Microstructure and Mechanical Properties of Microalloyed Steels Containing Molybdenum

Abstract

Microalloyed steels have a maximum of 2% in alloying elements and are used in the automotive and petrochemical industries. The microstructure and mechanical properties of these steels depend on chemical composition, processing and addition of molybdenum, niobium, titanium and vanadium. To evaluate the molybdenum effect in microstructure and mechanical properties, two microalloyed steels, with similar levels of niobium, titanium and vanadium, were prepared and forged. The steels have 0.056 and 0.160 percent by weight of molybdenum. The bars were homogenized, quenched and tempered. The specimens were machined for tensile and impact tests, hardness and microstructural analyzes by confocal and scanning electron microscopy. The ThermoCalc software was used to evaluate the carbides characteristics. The results show that steel with 0.160% Mo presents greater amount of bainite and austenite retained. It’s possible that formation of carbides by the secondary hardening mechanism increase in mechanical strength and a reduction in toughness.

Keywords:
Microalloyed steel; molybdenum; API steel; ThermoCalc