Microstructure-crystallographic texture and substructure evolution in unpeened and laser shock peened HSLA steel upon ratcheting deformation

ABSTRACT Uniaxial ratcheting behaviours associated with microstructural development of unpeened and laser shock peened ASTM A 588 Grade D High Strength Low Alloy (HSLA) steel were studied in this investigation. The mechanism of plastic deformation and crystallographic texture evolution during ratcheting was also studied. For this, the primary experimental works involved were stress-controlled ratcheting fatigue tests (on unpeened/laser-peened specimens) at room temperature. Followed by this, microstructure and texture evolution on the surfaces and/or cross sections of the deformed specimens, using electron back scattered diffraction (EBSD) were studied in detail. Additionally, the substructural evolution of some selected samples was also studied using transmission electron microscopy (TEM). The results indicated that the average grain size of all the unpeened ratcheted specimens was marginally reduced after fatigue tests. The laser-peened specimen, however, showed a marginal increase in average grain size after ratcheting. Continuous dynamic recovery and recrystallisation (CDRR) during ratcheting was thought to be the cause of the observed reduction in average grain size in unpeened specimens, whereas continuous dynamic recrystallisation (CDRX) was believed to be the controlling factor for marginal accretion of grain size in laser-peened specimens. The plastic deformation of investigated steel was qualitatively explained by the observed dislocation patterns and their evolution.