Comparison of microstructure and mechanical properties of in-service TP347HFG steel tubes with different grain sizes
Microstructure and mechanical properties of TP347HFG high-temperature reheater tubes with austenite grain sizes of grade 7(coarse-grain)and grade 10(fine-grain)after about 50000 h of service at 600 ℃ were studied by means of scanning electron microscopy,X-ray diffraction and electronic universal testing machine.The results show that the microstructure of the in-service TP347HFG steel tubes with two different grain sizes has undergone varying degrees of coarsening,and the coarsening degree of the coarse-grain tube is lower than that of the fine-grain tube.The coarse-grain tube has a large austenite grain size,and contains a large number of coarse primary MX phase particles,nanoscale secondary MX particles precipitated within the austenite grains,and M23C6 phase particles precipitated at the austenite grain boundaries.On the contrary,although the austenite grains in the fine-grain tube are small,the microstructure coarsens more severely,with a large number of precipitated second phase particles,mainly M23C6 phase particles,fewer secondary MX particles,and no primary MX phase particles.The room temperature and high temperature tensile strength and yield strengh of the fine-grain tube are higher than that of the coarse-grain tube,but its elongation and the plastic deformation ability is lower.The difference in yield strength ratio between coarse-grain and fine-grain TP347HFG steel tubes at high temperatures is greater,and the coarse-grain tube has higher service safety.
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万方数据
维普
