| The field of ultra-supercritical thermal power technology has become one of the most important research fields in the world, due to the great advantage of energy conservation and emission reduction. Heat transfer tubes need to withstand higher temperature and pressure for improving thermal efficiency of power units. Super304H alloy is one of the preferred materials for heat transfer tube of ultra-supercritical thermal power units, but there are a lot of problems in the microstructure affecting the service life of heat transfer tubes directly. The solid solution strengthening effect of austenite stabilizer N is stronger than that of C. Increasing Carbon equivalent in alloys by improving N content and reducing C content can promote precipitation of strengthening phase Nb(CN) and avoid chrominum depletion in the intergranular. Considering these factors, the research group researched two kinds of new Fe-Cr-Ni alloys signed as CHDG-A05 alloy and CHDG-A06 alloy by adjusting the component of Super304H alloy. In this paper, the microstructure, tensile properties and creep properties of traditional Super304H alloy, CHDG-A05 alloy and CHDG-A06 alloy were compared and analyzed.After the solution treatment at 1050℃ for 0.5 h, the grain size number of Super304H alloy is 7.5. A small amount of twins exist in grains of Super304H alloy and a few M23C6 precipitates exist in its boundary. After holding at 1100℃ for 0.5 h, the grain size number of CHDG-A05 alloy is 4.5. Lots of twins exist in grains of CHDG-A05 alloy and no M23C6 precipitates are found in the boundary. After holding at 1150℃ for 1 h, the grain size number of CHDG-A06 alloy is 6. Lots of twins exist in grains of CHDG-A06 alloy and no M23C6 precipitates are found in the boundary.In the condition of room temperature, the tensile strength of Super304H alloy, CHDG-A05 alloy and CHDG-A06 alloy is 597 MPa,576 MPa and 551 MPa. The yield strength is 273 MPa,298 MPa and 273 MPa. The elongation of the alloys is 47%, 47% and 51%. At 650℃, the tensile strength of Super304H alloy, CHDG-A05 alloy and CHDG-A06 alloy is 409 MPa,399 MPa and 396 MPa. The yield strength is 203 MPa,212 MPa and 209 MPa. The elongation of the alloys is 36%,36% and 37%.The creep tests of Super304H alloy, CHDG-A05 alloy and CHDG-A06 alloy were carried out at different stress levels. The creep limit σ1×10-4650 of Super304H alloy, CHDG-A05 alloy and CHDG-A06 alloy was calculated as 114 MPa,139 MPa and 141 MPa. The creep limit σ1×10-5650 of them was calculated as 67 MPa,100 MPa and 115 MPa. The lasting strength σ1×104650 of them was calculated as 126 MPa,125 MPa and 125 MPa. The lasting strength σ1×105650 of them was calculated as 88 MPa,84 MPa and 96 MPa. The main strengthening phases in the three alloys are M23C6, Nb(CN) and Cu rich phase. In the creep process, a large number of Cu rich phase dispersed in the alloys, and the size was extremely stable. In Super304H alloy, a large number of M23C6 strengthening the alloy precipitated at its grain boundary. With the extension of time, the quantity of Nb(CN) gradually increased, but overall amount of Nb(CN) precipitating after testing for a long time was less than CHDG-A05 alloy and CHDG-A06 alloy. In CHDG-A05 alloy, a few of M23C6 precipitated at grain boundary. In the steady creep stage, a large amount of Nb(CN) precipitated, which could effectively prevent the dislocation movement. In CHDG-A06 alloy, fewer M23C6 precipitated than CHDG-A05 alloy at grain boundary. CHDG-A06 alloy was strengthened mainly depending on the Cu rich phase and the twin boundary in the early stage of creep. After a long time of creep, Nb(CN) had become the most important strengthening phase.Above all, through the short-time tensile strength of new alloys are lower than Super304H alloy, high temperature creep properties of them are better. |
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