Effects of Quenching Media and Heat Transfer Rate on the Hardness and Microstructure of Low-Carbon Steel

• Francis O. BOROKINNI

  Author

• Olarewaju T. OGINNI

  Author

• Ridwan O. RAJI

  Author

• Kolawole ALONGE

  Author

This paper examines the impact of heat transfer during quenching on the hardness and mechanical properties of low carbon steel, specifically evaluating how various cooling media affect the microstructure and mechanical behavior of the material. Steel samples underwent heat treatment involving austenitizing at about 800 °C for 30 minutes, followed by quenching in water, engine oil, and air cooling (normalizing) to achieve uniform temperature and complete phase transformation.  Mechanical characterization of impact, tensile and microstructural examination using optical microscopy test were carried out.  The energy absorption values for the samples increased with different quenching methods with control (18.15 Joules), air-cooled (21.22 Joules), water-quenched (23.82 Joules), and highest for engine oil quenched (25.19 Joules). Hardness also improved, with air-cooled at 243.2 HV, water-quenched at 278.4 HV, and engine oil at 258.9 HV, all exceeding the control's 230.0 HV. Tensile strengths were 583.87 MPa for control, 589.03 MPa for air-cooled, 530.3 MPa for water-quenched, and 525.1 MPa for engine oil-quenched. The study reveals that cooling rates in quenching media affect microstructure and hardness, with water-quenching leading to the highest hardness due to increased martensite. Oil-quenching results in lower hardness but better impact energy, while air-cooled samples show a ferrite-pearlite structure. The findings highlight the trade-offs between hardness, tensile strength, and ductility, emphasizing the need to choose appropriate quenching media for optimal performance in engineering applications.

• FJET_21_56_56

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