A new experimental technique for measuring strain and residual stresses during a laser remelting process

Abstract

Laser hardening by remelting thin surface layer is a very promising hardening method for ferrous and non-ferrous alloys with non-homogeneous microstructural state. The paper deals with strain changes of thin flat specimens of nodular cast iron 500-7 during the laser remelting process. The thin flat specimen is during laser surface remelting strain influenced by thermal expansion causing volumen changes of the material and volume changes due to microstructure transformations. Volume changes mostly act upon solidification of the remelted layer after the remelting process. We have applied online experimental technique for measuring the strain of the specimen during the laser surface remelting process. The strain was measured by resistance rosette that was placed on the bottom side of the remelted layer. Simultaneously at the some place on the specimen, the temperature was measured too. During the laser surface remelting of a specimen the remelting conditions were controlled in such a way, that a uniform thickness of the modified layer was obtained in spite of different laser beam guiding modes and different overlapping degrees applied over the specimen surface. The on-line strain and temperature results of the specimen with known residual stress state in the modified surface layer showed us the way of optimization the laser remelting process.