Recyclability of Mixed Maraging and Stainless Steel Scraps

B, Santhosh and Chatterjee, Subhradeep (2018) Recyclability of Mixed Maraging and Stainless Steel Scraps. Masters thesis, Indian Institute of Technology Hyderabad.

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Abstract

The broad goal of this work is to investigate the recyclability of a mixed steel scrap material through the application of simple metallurgical principles. This scrap is a combination of maraging and stainless steels materials generated during various industrial forming and machining operations such as milling, turning and grinding. This mill scrap was melted and cast into small ingots. Thermodynamic analysis of the system was carried out using the Termo-CalC software. Microstructure of the as-cast ingots was studied using optical microscope (OM), X-ray diffraction/diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). In this initialstudy, it was observed that microstructure consisted of a dendritic matrix and one or more inter-dendritic phases. XRD analysis of the peak intensities suggested that the majority phase is FCC and there is also a BCC with lower volume fraction. TEM study confirmed this; it also showed a Co2Mo3 type intermetallic with very less fraction. Mechanical properties of the as-cast material was characterized using hardness test and uniaxial tensile test. In order to improve the mechanical properties of the as-cast material, we used a combination of warm rolling and heat treatments. In rolling route, 78% material deformation was done by using warm rolling at a temperature of 600°C, then solution treatment was done at a temperature of 1150°C for 12hrs to homogenization the material and to release the internal stresses. After the solution treatment, aging/tempering treatment was done at a temperature of 480°C for 3hrs and 12hrs. Microstructural characterization of the rolled and heat treated specimens was carried out in the same fashion as that for the cast materials. We also did the solution treatment followed by aging without prior deformation to dissolve inter-dendritic secondary phase and compare the results with those with rolling. After doing the all the characterization and mechanical testing it has been observed that in the rolling route there is drastic increasing of yield strength and ultimate tensile strength although ductility suffered a reduction. In heat treatment route without rolling, it is quite opposite to the rolling route: in this, is better compared to the rolled samples but yield strength and ultimate tensile strength are very less.

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