required radius using a press. All the leaves are tested for required radius using cambering gauges.
# '''Quenching :''' Hot bent leaves kept in tray and quenched in oil bath to get martensite structure. Martensite is the hardest form of steel crystalline structure. Martensite is formed in carbon steels by rapid cooling that is quenching of austenite form of iron. The machine used is a conveyorised quench oil bath. The fire point of quenching oil is about 200°C and it is seen to that the oil temperature does not exceed 80°C. After quenching, the structure of the leaf spring becomes very hard and this property is not required. But this process is required to set the leaves to the correct radius after cambering. To remove hardness, tempering is done.
# '''Tempering:''' Tempering is a process of heat treating, which is used to increase the toughness. Quenched leaves are reheated to drop hardness to the required level. An electrically heated temperature furnace is used for this process. Hardness of the leaves is determined using Brinell hardness testing, a process that also relieves stresses. The temperature inside the machine is maintained between 540 and 680°C. The tempering process involves heating of leaves below their re-crystallization temperature then cooling them using water or air.