Mechanical Characteristics Evaluation of Conventional and Special Hardening Treatments on Aisi 4340 Steel
Application of steel demands propertiesto enhance durability, dimensional stability and flexibility to alter
properties depending on application conditions. Generally to improve some of the propertiessteel is heat treated.The present
work aims at experimentally investigate the effects of conventional heat treatments like annealing, normalizing and special
hardening techniques like austempering and time quenching on AISI 4340 (EN24) steel. The test specimens are machined as
per ASTM standards and then different tests like microstructure analysis, hardness test, tensile test, impact test were carried
out after the heat treatment processes. Annealed steel is observed to be soft, normalized steel moderate hard, austempered is
tough with balanced hardness while time quenched steel is hardest at the surface compared to inner core.The microstructure
shows coarse grain structure in annealed, fine in normalized with finest in austemperedandmartensite structure at the surface
of the time quenched specimen.An increase in brittleness was observed with the increase in hardness during time quenching
displaying lesser impact strength compared to austempered one.
Keywords- Normalizing,annealing, austempering, microstructure, martensite.