A user flow is focused on making it clear what needs to be coded. If user does x then y should happen etc.
A user journey is focused on reconciling the design with the anticipated user's personality, motivations and the context in which they are using the software. It's a way of planning out a site/software that keeps the focus constantly on the user.
User journeys can appear early in the design process when vague ideas are still being thrashed about. A user journey need not be very detailed. A user flow isn't necessary until ideas have become more concrete and generally needs to be quite precise.