| Duplex Stainless Steel, constituted of ferrite and austenite, is an important branch of Stainless Steel. In this kind of steel, usually ferrite is the matrix and austenite is the second phase. Because it has high stress corrosion cracking resistance, resistant to pitting and crevice corrosion performance and good mechanical properties, etc., more and more DSS is being applied in chemistry, petrochemistry, paper pulp, papermaking and petroleum industries. However, during high-temperature thermal processing deformation, the two phases have different softening mechanism, easily to making crack nucleation and extend at the phase boundary, resulting in Duplex Stainless Steel poor hot-working properties.In this paper, as-cast 00Cr25Ni7Mo4N super duplex stainless steel (SDSS)adding the rare earth element Cerium as the research object is investigated by using metallographic observation, scanning electron microscopy(SEM), microhardness, thermal simulation of tensile/ compression experiments, the impact experiment research methods,etc. Through investigating microstructure, mechanical properties at room temperature and high temperature deformation behavior of SDSS with different addition amount of rare earth element Cerium, dicuss rare earth element Cerium refining, purification, micro-alloying and modify inclusion effects, and the focus of analysis is to reveal the mechanism of rare earth element Cerium improving hot-working properties of super-duplex stainless steel.The study of As-Cast 00Cr25Ni7Mo4N super duplex stainless steel microstructure shows that Cerium is a kind of austenite forming elements which can refine microstructure, increasing equiaxed grain region, reducing large dendrite region; Rare earth element Cerium with strong deoxidization desulfurization capacity can react with oxygen, sulfur element to produce spherical or elliptical rare earth oxides(REO2), rare earth oxysulfide (RE2O2S) or rare earth sulfides (RE2S3), replacing the long strip of sulfide inclusions and improve the toughness of steel. In particular, to improve transverse impact properties and the steel anisotropy.Compared with 00Cr25Ni7Mo4N super duplex stainless steel without Cerium additions, the impact energy of the samples with 0.110% and 0.220% content of Cerium were increased by 21.9% and 61.4%, 14J and 61J respectively. Observation of the impact fracture of specimens shows that Cerium make fracture morphology changing from the quasi-cleavage fracture to dimples ductile fracture, small globular rare earth inclusions appear in dimples is the main reason for the change. The improvement of impact toughness is beneficial to super duplex stainless steel hot processing, which also reduced the cost of steel, providing a new way of enhancing economic efficiency.Hot deformation behavior of as-cast 00Cr25Ni7Mo4N SDSS was investigated using the Gleeble-3800 simulator, by which a simulated deformation equation is obtained. The addition of Cerium can increase deformation resistance of the hot compression process and reduce hot-cracking tendency during steel hot-working processes. Using Zener-Hollomon relation, through the linear regression calculate thermal deformation activation energy of super duplex stainless steel. The apparent activation energy and stress exponent are about 522 kJ/mol and 5.84, respectively.Obtain the relationship between deformation resistance (peak stress) and the Z parameters is as follows:The results showed that: in the same hot compression deformation conditions, adding an appropriate amount of rare earth element Cerium can effectively reduce thermal deformation activation energy of the super duplex stainless steel. The strain rate sensitivity and efficiency of power dissipation under different hot deformation conditions are also determined; with this the processing maps are established and interpreted on the basis of microstructure observation. |
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