Property and Microstructure Evolution of 20G Steel under High Temperature Loading

Tensile testing from room temperature to 850℃ and synchronous creep testing (stress of 62 MPa) and aging treatment (no stress) at 550-850℃ were conducted on 20G steel for water wall tube. The effects of temperature on tensile properties and involution of structure and properties after creep and aging were studied. The results show that the microstructures of tested steel after creep and aging were all composed of ferrite and pearlite. The applied stress improved the spheroidization of pearlite. With imcreasing temperature, the tensile strength of tested steel decreased slightly and then increased and then decreased rapidly; the yield strength decreased approximately linearly; the elongation decreased and then increased and then decreased in fluctuations. With the rise of temperature, the creep fracture time of tested steel was shortened rapidly and then became stable. The creep fracture was controlled by creep cavity nucleation at grain boundaries at 550℃ while by plasticity damage at 650℃.