Effect of a Thermal Hardening Method on the Structure and Mechanical Properties of 20GL Steel

The structure and mechanical properties of 20GL steel are studied and compared after various types of thermal hardening, namely, normalizing, water quenching, and quenching by a fast-moving water flow. Water quenching is shown to cause the highest strength of 20GL steel (ultimate tensile strength is σu > 1500 MPa) at a relative elongation δ = 3–8%. Quenching by a fast-moving water flow under certain conditions forms a favorable gradient structure and ensures a combination of a high strength and high ductility of 20GL steel: σu is up to 720 MPa (1.6 times higher than after normalizing) and δ = 18–25%.