Effects of Tempering Temperature on Mechanical Properties and Fracture Morphology of 3Cr3Mo3VNb Steel
3Cr3Mo3VNb steels with different mechanical properties were obtained by controlling tempering temperature.The test results show that,in the tempering temperature range of 300-680℃,the hardness of the test steel shows a downward trend as a whole,the secondary hardening phenomenon occurs when tempering at 500℃,and the accelerated softening of the test steel occurs in high temperature tempering above 600℃.The impact toughness increases gradually in the tempering temperature range of 300-680℃,and increases rapidly after tempering above 650℃.After tempering at different temperatures,different room temperature microstructure for 3Cr3Mo3VNb steel is obtained and its microstructure is transformed from tempered martensite to tempered troostite and tempered sorbite.The morphology of carbide changes from granular to strip,and finally to block.The fracture modes of the test steel are quasi cleavage fracture and ductile fracture.The quasi-cleavage fracture occurs in the temperature range of 300-650℃,and the ductile fracture occurs in the high temperature temper of 680℃.The impact toughness of the test steel is greatly affected by microstructure and carbide.
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