I'm writing bios for a company newsletter. If I were to write Mr. Smith is a graduated engineer in electrical engineering or Mr. Smith holds a PhD in Electrochemistry - how do you know when it is appropriate to capitalize these things?
Conventions vary, but my own method is to use capitals when one is speaking specifically. As far as I'm concerned you have got it just right in your OP.
'Mr Smith is a graduate engineer', should not, in my view, involve capitals, but 'Mr Smith holds a PhD in Electrochemistry correctly does have.
John Hutchings is a historian.
Professor John Hutchings, a 17th-century historian, has been appointed as 'Historian to the Fabb Educational Trust'.
Most university history departments, employ historians with a range of historical interests. A typical letter head might read: University of Ambrosia, Department of History.