Residual Stress Profiles of the Laser Surface Remelted Nodular Irons

Abstract

Laser remelting process is a very promising hardening method for ferrous and nonferrous alloys, which do not show a homogeneous microstructural state after having been heattreated in a traditional way. Consequently, the alloys concerned do not achieve the required hardness of the surface layer and do not provide the required wear resistance either. The paper deals with residual stresses of thin flat specimens of nodular cast iron 500-7 in the laser remelting process. In the process of gradual remelting of the specimen surface, that is during its heating and cooling, volume changes of the specimen occur due to thermal and microstructural changes. For a better knowledge of volume changes in the thin surface layer of the specimen, the latter were evaluated by residual-stress measurement in the thin modified surface layer after the remelting process. In laser remelting of a workpiece such remelting conditions should be ensured that a uniform thickness of the modified layer could be obtained in spite of several laser-beam passages across the workpiece surface. Because of a multiple laser-beam passage across the workpiece surface, the state of internal stress in the workpiece changes. Optimal laser surface remelting conditions on the basis of knowing the residual stresses were chosen, while the way of guiding the laser beam over the surface of flat samples and degree of overlapping were varied.