STUDY OF MECHANICAL AND CORROSION BEHAVIOR OF PHOSPHORIC IRON AND ITS WELDMENT

Abstract

The prevention of corrosion of steel, used for engineering components in industry and structures, has been a major challenge for every country. In particular, several protection methods are used to increase the lifespan of the materials. One the best method of corrosion prevention is the use of corrosion- resistant material. The present thesis explores the corrosion behavior of new class of materials, namely phosphoric irons, for different applications. Phosphorous is traditionally known to be detrimental to the mechanical properties of steel and therefore avoided. However, the beneficial effect of phosphorus in conferring corrosion resistance attested by several archaeological iron structure in India, one famous examples being the 1600- year old Delhi Iron Pillar. The iron of the Pillar contains an average amount of 0.25 wt % phosphorus. Therefore, there was need for a detailed research on corrosion resistance of the iron containing phosphorus. Iron-phosphorous alloys containing high amount of phosphorus are termed as phosphoric iron. The aim of the present thesis was to determine the corrosion behavior of the three phosphoric irons and compare low carbon to high carbon phosphoric iron. The secondary aim was to understand the effect of phosphorus on the microstructure, mechanical behavior of iron and its weldment. Phosphoric iron of three different compositions, namely Pl (Fe-0.29P-0.034C), P2 (Fe-0.30P-0.030C), and P3 (Fe-0.31P-0.23C, wt %) were first prepared by ingot casting route. The carbon. content was controlled according to composition. The plate is then soaked and forged at 1150°C in the dual phase region to avoid grain boundary embrittlement. The as received Phosphoric Irons Pi, P2 and P3 revealed duplex microstructure. This duplex microstructure consisted of prior austenite at the grain boundaries of ferrite. The mechanical properties of as received samples Phosphoric Iron were determined. The hardness, yield stress and ultimate tensile stress (UTS) of as received phosphoric iron increased. All the samples failed in the ductile manner. The hardness of the as-received phosphoric irons decreased with increasing carbon content. The fracture surface of tensile specimens of as received and soaked Pi, P2 and P3 revealed equiaxed and elliptical dimples under SEM.