The Microstructures and Energy Dispersive Spectroscopy Analysis of a Hypoeutectoid Steels With 1% Cr

Abstract

Abstract The results of a microstructure, Energy Dispersive Spectroscopy analysis and hardness investigations of the hypoeutectoid steels with 1% Cr, imitating by its chemical composition toughening steels, are presented in the paper. Dilatometric tests were performed using L78R.I.T.A dilatometer of the German company LINSEIS. Using dilatometer the changes of elongation (Δl) of the samples with dimensions φ 3X10mm as a function of temperature (T) were registered. Obtained heating curves were used to precisely determine the critical temperatures (critical points) for the tested steels, while the differentiation of obtained cooling curves allowed to precisely define the temperatures of the beginning and the end of particular transition to draw two CCT diagrams. The analysis of the chemical composition of the phases present in the studied steels for different cooling rates were performed using an electron microprobe (X-ray microanalyzer). In this study a point, linear and a fixed area analysis techniques were used. After placing the samples tested steels in the chamber and the achievement of appropriate vacuum, spots for analysis were identified and the EDS analysis (Energy Dispersive Spectroscopy) was performed. EDS analyzes were performed using Nova NanoSEM 450 scanning electron transmission microscope. Developed CCT diagrams in accordance with the Rose and Wever classification are of type IV, which means that the diffusional transformations are separated by a stability range of the undercooled austenite and have the shape of the letter ”C”. The hardenability of tested steels is similar, but molybdenum acts much more effectively than nickel. Molybdenum occupies the I-st place among the effectiveness of alloying elements for the steels designed for low tempering, where the ”background” of other elements is weak. For both tested hypoeutectoid steels an EDS analysis revealed the precipitation of alloyed cementite at the grain boundaries. Chromium, as a ferrite creative element, quite strongly diffuses into the grain boundaries. It is visible with the change of chromium distribution along pearlite/ferrite grains boundaries.