General Processes Of Selective Hardening
Flame Hardening: In this process, a high concentration oxy-acetylene flame is directed on the selective area. The temperature is increased adequately in the range of Austenite transformation. The correct temperature is established based on component color. The heat transfer is controlled due to which the core does not reach a higher temperature. Quenching of the heated region is executed to obtain the recommended hardness. Tempering is followed to minimize brittleness. The hardening depth is improved by an increase in the heating time.
Laser Beam Hardening: Laser beam hardening is an alternative type of flame hardening. A coating of phosphate is used to assist i n the laser energy absorption. Laser energy is applied on selected regions. Thus, selected regions are heated. By changing the laser power, heat absorption depth is controlled. The components are quenched, and then tempered. The process is accurate for the application of selective heat to the regions that require being heat treated. This process creates slight distortion.
Electron Beam Hardening: This process is analogous to hardening by laser beam. The source of heat consists of electrons with a high energy. Their intensity is controlled by the use of electromagnetic coils. The process can be automatic and has to be executed in a vacuum environment as the electron beam dissipates readily in air. The surface is hardened precisely in location and depth.
Softening: Softening is executed for reduction in hardness, removal of residual stresses, improvement in toughness, restoration of ductility, and refinement of the grain size. The component electromagnetic properties are changed by softening. The removal of residual stresses is essential and involves cold working.