Rufus McLean, another wing, crossed for two tries in the opening 15 minutes, while prop Pierre Schoeman also marked his first cap with a first-half try.
There were second-half tries from George Turner and substitutes Nick Haining and Oli Kebble as Scotland romped to victory in its first match in front of a crowd at Murrayfield in 19 months.
Steyn was starting for the first time for the Dark Blues and became the first Scotland player to score four tries in a match since Gavin Hastings against Ivory Coast at the 1995 Rugby World Cup.
