| Duplex Stainless Steels consisted of austenite phase and ferrite phase which exhibit excellent mechanical properties and high corrosion resistance,it is used in petrochemical,power generation,marine engineering and paper industries.Therefore,it is important to study the microstructure and properties of duplex stainless steel.This paper studies two casting duplex stainless steels which are ZG0CrXNiXMo2Mn and ZG0Cr26Ni5Mo3CuX,where X is a variable.ZG0Cr28Ni4.5Mo2Mn,ZG0Cr28Ni6Mo2Mn,ZG0Cr25Ni4.5Mo2Mn and ZG0Cr25Ni6Mo2Mn were solution treated at 1050?and 1100?.ZG0Cr26Ni5Mo3Cu2.75 and ZG0Cr26Ni5Mo3Cu2.95 were tempered at 720?,750?and 780?after solution treatment at1060?.Microstructure evolution of two duplex stainless steels were analyzed using X-ray diffraction?XRD?,scanning electron microscope?SEM?,energy dispersal spectroscopy?EDS?and leica microscope.Mechanical properties,corrosion resistance and erosion corrosion wear of steels were measured by optical hardness tester,micro-hardness tester,instrumented impact tester,tensile testing machine,electrochemical workstation and erosion wear tester.Research showed that microstructures of ZG0CrXNiXMo2Mn after solution treatment at1050?and 1100?consisted of?phase and?phase,light areas in the micrograph with island-shaped,spherical,acicular-like and elongated morphologies were?phases,and the dark matrix was?phase.The proportion of?phase decreases and the proportion of?phase increased with the increased of the content of Cr;the proportion of?phase increased with the increasd of the content of Ni,and the change of?phase contrast was opposite.With the increased of the solution temperature,the changes of proportion of two phaes were not obvious,the proportion of?phase increased slightly and?phase decreased slightly.The proportion of two phases were closest to 1:1 in steels when content of Cr was 25%,content of Ni was 6%and solution temperature was 1050?.There was no?phase precipitation when ZG0Cr26Ni5Mo3CuX DSS was only solution treated at 1060?.?phase was preferentially precipitated at the?/?phase boundary,and then inside the?phase,through the eutectoid reaction???+?2 when steel was tempered at 720?,750?and 780?after solution treatment.The volume fraction and dimensions of?increased with increasing tempering temperature;the proportion of?phase increased slightly and?phase decreased obviously with the increase of tempering temperature.Hardness,tensile strength and yield strength of ZG0CrXNiXMo2Mn increased and its impact energy and elongation decreased with an increasing content of Cr.When the solution temperature increased,hardness,tensile strength and yield strength of steels increased slightly,impact energy decreased slightly,the change of elongation was not obvious.When content of Ni increased,hardness,tensile strength and yield strength of steels decreased slightly,impact energy and elongation increased.Corrosion resistance of steels was best with maximum corrosion potential?-0.225V?and minimal corrosion current density(1.07×10-2?A/cm2)when content of Cr was 25%,content of Ni was 6%and solution temperature was 1050?.With the tempering temperature increased,hardness of ZG0Cr26Ni5Mo3CuX increased,and its impact energy,tensile strength,yield strength and elongation decreased.When steel was only solution treated with 2.75%content of Cu,hardness was 244.0 HB,imPact energy was61.1 J,tensile strength was 737.2 MPa,yield strength was 582.6 MPa and elongation was19.7%.Hardness was 391.8 HB,impact energy was 1.51 J,tensile strength was 651.2 MPa,yield strength was 450.2 MPa and elongation was 2.4%when the steel was tempered at 780?.When content of Cu rose from 2.75%to 2.95%,hardness,tensile strength and yield strength of steel decreased slightly,impact energy and elongation increased slightly.Potentiodynamic polarization curve results of erosion wear test of ZG0Cr26Ni5Mo3Cu2.75 in simulated seawater with silica sand at low flow rate?5m/s?showed that corrosion potential was highest?-0.108V?and corrosion current density was lowest?6.512?A/cm2?when steel was only solution treated at 1060?,and it had better erosion resistance at low flow rates.When the flow rate increased to 15m/s,corrosion potential and corrosion current density of the steels that tempeed at 750?and 780?are similar,corrosion potential was larger?-0.336V and-0.335V?and corrosion current density was lower?7.675?A/cm2 and 7.702?A/cm2?;it had the best erosion resistance with few erosion pit. |
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