A DESRABLE NANO CRYSTALLIZATION OF SURFACE BY SHOT PEENING ON METALLC PARTS

When metals induced by severe plastic deformation their grains break to smaller grains which their size are in the range of mano scale [1]. Shot-peening process will; 1- increase hardness of metal significantly 2- increase resistance of Wear corrosion in all pH 3- increase of fatigue life up to 20%. 4- increase of exchange current density. Shot-peening have many important parameters which the first one is instrument selection.Shot-peening Machines are classified by method of giving the energy to the peens: 1- Air blast or air shot-peening, 2- centrifuge shot-peening and 3- Ultrasonic shot-peening. In order to get similar results on shot-peening process, shot-peening should be done according to standards.Some of important parameters in shot-peening are: 1-intensity, 2-pecent of coverage, 3-size of peens and their materials, 4- angel of shots flow, 5- velocity of shots and 6-hardness of peens, For calibration it is necessary to measure intensity according to Almen Strip and percentage of Coverage. Drawing Almen- intensity curve for each shot peening machine for every desirable intensity and corresponding time is an important aid to shot-peening process. The number of passes or times for samples to be in the chamber of shot peening can be derived.