Alloying status of martensite/austenite heat-resistant steel containing Nb for ultra-supercritical power station
In order to improve the high-temperature strength of heat-resistant steel,adding trace alloying elements to the steel is an effective measure when designing alloy.Nb microalloying is the main strengthening method of heat-re-sistant steel and has always been a hot research topic in heat-resistant steel.Based on the application of Nb,the allo-ying development process and current situation of martensitic heat-resistant steel for steam generator rotor,marten-sitic heat-resistant steel and austenitic heat-resistant steel for ultra-supercritical boiler are described.Most of the ro-tor martensitic heat-resistant steels contain a small amount of Nb,especially the martensitic rotor steels developed in the last 40 years contain about 0.05％Nb(mass fraction).The general Nb mass fraction of martensitic heat-resist-ant steel for small and medium-size parts of steam turbines is about 0.05％-0.25％.The Nb mass fraction of mar-tensitic heat-resistant steel used for steam turbine shell is about 0.05％-0.10％.And T/P91 and T/P92 steels for main steam pipes and heat exchange tubes are containing 0.04％-0.25％Nb.Nb and V is used together in martensit-ic heat-resistant steel,and the V content is about 2 to 4 times that of Nb.The content of Nb in typical austenitic heat-resistant steel is about an order of magnitude higher than that in martensitic heat-resistant steel,and Nb is gen-erally added separately in austenitic heat-resistant steel,or a small amount of Ti is added in combination.On the whole,with the increase of steam parameters for power plant boiler,the alloying degree of martensitic heat-resistant steel and austenitic heat-resistant steel becomes higher and higher,and the types of alloying elements in steel become more and more.For austenitic heat-resistant steels,controlling and improving the existing form of primary Nb-rich phase is the main focus in the future.With the increase of strengthening factors in steel,the qualitative/quantitative interaction between strengthening factors may become a key research direction.
martensitic heat-resistant steelaustenitic heat-resistant steelapplication of NballoyingM23C6 phase
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