Answer:
Spheroidite < Pearlite < Bainite < Martensite
Explanation:
Given materials in the question :
Pearlite, martensite, bainite and spheroidite
Now,
the correct order of the increasing toughness out of the given materials is
Spheroidite < Pearlite < Bainite < Martensite
These all are the forms of steel formed by different heating and cooling processes.
