Grain structure, Microstructure, Dimensional distortion, Fractography, Steel, Gears, Heat-treating furnaces, Metallography, Annealing, Normalizing, Quenching, Carburizing, Induction surface hardening, Nitriding, Through hardening, Tempering, Grinding, Shot peening, Alloy composition, Hardenability, Bending fatigue, Cyclic fatigue, Fatigue limit, Wear resistance, Core hardness, Microhardness, Stress-strain curves, Engineering design, Fatigue life testing, Rack and pinion drives, Phase diagrams, Time-temperature transformation diagram, Heat treatment