Archaeology
Chakrabarti (1976) has identified six early iron-using centres in India: Baluchistan, the Northwest, the Indo-Gangetic divide and the upper Gangetic valley, eastern India, Malwa and Berar in central India and the megalithic south India. The central Indian region seems to be the earliest iron-using centre.
According to Tewari, iron using and iron "was prevalent in the Central Ganga Plain and the Eastern Vindhyas from the early second millennium BC."
The earliest evidence for smelted iron in India dates to 1300 to 1000 BCE. These early findings also occur in places like the Deccan and the earliest evidence for smelted iron occurs in Central India, not in north-western India. Moreover, the dates for iron in India are not later than in those of Central Asia, and according to some scholars (e.g. Koshelenko 1986) the dates for smelted iron may actually be earlier in India than in Central Asia and Iran. The Iron Age did however not necessary imply a major social transformation, and Gregory Possehl wrote that "the Iron Age is more of a continuation of the past then a break with it".
Archaeological data suggests that India was a "an independent and early centre of iron technology." According to Shaffer, the "nature and context of the iron objects involved are very different from early iron objects found in Southwest Asia." In Central Asia, the development of iron technology was not necessarily connected with Indo-Iranian migrations either.
J.M. Kenoyer (1995) also remarks that there is a "long break in tin acquisition" necessary for the production of "tin bronzes" in the Indus Valley region, suggesting a lack of contact with Baluchistan and northern Afghanistan, or the lack of migrants from the north-west who could have procured tin.
Read more about this topic: History Of Metallurgy In The Indian Subcontinent