You can get the Job in Indian Railways after completing Mechanical Engineering. There are TWO EXAMS conducted by UPSC every year:

RRB EXAM (railway recruitment board)
IES (Indian Engineering Services)

You need to crack one of above examination. But it’s very tough to crack IES exam because unless until you have good technical knowledge about the subjects in Mechanical

RRB offers jobs for mechanical graduates at following posts:

Executive Engineers
Assistant Executive Engineers
Superintendent Engineer
Assistant Mechanical Engineers
station master.
TC OR TT