Mechanical properties and fracture behavior of intercritically annealed AISI 4130 chromoly steel

The effect of intercritical annealing on the microstructure, mechanical properties, and fracture behavior of AISI 4130 steel was investigated. The presence of pearlite up to formation of large amounts of austenite (and martensite after quenching) was found to be inevitable, which was related to the presence of chromium and its effect on increasing the pearlite dissolution finish temperature (AC(1f)). At low martensite fractions, some improvement in tensile strength was achieved with the disappearance of yield-point phenomenon while maintaining the ductile fracture behavior. However, at high martensite fractions, as the carbon content of the AISI 4130 steel is high, a brittle behavior characterized by the cleavage facets on the fracture surface and the absence of necking was observed. The applicability of composite models for describing the tensile stress-strain curves at high martensite fractions was also briefly discussed.