Study On Shot Peening Induced Strengthening Of 17Cr2Ni2Mo Steel

This article studied the influence of steel pellet shot peening, compound pellet shotpeening and ceramic pellet shot peeing on 17Cr2Ni2Mo steel. Distribution of residualstress, micro hardness, FWHM (half height width), surface roughness and residualaustenite along the depth of shot peened specimens have been measured and thecorresponding strengthening mechanisms have been discussed.After studying the distribution of residual stress along the depth of shot peenedspecimens, it was found that first of all, the larger the shot peening intensity, thehigher the largest residual stress and the deeper the residual stress field; secondly,compound pellet shot peening generates higher residual stress value and deeperresidual stress field; thirdly, ceramic pellet shot peening generates high residual stressvalue with relatively low shot peening intensity, but the residual stress field is lessdeep.The FWHM of shot peened specimens have been measured, it was found that theFWHM value at the surface of all the specimens were significantly reduced,signifying that shot peening weakens the material, which is the opposite of theknowledge on the process. After detailed research, it was finally found that theFWHM has some limit in characterizing the mechanical property of hard statematerials, although the FWHM value dropped, the yield strength rose a lot, whichmeans that the material is actually strengthened rather than weakened.The distribution of residual strength along the depth of shot peened specimens havebeen measured and findings are as follows: first of all, the larger the shot peeningintensity, the higher the micro hardness value and the deeper the strengthened field;secondly, compound pellet shot peening does not increase the depth of thestrengthened field, but increased the micro hardness value; thirdly, ceramic pellet shotpeening can get high micro hardness with relatively low shot peening intensity, but the strengthened field is also shallow.The surface roughness of shot peened specimens are also related to the shot peeningintensity, the larger the intensity, the rougher the surface is; compound shot peeningand ceramic pallet shot peening both significantly increase the surface roughness, andthe depth of the affected zone of ceramic pellet shot peening is low.At last, the distribution of residual austenite along the depth of shot peened specimenshave also been measured, findings are as follows: first of all, the higher the shotpeening intensity, the higher the percentage of residual austenite changing intomartensite, and the deeper the transformation zone; secondly, compound pellet shotpeening increase the quantity of martensite transformation, but not the depth; thirdly,ceramic pellet shot peening induced fewer austenite to change into martensite, and thetransformation zone is also shallow.