Answer: Excellent quality steel
Notes: The Iron Pillar named as Mehrauli Pillar located in Delhi, is a 7 m (23 ft) column in the Qutub complex, notable for the rustresistant composition of the metals used in its construction. The pillar has attracted the attention of archaeologists and materials scientists because of its high resistance to corrosion. The corrosion resistance results from an even layer of crystalline iron hydrogen phosphate hydrate forming on the high phosphorus content iron, which serves to protect it from climate.
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