Research On The Heat Treatments Progress And The CTOD Fracture Toughness Of Thick Steel Plates Used For Wind Towers

Heat treatment processes of three kinds of steel plates, mechanical properties and metallographic microstructure have been researched. Then the fracture toughness of steel plate used in wind towers and its weld joints has been assessed at room temperature.According to the research, metallographic microstructure of steel plates which have been quenched and tempered is sorbite tissue, and their mechanical properties have no significant variation with increasing quenching temperature. But with temper temperature ascending, intensity and hardness is descending while low temperature iMPact toughness is growing. When thickness of steel plates is reduced, their mechanical properties have become better.Static toughness of steel plates normalized becomes lower than just tempered, while low temperature iMPact toughness performs conversely. metallographic microstructure of steel plates normalized is fine grain ferrite and pearlite structure with thin ribbon and massive distribution.After second tempered, intensity and hardness of steel plates performs lower than tempered and their low temperature iMPact toughness is still not good enough to meet standard. Mechanical properties and metallographic microstructure of steel plates perform similarly along the rolling width direction.The applicability of the CTOD toughness evaluation is demonstrated in heat affected zones and weld fusion zone of the thick steel plate weld joints. At room temperature of26℃, CTOD values of D steel plates’ weld fusion is higher than that of HAZ near weld fusion, and CTOD values of HAZ near base material are close to that of base material. When weld joints are treated with stress relief annealing, higher CTOD values of weld fusion and HAZ near weld fusion and base material are acquired. As a result, the former two zones’CTOD values are higher than CTOD value of base material while the last zone’s is still lower.Metallographic microstructure of base material is fine grain ferrite and pearlite structure with thin ribbon distribution. Weld fusion zone consists of columnar crystal, and HAZ is composed of fine grains.