A Comparison of Microstructural and Mechanical Properties of 0.35% C - 0.85 %Mn Steel Under Different Inter-Critical and Sub-Critical Heat Treatment Conditions

This work compared microstructural and mechanical properties of 0.35%C-0.85%Mn steel under different inter-critical and sub-critical heat treatment conditions. Nine steel samples were machined to standard for tensile strength test; an example was used as a control sample, while the other eight were grouped into two. Four samples were heated to 860^oC representing inter - critical temperature, and the other four samples were heated to 700 ^oC subcritical temperature, after which the samples held for 30 minutes each and were subjected to the following treatments: Annealing, Normalizing, Oil Quenching, Quenching, and Tempering. All the samples, including the as-received samples subjected to hardness test, tensile strength test, and microstructural test using Rockwell hardness machine, table tensiometer, and inverted Metallurgical Microscope, XJL - 17 model. The Rockwell hardness values were high ranging between; 92.6 HRC (for control sample), 99.8HRC (Quenched at 860 ^oC), 99.6HRC (Quenched at 700 ^oC), to 99.1HRC (for sample Annealed at 860 ^oC), 83.5HRC (for sample Annealed at 700 ^oC). The ultimate tensile strength values were; 126.59MPa (for control sample) 198.24 MPa (sample quenched and tempered at 860 ^oC), 168.98 MPa (sample quenched and tempered at 700 ^oC) to, 95.78 MPa (for sample Annealed at 860 ^oC) and 89.75 MPa (for sample Annealed at 700 ^oC).