Abstract
The formation of second phase particles in the steel matrix during melting and casting plays an important role in controlling the grain size of steel. An attempt is made in the present work to find the role of nitrogen on forming nitride particles either with aluminum or titanium. Two steel samples with the same titanium and aluminum weight percent in their chemical composition were collected after the hot rolling process. Solution heat treatment at 1350°C for 60min holding time was used to dissolve the particles and then the steel samples were reheated at 800°C for 60min, water quenched and their microstructure was revealed by usual grinding and polishing process using 2% Nital. A transmission electron microscope connected with EDS was used to reveal the morphology of the second phase particles. The samples for TEM analysis were prepared by the replica extraction method in 5% Nital solution. The samples were then caught in 3mm copper grid for TEM analysis. TEM micrographs revealed the second phase particles in the matrix of steel. EDS peaks were studied and titanium peaks were found in both samples and surprisingly there was not any peak found for aluminum.
Highlights
Whenever titanium and aluminum are the alloying elements at the same time, it is quite difficult to find if nitrogen will be combined with only aluminum, only titanium or with both elements to form nitride particles, which, due to their higher melting point and stability, remain in the solid state when the steel is cooled from its melting point
Researchers working on grain refinement add deliberately aluminum in combination with nitrogen to form second phase particles, commonly known as aluminum nitride (AlN) particles, which can be formed during melting and casting [15]
These are strong impurity elements which get together around the grain boundaries and provide dragging force that stops the mobility of the grain boundary when the steel is reheated or during heat treatment
Summary
Grain size control is always a priority in obtaining small grains which simultaneously increase hardness and toughness. Whenever titanium and aluminum are the alloying elements at the same time, it is quite difficult to find if nitrogen will be combined with only aluminum, only titanium or with both elements to form nitride particles, which, due to their higher melting point and stability, remain in the solid state when the steel is cooled from its melting point This investigation took place in order to study and understand this effect. Researchers working on grain refinement add deliberately aluminum in combination with nitrogen to form second phase particles, commonly known as aluminum nitride (AlN) particles, which can be formed during melting and casting [15] These are strong impurity elements which get together around the grain boundaries and provide dragging force that stops the mobility of the grain boundary when the steel is reheated or during heat treatment. To investigate the effective influence of particles, both samples were re-heated at the moderate temperature of 800°C
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