TO DEVELOP HIGH STRENGTH STEEL WIRE THROUGH INTER-CRITICAL HEAT TREATMENT

Abstract

1-ugh strength steel wire is developed through the inter-critical heat treatment of low carbon steel between A1 and A3 temperatures. The steel was inter-critically heat treated by different methods viz, continuous annealing cycle, direct annealing cycle, direct inter-critical heat treatment without any pre or post heat treatment at 760, 790 and 820 degree Celsius for 15 minutes followed by water quenching and also the number of multiple quenching operation cycles of 2 minutes each was performed on low carbon steel wire specimen. The properties of tensile strength, hardness, toughness and microstructure were evaluated from the mechanical test and metallographic analysis, respectively. The microstructure shows that the martensite volume fraction increases with increase in inter-critical temperature but to different extent for different heat treatment method and also the ferrite grain size vary with the different inter-critical heat treatment method and the experimental results showed that the ultimate tensile strength and hardness increases with the increase in martensite volume fraction but the total elongation value decreases when the amount of martensite increase. Also the dual phase microstructure developed in the steel shows no yield point phenomena due to the presence of strong martensite in ductile ferrite matrix.