| Reduced activation ferritic/martensitic steel(RAFM)is a kind of high purity nuclear grade material.Because of its good neutron radiation resistance,low activation and relatively mature industrial technology,it is generally considered to be the key structural material of nuclear fusion reactor that is most likely to realize commercial application in the future.In this paper,CLAM steel containing Ta,Ti,Zr and Ti Zr(hereinafter referred to as Ta-CLAM,Ti-CLAM,Zr-CLAM and TiZr-CLAM)was prepared by VIM process.The influence of Ti and Zr replacing Ta on inclusions and precipitates in experimental steel and the evolution of inclusions in experimental steel during hot working were systematically studied.At the same time,the influence mechanism of Ti and Zr on the properties of CLAM steel was analyzed according to the microstructure and mechanical properties of experimental steel under different heat treatment systems.The main conclusions are as follows:(1)The effects of Ti,Zr and Ti-Zr on inclusions in as cast steel were studied.Inclusions in Ta-CLAM steel are mainly spherical Ta-O-Mn-S phase,and inclusions in Ti-CLAM steel are mainly single TiN,TiN-TiO2 type composite inclusions,Ti-O-S type inclusions and a small amount of Ti-Mn-S type inclusions;inclusions in Zr-CLAM steel are mainly FeZrx phase,oxides,nitrides,sulfides of Zr and composite inclusions formed with MnS;inclusions in TiZr-CLAM steel are mainly Ti-Zr-O composite inclusions and inclusions with Zr-O phase or Ti-Zr-O phase as the core,and some Ti-N-O inclusions exist at the same time.On the whole,Ti and Zr are used to replace Ta element,and inclusions in experimental steel are effectively refined.(2)The evolution rule of typical inclusions in hot working process was studied,and the inclusions in steel were analyzed by quantitative metallography.After forging and rolling,a large number of Ta-Mn-S phases are formed on the surface of ta-clam steel,the size of inclusions is almost the same,but the number is increased;TiN inclusions in Ti-CLAM steel spheroidize and a small amount of rod-shaped Ti-S phases are precipitated,the number and size distribution of inclusions are basically the same;Zr-Mn-S phases are formed on the surface of ZrO2 inclusions in Zr-CLAM steel,the average diameter of inclusions is slightly increased;TiN inclusions spheroidized in TiZr CLAM steel,cracks appeared on the surface of Ti-Zr-O phase,and the average diameter of inclusions increased slightly.(3)The optimum quenching temperature of four heats of experimental steel are 980℃,980℃,930℃ and 980℃ respectively,and the microstructure of experimental steels are quenched martensite at room temperature.The precipitates in Ta-CLAM steel are mainly spherical M23C6 and Ta riched MX phases,the precipitates in Ti-CLAM steel are mainly spherical M23C6 and Ti riched MX phases,the precipitates in Zr CLAM steel are mainly spherical M23C6 and a small amount of Zr,V composite phases,and the precipitates in TiZrCLAM steel are mainly M23C6 and small particle Ti,Zr composite phases.(4)The tempering temperature has a significant effect on the precipitation behavior of M23C6-With the increase of tempering temperature,the size and volume fraction of M23C6 precipitates increase in varying degrees.The tempering temperature has little effect on the MX precipitate of the four furnace experimental steel.The MX phase in Ta-CLAM steel is still Ta riched MX phase,and(Ti,W)C appears in Ti-CLAM steel,the MX phase in Zr-CLAM steel is(Zr,V)(C,N),and the MX phase in TiZr-CLAM steel is mainly(Zr,Ti)(C,N).According to the quantitative statistical results of precipitates,the addition of Ti can refine the M23C6 precipitates,while the M23C6 precipitates in Zr-CLAM steel coarsen.(5)The optimum tempering temperature of four furnaces of experimental steel is 750℃,650℃,700℃ and 700℃ respectively.As for Ta-CLAM steel,the tensile strength is 691 MPa,yield strength is 565 MPa,elongation is 23.3%,room temperature impact energy is 210 J.As for Ti-CLAM steel,the tensile strength is 721 MPa,yield strength is 610 MPa,elongation is 23.3%,room temperature impact energy is 259 J.As for Zr-CLAM steel,the tensile strength is 702 MPa,yield strength is 595 MPa,elongation is 23.5%,room temperature impact energy is 254 J.As for TiZr-CLAM steel,the tensile strength is 705 MPa,yield strength is 570 MPa,elongation is 25.5%,room temperature impact energy is 261 J. |
