The boy was lured to a house in Oldham, where he was stripped and branded, before lemon juice was poured on the burns, Greater Manchester Police said.
He was also bound with tape, beaten and had his hair cut off.
The teenagers, aged between 15 and 17 and from Oldham, were sentenced at Manchester Minshull Street Crown Court.
The attack happened on the afternoon of 5 October 2015 at a house in the Werneth area of Oldham, police said.
Once at the house, the boy was tied up with tape around his mouth, hands and feet and punched and kicked.
A knife was also used to cut his back, before the hot iron, salt and lemon juice were used.
After several hours the victim was allowed to leave, having suffered terrible injuries.
Shohaib Khan, Adam Hussain, Sufyan Yaqub each admitted blackmail, false imprisonment and wounding with intent at an earlier hearing.
Khan, 17, of Grange Avenue, was sentenced to six years and six months in a young offenders' institution while Hussain, 16, of Olivers Court, and Yaqub, 16, of Park Road, each received four year sentences.
Ahsan Khan, 15, of Cornwall Street, was convicted of the same offences and ordered to be detained for five years.
Naseem Ali, 17, admitted false imprisonment and was sentenced to a 12-month supervision order with a night-time curfew.
After sentencing on Thursday, Det Insp Paul Walker said the attack had been "sickening and prolonged" and left the boy "terrified".
He added: "The emotional scars from this shocking attack will haunt him for the rest of his life and I could not even begin to imagine the agony and suffering that he endured."
Det Insp Walker paid tribute to the victim and his family for coming forward and giving evidence.
Five teenagers who tortured a 16-year-old boy over an £80 debt in a "sickening" hot iron attack have been sentenced.