EFFECTS OF VARIOUS QUENCHING MEDIA ON THE MECHANICAL PROPERTIES OF INTERCRITICALLY ANNEALED 0.15Wt%C – 0.43Wt%Mn STEEL

Abstract

Effects of various quenching media on the mechanical properties of intercritically annealed 0.15wt%C – 0.43wt%Mn were studied. Prequenching of a hot rolled low carbon steel was previously done from 900^oC (within the full austenitic range) using SAE 40 engine oil as quenchant. Sets of steel samples made from the previously quenched steel samples were intercritically heat treated from 750^oC to 810^oC at intervals of 10^oC for 1 hr in a laboratory muffle furnace and quenched in SAE 40 engine oil, water and brine quenchants respectively. The effects of quenching media used and the intercritical annealing temperatures on tensile, hardness, ductility and notch impact toughness properties are discussed. The quenching media increased the strength and hardness properties but decreased the ductility and notch impact properties of the original hot-rolled steel. Steel quenched in brine had the highest strength (708.02N/mm² at 810EC) and hardness values (233 BHN at 810EC) followed by those quenched in water (666.73 N/mm² at 810EC and 226 BHN at 810EC respectively) while those quenched in oil had the least values (618.56 N/mm² at 810EC and 215 BHN at 810EC respectively). Steel quenched in oil had highest ductility and notch impact toughness values (24.07% at 750EC and 22.8 J/cm² at 750EC respectively), followed by those quenched in water (20.33% at 750EC and 18.14 J/cm² at 750EC  respectively) while those quenched in brine had the least values (16.49% at 750EC and 13.96 J/cm² at 750EC respectively). Higher intercritical annealing temperatures gave higher strength and hardness values (from 445.94 N/mm² at 750EC to 708 N/mm² at 810EC and from 165 BHN at 750EC to 233BHN at 810EC respectively), but lower ductility and notch impact toughness values (from 10.71% at 810EC to 16.49% at 750EC and from 7.38J/cm² at 810EC to 13.96J/cm² at 750EC).