| S30432 is a high-class heat-resistant steel used for components of most advanced USC boiler in the world. By means of SEM, TEM, HR-TEM and thermal simulator, the intergranular corrosion resistance, the mechanical properties, the microstructure evolution under the stress condition at high temperature, the strengthening mechanism and the hot deformation behavior of S30432 steel were investigated in order to accelerate its domestic production.The results show that the effect of carbon content on intergranular corrosion secretiveness of S30432 steel is more remarkable than that of niobium content. When the ratio of niobium content and carbon content is above 5.8, intergranular corrosion will be suppressed.With increasing of solid-solution temperature, the intergranular corrosion sensitivity decreases gradually. In the case of solution temperature exceeds 1100℃and carbon content is lower than 0.083wt% , intergranular corrosion can be avoided. To prevent intergranular corrosion sensitivity caused by M23C6 phase precipitation, long hold-up time around 840℃must be avoided by rapid cooling after solid-solution treatment.Temperature and time of solid-solution treatment affects the strength at room temperature obviously. When solution temperature exceeds 1150℃, the strength decreases apparently. Impact toughness decreases with aging time increasing and get even after 2000 hours. Carbon content affects the strength obviously and niobium content has minor effect on strength at room temperature.Creep rupture strength of tested steels aged at 650℃for 4 hours is higher than that of tested steels aged at 700℃. The steel with low carbon content and middle niobium content possess the highest creep rupture strength. The strengthing equivalent parameters of copper, niobium, carbon, nitrogen and boron elements are 1, 1, 4, 20, and 337 respectively.MX phase is the predominant strengthening phase in S30432 steel, and makes largest contribution to elevated temperature strength. The size of MX phase is about 50~120nm, and it has strong interaction with dislocation causing the increasing of deformation resistance.Compared with aging at 650℃for 4 hours, niobium content and nitrogen content in MX phase increased only 5.50% and 2.72% respectively when aging for 2000 hours, and these slow changes are beneficial to maitain its strengthening effect.M23C6 phase phase is major strengthening phase in S30432 steel. The size of M23C6 phase is about 0.3μm ~0.8μm. Most of M23C6 phase distributed in grain boundary, and also distributed in innergrain. After aging for 2000 hours at 650℃, the precipitation amount of M23C6 increased about 16.74 times than that of 4 hours, and its size increased evidently. Large size M23C6 can't play strengthening effect and becomes harmful to high temperature strength.Cu-rich phase plays important role in strengthening of S30432 steel. The size of Cu-rich is about 3nm ~30nm and average size is about 10nm. Cu-rich phase distributes dispersively in grain boundary and innergrain. Cu-rich phase strengthen the steel by hindering the movement of dislocation. Meanwhile, Cu-rich phase existing in sub-structure and twin grains can impede the movement of dislocation further to improve the strength of steel.The flow curves under various strain rates and different deformation temperature conditions were obtained through test by Gleeble3500 thermal-mechanical simulator and the peak stress and peak stain under different deformation conditions were obtained. Under the strain rate of 0.005 s-1~5 s-1 at the temperature range of 800℃to 1200℃, the hot deformation activation energy of the steel is 485kJ/mol and the hot deformation equation was got.The relationship between critical stress for dynamic recrystallization and Zener-Hollomon parameter was determined.The dynamic microstructure diagram of S30432 steel under the deformation temperature range of 800℃~1200℃and the strain rate range of 0.005s-1~5s-1 were established. The quantitative relationship between the size D of S30432 steel dynamic recrystallization grain and its Zener-Hollomon parameter and A parameter was determined.Processing maps for S30432 steel under different strain conditions were set up. Typical deformation mechanisms in processing maps were discussed and hot-tension ductility diagram was obtained.
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