NFLUENCE OF THE STRUCTURESUCCESSION ON THE VOLUME FRACTION OF MARTENSITE ANDFERRITE MICROHARDNESS IN A DUAL-PHASE STEEL WITH LOW MANGANESE CONTENT.

The article presents results of the studiesconducted by the authors for determining the influence of the structuresuccessiononthe volume fraction of martensite andferrite microhardness in a dual-phase steel with low manganese content.For the research in discussion,an alloy with 0.094% C and 0.53% Mn (Si, Cr, Ni, Mo, Al, Cu, P, and S below 0.1%)was used.This alloywas subjected to several cycles of heat treatments (consisting of full annealing, normalizing, subcritical annealing, full quenching, intercritical quenching).The metallographic analyzes were performed witha LEXT OLS4100 Laser Microscope,(OlympusCorporation, Japan) andOLYMPUS Stream MOTION Image Analysis Software. Theferrite microhardness was determined with a MicroHardness Tester DuraScan 70 (Emco Prüfmaschinen-Test GmbH, Austria), the test load of the Vickers indenter being 0.098 N (0.01 kgf). The full annealing, the normalizing,the cycle made up of normalizing and subcritical annealing led to obtaining ferrite-pearlite structures with different structural aspects and with different percentages of ferrite and pearlite, whilethe full quenching caused the formation of martensite and a small volume fraction of residual austenite.The intercritical quenching, which ended the cycles of the heat treatments, ensured the obtaining of ferrite-martensite structures specific todual-phase steels. In this structures, thevolume fraction of martensite (VM) was (depending on the cycle of the heat treatments) between 17.44 and 26.16%; this volume fraction, as well as the shape, size and distribution of the martensite were influenced by the heat treatments prior to the intercritical quenching.The ferrite microhardnesswas also influenced by the applied cycle of the heat treatments, the value being between 177.91 and 183.69 HV. [ABSTRACT FROM AUTHOR]