Effect Of Deformation/Heat Treatment On Microstructure Distribution And Properties Of HR3C Heat-resistant Steel

For some time to come,the coal-based energy structure of China determines that the power structure would still be dominated by thermal power generation,making the relatively efficient and energy-saving ultra-supercritical units(USC)would be sustainable development.Due to the excellent high temperature performance,steam oxidation resistance and flue gas corrosion resistance,HR3C austenitic heat-resistant steel is widely used in the harsh working environment of ultra-supercritical units such as superheaters and reheaters.However,a large number of research results show that due to changes in the structure and precipitate phases,the brittleness of HR3C steel would increase significantly during high-temperature service,which is undoubtedly a hidden danger to the safe operation of the unit.Therefore,in terms of the common phenomenon of HR3C steel along the crystal brittle fracture after service,this research made an in-depth discussion on the basis of the research of HR3C steel by the predecessors of the research group.Therefore,in view of the common phenomenon of intergranular brittle fracture of HR3C steel after service,this paper designs different deformation and heat treatment processes to change the microstructure and distribution of HR3C steel,and analyzes its influence on the precipitated phase and mechanical properties after aging.Hope it can be proposed a process that enables HR3C heat-resistant steel to obtain a more reasonable grain structure while also having excellent mechanical properties,which provides a basis for improving the ageing brittleness of HR3C steel.This article mainly focuses on the hot-rolled and the as received HR3C steel as the research objects.The hot-rolled HR3C steel has undergone cold rolling deformation 8%(L8%-HR3C)and hot forging deformation 50%(RD50%-HR3C)respectively,and part of the as received HR3C steel(TG-HR3C)has undergone cold rolling(L8%-TG-HR3C)processing.Among them,L8%-HR3C and L8%-TG-HR3C were solid-dissolved at 1093°C and cooled in different ways to study their influence on grain boundary morphology;RD50%-HR3C were at different temperatures(1143°C,1230°C)Solid solution treatment to study its effect on the grain size;RD50%-HR3C and TG-HR3C were solid solution at 1093?for different time(2h,24h)to study their influence on the precipitation of?phase after aging.Optical microscope,SEM,and Nano particle size analyzer were used to characterize the crystal grain morphology and distribution,the precipitation morphology and composition,and the impact fracture morphology of the samples.At the same time,the effects of various treatment processes on the hardness,room temperature impact toughness and high temperature creep properties of materials before and after aging were studied,and the relationship between them and the micro morphology was analyzed.The research results indicate that the difference in grain boundary morphology of L8%-HR3C steel is mainly related to grain boundary carbides.The hardness and impact toughness of the fast-cooled samples after solid solution are slightly higher than that of the slow-cooled samples.The hardness and impact toughness of the RD50%-HR3C fine-grained sample(1143?)after aging are higher than those of the coarse-grained sample(1230?).The grain boundary M₂₃C₆ of the coarse grain sample is more continuous,and the ageing brittleness is more obvious.However,the creep resistance at high temperature is better.The HR3C samples that were solid-dissolved at different times were aged for the same time at different temperatures,and the precipitation of?phase decreased with the extension of the solid-solution time.Compared with the short-term solid solution sample of RD50%-HR3C,the impact toughness and creep rate of the long-term solid solution sample are significantly improved.Since the impact fracture characteristics along the grain after aging are more obvious,the influence of?precipitation of TG-HR3C solid solution samples at different times is reduced,which makes the impact toughness of long-term solid solution samples not effectively improved.However,compared with the supplied TG-HR3C,its creep rupture time and creep resistance are increased.Comprehensive comparison results show that the RD50%-HR3C fine-grained sample and the long-term solid solution sample have a certain effect on improving the aging brittleness.And the creep resistance of the long-term solid solution sample is slightly higher than that of the fine-grained sample.