THE INFLUENCE OF THE MICROALLOYING ELEMENTS OF HSLA STEEL ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES

摘要

In this work, hot-forged, high-strength, low-alloy (HSLA) steels based on the chemical composition 34CrNiMo6 were investigated in order to determine the type of precipitates forming and their effect on the mechanical properties. The individual steels were microalloyed with one of the following elements or a combination of elements: niobium, titanium or zirconium and vanadium. The compositional changes in the microstructure and the various kinds of precipitates observed in the microalloyed steels were examined using energy-dispersive spectroscopy (EDS). Optical and scanning electron microscopy studies revealed that the addition of microalloying elements did not change very much the main microstructural features due to the fact that all the microstructures consisted of tempered martensite and finely dispersed carbide precipitates along martensite laths. In all the microstructures relatively large precipitates of the microalloyed elements were observed. This could be a possible reason for observing no significant improvement in the mechanical properties.