Development of gradient microstructures in AISI 1010 steel using integrated surface thermomechanical treatment and cold rolling

The microstructure and mechanical characteristics of cold-rolled AISI 1010 steel sheets were examined after undergoing surface thermomechanical processing (STMP) at different traverse speeds. The findings revealed that STMP caused the elongated ferrite and pearlite structures on the processed surface of as-rolled AISI 1010 steel to transform into fine, equiaxed ferrite grains, with cementite precipitates forming along the ferrite grain boundaries. The grain size within the processed zone increased from 0.25 ± 0.04 μm to 1.61 ± 0.09 μm as the traverse speed was reduced from 125 mm/min to 25 mm/min. The maximum hardness recorded was 298.3 HV at 125 mm/min, which diminished to 203.96 HV at 25 mm/min. This reduction in hardness at lower traverse speeds was attributed to thermal softening and grain coarsening, especially at the surface, where dynamic recrystallization (DRX) occurred. Mechanical testing demonstrated a decline in both yield strength (YS) and ultimate tensile strength (UTS) as traverse speed decreased. Specifically, YS fell from 893.2 ± 11.8 MPa to 701.4 ± 12.2 MPa, while UTS dropped from 910.4 ± 13.9 MPa to 713.7 ± 13.4 MPa as the speed decreased from 125 mm/min to 25 mm/min. Conversely, tensile toughness exhibited an initial increase, rising from 50.5 ± 1.9 MJ/mm 3 at 125 mm/min to 108.9 ± 1.4 MJ/mm 3 at 50 mm/min, before declining to 95.42 ± 1.9 MJ/mm 3 at 25 mm/min. These trends indicate a trade-off between strength and ductility, governed by the heat input's influence on grain refinement and hardness.