MECHANICAL PROPERTIES OF 0.14WT%C – 0.56WT%Mn – 0.13WT%Si STRUCTURAL STEEL.

Abstract

Effect of intercritical heat treatment on 0.14wt%C – 0.56wt%Mn – 0.13wt%Si structural steel has been investigated. Specimens for single quenching and those for double quenching were prepared for intercritical heat treatment.  The heat treatment of the experimental steel was based on intercritical annealing in the ferrite + austenite temperature range of the Fe – C phase diagram at temperatures745^oC, 755^oC, 765^oC, 775^oC, 785^oC, 795^oC and 805^oC for 1 hour at each temperature  in a laboratory  muffle heat treatment furnace followed by quenching in plain water to room temperature. Specimens for single quenching were subjected to the above heat treatment route once while those for double quenching were subjected to the heat treatment route twice. Afterwards the specimens that were subjected to single quenching and those that were subjected to double quenching were separately tempered in a laboratory muffle heat treatment furnace at a temperature of 200^oC for 1hour and cooled to room temperature in still air. The results revealed that single quenching eliminated the yield strength, increased the tensile strength and hardness properties but decreased the ductility and notch impact toughness properties of the experimental steel. Moreover, the results also revealed that double quenching eliminated the yield strength, and produced a greater increase in tensile strength and hardness properties than single quenching but a greater decrease in the ductility and notch impact toughness properties than single quenching of the experimental steel. Tempering increased the yield strength, ductility and notch impact toughness properties of the quenched steels but decreased their tensile strength and hardness properties. The established heat treatment conditions can be useful for manufacturing steels of high strength and hardness and good ductile and notch impact toughness properties.