Research On Mechanical Properties And High Temperature Oxidation Mechanism Of New Austenitic Heat-resistant Alloys

With the rapid development of global nuclear energy,higher requirements for the hightemperature performance of materials for key components of nuclear power equipment have been put forward.The steam pipe used in China is basically dependent on imports.Therefore,it is extremely urgent to develop heat transfer pipes with independent intellectual property rights.Through a large number of experimental studies and theoretical analysis in the previous period,the research group added an appropriate amount of Nb element to replace the Ti element to form a more stable dispersed carbide based on the 800 H alloy of the traditional heat transfer tube material,and added the appropriate Al element to strengthen the alloy.High temperature oxidation resistance,designed heat resistant alloy CHDG-B06 series,and prepared CHDG-B06-1?Fe-30Ni-18Cr-0.4Nb-2Al?and CHDG-B06-2?Fe-30Ni-18Cr-0.4Nb-3Al?Two alloys.The oxidation kinetics and thermodynamics of the alloy were studied by oxidation weight gain method.The oxidized films of the two alloys under different oxidation conditions were studied by means of SEM,EDS,XPS and XRD.The high temperature oxidation mechanism was systematically studied.The main findings are as follows:1.Determine the solid solution treatment parameters of CHDG-B06-1 and CHDG-B06-2 alloy for 30 min at 1100 ? and 45 min at 1150 ?;the tensile strength of the alloy after solution treatment is 562 MPa and 575 MPa,respectively;The Vickers hardness is 177 and 180,respectively;the grain size is 5.5;the grains have no obvious abnormal growth;the bulk and the second phase in the grain and the grain boundary are obviously reduced,and the alloy composition is relatively uniform.2.During the oxidation of CHDG-B06-1 and CHDG-B06-2 alloys at three temperatures of 700 ?,800 ? and 900 ? for 500 h,the oxide film did not peel off,and the oxidation kinetic curve generally followed the parabolic law.The final weight gain of CHDG-B06-1 alloy at three oxidation temperatures was 0.0661 mg/cm²,0.129 mg/cm²,0.414 mg/cm²,respectively.The final oxidation weight gain of CHDG-B06-2 alloy was 0.0354 mg/cm²,0.0778 mg,respectively./cm²,0.2811 mg/cm²,the oxidation resistance of the two alloys above 700 ? is better than that of 800 H alloy.The oxidation weight gain of CHDG-B06-2 alloy is obviously lower than that of CHDG-B06-1 alloy,and the oxidation resistance is better.excellent.Both alloys gained significant weight at the early stage of oxidation at 900 ?,and increased linearly from 0 to 20 h,and then the weight gain was slowed down.The oxidation activation energies of the alloys CHDG-B06-1 and CHDG-B06-2 were QB06-1=165.7KJ/mol and QB06-2=183.2KJ/mol,respectively.The oxidation rate K+ is less than 0.1 and belongs to the complete antioxidant level.3.During the oxidation test of CHDG-B06-1 and CHDG-B06-2 alloys,the oxide film remains intact.At 700 ?,the oxide films of both alloys are double-layered,containing Al₂O₃ film layer close to the matrix and Cr-rich outer layer.,a mixed oxide layer of Fe.At 800 ? and 900 ?,the oxide film layer is divided into Al₂O₃ of the inner oxide layer,Cr-rich,subsurface layer of Fe,a small amount of Mn oxide,and an outer layer of spinel structure oxide,of which CHDG-B06-1 alloy oxide film surface layer is FeCr₂O₄ spinel oxide,CHDG-B06-2 alloy oxide film surface layer is Fe?Al,Cr?₂O₄ mixed spinel oxide.At 900 ?,rod-like and massive Al N appeared at the interface between the oxide film and the matrix of CHDG-B06-1 and CHDG-B06-2.The test data and results analysis show that the basic mechanical properties of the CHDG-B06 series alloys with composition optimization meet the requirements of materials for heat transfer tubes,and the high temperature oxidation performance is significantly better than the 800 H alloy for traditional heat transfer tubes.It is beneficial to reduce the large insoluble second phase and homogenize the alloy structure with the C content decreases within a certain range.The increase of Al content in a certain range can significantly improve the high temperature oxidation resistance of the alloy.