Fire does ×2 to Steel

Generations VI to IX, single types. The other way round, Steel against Fire, is ×½.

81 Fire and 65 Steel species among the 1025 this site covers.

Attacker, Fire and Ghost Blacephalon sprite

damage×2Generations VI to IX

Defender, Steel and Ground Steelix sprite

Steelix #0208

Steel did not exist in Generation I, so Fire against Steel has no value there.

Strongest Fire attackers

Blacephalon leads Fire at Sp. Atk 151

Sturdiest Steel defenders

Dual types that change the answer