Niobium addition effect of SAE 4320 steel properties after annealing and normalizing stages of the automotive carburized component manufacturing

Steel is the material mostly used in automotive industry to produce lighter and economy cars without abstaining from safety and minimizing pollutant emissions.However, this material faces challenges in meeting mechanical, competitive, and good formability properties.Microalloyed steels emerges as a response to this demand as it comines high mechanical strength with good toughness and ductility due to an appropriate alloy design that is linked to low carbon contents and use of microalloys such as Nb, V and Ti which provide precipitation hardening, solid solution, and grain refinement.This study investigated the effect of Nb addition at different processing stages of case-hardened automotive component (after annealing and normalizing) by quantifying how this element influences grain size, hardness, yield strength, ultimate strength, elongation, area reduction and impact test.Results indicate that niobium addition between 200 to 500 ppm improves yield strength by 7%, ultimate strength by 3%, and hardness by 10% for annealed condition, whereas for normalized condition the absorbed energy increases by 18%.Although it has a widely known effect on grain refinement, Nb showed no consistent effects on this feature.For properties in which there was no substantial improvement, Nb presented no deleterious effect.