Abstract
It is common practice that formation of second phase particles such as nitrides or carbides in the steel matrix has significant role to control the grain size of steel. An attempt is made in the present research work to find out the role of nitrogen to form the nitride particles either with Al, Ti, B, Cr or Si. Two steel samples Steel-A and Steel-B with same titanium and aluminum weight percent in the chemical composition were obtained in hot rolled conditions from international market with only the difference of presence of Niobium in Steel-A. Solution heat treatment was performed at 1350°C with 60 minutes holding time in protherm heat treatment furnace available locally was used to dissolve the particles and then steel samples were reheat treated at 800°C with holding time of 60 minutes and water quenched and microstructure was revealed. Transmission electron microscope connected with Ehlers-Danlos Syndrome (EDS) was used to reveal the morphology of second phase particles. Both samples for a high resolution power Transmission Electron Microscopy (TEM) (Jeol JEM 3010) analysis were prepared by using carbon extraction replica method in 5% Nital solution as an etching technique. Both samples were then caught in copper grid of 3mm for using TEM analysis. TEM micrographs clearly revealed the second phase particles in the matrix of steel. The EDS peaks were studied and it was found that the peaks showed the titanium peaks in both the samples A and B and surprisingly there was no any peak found for aluminum. Stoichiometric calculations were carried out and it was found that weight percent nitrogen required for forming TiN is 0.0073, however the total nitrogen present in both the steels A and B is 0.0058 and 0.0061 respectively. That means that all the nitrogen present in the steel matrix was consumed by titanium to form the Titanium Nitride (TiN) so there was no nitrogen remain to fulfil the requirement of aluminum to form the Aluminum Nitride (AlN) particles.
Highlights
The Cold Heading Quality (CHQ) steels are assumed to be non-heat treatable so strengthening by cold forming which is a quick and mass production makes these steel a low cost solution for various applications
Gong et al.[1] studied the dissolution and precipitation behaviour in micro alloyed steels of Nb steel and NbTi steel, both steels indicated the dissolution of Nb in austenite upon reheating in both the Nb and Nb–Ti steels but the dissolution was faster for Nb steel as
Whenever titanium and aluminum are the alloying elements at the same time, there is quite difficult to find out that nitrogen will either combines with only aluminum or only titanium or with both elements to form the nitride particles which are known as second phase particles and due to their higher melting point and stability they remain in the solution in the solid state when steel is cooled from its melting point
Summary
The Cold Heading Quality (CHQ) steels are assumed to be non-heat treatable so strengthening by cold forming which is a quick and mass production makes these steel a low cost solution for various applications. The microalloying addition of various elements, especially Al, has significant effect on the quality of CHQ steel. Gong et al.[1] studied the dissolution and precipitation behaviour in micro alloyed steels of Nb steel and NbTi steel, both steels indicated the dissolution of Nb in austenite upon reheating in both the Nb and Nb–Ti steels but the dissolution was faster for Nb steel as. None of anyone has studied this effect in CHQ steels
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