Effect of cold deformation in quench and tempered medium-carbon steel bars microstructure

Tempered AISI 4140 steel bars were processed by cold drawing. An effective deformation of approximate to 0.9 was achieved. The quench and tempered, and the subsequently deformed microstructures were analysed by optical and transmission electron microscopy. Intralath, interlath and spherically shaped carbides were identified in both cases. The deformed specimens revealed a mixed structure of thinned laths and dislocations cell-blocks composed of cell-block and cell boundaries. After the deformation process, alignment and fragmentation of the carbides occurred, mainly of those located in lath boundaries what would explain the partial preservation of the lath boundaries after drawing as they would arrest the destruction of lath martensite boundaries. These microstructural characteristics shall play an important role to enhance grain refinement in subsequent heat treatments.