High Temperature Strengthening Of Aluminium Contained Austenitic Steel Used In700℃Ultra-supercritical Power Station

New Al-Containing Austenitic Stainless Steel has excellent hightemperature creep and oxidation resistance properties and at the sametime cost lower, is expected to become a new generation of hightemperature resistant material used in700℃ultra supercritical boiler, itshigh temperature oxidation resistance is better than the commercial heatresistant steel and high temperature alloy.This paper researched the composition design principle andorganizational control measures of new Al2O3-Forming AusteniticStainless Steel, which meeting the requirement of700℃ultra-supercritical units through key element content correction,combined with the preparation process adjustment. Evaluated the hightemperature creep/rupture performance, and studied the microstructureevolution before and after high temperature creep/rupture.Strengthening mechanism of AFA is mainly rely on MX phase (NbC)precipitation strengthening and Nb solid solution strengthening. So it’s very important that NbC is present in nano scale precipitation, anduniform distribution in the matrix. We found from equilibrium phasediagram calculated by JMatPro that NbC will precipitate at1360℃fromliquid first, easy to form large liquation NbC phase, which is difficult tosolution in heat treatment and reduce high temperature properties of AFA.Adding rare earth element in AFA can inhibit liquation NbC precipitation,and reduce the influence of large NbC to the performance of the sample.Thermal mechanical treatment processing can inhibit grain growth insolid solution treatment so that to get fine grain organization. Thestrengthening effect of Multiply adding Nb-V is much better than singleadding Nb and V. Lower C content can fundamentally effectively restrainthe large liquation NbC precipitates, which is helpful to get small anduniform distribution NbC precipitates in the subsequent processing andgreatly improve the performance of the samples.Yield strength is not the only indicator to measure creepperformance of AFA, in order to compare plastic deformation resistanceability of each sample more intuitively so as to judge which sample hashigher temperature creep performance, we calculated strain hardeningindex n, n value stands for material strain strengthen capacity or furtherplastic deformation resistance.We obtained the best AFA component proportion and processingtechnology through a series of contrast test, the creep rupture life of the sample at700℃and150MPa is1536.9hours, which completely achivedthe experiment expectation. There are only small NbC precipitates about10nm, which take mainly strengthening effect in the creep processing,found in the sample before creep test, but NiAl about100nm and Lavesphase about100nm are found after creep rupture.