Effects of Mn and Nb on the macro- and microsegregation in high-Mn high-Al TRIP steels
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Purpose: The aim of the paper is to determine the effects of Mn and Nb on the macro- and microsegregation of new-developed (3-5)Mn 1.5Al TRIP steels in the as-cast state and after hot forging. Design/methodology/approach: To assess possible macro- and microsegregation the chemical composition was investigated in the macro scale by OES and by the use of EDS in microregions. To reveal the macrostructure the ingots were etched by Oberhoffer’s reagent. The chemical composition along a diameter of the ingots was tested as well as in different regions of the plastically deformed flats. Metallographic investigations were carried out using optical (OM) and scanning electron microscopy (SEM). Findings: The Mn and Nb contents have significant effects on the obtained bainitic-martensitic structures and the morphology of retained austenite. The tendency to macrosegregation of Mn and Al between middle and external parts of the as-cast ingots and hot forged flats was detected. The Nb micoalloying results in the overall refinement of obtained microstructures and reduces the identified segregation of Al and Mn. A little microsegregation of these alloying elements between structural constituents was also detected. Research limitations/implications: Further investigations to describe in detail the identified structural constituents and the tendency of alloying elements to segregation in the thermomechanically rolled sheets are in progress. Practical implications: The knowledge of the macro- and microsegregation of Mn and Al in the TRIP steels with a high fraction of retained austenite is of primary importance for the manufacturing paths of these multiphase structure steels. Originality/value: A problem of segregation of Al and Mn in advanced high strength steels with and without Nb microaddition was described and interesting types of bainitic structures were identified.
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