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| EFFECT OF CARBON AND NIOBIUM CONTENTS ON PHASE PARAMETERS AND CREEP RUPTURE TIME AT 650 ℃ FOR TP347HFG STEEL |
| PENG Zhifang1, DANG Yingying1,PENG Fangfang2 |
1. School of Power and Mechanical Engineering, Wuhan University, Wuhan 430072
2. Materials Research Department, Dongfang Boiler Group Co. LTD., Zigong 643001 |
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Cite this article:
PENG Zhifang, DANG Yingying,PENG Fangfang. EFFECT OF CARBON AND NIOBIUM CONTENTS ON PHASE PARAMETERS AND CREEP RUPTURE TIME AT 650 ℃ FOR TP347HFG STEEL. Acta Metall Sin, 2012, 48(4): 450-454.
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Abstract TP347HFG is an austenitic stainless steel which is considered to be among the grades with the highest potential for use in super critical boilers. It has been reported that micro-addition of Nb and a relatively low level of carbon content can obviously enhance creep resistance in this class of materials. Thus, C and Nb content optimization is of significant interest within the composition range from ASME standard. In this study, the effect of carbon and niobium contents on phase parameters (phase composition, volume fraction and size) and creep rupture time and the related mechanism were investigated for TP347HFG steel. Creep rupture tests were carried out under applied stresses of 230 and 150 MPa, respectively, at 650 ℃. The rupture times of two samples with different C and Nb contents were 199 and 420 h at 230 MPa, 2426 and 8837 h at 150 MPa, respectively. The sample with lower C content and higher Nb content corresponded to longer rupture time at each of the stress level. The EPMA-EDS+MPSM (multiphase separation method) and TEM-EDS results show that the creep rupture times were remarkably increased for the sample with relatively lower C and higher Nb contents, which correspond to increasing the volume fraction of nano-scale MX and decreasing that of M23C6 as well as retarding the coarsening of M23C6. On the other hand, more Cr maintained in matrix could also benefit the creep rupture lives. In addition, Thermo-Calc software was used to calculate the mole fraction and the concentration of precipitated phases with various combinations of C and Nb contents over the range of 500-1300℃ and the results were in good agreement with the experimental ones.
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Received: 01 November 2011
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