Mechanical tools

. n ame four different types of surface hardening process . the purpose of case hardening . the purpose of carburising . the process of gas carburising Most of the components must have a hard, wear resisting surface supported by a tough, shock resisting core for better service condition and longer life. This combination of different properties can be obtained in single piece of steel by surface hardening. Types of surface hardening Case hardening Nitriding Flame hardening Induction hardening Surface hardening processes can be classified as -processes in which the whole component is heated, Eg. Case hardening and nitriding -processes in which only the surface of the component is heated Eg. Flame hardening and induction hardening Case hardening Parts to be hardened by this process are made from a steel with a carbon content of 0.15% so that they will not respond to direct hardening. The steel is subjected to treatment in which the carbon content of the surface layer is increased to about...

. the principle of hardening . the effect of the carbon content in hardening . the process of hardening . the tempering of steel . the purpose of temaparing Introduction If a piece of steel is heated to a sufficiently high temparature, all the carbon will be dissolved in the solid iron to form the solid solution, austenite of the steel. When it is slowly cooled, the change in the arrangement of the iron atoms will cause a solid solution can only contain up to 0.006% carbon, and so the excess carbon will be forced to leave the solid solution, and produce cementite. This will, with ferrite, form a laminated structure called pearlite. The principle of hardening If steel is cooled rapidly (quenched ) the excess carbon will not have sufficient time to leave the solid solution with the  result that it will be trapped in the iron, and so cause an internal distortion. This internal distortion is the cause for the increase in the hardness of steel with a corresponding reduction in its stren...