Yes, as an engineering alloy steel, 4140 steel requires heat treatment.
Untreated 4140 steel (hot-rolled/forged) has an uneven microstructure and insufficient properties, making it generally unsuitable for directly manufacturing mechanical parts with mechanical property requirements.
Heat treatment of 4140 steel can be divided into normalizing, annealing, and quenching and tempering, with the main purposes being to improve mechanical properties, eliminate residual stress, and enhance its machinability.
Therefore, 4140 steel, with its excellent heat treatability, can be flexibly adjusted in terms of hardness, strength, and toughness to meet different needs, from non-critical components to core load-bearing components.