The road from Nazareth (the historical Jesus) to Nicaea (affirmation of a fully divine Son) is full of express lanes, roadblocks, detours, one-way streets, roundabouts, protests, and even the odd Gnostic mardi gras parade.
For instance, in the writings of Justin, you have a strong emphasis on Jesus as the Logos, the eternal word of God, but he otherwise treats the Spirit as merely the Spirit of prophecy and he might even conflate the Son and the Spirit in places. Irenaeus is more interested in the economic Trinity than in a shared divine nature of the Son and Spirit with the Father. Origen seems to think that the Logos is 99.9% God.
Even so, among other second century apologists, the doctrine of the incarnation and Trinity begins to crystallize. In the Epistle to Diognetus (ca. 150-200 AD) we are given a short description about the nature of the Son inferred from the sending of the Son. He was not sent by the Father in tyranny and terror, rather the author says, the Son was sent “as a king sending a son who is also a king, he sent him as God, he sent him as a human to humans.” This short and succinct statement expresses what in later technical terminology would be called consubstantiality, the doctrine that the Son possesses everything that is true of divinity and everything that is true of humanity, in other words, vere homo et vere deus (“truly human and truly God”). Even more elaborate, although somewhat imprecise in places, is the statement of Athenagoras of Athens (ca. 177 AD), harnessing the metaphors of mind-idea and sun-light to explain the Father-Son and Father-Spirit relationships:
 Ep. Diogn. 7.4 (trans. M.F. Bird).
 Athenagoras, Plea 10 (trans. M.F. Bird).