CHARACTERIZATION OF SHOT PENNING HARDENING FOR SEVERAL GROUPS OF SPRING STEEL HAVING DIFFERENT HARDN

Material hardness has significant effects on shot penning hardening. The indexes which are frequently used so far to express shot penning hardening are half width of X-ray interference lines of the surface layer and the micro-hardness. But the conflict results will be got from the two indexes. The stress of material surface can be measured by X-ray stress analytic techniques, hence, the surface yield strength can be obtained. It is found in several groups of alloy steel having different hardness by changing the heat treatment regime or chemical constituents that shot penning strengthening treatment can increase the half width of the soft surface obviously, and at the same time, remarkably improving their yield strength.Shot penning reduces the half width of the hard surfaces wholly in a wide range, but it can improve the yield strength to varying degrees.As to the middle hard surfaces,the effect of shot penning on half width is weakness,but it reduced the yield strength for most part of the experimental surfaces.The result illustrates that wrong information may be concluded from the frequently-used method of deducing the surface strength from the parameter half width. The new index of the surface yield strength reflects mechanics characteristics of material surface better than the normally used index of the half width does.