Q195 carbon steel is widely used in the manufacturing of various products. In order to understand its microstructure, an experiment was performed using liquid chromium-plating 6 h at 950℃. The aim of this experiment was to determine the metallographic characteristics of the material.
The experiment started with a sample of Q195 carbon steel cut into specimen pieces of the required size. The specimens were then mounted on a steel holder to be held securely during polishing and observation under the microscope.
The specimens were then subjected to the chromating bath. A solution of chromic acid in aqueous solution was used. The absolute concentration of chromic acid and the duration of the chromating process were adjusted to suit the specific requirements of the experiment.
The chromated specimens were then polished with grade-one abrasive paper. A specially designed apparatus was used for the purpose. Primary, secondary, and tertiary abrasive polishing enabled the observation of microstructural features of the specimens on the etched surface.
The flow of electrolytic current passes through the specimen during the etching process. The preferential attack on the chromium-rich phase results in selective and quantitative etching of the latter phase. This exposes the microstructural features of the specimen.
The observed microstructure of the Q195 carbon steel samples consisted of alternating zones of ferrite and pearlite. The pearlite was formed as a result of the isothermal transformation of the austenite during chromating. The contrast in the ferrite-to-pearlite volume ratio was clearly visible under the optical microscope.
Back-scattered electron images of the samples captured at high magnification provided additional insights into the samples’ microstructure. Visual inspection efforts in this regard confirmed the mere presence of ferrite and pearlite zones in the sample. In addition, eye-catching streaks of delta ferrite were seen in the samples.
These streaks of delta ferrite have been found to have a beneficial effect on the strength of the sample under discussed conditions. As such, these features can be considered valuable for strengthening the sample in comparison to a more homogenous microstructure of equal parts ferrite and pearlite.
To conclude, the results of the experiment performed on Q195 carbon steel using liquid chromium-plating 6 h at 950℃ suggest several beneficial microstructural features. The notion of a contrast in the ferrite-to-pearlite volume ratio was confirmed through observations under the optical microscope. Electron microscopy results further highlighted the beneficial presence of delta ferrite phases which may help to improve the strength of the sample. In general, the findings are in line with expectations derived from the composition and thermal history of the sample.
